Paul, At what RPM would you say a p ported one rotor would make more power
than a side ported engine with large side housing, like 3rd gen Rx7 or 20B
housings? Has anyone dyno tested to find out? What RPM are the 13b aircraft
engines at max take off power? Cruise?

Curious

Skip Gorman

With the proper length and diameter of intake pipes it could be as low
as 4000 RPM. However since HP and HP to weight ratio is a direct function
of RPM it would be very dumb not to tune for 7500 RPM max or more.

HP = RPM X TORQUE / 5252

My crude guess is max HP at 4000 would be 4000/7000 X 120 or 70 HP.
That is assuming the engine is geared and can swing an 85% efficient
large diameter prop. The net HP out of the prop will
then be 70 X .85 or 60 HP.

If not geared and running the largest diameter prop possible
at 4000 RPM the prop efficiency will drop off to 50 to 60% efficient.
Now the net HP out of the prop becomes .6 times 70 HP or 42 HP.
Not enough for just about any aircraft with a 200 pound lump in
the engine compartment.

If you are going to handicap the power to weight ratio of a one rotor why
bother with a rotary engine? Just install a 90 HP geared Rotax 912 or better
yet a 200 pound direct drive 100 HP O-200 Continental. A lot less work.

However if you want fundamental structural reliability and a good HP
to weight ratio with lower cost go with a 120 HP p-port all aluminum
rotary with a 2.85:1 gear box.

Paul Lamar

Paul,


I'm getting a little lost between your paragraphs. So you're
saying that the a/c version of the 13b is turning 7500 + RPM
to get the most hp out of the p port? I quite familiar with
the HP - torque formulas. I'm just trying to get a feel for
what is going on now and just do half with the one rotor.
What are the guys turning for cruise RPM?

Skip Gorman

Not the MOST HP. One would get the most HP at the maximum
RPM the Mazda rotary could turn with cast iron rotors. Currently
that is about 11,000 RPM. With Be/Al alloy rotors it would be
about 20,000 RPM.

We choose 7500 RPM because 2.85:1 is the highest gear
ratio we had available with the Ford A4OD planetary gear set.
That gave us 2600 RPM for the prop which is about 70
inches in diameter and about 85% or more prop efficiency.
Ken Welter uses a 3:1 belt drive and he turns a really
BIG 5 bladed prop to get his 3000 pound Coot off
the water.

One can cruise anywhere between 4500 RPM and 7500 RPM
depending one what one wants to do. Cruising at 6000 RPM
is a sweet spot as the BSFC is the lowest and the loads
on the rotor bearing are the lowest. (Same pipe length
and diameter as the Le Mans engine.) Here are the rotor
bearing loads as a function of RPM as well as the BSFC
chart.

BTW I might point out most NA airplanes cruise WOT at
anything over 8000 feet as the air density is down to
the point where you only have 80% power of what it is
at sea level. The RPM is whatever the RPM is.

Paul Lamar


Right now the engine is making 50hp @4,000 and 90hp @ 6500.
I just looked it up.

As I said my real project is not a/c engine. The above engine
is getting a turbo with 25-30 psi boost. We are looking to
get 300hp out of a one rotor. Sounds by your calculations it
might be possible with the p port.

Skip Gorman.

My guess was 70 HP at 4000.
What did you do wrong? :)
Got any pictures of the intake manifold?

600 HP out of turbo 2 rotor p-port is done every day somewhere
in the world. 300 HP per rotor out of a turbo p-port
is no big deal.

Here is one Jim had on the dyno.
Got any dyno charts for your engine?

I would not put it in an airplane unless I was going Reno
racing.

Paul Lamar

Paul,
Thanks a bunch. I see clearly now. Ask Ken if he remembers
me when we were doing NOS to get that coot off the water.

Skip Gorman

How about those pictures of the intake manifold and
dyno charts?

Paul Lamar

Great stuff Paul. But my point is not getting across.
I was just asking what you aviators were doing. I'm not
going to build an a/c engine. What I want is a test on
the longevity of the basic block. I want to say and
prove that it runs for xyz time.

I wanted ask you and your fellow aviators what kind of
run test you would suggest to be able to say now that's
an engine. We took the engine out of the Ranger and
now going to run it continually. Full data logging.

Yes I have dyno sheets from 4,000 up RPM. The intake
is not a Paul Lamar design. ( yet ). I want to see the
wear after extended hours. Then I can get after the
horsepower. If you guys want to fool around with the
aviation great but I've got to do my other commitment.

How about some test called the STP, or STM, AST,
can't remember exactly? Supposed to be for engine MFG.
Accelerated hours?

Really want feedback on a test procedure.
Did you ever get the Rotamax engine drive ratio and
prop tests chart? USPS while you were away.


Skip

Yes I got the charts. As I recall the FAA cert test is
150 hours. 5 mins for full power than 5 hours at 70%
power... shut down.... cool it off and do it over and over again
for 150 hours. Tear down the engine and measure the wear.
The wear rate is going to depend on the horse power.
Project the TBO based on the wear rate. Something like
that. It is in the FARS.

The manifold design is not mine. I copied the Mazda LeMans
design. Take some pictures of your manifold and email
them to me.

Paul Lamar

Paul,

That's the test. Would you mind getting that for us.

Darn you I know you are going to throw me under the bus
with this intake stuff. I did this design twelve years ago
for an all around engine.

Skip Gorman

You can get it as easy as I can. Call your local FAA office
and tell them you want to certify an engine and ask for the
rules.

Paul Lamar