Number of blades on a propeller
Dave Eadsforth
Good day, good people,
I wondered whether anyone could provide a thumbnail outline of the
effective differences between the three blade and four blade propellers,
as fitted to various WWII fighters. I know that having more blades
could provide more thrust for a smaller diameter prop disk, and I can
visualise a number of other differences; such as the blades of a three
blade prop perhaps having to be set at a slightly coarser pitch than a
four blade prop to provide the same thrust; and perhaps suffering a loss
of efficiency because of this. But it seems that a number of Luftwaffe
aircraft put in very high performance on three blade props when compared
with the four bladers of the allied machines. And were three or four
bladers particularly renowned for performance at low/high altitudes?
So, is there a short explanation of the relative merits of three and
four bladers at the time of WWII that anyone can provide?
Apologies if this question has been asked and answered in the past, but
I sometimes miss this newsgroup for significant periods - any info would
be very much appreciated.
Cheers,
Dave
--
Dave Eadsforth
Rob Arndt
Supermarine Spiteful (5):
http://tanks45.tripod.com/Jets45/Histories/Supermarine-Attacker/Spitefu.jpg
Kyushu Shinden (6):
http://www.nasm.si.edu/research/aero/aircraft/images/kyushu_shinden.jpg
DT88
Eunometic
configuration. (There was an article on Propellers in Scientiffic
American about 15-20 years ago that stated this; I havent been into the
theory myself, you might try and search their indexes)
Notice also that most windmills are also three bladed.
Four or more blades are used to absorb the higher power levels in a
diameter suitable for ground clearence where extending the
underacarriage is not practicalble in terms of space to retract it or
weight.
Note that the B-36 had three bladed propellors.
German aircraft like the Fw-190D-9 and Ta152 used 3 large bladed wooden
propellors. The designe (VS I think) was quite efficient and relied on
3 relatively wide chorded blades of optimal profile rather than 4
smaller chorded blades that were straight all the way to the root.
Naturally the use of wood conserved a great deal of valuable aluminium
and perhaps it was this use of wood that prushed a difference in allied
and german propellors types?
Another aspect was torgue that the propellor produced. Post war the
Avia company of czechoslovakia put Junkers engines into Me 109 aircraft
instead of DB605s and found that the greater torque of the big prop
gave them a lot of difficulty.
Early Chance-Vought Corsairs used used 3 bladed propellors. (the gull
wing of the corsair was to help with ground clearence while that of the
Stuka was to keep the dragy undercarriage short). The P47's ended up
with cooling cuffs near the blade roots so had a straighter appearence,
the BMW801 radials on the other hand used a tight cowling and spinner
with a high speed gear driven cooling fan.
There is also a modern trend towards multibladed propellors so as to
keep tip speeds low in order to help with noise level emision laws
compliance.
Flyingmonk
Not necessarily so, the three blades can have wider cord than the four
blades of same length to produce equivalent thrust w/o over pitching.
WaltBJ
efficient prop airfoil is at converting torque to thrust. FW190 had
excellent prop activity. Tip speed has to be kept below Mach 1 for
efficiency. Ground clearance. Engine power/torque available. So -
bigger engines, more prop area required, 'prop area' increased by more
blades. Note that P47D25 had better prop airfoil than earlier Jugs and
performance esp climb was greatly improved. Spits got Griffon vice
Merlin - more HP, prop had to absorb it, can't make them longer, so -
more blades. BTW prop angle of attack doesn't vary much. Believe normal
range is about 5-7 degrees. looks much bigger in pictures but remeber
airstream is moving past very fast and AOA is function of rotating
speed plus firward speed. Saw a picture of a racing Fury and blade
angle looked about 45 degrees. likewise props on Bear turboprop bomber
have very coarse angle to shaft when at cruise. Bear makes hellacious
noise on takeoff because tips running close to or at M 1.0. Same with
unlimited racers - I still remeber the howl the Furies made rounding
the far pylon at Reno. The B36 was fast yet had huge props but they
were geared way down to about 900 rpm to control the tip speed up high.
(M1.0 about 573 Kts/968 fps in stratosphere). RB36s went well up into
stratosphere, above 50 grand. Another reason not heretofore mentioned
is noise; more blades let prop turn slower to absorb same HP. Hence 5
and 6 bladed commercial turboprops to minimize both inside and outside
noise..
Walt BJ
Dan, U.S. Air Force, retired
<snip>
>
> German aircraft like the Fw-190D-9 and Ta152 used 3 large bladed wooden
> propellors.
How do you get 3 propellers on a single engine aircraft?
Dan, U.S. Air Force, retired
Rob Arndt
Do you see THREE propellers on these Focke Wulfs?:
http://www.luchtoorlog.be/fwta152h_f.htm
Three BLADES idiot!
You must as dense as lead...
DT88
Peter Stickney
>
> Good day, good people,
>
> I wondered whether anyone could provide a thumbnail outline of the
> effective differences between the three blade and four blade
> propellers,
> as fitted to various WWII fighters. I know that having more blades
> could provide more thrust for a smaller diameter prop disk, and I
> can visualise a number of other differences; such as the blades of a
> three blade prop perhaps having to be set at a slightly coarser
> pitch than a four blade prop to provide the same thrust; and perhaps
> suffering a loss
> of efficiency because of this. But it seems that a number of
> Luftwaffe aircraft put in very high performance on three blade props
> when compared
> with the four bladers of the allied machines. And were three or
> four bladers particularly renowned for performance at low/high
> altitudes?
Altitude isn't really relevant - the factors that go into a
propeller's efficiency cancel altitude out.
>
> So, is there a short explanation of the relative merits of three and
> four bladers at the time of WWII that anyone can provide?
>
> Apologies if this question has been asked and answered in the past,
> but I sometimes miss this newsgroup for significant periods - any
> info would be very much appreciated.
Oddly enough, I've been marching through this stuff recently.
Like everything else in aviation, it's a balancing act.
A propeller is basically a set of wings, rather than a wood screw.
It produces thrust by using the vector sum of the propeller's
rotational speed and the airplane's forward speed to generate lift.
(Vector Sum in this case being a fancy term for the sqrt(True Airspeed
^2 + Rotational Speed ^2).
But - not only does it generate lift, it makes various sorts of drag,
as well. These cause losses.
At low speeds, what's more important is the solidity, or the
percentage of the area of the propeller disk that's taken up by the
propeller. This is necessary so that the propeller can generate
enough forward thrust (lift perpendicular to the propeller) without
requiring the airfoil used in the propeller to be stalled.
There's a stylized measure for solitidy called Activity Factor. The
higher the Activity Factor, the higher the Solidity.
At low speeds, it really doesn't matter whether the solidity comes
from having a large number of blades, or fewer wide propeller blades.
There are some penalties from the higher induced drag of wider
propeller blades, and some penalties from losses at the blade tips -
basically, the losses from wide "paddle" blades are matched by the
tip losses for more blades. Generally, propeller with, say, a 50%
higher Activity Factor will perform 2-3% better at speeds below, say,
200 mph.
At high speeds, the higher profile drag of wider propeller blades
outstrip the tip losses. Since the propeller's got plenty of air
flowing over it, you also don't need as much blade area. So - having
a larger number of skinny blades is better.
Note that the differences here aren't all that great - about 2%
between a 3 blade and 4 blade propeller with the same Activity
Factor. The practical differences here are slight - Because of the
relationship between Speed, Power, and Thrust, the thrust of a
propeller decreases as speed increases - so at, say, 400 mph, 2-3%
would be 10-15 lbs of thrust.
Then you get losses due to the rotation of the propwash.
Dual rotation propellers, (Contraprops) can, if well designed, cancel
that out, and gain enough over the interference losses of the two
tandem propellers to gain another couple of % of efficiency at high
speeds.
What's most important is that there be enough propeller (Activity
Factor) to efficiently absorb the power being fed to the propeller.
If your manufacturing capability allows it, The largest number of
blades you can use is the best way to go. If high speed performance
is desired, or you need to restrict propeller diameter, go with a
contraprop.
If you need takeoff or climb performance, go with the biggest blades
you can.
If you're looking for high speed performance, go with as many skinny
blades as you can get - the skinnier the better.
Note that controllable pitch propeller hubs are fiddly, precise pieces
of machinery that require close tolerances and lots of stuff like
ball bearings. That may be why the Germans chose to stick pretty
much with 3 blade props - while they lost some efficiency at high
speeds, you could build 4 3 blade propellers for the parts count of 3
4 blade props.
A good summary of the factors that affect propellers, and some good
graphs that show the values of the tradeoffs of various design
decisions can be found in NACA Technical Note 2966, "Propeller
Performance Charts for Transport Airplanes", John Gilman, Jr, Langley
Aeronautical Laboratory, July, 1947. It's available on line from the
NACA Technical Reports Server:
< http://naca.larc.nasa.gov/ >
--
Pete Stickney
--
Pete Stickney
Java Man knew nothing about coffee.
Flyingmonk
Dan, U.S. Air Force, retired
said there were 3 large bladed wooden propellors (sic). While you are at
it learn how to attribute, OK?
ianpa...@gmail.com
touhed on. Thrust is provided by throwing air back (Conservation of
momentum). Now the following blade has to see air that (relative to
aircraft) s moving backwards at the speed of the plane, in other words
static and not going backwards any faster. This means that the slither
of air intercepted by a blade should be clear of the next blade.
Otherwise you get turbulence.
Blades produce tubulence. The theory of chaos again tells us that a
blade (or wing) in turbulent air will be less efficient and produce
turbulent drag which is friction to you and me.
The number of blades therefore depends critically on rotation speed and
speed of aircraft.
bbrought
> There are fundamental aerodynamic issues which I don't think have been
> touhed on. Thrust is provided by throwing air back (Conservation of
> momentum). Now the following blade has to see air that (relative to
> aircraft) s moving backwards at the speed of the plane, in other words
> static and not going backwards any faster. This means that the slither
> of air intercepted by a blade should be clear of the next blade.
> Otherwise you get turbulence.
As you stated, the air is moving backwards during flight or even when
the aircraft is static and the blades are not stalled. Even if you have
lots of blades (e.g. a fan), the air coming off in the wake of one
blade will usually miss the next blade in the same disc. The only
condition where this will not be true is if you have fully stalled
blades and a stationary aircraft. That being said, in the case of very
closely spaced blades such as in a compressor disc, there is a mutual
interference between blades as they form a cascade. This does not have
anything to do with turbulence though.
Of course, if you have multiple discs (like a turbine compressor) the
wakes coming off the first disc can obviously intersect the blades of
discs downstream. The same would be true for contra-rotating
propellers.
> Blades produce tubulence. The theory of chaos again tells us that a
> blade (or wing) in turbulent air will be less efficient and produce
> turbulent drag which is friction to you and me.
The turbulence produced by a blade is concentrated in a fairly thin
sliver of air in the wake behind that blade. This wake is washed
downstream, so a following blade in the same propeller disc will not
see that turbulence.
> The number of blades therefore depends critically on rotation speed and
> speed of aircraft.
That is indeed true, among other things, but not for the reasons you
stated.
ianpa...@gmail.com
ailette (little wing). A wing has a zone of influence which is larger
than its physical size. Take a look at the graphical representation of
airflow.
Straight and level at cruising speed, blades just miss the wash of the
previous blade. All the air entering the subtended circle is
accelerated. The same thing is true of helicopter rotors.
Eunometic
The lay explanation is that if faced with having to increase blade area
without increasing propeller diameter there are two choices:
1 Increase the chord of the blade, or
2 Increase the number of blades.
Option 1 is structurally more sound but option 2 produces higher aspect
ratio blades that are aerodynamically more efficient but becuase they
are structurally less efficient the gains can be offset by weight
increases. Unrestrained by diameter issues 3 blades I believe still
tend to win out over both wider chord or narrower blades.
To get an idea of how truelly freakishly wide chorded the VS propellers
of the Fw 190 were becoming have a look at this photograph of a Fw 190
D-13. It has to be seen to be believed:
http://www.cebudanderson.com/yellow10model.htm
Only a handfull of Fw 190D-13's were flown in combat. Like the Fw
190D-9 they had a water cooled Jumo 213 engine, however while engine on
the Fw 190D-9 was a Jumo 213A-1 with a single stage supercharger that
was surplus to bomber production theengine on the Fw 190D-13 was a Jumo
213F which had a two stage instead of a single stage supercharger (
Jumo 213F was without intercooler though there was an intercooler on
the Ta 152H Jumo 213E-1), provision for mounting a motor canon firing
through the propeller boss. The aircraft can be externally
differentiated by the larger oval as opposed to circular intake, the
propeller boss gun, the absence of synchronised cowling guns.
Now the Jumo 213A-1 of the Fw 190D-9 went through three power increase
that were fitted in the field: 1 a system for injection of fuel into
the intake to charge cool a rich mixture, 2 a low pressue 'third
party' water methanol system and 3 a more powerfull junkers high
pressure water methanol system: in the end it ended up with a power
increase from 1750hp to well over 2240hp (hence the confusion over Fw
190D-9 performance).
The Fw 190D-13s jumo 213F seems to have had no more power except that
it maintained power to higher altitudes.
Interestingly I've read several times that the wide chords were
developed to help maintain performance at high altitude.
I believe these propellers were well researched. They were made of
wood though one wonder if they were solid, or built up of laminates or
whether they had a steel core.
bbrought
> As has been stated a blade is a wing. The French word for a blade is
> ailette (little wing). A wing has a zone of influence which is larger
> than its physical size. Take a look at the graphical representation of
> airflow.
Indeed: it does have a zone of influence larger than its physical size.
It induces different velocities all around it. As I stated in my first
response, in the case of a fan the blades are so close together that
they have a very strong influence on each other. This influence,
however, has very little to do with the turbulence that you refered to
in your first post. In fact, you can predict the mutual interference of
the blades, even for a fan, very well with potential flow theory for
the subsonic case or using an Euler method when shocks are present. In
the case of a propeller, even one with large paddle blades or more than
four blades, the blades are so far apart that the mutual interference
of one blade on another is very small. Again, the interference referred
to here is something different than the turbulence that you talked
about.
> Straight and level at cruising speed, blades just miss the wash of the
> previous blade. All the air entering the subtended circle is
> accelerated. The same thing is true of helicopter rotors.
As I stated in the first post, unless you have stalled blades on a
stationary aircraft, the wake of one blade does not intersect the
following blade. The turbulence generated by a blade that is not
stalled is concentrated in the boundary layer close to the surface of
that blade and in the relatively thin wake downstream of the blade.
Since this wake does not intersect another blade in the same propeller
disc (with the exception noted above), the turbulence generated by one
blade has no effect on the flow quality that a following blade
experiences.
I am not disputing the fact that the blades of a single propeller disc
have an influence on each other (although this influence is very small
for a propeller), I am disputing your claim that choosing the number of
blades on a propeller disc has something to do with mutually induced
turbulence.
frank
Greg Hennessy
<B2...@aol.com> wrote:
>Eunometic wrote:
>
><snip>
>>
>> German aircraft like the Fw-190D-9 and Ta152 used 3 large bladed wooden
>> propellors.
>
>
> How do you get 3 propellers on a single engine aircraft?
That requires 2 hundredweight of goose fat and an depraved sex act
involving a Junkers Ju-52.......
--
"Access to a waiting list is not access to health care"
Dan, U.S. Air Force, retired
> On Tue, 29 Nov 2005 23:02:17 -0600, "Dan, U.S. Air Force, retired"
> <B2...@aol.com> wrote:
>
>
>>Eunometic wrote:
>>
>><snip>
>>
>>>German aircraft like the Fw-190D-9 and Ta152 used 3 large bladed wooden
>>>propellors.
>>
>>
>> How do you get 3 propellers on a single engine aircraft?
>
>
> That requires 2 hundredweight of goose fat and an depraved sex act
> involving a Junkers Ju-52.......
Aha, I knew Ju523M were sluts!!
MajorOz
...and, it would appear, you have a sense of humor thinner than that of
your grammar.
cheers
oz, recommending the best selling book: Eats, Shoots, and Leaves
Eunometic
Peter Stickney wrote:
>
> That may be why the Germans chose to stick pretty
> much with 3 blade props - while they lost some efficiency at high
> speeds, you could build 4 3 blade propellers for the parts count of 3
> 4 blade props.
Possibly gun through prop synchronisation issues: All the
Fw-190/Ta-152 series had electrically synchronised 20mm Mk 151 canon in
the wing roots that fired through the propeller; electric ignition and
pneumatic opperation made synchronisation relatively simple.
Fw 190 v18 used a 4 bladed prop.
http://www.internetmodeler.com/2003/february/aviation/rv_fw190v18.htm
Note even with 4 blades the germans chose large paddle bladed props.
Eunometic
The grammar is correct I believe, the precise meaning must be rendered
unambiguous by the common sense given by context if the sentence is
conveyed vocally or optionally rendered unambiguous by the placement of
commas.
Bill Shatzer
> Eunometic wrote:
> <snip>
>> German aircraft like the Fw-190D-9 and Ta152 used 3 large bladed wooden
>> propellors.
> How do you get 3 propellers on a single engine aircraft?
Well, the Wrights got two props on their single-engine Flyer -
adding a third prop would seem do-able if a bit complicated.
Cheers and all,
Bill Shatzer
> There are fundamental aerodynamic issues which I don't think have been
> touhed on. Thrust is provided by throwing air back (Conservation of
> momentum).
Props are airfoils, right?
I don't think it's any more accurate to say that thrust is provided
by throwing air back than to say lift is provided by throwing air down.
Cheers and all,
Al
> I don't think it's any more accurate to say that thrust is provided
> by throwing air back than to say lift is provided by throwing air down.
>
Which is entirely accurate.
Al
"Bill Shatzer" <aw...@FreeNet.Carleton.CA> wrote in message
news:dmo1g4$r7r$1...@theodyn.ncf.ca...
MajorOz
...yeah, right...
Sister Mary Theresa would smack your knuckles bloody.
"Orange, purple, and red, the artist viewed the sunset"
Context is nice; being correct is better.
cheers
oz, who still recommends the book.
Charles K. Scott
wrote:
>I believe these propellers were well researched. They were made of
>wood though one wonder if they were solid, or built up of laminates or
>whether they had a steel core.
I'm not absolutely positive about this but I'm pretty sure the Germans
would have prefered to make their props out of aluminum, if they had
it.
Towards the end of the war when such materials were extremely scarce,
the Germans were forced to use wood for props. There's no way a wood
bladed prop, even a VERY well designed wood bladed prop, would have
the efficiency of a metal bladed prop.
Corky Scott
frank
imagine those being ineffecient considering their performance. Didn't
the Brits have enough metal? Why were those made of wood?
Charles K. Scott
I think you meant early model Spitfires because none of the later ones
had wooden props.
The Mk 1 Spitfire and all (I think) Hurricanes deployed in France had
two bladed wooden props. Even during the Battle of Britain, when the
Hurricanes had three bladed constant speed props, the performance
disparity between that airplane and the Me109E's they were confronted
with put them at a distinct disadvantage in level speed, climb and
dive. The Hurricanes might have been able to turn a slightly tighter
circle but in the crucible of battle, many of the British pilots were
relatively un tested and learned to fight in their first engagements.
This very frequently resulted in their being shot down as there was a
LOT to think about and react to in combat.
But we were discussing wooden props, and since they could be optimized
to only one specific speed, the Hurricanes equipped with them
demonstrated an even greater performance disparity to the Me109E over
France than over England only several months later.
Several things came together in England's favor just prior to the
beginning of the Battle of Britain began: 1. Representatives from
Hamilton prop came by each squadron and demonstrated how to install a
three bladed prop onto the Spitfire or Hurricane's based at that
field. They demonstrated, walked the fitters through another and then
watched them do a third. Then they packed up and headed for the next
airfield to do it all over again. 2. The US made 100 octane aviation
fuel available to England just at the time Rolls Royce finished up the
modifications they could make to the Merlin engine to take advantage
of this fuel. The modifications basically allowed a higher boost
pressure than possible with the earlier 80 or 85 octane fuel, without
engine detonation. This little known occurance resulted in a big
boost in engine performance that brought the Spitfire (with it's new
three bladed constant speed prop) to virtual parity with the Me109E,
and allowed the Hurricane to at least not be such a sitting duck.
There was of course the third thing, that of a workable interception
system based on radar. The Germans initially thought that such a
system would actually handicap the Britons by anchoring them to a
specific place.
Corky Scott
frank
frank
wood. Why is a wooden prop blade only optimized for a certain speed?
So, how much better would the late Spits have been with more effecient
metal blades?
Rob Arndt
http://www.mujweb.cz/veda/airwar/muzeum/nemecko/fw_190/clipart/f_t31.jpg
(aka V32)
DT88 ;)
Alan Dicey
The material the blade is made out of has no bearing on whether it is
attached to a variable-pitch hub or not.
The two-bladed prop on early Spitfires and Hurricanes was indeed
fixed-pitch, so only optimised for one airspeed. De Havilland was
working on variable pitch props but initially licensed the
Hamilton-Standard design, with metal blades, fitting them to Spitfires
and Hurricanes just in time for the Battle of Britain.
However wooden and composite blades continued to be used, I think
because they could be lighter, in four and five-bladed variable pitch
hubs.
Just by way of contrast, the Swordfish had a three-bladed metal
*fixed-pitch* propellor.
frank
wood, metal or composite? Why is a wooden blade only effecient at a
single speed? That made no sense at all since a variable pitch prop
changes for its performance. Now, a fixed pitch prop, whether wood,
metal or composite, does have performance limitations, but since we
were talking about wooden prop blades, not fixed pitch props, this
efficiency talk makes no sense at all, wood, metal or composite.
Dan, U.S. Air Force, retired
Think of thick wings compared to thin wings. At slow speeds thick
wings really don't cause drag problems. Take a thick wing to higher
speeds and you run into flow problems which means drag which means it is
less efficient, you need more power to over come that drag. Take a thin
wing and you can delay drag problems until a much higher velocity.
Compare a thick wing and a thin wing at 500 kt and you'll see what I mean.
Now then, which can me made into a thinner airfoil, metal or wood?
As for fixed props they tend to be optimised for cruise OR climb. A
climb prop isn't effcient at cruise and vice versa. Constant speed or
variable pitch props solve this problem with a cost in weight and
complexity.
steve gallacci
Actually, only Jumo211/213 commonly drove wooden props, among WWII
German high performance engines. And the wooden props were not inferior
in performance, as they were tailored for the particular combination of
RPM and thrust of those engines. The DB600 series engines all had metal
props, but there were applications inwhich wooden props would not have
been a compromising choice.
Narrow cord, thin section blades do need metal for construction, and run
at a combination of RPM and pitch to make the most of that pattern.
Wide cord, somewhat thicker section "paddle" blades, usually made of
wood for weight considerations more than metal saving, have their own
range of best RPM and pitch and work just fine.
Geoffrey Sinclair
>On 9 Dec 2005 06:04:30 -0800, "frank" <famv...@webtv.net> wrote:
>
>>Didn't the late model Spitfires use wooden prop blades? It's hard to
>>imagine those being ineffecient considering their performance. Didn't
>>the Brits have enough metal? Why were those made of wood?
>
>I think you meant early model Spitfires because none of the later ones
>had wooden props.
No, the Spitfires uses a variety of propellers with wooden and
metal blades. For example Morgan and Shacklady in Spitfire
the history note the weight figures for the Spitfire IX are for an
aircraft with a Rotol propeller with wooden blades. Seems the
wooden propeller was lighter in this case, though this is not
entirely clear.
The Spitfire mark IX propellers are listed as,
Merlin 61 Rotol 4 blade R.3/4F5/2 Dural 30 degree pitch.
Merlin 63 Rotol 4 blade R.5/4F5/2 Jablo or Hydulignum 30 degree
pitch or R.3/4F5/2 Dural 35 degree pitch.
Merlin 63A Rotol 4 blade R.12/4F5/2 Jablo or Hydulignum or
R.5/4F5/2 Dural 30 degree pitch
The Jablos were the wooden blades.
Seems the mark XIV came with a Rotol R16/5F5/1 5 bladed Jablo,
pitch range 35 degrees.
>The Mk 1 Spitfire and all (I think) Hurricanes deployed in France had
>two bladed wooden props.
The Spitfire prototype and the first 77 production examples (to
early May 1939) had a Weybridge mahogany 2 blade fixed pitch
(20 degrees) wooden propeller, then until around June 1940
they were fitted with the De Havilland 3 blade 2 pitch propeller
(with the earlier production being retrofitted with the new propeller
as well) with metal blades (though some of the 2 pitch propeller
blades were wooden), before going over to the De Havilland
constant speed unit in mid 1940. Priority was given to the
conversion of the aircraft in RAF hands which meant around 2/3
the newly manufactured Spitfires had the constant speed propellers
until this was done. Between June 25 and August 15th some 1,051
Hurricanes and Spitfires had been converted, with priority going to
the Spitfires, at the start of the conversion it was estimated all
Spitfires would be converted by 20 July. By 16 August every Spitfire
and Hurricane, including those in reserve had been converted. Note
the Defiants were also given constant speed propellers.
As for the Hurricane production did not change over from the fixed
pitch 2 bladed Watts propeller until after the initial order for 600
had been completed, in September 1939 and the change to metal
covered wings was 80 aircraft later, or around a month. The units
in France were given priority for the Hurricanes with the new propeller.
As with the Spitfire the earlier aircraft were retrofitted with the new
propellers. Some earlier Hurricanes were also given metal covered
wings.
De Havilland were using Hamilton Standard technology but Rotol
constant speed units were also used.
(snip)
>Several things came together in England's favor just prior to the
>beginning of the Battle of Britain began: 1. Representatives from
>Hamilton prop came by each squadron and demonstrated how to install a
>three bladed prop onto the Spitfire or Hurricane's based at that
>field. They demonstrated, walked the fitters through another and then
>watched them do a third. Then they packed up and headed for the next
>airfield to do it all over again. 2. The US made 100 octane aviation
>fuel available to England just at the time Rolls Royce finished up the
>modifications they could make to the Merlin engine to take advantage
>of this fuel.
Point 1 needs the rider that the De Havilland engineers did not
automatically leave after the 3rd aircraft was converted, but only
after a conversion was considered to have been done correctly
by the service personnel, which usually was the 3rd aircraft.
Point 2 is incorrect, the RAF had its own supply of 100 Octane,
from Commonwealth controlled refineries, it did not change over
to the new grade until stocks had been built up in 1939 and 1940.
The RAF was using 100 Octane for the aircraft of 3 squadrons
in November 1937, using fuel from refineries in the USA. A
meeting on 16 March 1939 decided to introduce the fuel into
general use with 16 fighter and 2 twin engined bomber squadrons
switched by September 1940, with an 800,000 ton stock built up.
Trials with a Spitfire began in September 1939, it cost around 53
pounds to do the conversion. Refineries at Adaban and in Trinidad
were under British control.
The fact the British could also obtain the fuel from the USA
was important given where the Commonwealth controlled
refineries were, but the RAF did not rely on US supplies.
I have not yet checked the following claim about the actual
British supply sources in 1940,
"In November 1940, UK supplies of high octane aviation fuel
were derived from three Esso refineries handling Venezuelan
oil, two in the US and one in the Caribbean (about 45%), the
Anglo-Iranian Oil refinery at Abadan (25%) and Shell
refineries in Borneo (30%). Half the British supply was
non-US in origin.
Source for above: "The History of the British Petroleum
Company" (Cambridge University Press, 1994). You might also
consult the British Official History volume entitled "Oil",
by Payton-Smith, (HMSO, 1971)."
(snip)
Geoffrey Sinclair
Remove the nb for email.
Eunometic
> Didn't the late model Spitfires use wooden prop blades? It's hard to
> imagine those being ineffecient considering their performance. Didn't
> the Brits have enough metal?
They had more than the Germans but Aluminium was still in short supply.
> Why were those made of wood?
It appears the 4 bladed prop on the Spitfire Mk IX was also wood.
There goes my theory that the Germans turned to wide chorded paddle
bladed 3 blade props becuase it was structurally easier to make in 3
bladed props than 4 bladed when wood was the only available material.
Late model Spitfires clearly used 4 and 5 bladed props made of wood
while Me 109's seem to have used all metal propellers.
There may be aspects of the type and quality and type of of wood
accesible to the Germans that enter into this.
The Fw 190 Dora (D-9: VS 111; D-11 - D-13: VS 10; and Tanks Ta 152 (VDM
VP)had wooden propellers. The leading edge had a sheet metal
incorporated to protect it against stones, etc. Perhaps the wider
chord propeller helped keep the thickness ratio low and this helped
with high speed performance.
Engineering decisions are often a complicate amalgam of practical
considerations.
steve gallacci
Wood versus metal seems to be a function of wieght/rpm/pitch
considerations rather than scarcity of metal. Jumo engines seem to have
used wooden props almost exclusively, certainly as they increased HP
output. Note history of the Ju87 or He111 inwhich they started off with
thin metal blades and then increasingly broad wooden blades.
I'd guess the wooden props ran a bit slower and at a courser pitch to
make the most of the broader cord, compared to thin metal blades at
higher RPM and finer pitch. Likely a matter of optimal gearing in the engines.