Corvair conversion engines

clare at snyder.on.ca wrote in message
...
On Wed, 25 Jan 2006 19:47:08 -0500, "Morgans"
wrote:


"Peter Dohm" wrote

Interesting. I had assumed they were originally flying with 80HP or
less,
but had no idea it was that much less. Thanks.

You could find many people that would argue that low of a HP figure. I
think your 80 is closer, and in might be a few more than that.


Original flying corvairs were the little engine - 145 cu inch, IIRC,
producing 128 ft lb gross torque at 2300 RPM. So, at 2300, 56 hp.
If run at 2700 rpm, torque approx 125 ft lb, and 64 hp.

The 164 inch engines produced up to 160 ft lb torque at 2600 or 2800
rpm depending on the engine, for 80 hp at 2600, or 85 at 2800. Mine
produces 90 at 3000.

With a fancy cam and a bit of rework they will put out closer to 170
ft lb - and at 3200 RPM with a small prop, that is 103 hp almost 115
at 3500 rpm. The factory 140 hp engine supposedly produced 140hp at
5200 rpm and 160 max torque at 3600. That means the torque dropped off
to 140 at 5200. The 110 does not breathe nearly as well at speed, so
the 14% torqe drop of the 140 would be more like 20% on a 110 - or 122
ft lbs at 5200 for 120 hp if you ran a 2:1 PSRU for a 2600rpm prop.
And that's being optimistic.

Assuming 170 peak torque at 3000 RPM (likely pretty close with OT10
cam and properly prepared for aircraft use) it is pretty close to a
100 hp engine .For the extra 10 HP there is a couple hundred dollars
worth of Camshaft etc required over and above what I've got -so I'm
satisfied, so far, with what I've got. We'll see what 90 HP does in a
Pegazair when we get it together.

My engine has 180 degree equal length headers and a short smooth equal
length intake with a 50mm carb, and it's a 140 based engine, so it
breaths a bit better than a "stock" 110 at 3000 RPM

Thanks, Clare, for a lot of excellent specifics and history.

It seems that those original engines were smaller than I remembered, and
produced less maximum torque even for their size. That shouldn't surprise
me, considering the power levels of the compact cars the Corvair was
designed to compete with and the people it was designed to serve.

I always tend to think of these little engines in terms of installing them
in go-fast machines, for their power. To me, that means turning a 52 inch
propeller about 3500 to 3600 rpm. So 95 to 100 hp may not be all that
crazy--especially with a rear drive installation such as offered by Great
Plains for their VW based engines. That is similar to Steve Whittman's V8
canversion, and presumably to his Formula-Vee racing installation as well.
Thanks to Richard Lamb for the link to Great Plains earlier in this thread.

OTOH, before someone else posts yet another recitation that more propeller
disk area equals more thrust and therefore more performance...

I took a quick look at a set of posted specs for the Pegazair, on
UltralightNews.com, and suspect that you are just about at the top of the
horsepower and rpm range for that installation. It would not surprise me at
all, using your numbers above, it the 80 hp version gave identical
performance to the 90 hp version in the Pegazair's speed range.
(Discalimer: I am not qualified to make this observation.)

Peter

"Peter Dohm" wrote

I always tend to think of these little engines in terms of installing them
in go-fast machines, for their power. To me, that means turning a 52 inch
propeller about 3500 to 3600 rpm.

Willim Wynne does not reccomend turning the Corvair engine at more than 3000
RPM, and pretty much says right out, that doing so has been shown to break
the crank, in all of the cases he has studied.

So 95 to 100 hp may not be all that
crazy--especially with a rear drive installation such as offered by Great
Plains for their VW based engines.

Some pretty experienced people (in VW engines) have said that the valves are
the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC

"Morgans" wrote in message
...

"Peter Dohm" wrote

I always tend to think of these little engines in terms of installing
them
in go-fast machines, for their power. To me, that means turning a 52
inch
propeller about 3500 to 3600 rpm.

Willim Wynne does not reccomend turning the Corvair engine at more than
3000
RPM, and pretty much says right out, that doing so has been shown to break
the crank, in all of the cases he has studied.

So 95 to 100 hp may not be all that
crazy--especially with a rear drive installation such as offered by
Great
Plains for their VW based engines.

Some pretty experienced people (in VW engines) have said that the valves
are
the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC

That is an interesting assertion. I really don't know. The number would
conform quite nicely to a 1600cc/96cid engine producing around 60hp; as well
as most older normally aspirated aircraft engines, which seem to have
maximum continuous power figures in the 0.5 hp/cid range. There is even a
rather famous dissertation, supposedly published in Contact!, which suggests
failure due to heat dissipation problems in the valves and/or heads of
automotive engines operated above continuously that power level.

As it happens, I am really on both sides of this issue--and may not be
technically qualified on either. (Required disclaimer as I am neither a
mechanical engineer nor a mechanic)

On the "this is unadulterated manure" side: there is a dissertation
attributed to an engineer at one of the big three auto makers and posted
here a couple of times, possibly by Corky, asserting that manufacturer
testing includes a 100 hour run at full rated power--and that the failure
about which they are concerned is the harmonic dampener. That is in keeping
with articles I read more than 30 years ago in my school days, which stated
that the exhaust manifolds glow incandescent during this proceedure.
However, the colant and oil are maintained within their normal temperature
range during that portion of the testing proceedures. On modern automotive
engines, this equates to more than 1.0 hp/cid; and 100 hours is clearly much
more than a few minutes.

However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve. I do know of two broker cranks on
Corvair conversions (same person) and at least one, and possibly two, broken
cranks on VW conversions (same other person). Both are mentioned on the
FlyCorvair site, so I am really not adding much that is new. I am convinced
that all of the failures were torsional damping issues. The only burned
valve that I know of on an automotive conversion was on a liquid cooled
Geo/Suzuki engine and was traced to a carburetion problem--which was run at
a much higher power level. I was told that the carburetion problem was
corrected and has not recurred.

On the other hand, I strongly suspect that very high power levels equate to
accelerated wear; and I really dislike very short TBOs. So all of my own
scratch pad doodles are based on continuous power levels of less than 0.5
hp/cid, and usually significantly less.

Peter

"Peter Dohm" wrote in message
. ..
However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve.

The 140 hp Corvair engines tend to lose valve seat inserts if overheated.

Rich S.

On Fri, 27 Jan 2006 21:49:21 -0500, "Peter Dohm"
wrote:


"Morgans" wrote in message
...

"Peter Dohm" wrote

I always tend to think of these little engines in terms of installing
them
in go-fast machines, for their power. To me, that means turning a 52
inch
propeller about 3500 to 3600 rpm.

Willim Wynne does not reccomend turning the Corvair engine at more than
3000
RPM, and pretty much says right out, that doing so has been shown to break
the crank, in all of the cases he has studied.

So 95 to 100 hp may not be all that
crazy--especially with a rear drive installation such as offered by
Great
Plains for their VW based engines.

Some pretty experienced people (in VW engines) have said that the valves
are
the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC

That is an interesting assertion. I really don't know. The number would
conform quite nicely to a 1600cc/96cid engine producing around 60hp; as well
as most older normally aspirated aircraft engines, which seem to have
maximum continuous power figures in the 0.5 hp/cid range. There is even a
rather famous dissertation, supposedly published in Contact!, which suggests
failure due to heat dissipation problems in the valves and/or heads of
automotive engines operated above continuously that power level.

As it happens, I am really on both sides of this issue--and may not be
technically qualified on either. (Required disclaimer as I am neither a
mechanical engineer nor a mechanic)

On the "this is unadulterated manure" side: there is a dissertation
attributed to an engineer at one of the big three auto makers and posted
here a couple of times, possibly by Corky, asserting that manufacturer
testing includes a 100 hour run at full rated power--and that the failure
about which they are concerned is the harmonic dampener. That is in keeping
with articles I read more than 30 years ago in my school days, which stated
that the exhaust manifolds glow incandescent during this proceedure.
However, the colant and oil are maintained within their normal temperature
range during that portion of the testing proceedures. On modern automotive
engines, this equates to more than 1.0 hp/cid; and 100 hours is clearly much
more than a few minutes.

However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve. I do know of two broker cranks on
Corvair conversions (same person) and at least one, and possibly two, broken
cranks on VW conversions (same other person). Both are mentioned on the
FlyCorvair site, so I am really not adding much that is new. I am convinced
that all of the failures were torsional damping issues. The only burned
valve that I know of on an automotive conversion was on a liquid cooled
Geo/Suzuki engine and was traced to a carburetion problem--which was run at
a much higher power level. I was told that the carburetion problem was
corrected and has not recurred.

On the other hand, I strongly suspect that very high power levels equate to
accelerated wear; and I really dislike very short TBOs. So all of my own
scratch pad doodles are based on continuous power levels of less than 0.5
hp/cid, and usually significantly less.

Peter

On VW engines the problem is a lack of fin area on the heads, combined
with limitted thermal mass. Anything over 40HP produces more heat than
the heads can dissipate, and the thermal mass is low enough to limit
any operation above that level to a matter of a very few minutes.

Corvairs do not suffer this lack of fin area.

Peter Dohm wrote:


Some pretty experienced people (in VW engines) have said that the valves

are

the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC


For what it's worth, I'd have to agree, with the thought that you can
operate at higher power - until - the heads are heat soaked.
Then it's 45 HP or bust.

I think the thinking is that the engine needs to turn up fast to make
maximum engine power. Which may be true drag racing dune buggies.
Grab a gear and spin that puppy up!

Fixed pitch props don't do that.

Think one speed automatic transmission - with a lot of slip.
Pure torque converter.

IIRC, and it's been a while, the VW factory specs said max rpm ws 4200?
The torque curve peaked about 3000 (?)

Swinging a propeller at 2500 to 3000 RPM puts us on the rising part of
the curve - approaching peak.
The faster it turns - the more torque it makes - the faster it turns.
That's fun!

I think that's why VW powered parasols and biplanes tend to be faster
than their two-stroke powered brothers.

For a VW to turn a propeller ~~3000 rpm means...
1600cc 54-56" prop diameter
1835cc 56-56"
2180cc 58-60"

Our little low and slow airframes lean toward the long end.
Swing as big a stick as you can.
It pays off in prop efficiency, disk area, and tip circumference.
(compared to a 66"~68" prop on a Rotax 503, VW's climb like sea slugs)

Faster airframes tend to use shorter props and throw the excess torque
into pitch to go faster! But at high cost in prop efficiency (again).

Well, like I said, for what it's worth...


Richard

Rich S. wrote:

"Peter Dohm" wrote in message
. ..

However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve.


The 140 hp Corvair engines tend to lose valve seat inserts if overheated.

Rich S.


Same with VW.

Probably the same with any shrink in valve seats...

Richard

"Peter Dohm" wrote

That is an interesting assertion. I really don't know. The number would
conform quite nicely to a 1600cc/96cid engine producing around 60hp; as
well
as most older normally aspirated aircraft engines, which seem to have
maximum continuous power figures in the 0.5 hp/cid range. There is even a
rather famous dissertation, supposedly published in Contact!, which
suggests
failure due to heat dissipation problems in the valves and/or heads of
automotive engines operated above continuously that power level.

You have no doubt read ditties from VeeDubber here, and one of them was on
VW engines, and how many HP they really can sustain.

Seem as though (from nearest I can remember) the amount of cooling fins in
the area of the valve guides and seats, and the cross area is insufficient
to carry away the amount of heat that is flowing through that area, if it is
run flat out with a big enough prop for very long.

Remember, heads in most auto engines nowadays, are cooled by water
circulating through the head. Flow some oil past the critical areas, and
heat can be dealt with. Air cooled engines must depend on cooling fins, and
enough metal to carry the amount of heat produced to the fins.

Perhaps VeeDubber will be kind enough to repost that treatise? g
--
Jim in NC

clare at snyder.on.ca wrote:
On Thu, 19 Jan 2006 15:35:13 -0500, "Morgans"
wrote:


"Bret Ludwig" wrote in message
groups.com...

I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?

That is my opinion, also.


What isn't there can't break. That's my reson for a direct drive 'vair
insted of a geared Soob - same weight - same HP.

Exactly right Clare. The soob has a bulletproof interior but the use of
liquid cooling plus a drive system adds two complete failure modes that
aren't there at all with the Corvair. With the Corvair if you take care
of the systems design aspect, basically by using sound aircraft design
practices for carburation and ignition, you address the vast majority of
the reliability issue and the only open question left is how strong are
the basic mechanicals and that is something that is finally being addressed.

I'm kinda glad that these crank failures have come about because it was
always clear to me that the crank configuration should be considered
"marginal" when subjected to prop gyro loads at higher power outputs,
since simply by looking at it you see that bending loads can't be
absorbed by the 1st bearing and bending is happening. One bit of good
news is that the failure mode contains the end of the crank and does not
result in the prop leaving the aircraft.

I thought from the get go that the guys using extension shafts were
nuts. However they have unwittingly provided a service by finally
uncovering the crank's weak point in what amounted to a severe service
qualification endurance test, ending that uncomfortable sense that
nobody really knew just how strong the crank was or wasn't, or exactly
where its weak point was. It's a great credit to William that he
immediately responded by publicizing the issue and conducting further
testing. As someone with a job that provides a ringside to seat to
qualification, certification and continuing airworthiness of components
on regional jets, I found his approach to be very much like, and
sometimes superior to, the commercial world (in terms of letting it all
hang out and responding to crises).

Anyway, mistakes in calculations or engineering judgment in
certification of commercial airliner components sometimes results in
certified parts that are not up to snuff and fail in service well before
predicted (I see this all the time). Truth is, sometimes the only thing
that keeps commercial jets raining down on peoples' heads is double and
triple redundancy, not the super duper construction of their components.

There is still an unknown though. What I'd personally like to see
William do is send the fracture results and the metallurgical data on
the crank to a metallurgical and dynamic stress specialist who can
calculate the loads/cycles that it took to initiate and propagate the
cracks, then work backwards to establish the gyro forces and torque
forces required to generate those loads, then apply a safety factor and
establish safe propeller weight/length/horsepower limits for the
existing configuration with a nitrided crank (the calculated limits may
make a lot of people unhappy though). Builders need to know just where
the safety boundaries are for the existing config.

Myself I am still a big fan of the Corvair but will probably adopt the
extra bearing mod he's working on if I ever get to that point.

John Kahn
Montreal

On Fri, 27 Jan 2006 19:13:28 -0800, "Rich S."
wrote:

"Peter Dohm" wrote in message
...
However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve.

The 140 hp Corvair engines tend to lose valve seat inserts if overheated.

Rich S.

ANY aluminum head engine can loose valve seats. The secret is not to
expect more of the engine than it can safely produce. They guy who
did mine pinned them, but I don't plan on putting the pins to the
test.