Paul,


 I'm looking into the possibility of using the '89-'92 year  9.7:1 rotors
 on the P.P test engine.  Do you happen to know the redline for these
 rotors?

  T.O. will be at 8300, but I would like the engine  redline to be 9,000
 which is less than the Renesis engine I believe.

 I may have to have the 9.7:1 rotors lightened a bit.

 http://www.mazdatrix.com/faq/rotorwgt.htm

 I was going to go with  Renesis rotors for the 110 grams reduction in
 weight and the slight increase in compression ratio, but to use them
in a
 13B engine I would have to incorporate lots of the Renesis engine parts.
 E-shaft, stationary gears, counter weights etc.   The biggest issue
is the
 durability of the stock apex seals going over the P-ports. The Renesis
 rotors would have to be machined both to accept a deeper 2mm apex seals,
 and fix side clearance issues encountered when used with 13B housings.

 Doug in Japan

 It is the rotor bearing that is the limit. As I recall the "windowed"
 version of the rotor bearing is good to 11,000 RPM with just about
 all stock cast iron rotors. The RX8 rotors are just a little bit
lighter.
 Racing Beat uses a 3D NC mill to get a few ounces out of the stock
rotors
 at great expense. M V squared over R.

 The 13B intake p-port, if anything, is better than 13B side input
port as
 the
 apex seals are cooled better. The worst effect on the apex seals
 comes from the p-port exhaust. Not the p-port intakes. RX8 side exhaust
 are
 easier on the apex seals. The P-port RX8 engine IMHO is the best of all
 worlds.

 If money is no object why fool around? Go with Iannette silicon nitride
 apex seals. Guaranteed to last for ever and be unbreakable.
 Dave Lemon at Mazdatrix melted a steel rotor housing liner by running
the
 engine
 long after all the coolant blew out. He took the Iannette seals
 out and is still running them to this day in new engines.

 Paul Lamar

Paul,
The "window" bearings are the main bearings in the stationary gears.
For an engine that will see sustained high rpm, the high power RX8
stationary gears should be used. They incorporate many of the changes
used
for years in racing.
The rotor gear will walk out and bind the rotor between the side
housings if
used for sustained high rpm. there are a couple of methods to stop it
with
the most popular being having racing beat snap ring the gear into the
rotor.
May not be an issue on RX8 rotors (one reason to use them!)
That's my 2 cents on making them last at sustained rpm.
Can you do me a favor and see if  Dave Lemon has a scrap late model
(2010 or
2011) RX8 rotor housing he can sell me?
Thanks,
Larry

He usually has scrap housing of all types for sale at around $30.
562-426-7960


Paul Lamar


Hi Doug;
IIRC, the 89-92 stock NA redline was 8000rpm.
The RX8 high powered stationary gears are a cheap upgrade for the older
pre93 rx7 engines.
Take a look at the racing beat tech tips.
http://www.racingbeat.com/mazda/performance/rotary-tech-tips/rotors.html
In particular, look at race clearancing (beveling) the rotor tips for
the older S5 NA 9.7 rotors.
Run higher oil pressure.
Lynn and others have posted high rpm mods in places such as .  e.g.
pinning rotor bearings
www.nopistons.com
Cheers
Cary

Cary, we could not get to 8000 RPM if we tried. The prop load is always
on the engine and that limits the RPM to about 7500 max. We cannot just push
in the clutch pedal. There is no clutch. Then only for a few minutes.
The guys are cruising the motors at 4500 to 6000.

All these race modification are pretty much unnecessary at these RPMs.
You are going to scare some people.

Paul Lamar

Hey Paul;
(you have succeeded in getting me to elaborate again ;)

I'm not trying to scare anyone.  STOCK is fine.

The Racing beat tech tips are definitely worth a read for anyone that
hasn't seen them.  Years ago you had to buy their book for this valuable
information.

Doug mentioned 8300 TO and 9000 redline.
At or above 8500rpm, Racing beat recommends reliability mods.
carbon/ceramic apex seals are recommended above 9k.

In fact, since there is no clutch (accompanied by the occasional bad
shift), sudden over rev and many other "problems" will likely cease to be
an issue...

8300/2.85=2900rpm is in the range of current props.  The losses for a
matched (constant? speed) prop at velocity would be minimal.

Drivers habitually run cars to 9k red line.  Many racers do little more
than bevel the rotors and use carbon apex seals for 11k.
Cheers
Cary

I disagree. If you ask the people that are flying with 2.85:1 PSRU nobody
has reported over 7300 RPM. Mark Steitle has a MT or Hoffman 3 blade
constant speeds or variable pitch prop.  That is 2561 prop RPM.
Ken Welter, as far as I know, is the only other guy besides Doug that
Has a 3:1 PSRU and as far as I know he has never seen 7000. Even with NOS and 300 HP.

The max RPM on the CS metal prop on the 230 HP C182 is 2400 RPM.

The people that run over 3000 on the prop is the VW and O-200 F1 guys and the
diameter is about 54 inches as I recall. Prop efficiency falls off drastically
as the diameter drops below 70 inches. Particularly low speed thrust as needed

by a sea plane in the zero to 50 MPH range.

Here are some curves on the subject from the late great Vance Jaqua.
Rocket scientist extraordinair.


Paul Lamar


Paul,

How about this explanation. Gearbox inefficiencies:

Work load limits engine rpm. Work is the energy absorbed by turning the prop, gearbox and attached engine accessories.

I propose a mind exercise:
Imagine two engines on identical airplanes with identical C/S props.  Both have the pitch set flat and are spinning at 2700 rpms.  Both props shafts are seeing 290Hp. of power.  One engine is an Lycoming  IO-540 and the other is a rotary. If you like, imagine both  identical airplanes are amphibians and that it has been proven  both take off just fine at these power settings. The rotary could be an 'enhanced' 13B or 20B. Either one is within the realm of technical reality.  . Selecting which engine to use in an airplane is an exercise in optimizing the power to weight ratio. That often means operating the engine near it's peak efficiency point for the five minutes during the T.O. and climb event. Unlike the Lycoming however the rotary will have to produce over 300 hp,  Here's why.

The rotary engine is turning  the prop through a gearbox.  This gearbox reduces the e-shaft engine rpm and increases the torque the propeller shaft sees in direct relationship to its' gear set ratio. It also reduces power to the prop by incurring friction loses. Said another way the gear box acts like a drag lowering engine rpm and hence some power output is absorbed by the gearbox and turns to heat.  Some gear box designs are more efficient then others. The number of gears, contact area, gear profile and cut, line speed, oiling method, planetary bearing type and  windage all affect the gearbox losses.  No gearbox is almighty but some designs are less draggy than others without compromising reliability. A robust planetary cluster able to handle huge torque loads does not necessary mean it is designed to handle high speeds without incurring huge losses.

For planetary gear boxes,  a 2% efficiency loss per step down stage is consider state-of-the-art in large megawatt wind turbine applications.  These are megabuck designs resulting from megabuck R&D programs. The transmissions are usually two stages and input and output a maximum of 60 and 1800 rpms respectively.  That's a 6:1 ratio followed by a 5:1 ratio.

For Tracy's  2:85:1  gearbox,  I'd guess the efficiency is in the neighborhood of 95%  +/- 1%. Anyone monitoring gear box temperatures?

In our above example this loss of power through friction is going to cost the rotary engine rpms and hence power.  How much prop power loss depends on the power curve shape and where on the curve the gearbox is set-up to operate.

In conclusion for any engine with PSRU attached, it is going to have to produce more power to overcome gearbox parasitic losses.
Prop pitch and prop efficiencies are other variables affecting engine rpm. Those effects are multiplied by gearbox inefficiencies.

Doug in Japan

5% of 250 HP is 1.25 HP. At 745 watts per HP that would be almost
1000 watts. I doubt seriously Tracy's gear box is generating 1000
watts of heat.

Here is a P&W planetary that is over 99.5% efficient from 60% to 100% power.

Doug, please try limiting the line length to 75 characters.
I am trying to figure out what is going on.

Paul Lamar


Paul,

Nice planetary on the turbo prop.  However it is in the class of what could be, not what is.
5% of 250hp.  is 12.5hp, even a  97% efficient unit lose  5.7kW to friction. It does sound like a high number if we consider putting our hand  near such a heat source.  However the engine is rejecting over to 189kW of heat energy to the ambient. What could that heat? Your neighborhood?  Of course the friction loses in the gear box also depend on the prop and the load is placing on it.

Here is a great PDF I found on high speed gear boxes. Especially pertinent info can be found about  gear shape contact area and bearing type after page 50.

Say, I don't see any option in my pull down Format menu to limit line length. I vary the window size and the document automatically formats.

Regards

Doug in Japan

The P&W 99.5% efficient planetary is used in a turbo fan now in production.
Those pictures are ten years old.

The NASA pdf is too big to publish. No simple configuration in there
but lots of good gear stress and temp data. The temperature is typically
150 F which is about what we are seeing.

Do you have the link where you found it?

The rotary engine heat rejection is mostly in the 1400 to 1800 F exhaust.

Paul Lamar