A Simple Auto Engine Conversion

On Aug 27, 3:32 pm, "Peter Dohm" wrote:
"Jim Logajan" wrote in message

.. .

Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "
wrote:

everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

But doesn't the Rotax 912 have reduction gearing and liquid cooling? It is
getting put into an awful lot of aircraft models - particularly LSAs.

That's true, and the biggest annoyance (of which I am aware) is that they
have increased the recommended "idle" speed to increase the service life of
the PSRU--which is of the spur gear type. I don't know whether any of the
belt or chain type PSRU installations have a similar requirement.

As to cooling: there were a lot of liquid cooled aircraft engines in WWII,
but the the aircraft they in which they were installed looked a lot
different from their air cooled counterparts.

Peter

Even belted PSRUs have vibration nodes. The Glastar in which
we put a PSRU'd Soob didn't like 1400 engine RPM; it semed to be an
argument between the flywheel's inertia and the prop's. Running it at
that RPM for long would have torn the teeth off the belt. I didn't
notice if there were further nodes at 2800 and 5600. Adjusting belt
tension didn't change anything.
I've read about (and encountered) cases of cooling problems in
auto conversions. Many builders underestimate the amount of heat that
needs discarding, and also make mistakes in radiator installation and
baffling. I've seen rads mounted out in the breeze where they not only
slow the airplane but suffer from airflow problems created by the
vortices generated around the rad. I've seen a couple of small rads
mounted behine the front cowl openings, where they're supposed to get
ram air, but without proper baffling to separate the incoming air from
the air behind the rads the pressure differential is minimal, causing
low flow, and air eddying around the rad further interferes with
flow.
In the Glastar I mounted the big, full-size rad (from the same
car as the engine) behind the engine, at an angle so that the top edge
was at the firewall and the bottom was forward about 8". Baffling
around the rad made sure that ALL air leaving the cowl (except for a
bit leaving around the hot exhaust pipes) had to go through the rad,
so I had maximum flow. A lip on the cowl outlet to accelerate air away
from the opening lowered the pressure further so that max differential
was maintained between the front and rear of the rad. And even with
all this the engine's coolant temp reached max in an extended full-
power climb on a summer day.
The P-51 had an underbelly scoop and a variable-geometry outlet
behind it. The rad was in this housing. Inlet and outlet shape and
size were critical, and I've heard that the designers were so clever
that they even got a little thrust as the cooling air expanded and was
accelerated a little when it left the outlet. OWT, maybe, but there's
lots to learn from their design anyway. It's worth noting that the
inlet was much smaller than the rad's area; Mr. Bernoulli tells us
that pressure increases as airflow slows and decreases as it
accelerates, so the divergent duct between the inlet and rad face
slowed the air and increased its pressure. Same principle used in
numerous places in a jet engine.

Dan

wrote in message
...
On Aug 27, 3:32 pm, "Peter Dohm" wrote:
"Jim Logajan" wrote in message

.. .

Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "
wrote:

everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

But doesn't the Rotax 912 have reduction gearing and liquid cooling? It
is
getting put into an awful lot of aircraft models - particularly LSAs.

That's true, and the biggest annoyance (of which I am aware) is that they
have increased the recommended "idle" speed to increase the service life
of
the PSRU--which is of the spur gear type. I don't know whether any of
the
belt or chain type PSRU installations have a similar requirement.

As to cooling: there were a lot of liquid cooled aircraft engines in
WWII,
but the the aircraft they in which they were installed looked a lot
different from their air cooled counterparts.

Peter

Even belted PSRUs have vibration nodes. The Glastar in which
we put a PSRU'd Soob didn't like 1400 engine RPM; it semed to be an
argument between the flywheel's inertia and the prop's. Running it at
that RPM for long would have torn the teeth off the belt. I didn't
notice if there were further nodes at 2800 and 5600. Adjusting belt
tension didn't change anything.
I've read about (and encountered) cases of cooling problems in
auto conversions. Many builders underestimate the amount of heat that
needs discarding, and also make mistakes in radiator installation and
baffling. I've seen rads mounted out in the breeze where they not only
slow the airplane but suffer from airflow problems created by the
vortices generated around the rad. I've seen a couple of small rads
mounted behine the front cowl openings, where they're supposed to get
ram air, but without proper baffling to separate the incoming air from
the air behind the rads the pressure differential is minimal, causing
low flow, and air eddying around the rad further interferes with
flow.
In the Glastar I mounted the big, full-size rad (from the same
car as the engine) behind the engine, at an angle so that the top edge
was at the firewall and the bottom was forward about 8". Baffling
around the rad made sure that ALL air leaving the cowl (except for a
bit leaving around the hot exhaust pipes) had to go through the rad,
so I had maximum flow. A lip on the cowl outlet to accelerate air away
from the opening lowered the pressure further so that max differential
was maintained between the front and rear of the rad. And even with
all this the engine's coolant temp reached max in an extended full-
power climb on a summer day.
The P-51 had an underbelly scoop and a variable-geometry outlet
behind it. The rad was in this housing. Inlet and outlet shape and
size were critical, and I've heard that the designers were so clever
that they even got a little thrust as the cooling air expanded and was
accelerated a little when it left the outlet. OWT, maybe, but there's
lots to learn from their design anyway. It's worth noting that the
inlet was much smaller than the rad's area; Mr. Bernoulli tells us
that pressure increases as airflow slows and decreases as it
accelerates, so the divergent duct between the inlet and rad face
slowed the air and increased its pressure. Same principle used in
numerous places in a jet engine.

Dan

Interesting post, Dan.

I've seen cylindrical "barrel" type heat exchangers intended for
installation in a round duct. I wonder if these might be an alternative
choice to the flat automotive-type radiators.

On Aug 26, 11:14*pm, Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "

wrote:
everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

Ron Wanttaja

i heard the e racer had an inflight engine fire and eventually the
designer through in the towl on auto engines. anyone remember why?

On Wed, 27 Aug 2008 16:11:51 -0500, Jim Logajan wrote:

Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "
wrote:

everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

But doesn't the Rotax 912 have reduction gearing and liquid cooling? It is
getting put into an awful lot of aircraft models - particularly LSAs.

Certainly, and my data shows that the Rotax 912, in homebuilts at least, has a
safety record pretty much equal to that of traditional certified engines.

My posting was an attempt to answer the OP's question on why some people believe
auto engine conversions are dangerous. The three items I mentioned are in the
top four causes of auto-engine failures. Looking at my 1998-2006 homebuilt
accident database and comparing fixed-wing applications, the rate of occurrence
of ignition system problems is four times higher for auto conversions than
traditional engines. And the traditional engines had no cases of PSRU or
cooling failure.

I believe it's possible to convert an auto engine and achieve reliabilities
equal to that of a traditional certified engine. It's just that the accident
reports show that many people can't achieve that goal. It's basically the same
people installing the Continentals as the Subarus, or the Rotax 912s and the
Fords. But the average builder seems to have less problems getting the Lyconts
and Rotaxen to be reliable.

Ron Wanttaja

On Aug 27, 7:01*pm, "
wrote:
On Aug 26, 11:14*pm, Ron Wanttaja wrote:

On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "

wrote:
everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

Ron Wanttaja

i heard the e racer had an inflight engine fire and eventually the
designer through in the towl on auto engines. *anyone remember why?

Sure do.

"From: Dorothy Dickey
Sent: Monday, January 24, 2000 8:46 PM
To: Young, Ryan
Subject: Engines for E-racers
There is nothing wrong with the Buick engine it's just that I no
longer favor
auto engines for aircraft applications. This is because it is not
possible
to achieve equivalent reliability and performance of an aircraft
engine for
the same or less money... So why do it? Shirl"

Remember, this is a guy who designed an airplane around an auto
conversion, and devoted serious time, money, and twice, almost his
life to making this idea work. If you think you can do better, step
right up.

This whole thread smacks of TROLL, but you can read what more of what
I think, along with the E-Racer guy (Shirl Dickey), and a little from
the Belted Air Power reduction guy (Jess Myers) he

http://users.lmi.net/~ryoung/Sonerai/BOP.htm

You can also search this newsgroup for anything by Corky Scott, and
watch his chronicle. He never flew his auto engine conversion, after
working on it for years.

wrote in message
...
On Aug 27, 3:32 pm, "Peter Dohm" wrote:
"Jim Logajan" wrote in message

.. .

Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "
wrote:

everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

But doesn't the Rotax 912 have reduction gearing and liquid cooling? It
is
getting put into an awful lot of aircraft models - particularly LSAs.

That's true, and the biggest annoyance (of which I am aware) is that they
have increased the recommended "idle" speed to increase the service life
of
the PSRU--which is of the spur gear type. I don't know whether any of
the
belt or chain type PSRU installations have a similar requirement.

As to cooling: there were a lot of liquid cooled aircraft engines in
WWII,
but the the aircraft they in which they were installed looked a lot
different from their air cooled counterparts.

Peter

Even belted PSRUs have vibration nodes. The Glastar in which
we put a PSRU'd Soob didn't like 1400 engine RPM; it semed to be an
argument between the flywheel's inertia and the prop's. Running it at
that RPM for long would have torn the teeth off the belt. I didn't
notice if there were further nodes at 2800 and 5600. Adjusting belt
tension didn't change anything.
I've read about (and encountered) cases of cooling problems in
auto conversions. Many builders underestimate the amount of heat that
needs discarding, and also make mistakes in radiator installation and
baffling. I've seen rads mounted out in the breeze where they not only
slow the airplane but suffer from airflow problems created by the
vortices generated around the rad. I've seen a couple of small rads
mounted behine the front cowl openings, where they're supposed to get
ram air, but without proper baffling to separate the incoming air from
the air behind the rads the pressure differential is minimal, causing
low flow, and air eddying around the rad further interferes with
flow.
In the Glastar I mounted the big, full-size rad (from the same
car as the engine) behind the engine, at an angle so that the top edge
was at the firewall and the bottom was forward about 8". Baffling
around the rad made sure that ALL air leaving the cowl (except for a
bit leaving around the hot exhaust pipes) had to go through the rad,
so I had maximum flow. A lip on the cowl outlet to accelerate air away
from the opening lowered the pressure further so that max differential
was maintained between the front and rear of the rad. And even with
all this the engine's coolant temp reached max in an extended full-
power climb on a summer day.
The P-51 had an underbelly scoop and a variable-geometry outlet
behind it. The rad was in this housing. Inlet and outlet shape and
size were critical, and I've heard that the designers were so clever
that they even got a little thrust as the cooling air expanded and was
accelerated a little when it left the outlet. OWT, maybe, but there's
lots to learn from their design anyway. It's worth noting that the
inlet was much smaller than the rad's area; Mr. Bernoulli tells us
that pressure increases as airflow slows and decreases as it
accelerates, so the divergent duct between the inlet and rad face
slowed the air and increased its pressure. Same principle used in
numerous places in a jet engine.

Dan
I was only thinking of the exact ratios that place the same teeth in use on
each successive rotation of the belt.

Torsional resonance can be extremely difficult to monitor andI am glad that
you were able to identify it before it became a dissaster. For the moment,
my own project and the decision to build around a PSRU or use a direct drive
aircraft engine has been pushed further into the future. But I have
wondered whether the elimination of critical speeds might be the true
purpose of those little springs in the driven plate of a manual clutch.

"flybynightkarmarepair" wrote in message
...

FBNKR: This whole thread smacks of TROLL, but you can read what more of
what
I think, along with the E-Racer guy (Shirl Dickey), and a little from
the Belted Air Power reduction guy (Jess Myers) he

Peter: I agree about the Troll, but sometimes one just can't resist...

FBNKR: http://users.lmi.net/~ryoung/Sonerai/BOP.htm

FBNKR: You can also search this newsgroup for anything by Corky Scott, and
watch his chronicle. He never flew his auto engine conversion, after
working on it for years.

Peter: I had wondered about what Corky finally did, but did recall that he
was giving up on the auto conversion idea--although IIRC his aircraft was a
four seater.

The problematic word in the subject of this thread is "simple".

An aluminum V8 auto-derived engine is not an aircraft engine - yet. It
needs a lot of engineering work to become one. If the engineering is well
done, the resulting aircraft engine will be successful. If it isn't.....
Many auto conversions weren't. It isn't easy.

Auto engines are high revving compared to direct drive aircraft engines so
to get a reasonable power to weight ratio, a PSRU is needed. But, isn't a
PSRU heavy? Yes, but so is the crankshaft of a direct drive engine - it has
to be to handle the torque. Auto engines have light cranks which are just
as strong on a HP to HP comparison since they rev higher. HP is just torque
(Ft Lbs) times RPM divided by 5252. Compare the weight of a direct drive
crank vs. the crank + PSRU weight of an auto conversion - not so much
difference as thought.

To minimize the re-engineering, keep the engine core working as nearly the
same as in a road vehicle but make sure it uses the best forged racing parts
like rods and pistons for durability. Use the lightest flywheel that allows
an even idle.

The PSRU is just a special PTO (Power Take Off) with gears. It mounts to
the flywheel housing and connects to the flywheel with a flex plate.
Millions of PTO's are in use as irrigation pumps so somebody knows how to do
it. It takes all the gyroscopic and thrust loads away from the crank which
'sees' no loads except torque. Make it from billet aluminum and use the
best bearing money can buy. I'd use a very close tolerance planetary
gearset for durability.

It will withstand high contineous power if you keep it cool. Design the
radiator for worst case cooling conditions and then control the airflow with
variable baffles. I'd feed a pair 12" diameter "barrel" radiators with jet
like wing root air intakes and rear fusalage exhaust . I'd augment the
radiator outflow with engine exhaust which keeps the radiator intakes from
ingesting hot engine exhaust while increasing airflow through the radiator.

I'd use 100PSI racing type fuel injection with in-tank pumps to prevent
vapor lock. I'd use closed loop mixture control with an O2 sensor. No
fussy carburator - no carb ice.

Would I put this thing in an airplane and fly it over the mountains at
night? Not at first - not by a long shot. I'd build it on a trailer so I
could run it in non-noise sensitive areas. I'd take it to air shows to
entertain but mainly I'd just run it on the trailer trying to break it. If
after a few years I still couldn't break it, then maybe in an airplane.
Ground testing is the expensive part. 2000 hours at 10GPH = 20,000 gallons
at $4 each = $80,000. Nobody said it was cheap.

"Bill Daniels" bildan@comcast-dot-net wrote

I've seen cylindrical "barrel" type heat exchangers intended for
installation in a round duct. I wonder if these might be an alternative
choice to the flat automotive-type radiators.


Doubtful that you could get enough surface area in a round radiator. If you
just made it longer, efficiency would suffer, since the half that is
downstream would only be getting hot air.

Dan is absolutely correct, about the ducting and baffles being important.
In the P-51 (probably the best cooling design ever) the duct intake was
small, then the important part was the shape as the duct got bigger, to slow
the speed the air went through the radiator, and also like he said, gain a
little pressure.
--
Jim in NC

"Peter Dohm" wrote

Torsional resonance can be extremely difficult to monitor andI am glad
that you were able to identify it before it became a dissaster. For the
moment, my own project and the decision to build around a PSRU or use a
direct drive aircraft engine has been pushed further into the future. But
I have wondered whether the elimination of critical speeds might be the
true purpose of those little springs in the driven plate of a manual
clutch.

I have read about the issue of whether to have ratios to get a constantly
different belt to tooth interface, and I wish I could remember more of what
it said.

I recall that while it is important to vary ratios in a toothed gear redrive
away from exact ratios like 2:1, so different teeth mate with both gears
(prevents wearing a certain pattern in each other) that is not a necessary
condition for toothed belt redrives. I recall that in fact, it is not
desirable to do that, but again, my recall is incomplete.

The information is out there, though.

I would love to design my own belt redrive, but when the time comes, I know
I would be more comfortable going with a company that has a well proven
track record with many of their drives in active, high time service.
--
Jim in NC