Hello from Ohio.

[Waiex191]

Coolest bike ever ridden: I got to ride almost 1000 miles on a Norton F1 twin-rotor Wankel.  There is an airplane related story here for another section of the board.

In another life I was the flight controls engineer and the pilot for Sikorsky's Cypher UAV.  It had a single rotor UAV engines powerplant which was a spinoff of the Norton motor. It's the flying saucer looking thing in my avatar.  You can almost see the engine under the cover.

[mopic_camera_guy]

Yup the UAV company bought the rights to the Norton airrotor engine line.

Norton had partnered with Continental to market the 100hp and 60HP engines.  Continental called them the GR-36 and GR-18.

Continental was not satisfied with the reduction gearboxes and dropped them.

I got one at surplus prices and used it to complete a BD-5B... which is another story on itself.

The F1 though was the 100HP twin rotor bike.  It is awesome to ride.  A lot of Yamaha shelf stuff on there, but overall a unique machine.

Norton had real problems making it idle and they had a clever solution... The ECM would monitor the throttle position and if it detected "shut" it would alternately shut off cylinders until the engine slowed to the "idle" RPM.

It made for interesting trail-braking sometimes.  Honestly though, that exhaust note gives me chills sitting here, now.


Oh crap.  WAAAY off topic, sorry.

Hi, I'm Jerry and thanks for being nice to me.

[Waiex191]

It would be an awesome engine for a BD5 or many other aircraft, except for the rebuilding required.  Our installation would start getting tired around the 20 hour mark.  Was it better in the BD5?  We could never figure out induction filtering without killing performance. We did a lot of muffler development which brought the noise from brain damaging to merely deafening.

[Pat Conlon]

Jerry, no worries, consider this forum kinda like sitting around the camp fire, no telling where the conversation leads....

The only thing we ask is if you have some FJ problems, solutions, or neat mods, put those posts in the right section so others can find them... put the gun discussions down below, other than that, carry on...

I find discussions on aviation fascinating. Lycoming/Continental/Wankel engines more so....

Cheers

[mopic_camera_guy]

Thanks for the info Pat.  I don't want to get in trouble here.

Well...  The GR-36/Airrotor 110/UAV 100 that we had used was pretty robust if the exhaust scavenging was decent (still a tremendous wail...)and the cooling was adequate.  We used the Norton total loss oiling system on the rotors and setting that metering was crucial for the apex seals to keep sealing.

We also had a coalescing filter to re-capture some of that lube in each exhaust.  Fortunately there was adequate space below and behind the engine for all of that plumbing.  The oil tank fill was behind the headrest.  That gallon would last about two full fuel loads before lighting the "low oil" light.  We'd capture around 25% with the coalescing filters.


The "book" listed a 1000hr. TBO.  Skeptical because of the general weirdness of the thing we did parade rest teardowns at 100hr and 500hr.  100hr showed "typical" wankel seating markings on the rotor housings but nothing else exceptional. 
At 500hr there was essentially no change.  I got rid of the plane at just over 800hr (engine time).  And the follow-on owner did the 1000hr overhaul and it looked very good.  Apex and side seals and one thrust bearing were all that it took.


This was the second gasoline powered BD that I had done and the difference was really noted on the drive-line components.  The first plane had the turbo Honda which was the de-facto "good" setup for the plane at the time.

The shaft sprag clutch lasted about 4-500hr with the Honda and the shaft itself had a recommended lifespan of 2500hr.  I inspected the sprag on the wankel at 500hr and there was essentially no wear.

For those of you who are unfamiliar, this aircraft had a very long driveshaft between the engine belt reduction and the propeller. 

The physics here is a big drink, but I will do my best to Saganize it.

WARNING: LONG AND POSSIBLY BORING PARAGRAPHS BELOW!

Skip to the stars ********* if you could care less.

On a shaft drive road vehicle, the interface between tire and road (most of the time) is very firm.  So, when individual power peaks from pistons make their way down the drivetrain, they are (essentially) absorbed by the friction of the tire/road interface and the inertia of the vehicle.  Only rarely (like with farm implements) will those rhythmic pulses set up a resonance in the drive line... Or if your chain is slack and the bike is lurching at certain speeds.

With airplanes, however, the interface between propeller and air is not so firm.  So, when individual power peaks from pistons make their way down the drive train they tend to "wind-up" the shaft. Then the shaft, being not very constrained by friction, snaps forward to release the pent-up energy.  Then winds up the other way and snaps back... over and over... So, at certain RPMs the system will resonate at a frequency relative to the length of the shaft and its diameter and the mass of the propeller.  What is fascinating is that the pent up energy in the resonate state climbs to (mathematical) nearly infinity.  So, stuff breaks.  Sometimes spectacularly.

In most aircraft with reciprocating engines the longest direct-drive propeller shaft is about 3".

The original BD5 shaft was 2.5" in diameter and about 4' long.  It resonated at a pretty high frequency... usually in the power-range of the engine.  Not awesome.

Several ways to fix this... increase or decrease the diameter of the shaft to get the resonate frequency above or below the operating range of the engine.  Build in a one-way (sprag) clutch so that the thing can wind up with energy but when it goes to rebound it free-wheels instead.

Rutan and those folks at BEDE in the 70s tried the smaller shaft idea first, going to a 1" in diameter shaft.  This moved the frequency down to starting RPMs which was zany to watch because it was possible to see the system winding up. 
But once it was running it was smooth.

So, to solve the low frequency resonance they added the sprag clutch.

Now the system didn't resonate anywhere in the operational band of the engine.

It is interesting to note that the relative strength difference in torsion between a 2.5" shaft and a 1" shaft is not as signifigent as it might seem.

That 1" shaft handled up to 155HP in some applications just fine.

**********

So all of that describes "torsional resonance". 

Physics lesson over...

Point being, the wankel was very, very smooth.  It's power pulses ran more like waves than the spikes from a reciprocating engine.

This is also why wankels, in general, have very high HP for a given displacement but less torque.

So this shaft mounted sprag clutch wears out eventually.  It has feeler gauge openings to determine it's fitness for duty.

The wankel one didn't seem to be wearing at all/much and the reciprocating Honda was almost done at 400hrs.

That's probably enough for today.


PS: Torque is what pulls you away from the stoplight and makes your partner have to hold onto you tighter.
Horsepower is what pushes the air out of the way as you go faster.

It is why engine nerds are always dazzled by a high HP figure, but are VERY dazzled by a high torque figure.

Or: torque is felt in your bottom, horsepower is seen on the speedometer.