Hi
 Do you have a HP / RPM graph for a 13B engine.
Paul M


Stock side port or or P-port?
Here is an early 13B of around 1989 and some others.
 Note the 800 HP drag engine is running on Alcohol
 and can drive a 2000 pound car to 153 MPH in the
 quarter in less than 8.66 seconds.
 The engine is VERY ROBUST. That is about 4 HP
 per pound of engine weight.
Paul Lamar

Paul,
Looking at your Mazdatrix dyno, the power drops off considerably as
the RPM drops from the 7000 range to 5000. 5000 would be a bit low
for cruise but even 6000 is down a lot. What do you attribute the
drop to; intake length, exhaust tuning? Boing Boing engines can
have  a dip when cam, heads and manifolding do not match up.

Dale Davies

This is what you will get with a highly

tuned engine.
The RX8 has a very complicated intake system to tune
the engine over a wide RPM band. You don't need it in
an aircraft engine. Cruise at the 6000 RPM torque peak
for lowest BSFC.

6000 RPM is the sweet spot in a Mazda engine as that is where
the bearing loads are lowest.

Lets say one is real cheap and one wants it all including max power
on the top end. One has a constant speed prop and wants to run the
engine at only 4000 RPM and fly the airplane in the bottom of the
drag bucket around 140 MPH to maximize the MPG.

Then implement this.

I think Cary built an engine like this but I lost the pictures.
Cary can you send those pictures again?

Paul Lamar

Hi Paul,

That is what I was getting at. If you want to cruise at 6000 RPM,
 would you not want to tune it for a torque peak at that RPM? Fuel
efficiency should be better that way. Your dyno sheet shows about
140ft/lbs at 6000RPM. Or was that with an intake more suited for
access on the dyno?

Dale Davies

Which dyno sheet? I sent a lot of them.

This is the p-port engine I am advocating.
about 195 foot pounds at 6000 and 250 HP
at 7500 RPM.

Yes that is exactly what we did with the P-port.
The best BSFC is always at the torque peak.

That is not necessarily the best MPG however.
That usually happens down in the drag bucket.

Paul Lamar


Paul,
I was referring to the Mazdatrix RX8 PPort dyno as I stated in the first
e-mail. The Power Sport dyno definitely looks better as it does not drop off
in the 6000 RPM range like the Mazdatrix dyno does. What were the differences
in the engines involved?

Dale Davies

Well the PS torque peak is lower so it has less HP. Of course PS drops
off less at 6000 RPM. In the airplanes the gear box ratios
varied as well. The PS had 2.4:1 and the Mazdatrix engine had
2.85:1.

Why not choose 3000 RPM?

Airplane fly on HP. What are your goals?

Make the runners longer and the torque peak will lower and the
max HP will be reduced.

HP is RPM times torque. In a rotary torque is more or less constant.
A good side has 160 foot pounds and a p-port has 200 foot pounds.

The bottom line is VE. Air is going in the engine at up to 400 MPH.
Skin friction drag in the runner is a function of air velocity
squared.

The VE is higher on the Mazdatrix engine because the runners are
a bit larger in diameter and the length a bit shorter. Which one
do you want?

Read http://www.rotaryeng.net/fund-of-intake.html

This is what Mark Steitle said about his P-port 3 rotor engine compared
to his side port 3 rotor engine. Same prop and airplane.

"The runners are 27" measured from the bellmouth to the
rotor face.  I would prefer the hp to peak around 6500-7000"

snips..

"On the positive side, I flew it a week ago and saw a 10 knot improvement
in "economy cruise", which is 1700 prop rpm, 5100 engine rpm, WOT."

Mark

He is still tuning it.

Paul Lamar