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

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 :-)

Bob wrote:
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 :-)

If 40 hp will do it, the new 'industrial' engines are looking really
good at this point. I follow an email list that focuses on small 4stroke
engines for a/c, & most of the discussion lately has been about these
engines. One guy is converting a vertical shaft lawn tractor motor (~32 hp).

These engines aren't at the 40 hp level yet, but it's easy to see bigger
ones coming out in the future. The nice thing about an industrial engine
is the output shaft & bearing is usually designed to take the horrendous
side loads of a reduction drive, so an a/c reduction or prop bending
load shouldn't be too much of a problem, and they are designed for
continuous output, not intermittent or varying load like most engines.

The guys at Valley Engineering seem to have found a very simple way to
make a reduction drive for these engines, and they even have one running
direct drive.

Large quantities, relatively low cost even for a new one, and great
deals as more & more show up on the used market. I like it.

Charlie

On Wed, 20 May 2009 11:23:33 -0700 (PDT), Bob
wrote:



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


the most likely engine for india is a conversion of something out of
TATA. I dont think we would see many of those engines in the west
although if the $2,000 car was marketed here and it's engine was
suitable we could probably think of it as an engine supplied in a
metal box :-)

it is an interesting conundrum because as simple as it sounds no one
markets a lightweight 40hp aero engine suitable for a single seat
aircraft. not that I'm aware of. (rotax 2 strokes I'm not interested
in)

none of the manufacturers I've looked at will supply an engine not
wrapped in a car. the smart car engine seemed a promise but in the
local distributors no one would even talk to me. ( I must have left my
top hat home that day)

all successful aircraft designs start with a successful engine.

Stealth Pilot

"Bob" wrote in message
...
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.

----------much snipped---------
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

Bob,

Lots of great info as usual, and there are some additional excellent
possibilities that were imported here in the states untill very
recently--although I can not find any linkage to current useage and
availability as new engines.

One example is the Suzuki 4 cylinder 1300cc, and its 3 cylinder 1000cc
variant, used in the Suzuki Swift and Geo Metro. The 1300cc engine was
rated at 79 HP at just over 5000 rpm, and would clearly produce 40 HP at
propeller speed--or somewhat more on a sleek design that could make use of a
smaller and faster turning propeller. There have also been a number of
articles written regarding the conversion, expecially of the 3 cylinder
version, using belt reduction systems--including some using multiple
v-belts. There has been coverage at various times in Kit Planes and also in
EAA's old Experimenter magazine.

A second, and very similar, engine was a 4 cylinder 1300cc engine made by
Kia which was used in the Ford Aspire and rated at 70 HP at just over 5000
RPM. The Kia engine would be expected to produce similar torque at mid
range speeds, when compared to the Suzuki engine.

Both Suzuki and Kia, as well as Toyota and Honda, still produce similar
1600cc engines which are currently sold in compact cars here in the US.
Most are now rated at 6000 RPM or higher, although the Kia engine was
formerly rated at 90 HP and around 5000 RPM in the older Kia Rio cars.
Also, the Leon brothers used a pair of the Suzuki engines in their Coxy IV
with the coaxially driven propellers and operated (or probably still do)
their engines at 6000 RPM or a little more--using a pair of multiple v-belt
reduction units.

I have not kept up on the matter and don't have any information on how any
of theres engines may have fared in extended service; but I expect that many
or them have done quite well.

Peter

Wow!

Now that's what I was hoping to see.

Okay, maybe a PSRU using belts. But not vee-belts. There is two
examples of v-belt drives we can use to draw data from, the one on
the Headwind, another on the PL-4. Both call for some wizard
machining and both need matched sets of belts, in that v-belts stretch
and you end up with slippage. This was covered... 'way back when
sometime (and I've probably got the details wrong).

The folks at Valley Engineering (sp?) have shown us how to do it with
a cog-tooth belt... which may also apply to some sort of serpentine
arrangement.

Would a timing belt work? I usta have a Pontiac that had a belt-
driven cam...

I'm thinking more of the machining here rather than the belt, on the
assumption that a cog-tooth belt WILL work... the main question being
how LONG it will do so. Which brings to mind the mention of a rear
axel something. Turns out, the bearing used for a rear axle is NOT
suitable for any kind of prop-drive. Slow prop turns more than 1200
rpm whereas a fast rear wheel is something less than that. Kinda like
the belt problem... you have to keep changing the thing BEFORE it can
fail, which it will in fairly short order. Cost is probably another
factor that needs to be considered here, in that a bearing that WILL
hold up at prop-speeds is probably priced a lot higher than your basic
rear wheel bearing.

Then there's the problem of starting the thing. Direct-drive we can
tweak the timing so it will start at a flip of the prop. But put a
PSRU in there we've got to 'wind it up' to get it to the proper firing
point.

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

I wish I had a shop full of TATA engines to play with. There may be a
combination of cam & rod-length that can give a reliable 40hp at an
rpm most suitable for a prop.

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

Speaking of props, has anyone ever heard of one made from bamboo?

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

I've got to go. Zometa. IV. About a quart. Takes a while (drip-
drip-drip...) Then I gotta look at a faucet that is doing the same
thing (drip-drip-drip...)

-Bob

vaughn wrote:
"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?

Bob was talking VWs, and you suggested Rotecs as an alternative. I
never made one peep about Pobjoys.

Ron Wanttaja