Paul,

How tough to add a compression release (and would it buy you anything
on a low compression rotary)?  I imagine it would take less horsepower
(amps, watts) to turn over if the compression were released at the
correct time.

How slowly could a rotary be turned to start if the ideal mixture and
spark timing were available (along with a compression release)?  Most
systems seem crude in this regard - making a rough stab at ignition
timing and fuel delivery.

The Russian radials use air start - and are apparently lighter and
more reliable than the equivalent electric start systems.  The Yaks
I've been around seem to start almost instantly compared to the
Pratt's, Jakes, and Continentals.

I have read accounts of people needing to push start their rotary
powered car, though I suspect that's driven by tuning, ignition, fuel
delivery design, electrical system inefficiency, and maybe port timing
more than rotary engines being hard to start.  Are p-ports harder,
easier, or about the same to start?

The cost/benefit ratio of weight savings for airplanes is different
than for cars.  Big bore Continental starter drives are around $800
rebuilt (without the electric motor).  Surely there's some room in the
budget for innovation...


Regards,

Matt-

So far I have not noticed p-ports are harder to start.
Some rotaries get stuck apex seals due to injecting used crank case oil
to the apex seals.

In that case a shot of ether works wonders :)
Once the engine warms up the seals un stick.

Paul Lamar

Paul, our experience was same as yours regarding Matt's questions of
comparative starting characteristics of different configurations of rotary
engines.  Below are a few notes regarding different combinations tested over
a fifteen year period.  During this time we owned every major iteration of
RX-7 until they were no longer sold new here and we dyno tested a prototype
dual side port engine and test flew different configuration peripheral port
engines for many years and could not tell a major difference in ease of
starting for any of them.  Don't know if this experience is meaningful due
to the fact that we were constantly testing so many different oddball
combinations.  For example, the peripheral port rotary was test flown first
with a one-off system we built using a belt driven Hillborn pump, nozzles
and barrel valve, followed by a Holley/Weber carb, then  a one-off system
using a venturi we made to provide signal to a servo we also made, and it
used Hillborn nozzles.  Those were followed by a system using a modified
Airflow Performance fuel injection and nozzles, then finally a system with
our venturi in combination with an Airflow Performance servo/fuel controller
with Airflow Performance and Hillborn injection nozzles (vented for direct
trochoid injection and unvented at the port/runner).  Other combinations
also tested.  All started very easily and no hot-start continuity problems
on any of the fuel injected engines.  If anything, the very first engine,
the dual side port with injectors in the velocity stacks above the throttle
plates which were above the plenum, took just a tad longer to fire than all
the peripheral port variants, but not much.

Steve Beckham