To the KR community and to Mike Arnold,
My post on engine conversion was not meant in any way to disparage
Aeromomentum. I don't think this is the company that was around
developing Suzuki engines for ultralight and powered parachute aircraft
over a decade ago. I have great admiration for the work that that
company did on the Suzuki. (I've lost my notes on that company's
conversion).
My comment was triggered because I had deep distrust of the ethics and
business practices of another automotive conversion company, which, in a
previous incarnation, sold many auto conversion engines that few, if
any, customers ever got to work successfully, due to both engine and
reduction drive problems. Their (I assume) owner made bold claims about
their conversion's power, reliability, and weight, and, if anyone
questioned them or was critical, were treated with scorn, and their
question was deleted from the forum owned by the company. It seemed as
if they were using their customer base to test their conversions.
I went to an alternative engines forum put on by Contact! magazine when
that company was in business and I was surprised when the mere mention
of the company brought boos from the audience. That company abruptly
went out of business shortly after that, leaving many customers with
what can only be called, charitably, "boat anchors".
That same head of the company emerged later, flogging engines from
different automobiles, with a flashy website and ads extolling the
virtues of its engines and featuring people who have just taken
delivery. I'm more interested in engines that are flying successfully.
They are still in business today, and while I don't really know how
reliable their present auto conversions are, I hope they are much better
than their previous business. Caveat emptor.
I know that many of you probably weren't around when Burt Rutan was
selling plans for the Varieze and the Long-Eze, but he set what I
consider is the gold standard in experimental aviation. If there was a
problem with a plane, he immediately let the community of builders know
about it. (There was no internet, so builders depended on the Canard
Pusher newsletter, letters, and phone calls). A few years ago, at
Oshkosh, I got to tell Burt that he set the gold standard.
Best of luck, Mike, on your engine and airplane. Keep us posted on your
progress.
Dan Branstrom
------------------------------------------------------------------------
Ok I tried to stay out of this but, as some of you know I am putting a
Suzuki G15 in my KR2S. Full disclosure I am a dealer for Aeromomentum.
Forgetting that, I think the Suzuki is a great option for a KR. Great
performance, light weight, great fuel economy, overhaul is very affordable.
Can't beat the price. This basic engine has been around for decades and
proven to be tuff. These engines are all brand new not rebuilds. I am not
going to write a novel on this net about it, but if you want more
information on it contact me. Mine will be in this year for sure.
On Tue, Oct 22, 2019, 6:23 PM donald january via KRnet<krnet@list.krnet.org>
wrote:
If you can get your hands on "Converting Auto Engines for Experimental
Aircraft" Second Edition by Richard Finch I recommend it for good reading
and great insight. FWIW
On Tue, Oct 22, 2019 at 2:56 PM Daniel Branstrom via KRnet <
krnet@list.krnet.org> wrote:
I am not an engineer, and my comment here is based on some reading and
observations that I have made over the years in aviation. My opinion is
worth the electrons that were used to produce this post.
In every machine that has rotating parts, torsional harmonic vibration
is present. I'll call it THV. If a vibration coincides with an operating
range of the machine, the THV can destroy the machine. If the frequency
is above or below the operating rotation, it becomes much less of a
problem. In an automobile, THV is damped by the rubber tires, and the
greater rotation mass of the flywheel, and, often, automatic
transmissions. On an airplane, the power pulses go undampened to a
propeller, which has its own harmonic vibration that can be fed back to
the engine at certain frequencies and can destroy the engine. Wooden
propellers tend to dampen this because of their composition.
Aircraft engine manufacturers take torsional harmonic vibration into
account when designing their engines. That's why some certified direct
drive engines come with a warning not to operate them at certain rpms
with certain propellers, or they have counterweights to smooth things
out. Rotax engines, for example, have a coupling that dampens THV.
Engines are certified in aircraft with designated propellers for that
reason.
Torsional harmonic vibration can snap crankshafts and destroy reduction
drives. It is similar in concept to aerodynamic flutter in flight
controls. The THV does not disappear where the power pulses are
overlapping, so that all of the forces going in same direction as they
are in 6 or 8 cylinder engines, but at least all of the force going to
the prop is in one direction. 4 or less cylinder engines have periods in
their rotation when there is a backward force on the power output. The
inertia in the engine, as well as flywheels or propellers keep the
engine turning.
There are very few companies that have been successful in experimental
aviation with reduction drives. That doesn't mean that there aren't good
ones out there, but the amount of engineering and manufacturing skill
needed to build them can be immense and costly, and they have to have a
big enough market to be profitable. It's also my opinion that as the
power of the engine goes up, the forces on any reduction drive go up
exponentially, and that's why it's easier to make a drive for an engine
developing under 100 hp (which seems to be the dividing line) than one
that has more power. It's for those reasons that I don't believe you
will see a Rotax 200 hp engine.
Years ago, there was a manufacturer of a redrive that was used on large
engine conversions. It seemed to be a good one, with few problems, but
when the drive was manufactured by someone new, the drives started
breaking. I credit the problems to manufacturing technique.
I have flown behind a Cessna 175, which has a geared engine. It was
excellent both in climb ability and cruise speed, I found it close to
the performance of a 182, and it had a fixed pitch propeller. The 175
got a bad reputation, I believe, because pilots tried to operate it like
an ungeard engine. The engine was designed to run at above the red line
of ungeared engines, and operating it at low ungeared rpms is very hard
on it. Also, it was not good practice to let the prop drive the engine.
Consider the reputation of anyone making a reduction drive, and look for
reports of people that have problems with it. Google engine problems or
engine issues, and look at what other engines they have sold in the past.
That's my 2 cents. Your mileage may vary.
Dan Branstrom
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