what engines are making successful aero engine conversions?

On Thu, 14 May 2009 13:34:22 -0700 (PDT), wrote:

Dear Stealth (and the Group)

We may be looking it this the wrong 'way 'round.

snip

The point of all this is that the lack of Volkswagens or other air-
cooled engines should not be taken as an automatic out. If push comes
to shove I could always convert a stray Holden, offering it up to
something like a Pietenpohl.

-R.S.Hoover

hoover you are proof positive that old dogs can learn new tricks!
I note the use of the word Holden :-) and punch that upturned thumb to
the sky thinking yesss hoover you are a champion :-) :-)

this is a subject pregnant with information shall we say but in
looking at the converted aero engine, or more specifically the
dismantled VW engine on my workbench, a weighup shows that the
chankshaft is the heaviest part in the engine.
making it lighter isnt an option by which I mean making the existing
crankshaft less substantial.
so one weight reduction option is to make it shorter, which leads to
looking again at the pobjoy geared radial made back in 1934. I've
always believed that a modern technology revisit to this design would
pay dividends. at 23inches diameter and delivering 90hp it has to be a
winner.

the great bugbear of the radial of course is the increased drag of the
flat round radial engine when compared to the flat four engine or
inline engine or even v12 layout. ...so history tells us.

I read this today in Bill Gunstons book "Development of Piston Aero
Engines"...

"Nowhere was the process [of drag reduction] more effective than in
the case of radial engines, where instead of offering an ungainly
shape - called by aerodynamicists a "bluff body"- they were enclosed
in a tight cowling in such a way that overall drag was often zero,
thrust from the heated cooling air more than countering drag from
other causes."

I was gobsmacked. NO cooling drag from a tightly cowled radial engine!
(The Hawker Fury was offered as an example)
Cooling drag in a Wittman W8 Tailwind was measured by Raspet to be 10%
of total drag at speeds over 120mph (104 and a bit knots)
I've never ever heard of a flat 4 having no cooling drag.

far from being a hackneyed subject the challenge of locating or
designing and building a 40hp aero engine presents some amazingly
fertile challenges.

one of the real plusses in this quest is that your approach is totally
different from mine and yet both are totally valid paths to follow.
Remember George Graham using a mazda rotary in second gear? That was
another path. he proved the concept but the gearbox failing just
pointed to a more substantial gearbox being needed.
I suppose the real challenge is not to be enthused by the
possibilities but to get machining and put examples in the air.

we arent done yet bob.

Stealth Pilot

On May 15, 1:37*am, Stealth Pilot
wrote:

this is a subject pregnant with information shall we say but in
looking at the converted aero engine, or more specifically the
dismantled VW engine on my workbench, a weighup shows that the
chankshaft is the heaviest part in the engine.
making it lighter isnt an option by which I mean making the existing
crankshaft less substantial.
so one weight reduction option is to make it shorter
----------------------------------------------------------

Ummm....(picking lint from my bolly-holy) actually you CAN lighten the
VW crank by a fair amount. Take a look at the crankshaft of a real
aircraft engine. (No, closer than that...) Look at the con-rod
journals. On most engines, they are hollow. A couple of after-market
crankshaft makers here in Southern California offered such cranks.
Most of them suffered from cracks but boy would they spin! Which was
the goal. As in drag racing.

Another option is to make the con-rod journals SMALLER, as in 50mm vs
55. I know it tain't much but when every little bit helps...

Of course, the real question is WHY do you want to make it lighter?
(No, don't tell me. I'd probably just break down and cry.) Because
if you are sooper-serious about reducing the weight of the VW engine
there are a few options you apparently have not yet explored, such as
using steel tubing for the barrels. And drilling-out the rocker-arm
shafts. And the cam shaft. And throwing away that steel sump
plate... (Make a new drain by drilling & tapping an M8 hole in the
outer corner next to the hole in the sump... the one for the Type III
dip-stick & filler. Now there is no reason NOT to use an aluminum
panel for your sump plate. Indeed, you can rivet brackets to it; help
support the carb-heat box and whatever)

Your rods can stand a bit of dieting. Some guys turn them into
carefully balanced Swiss cheese, replace them every couple of races
(or risk having one snap in two).

But probably the biggest weight reduction is to put the prop on the
clutch-end of the engine, reducing your prop hub to a flange and a
spool-type spacer, the combination of which typically weighs less than
a long/thick prop-hub for the other end of the crankshaft.

Ditto for MOUNTING the engine. With the prop on the proper end of the
crankshaft you may use the existing threaded bosses on either side of
the pump opening and build yourself a space-frame type mount. No
'accessory housing'. Mount the dynamo directly to the crankcase..
itty-bitty flanged driver for the magnets.

All-aluminum intake manifolding. Single-port heads.

Trick here, another there, bottom line is on the order of 140 pounds.
Which you gotta admit is pretty light for a veedub.

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


, which leads to
looking again at the pobjoy geared radial made back in 1934. I've
always believed that a modern technology revisit to this design would
pay dividends. at 23inches diameter and delivering 90hp it has to be a
winner.
-----------------------------------------------------------------------------

As for the shorter crankshaft weighing LESS... I think I'd have to
see it. Typical radial crank calls for a massive master-rod, bolted-
on counter weights, etc. And three jugs wouldn't get you very much. I
think you'd need five or seven before you'd start to see any
improvement in the pwr vs weight department.

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

the great bugbear of the radial of course is the increased drag of the
flat round radial engine when compared to the flat four engine or
inline engine or even v12 layout. ...so history tells us.
-----------------------------------------------------------------------------------

Dig deeper. Search seed: NACA cowling. Magic!

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

I read this today in Bill Gunstons book "Development of Piston Aero
Engines"...

"Nowhere was the process [of drag reduction] more effective than in
the case of radial engines, where instead of offering an ungainly
shape - called by aerodynamicists a "bluff body"- they were enclosed
in a tight cowling in such a way that overall drag was often zero,
thrust from the heated cooling air more than countering drag from
other causes."

I was gobsmacked. NO cooling drag from a tightly cowled radial engine!
(The Hawker Fury was offered as an example)
Cooling drag in a Wittman W8 Tailwind was measured by Raspet to be 10%
of total drag at speeds over 120mph (104 and a bit knots)
I've never ever heard of a flat 4 having no cooling drag.
-------------------------------------------------------------------------------------------------

Me neither... if the thing is air-cooled. But zero-D IS a possibiity
with liquid cooling. Tank fulla Prestone lets you move the cooling
drag to some area where it ain't. Drag. Get the input/output ratios
right you get NEGATIVE drag... which is called Thrust. (More Magic,
as per F-51)

------------------------------------------------------------------------------------------------
far from being a hackneyed subject the challenge of locating or
designing and building a 40hp aero engine presents some amazingly
fertile challenges.

one of the real plusses in this quest is that your approach is totally
different from mine and yet both are totally valid paths to follow.
Remember George Graham using a mazda rotary in second gear? That was
another path. he proved the concept but the gearbox failing just
pointed to a more substantial gearbox being needed.
I suppose the real challenge is not to be enthused by the
possibilities but to get machining and put examples in the air.
----------------------------------------------------------------------

Yeah, something like that. Except you need someone to run the numbers
on the GEAR TEETH or you get these horrible screechy noises

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

we arent done yet bob.
------------------------------------------------------------

Heaven's no! (Swapping his scones recipe for biscuits... and finding
out they're the same thing!)

Maybe mixing up some Secret Sauce for the exhaust stack & ports that
moves the heat farther down the pipe before it begins to cool. That
maintains the VELOCITY of the exhaust gases and other noxious fumes,
allows you to move the same amount of gas in less time through a
smaller pipe, creates a deep area of low pressure in the combustion
chamber just when the poppet valve pops it... SUCKS the fuel/air
charge into the cylinder doing all sorts of nice things to the
Volumetric Efficiency along the way. Super charging without that
little turbine ...less weight, even when plumbing 1 into 3 and 2 into
4. Not a big improvement but some.

Add all the somes (sums?) and while you can't point your finger at any
single one of them an say 'Ah ha!' you get to wave your arms at the
whole engine and the DOZENS of incremental improvements -- all those
'unimportant' details the Experts are always telling us we can
ignore. Add them up and while any single ONE may be 'unimportant'
their total adds up in a remarkable fashion.

Impossible, the experts say. Like the NACA ring-cowling. (Put one on
the NYP and Charlie could have made it to Moscow with fuel to spare.)

In article ,
Stealth Pilot wrote:

(snip)
so one weight reduction option is to make it shorter, which leads to
looking again at the pobjoy geared radial made back in 1934. I've
always believed that a modern technology revisit to this design would
pay dividends. at 23inches diameter and delivering 90hp it has to be a
winner.

From what I have heard, the Pobjoy was NO joy to fly! Apparently it was
highly unreliable and would quit at the least desirable times.

The Pobjoy factory was destroyed during a WW-II bombing raid (perhaps by
disgruntled RAF pilots who had flown one?).

(snip)

--
Remove _'s from email address to talk to me.

On Fri, 15 May 2009 13:26:27 -0400, Orval Fairbairn
wrote:

In article ,
Stealth Pilot wrote:

(snip)
so one weight reduction option is to make it shorter, which leads to
looking again at the pobjoy geared radial made back in 1934. I've
always believed that a modern technology revisit to this design would
pay dividends. at 23inches diameter and delivering 90hp it has to be a
winner.

From what I have heard, the Pobjoy was NO joy to fly! Apparently it was
highly unreliable and would quit at the least desirable times.

The Pobjoy factory was destroyed during a WW-II bombing raid (perhaps by
disgruntled RAF pilots who had flown one?).

(snip)

I was talking with the Shuttleworth Trust guys about their Comper
Swift and its Pobjoy. evidently it has been made from a few different
models and is a nightmare for replacement parts. they have had it
embalmed for 3 years now. they usually rest aircraft for two years at
a time in rotation but the Pobjoy is problem enough that they didnt
take it out of preservation. It leaks oil like the best of british
engines evidently.
but the design of the pobjoy has aspects that are brilliant. picture
90 hp out of a little engine 22 inches in diameter.
it has one often overlooked claim to fame in that it was the first of
the high reving geared reduction engines.

I still maintain that this engine is worthy of a manufacturing revisit
and update for the homebuilder market.

does anyone know whether any of the drawings remain for any of the
pobjoy engines? I'd like to build one.

Short Brothers in Ireland evidently bought out Pobjoy when it went
toes up but I have not been able to find out whether any of the Pobjoy
factory drawings have survived.

Stealth Pilot.

"Stealth Pilot" wrote in message
...
On Fri, 15 May 2009 13:26:27 -0400, Orval Fairbairn
wrote:

In article ,
Stealth Pilot wrote:

(snip)
so one weight reduction option is to make it shorter, which leads to
looking again at the pobjoy geared radial made back in 1934. I've
always believed that a modern technology revisit to this design would
pay dividends. at 23inches diameter and delivering 90hp it has to be a
winner.

From what I have heard, the Pobjoy was NO joy to fly! Apparently it was
highly unreliable and would quit at the least desirable times.

The Pobjoy factory was destroyed during a WW-II bombing raid (perhaps by
disgruntled RAF pilots who had flown one?).

(snip)

I was talking with the Shuttleworth Trust guys about their Comper
Swift and its Pobjoy. evidently it has been made from a few different
models and is a nightmare for replacement parts. they have had it
embalmed for 3 years now. they usually rest aircraft for two years at
a time in rotation but the Pobjoy is problem enough that they didnt
take it out of preservation. It leaks oil like the best of british
engines evidently.
but the design of the pobjoy has aspects that are brilliant. picture
90 hp out of a little engine 22 inches in diameter.
it has one often overlooked claim to fame in that it was the first of
the high reving geared reduction engines.

I still maintain that this engine is worthy of a manufacturing revisit
and update for the homebuilder market.

does anyone know whether any of the drawings remain for any of the
pobjoy engines? I'd like to build one.

Short Brothers in Ireland evidently bought out Pobjoy when it went
toes up but I have not been able to find out whether any of the Pobjoy
factory drawings have survived.

Stealth Pilot.

I have heard that the (so called) area rule has a considerable effect on
drag at surprisingly low speeds.

Presuming that is the case, the benefit of the smaller diameter engine might
be trivial, except on a single seater or a tandem two seater, so you might
also consider the Rotec radial.

Peter

On Sat, 16 May 2009 10:58:14 -0400, "Peter Dohm"
wrote:



I have heard that the (so called) area rule has a considerable effect on
drag at surprisingly low speeds.

Presuming that is the case, the benefit of the smaller diameter engine might
be trivial, except on a single seater or a tandem two seater, so you might
also consider the Rotec radial.

Peter



rotec is not in consideration. my target is a light 40 hp engine for
single seat aircraft.

Stealth Pilot wrote:
On Sat, 16 May 2009 10:58:14 -0400, "Peter Dohm"
wrote:


I have heard that the (so called) area rule has a considerable effect on
drag at surprisingly low speeds.

Presuming that is the case, the benefit of the smaller diameter engine might
be trivial, except on a single seater or a tandem two seater, so you might
also consider the Rotec radial.

Peter



rotec is not in consideration. my target is a light 40 hp engine for
single seat aircraft.

Rotax 503, although I doubt that's what you'll want...

"Stealth Pilot" wrote

rotec is not in consideration. my target is a light 40 hp engine for
single seat aircraft.

How about a Harley Davidson motorcycle engine? I see some guy has been
using one for airplane use.

It seems like it would have a lot of things going for it. Air and oil
cooled, power output shaft designed to drive a primary drive belt, just like
could be used to drive a prop. Light and should have plenty of power for
your use. Plenty engines available, different sizes, and good supplies of
aftermarket parts.

The only drawback is the uneven drive pulses, and only two cylinders-at
that. Still, it seems to work for at least one guy.

I saw a three cylinder Harley-like engine on a TV motorcycle show once. I
wonder how that would work.

And, it sounds cool for a bonus!
--
Jim in NC

Morgans wrote:
How about a Harley Davidson motorcycle engine? I see some guy has been
using one for airplane use.

It seems like it would have a lot of things going for it. Air and oil
cooled, power output shaft designed to drive a primary drive belt, just like
could be used to drive a prop. Light and should have plenty of power for
your use. Plenty engines available, different sizes, and good supplies of
aftermarket parts.

The only drawback is the uneven drive pulses, and only two cylinders-at
that. Still, it seems to work for at least one guy.

I saw a three cylinder Harley-like engine on a TV motorcycle show once. I
wonder how that would work.

And, it sounds cool for a bonus!

I don't think a HD engine has sufficient cooling fins on the cylinder
heads to run at a steady power output and not melt. It's the VW problem
all over again. And as has already be discussed, casting cylinder heads
is no easy job.

If someone were to custom build an engine, there are HD parts that would
make the project go a bit quicker. I once sketched up an opposed twin
using parts from the all aluminum head HD engine back in the mid 1980s.
It was a somewhat doable project but I wasn't thinking of it as an
aircraft power plant but rather an modernization of the very rare WWII
military Harley XA.

Tony

"Morgans" wrote in message
...

"Stealth Pilot" wrote

rotec is not in consideration. my target is a light 40 hp engine for
single seat aircraft.

How about a Harley Davidson motorcycle engine? I see some guy has been
using one for airplane use.

It seems like it would have a lot of things going for it. Air and oil
cooled, power output shaft designed to drive a primary drive belt, just
like could be used to drive a prop. Light and should have plenty of power
for your use. Plenty engines available, different sizes, and good
supplies of aftermarket parts.

The only drawback is the uneven drive pulses, and only two cylinders-at
that. Still, it seems to work for at least one guy.

I saw a three cylinder Harley-like engine on a TV motorcycle show once. I
wonder how that would work.

And, it sounds cool for a bonus!
--
Jim in NC

IIRC, the then current Harley was a recommended powerplant for some ot the
Mignet "Flying-Flea" aircraft of the period c1970.

Peter