Alan Tolle wrote:

There is another issue that has been tossed around here lately to which I
can add some pertinent data.

Some of the readers here must get the notion that I am ttrying to peddle
Powersport products.  Not so.  I don't have now and I never did have any
financial stake in the company.  The engine was theirs, the airframe was
mine.  We were good friends.

I report on what Powersport did  because I know the data and because

Everett Hatch was about 10  years ahead of nearly everyone who writes on or
reads from these pages so

far as the rotary application to a fixed wing aircraft was concerned.  Take
the issue of iginition timing on the 13B.

Everett had made an extensive study of ignition timing both on the dyno and
in the air.  Dyno data showed that advancing the timing beyond 18 degrees
BTDC had absolutely no effect on hp output in the rpm range of 5000 to

6000.

The peripherally ported engine started easily and idled well at 18 degrees

BTDC.

With the throttle plates right at the trochoid housing the engine would

idle rock solid at 1400 rpm  (600 rpm on the prop.)

The importance of the solid 600 rpm idle should be emphasized.   First, the
pilot's worse fear is a dead engine on short final.   Second, until the
reasonably priced controlable pitch unit comes along we all must use fixed
pitch propellers.   Any such prop is a compromize and usually, to get the
best cross country performance, it is necessary to use a fairly high pitch
(the pitch of the RV-3 cruise prop was 98 inches)  The low idle speed is
necessary to reduce the thrust in the landing task.  With even an 800 prop
rpm idle you float, and float, and float.  This point has all but been
forgotten by those who fly a constant speed prop.  Flatten the prop and you
have a huge air brake.

But the dyno data wasn't enough.  Everett later rigged up for test purposes
a manual pull-push mechanism to advance the timing in the airplane and made
flight tests at  at various altitudes (up to 8,000 feet) and power settings.
Again there was no speed (power) increase beyond the 18 degree BTDC setting.
For most normally aspirated airplanes the design crusing altitude is around
8,000 feet.  So the number was always 18 degrees.  It was decreased by 5
degrees to run the nitrous oxide.

That number sounds conservative.  Plus we always used 100LL or 92 octane
unleaded premiun mogas to give a sure detonation margin.  We got all the
power possible with no concern about detonation.  And everything was simple.
There was no need for knock sensors.

The game about spark advance changes when one chooses to cruise at oxygen
requiring altitudes.  Advancing the spark there can help a lot as for
example Klaus Savier and his Vari Eze.

Great info Allan. It sounds like you are near running another rotary
I hope.

Good point on the idle. We had a guy smuk his brand new IO 540 Berkut
onto the freeway here not too long ago because the engine quit on
short final. Some people were hurt in a car. Second flight.
The engine quit after the first flight while taxiing back.
If your airplane starts talking to you had better start listening.

I always come in high and slip. Its safer and more fun.

PL 

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