The Christmas Engine

Veeduber

unread,

Dec 25, 2002, 4:41:32 AM12/25/02

to

To All:

Christmas sometimes brings a call from a homebuilder who has read one of my
articles or seen an ad in an old magazine and is convinced I'm the best person
to build an engine for their Dream Machine. For the last twenty years I've
always told them ‘no.'

I usta build engines for sale; had an ad in ‘Sport Aviation,' went to all the
airshows. Waste of time, pretty much. I put the prop on the wrong end and do a
lot of modifications others say aren't needed. Plus, my engines were never as
powerful as the ones built by the other guys. But they seemed to hold up
rather well.

This year the call came on Monday, 23 December 2002. The fellow wanted a
simple engine, a plain vanilla sixty horsepower powerplant based on VW
components. He wanted direct drive; in fact, he'd already bought the
propeller. To keep down the cost and make it easy to overhaul, he wanted it to
use the standard 69mm crankshaft and 85.5mm jugs. It was for a Texas Parasol
and there are several flying with exactly that engine, which has a displacement
of 1600cc.

The call represented a major decision on his part. Months of thought and
careful savings had culminated in this Christmas Present to himself. I could
hear the disappointment in his voice when I told him I'm too busy right now. I
suggested he contact someone else. But he was insistent, willing to wait until
I wasn't too busy. His disappointment became tinged with anger when he
realized I simply didn't want to build him an engine. I've a hunch he thought
I was trying to jack up the price; you could feel the tension mount as the
silence grew. Finally, I told him I don't know how to build a sixty horsepower
1600cc engine. Perhaps someone else could but I can't get that much power out
of 96 cubic inches when there's a prop on the crankshaft. His anger vanished,
replaced by confusion. How much power COULD I get?

"Maybe thirty-five, forty... somewhere in there."

Now he sounded amazed. Clearly, there was no secret to getting lots of power
from a VW engine. He started to rattle off horsepower figures from several
other engine builders until I stopped him.

"I guess I'm just not as good a mechanic as those other guys," I said. He
thought about that for a moment then wished me a merry Christmas and rang off.

In a way he was right. There's no secret to getting lots of power from an
internal combustion engine. Sir Harry Ricardo literally wrote the book on it
shortly after World War I. Since then the only things that are truly new are
thermal barrier coatings and some improvements in metallurgy, the basic
principles - and the equations defining them - remain unchanged. Using those
principles I've built VW-based engines that pulled over 200hp on the dyno, good
enough to see low twelves on the drag strip.

The problem I have here is that you've got to spin a 1600cc engine nearly five
thousand rpm to see an output of sixty horsepower. And you can only do that
for about a minute before the CHT runs into the red and you have to let it cool
down for half an hour or so before you do another pull. Fitted with a blower,
tightly shrouded, and installed in a car, you can get away with calling it a
sixty horsepower engine. But a car engine isn't an airplane engine.

The reality of airplane engines is conversion of torque into thrust. You may
insert horsepower into that equation if you wish but it serves no practical
purpose. When the task is generating thrust using a fan bolted directly to the
crankshaft, torque is the critical factor.

For an internal combustion engine, particularly a carburetted Otto-cycle
engine, maximum torque occurs at the point of maximum volumetric efficiency.
You can fiddle with the cam and induction system ‘til the cows come home
trying to improve the VE but with a displacement of only 96 cubic inches,
normal aspiration and a compression ratio you can live with, lighting the fire
is going to give you a certain quanta of heat and that's going to raise the
pressure in the combustion chamber to a certain level and it's that pressure -
you may call it BMEP if you wish - that turns the crankshaft. For a 1600cc
engine and that particular set of conditions, you're never going to see more
than about 80 lb-ft of torque. And at a fairly low rpm too, which ain't all
that bad because props are more efficient at lower speeds. (When the object is
to produce thrust, if you're honest the bottom line has to include the
propeller's efficiency factor.)

Eighty ft-lbs of torque at prop speed is closer to 40 horsepower than sixty.
But even that level of output will quickly exceed the thermal limitations of
the Volkswagen's heads, assuming a standard atmosphere and a cooling-air
pressure differential equal to six inches of water, about all you manage in a
tumbleweed like the Texas Parasol. Exceeding the thermal limits doesn't mean
the thing will explode but it does mean your MTBO takes a header into the
porcelain fixture, forcing you to top the valves every fifty or one hundred
hours. Not my idea of a durable engine.

The situation is even worse if the caller wants me to build him one of those
100hp VW engines he's heard about. Sorry, Charlie. I simply don't know how.
Unless you want to compare apples to oranges. Or dune buggies to airplanes.

Remember the Continental A40? (Even flown a Piper E-2? :-) The A40's
displacement is 112 cubic inches, about the same as an 1834cc VW conversion.
The A40 produced about 90 lb-ft of torque at about 2000 rpm for a TBO of 200
hours. (I'm pulling this out of the memory bank so you'll have to work with me
here.)

A standard equation for computing horsepower is to multiply the torque in
ft-lbs times the RPM and divide the result by 5252, which is sometimes called
the ‘winding constant,' as if the torque were acting through a lever a foot
long for a full minute. 90 times 2000, divided by 5252 equals 34.3 horsepower.
Which sez I've mis-remembered something because the A40 was rated at 37hp.
But you get the idea.

Ditto for the A65. Max torque was something like 145 lb-ft at 2400 rpm. From
a displacement of 171 cubic inches. (I'll let you do the math :-)

See that 2180cc VW hanging on the test stand out behind the shop? That's my
Hangar Queen. Since 1968 or thereabouts she's racked up better than fifteen
hundred noisy hours testing everything you've ever heard of and a lot that you
haven't. (I've torn-down the poor thing so many times I've lost track.) See
that box of wiggle sticks over there in the corner? Dig around, you'll find
stock VW cams along with several from Engle, Web and Schneider, both solids
and juicers, even a couple of special grinds I worked up myself, all chuggers
designed to give maximum torque across an RPM practical for a propeller. Forty
years of VW engine building experience, nearly two thousand hours of testing -
enough gasoline to float a boat - and the best I can do is about 115 lb-ft of
torque out of that thing. That's about 55hp. At prop speeds. Not 80 or 100
like all those other guys.

Of course, those hours of testing are comparing apples to apples. Or rather,
torque to torque. And at speeds suitable for slinging a prop efficiently. On
that basis I think it's fair to say I've managed to do about as well as
Continental or Lycoming when it comes to the power output of a small air-cooled
engine. The 2180, which is about 133cid, produces about 115 lb-ft of torque.
The A65's 171 cubic inches cranked out about 145, the A40's 112 cubes managed
about 90. And I've gotten as much as 80 ft-lbs out of a sorta-stock 1600
turning about 2600 rpm. But I've obviously got a long way to go to catch up
to those other VW engine builders. Based on their published figures volumetric
efficiencies regularly exceed 100%, specific fuel consumption on the order of
three tenths of a pound per horsepower-hour is not uncommon and pulling nearly
one horsepower per cubic inch for a TBO of 1500 hours is old hat. Truly
incredible engines.

No one in their right mind would buy a forty horse engine when they can buy a
sixty horse that weighs and costs the same. Which is why I no longer build
engines for sale.

Given the nature of this Newsgroup I'm sure some will detect a hint of sour
grapes in the message above. ( And they may be right. :-) But in doing so
they will miss the point entirely. The key to powered flight is the
powerplant. Ready availability of an inexpensive, reliable engine could play a
vital role in arresting the decline of General Aviation in America, whereas
fallacious claims of power or performance does exactly the opposite.

Such an engine has been available for more than a quarter of a century and a
number of airframes have been designed around it. Designs based on the
engine's actual output and durability have proven successful, those based on
it's fallacies have not.

-R.S.Hoover

Jim Austin

unread,

Dec 25, 2002, 9:06:32 AM12/25/02

to

Veeduber wrote:
> To All:
>
> Christmas sometimes brings a call from a homebuilder who has read one of my
> articles or seen an ad in an old magazine and is convinced I'm the best person
> to build an engine for their Dream Machine. For the last twenty years I've
> always told them ‘no.'

I really enjoyed reading this post, and I learned a lot, thanks
for writing it.

Jim Austin

Big John

unread,

Dec 25, 2002, 9:49:50 AM12/25/02

to

R.S. Hoover

What a wonderful Xmas present.

Want to thank you for taking the time to try to explain to the great
unwashed masses the facts of life in simple language that everyone can
understand (up is up and down is down).

If you save one individual from an untimely death chasing rainbows,
the good Lord will look down on you and smile.

Older than mud

Big John

On 25 Dec 2002 09:41:32 GMT, veed...@aol.com (Veeduber) wrote:

>
>To All:
>
>Christmas sometimes brings a call from a homebuilder who has read one of my
>articles or seen an ad in an old magazine and is convinced I'm the best person
>to build an engine for their Dream Machine. For the last twenty years I've

>always told them 創o.'
>
>I usta build engines for sale; had an ad in 全port Aviation,' went to all the

>You can fiddle with the cam and induction system 奏il the cows come home

>the 層inding constant,' as if the torque were acting through a lever a foot

frer...@ro-dot-.com

unread,

Dec 25, 2002, 2:21:21 PM12/25/02

to

Mr Hoover:
What you say agrees with every thing I have learned about engines.
Thank you for taking the time to write it down so clearly.
Have a merry Christmas
John Frerichs

On 25 Dec 2002 09:41:32 GMT, veed...@aol.com (Veeduber) wrote:

Richard Lamb

unread,

Dec 25, 2002, 3:48:25 PM12/25/02

to

Robert,

Thank you for shedding light on this subject. I get a lot of
the same kind of requests, but I'm not in the motor business.

I get a lot of requests for information on converting to a
half VW (!) because it looks so cute. I try hard to explain
that it's not enough motor for a draggy baby buggy, but often
that is not accepted and the builder goes ahead anyway.

My recommendation for the Texas Parasol (and Texas Ranger) is
for an 1835 VW (if the builder wants to use a VW at all. The
Rotax engines are lighter and swing a larger prop! But some
of us just have to have a 4 stroke.)

There has been so much misinformation about VW engines over
the years that it's hard to get the bottom line across.

Keep spreading the word. Eventully it will get across.

Richard Lamb

Roger Halstead

unread,

Dec 25, 2002, 9:35:51 PM12/25/02

to

On 25 Dec 2002 09:41:32 GMT, veed...@aol.com (Veeduber) wrote:

>
>To All:
>
>Christmas sometimes brings a call from a homebuilder who has read one of my
>articles or seen an ad in an old magazine and is convinced I'm the best person
>to build an engine for their Dream Machine. For the last twenty years I've
>always told them ‘no.'

Thank you for adding a big helping of education to the Christmas
dinner.

Roger Halstead (K8RI EN73)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

ro...@mauve.demon.co.uk

unread,

Dec 25, 2002, 10:32:17 PM12/25/02

to

Veeduber <veed...@aol.com> wrote:
>
> To All:
>
<snip>

> The reality of airplane engines is conversion of torque into thrust. You may
> insert horsepower into that equation if you wish but it serves no practical
> purpose. When the task is generating thrust using a fan bolted directly to the
> crankshaft, torque is the critical factor.

For a given propellor diameter, pitch, and airspeed, yes.
Increase the speed, drop the diameter, lower the pitch, and you
get more thrust for the nearly the same torque.

Unfortunately of course, this raises the noise, and makes any obstruction
behind the prop even worse, and small props are less efficiant.

Agree with everything else.

Unfortunately, props running at 5000 RPM are probably not actually usable
in most applications.

--
http://inquisitor.i.am/ | mailto:inqui...@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
Among a mans many good possessions, A good command of speech has no equal.

Richard Lamb

unread,

Dec 25, 2002, 11:48:13 PM12/25/02

to

ro...@mauve.demon.co.uk wrote:
>
> Veeduber <veed...@aol.com> wrote:
> >
> > To All:
> >
> <snip>
> > The reality of airplane engines is conversion of torque into thrust. You may
> > insert horsepower into that equation if you wish but it serves no practical
> > purpose. When the task is generating thrust using a fan bolted directly to the
> > crankshaft, torque is the critical factor.
>
> For a given propellor diameter, pitch, and airspeed, yes.
> Increase the speed, drop the diameter, lower the pitch, and you
> get more thrust for the nearly the same torque.
>
> Unfortunately of course, this raises the noise, and makes any obstruction
> behind the prop even worse, and small props are less efficiant.

Efficiency - and that's the whole point.

I've gone the other way and over propped the engine on my new parasol.
It has a 2180cc VW, which will not turn 3000 rpm static with this prop.

Yes, that reduces torque from the engine since it's running lower on the
torque curve.

My bet (a whole two cents cash money, if there are any gamblers in the
house)
is on increased prop effeciency making _enough_ thrust from the power
available
at the lower RPM.

Less (over)stress on the engine, and a better match to the airframe,
performance wise.

Lower fuel bill too.

At least that's what I'm hoping will happen ;)

Dennis O'Connor

unread,

Dec 26, 2002, 11:24:34 AM12/26/02

to

Damn straight, R.S.....

Denny
"Veeduber" <veed...@aol.com> wrote in message
news:20021225044132...@mb-fk.aol.com...

MJC

unread,

Dec 27, 2002, 5:13:36 PM12/27/02

to

Just think of all the explaining time you would save if you would simply
conjure up the most famous line by Jack Nicholson in "A Few Good Men" and
tell those horsepower optimists, as soon as you pick up the phone, and say:
"You can't handle the truth!". Then hang up on 'em.

M

"Veeduber" <veed...@aol.com> wrote in message
news:20021225044132...@mb-fk.aol.com...
>

James K

unread,

Dec 29, 2002, 5:54:31 PM12/29/02

to

On 25 Dec 2002 09:41:32 GMT, veed...@aol.com (Veeduber) wrote:

>The reality of airplane engines is conversion of torque into thrust. You may
>insert horsepower into that equation if you wish but it serves no practical
>purpose. When the task is generating thrust using a fan bolted directly to the
>crankshaft, torque is the critical factor.

Nonsense. Yours is just another silly notion in the oft confused topic
of HP vs. torque.

These are the full throttle sea level HP and torque values for a
Lycoming O-320E under load (dynamometer, prop, or whatever).

RPM HP Torque (ft-lb)
2300 131 299
2700 148 288

Note that torque is greater at 2300 RPM while HP is greater at 2700
RPM. Now take two identical planes, say RV-6's, equipped with the
above engine, one with a cruise prop optimized for max cruise at 2300
RPM and the other with a cruise prop optimized for max cruise at 2700
RPM. The 2700 RPM plane will cruise faster and the prop will produce
more cruise thrust than the 2300 RPM plane because the engine is
producing MORE HORSEPOWER at 2700 RPM. The reason why the boys who
race at Reno run their engines well past torque peak is because the
increased HP produces more thrust and therefore more speed.

Luke Scharf

unread,

Dec 29, 2002, 10:12:25 PM12/29/02

to

On Sun, 29 Dec 2002 17:54:31 -0500, James K wrote:
> Note that torque is greater at 2300 RPM while HP is greater at 2700 RPM.
> Now take two identical planes, say RV-6's, equipped with the above
> engine, one with a cruise prop optimized for max cruise at 2300 RPM and
> the other with a cruise prop optimized for max cruise at 2700 RPM. The
> 2700 RPM plane will cruise faster and the prop will produce more cruise
> thrust than the 2300 RPM plane because the engine is producing MORE
> HORSEPOWER at 2700 RPM. The reason why the boys who race at Reno run
> their engines well past torque peak is because the increased HP produces
> more thrust and therefore more speed.

Assuming that the aircraft uses a fixed-pitch prop, do their aircraft take
longer to get to their top speed than an aircraft with an engine that's
tuned at maximum torque?

Thanks,
-Luke

Dec 31, 2002, 8:15:02 PM12/31/02

to

Luke Scharf <lu...@vt.edu> wrote:

>What I was asking is what are the effects of running an engine at max RPM
>vs. max Torque?

Continuing with the engine exemplified earlier (O-320E) at full
throttle under standard sea level conditions. At peak torque (about
2200 RPM) the engine will produce about 125 HP. At max RPM (2700 RPM)
the engine will produce about 150 HP.

>I have a better physical intuation of torque vs. RPM in automobiles than I
>do in airplanes. But, if it seems to me that if an engine is limited by
>torque, it couldn't even spin the prop up to the desired RPM.

I have found that it is often best to forget about "intuition" in such
matters and instead look at what the equations say. Torque curves and
power curves for rotational shaft output are inexorably tied by the
relation, in traditional English units, Torque = (HP/RPM)*5252. The
constant 5252 will yield torque in lb-ft. If an engine can't rev
past, say, 2300 RPM because a prop is absorbing all the engine
*torque* at that RPM, then it is also true that the engine can't rev
past 2300 RPM because the prop is absorbing all the engine *power* at
that RPM -- and this remains true whether the 2300 RPM in the example
is before, at, or after the torque peak of the engine.

Dave O -- http://AirplaneZone.com

Bruce A. Frank

unread,

Jan 3, 2003, 12:12:33 AM1/3/03

to

R.S.,

It is too bad that you are disillusioned with the homebuilt aviation
mags' compensation. Articles like this or extrapolation on topics like
this would enlighten many people. Your information, and writing style,
is certainly an asset to this group.

Bruce A. Frank

Veeduber

unread,

Jan 3, 2003, 6:33:01 AM1/3/03

to

Bruce A. Frank wrote:
>It is too bad that you are disillusioned with the homebuilt aviation
>mags' compensation.

------------------------------------

Dear Bruce,

When it comes to the business side of writing I wasn't aware I had any
Illusions left to dis :-)

Magazines devoted to homebuilt aviation simply do not pay very well -- if at
all -- for content, with your request for free material being a case in point.
This isn't 'disillusion' it's an economic fact. I would be quite happy to sell
them content if they paid as well as other outlets. But they don't. And it's
not too hard to figure out why.

The stats show their readership is following the same decline as General
Aviation. Fewer readers means fewer advertisers and fewer advertisers means
smaller revenues. When it comes to content, magazines print the best material
they can afford. The aviation magazines obviously can't afford very much for
content from outside sources. I've no complaint with that. But neither do I
have any illusions about the publishing industry. Lo-ball your budget for
content and you end up with a lot of freebie ego-pieces and infomercials from
your advertisers. Or a lot of material written by the staff, which may know
everything about publishing but very little about airplanes.

Fortunately, there are many outlets that offer significantly more for technical
material than the aviation magazines. When someone is willing to pay you three
grand for a friendly, understandable manual explaining how to set-up, adjust
and maintain a Universal Grinder it simply doesn't make sense to sell that same
amount of labor to an aviation magazine for less money.

Writing's a funny business but it IS a business. The writer gets paid last and
as an occupational group, not very well. It's a tough way to earn a few bucks.
Ad copy, a puff-piece for a house organ or even an instruction manual for
software -- someone has to write it and when you're selling content you sell to
the highest bidder.

I don't think any of the above can be called disillusionment. In fact, I think
most folks call it reality :-)

-R.S.Hoover

Roger Halstead

unread,

Jan 3, 2003, 12:56:44 PM1/3/03

to

On 03 Jan 2003 11:33:01 GMT, veed...@aol.com (Veeduber) wrote:

>
>Bruce A. Frank wrote:
>>It is too bad that you are disillusioned with the homebuilt aviation
>>mags' compensation.

Far, far, away, log ago, in a distant Galaxie...and in another
life...My first wife and I were in the process of getting "unhitched".
Her lawyer was after everything (including my shorts) and not doing
very well...

After taking about 20 minutes of the court's time leading up to me
having written an article, thus making me "one of those highly paid
authors", he closed his questioning with out allowing me to say how
much I was paid.

Enter my lawyer who picked up on that last, right away...."And just
how much did you receive for writing this article?"...Me: "Thirty five
dollars." Lawyer: "Thirty five dollars? Are you sure?" Me: I made
a copy of the check, would you like to see it?". Lawyer: " Ahhh, no,
that won't be necessary.".

At this point, her lawyer who had been sitting with his chin propped
up by his hand with his elbow resting on the edge of the table...fell
off the table... It's amazing how some things in life stick out like
that even if it was 23 years ago <:-))

At any rate, her lawyer was under that same impression that writing
for any magazine pays well.

One note though...her lawyer succeeded in most of his endeavors, way
beyond his expectations...She got all the bills and I got to keep my
shorts...I came out wayyyyy ahead. <:-))

Roger Halstead (K8RI EN73 & ARRL Life Member)

www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)
>