J.Kahn wrote:
snip
Simple, light, reliable is the Prime Directive, regardless of how old
the technology is. When it comes to airplanes, that is sound design
practice, when considering ass pucker levels while in climbout over a
builtup area or over a tree line. I don't care if it's made of rocks.
If it's simple, light and reliable, the fact that it's derived from
tractors is irrelevant. The big radials of the old days, when you look
at it, were also very simple, light reliable designs in relative to the
alternatives in view of the power requirements. You will note that the
"more sophisticated" liquid cooled aircraft engines never survived in a
significant way past WWII in commercial service, with one unusual
exception, the Canadair North Star airliner, which used Merlins.
Everything else was radials because relatively speaking they were the
simplest and lightest and most reliable solutions before jet engines,
even if their air cooling and pressure carbs were "crude".

This is the point. If you want to take advantage of technology like
electronic control, you have to design for complete redundancy if your
control system has a sudden potential failure mode. Not practical for
the homebuilder. The farm tractor technology engine can have its
components built with sufficient inherent robustness, or have a very
gradual failure mode, to provide the required safety without needing
duplicate systems, (like a crude but simple carb) or at least a minimal
level of redundancy.

I am a fan of auto conversions, but believe that those conversions to be
viable must be as close as possible to a traditional aircraft engine
from the standpoint of simplicity and overall design, and the Corvair
using a Stromberg aircraft carb and a dual primary points ignition comes
closest to fitting the bill of any conversion I have seen besides a
Great Plains VW. Now that the crankshaft strength issues are known and
a way forward is clear, the Corvair engine's potential is even better
than before as a conversion IMHO.

Mechanical fuel injection with electronic trim is within the
competence of the homebuilt community and with the existing auto
manifolding it's doable. A modified auto carburetor is also useable and
just as reliable as an aircraft one. One consideration in auto
conversions is that Detroit (or Japan) has sunk billions in reliability
engineering and testing and maximizing use of that is critical.

The simplicity of the carbureted magneto Lycoming is enviable. Its
efficiency and brute force solution of problems are not. If it were
cheap enough these could be overlooked, but it isn't and they can't.

The simple life, as someone said, isn't so simple. Let's look at the
problems with the simple LyCon engine:

1. Free air cooling worked well in the J-3 Cub and the 6:1 cr A-65
Continental engine. The Cub had about a thirty knot airspeed range,
maybe forty, and the tops of the cylinders didn't get all that hot and
a 1000-hour life was considered fantastic anyway. It was a day VFR
airplane, there was no engine management to speak of (many didn't even
have a mixture knob, including the Champ I soloed in-in the mid-80s)
and you never flew higher than cars drove in the mountains, so you
didn't miss it.

Fast forward: the Bonanza with a TSIO-550 Continental. Not a
successful concept anymore. With no speed brakes, a very clean
airframe, and the expectation of single pilot IFR at FL180 and above by
non-full-time (say the word: amateur) aircrew.....engine management and
shock cooling (most owners would never execute a power-off approach,
not with the price of cylinders what it is!) played a big part in the
Bonanza debacle that could have put the keys to the Webb Ave.plant in a
plaintiff's pocket many times over. It didn't, but GA has never and may
never recover.

Single lever power control, is rationally necessary for safe single
pilot IFR. Someday the FAA will be forced to make it so. With a piston
engine this means, as far as I can tell, either liquid cooling or a
regulated, forced fan system. Shock cooling has to be made impossible,
even with a cruise power split-S and vertical dive. ( Spare me the no
acro airspace rant...unless you think the supposed liability crisis is
from people losing their licenses instead of the family into a
hillside.)

2. Direct drive means if you land gear up (spare me the you'll get a
30 day suspension anyway rant) it's probably time not only for a new
prop but also new crankshaft as well. This in turn makes insurance for
RG aircraft much higher. Also makes insurance for taildraggers much
higher because you might put it on its nose.

A good redrive will fail a belt or quill shaft first. This is called
weak link-strong link design. Everything will fail sooner or later. You
want a known point of first failure that is accessible, inexpensive,
and of predictable consequence. If you use a wood or composite blade on
a variable pitch or ground adjustable hub the blades will go and
probably protect the hub. And because they won't last "forever' anyway
there will be a competitive market for blades. Even if the hub dies,
it's a lot cheaper than a complete major OH and new crank.

There's also a 3 through about 7 or 8. But that's a good start.