VWs

I had posted a link to a vid of a 701 weaving through the trees over
on .piloting.

At some point down the line I expressed interest in a VW powered 701.

One guy said he figured a VW would melt down in an aircraft cowling
when producing no more that 50HP.

He provided a link to Bob Hoover's blog, which had an entry "The
Christmas Engine", in which he states pretty flatly that:

1) No way to get 80 (let alone 100) HP out of an aircooled VW for any
extended period of time.
2) No way to cool an engine at those HP values if you could get them,
so you either get meltdown or very low time between overhauls.

Bob's blog looks as though he's talking direct drive. That pretty much
lines up with what I've read on the Great Plains website. GP says you
can only get higher HP from the VW by PSRU. That I can believe, on the
general principle that any engine has higher HP at higher RPM. Since
the VW wasn't designed to spin propellers, well, the best HP values vs
RPM don't align nicely for a direct drive VW and a propeller, do they?
That stands to reason.

So I'm asking this: for you VW people builders, what about cooling,
and is there some dyno data available from VWs spinning props with
PSRUs and direct drive available? Something somebody has been willing
to publish?

What about meltdowns? Because if what Bob Hoover says is true then it
seems to me there's no way Great Plains should be making a living --
unless their customers never have checked the numbers they GP claims.
GP has a lot of customers. You'd think they'd be screaming bloody
murder if they couldn't at least get close to 80 for takeoff.

I'm more concerned with thrust and cooling, though, than some HP
number.

What gives? What's "the truth"?

On Mon, 28 Jan 2008 19:40:25 -0800 (PST),
wrote:

I had posted a link to a vid of a 701 weaving through the trees over
on .piloting.

At some point down the line I expressed interest in a VW powered 701.

One guy said he figured a VW would melt down in an aircraft cowling
when producing no more that 50HP.

He provided a link to Bob Hoover's blog, which had an entry "The
Christmas Engine", in which he states pretty flatly that:

1) No way to get 80 (let alone 100) HP out of an aircooled VW for any
extended period of time.
2) No way to cool an engine at those HP values if you could get them,
so you either get meltdown or very low time between overhauls.

Bob's blog looks as though he's talking direct drive. That pretty much
lines up with what I've read on the Great Plains website. GP says you
can only get higher HP from the VW by PSRU. That I can believe, on the
general principle that any engine has higher HP at higher RPM. Since
the VW wasn't designed to spin propellers, well, the best HP values vs
RPM don't align nicely for a direct drive VW and a propeller, do they?
That stands to reason.

So I'm asking this: for you VW people builders, what about cooling,
and is there some dyno data available from VWs spinning props with
PSRUs and direct drive available? Something somebody has been willing
to publish?

What about meltdowns? Because if what Bob Hoover says is true then it
seems to me there's no way Great Plains should be making a living --
unless their customers never have checked the numbers they GP claims.
GP has a lot of customers. You'd think they'd be screaming bloody
murder if they couldn't at least get close to 80 for takeoff.

I'm more concerned with thrust and cooling, though, than some HP
number.

What gives? What's "the truth"?

Doesn't matter what speed you run the V Dub, the stock cyl heads do
not have enough fin area to shed the heat of more than 40-50HP
longterm.. The mass of the heads allows short term higher output, but
the "thermal equalibrium" is reached just over 40HP.
If you thermal coat (ceramics) the combustion chamber and exhaust
ports, as well as the piston tops, you can likely push that 30% or
so..
You are still looking at a 50HP engine - and 50HP in a 701 is a
"ground hog". Just like the average dragonfly (although after off the
ground, a VW 'fly will REALLY go due to vastly superior aerodynamics.)

--
Posted via a free Usenet account from http://www.teranews.com

Old news.

As far back as Rockford, at least three builders of converted VW's
appealed to Pope Paul to use the EAA's bully pulpit for educating
homebuilders about the realities of automobile engine conversions. At
least two of us (me and Ted Barker) even offered to provide the
required torque-stand. But the EAA was (and is) more interested in
selling tent-space and full-page ads than in contributing to the basic
store of USEFUL homebuilt information.

My article you cited (The Christmas Engine) can be found at...

http://wapurl.co.uk/?IWL54GJ

....and I suggest you give it another read, paying particular attention
to the difference between PEAK and SUSTAINABLE output, and how long
you can expect to pull the former... if you're interested in a
reasonably long TBO.

As for the question of direct-drive vs a PSRU, I'm afraid you're a bit
behind the power curve, engineering-wise. Adding a PSRU does not
change the laws of physics which dictate the power & durability of an
engine. The use of a PSRU can allow a small engine, such as the
1300cc Rotax, to produce a prodigious amount of power, but only so
long as the waste heat is properly managed, which Rotax does by using
liquid-cooled heads... and lotsa money :-)

As for your expectation of discovering "the truth" by popping up on
the internet and polling the readers, you're about to get a valuable
lesson in human nature. After having paid $6000 US for what is
basically a $2500 dune buggy engine with a fan on the nose, an awful
lot of people are going to swear on a stack of Bibles that the
miraculous claims of power and durability that caused to spend that
amount of money are ALL TRUE. Never mind that their Specific Fuel
Consumption is 0.562 (or worse), or that they have to 'touch-up' the
valves now and then... because if that miraculous amount of power and
that remarkable TBO were NOT true... it would mean they were suckers,
being preyed upon by another EAA-endorsed huckster. And of course,
that can't be right.

For everyone else, as I said at the out-set this isn't a new topic.
Dig around, you'll find lots of valuable, quantified information here
and in the archives of the AirVW Group. You will also find lots of
the other kind of information as well, including full-page ads in
early issues of 'Sport Aviation,' along with infomercial 'articles.'
Read it. THINK FOR YOURSELF. Your life may literally depend upon it.

The saving grace in all this is the fact an engine is incapable of
lying. Build it, fly it, and what you see is what you get. Oddly
enough, what you get will come remarkably close to what physics,
thermodynamics and engineering has SAID you will get -- and have said
for the last hundred years.

-R.S.Hoover

wrote:

What about meltdowns? Because if what Bob Hoover says is true then it
seems to me there's no way Great Plains should be making a living --
unless their customers never have checked the numbers they GP claims.
GP has a lot of customers. You'd think they'd be screaming bloody
murder if they couldn't at least get close to 80 for takeoff.

I'm more concerned with thrust and cooling, though, than some HP
number.

What gives? What's "the truth"?

An 85 HP aircraft cylinder head:

http://www2.tech.purdue.edu/at/cours...arrel&head.jpg

A VW head:

http://www.allworldautomotive.com/ph...1817-15127.jpg


Charles

compared to the '85 HP aircraft cylinder head' the VW head doesn't look so
bad after all...


"Charles Vincent" schrieb im Newsbeitrag
. ..
wrote:

What about meltdowns? Because if what Bob Hoover says is true then it
seems to me there's no way Great Plains should be making a living --
unless their customers never have checked the numbers they GP claims.
GP has a lot of customers. You'd think they'd be screaming bloody
murder if they couldn't at least get close to 80 for takeoff.

I'm more concerned with thrust and cooling, though, than some HP
number.

What gives? What's "the truth"?

An 85 HP aircraft cylinder head:

http://www2.tech.purdue.edu/at/cours...arrel&head.jpg

A VW head:

http://www.allworldautomotive.com/ph...1817-15127.jpg


Charles

On Jan 29, 2:29 am, "oilsardine" wrote:
compared to the '85 HP aircraft cylinder head' the VW head doesn't look so
bad after all...
---------------------------------------------------------------------

Looks can be deceiving.

The maximum output of the carburetted 1600cc VW engine was the 1971
model which could produce about 57bhp... for about ONE MINUTE.
Maximum SUSTAINED output (ie, CHT of 450F) was about 44bhp under
Standard Day conditions. At that level of output you could expect the
exhaust valves to drop out of spec after about 200 hours. NOMINAL
output of the 1600VW was about 15bhp, which allowed the exhaust valves
to survive for up to 1000 hours (although 600 t0 750 was more the
norm). After-market 'hot-rod' heads do even worse since they have
less fin area. Volkswagen dealers commonly swapped-out worn heads
without bothering to inform the owner, other than to list their
replacement in the 'OTHER SERVICE - AS REQUIRED' block on the work-
order.

To understand why the VW head does so poorly simply compare it to the
early 1500cc (85hp) Porsche heads. Then compare those to the Corvair.

-R.S.Hoover

PS -- Here in the States many VW owners insist their vehicle NEVER
required anything other than normal maintenance when in fact,
examination of its service records usually shows periodic replacement
of heads, carb, distributor, clutch and oil pump with rebuilt units,
all for a nominal charge, when the vehicle was brought in for service.

Hear! Hear!

Back in my miss-spent youth, I worked in a VW independent repair shop in San
Mateo, Ca. A place called Father Noel's. I rebuilt three engines a week and
saw it all. The same 47 reasons why the air-cooled VW needed "periodic
replacement of heads, carb, distributor, clutch and oil pump with rebuilt
units, all for a nominal charge, when the vehicle was brought in for
service."

Here is a partial list of what WILL go wrong with your fan drive up front
WITH A STOCK TYPE ENGINE ( for those about to flame me, please read that
last statement several times least you look foolish):

Exhaust valve stems stretch to the point of the valve heads breaking off and
trashing engine. You'll know when this is about to happen when your engine
won't hold a valve adjustment.
Cylinder heads crack between seats.
Cylinder heads crack to spark plug hole. You'll know this when the spark
plug seizes when being removed because of accumulated carbon in the threads.
And then the spark plugs blow out...
Valve guides that wear out as soon as engine starts (a lot like old Triumph
motorcycle engines)
Cylinder head sealing surface leaks due to case studs stripping threads out
of the case. You'll know this when your brand new muffler sounds like it is
falling off under acceleration.
Ever present oil leaks from the case crack developing in the number 3
cylinder area behind the flywheel (ok...prop drive).
Loss of oil pressure at low rpm due to case separating at the center main
bearing area.
Flat cams and worn lifters due to great German metallurgy.
New version of air-cooling when rod escapes confines of case.
And on...and on...and on...

Granted, all of these things can be fixed with a generous infusion of money,
maybe two shoe-boxes full of 20's will do the trick. But the basic idea is
that this engine isn't adequate to push around a 1500 pound car at part
throttle let alone an aircraft. And by the time it is capable, it is more a
Lycoming (no great accomplishment in itself) than a VW i.e. a horizontally
opposed four cylinder engine in the same vein as a water-cooled chevy based
aircraft engine is no more a chevy than a Nascar prepped race engine with
origins in a dozen speed part catalogs.

A common statement by some of the longer haired VW owners ( this was the
70's) was that VW's were great because they were easy to work on to which I
would reply that is fortunate as one works on them a lot. We made a lot of
money off those types. Now today, would the owner of a present day vehicle,
with all of the subsequent technology advances, put up with that repair
frequency? Oh wait! They do! They are called Volvo, Mercedes and BMW owners.

If you are going to rely on a VW or other small displacement engine to keep
your aircraft an aircraft and not a smoking hole full of parts, build it
with the best parts possible with the best information available and don't
skimp.

By the way, I'm have not been immune from thinking poorly or emotionally. In
the 80's, I raced a Ducati bevel-drive twin in AMA Twins. It developed
enough horsepower to break cases every two races. I welded a chain to it and
took it fishing once. When I was done fishing, I cut the anchor chain and
went home.

Gotta realize when you have gone down a road too far...

Ready for flames now...

Dale Alexander


wrote in message
...
On Jan 29, 2:29 am, "oilsardine" wrote:
compared to the '85 HP aircraft cylinder head' the VW head doesn't look
so
bad after all...
---------------------------------------------------------------------

Looks can be deceiving.

The maximum output of the carburetted 1600cc VW engine was the 1971
model which could produce about 57bhp... for about ONE MINUTE.
Maximum SUSTAINED output (ie, CHT of 450F) was about 44bhp under
Standard Day conditions. At that level of output you could expect the
exhaust valves to drop out of spec after about 200 hours. NOMINAL
output of the 1600VW was about 15bhp, which allowed the exhaust valves
to survive for up to 1000 hours (although 600 t0 750 was more the
norm). After-market 'hot-rod' heads do even worse since they have
less fin area. Volkswagen dealers commonly swapped-out worn heads
without bothering to inform the owner, other than to list their
replacement in the 'OTHER SERVICE - AS REQUIRED' block on the work-
order.

To understand why the VW head does so poorly simply compare it to the
early 1500cc (85hp) Porsche heads. Then compare those to the Corvair.

-R.S.Hoover

PS -- Here in the States many VW owners insist their vehicle NEVER
required anything other than normal maintenance when in fact,
examination of its service records usually shows periodic replacement
of heads, carb, distributor, clutch and oil pump with rebuilt units,
all for a nominal charge, when the vehicle was brought in for service.

My article you cited (The Christmas Engine) can be found at...

http://wapurl.co.uk/?IWL54GJ

...and I suggest you give it another read, paying particular attention
to the difference between PEAK and SUSTAINABLE output, and how long
you can expect to pull the former... if you're interested in a
reasonably long TBO.

I very much will.

As for the question of direct-drive vs a PSRU, I'm afraid you're a bit
behind the power curve, engineering-wise. *Adding a PSRU does not
change the laws of physics which dictate the power & durability of an
engine.

Hold on a second. First, I am behind the power curve, engineering-
wise. I'm not a mechanic engineer, nor have I tinkered with VW (or
other engines) for years. So that puts me behind.

*The use of a PSRU can allow a small engine, such as the
1300cc Rotax, to produce a prodigious amount of power, but only so
long as the waste heat is properly managed, which Rotax does by using
liquid-cooled heads... and lotsa money :-)


This was the gist of my commen on PSRU. I wasn't speaking to the
cooling problem.

I notice that Great Plains offered liquid cooled heads in their 2007
catalog but not in their 2008. Hmm...

As for your expectation of discovering "the truth" by popping up on
the internet and polling the readers, you're about to get a valuable
lesson in human nature. *After having paid $6000 US for what is
basically a $2500 dune buggy engine with a fan on the nose, an awful
lot of people are going to swear on a stack of Bibles that the
miraculous claims of power and durability that caused to spend that
amount of money are ALL TRUE. *Never mind that their Specific Fuel
Consumption is 0.562 (or worse), or that they have to 'touch-up' the
valves now and then... *because if that miraculous amount of power and
that remarkable TBO were NOT true... it would mean they were suckers,
being preyed upon by another EAA-endorsed huckster. *And of course,
that can't be right.


I put "the truth" in quotation marks on purpose. For reasons you
allude to.

For everyone else, as I said at the out-set this isn't a new topic.
Dig around, you'll find lots of valuable, quantified information here
and in the archives of the AirVW Group. *You will also find lots of
the other kind of information as well, including full-page ads in
early issues of 'Sport Aviation,' along with infomercial 'articles.'
Read it. *THINK FOR YOURSELF. *Your life may literally depend upon it.

Thanks, I'll look for it.

The saving grace in all this is the fact an engine is incapable of
lying. *Build it, fly it, and what you see is what you get. *Oddly
enough, what you get will come remarkably close to what physics,
thermodynamics and engineering has SAID you will get -- and have said
for the last hundred years.

-R.S.Hoover

What are the best VW books in general? I'm working through the one by
Tom Wilson, but it doesn't cover these issues we're talking about.
Great Plains offers a VW conversion manual, is it good? I've looked
for VW aero-conversion books online but haven't found much.

oilsardine wrote:
compared to the '85 HP aircraft cylinder head' the VW head doesn't look so
bad after all...


Really? When I look at the VW head image, I see two cylinder heads cast
together in a manner that reduces the total fin area and obstructs
cooling flow. I see a cylinder head with cylinder stud bosses that not
only reduce fin area, but are actually blocking cooling air just where
it is needed. Same with the studs themselves. I see a cylinder head
with a single pompadour cooling fin in the extremely critical area
between the valves and spark plug boss. If you could actually hold a
C-85 and VW both in your hand the differences would be even more striking.

Charles


"Charles Vincent" schrieb im Newsbeitrag
An 85 HP aircraft cylinder head:

http://www2.tech.purdue.edu/at/cours...arrel&head.jpg

A VW head:

http://www.allworldautomotive.com/ph...1817-15127.jpg


Charles

Really? *When I look at the VW head image, I see two cylinder heads cast
together in a manner that reduces the total fin area and obstructs
cooling flow. *I see a cylinder head with cylinder stud bosses that not
only reduce fin area, but are actually blocking cooling air just where
it is needed. *Same with the studs themselves. *I see a cylinder head
with a single pompadour cooling *fin in the extremely critical area
between the valves and spark plug boss. *If you could actually hold a
C-85 and VW both in your hand the differences would be even more striking.

Charles

Has anyone ever tried adapting aero head designs to the VW block and
cylinders?

Yes I know that would be a considerable effort. I guess no one has
otherwise we'd see references to it. If I were really good with CAD I
would consider giving it a shot. I know a guy who has the CNC
equipment and could probably machine aero style heads (although I
don't know what would be the right material).

An interesting experiment if you had cash and time on your hands. It
seems from what veeduber writes that this is a matter of cooling
efficiency for durability, rather than HP or torque per se.