On Mar 6, 8:38*am, "vaughn" wrote:
"bod43" wrote in message

...

I have the idea that mechanical failure of the original 4 cyl
engines (or any high performance japanese bike engine) is
pretty much unheard of but I am not at all sure.

* *It matters little, because now you are making a whole new engine for a
totally different application, with no track record and the distinct
possibility of new and exciting failure modes. *Further, the same can be
said about the reiliability for most any automotive engine in its intended
application, but the track record of automotive aero conversions is spotty
at best.

Just thinking outside the box... *Since the proposed Hyabusa Flat 8 engine
will need a PSRU anyhow; how about two Hyabusa engines put together into a
twin-pack? *The result would likely weigh a tad more than a simple flat 8,
but now you have two known engines combined with twin-engine redundancy.

Vaughn

There is little difference between the existing V8 Hyabusa and a flat
8 in terms of bottom end design. The V8 has proved bulletproof
@400HP. Pretty much everything learned with the V8 Hyabusa conversion
applies to a flat 8.

Of course it would need to be geared - torque peak is near 8000 RPM.
However, there is a weight trade off. These little screamers, which
are more like turbines than tractors, can use a light crank because
they use a whole lot of tiny power pulses instead of a few humongous
ones to produce power. The Hyabusa is on the extreme opposite end of
the power/RPM spectrum from a Lycoming.

Weight savings in the crank can be shifted to the PSRU which would be
a planetary gearset with maybe 5 planet gears for lots of tooth
engagement and strength. The gear ratio would need to be 4 or 5:1 so
spur gears or cog belts aren't the best choice since the small gear or
cog would be small with too few teeth engaged. A planetary allows
large ratios with lots of tooth engagement for strength.

Keep in mind how the motorcycle works. The bike has a 6-speed gearbox
whereas the airplane engine would have only one. The standard sport
bike shift technique, approved by the factory, is to apply a large
force to the shift lever and then tap the clutch lever when the rider
wants to shift. This results in an instant shift with horrific
transient loads suffered by the crank and drive train. An aircraft
powerplant would never see this abuse.

Why is a flat 8 better than a V8? Mainly a higher thrust line for
prop clearance and better ballance. To do that with a V8, it would
have to be inverted.