REFLECTOR: alternative engines

Wed Dec 5 14:40:10 CST 2007

I might add that when I was doing my research before deciding on the Subaru,
I found their test schedule- can't remember now, but they pull off of the
line and test run engines at cycles up to 10,000 rpm for extended periods
(hours) at a time to test for failure modes- My engine will be loafing at
around 5600 rpm, but it is nice to know that that is not a strain - I have
never heard of a crank failure in even a race version of a Subaru or Honda
or Toyota engine- (yes I know the pro race versions are built differently)
did hear about a broken Honda valve once though on an F1 car, but that was
running at about 22,000 rpm or so, (the FIA has recently limited rpm to a
paltry 19,000 for safety reasons) so I can't really complain - not saying
that it is not possible, but I will stand behind the Japanese quality
control and design ability anytime- my design ability is another matter of
course, but I have been very judicious in what I have done, and certainly
will give it a good workout before getting airborne... I have no concerns
about the mechanical ability of the engine to reliably produce power for the
aircraft, but I will maintain a vigilant watch on my cooling and fuel
systems, because if it does ever go quiet, it will almost certainly be
because of one of those two things..

Alex

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Jim Agnew
Sent: Wednesday, December 05, 2007 1:07 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: alternative engines

I'll add to Al's comments, you have never driven on the German Autobahns
where the throttle is a binary device as in idle and flat out.

Or how about marine conversions that spend most of the time close to wide
open.

Jim

James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying 

----- Original Message ----
From: Al Gietzen <ALVentures at cox.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Wednesday, December 5, 2007 1:19:51 PM
Subject: REFLECTOR: alternative engines

Gary wrote:

Also be aware that 

most insurance companies will not insure an auto conversion. With the 

limited companies writing experimental policies you may not get insurance. 

I wouldn't argue against using a Lycoming, but I have not found insurance to
be a reason to use one.  When I went to get insurance I had two quotes to
choose from. And I was a relatively low time pilot (200 hrs) and had no
canard time.

The fact is auto engines were designed to operate under a totally different 

environment. They typically work at 15% of their maximum power most of their

lives. 

You're right that the average duty cycle is low, although I think 15% is
understating it a bit.  But if you look at the test programs that the
engines are subjected to in development testing you'll find that it is very
rigorous, perhaps more severe than certified engines. Many hours of full
throttle operation, and hundreds of full throttle simulated acceleration
cycles.  

The aircraft engine is also derated by limiting its rpm to somewhere around
3000.  It's peak power capability is somewhere considerably above that.

I have heard of more crankshaft, connecting rod and valve failures on
aircraft engines than on auto engines; even when used in aircraft.  The vast
majority of issues with auto engine conversions in aircraft are related to
installation factors, and possibly the re-drive, rather than the basics of
the engine.  These are the challenges for the builder.  Every conversion
installation has some first-of-a-kind features.

My personal conclusion was that if the choice was limited to pistons, rods
and valves; I may as well stick with a certified engine.  The rotary is a
significant departure, and offers potential advantages; that's my opinion
FWIW. And if the issues truly are related to installation factors rather
than the choice of engines; then perhaps it doesn't matter.

I have 70 hours now on my rotary installation, and all is well.  A long way
to go to 1500-2000 hrs; but I'm about past the 'infant mortality' kinds of
issues, and I'd fully expect the engine to get there (definitely it will
outlast me). Yeah; in warm weather my oil temps mean that, after the first
couple thousand feet at well over 1000 fpm, I have to limit my climb rate to
something more typical of a Cessna cool day. I know of ways to resolve that
issue - and will when we get back toward summer, but that is not an issue
unique to an alternative engine.

I recently gave a ride to a guy who flies a Baron and a Cozy.  In a followup
e-mail he says: "I enjoyed looking at and flying your airplane.  The power,
smoothness and sound of the rotary was very impressive.  I'll take that.

Al

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