> Has anyone heard of an experimental aircraft using a japanese
> 4-cylinder motorcycle engine? The advantages seem obvious when
> compared to other non-rotary auto conversion choices. Modern 1000cc
> engines make 180hp, are liquid-cooled, lightweight, and inexpensive.
> If such an engine was de-tuned to 100-120hp by lowering the redline
> (say from 13k to 9-10k), it might give close to a 1:1 power:weight
> ratio with high reliability.
>
> I can't be the first person to think of this. If it hasn't been done
> before, why?
>
> -Chris Wood
>
> Probably a cooling issue. Motor cycle engines, like car engines, are
> light duty. Several people have tried air cooled BMW engines for the
past twenty
> years but they never caught on.
>
>
http://www.kawasaki.com/Products/product-specifications.aspx?id=345
> Engine Type Four-stroke, liquid-cooled, DOHC, four valve per cylinder,
> inline-four with VVT
> Displacement 1,352 cc
>
> Maximum Torque 100.3 LbFt @ 6,200 rpm
> Compression Ratio 10.7:1
>
> Curb Weight 670.3 lbs. 679.1 lbs. (ABS model)
>
> ------------------------------------------------------
>
> No mention is made of the red line or the HP surprisingly.
> At 670 pounds for the whole bike the engine block could easily
> weigh 200 pounds or more.
>
> 100 ft pounds of torque at 6200 RPM is 119 HP. About the same power
to weight
> ratio as a Continental O-200 direct drive aircraft engine. Of course
you will
> still need a 20 to 30 pound gear box. Motor cycles are designed for
side ways
> mounting... chain drive so it is no easy matter to design a gear box
that will
> take the power out inline or turn the drive 90 degrees for a propeller.
>
> That is also half the displacement of a Mazda 13B rotary engine with
about the
> same block weight but the rotary will easily put out 200 HP in side
port form
> and 250 HP in p-port form.
>
> These engines in new shape are also not cheap.
> Paul Lamar
The typical problem with motorcycle engines are the gearbox which is
integral to
the engine cases, adding much unnecessary weight. The BMW engines have been
moderately sucessful in Europe as the transmission unbolts from the case and
aftermarket redrives are available. Too expensive in the US tho.
Takeoff-BMW is
the largest BMW engine conversion specialist in Europe:
http://www.takeoff-ul.de/
An engine I have considered for a while is the Rotax 4-tec 4 stroke 3
cyl supercharged
and intercooled watercraft engine. This is 255 hp in a very small and
light package.
There is no gearbox to detach and has a closed loop cooling system which
is unlike
most other watercraft that use the operating medium in an open loop system.
These engines are designed for sustained WOT operation as users race
them at top
speed for hours. A complete watercraft using this engine is around
$12,000. Wrecked
units are often available at less than half price at
motorcycle/watercraft/snowmobile salvage
operations when usually inebriated operators race them onto the beach at
maximum speed encountering solid
objects. There is also a two NA versions with 155 and 130 hp.
http://www.sea-doo.com/en-US/watercraft/musclecraft/rxt/ (Watch the
Rotax 4 tec flash video) These engines would require
an aviation based redrive to be fitted, possibly the SPG-2 box available
here:
http://www.airtrikes.net/engines.shtml A custom adapter would
need to be fabricated but is fairly
straightforward.
Glenn
Recreational water craft engines (even racing version rarely) get more than
a few hours a year. There is no reason to believe the materials and technology
in these engines is any better than the Rotax aircraft engines. Rotax engines
have a TBO of 1500 hours and then you must replace most of the parts such as
crankshaft and connecting rods. Piston engine parts fatigue and rotary engine
parts do not.
http://www.rotaryeng.net/Rotar-v-Piston.html
The Rotax 912 engines weigh about 150 pounds which is a pretty good power to
weight ratio. Better than an O-200 AC engine. An all aluminum P-port 120 HP
Mazda one rotor would weigh well under 100 pounds.
The current cost of a 912 is about $20,000 US.
A brand new RX8 engine is $5800 retail and about $3800 wholesale if you are a
car repair shop.
Paul Lamar
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