On Aug 26, 11:43 pm, "Morgans" wrote:
wrote

OP: a dry sump isn't absolutely necessary...neither is fuel
injection....neither is a magneto.
just a good way to hedge your bets. say your're in the mountains,
it's stormy, and you have turbulence. no matter what Gs or static you
are subjected to, the engine would get a steady supply of oil, fuel
and electricity.

You'd better think twice about being in the mountains in
stormy weather and turbulence. You'll have other problems besides oil
supply. In any case, wet-sump aircraft engines fly in the mountains
and turbulence all the time and have no oil issues. It's the weather
that kills the flier.

Morg: Magnetos over electronic ignition? What breaks down more often, a
magneto, or electronic ignition? What is better at making an easy starting
engine, running with the spark at the appropriate timing? Magnetos are old
hat, so if you want reliable, go with dual pickup, dual coil(s) redundant
electronic ignition with a battery supplied emergency backup power source
for the ignitions. The not having a dual plug is the only slight trade off,
because you can use a two into one spark system to tie the dual ignition to
the one plug.

The use of 100LL fouls plugs rather often. Two plugs are handy
for that, and the extra plug improves power output.

OP: i know resale value is diminished and the public perception is not
good. i'm just trying to understand the specific technical reasons
why. all i hear is that 1-auto engines MUST have psru and 2-therefore
turn high/spooky rpm continuously. then i fail to hear of any case
where a conversion project stumbles for lack of a psru.


Morg: Bottom line, it would be very wise to use some type of extra external
bearing to help with soaking up the thrust loads and gyroscopic loads. A
PSRU does that for you. The PSRU also gets some more HP so the HP to weight
ratio is better. As far as spooky high continuous RPMs go, I think you
have been listening to some of the critics of conversions too much.

Very good point. Auto cranks were designed for torsion loads only,
not thrust or gyroscopic loads, and they tend to break when subjected
to such loads.

Morg: When have you heard of people being concerned at running a marine
auto engine at too high constant RPMs? Never. They run at RPMs that would
worry me much more, and faster than most people run airplane conversions.
You can choose what drive ratio you want to run. A conversion running at
3,000 RPM is too fast for a prop, but not too fast to make me uncomfortable.
I would not worry at running a conversion at 3,800 RPM for extended periods
of time. I sure run my boat engine at higher RPMs than that.

Marine engines have a couple of advantages that aircraft
conversions do not: A ready supply of cold coolant, and a drive system
that doesn't apply and thrust or gyroscopic loads on the crank.
Running an auto engine at or near max power settings, like we do in
boats or airplanes, generates huge amounts of waste heat that autos
don't when they're cruising unless they're pulling heavy trailers, in
which case a trailer-towing package becomes necessary. This includes
much larger cooling capacity. Autos typically cruise at around 25-30%
power, boats and airplanes at 65-80%. I have experience with both
marine and aircraft liquid-cooled conversions, and believe me, the
boat is easy to keep cool.
Aircraft engines are built with big cooling capacity right from
the start. And they're designed to produce large amounts of torque at
lower RPM, which means the basic cylinder geometry is different. And
they're designed to do all this without weighing as much as a bridge.

OP: everyone who
dares to run direct is glad, and most of us agree there is nothing
scary about driving all day, every day, at 2900 rpm with a car
engine. you won't get 100% hp, but a camshaft and dual plane intake
change could help with that.

You still won't get 100% unless you're at rated redline, which no
prop will stand for. Most direct-drive conversions run a much shorter
prop to allow a higher RPM (propeller tip speed and centrifugal forces
are the concern) and shorter props lose efficiency big time, so
performance, especially takeoff and climb, suffer considerably.
One horsepower is 33,000 foot-pounds per minute. To get it we do
this: Torque x RPM x 6.28 divided by 33,000. RPM is one of the
factors, and a PSRU is usually needed to get the engine's RPM up to
its designed redline so it'll generate the claimed HP. Anything less
represents a loss, which means a heavy, underpowered airplane.


OP: maybe aircraft engines have dual spark plugs...each cylinder fed by
two independent magnetos..is that the case? is that the safety
measure lacking in auto conversions? aside from the "psru myth", the
dual plugs are all i can think of.

Boy oh boy, are we at that level of expertise? You'd better do
a LOT of research here before deciding that you have answers that the
rest of us don't.

I hope I gave you a little to think about. There are companies out there
with well engineered, time tested, reliable PSRUs. To me, it is not the
myth that would keep me running direct drive, but the desire to get a better
powered package, with the isolation of prop loads on a crankshaft that IS
NOT DESIGNED to take prop loads.

Yup. Lots of folks have done the work already and found it much
more difficult than they imagined when they started out. I wouldn't
want to think that I could improve on any of it on a first try.

Dan