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.

Morg: I think you are hung up on the features of that overpriced aircraft
engine. It is hard to believe that the dry sump will do any better than a
good old oil pan, unless you plan on some inverted flight, and if you
worried about some turbulence, an oil accumulator would keep oil flow
temporarily. Anyway, most aircraft engines do not have dry sumps.

Morg: Unless you use a header tank, fuel injection will not guarantee
keeping fuel going to run the engine. I do like fuel injection, and there
is no reason to not have it, and lots of other reasons to have it, but
again, not absolutely necessary unless you are going for an inverted
package.

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.


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: PSRUs have another value over direct drive, in that the prop
gyroscopic loads and thrust loads are removed from the crankshaft. They can
be MAJOR problems, up to and including broken crankshafts. An example are
the Corvair cranks broken (in part) from prop adapters that are too long,
with heavy props. With a V-8, you are going to have a heavy prop, and a
short adapter will make an unstreamlined cowl. The PSRU also raises the
thrust line to get better prop to ground clearance. So yes, those are some
reasons a conversion stumbles without 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.

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.

Morg: In short, I think your concerns about PSRUs are unfounded. You can
run any speed you want to, and higher than a normal prop speed. You get the
other advantages I identified, and get more HP from your heavy engine. You
don't have to run at peak HP, but it sure would not hurt to run faster than
prop speed.

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.

OP: the rotaries need a lot of rpm to make decent power. so much that the
propeller is spinning too fast. i'm aware of this, but the plug and
ply magnetos i'm referring to are not avail for rotaries.

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.

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.
--
Jim in NC