what engines are making successful aero engine conversions?

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.

On May 14, 2:34*pm, wrote:
Dear Stealth (and the Group)

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

There are plenty of engines which offer excellent power-to-weight
ratios. *Unfortunately, they do so at rpm's which make them
impractical for slinging a prop UNLESS a PSRU is used.

A good case-in-point is the Rotax. *The Rotax engine is only 1300cc
but it is designed to operate near 6000 rpm. *What makes the engine
successful is the PSRU between the engine and the prop.

There are two obvious conclusions we can draw from this. *The first is
that the engines themselves, despite any practical combination of cam
& cooling, are simply too small to be used with the propeller mounted
directed to the crankshaft. *(This leads to another series of
questions worthy of discussion but which I will leave untouched at
this time.)

The second point is that the PSRU, which does NOT enjoy the same TBO
as the engine itself, has been designed specifically for this
application, taking advantage of the engine's torque & power curves,
and including mechanical features that make it suitable for the
mounting of a propeller; mounting the engine to an airframe and so
forth.

It may then be argued that we are wasting our time by focusing on the
ENGINE; that we should be devoting our energies to a suitable PSRU
that may be attached to a WIDE VARIETY of engines.

Having devoted most of my attention to the VW engine, I have little to
offer the Group should the discussion turn to PSRU's but it would seem
that the hand-maiden of these light-weight, powerful engines MUST be
an automotive TRANSMISSION having similar features of light-weight and
power-handling capacity. *Here again, I lack the background and
experience to do more than mutter; there are aspects of PSRU's,
transmissions and torque converters about which I know nothing at
all... other than the fact they must exist (since the engines exist).

At the very least, I know the GEARS must exist.

Were I in Western Australia, rather than curse the darkness (and wish
for a Corvair to suddenly appear on my doorstep) I think I would light
a single candle by diving into whatever came my way in the form of
light-weight engines and trannies.

I suppose there has to be a clutch in there somewhere, so that means
I'm probably looking at a flywheel as well... fate stacking the weight
against my urge to fly. *But perhaps some of those powerful, light-
weight engines ARE large enough to be able to drive a prop directly,
even if I had to find someone to grind me a new cam.
Re. PSRU's

There is a gear reduction unit that handles massive torque and power
the size of a a one-pound coffee can - it's the planetary gearset from
an automatic transmission. I have two in my Jeep Grand Cherokee
'airport car' transmission that have lasted 300,000 miles - so far.
These things are built to very tight tolerances and are VERY tough.

If you want still tougher, speed shops sell replacement planetaries
that can handle 1500HP or more. Ask one to handle only 100HP and
they should last forever. You can specify just about any reduction
ratio you want.

All you have to do is machine a nose case from billet aluminum to hold
the planetary gearset and the thrust bearing.

On May 16, 4:13 pm, bildan wrote:
Re. PSRU's

There is a gear reduction unit that handles massive torque and power
the size of a a one-pound coffee can - it's the planetary gearset from
an automatic transmission. I have two in my Jeep Grand Cherokee
'airport car' transmission that have lasted 300,000 miles - so far.
These things are built to very tight tolerances and are VERY tough.

If you want still tougher, speed shops sell replacement planetaries
that can handle 1500HP or more. Ask one to handle only 100HP and
they should last forever. You can specify just about any reduction
ratio you want.

All you have to do is machine a nose case from billet aluminum to hold
the planetary gearset and the thrust bearing.

I wish it was so simple. Without a flywheel and/or torque converter
to damp the engine's power pulses, the engine's desire to run in a
vibratory fashion will conflict with the prop's desire to run
smoothly, and at some resonant RPM the gears can die. They need almost
zero lash, or some heavy flywheel on the engine, or the damping of a
torque converter.

Dan

Stealth Pilot wrote:
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.


A Comper Swift flew out of Coventry (UK) in the 60s-70s time frame.
It had the unexpected attribute that it could climb almost twice as fast
as a C150 - though its top speed was nothing to write home about.
It was called "Scarlet Angel". It was the plane that had flown home from
India. I later regretted not taking up the offer to buy it when the
opportunity came along.

Brian W

On May 16, 4:34*pm, wrote:
On May 16, 4:13 pm, bildan wrote:

Re. PSRU's

There is a gear reduction unit that handles massive torque and power
the size of a a one-pound coffee can - it's the planetary gearset from
an automatic transmission. *I have two in my Jeep Grand Cherokee
'airport car' transmission that have lasted 300,000 miles - so far.
These things are built to very tight tolerances and are VERY tough.

If you want still tougher, speed shops sell replacement planetaries
that can handle 1500HP or more. *Ask *one to handle only 100HP and
they should last forever. *You can specify just about any reduction
ratio you want.

All you have to do is machine a nose case from billet aluminum to hold
the planetary gearset and the thrust bearing.

* *I wish it was so simple. Without a flywheel and/or torque converter
to damp the engine's power pulses, the engine's desire to run in a
vibratory fashion will conflict with the prop's desire to run
smoothly, and at some resonant RPM the gears can die. They need almost
zero lash, or some heavy flywheel on the engine, or the damping of a
torque converter.

Dan

I didn't suggest that no flywheel would be necessary but it also
depends on the number of cylinders. A 4-cyl will need a heavy one but
an 8 cylinder could do with less.

bildan wrote:
....
Re. PSRU's
There is a gear reduction unit that handles massive torque and power
the size of a a one-pound coffee can - it's the planetary gearset from
an automatic transmission. ...
*
*
... Without a flywheel and/or torque converter
to damp the engine's power pulses, the engine's desire to run in a
vibratory fashion will conflict with the prop's desire to run
smoothly, and at some resonant RPM the gears can die....
Dan

... it also depends on the number of cylinders.
A 4-cyl will need a heavy one but an 8 cylinder could do with less.

Car engines often feature a crank damper on the front end.
This stops the angular oscillations that lead to crack ups.
Manual transmissions feature sprung drive on the live clutch plate.
This can serve a similar purpose. Besides the fluid flywheel there is
also the rubber spider drive to the half shaft, on some sports coupes.

As an odd-ball thought, wouldn't it be nice if two tubes sized to fit a
fabric reinforced hose pipe between them, and epoxied to both tubes
were arranged with a gap in the inner steel tube, then a gap in the
outer tube alternately - arranged to provide angular give in 'series'
for a soft, vibration absorbing drive shaft....

Brian W

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...

Peter Dohm wrote:
"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




Interesting point, Peter.

The skinny tandem Piper Cub, for instance, has much higher equevilant
flat plate area than a fat side by side Taylorcraft.