COOLING DRAG
Greig Huggins
I have been told that cooling drag for an aircraft engine is
significant. My question is:
Is there any difference in the amount of cooling drag between liquid
cooling,(using an automotive conversion and a radiator)and air cooling
(aviation engine with air cooling and a well designed baffeling system)?
Lets assume the weights of the engines and the HP is the same....
Greig Huggins
(White Lightning 1/2 done)
QDurham
Greig huggins wrote:>I have been told that cooling drag for an aircraft engine
is
>significant. My question is:
>
>Is there any difference in the amount of cooling drag between liquid
>cooling,(using an automotive conversion and a radiator)and air cooling
>(aviation engine with air cooling and a well designed baffeling system)?
I seem to recall Brian Seeley (of numerous Sport Aviation articles) suggesting
that cooling drag on a Cessna ran about 30% of total. (!) I have read several
places that the lovely belly radiator on the Mustage was a wash-item,
drag-wise. Provided as much thrust (cold air in, hot air out) as it cost in
drag.
I still have a hard time understanding why a decent skin radiator -- maybe out
to the wingtips and back on an (aluminum) wing's underside -- wouldn't provide
necessary cooling without causing any cooling drag whatever.
The ME 109 that broke Howard Hughes' long-standing land speed record had no
cooling drag. Easily accomplished: remove the entire cooling system and
somehow manage to make the required passes prior to utter destruction. (Read
the engine was packed in dry ice -- hard to believe.)
A real benefit of liquid cooling is that the radiator can be placed virtually
anywhere -- unlike gaping holes on the front of the cowl.
And let's not hear any drivel about reliability. When has anyone's Honda blown
up? Further, I understand that because it is possible to direct the cooling
medium more accurately, liquid engines can safely run hotter, and are to that
extent more efficient. They are also quieter -- and allow for delicious cabin
heaters!
Someday!
Quent
mark.j...@mindspring.com
aircraft. Here is a listing of a few WW2 fighters (all liquid cooled)
pulled from a few technical reports and textbooks:
Aircraft Cooling drag (% of total)
Me109 16%
Spitfire 17.3%
Beaufighter II 6.0%
Mosquito 4.0%
P-51 3.0%
As you can see there is a wide variation in the effect of the cooling
installation on drag.
It is arguable if one type of cooling system (liquid or air) will result in
a lower drag installation. I've done some cooling system design and
analysis work on some concept airplanes and . My opinion is that either
type of cooling, when properly designed should have the same drag for a
given amount of heat rejection (or horsepower). A well designed air cooled
radial engine installation is capable of achieving the same low drag as a
sleek liquid cooled inline installation. A good demonstration of this would
be the last 11 years of unlimited racing at Reno between Rare Bear and
Strega. The wins are about equally divided between the two.
No doubt some of the resident experts will also provide their input as well.
Also, if you do a search through Deja News on cooling you can find a lot of
information on cooling that has been posted in the past. ...and you won't
have to wade through a lot of "bullzoom" :-)
Hope this helps
Mark Johnston
mark.j...@mindspring.com
Greig Huggins wrote in message <3613E4...@kingswest.com>...
>Ok, another question to debate:
>
>I have been told that cooling drag for an aircraft engine is
>significant.
>[snip]
Gregory Travis
QDurham <qdu...@aol.com> wrote:
>up? Further, I understand that because it is possible to direct the cooling
>medium more accurately, liquid engines can safely run hotter, and are to that
>extent more efficient. They are also quieter -- and allow for delicious cabin
>heaters!
This is simply untrue. An engine that intersperses a liquid transfer
medium between the cylinder and the air (all engines are air-cooled)
currently suffers from the fact that the coolant cannot, for all
practical purposes, exceed about 240 degrees F.
Contrast that with an air-cooled engine where the interface between the
cylinder and the coolant (air) is roughly 300-400F.
Since heat transfer rate is a function of delta-T, it's elementary to
demonstrate that the so-called "air-cooled" engine has a much higher
potential for reducing cooling drag than the "liquid-cooled" engine.
A well designed air-cooled installation will almost always have a lower
coolant drag than an equivalent "liquid-cooled" installation simply because
the radiator in the liquid-cooled installation must run so much cooler
than an air-cooled cylinder's fins. This, of course, ignores some
of the advantageous placement options that a liquid-cooled installation
allows.
greg
--
gregory travis |"If you're going to kill someone there isn't much reason
gr...@littlebear.com|to get angry. You just pull the trigger. We need to smile
|with Novell when we pull the trigger." MSFT's Jim Allchin
jj...@dow.com
ghug...@kingswest.com wrote:
> Ok, another question to debate:
>
> I have been told that cooling drag for an aircraft engine is
> significant.
"Actually, only about 10% of the air in the path of the engine is forced
through the cowl, the remainder passing smoothly over the outside of the
cowling. As a result there is little cooling drag-the power consumed in
cooling amounts to roughly 5% of the bhp"
The Aircraft Engine and Its Operation
Pratt & Whitney Aircraft
My question is:
>
> Is there any difference in the amount of cooling drag between liquid
> cooling,(using an automotive conversion and a radiator)and air cooling
> (aviation engine with air cooling and a well designed baffeling system)?
>
> Lets assume the weights of the engines and the HP is the same....
>
> Greig Huggins
> (White Lightning 1/2 done)
>
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Bruce A. Frank
a bit faster. But, years ago I played around with a DOS computer program
on drag and airfoil shape and boundry layer. There appeared to be a
problem in that there was little turbulance over those surfaces and
boundry layer effectively cut convection cooling to almost zero. The
program indicated that for the wings to be efficient radiators there
would have to be verticle fins standing up like stall fences (though
shorter) side by side. That really took the drag up the scale. Larger
areas of wing skin radiator might work because the skin would actually
become a "radiator" rather than a convection cooler.
I, for years, have played with the idea of running tubes in a continious
loop inside of the leading edge of my wings heat sinked to the aluminum
(high wing, Cub type) nose of the airfoil. Calculations indicate that
I'd probably need a 60 foot span to cool my Ford 3.8L engine.
To sum it up, it looks like an aluminum automotive type radiator
provides the best trade-off for weight and cooling efficiency and if you
have room to design intakes and exits correctly heated air thrust, it is
said, could balance the drag through the radiator.
Any thermodynamicists here who might think outloud about these ideas?
QDurham wrote:
>
> Greig huggins wrote:>I have been told that cooling drag for an aircraft engine
> is
> >significant. My question is:
> >
> >Is there any difference in the amount of cooling drag between liquid
> >cooling,(using an automotive conversion and a radiator)and air cooling
> >(aviation engine with air cooling and a well designed baffeling system)?
>
> I seem to recall Brian Seeley (of numerous Sport Aviation articles) suggesting
> that cooling drag on a Cessna ran about 30% of total. (!) I have read several
> places that the lovely belly radiator on the Mustage was a wash-item,
> drag-wise. Provided as much thrust (cold air in, hot air out) as it cost in
> drag.
>
> I still have a hard time understanding why a decent skin radiator -- maybe out
> to the wingtips and back on an (aluminum) wing's underside -- wouldn't provide
> necessary cooling without causing any cooling drag whatever.
>
> The ME 109 that broke Howard Hughes' long-standing land speed record had no
> cooling drag. Easily accomplished: remove the entire cooling system and
> somehow manage to make the required passes prior to utter destruction. (Read
> the engine was packed in dry ice -- hard to believe.)
>
> A real benefit of liquid cooling is that the radiator can be placed virtually
> anywhere -- unlike gaping holes on the front of the cowl.
>
> And let's not hear any drivel about reliability. When has anyone's Honda blown
> up? Further, I understand that because it is possible to direct the cooling
> medium more accurately, liquid engines can safely run hotter, and are to that
> extent more efficient. They are also quieter -- and allow for delicious cabin
> heaters!
>
> Someday!
>
> Quent
--
Bruce A. Frank, Editor "Ford 3.8/4.2L Engine and V-6 STOL
BAF...@worldnet.att.net Homebuilt Aircraft Newsletter"
| Publishing interesting material|
| on all aspects of alternative |
| engines and homebuilt aircraft.|
*------------------------------**----*
\(-o-)/ AIRCRAFT PROJECTS CO.
\___/ Manufacturing parts & pieces
/ \ for homebuilt aircraft,
0 0 TIG welding
While trying to find the time to finish mine.
QDurham
>I'd probably need a 60 foot span to cool my Ford 3.8L engine.>
QDurham
>This is simply untrue.>
Of course. This obviously explains why ALL racing automobiles (sans maybe
porsche) are liquid cooled.
Quent
QDurham
>Since heat transfer rate is a function of delta-T, it's elementary to
Delta T also depends on the heat constant of the "fluid." Go read your book
further.
Quent
QDurham
>A well designed air-cooled installation will almost always have a lower
>coolant drag than an equivalent "liquid-cooled" installation simply because
>the radiator in the liquid-cooled installation must run so much cooler
>than an air-cooled cylinder's fins.
Total garbage, and completely disproved by generations of racing aircraft.
Quent
QDurham
>I question your premise.
>
>"Actually, only about 10% of the air in the path of the engine is forced
>through the cowl, the remainder passing smoothly over the outside of the
>cowling. As a result there is little cooling drag-the power consumed in
Please refer to the figures quoted in earlier posts. Further, Pratt and
Whitney might not be expected to be a big booster of liquid cooled engines.
Quent
Mark Mallory
: Delta T also depends on the heat constant of the "fluid."
What is the definition of "heat constant"?
dion.m...@pobox.com
BAFRANK@**MailBlockŽ**.worldnet.att.net wrote:
...
> I, for years, have played with the idea of running tubes in a continious
> loop inside of the leading edge of my wings heat sinked to the aluminum
> (high wing, Cub type) nose of the airfoil. Calculations indicate that
>
> provides the best trade-off for weight and cooling efficiency and if you
> have room to design intakes and exits correctly heated air thrust, it is
> said, could balance the drag through the radiator.
>
> Any thermodynamicists here who might think outloud about these ideas?
>
I'm stepping way outside of my area of expertise here (big deal, I have to do
that to post just about anything on R.A.H.), But could you save on drag by
combining your idea here with a smaller conventional automotive radiator, or
would the additional complexity waste away any savings?
Dion
Charles K. Scott
Greig Huggins <ghug...@kingswest.com> writes:
> Ok, another question to debate:
>
> I have been told that cooling drag for an aircraft engine is
> significant. My question is:
>
> Is there any difference in the amount of cooling drag between liquid
> cooling,(using an automotive conversion and a radiator)and air cooling
> (aviation engine with air cooling and a well designed baffeling system)?
>
> Lets assume the weights of the engines and the HP is the same....
>
> Greig Huggins
> (White Lightning 1/2 done)
There were some great columns on this subject over the last several
years by Barnaby Wainfan in Kitplanes. He got into duct design and
drag issues.
He explained that excessive drag will result in abrupt turns within the
duct or if air has to flow over sharp protrusions.
It's obvious that heated air doesn't want to go down, it wants to rise.
So systems that require the air to move over many protrusions, soak up
heat and then bend downward before the air can be exhausted is going to
require a LOT of energy to manage that.
The best heat exchanger type system would be one that has it's intake
in a high pressure zone, flows without impediment to the heat exchanger
with little or no turns and then accelerates to the rear where it is
exhausted into a low pressure zone.
The fabled P-51 had no less than three different heat exchangers
through which air had to flow before it was exhausted. And the
radiators weren't in line with the airflow, they were nestled up in the
fuselage so the air had to be bent up into them and then back down and
turned to the rear before exiting.
As the air became heated, it gained in volume and the flow became
accelerated. The exhaust duct was aimed to the rear to take advantage
of what thrust was available from the accelerated flow. All cooling
systems try to do this to some extent but the P-51 is probably the most
successfull example (of WWII fighters).
As you would imagine, this system worked best at certain altitudes
(high), power settings (also high) and air speed (again high).
But getting back to cooling systems, the ideal setup is not always
attainable. Most of the radiator installations you see are HUGE
compromises due to the size of the radiator and the limited space
within the cowling. Many radiators lay horizontally requiring the air
to make a 90 degree turn to pass through it then turn 90 degrees again
to head aft.
The ductwork should be smooth and as round as possible, again causing
compromise problems since most radiators are rectangular. Those
bendable segmented tubes you can buy from heating contractors should be
avoided because they cause excessive drag on the airflow.
One last tantalizing hint. The CAFE group at EAA have come up with
some interesting suggestions for inlet openings. They said that the
opening should have raised, thick lips. Not sharp lips and not flush.
If the scoop is below the fuselage the opening should be spaced away
from the fuselage to keep the inlet out of the turbulent boundary flow
ala P-51 Mustang.
Sizing the radiator isn't a big deal, or doesn't seem to be to me. You
don't have to agonize over what size you need, just contact one of the
several businesses that supply radiators to racers. All they need to
know is how much power your engine develops and about how fast you will
be going. They can either custom size a unit for you or they'll have
something on the shelf they can sell you. The good thing about this
type of heat exchanger is that it is designed for high speed air flow
and you know it will cool your engine if you get the right amount of
air to it. Rather, if you draw the right amount of air THROUGH it
because many a homebuilt cooling system came to grief when little or no
flow occured through the system because the air was exhausted into a
high pressure area.
The only thing you really have to agonize over is the size of the inlet
opening. That's still black magic to me.
Corky Scott
PS, I didn't even bring up exhaust augmentation.
BJ
Mark Mallory wrote in message ...
>QDurham (qdu...@aol.com) wrote:
>: Delta T also depends on the heat constant of the "fluid."
>
>What is the definition of "heat constant"?
>
Specific heat - normally specified at either constant pressure as Cp or
constant volume as Cv - is a measure of the amount of heat needed to
increase a mass of matter by a given temperature change. Typical units in
the US are Btus per pound mass per degree F.
By definition, a British thermal unit (Btu) is the amount of heat required
to raise the temperature of one pound mass of water from 59.5 degrees F to
60.5 degrees F.
Now, for the torque vs. HP discussions crowd:
1 Btu = 778 ft - lbs
2545 Btu = 1 HP- hr = 746 Watt - hrs
Enjoy,
BJC
highflyer
>
> Ok, another question to debate:
>
> I have been told that cooling drag for an aircraft engine is
> significant. My question is:
>
> Is there any difference in the amount of cooling drag between liquid
> cooling,(using an automotive conversion and a radiator)and air cooling
> (aviation engine with air cooling and a well designed baffeling system)?
>
> Lets assume the weights of the engines and the HP is the same....
>
> Greig Huggins
> (White Lightning 1/2 done)
Cooling drag is extremely sensitive to detail design of the cowling
and cooling area. The differences between installations are so
great that it would be meaningless to compare air and liquid cooling
drag. Theoretically, you should be able to attain a lower cooling
drag with liquid cooling. In practice ...
hf
highflyer
>
> Greig huggins wrote:>I have been told that cooling drag for an aircraft engine
> is
> >significant. My question is:
> >
> >Is there any difference in the amount of cooling drag between liquid
> >cooling,(using an automotive conversion and a radiator)and air cooling
> >(aviation engine with air cooling and a well designed baffeling system)?
>
> that cooling drag on a Cessna ran about 30% of total. (!) I have read several
> places that the lovely belly radiator on the Mustage was a wash-item,
> drag-wise. Provided as much thrust (cold air in, hot air out) as it cost in
> drag.
>
> I still have a hard time understanding why a decent skin radiator -- maybe out
> to the wingtips and back on an (aluminum) wing's underside -- wouldn't provide
> necessary cooling without causing any cooling drag whatever.
the drag significantly. It was tried by Supermarine before they built
the Spitfire, which did NOT use the wet wing. Boundary layer buildup
on an airfoil is not well understood outside of engineering circles.
>
> The ME 109 that broke Howard Hughes' long-standing land speed record had no
> cooling drag. Easily accomplished: remove the entire cooling system and
> somehow manage to make the required passes prior to utter destruction. (Read
> the engine was packed in dry ice -- hard to believe.)
>
> A real benefit of liquid cooling is that the radiator can be placed virtually
> anywhere -- unlike gaping holes on the front of the cowl.
>
Actually, gaping holes on the front of the cowl really do not have to
cost you a great deal in drag. Placing the radiator very far away
adds a LOT quickly to the weight and complexity of the system. My
car has a mid engine and a front radiator. Refilling the radiator is
quite a chore and was obviously figured out by a Philadelphia lawyer.
> And let's not hear any drivel about reliability. When has anyone's Honda blown
> up?
The radiator on my car blew up last year. Blew out all the water
and warped the cylinder head in minutes. I certainly never had a
problem like that with my Lycoming.
In WWII the most fragile part of the liquid cooled fighters was the
cooling system.
> Further, I understand that because it is possible to direct the cooling
> medium more accurately, liquid engines can safely run hotter, and are to that
> extent more efficient.
No they cannot safely run hotter. To keep the liquid a liquid at the
cylinder head temps you run at with a typical aircooled installation
you would need some pretty unbelieveable pressures in your cooling
system. I would not want to be near when a hose let go! Not a
pretty sight.
On the other hand, because the run cooler and within a narrower range
of temperatures in the working section, they can run with closer
internal tolerances which allows a little better specific fuel
consumption, a little lower specific oil consumption, and perhaps
a longer component life.
They are also quieter -- and allow for delicious cabin
> heaters!
THAT is true.
highflyer
Yes Quent, but the fluid that determines it is AIR in both cases.
You need less fin area than you do radiator area to obtain the
same heat transfer rate to the environment because the fins on
the cylinder head are twice as hot as the radiator. The greater
the differential the greater the flow rate. And the flow that is
critical is from the metal FIN to air or from the metal RADIATOR to
air. The fluid merely serves to carry the heat from hard to reach
spots in the block out where the air can see it.
highflyer
Most of which are, of course, AIR cooled.
highflyer
> > significant.
>
> "Actually, only about 10% of the air in the path of the engine is forced
> through the cowl, the remainder passing smoothly over the outside of the
> cowling. As a result there is little cooling drag-the power consumed in
>
> The Aircraft Engine and Its Operation
> Pratt & Whitney Aircraft
>
Of course the cooling drag is the drag due to cooling the engine
and doesn't necessarily correspond in any way to the amount of air
actually being forced to pass through the cowling. In my airplane
most of the air that goes INTO the cowling comes right back out the
FRONT of the cowling. I am sure that that air coming back out the
front adds to the cooling drag, even if it doesn't pass through the
fins on my engine.
hf
T. Bert Penney
highflyer <high...@alt.net> wrote in message 361540...@alt.net...
IIRC, that's called 'spillage drag'. It is a problem anywhere you have an
orifice in an aircraft designed to allow air to enter. Apparently, it is a
very large problem in the design of air intakes for jet engines on fighters.
That's why you see some very complicated geometry on some (F-111 comes to
mind) supersonic jets.
Bert
Chasmo
It has always seemed to me that ease of manufacuring was the #!
criterion in cowling design (for light planes).
I recall an article where an owner had extensively modified his Mooney
cowling.using a annular intake doing much interior baffling wotk coupled
with a really neat exhaust arrangement, using exhaust gases to augment
cooling. Nothing protruded into the airstream, open or closed. I believe
he was cooling 180 hp with 11 sq ins. of inlet. I was incredulous then
(and now) But the photo's appeared to confirm that.
The point being it seems to be an after-thought too much of the time,
and not given the engineering resources due to the cost factor.
highflyer wrote:
>
> Greig Huggins wrote:
> >
> > Ok, another question to debate:
> >
> > I have been told that cooling drag for an aircraft engine is
> > significant. My question is:
> >
> > Is there any difference in the amount of cooling drag between liquid
> > cooling,(using an automotive conversion and a radiator)and air cooling
> > (aviation engine with air cooling and a well designed baffeling system)?
> >
> > Lets assume the weights of the engines and the HP is the same....
> >
> > Greig Huggins
> > (White Lightning 1/2 done)
>
> Cooling drag is extremely sensitive to detail design of the cowling
> and cooling area. The differences between installations are so
> great that it would be meaningless to compare air and liquid cooling
> drag. Theoretically, you should be able to attain a lower cooling
> drag with liquid cooling. In practice ...
>
> hf
--
Charles Black
QDurham
>The fluid merely serves to carry the heat from hard to reach spots in the
block out where the air can see it.>
temperatures is a major plus for liquid cooling.
Also, are you suggesting that the kind of fluid (air/water/ a non-commital
little Riesling ) passing over the hot surface is, all else equal, irrelevant?
Another small point maybe not to you, but to somebody, not all engines are
aircooled. Marine stuff for example.
QDurham
>The radiator on my car blew up last year. Blew out all the water
>and warped the cylinder head in minutes. I certainly never had a
>problem like that with my Lycoming.
I sure did with my Porsche.
>In WWII the most fragile part of the liquid cooled fighters was the
>cooling system.
Gunfire, 1940s hoses and plumbing, umpty-thousand horsepower, great altitude
-- not really relevant to current discussion.
>hey can run with closer
>internal tolerances which allows a little better specific fuel
>consumption, a little lower specific oil consumption, and perhaps
>a longer component life.
Sounds good to me.
Quent
QDurham
>In my airplane
>most of the air that goes INTO the cowling comes right back out the
>FRONT of the cowling.
Exactly as Seeley found. Tufts on the upper lip of an intake sticking straight
forward. He also reported that at least one of the Cessnas (182?) was faster
with cowl flaps open than closed. Lovely design!
QDurham
>I recall an article where an owner had extensively modified his Mooney
>cowling.using a annular intake doing much interior baffling wotk coupled
>with a really neat exhaust arrangement, using exhaust gases to augment
cooling. Nothing protruded into the airstream, open or closed. I believe he was
cooling 180 hp with 11 sq ins. of inlet. I was incredulous then (and now) But
the photo's appeared to confirm that>>.
Gotta be Seeley's Mooney
Quent
Gregory Travis
QDurham <qdu...@aol.com> wrote:
>
>>Since heat transfer rate is a function of delta-T, it's elementary to
>>demonstrate...>
>
>Delta T also depends on the heat constant of the "fluid." Go read your book
>further.
The fluid to which the heat is being rejected, in both cases, is air.
Therefore the heat constant is equivalent.
Gregory Travis
AFAIK the oceans, rivers, and lakes alike reject their heat to the atmosphere.
Chasmo
I was impressed, any more info out there on it?
--
Charles Black
Don McCall
Cooling doesn't always have to result in detrimental drag.
Interesting article in Boeing News today about Lee Atwood, the famous
designer and North American Rockwell executive who was largely responsible
for the T-6 Texan, B-25 Mitchell, P-51 Mustang, F-86 Sabre, F-100 Super
Sabre, X-15, XB-70 Valkyrie, Apollo, and B-1. Excerpts:
"During WW II, everyone was trying to figure out how the P-51 Mustang was
out-performing German fighters as well as the British Spitfire, which had
more horsepower and was 1,000 pounds lighter. The German aircraft
manufacturer, Messerschmitt, was also researching the Mustang's performance
to no avail.
"Atwood explained, 'Both the British and the German engineers at the time
thought you could test a scale model in a wind tunnel. But the wind
tunnel models didn't generate the engine-heat factor, which we
successfully controlled within the air scoop to create positive thrust.
They were all looking at Mustang's laminar flow wing, which was noted for
reducing air friction over the surface of aircraft wings.'
"Pointing to several mathematical equations, Atwood continued 'The laminar
flow wing is great for jet airplanes or in a high-speed dive but had little
effect on the P-51's overall performance envelope. You have to attribute the
speed increase to the radiator energy recovery (positive thrust), not the
characteristic of the wing itself. The wing did help in a dive -- not in
level flight. I never mentioned this to anyone during the war.'
"Atwood credits F.W. Meredith of the RAE Farnborough, U.K., whose August
1935 report known as the Meredith Effect greatly influenced his work on
the P-51 cooling radiator."
QDurham
>The fluid to which the heat is being rejected, in both cases, is air.
>Therefore the heat constant is equivalent.
Can't buy it. The engine rejects its heat to water. The radiator rejects its
heat to air.
Quent
QDurham
>AFAIK the oceans, rivers, and lakes alike reject their heat to the
>atmosphere.
Yeah. I don't know either. But pretty far afield from current discussion.
Quent
QDurham
>Is his first name Brian?
>I was impressed, any more info out there on it?
Indeed. Deservedly major wheel in the CAFE business. Great stuff. He's an
excellent speaker and writer. Can be reached via Dr. Lyle Powell, EAA Chapter
393, c/o Airport Manager, Concord Airport, Concord CA. Or ask me again and
I'll really look it up.
QDurham
Don McCall wrote:
>>...But the wind
>successfully controlled within the air scoop to create positive thrust.
>They were all looking at Mustang's laminar flow wing, which was noted for
>reducing air friction over the surface of aircraft wings.'>>
>"Pointing to several mathematical equations, Atwood continued 'The laminar
>flow wing is great for jet airplanes or in a high-speed dive but had little
>effect on the P-51's overall performance envelope. You have to attribute the
>speed increase to the radiator energy recovery (positive thrust), not the
>characteristic of the wing itself. >>
Nice informative post, Don. However, I wonder how much relevance the heat
rejection concerns of a Mustang have to, say, a Tailwind's heat rejection
concerns. Several orders of difference.
>
Don Campbell
would be your rejecting the heat) there is only heating. You use the engine to
heat the water then you use water to heat the air. In each case, when the heat is
moved from one place to the other, it leaves the first place cooler.
Do I have that right?
Don
QDurham
>In each case, when the heat is
>moved from one place to the other, it leaves the first place cooler.
Right. And heats the other place. What's the problem?
Quent
Richard White
> IIRC, that's called 'spillage drag'. It is a problem anywhere you
> have an orifice in an aircraft designed to allow air to enter.
> Apparently, it is a very large problem in the design of air intakes
> for jet engines on fighters. That's why you see some very
> complicated geometry on some (F-111 comes to mind)
> supersonic jets.
Fascinating. Please write some more about 'spillage drag' and jet
fighter engine intake geometry. Thanks.
Richard.
morgans
Chasmo wrote in message <6v3nd5$jmc$2...@news-1.news.gte.net>...
>Is his first name Brian?
>I was impressed, any more info out there on it?
>
>>
>> >I recall an article where an owner had extensively modified his Mooney
>> >cowling.using a annular intake doing much interior baffling wotk
snip
How would it work to put a NASA type air scoop on the cowl above the jugs
(on an opposed type air cooled) and eliminate the front intakes, or is that
in too low of a pressure region to work? Has it been done?
Just an idea.
Jim
Glenn Scherer
wrote:
>In article <19981002174313...@ng135.aol.com>,
>QDurham <qdu...@aol.com> wrote:
>>Another small point maybe not to you, but to somebody, not all engines are
>>aircooled. Marine stuff for example.
>
>AFAIK the oceans, rivers, and lakes alike reject their heat to the atmosphere.
You're reaching with this one, Greg. Once it gets out of the airplane,
I don't *care* where it goes. :)
Glenn "practical" Scherer
Louis Kitz
reason is that at high angles of attack (such as high power climb-out) when
you need the most cooling, your cowling becomes something of a high camber
airfoil and the pressure drop is at it's greatest point. One on the lower
cowl would do better.
Good luck.
Louis Kitz
"The powers not delegated to the United States by the Constitution, nor
prohibited by it to the states, are reserved to the states respectively, or
to the people. "
10th Amendment to the U.S. Constitution
morgans wrote in message <6v6jti$3ca$1...@news5.ispnews.com>...
T. Bert Penney
anything about this. I'll see what I can dig up.
I seem to recall seeing Mary Schafer's name in this NG. I know that she
frequents the RAM group and she could probably tell all you want to know
about aerodynamics.
Bert
Richard White <wh...@csee.usf.edu> wrote in message
6v633o$c...@bgtnsc02.worldnet.att.net...
highflyer
>
> "hf":
> It has always seemed to me that ease of manufacuring was the #!
> criterion in cowling design (for light planes).
> with a really neat exhaust arrangement, using exhaust gases to augment
> cooling. Nothing protruded into the airstream, open or closed. I believe
> he was cooling 180 hp with 11 sq ins. of inlet. I was incredulous then
> The point being it seems to be an after-thought too much of the time,
> and not given the engineering resources due to the cost factor.
>
Lets just say that it is one of the most productive areas for
performance improvement on most aircraft. :-)
highflyer
>
> >The fluid merely serves to carry the heat from hard to reach spots in the
> block out where the air can see it.>
> Very true. And this ability to control more carefully internal engine
> temperatures is a major plus for liquid cooling.
>
> Also, are you suggesting that the kind of fluid (air/water/ a non-commital
> little Riesling ) passing over the hot surface is, all else equal, irrelevant?
>
> aircooled. Marine stuff for example.
Yes, marine engines are a common exception. Automobile and aircraft
engines, however, BOTH transfer the heat to the air. The intermediate
fluid cooling system does provide some advantages within the engine.
However, the ultimate transfer to the air does require MORE heat
exchanger area than for the air cooled engine. That does NOT imply
any other advantage/disadvantage to the two different options, which
are a liquid intermediate stage or NO liquid intermediate stage.
The intermediate fluid, whether water, glycol, or Reisling, has little
or no effect on the number of square inchs of heat exchanger area
required on the fluid to air heat exchanger which terminates the
chain. However, the fluid used, its operating temperature, its
freezing temperature, and it thermal capacity DO certainly matter in
the FIRST stage heat transfer in the system with the liquid intermediary
stage in the cooling system.
highflyer
>
> On 2 Oct 1998, QDurham wrote:
>
> >
> Interesting article in Boeing News today about Lee Atwood, the famous
> designer and North American Rockwell executive who was largely responsible
> for the T-6 Texan, B-25 Mitchell, P-51 Mustang, F-86 Sabre, F-100 Super
> Sabre, X-15, XB-70 Valkyrie, Apollo, and B-1. Excerpts:
>
> "During WW II, everyone was trying to figure out how the P-51 Mustang was
> out-performing German fighters as well as the British Spitfire, which had
> more horsepower and was 1,000 pounds lighter. The German aircraft
> manufacturer, Messerschmitt, was also researching the Mustang's performance
> to no avail.
>
Rolls Royce Merlin engine. The engines were license built by
Packard in the US.
> "Atwood explained, 'Both the British and the German engineers at the time
> thought you could test a scale model in a wind tunnel. But the wind
> tunnel models didn't generate the engine-heat factor, which we
> successfully controlled within the air scoop to create positive thrust.
> They were all looking at Mustang's laminar flow wing, which was noted for
> reducing air friction over the surface of aircraft wings.'
>
> "Pointing to several mathematical equations, Atwood continued 'The laminar
> flow wing is great for jet airplanes or in a high-speed dive but had little
> effect on the P-51's overall performance envelope. You have to attribute the
> speed increase to the radiator energy recovery (positive thrust), not the
> characteristic of the wing itself. The wing did help in a dive -- not in
> level flight. I never mentioned this to anyone during the war.'
>
> "Atwood credits F.W. Meredith of the RAE Farnborough, U.K., whose August
> 1935 report known as the Meredith Effect greatly influenced his work on
> the P-51 cooling radiator."
It is hard for me to believe that the performance of the Mustang was
due to its radiator. Most of the studies I have seen indicate that
the P-51 did indeed have significant cooling drag, although its
cooling drag was comparable to the cooling drag on the Spitfire and
about half of the cooling drag on the Messerschmidt 109.
The thing that made the Mustang so useful in the European theater
during WWII was not its high speed or it excellent radiator design.
It was its ability to throttle back and go slowly without burning
fuel like it was going fast. The P-47, when it throttled back,
still burned almost as much fuel as it did at normal cruise speeds,
because the wing rapidly became inefficient when it got too far
off of its design angle of attack. The Mustang, on the other hand
could be slowed to 200 mph and the fuel burn went down to less than
75 gallons per hour. This allowed the P-51, with drop tanks added
of course, to keep company with the B-17's for most of their runs,
providing air cover to minimize the effect of the ME-109's and the
Focke Wulfe's on the B-17 bomber formations.
highflyer
>
> >The fluid to which the heat is being rejected, in both cases, is air.
> >Therefore the heat constant is equivalent.
>
> Can't buy it. The engine rejects its heat to water. The radiator rejects its
> heat to air.
>
> Quent
Right. The liquid is merely an extra intermediate step. If the
liquid does not manage to reject aLL of its heat gain to the air
through the radiator the liquid portion of the system quickly
becomes dysfunctional.
highflyer
>
> This might be a word game but, there is no such thing as cooling ( i think that
> would be your rejecting the heat) there is only heating. You use the engine to
> moved from one place to the other, it leaves the first place cooler.
>
>
> Don
>
You have got it absolutely right, Don. Good for you. That is why
the temperature of the ambient environment is so critical as well.
If it is already hotter than you want to be you are out of luck!
QDurham
Highflyer wrote:
>The intermediate fluid, whether water, glycol, or Reisling, has little or no
effect on the number of square inchs of heat exchanger area required on the
fluid to air heat exchanger which terminates the chain. >
Nice response, Highflyer. I've no argument -- particularly with the Reisling.
<However, the fluid used, its operating temperature, its freezing temperature,
and it thermal capacity DO certainly matter in the FIRST stage heat transfer in
the system with the liquid intermediary stage in the cooling system.
>
Bingo. My thoughts exactly -- but I couldn't drag the expression "thermal
capacity" into mind -- kept running up against "heat content".
As far as radiating/conducting area, methinks still, the underside of any
aluminum wing is several orders of magnitude beyond what could be necessary --
at zero cooling drag. Run some pipes out there, thermally conect pipes to
aluminum skin with appropriate goop -- and away we go. Would work best at high
angles of attack -- and tend to keep one snuggy when one is under the wing
waiting for the rain to stop.
Quent
Quent
>
>
>
>
Charles K. Scott
highflyer <high...@alt.net> writes:
> It is hard for me to believe that the performance of the Mustang was
> due to its radiator. Most of the studies I have seen indicate that
> the P-51 did indeed have significant cooling drag, although its
> cooling drag was comparable to the cooling drag on the Spitfire and
> about half of the cooling drag on the Messerschmidt 109.
>
> The thing that made the Mustang so useful in the European theater
> during WWII was not its high speed or it excellent radiator design.
> It was its ability to throttle back and go slowly without burning
> fuel like it was going fast. The P-47, when it throttled back,
> still burned almost as much fuel as it did at normal cruise speeds,
> because the wing rapidly became inefficient when it got too far
> off of its design angle of attack. The Mustang, on the other hand
> could be slowed to 200 mph and the fuel burn went down to less than
> 75 gallons per hour. This allowed the P-51, with drop tanks added
> of course, to keep company with the B-17's for most of their runs,
> providing air cover to minimize the effect of the ME-109's and the
> Focke Wulfe's on the B-17 bomber formations.
David Lednicer, who is an aerodynamics engineer specializing in drag
profiles of aircraft has done some significant studies of WWII
fighters. His analysis confirms that the Messerschmitt 109, in all
it's variants was one of the most draggy of all fighters. The Spitfire
also had significant drag problems. The proof of the efficiency of the
P-51's cooling system is in the comparison between the Mustang and the
Spitfire. Virtually the same engine but significant performance
differences and the Mustang was a larger airplane carrying MUCH more
fuel.
My understanding was that at it's best height and speed, the thrust
developed from the effect of accelerating the exhaust air from the
cooling system out the exit duct *almost* but did not quite eliminate
the affect of cooling drag entirely.
By the way, the Mustangs may have at first flown with the bombers to
escort them but escort tactics changed almost immediately when fighters
realised that they had to maintain speed in enemy territory and they
could not stooge around at the bombers speed and be a threat. They
were slow targets at that speed. The fix was a series of relays in
which the bombers were escorted into France by squadrons of Spitfires,
from France into Germany by the Thunderbolts and from Germany on to the
target and return by squadrons of Mustangs. Each group of fighters
took off in time to be at their rendezvous with the bombers.
This allowed the Mustangs to cruise in a straight line to their
rendezvous without any fuel wasting "S" turns or staggering around
heavily loaded and nose high trying to stay with the slow bomber
formations. They could enter the combat zone at best height and speed
and be ready to attack when and if the Luftwaffe chose to challenge.
The problem with this type of arrangement of course, is that timing is
everything. If the fighters were early or the bombers late, they could
and did miss each other entirely although you'd think that thirty or
forty miles of heavy bombers would be hard to miss. It can sometimes
be a very big sky. The Germans at one time tried to interfere with
this unmolested cruise to the rendezvous but lost too many fighters to
continue to challenge the Mustangs directly. Also, they were
specifically ordered to ignor fighters and stop the bombers. Had they
had enough experienced fighters to challenge the Mustangs early causing
them to drop their external tanks and do battle, leaving another group
to deal with the bombers, it might have caused severe bomber losses for
a while. But not for long, the AAF would have just detailed another
group to hit the hitters leaving the long range escort to continue.
Non of this was successfull intantaneously, it took some bitter lessons
to get it right and a lot of lives were lost in the process. You've
heard of the "Aluminum Overcast" which I believe is the EAA's B-17?
Well when things didn't go right the result was an aluminum rainstorm.
Corky Scott
highflyer
The only problem with the underwing skin radiator, as they discovered
in the 1920's, is that they don't cool the water! Air is a good
insulator. In fact most "insulating" materials are merely ways to
trap and hold air and keep it from moving. That is exactly what
happens on the underside of your wing. On the top side as well,
actually. It is called boundary layer, and it gets progressively
thicker as you move toward the trailing edge of your wing. It
thickens quite rapidly when the wing skin starts moving AWAY from
the airflow like it does when the wing thickness decreases behind
the point of maximum thickness.
The net result is very poor cooling. As I mentioned once before in
this thread. Supermarine tried wing skin radiators, thinking they
would provide minimal cooling drag on their Schnieder Cup racers.
When Supermarine built the Spitfire, which built on much of what
they had learned with the Schnieder Cup airplanes, they used an
underwing radiator, but the stuck it down far enough to get out of
the boundary layer. The Spitfire had about half the cooling drag of
the contemporary ME-109, and Willy Messerschmidt understood his
aerodynamics better than most of his contemporaries.
For example, Willy lapped his skins from the back forwarn, so the
rise in the surface would cause the airflow to reattach and hold
down the buildup of the boundary layer.
hf
> >
> >
QDurham
Highflyer wrote:
<... Supermarine tried wing skin radiators, thinking they would provide
minimal cooling drag on their Schnieder Cup racers.>
Not to nitpick, hf, but their racers indeed had adequate cooling to win all
sorts of races. They worked very well in a racing environment.
<When Supermarine built the Spitfire, which built on much of what they had
learned with the Schnieder Cup airplanes, they used an
underwing radiator, but the stuck it down far enough to get out of the boundary
layer..>
Perhaps other considerations became more important. I'm sure that with their
greater area, skin radiators would be far more sensitive to a few unfortunate
bullet holes scattered hither and yon.
Further, the total heat rejection problem for Merlins, Allisons, et al. ,must
be several order of magnitude beyond any lightplane engine. The theory may be
the same, but the practice surely is in a different ballpark.
Anybody know of any skin radiator experimentation in light aircraft? Not I.
Quent
Shanley Mark Stephen
> The only problem with the underwing skin radiator, as they discovered
> in the 1920's, is that they don't cool the water! Air is a good
> insulator.
Another good example of just how effective an insulator air can be is
demonstated in turbine engine hot sections. The ability of a small layer
of air to isulate blades from the surrounding 1700C air at 2500ft/sec is
impressive.
QDurham
>Another good example of just how effective an insulator air can be is
>demonstated in turbine engine hot sections. The ability of a small layer
>of air to isulate blades from the surrounding 1700C air at 2500ft/sec is
>impressive.
But then, the entire engine is, has been pointed out before, is ultimately
cooled by air.
Quent
Gregory Travis
Shanley Mark Stephen <qu...@sol.acs.unt.edu> wrote:
>On Tue, 6 Oct 1998, highflyer wrote:
>
>> The only problem with the underwing skin radiator, as they discovered
>> in the 1920's, is that they don't cool the water! Air is a good
>> insulator.
>
>demonstated in turbine engine hot sections. The ability of a small layer
>of air to isulate blades from the surrounding 1700C air at 2500ft/sec is
>impressive.
Indeed. On a smaller scale it's what allows us to run aluminum pistons,
with melting points in the 600-700F range, in combustion chambers that
see 1800+F temperatures.
QDurham
Greg wrote:
>Indeed. On a smaller scale it's what allows us to run aluminum pistons, with
melting points in the 600-700F range, in combustion chambers that see 1800+F
temperatures.>
You lost me on this one, Greg. Those temps, in contrast to turbine blade
temps, happen briefly and intermittently -- average is far lower. The pistons
don't melt because there is time between peaks for the heat to transfer via of
other cooling agents -- oil cooling, conduction via rings to walls, cool intake
charge, etc. I don't see how the (significant) insulating value of air is
relevant . Explain?
Quent
Gregory Travis
QDurham <qdu...@aol.com> wrote:
>
>Greg wrote:
>>Indeed. On a smaller scale it's what allows us to run aluminum pistons, with
>melting points in the 600-700F range, in combustion chambers that see 1800+F
>temperatures.>
>
>You lost me on this one, Greg. Those temps, in contrast to turbine blade
>temps, happen briefly and intermittently -- average is far lower.
The average is, actually, not that far lower. Consider the lowly EGT probe
in a multi-probe engine. It, basically, interpolates the average for you -
after all, 3/4ths of the time (or thereabouts) there is virtually no
exhaust flow whatsoever past the probe. Yet EGT readings are commonly in
the 1200-1500F range. If the intermittent exhaust can maintain an EGT probe
at twice the melting point of aluminum then why don't we see melting of the
aluminum exhaust ports in the head?
You might reply that that is because the aluminum can conduct the exhaust
heat away rapidly enough to prevent melting. That, however, wouldn't
explain the rapid melting that can occur with a blown exhaust gasket.
>The pistons
>don't melt because there is time between peaks for the heat to transfer via of
>other cooling agents -- oil cooling, conduction via rings to walls, cool
>intake charge, etc. I don't see how the (significant) insulating value
>of air is relevant . Explain?
No. The pistons don't melt because there is an insulating layer of air,
below the temperature of combustion, above the piston.
This layer can be breached by detonation which leaves a signature of
melted aluminum.
QDurham
>No. The pistons don't melt because there is an insulating layer of air, below
the temperature of combustion, above the piston.
>
air on the piston tops amidst all the fire, brimstone, donner and blitzen
there.
I've been told that the temperatures of detonation are much higher than the
usual, and the most diligent aluminum can only conduct heat just so fast.
>You might reply that that is because the aluminum can conduct the exhaust heat
away rapidly enough to prevent melting. >
Seems reasonable to me.
> That, however, wouldn't explain the rapid melting that can occur with a blown
exhaust gasket.>
Sure it would. Too much heat in too small a space. Nothing to do with absence
or presence a protective layer of air.
I look forward to others' input.
Quent
Chasmo
immediately canceled mine.
It is an interesting thread though, some where a while back the mention
was made of leading edge skin coolers ai ugmented by a regular radiator.
Excellent idea!
I've wondered about using Nitrous to cool then to inject for power, it
might have applcation in an unlimited. I'm also curious about some of
these hi-conductive polymers for use in radiator construction.
Chasmo
QDurham wrote:
>
> >What did I miss here? Neither the P-51 or Spit used skin radiators!!
> >Chasmo
>
> Exactly. The Supermarine racers did use skin radiators very successfully.
>
> Come-on, Chasmo. Don't come into the middle of a thread and betray perplexity.
>
> Quent.
--
Charles Black
R J Skinner
Aluminum which manufactures a radiator made from two thin layers of
aluminum. It is used primarily for refigerators I believe, but their
literature shows an Indy type racer with two sheets of this material,
one on each side of the car.
The claim is that the car raced successfully to the point where it was
hit broadside by another leaving tire marks in the "radiator surface"
but no leaks.
RJS.
QDurham
>So critical did engine heat become on
>these less than hour long races...>
How long would a Spitfire/Mustang/Me 109 fly at these power settings? Seems to
me the skin radiators worked very well.
Quent.
jj...@dow.com
qdu...@aol.com (QDurham) wrote:
>
> Highflyer wrote:
>
> <... Supermarine tried wing skin radiators, thinking they would provide
> minimal cooling drag on their Schnieder Cup racers.>
>
> Not to nitpick, hf, but their racers indeed had adequate cooling to win all
> sorts of races. They worked very well in a racing environment.
>
"By 1929 Schneider engines had grown so powerful that designers were hard
pressed to devise methods of keeping them cool at full throttle. The
flush-wing radiatior, introduced by the Americans on the 1923 Curtiss plane
and used on all participating planes in subsequent years, had worked well
enough for the lower power engines. But it was never wholly satisfactory for
the larger engines, and proved completely inadequate for the 1900 horsepower
Rolls Royce in the S-6 which generated more heat than any engine built
before.
To cool it, Supermarine engineers converted the entire wing into a radiator
by enveloping it witha duraluminum water jacket through which flowed the
nearly steaming water from the hot engine.
Lubricating oil, pumped hot at eight gallons a minute, passed through finned
tubes on each side of the fuselage to a cooling tank in the vertical
stabilizer, thence back to the engine. So critical did engine heat become on
these less than hour long races, that pilots flew entirely by the water
temperature gauge holding them between 200 and 210 by skillful throttle
jockeying."
excerpted from "The Story of the Schneider Trophy Race"
by Henry R. Palmer, Jr.
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
QDurham
Charles K. Scott
qdu...@aol.com (QDurham) writes:
> >So critical did engine heat become on
> >these less than hour long races...>
>
> How long would a Spitfire/Mustang/Me 109 fly at these power settings? Seems to
> me the skin radiators worked very well.
>
> Quent.
Well not exactly Quent, the pilots had to fly with one eye on the
horizon and course and the other on the temperature guage. They had to
vary the temperature of the engine by varying the throttle.
In combat, however, one didn't want to be limited to such "eyes in
cockpit" distractions. Many of the ex figher pilots I've spoken with
explained that once they entered combat the dictum "never throttle
back" became fairly prominant. Sometimes of course you did have to
throttle back but speed was life. You wanted to be able to ram it up
to maximum power and not have to worry about having to jockey the
throttle around to prevent overheating. Sometimes you even wanted to
go to "War Emergency Boost", if your life depended on it.
Corky Scott
Bill Daniels
a skin radiators - battle damage. Skin radiators just presented too large a
target. A compact under-wing radiator was a much smaller target.
Bill Daniels
Chasmo wrote in message <6veube$fh$1...@news-1.news.gte.net>...
>No way Jose, a slightly ambiguous post of yours. notice I almost
>immediately canceled mine.
>It is an interesting thread though, some where a while back the mention
>was made of leading edge skin coolers ai ugmented by a regular radiator.
>Excellent idea!
>I've wondered about using Nitrous to cool then to inject for power, it
>might have applcation in an unlimited. I'm also curious about some of
>these hi-conductive polymers for use in radiator construction.
>Chasmo
>
>QDurham wrote:
>>
>--
>Charles Black
highflyer
>
> Highflyer wrote:
>
> <... Supermarine tried wing skin radiators, thinking they would provide
> minimal cooling drag on their Schnieder Cup racers.>
>
> Not to nitpick, hf, but their racers indeed had adequate cooling to win all
> sorts of races. They worked very well in a racing environment.
>
> learned with the Schnieder Cup airplanes, they used an
> underwing radiator, but the stuck it down far enough to get out of the boundary
> layer..>
>
> Perhaps other considerations became more important. I'm sure that with their
> greater area, skin radiators would be far more sensitive to a few unfortunate
> bullet holes scattered hither and yon.
>
> Further, the total heat rejection problem for Merlins, Allisons, et al. ,must
> be several order of magnitude beyond any lightplane engine. The theory may be
> the same, but the practice surely is in a different ballpark.
>
> Anybody know of any skin radiator experimentation in light aircraft? Not I.
>
> Quent
Quent, they were tried with little success in WWI also, when most
aviation engines were liquid cooled. I don't think possible bullet
holes had much to do with it. There has been research. I have told
you what the research discovered. Feel free to ignore it. Where
would we be if we could not keep repeating the same mistakes?
hf
highflyer
>
> On Tue, 6 Oct 1998, highflyer wrote:
>
> > The only problem with the underwing skin radiator, as they discovered
> > in the 1920's, is that they don't cool the water! Air is a good
> > insulator.
>
> Another good example of just how effective an insulator air can be is
> demonstated in turbine engine hot sections. The ability of a small layer
> of air to isulate blades from the surrounding 1700C air at 2500ft/sec is
> impressive.
Mainly the air blanket keeps the engine from melting. If you can
imagine a fire going that is hot enough to slag brass inches away
from a thin aluminum shell, something has to keep it from melting.
Even a simple fire going in the tail cone with the engine not even
running will melt the engine down in no time. That air blanket is
important.
QDurham
Corky wrote:
>...once they entered combat the dictum "never throttle back" became fairly
prominant.>
Hard to find even a teenie-weenie flaw in that logic. I've spend some time
sitting between R3350s and always appreciated the availability of water
injection. in various pucker-causing events. However, unlike the racers
mentioned in earlier posts, combat rarely lasted more than a few minutes. The
skin radiators worked very well in non-combat roles. My point is that
considering the lightplane's far less-rigorous conditions, skin radiators would
work even better -- with nearly-nil cooling drag penalty.
Quent
QDurham
>I don't think possible bullet holes had much to do with it>
Which is most bullet-hole sensitive -- a large area skin radiator or a small
"conventional" radaitor?
<There has been research.>
I must have missed it. Cite please?
<I have told you what the research discovered.>
What might that be? That bullet holes in a warplane's cooling system can be
largely ignored? That cooling technology and materials have gone nowhere since
1917?
>Where would we be if we could not keep repeating the same mistakes?>
Right where we are with the typical lightplane's cooling drag running around
30%. ( Brian Seeley's figure as quoted in Sport Aviation.)
Quent
JStricker
I can certainly see where the heated air can cause problems like boundary
layer control, etc. So, this brings me to another question.
Which is worse with respect to de-ice/anti-ice, 1) heated leading edges, 2)
boots, 3) TKS (weeping wing)?
I realize all of them are "necessary evils" but my suspicion is that the TKS
system while the most problematic to manufacture, pays the least penalty
because the wing is, for all intents and purposes, completely normal unless
the system is "on".
Comments?
John Stricker
--
Remove the "nosp..........." Oh hell, you folks know what to do and
why I had to put it in. If one of you real humans wants to contact me:
"I didn't spend all these years getting to the top of the food chain
just to become a vegetarian"
highflyer wrote in message <361B77...@alt.net>...
>you what the research discovered. Feel free to ignore it. Where
>would we be if we could not keep repeating the same mistakes?
>
>hf
Gregory Travis
JStricker <jstr...@odsys.NOSPAM.net> wrote:
>flyer,
>
>I can certainly see where the heated air can cause problems like boundary
>layer control, etc. So, this brings me to another question.
>
>Which is worse with respect to de-ice/anti-ice, 1) heated leading edges, 2)
>boots, 3) TKS (weeping wing)?
>
>I realize all of them are "necessary evils" but my suspicion is that the TKS
>system while the most problematic to manufacture, pays the least penalty
>because the wing is, for all intents and purposes, completely normal unless
>the system is "on".
Actually, aerodynamically I would expect a heated leading edge to give the
least grief - so long as the heat wasn't activated. The TKS system requires
a leading edge strip which slightly disrupts airflow - I've heard Mooney
drivers talk about losing some knots - similar to what one would expect
with pneumatic boots.
On the other hand, a heated leading edge takes a TREMENDOUS amount of
energy. Peter Garrison and I went into this a month or so ago when exploring
the possibility of using engine waste heat to deice flying surfaces. In
short, there simply isn't enough heat "left over" from an O-360 to
sufficiently de-ice even a 172.
Another way to look at it is the following: an O-360 at typical cruise
(70% horsepower) consumes about 9 gallons of fuel per hour. 9 gallons
per hour is just a little over a million BTUs. 126HP is equivalent to
320,595 BTUs which means that our O-360 is 31% efficient at turning gasoline
into useful power - a number that's entirely reasonable.
Thus an O-360 wastes nearly 700,000 BTU. Standard rules of thumb say that,
of that 700,000 BTU, roughly 500,000 go out the exhaust and 200,000 BTU
go out the cooling fins.
I did some rough calculations and calculated that it would take about
650,000 to maintain 100 square feet of aluminum skin at
200F against a 0F 150MPH wind. 100 square feet is about how much area
needs to be "protected" on a 172.
Given all that, it seems clear to me that you would need to burn about
7-8 GPH of fuel, in a separate burner, to sufficiently deice a 172s
wings with heat.
QDurham
jjmaj wrote:
>To cool it, Supermarine engineers converted the entire wing into a radiator
>by enveloping it witha duraluminum water jacket through which flowed the
>nearly steaming water from the hot engine.>
Worked, didn't it? And under conditions wildly beyond anything a light plane
ever encounters.
Quent
Charles K. Scott
qdu...@aol.com (QDurham) writes:
> Right where we are with the typical lightplane's cooling drag running around
> 30%. ( Brian Seeley's figure as quoted in Sport Aviation.)
I really wish there were some sort of "bible" that contained all the
necessary formula's, drawings, diagrams and text that could help
homebuilders design an efficient cooling system for liquid cooled
engines in the 100 to 300 hp range.
There is in a way, the RAA technical tips section on their web page has
a four part article that has lots of tips but the author of the
article, Hans Mayer, is a proponent of belly scoops or underwing scoops
and for many reasons I don't want to go that way. The rest of the
article has some possibly helpful information except that the only
radiator suggested is a VW Rabbit type without giving any assistance to
those who may need more or less fin area.
What is needed, in my opinion, is a way to figure inlet size as related
to the radiator size. This formula, I'm guessing, would vary
hopelessly with the various speeds of the various airplanes and also by
location, length of duct and who knows what other variables.
I know what the shape and location of the cooling system I'm going to
use will look like. I'm sure I will come close with the first effort.
I'd just rather KNOW the cooling system will work without much
modification before going through the effort of fabricating it.
Corky Scott
highflyer
>
> Let me jump in here and suggest a reason that the WWII fighters did not use
> a skin radiators - battle damage. Skin radiators just presented too large a
> target. A compact under-wing radiator was a much smaller target.
>
> Bill Daniels
While battle damage may have contributed to the decision, the fact
remains, the more compact radiators with well designed inlets and
outlets actually cost less power for cooling than the skin radiators.
NOTHING is free in aerodynamics.
hf
highflyer
>
> >I don't think possible bullet holes had much to do with it>
>
> Which is most bullet-hole sensitive -- a large area skin radiator or a small
> "conventional" radaitor?
>
>
>
> <I have told you what the research discovered.>
>
> What might that be? That bullet holes in a warplane's cooling system can be
> largely ignored? That cooling technology and materials have gone nowhere since
> 1917?
>
Liquid cooling technology and materials HAVE gone nowhere since 1917.
Unless you consider plastic radiators a major advancement over brass
ones. :-)
Aerodynamics hasn't changed a great deal since then either. We have
learned some more about it, but it is still the same as it has always
been. Of course, we can always ignore that an apply the 1917
aerodynamics because it sounds right to us.
> >Where would we be if we could not keep repeating the same mistakes?>
>
> Right where we are with the typical lightplane's cooling drag running around
> 30%. ( Brian Seeley's figure as quoted in Sport Aviation.)
>
> Quent
Yet we have built many airplanes with cooling drag a third of that.
But ONLY by paying attention to AERODYNAMICS. You might ask why
almost all airplanes went from liquid cooling to air cooling as soon
as the manufacturing technologies allowed them to make cylinders with
sufficient fin area to cool without the intermediate liquid and the
radiator. There were a few hangovers in WWII because of the need to
squeeze as much power out of a small engine as possible. However,
by the time pistons were replaced by jets, there were NO liquid cooled
aircraft engines in use. Why?
hf
QDurham
>While battle damage may have contributed to the decision>, the fact
>outlets actually cost less power for cooling than the skin radiators.
>
Nope. The fastest planes in the world used skin radiators. How can you insist
that a radiator sticking out into the slipstream, with or without lovely inlet
design, has less drag than an existing wing surface?
Quent
QDurham
>However, by the time pistons were replaced by jets, there were NO liquid
cooled aircraft engines in use. >
Are we choosing to ignore the fact that some of the fastest piston-engined
planes in the world today are liquid cooled? And that prior to WWII the
fastest planes (Supermarine stuff) were liquid cooled? Or that Willie
Messerschmidt took the world's speed record away from Hughes' aircooled racer
with a liquid-cooled airplane?
>There were a few hangovers in WWII...>
"Hangovers" like the Mustang, P-38, Messerschmidt, Spitfire, Hurricane, et al.
Quent
Tim Friendshuh
highflyer wrote in message <361CD4...@alt.net>...
>Yet we have built many airplanes with cooling drag a third of that.
>But ONLY by paying attention to AERODYNAMICS. You might ask why
>almost all airplanes went from liquid cooling to air cooling as soon
>as the manufacturing technologies allowed them to make cylinders with
>sufficient fin area to cool without the intermediate liquid and the
>radiator. There were a few hangovers in WWII because of the need to
>squeeze as much power out of a small engine as possible. However,
>by the time pistons were replaced by jets, there were NO liquid cooled
>aircraft engines in use. Why?
>
>hf
While air cooled engines seem to have the advantage strictly from
efficiency/power to weight etc, of course they have other problems. Some
find water cooling attactive mainly from the perspective of lower
maintenance costs of automotive power plants.
Also, manufacturing technology has progressed enourmously in the last 25
years especially in the automotive business. Modern automobile engines are
many orders of magnitude more efficient, reliable (and cheaper) than they
used to be due largly to advances in manufacturing.
I am woefully ignorant however about aviation manufacturing. Without the
brutal competition experienced by the automotive industry in the late 70's
and early 80's, have the aircraft engine manufacturers made the same types
of advances? Is a 1998 Lycoming made to better tolerances than a 1998
Subaru? Is a 1978 Lycoming better made than a 1998 Subaru? (I already
know which costs less...;-) )
Tim F
Terry Schell
>Also, manufacturing technology has progressed enourmously in the last 25
>years especially in the automotive business. Modern automobile engines are
>many orders of magnitude more efficient, reliable (and cheaper) than they
>used to be due largly to advances in manufacturing.
<snip>
Just one nit... engine efficiency has not improved "many orders of
magnitude". In fact, for engines running near full rated power (75%)
engine efficiency has improved about 20% in the last 25 years.
Those damn carnot cycle physics are a bitch.
Charles K. Scott
highflyer <high...@alt.net> writes:
> There were a few hangovers in WWII because of the need to
> squeeze as much power out of a small engine as possible. However,
> by the time pistons were replaced by jets, there were NO liquid cooled
> aircraft engines in use. Why?
Hmmm, I was going to answer this in terms of weight differences saying
that the Merlin weighed more but it doesn't, or didn't. A quick search
on the internet under "Rolls Royce Merlin" and "Pratt and Whitney
R-2800" brought the following information: Merlin weight 800 Kg or 1764
lbs. R-2800 2,350 lbs.
So there goes my "The Merlin was heavier" argument.
I'm left with current design and production inertia as a plausable
theory. By the time Jets took over almost all the worlds airliners
were US produced, and those airplanes were equipped with radial
engines.
The big question is why radial engines became so popular in America
while Europe developed mostly inline liquid cooled engines.
Could it be that the radial were easier to produce and assemble?
Corky Scott
Gregory Travis
Terry Schell <tsc...@s.psych.uiuc.edu> wrote:
>Just one nit... engine efficiency has not improved "many orders of
>magnitude". In fact, for engines running near full rated power (75%)
>engine efficiency has improved about 20% in the last 25 years.
I'm not sure this is true even within automobile engines. 5% I can
believe, but not 20%.
Yeah, at idle and near idle we've seen those kinds of improvements but
not at 75%.
QDurham
Corky wrote:
>Could it be that the radial were easier to produce and assemble?>
Maybe. But I seem to recall that the atmospheric pressure at PanAm altitudes
suggested some cleverness. Pressurized mags and plug wires, probably coolant
boiling concerns...
Story is that the US Navy preferred aircooled radials because of maintenance
concerns in space-constrained carrier work spaces.
Quent
Charles K. Scott
tsc...@s.psych.uiuc.edu (Terry Schell) writes:
> Just one nit... engine efficiency has not improved "many orders of
> magnitude". In fact, for engines running near full rated power (75%)
> engine efficiency has improved about 20% in the last 25 years.
>
> Those damn carnot cycle physics are a bitch.
So Terry, how can we reduce things for a meaningful comparison? Is
this even possible? Do figures from auto manufacturers that are
comparable to aircraft engine fuel burn specs exist? Would the BSFC
figure be usable, should it be possible to get it? Of course, it would
have to be at 75% power so that things are equal across the board.
How about it? Can anyone give us a Subie BSFC? Surely some of the
lurkers are actually flying behind them. How about Nigel Field?
Anyone?
Thanks, Corky Scott
Student Pilot
wrote:
>"Tim Friendshuh" <ethe...@spamnet.att.net> writes:
>
>>Also, manufacturing technology has progressed enourmously in the last 25
>>years especially in the automotive business. Modern automobile engines are
>>many orders of magnitude more efficient, reliable (and cheaper) than they
>>used to be due largly to advances in manufacturing.
>
><snip>
>
>Just one nit... engine efficiency has not improved "many orders of
>magnitude". In fact, for engines running near full rated power (75%)
>engine efficiency has improved about 20% in the last 25 years.
>
>Those damn carnot cycle physics are a bitch.
You're correct of course about efficiency, that was an exaggeration on
my part, but gains have still been made. (I am mentally comparing my
1972 Plymouth Valient (318 V8, 12mpg, 2 door, 6 pax) to my brothers
Ford Explorer, (3.0L(182CID) V6, 20mpg, 4 door, 6 pax etc etc)
timf
(replace SPAMnet with worldnet in email address to reply)
Gregory Travis
Charles K. Scott <Charles.K.Scott@**NOSPAM**.dartmouth.edu> wrote:
>So Terry, how can we reduce things for a meaningful comparison? Is
>this even possible? Do figures from auto manufacturers that are
>comparable to aircraft engine fuel burn specs exist? Would the BSFC
>figure be usable, should it be possible to get it? Of course, it would
>have to be at 75% power so that things are equal across the board.
Corky,
I spoke at length with Ford's David Hunt nearly two years ago as part
of some research for an article I did for Aviation Consumer.
He got me Ford's dyno data for both the 200HP Duratec engine and
the 235 HP Yamaha SHO engine. I picked those two engines, frankly, because
Mr. Hunt was actually helpful in getting me the dyno info (the other
mgfs. wouldn't release it) and, at 200 and 235 HP, they were comparable in
output to the Lycoming IO-360 and 235HP IO-540.
According to Mr. Hunt, the 200HP Duratec engine achieved a fuel conversion
efficiency of 0.46BSFC at 75% power. This is for a totally stock engine
on the dyno and measured in accordance with SAE J1349 enviro specifications.
To compare with aircraft engine BSFC, drop a couple hundredths and call it
0.44BSFC.
The 235 HP SHO came in a little better at 0.43BSFC on the automotive scale,
call it 0.43 on the aero scale.
The 200HP high compression IO-360 comes in at about 0.41-0.42 on the
aero scale. This I have directly from dyno data from Unison (given to
me by their Vice President, Brad Mottier) during their certification
tests of LASAR. Thus, despite its 40 year old technology, it still beats
the auto engines on fuel conversion. That the IO-360 does this while
still sporting a fixed advance ignition and mechanical fuel injection
is all the more illuminating.
Yes, it's possible that one could improve on the Duratec/SHO's numbers
somewhat by replacing the stock cam with one optimized for 75% power. But
then, you could also throw a LASAR ignition on the IO-360 and keep them
neck and neck (LASAR improved the IO-360s fuel conversion efficiency by at
least 0.03BSFC IIRC). .
Ref: http://www.prime-mover.org/Engines/GArticles/article2.html
The difference in fuel conversion efficiency is, as I almost always believe,
due to the lower RPM and larger displacement of the IO-360 over the
Duratec/SHO. Once again, there's no replacement for displacement. There's
no magic. Running the engine slower is a lot easier way to improve
fuel efficiency than throwing advanced ignition systems, fuel systems,
etc.
>How about it? Can anyone give us a Subie BSFC? Surely some of the
>lurkers are actually flying behind them. How about Nigel Field?
>Anyone?
The numbers I have seen, at Reiner's page, for Subie BSFC were in the
0.46 range as I recall. This was for the older, lower compression, engine.
Gregory Travis
Most of that improvement came from two, possibly three, sources:
a). Your Explorer is a whole lot more aerodynamic than
your Plymouth.
b). Your Explorer's engine is a whole lot smaller than your
Plymouth's. All piston reciprocating engines achieve their
best fuel-conversion efficiency somewhere around 60-80% of
their maximum rated power. The farther you get from that
maxima, on either side, the worse the fuel efficiency.
Your Explorer's engine, under normal conditions, is operating
a lot closer to its maximum efficiency point than was the
Plymouth engine.
c). It's quite possible that your Explorer is lighter than
the Valiant. I don't have that data however.
In GENERAL terms, the advances in auto engine "efficiency" have come
from:
1. MUCH lighter automobiles
2. Improved idle and off-idle fuel consumption via EFI
3. Smaller engines for a given vehicle size.
Shanley Mark Stephen
> Hmmm, I was going to answer this in terms of weight differences saying
> that the Merlin weighed more but it doesn't, or didn't. A quick search
> on the internet under "Rolls Royce Merlin" and "Pratt and Whitney
> R-2800" brought the following information: Merlin weight 800 Kg or 1764
> lbs. R-2800 2,350 lbs.
>
> So there goes my "The Merlin was heavier" argument.
Even in the mid 50's the typical rating on the V1650 was 1500hp and the
rating on the R2800 was 2500hp. The V1650 was still 1.2lb/hp and the R2800
was .94lb/hp.
> I'm left with current design and production inertia as a plausable
> theory. By the time Jets took over almost all the worlds airliners
> were US produced, and those airplanes were equipped with radial
> engines.
With all the WW2 funds that were dumped into the R3350 and R4360 engines,
why not use them to power airliners? The military may not care how much it
cost to develop a new 4000hp engine, however the airlines and the people
that build airliners certainly did.
> Could it be that the radial were easier to produce and assemble?
> Corky Scott
In the early 40s the jet engine and the swept wing signaled the end of the
large piston engine.
Student Pilot
wrote:
<LOTSA GOOD STUFF SNIPPED>
So how about reliability? How do you think a 1998 aircraft engine
compares to a 1998 auto engine? Or a 1978 aircraft to the 1998 auto?
Modern auto's are certainly much more reliable than old ones. Is the
same true for a/c?
Tim (trying to get smart) Friendshuh
JStricker
I wouldn't bet my house on it. Not yet anyway. Maybe when Johnny and some
of the others routinely get 2,000 hrs TBO on their engines like you can on a
Lyc 320 or 360 then we can talk, but I don't think they are. Yet.
But, as has been pointed out before, if overhauls are $2,000 instead of
$12,000, you don't really have to insist on 2,000+ hours. However, the
question wasn't about the $$$, it was just about reliability.
John Stricker
--
Remove the "nosp..........." Oh hell, you folks know what to do and
why I had to put it in. If one of you real humans wants to contact me:
"I didn't spend all these years getting to the top of the food chain
just to become a vegetarian"
Student Pilot wrote in message
<36203464...@netnews.worldnet.att.net>...
mark.j...@mindspring.com
highflyer wrote in message <361CD2...@alt.net>...
>[snip]
>While battle damage may have contributed to the decision, the fact
>remains, the more compact radiators with well designed inlets and
>outlets actually cost less power for cooling than the skin radiators.
>
>
A couple of thoughts along that line...
For optimum heat transfer from water to air, you want to have 4 - 5 times
more surface area on the air side than on the water side (primarily due to
difference in specific heat of the fluids). If you try to spread this out
on a wing surface, you wind up with either some awfully big fins (read lots
of wetted area ==> mucho drag) or you have more surface area wetted by the
coolant than you need (read more weight). A compact heat exchanger (i.e.; a
radiator) can achieve the necessary surface area relationship is a
relatively small area.
There is also a bigger payoff when the actual heat transfer takes place at
velocities lower than flight. For example, the radiator core from a
Spitfire showed that heat transfer was proportional to the core airflow
velocity to the 0.75 power, while the pressure drop was proportional to the
1.75 power of velocity. (ref: The Aerodynamics of the Cooling of Aircraft
Reciprocating Engines, ARC R&M 2498, pg. 13) Putting the radiator core
behind a diffuser lowers the velocity (.15 to .30 of flight is a good rule
of thumb for design) and gives a low pressure drop through the core.
This general relationship should also hold true if you would "unfold" the
radiator core on the wing skin. The average velocities on the wing surface
are pretty high (the upper surfaces are higher than flight velocity) and
would result in a high pressure drop.
I would argue than the Schnider cup racers were designed before there was a
solid understanding of the aerodynamics of cooling. One wonders what the
performance of an Supermarine S6B with a P-51 style radiator installation
would have been.
Mark Johnston
mark.j...@mindspring.com
Gregory Travis
Terry Schell <tsc...@s.psych.uiuc.edu> wrote:
>gr...@sherrill.kiva.net (Gregory Travis) writes:
><snip>
>>According to Mr. Hunt, the 200HP Duratec engine achieved a fuel conversion
>>efficiency of 0.46BSFC at 75% power. This is for a totally stock engine
>>on the dyno and measured in accordance with SAE J1349 enviro specifications.
>>To compare with aircraft engine BSFC, drop a couple hundredths and call it
>>0.44BSFC.
>
>
>Let's be fair, you shouldn't compare BSFC across engines that are
>burning different fuels. What would those aero engines rate if they
>had the low-compression ratios they would require to run on the same
>fuel?
Well that's a very good point and well taken. On the other hand, my
opinion is that the octane requirements of aero engines are more
dictated by certification requirements than anything else. I'm just
not sure we can make an apples to apples comparison without controlling
for a whole lot of variables.
Charles Black
Bearcat, both heavily modified, neither using surface cooling.
Chas
QDurham wrote:
>
> >I would argue than the Schnider cup racers were designed before there was a
> >solid understanding of the aerodynamics of cooling. One wonders what the
> >performance of an Supermarine S6B with a P-51 style radiator installation
> >would have been.
>
> Argue as you will. The fastest planes in the world were liquid cooled wth skin
> radiators.
>
> Quent
--
Charles Black
Terry Schell
>In article <6vioco$1km$1...@vixen.cso.uiuc.edu>,
>Terry Schell <tsc...@s.psych.uiuc.edu> wrote:
>>Just one nit... engine efficiency has not improved "many orders of
>>magnitude". In fact, for engines running near full rated power (75%)
>>engine efficiency has improved about 20% in the last 25 years.
>I'm not sure this is true even within automobile engines. 5% I can
>believe, but not 20%.
>Yeah, at idle and near idle we've seen those kinds of improvements but
>not at 75%.
I was being generous. There have been some advances in combustion
chambers, ignition, and heat management (like those hot new thermos) that
have made real improvements for high power efficiency. I am sure it
is less than 20% on averge, but I am also sure someone can find a 1970
engine with a bsfc at 75% of .49 and a 1998 engine with a BSFC of .39.
Thus the 20% claim.
Terry Schell
QDurham
Scott McQ
What would be the point in maintaining the skin of a wing at 200F?
Maintaining the surface at a minimum 40F should prevent any ice
problems.
It seems to me that a fifty degree difference between OAT and the skin
surface would be adequate for the conditions where icing is considered
a problem. Wouldn't that reduce your heat requirement to about
165,000 BTU? At 200,000 BTU out the cooling system the heat supply
should be in the ball park.
Scott McQ
In article <6vg52j$v74$1...@sherrill.kiva.net>, gr...@sherrill.kiva.net
Gregory Travis
>
>What would be the point in maintaining the skin of a wing at 200F?
>Maintaining the surface at a minimum 40F should prevent any ice
>problems.
>
>It seems to me that a fifty degree difference between OAT and the skin
>surface would be adequate for the conditions where icing is considered
>a problem. Wouldn't that reduce your heat requirement to about
>165,000 BTU? At 200,000 BTU out the cooling system the heat supply
>should be in the ball park.
40F isn't sufficient to prevent the melted ice from running back along
the wing and freezing behind the heated portion.
mark.j...@mindspring.com
QDurham wrote in message <19981009002418...@ng133.aol.com>...
>
>[portion of my previous post snipped]
>
>Argue as you will. The fastest planes in the world were liquid cooled wth
skin
>radiators.
>
>Quent
>
Conquest 1 (air cooled), Red Baron (liquid cooled), and Rare Bear (air
cooled) have all beat the Me209's 1939 speed record. The skin cooled Macchi
M72 still holds the float plane record, though.
After posting my original message last night, I was browsing through my copy
of "Aerodynamics of Propulsion" by Kuchemann and Weber. The chapter on
cooling has a brief mention of skin cooling. It states:
"On the whole this method of cooling is promising, because there need
be no
cooling loss. (Note - I'm still skeptical) Its main drawbacks are
structural
difficulties and the fact that, in the case of small aircraft
(fighters, etc.), the
whole wing surface would not provide a large enough cooling surface,
and an
ordinary heat exchangers would still be needed, at least as an
auxiliary."
Most of the cooling analysis I've done was for large engines (RR Merlin) at
high speeds (450 mph+). For a light aircraft at typical speeds, the trade
offs may be a little different. Perhaps I need to dust off a few more old
text books and see what the numbers say. According to Omar's law, "One
fact is worth a thousand opinions".
Mark "still a skeptic" Johnston
mark.j...@mindspring.com
Charles K. Scott
bring up the anomoly of the Continental 0-200 which, contrary to most
aircraft engines, does not appear be a great economizer.
I know that Reiner Hoffman recorded a better fuel burn than his friend
did during their trip to Florida from Washington State. The conditions
were Reiner: Cessna 150 with tri gear and his own EA 81 Subaru engine
with a three bladed prop vs his friend in a Cessna 150 with O-200 and a
two bladed prop. It also had a tail gear conversion. Both flew
together in loose formation, taking off and landing within minutes of
each other. Both calculated their fuel burn at refueling stops.
I've been told over and over by many who have flown behind them that
the 0-200 BSFC is in the .50 range and higher while as stated by Greg,
the EA 81 recorded .46.
Can anyone explain why this engine seems such a comparitive fuel hog?
Corky Scott
Charles K. Scott
gr...@sherrill.kiva.net (Gregory Travis) writes:
> To compare with aircraft engine BSFC, drop a couple hundredths and call it
> 0.44BSFC.
>
> The 235 HP SHO came in a little better at 0.43BSFC on the automotive scale,
> call it 0.43 on the aero scale.
>
> The 200HP high compression IO-360 comes in at about 0.41-0.42 on the
> aero scale. This I have directly from dyno data from Unison (given to
> me by their Vice President, Brad Mottier) during their certification
> tests of LASAR. Thus, despite its 40 year old technology, it still beats
> the auto engines on fuel conversion. That the IO-360 does this while
> still sporting a fixed advance ignition and mechanical fuel injection
> is all the more illuminating.
Thanks Greg, this is a keeper. Goes in the "Engine stuff" file for
future reference. Should be part of the FAC, in my opinion.
Corky Scott
Charles Black
A couple of quick thoughts as I "mad dash it out the door"
All KINDS of variables here.
A few possiblilties;
1. A/C rigged identically?
2. Engines tuned optimately?
3. Engines proped properly?
I would think one wheel pant askew would account for the difference, and
more.
LOT'S of variables here!
Charlie
--
Charles Black
Joe Della Barba
There is nothing wrong with the big bore slow turning design of
aircraft engines. This has been shown again and again to be the best
design for aiplanes.
Car engines have far more complex demands on them then aircraft
engines. Cars most operate smoothly and reliably at all power settings
and not foul plugs or waste fuel. Fixed ignition and mechanical fuel
injection are not too bad if operating in a narrow RPM range. Water
cooling is a big plus for efficiency since combustion chamber
temperatures and engine tolerances can be much more closely
controlled. It would seem the best thing would be a new aircraft
engine with the basic layout of an IO-360 with dual redundant
electronic ignition and electronic fuel injection. Or look at the
Rotax 912. What is it's BSFC?
TBO - An engines cost of operation per hour is TBO/overhaul cost.
Reliability is NOT a function of TBO, but a function of how often an
engine fails BEFORE TBO! A car engine that lasted 500 hours and cost
$1000 to overhaul would be a great deal if it didn't fail before 500
hours any more often than a Lycoming. And a long TBO is not really a
good thing for aircraft that fly 100 hours per year. Many egine parts
give up the ghost based on age, not hours.
A closing thought - I have been stuck with airplane engine problems
far more than car problems ever since I sold my MG.
Joe Della Barba