AN ENGINE FOR HOMEBUILDERS

As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions. While such conversions may be as large as
140cid (2332cc) when using a Type I crankcase -- and up to 170cid
(2884cc) if you begin with the heavier Type IV -- the SUSTAINABLE
output of these engines is thermally limited by the design of their
heads, which were designed for a 40hp engine. But the root problem is
much worse than many imagine.

In a recent thread in this Group it was pointed out that in some
locales the aircooled Volkswagen engines have become rare and the
price of a suitable conversion. This makes any discussion of the most
appropriate VW conversion moot since we are running out of VW's to
convert.

This lead to a general discussion regarding engines in general which
evolved into several specific messages discussing the conversion of
other, water-cooled engines.

Using history as my guide it appears that the ideal engine for home-
builders has already come and gone. It was the Pobjoy radial, first
built in 1926 and abandoned at the close of World War II. The rights
to the 7-cylinder, 130 lb, 75hp engine is presently held by the same
people who manufacture the Rotax, who have no plans for its re-
introduction, although its STC remains valid. This geared (double-
herringbone) radial was rated at 75hp @ 3000 rpm, 85hp @ 3300, with a
TBO between 1500 and 2000 hours. The exceptional TBO was largely due
to the incorporation of a centrifugal oil filter, a feature not seen
on other engines until the mid-1950's. With equal-length intake
runners and a heated intake manifold, the engine was remarkably
efficient, having a specific fuel consumption which rivaled that of
many large radials of the future (SFC 0.485 to 0.504). It managed to
do all that whilst burning 70 octane fuel using a CR of 6.5:1. This
outstanding thermal efficiency was largely due to the elimination of
ALL plain bearings, which are ball, needle or roller through-out.

Despite its sophistication his engine has a number of features that
make it a near perfect match for most of today's homebuilts.
Paramount among them is the high percentage of identical parts, such
as the cylinders, intake manifold(s) and valve train which make the
engine an excellent candidate for 'kitting.' It's weight of only 130
pounds is partly reflected by its small size. The cylinders are 75mm
bore (same as the early VW) by 87mm stroke, a classic high-torque
'under-square' design. Fully mantled and installed, the engine is
less than 24" in diameter. The 75mm pistons are fitted to flanged,
cast-iron barrels which are threaded to the dual-plug, cast aluminum
heads in what was to become an industry-wide technique.

At the time of its inception its designer understood that it could not
compete for price with the mono-bloc 4-cyl in-line engines being
produced by de Havilland but felt there was still a market for an
engine that got its power and fuel economy from a design having
inherently greater efficiency. This proved correct and for the next
twenty years Pobjoy engines went on to power an impressive number of
winning racers as well as setting many long-distance records (ie,
England to Australia; London to Cape Town, etc.)

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

As for least-cost, as mentioned above, the key factors were recognized
shortly after World War I, when the useful life of an engine was
measured in tens of hours. This lead to a family of strudy in-line
engine that remain in production today, an by doing so offer the
amateur builder of airplanes a well marked path to follow.

The least expensive engine will always be the one which is
manufactured in the largest numbers. In countries having few
petroleum resources -- where the price of fuel will always be a
determining factor -- the engine most commonly available will tend to
be quite small, typically 1300cc or less. In order to gain sufficient
torque to power a vehicle, these small engines will usually be fitted
with a cam that puts the power-curve at or above 3000rpm. These
engines are of little use for driving the propeller directly since the
propeller needs an rpm of 1500 to 2500 for best efficiency under
Standard Day conditions. It is possible to re-grind the cam so as to
move the torque-peak into the range most suitable for propellers but
the odds are, with a displacement of 1300cc or less, the amount of
thrust from a directly-driven propeller will not be enough to fly the
typical amateur-built design.

If a suitable Propeller Speed Reduction Unit (PSRU) is available, it
will have a radical effect on the equation. But it will also have a
remarkable effect on the WEIGHT, in that a PSRU of suitable
durability.

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

In much of the world the most practical engine for conversion will be
an in-line, liquid-cooled 4-cylinder engine having a displacement
between 1500 and 2000 cc. The propeller will be mounted directly to
the clutch-end of the crankshaft using an aluminum spool to extend the
propeller beyond the engine's transmission flange. Ideally, the
manufacturer of the engine will offer a range of cams. By rpm by
application is typically Marine Engine = highest rpm/torque curve,
Automobile Engine = high rpm/torque curve, Truck Engine = medium rpm/
torque curve, and Industrial Engine = lowest rpm/torque curve.

With the exception of the cam, which should be swapped to give maximum
torque at the lowest rpm, such an engine may be used WITHOUT further
conversion. However, it's high weight will limit its use to Single-
Place designs having a wing area typically of 120 square feet or more.
While the engine may be installed in aircraft having less wing area,
wing-loading will result in a stall and landing speed that may be
unacceptably high.

The most successful of several weight reduction efforts will be to
convert the engine to Composite Cooling, in which the heads are liquid-
cooled, the cylinder barrels and sump are air-cooled. This usually
involves the fabrication of a deeply finned aluminum sump. The
cylinder are cut off of the original engine casting and replaced with
after-market air-cooled barrels. The head is cut off from the
original engine's barrels and modified to mate with the replacement
air-cooled barrels. The head is modified so as to allow liquid
cooling and suitable arrangements are made for driving a water pump.
This assume that the person doing the conversion has access to a fully
equipped welding and machine shop. If that assumption is not valid,
or if the cost of the conversion is too high, then you will have to
fall back on the use of an un-converted engine, perhaps adjusting your
wing area to bring the stalling speed into an acceptable range.

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

Modifying an airframe so as to increase it's wing area is NOT a
trivial chore. But it is doable. Be sure to keep in mind that the
existing wing and tail is a SET. If the wing area is increased then
the moment between the wing's center of lift and the horizontal
stabilizers center of lift must be increased proportionally. In the
same vein, the Volume of the horizontal stabilizer and the vertical
stabilizer must retain the same RATIO with the new wing. As for
structural strength, you may use the dimensions of the existing spars
or struts, compared to the existing wing, and increase them according
to the RATIO of old vs new. This is NOT the correct way to do it but
since the standard practice is to provide for more than the required
strength in the original design, you will be reasonable correct so
long as you limit the load of any accelerated maneuvers to 3.3g or
less.

-R.S.Hoover

On May 19, 2:52*pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions. *While such conversions may be as large as
140cid (2332cc) when using a Type I crankcase -- and up to 170cid
(2884cc) if you begin with the heavier Type IV -- *the SUSTAINABLE
output of these engines is thermally limited by the design of their
heads, which were designed for a 40hp engine. But the root problem is
much worse than many imagine.

In a recent thread in this Group it was pointed out that in some
locales the aircooled Volkswagen engines have become rare and the
price of a suitable conversion. *This makes any discussion of the most
appropriate VW conversion moot since we are running out of VW's to
convert.

This lead to a general discussion regarding engines in general which
evolved into several specific messages discussing the conversion of
other, water-cooled engines.

Using history as my guide it appears that the ideal engine for home-
builders has already come and gone. *It was the Pobjoy radial, first
built in 1926 and abandoned at the close of World War II. *The rights
to the 7-cylinder, 130 lb, 75hp engine is presently held by the same
people who manufacture the Rotax, who have no plans for its re-
introduction, although its STC remains valid. *This geared (double-
herringbone) radial was rated at 75hp @ 3000 rpm, 85hp @ 3300, with a
TBO between 1500 and 2000 hours. *The exceptional TBO was largely due
to the incorporation of a centrifugal oil filter, a feature not seen
on other engines until the mid-1950's. *With equal-length intake
runners and a heated intake manifold, the engine was remarkably
efficient, having a specific fuel consumption which rivaled that of
many large radials of the future (SFC 0.485 to 0.504). *It managed to
do all that whilst burning 70 octane fuel using a CR of 6.5:1. This
outstanding thermal efficiency was largely due to the elimination of
ALL plain bearings, which are ball, needle or roller through-out.

Despite its sophistication his engine has a number of features that
make it a near perfect match for most of today's homebuilts.
Paramount among them is the high percentage of identical parts, such
as the cylinders, intake manifold(s) and valve train which make the
engine an excellent candidate for 'kitting.' *It's weight of only 130
pounds is partly reflected by its small size. *The cylinders are 75mm
bore (same as the early VW) by 87mm stroke, a classic high-torque
'under-square' design. *Fully mantled and installed, the engine is
less than 24" in diameter. *The 75mm pistons are fitted to flanged,
cast-iron barrels which are threaded to the dual-plug, cast aluminum
heads in what was to become an industry-wide technique.

At the time of its inception its designer understood that it could not
compete for price with the mono-bloc 4-cyl in-line engines being
produced by de Havilland but felt there was still a market for an
engine that got its power and fuel economy from a design having
inherently greater efficiency. *This proved correct and for the next
twenty years Pobjoy engines went on to power an impressive number of
winning racers as well as setting many long-distance records (ie,
England to Australia; London to Cape Town, etc.)

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

As for least-cost, as mentioned above, the key factors were recognized
shortly after World War I, when the useful life of an engine was
measured in tens of hours. *This lead to a family of strudy in-line
engine that remain in production today, an by doing so offer the
amateur builder of airplanes a well marked path to follow.

The least expensive engine will always be the one which is
manufactured in the largest numbers. *In countries having few
petroleum resources -- where the price of fuel will always be a
determining factor -- the engine most commonly available will tend to
be quite small, typically 1300cc or less. *In order to gain sufficient
torque to power a vehicle, these small engines will usually be fitted
with a cam that puts the power-curve at or above 3000rpm. *These
engines are of little use for driving the propeller directly since the
propeller needs an rpm of 1500 to 2500 for best efficiency under
Standard Day conditions. *It is possible to re-grind the cam so as to
move the torque-peak into the range most suitable for propellers but
the odds are, with a displacement of 1300cc or less, the amount of
thrust from a directly-driven propeller will not be enough to fly the
typical amateur-built design.

If a suitable Propeller Speed Reduction Unit (PSRU) is available, it
will have a radical effect on the equation. *But it will also have a
remarkable effect on the WEIGHT, in that a PSRU of suitable
durability.

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

In much of the world the most practical engine for conversion will be
an in-line, liquid-cooled 4-cylinder engine having a displacement
between 1500 and 2000 cc. *The propeller will be mounted directly to
the clutch-end of the crankshaft using an aluminum spool to extend the
propeller beyond the engine's transmission flange. *Ideally, the
manufacturer of the engine will offer a range of cams. *By rpm by
application is typically Marine Engine = highest rpm/torque curve,
Automobile Engine = high rpm/torque curve, Truck Engine = medium rpm/
torque curve, and Industrial Engine = lowest rpm/torque curve.

With the exception of the cam, which should be swapped to give maximum
torque at the lowest rpm, such an engine may be used WITHOUT further
conversion. *However, it's high weight will limit its use to Single-
Place designs having a wing area typically of 120 square feet or more.
While the engine may be installed in aircraft having less wing area,
wing-loading will result in a stall and landing speed that may be
unacceptably high.

The most successful of several weight reduction efforts will be to
convert the engine to Composite Cooling, in which the heads are liquid-
cooled, the cylinder barrels and sump are air-cooled. *This usually
involves the fabrication of a deeply finned aluminum sump. *The
cylinder are cut off of the original engine casting and replaced with
after-market air-cooled barrels. *The head is cut off from the
original engine's barrels and modified to mate *with the replacement
air-cooled barrels. *The head is modified so as to allow liquid
cooling and suitable arrangements are made for driving a water pump.
This assume that the person doing the conversion has access to a fully
equipped welding and machine shop. *If that assumption is not valid,
or if the cost of the conversion is too high, then you will have to
fall back on the use of an un-converted engine, perhaps adjusting your
wing area to bring the stalling speed into an acceptable range.

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

Modifying an airframe so as to increase it's wing area is NOT a
trivial chore. *But it is doable. *Be sure to keep in mind that the
existing wing and tail is a SET. *If the wing area is increased then
the moment between the wing's center of lift and the horizontal
stabilizers center of lift must be increased proportionally. *In the
same vein, the Volume of the horizontal stabilizer and the vertical
stabilizer must retain the same RATIO with the new wing. *As for
structural strength, you may use the dimensions of the existing spars
or struts, compared to the existing wing, and increase them according
to the RATIO of old vs new. *This is NOT the correct way to do it but
since the standard practice is to provide for more than the required
strength in the original design, you will be reasonable correct so
long as you limit the load of any accelerated maneuvers to 3.3g or
less.

-R.S.Hoover

How about: http://www.rotecradialengines.com/

bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.

How about: http://www.rotecradialengines.com/

Ever price one of those? You could probably build a half-dozen VWs like
Bob talks about for a single Rotec....

Ron Wanttaja

"Ron Wanttaja" wrote in message
...

How about: http://www.rotecradialengines.com/

Ever price one of those? You could probably build a half-dozen VWs like
Bob talks about for a single Rotec....

Do you think that a new-build Pobjoy radial would cost any less?

Vaughn

Ron Wanttaja wrote:
bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.

How about: http://www.rotecradialengines.com/

Ever price one of those? You could probably build a half-dozen VWs like
Bob talks about for a single Rotec....

Ron Wanttaja


Yeah, maybe so.

But no VW will ever fly a Flybaby..

"cavelamb" wrote in message
...
Ron Wanttaja wrote:
bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.

How about: http://www.rotecradialengines.com/

Ever price one of those? You could probably build a half-dozen VWs like
Bob talks about for a single Rotec....

Ron Wanttaja


Yeah, maybe so.

But no VW will ever fly a Flybaby..

Be Careful there. The Rotorway helicopter uses a liquid cooled engine that
came originally from VW stock and "Claims" nearly 150hp.



__________ Information from ESET NOD32 Antivirus, version of virus signature database 4091 (20090520) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

Stuart Fields wrote:
"cavelamb" wrote in message
...
Ron Wanttaja wrote:
bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.
How about: http://www.rotecradialengines.com/
Ever price one of those? You could probably build a half-dozen VWs like
Bob talks about for a single Rotec....

Ron Wanttaja

Yeah, maybe so.

But no VW will ever fly a Flybaby..

Be Careful there. The Rotorway helicopter uses a liquid cooled engine that
came originally from VW stock and "Claims" nearly 150hp.




I seriously doubt that Rotorway claims they are powered by a VW engine.

On May 20, 8:11*am, "vaughn"
wrote:

* *Do you think that a new-build Pobjoy radial would cost any less?
------------------------------------------------------------------------------------

No. In fact, I think I said it's day had already come and gone. I
described it for those who were not familiar with it. I tend to not
re-read what I've posted (which can be dangrous at tmes) but I had the
impression that the Pobjoy was a good candidate for kitting.

But the main purpose for creating this topic was sparked by Stealth
Pilot's proposal about a universally available 40 hp engine NOT based
on VW after-market components, which I'll address in a moment. The
stated problem was that VW engines were becoming too expensive... with
the implication he was speaking with regard to Australian home-
builders. Which means the same is probably true for home-builders in
South Africa, although they seem to have a higher percentage of Type
IV engines.

What's probably needed here is a more direct link to the Brazilian VW
after-market manufacturers, especially with regard to the crankcase
and heads. Being cast iron, I assume the Australians could either
make their own jugs, or establish links to the Chinese manufacturers,
which they would need to do in any case in order to obtain VW after-
market stroker crankshafts.

As for the 'links,' I am referring to import/export agents on both
ends of the system. These 'native' agents earn their piece of the pie
by identifying manufacturers in their own countries who are producing
a product for which there is a market in a foreign country. In most
cases, all it takes is an inquiry on letter-head stationary.

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

Getting back to the real purpose of this topic -- the universally
available 40hp engine -- We have the Continental A-40 to use as a
starting point... but one I hope will be used only for that. Despite
claims to the contrary, the A-40 was NOT a very good engine, although
it's last models were better than the first versions by an order of
magnitude. Even so, there were significant aspects begging for
improvement, such as the valve train and the L-head combustion
chamber. But even as it stands -- without any improvements -- it is an
STC'd aviation power-plant and a FACSIMILE should have no trouble with
local CAA officials.

What I'd hoped to engender was discussion regarding my comments about
how an existing water-cooled in-line 4-cylinder engine could be used
to produce an engine MORE SUITABLE for use in a home-built airplane.

Unspoken here was the assumption that home-builders of the future will
be coming from India and China. I base this assumption on the mail
I've received from those countries. I've taken that as meaning we are
going to see the need for Stealth's 40hp engine... but an EFFICIENT
40hp -- an engine that can be cobbled-up by a home-builder having an
income of less than 5k U.S.dollars per year. (Adjusted for local
prices [ie China & India] that level of income has approximately 3x
the buying power. But even 15k is a pretty small amount.)

The odds are overwhelmingly in favor for the existence of a suitable
base-engine (ie, 1.8 to 2.0l) already existing in those countries.
All we need to do is to show how such an engine can be turned into the
home-made equivalent of a de Havilland. (Easy, eh? :-)

-R.S.Hoover

-PS -- I'm doing the mail as I work my way thourgh my 'morning pills,'
some of which make me silly, others of which make me want to barf...
unless taken in the proper sequence. You can almost tell where I'm at
in the 'pilling' sequence by just reading what I've written :-)

"cavelamb" wrote in message
m...
Stuart Fields wrote:
"cavelamb" wrote in message
...
Ron Wanttaja wrote:
bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.
How about: http://www.rotecradialengines.com/
Ever price one of those? You could probably build a half-dozen VWs
like Bob talks about for a single Rotec....

Ron Wanttaja

Yeah, maybe so.

But no VW will ever fly a Flybaby..

Be Careful there. The Rotorway helicopter uses a liquid cooled engine
that came originally from VW stock and "Claims" nearly 150hp.

I seriously doubt that Rotorway claims they are powered by a VW engine.

You are absolutely correct. However the Rotorway engine was based
originally on a liquid cooled VW. It has been greatly modified since. Point
being you can modify a VW and get enough power to fly a Fly Baby. When is
a rose not a rose? I know that I had to remove the Lycoming tag from my
0320 because of modifications but it is easy to see with the words Lycoming
on the valve covers that it isn't an Evinrude. However it is 90% Lycoming
so what do I call it?



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The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

Stuart Fields wrote:
"cavelamb" wrote in message
m...
Stuart Fields wrote:
"cavelamb" wrote in message
...
Ron Wanttaja wrote:
bildan wrote:
On May 19, 2:52 pm, Bob wrote:
As of 2009 Amateur aircraft builders are largely limited to various
Volkswagen conversions.
How about: http://www.rotecradialengines.com/
Ever price one of those? You could probably build a half-dozen VWs
like Bob talks about for a single Rotec....

Ron Wanttaja
Yeah, maybe so.

But no VW will ever fly a Flybaby..
Be Careful there. The Rotorway helicopter uses a liquid cooled engine
that came originally from VW stock and "Claims" nearly 150hp.
I seriously doubt that Rotorway claims they are powered by a VW engine.

You are absolutely correct. However the Rotorway engine was based
originally on a liquid cooled VW. It has been greatly modified since. Point
being you can modify a VW and get enough power to fly a Fly Baby. When is
a rose not a rose? I know that I had to remove the Lycoming tag from my
0320 because of modifications but it is easy to see with the words Lycoming
on the valve covers that it isn't an Evinrude. However it is 90% Lycoming
so what do I call it?




A Stuart 0320?