From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Lehanover@aol.com
Sent: Sunday, December 24, 2006 6:47 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Dead Rotor at 3000ft

Hi Joe;

                Glad you got back on the ground safely. From the compression results I'd say your prognosis is accurate. How was the other rotor?

With one face still showing compression, that means that two apex seals on that rotor are still somewhat intact. So you lost one apex seal.

The loss of an apex seal at cruise would be a rare event indeed. However if you drop in a piece of porcelain

from a failed spark plug, then the chance that all of the apex seals will survive drops close to zero. That ceramic is the hardest thing in the engine. Also used as tooling media for lathes and milling machine heads.

Had two apex seals been damaged, there would have been no power available from the damaged rotor, and your range would have been just slightly over that of an engine out. 

Detonating a non turbo engine without a nitrous shot is virtually impossible. It is easy in a turbo or nitrous added engine.

Best power, over lean, over rich does not bother them at all.

They are insensitive to octane ratings as well. Used in fishing boats and run on 55 octane motor fuel. Used as water pump prime movers and run unattended for months at a time.

Too much advance just makes too much heat and poor power in a straight line to overheated coolant. Unless some pieces came loose during operation that could have changed the timing, I doubt that actual advance degrees was a factor. If you have personally identified TDC, and counted off the correct number of flex-plate teeth (turning the engine backwards) to establish a timing mark. And have checked that timing dynamically with a timing light at (say) 3,000 RPM? Then it probably isn't timing, (Ignition advance) related.

We raced the 12A for years at 20-22 degrees, for under 9,000 RPM. The store bought race engines use 24-27 degrees up to 9,600 RPM. I race on 87 or 93 octane fuel. Higher octane fuel is pointless. I have seen a 13B on the dyno making good power up to 35 degrees, but it was making a ton of extra heat as well. Very little additional power is available between 30 and 35 degrees. That kind of timing requires race gas, over 100 octane. The 13B can run a few extra degrees above a 12A on high octane fuel. On car gas 22-24 is plenty.

The object of timing (ignition advance) is to produce the highest cylinder pressure, at the ideal crank angle.

In piston engines, that would be 17-19 degrees after top dead center (ADTC). In the rotary that would be 40-50 degrees ATDC. The time that the rotary spends near TDC is way longer than the piston engine. The longer the better, as this when most of the fuel is being burned. That near TDC time is called dwell. Smoky increased it in his Chevrolets with longer rods. The rotary does it as a function of its design. 

But we still think of ignition timing in a rotary as though we are talking about piston engines. The rotary has much longer to burn its fuel than the piston engine, because the rotor (rotary piston) is moving in slow motion. At 1/3 the crank speed. For turbo's at high boost you might see 10 degrees total on leading and 5 after on trailing. And that is plenty of advance.

That leaves cross firing (possible) if there is high voltage ignition wire is used, or triggering shielding is not adequate. and, or if the plug failed first, (my thinking) too high a heat range.

Plugs get tired based on the number of times they fire, their temperature, and how much chamber pressure they see on each cycle. So in the rotary they fire twice as often, and at cruise in the aircraft at consistently high temperature and cylinder pressures.

So they should last half as long based on firing cycles, and then even less based on pressure cycles and nose temperature.

They work fine for years at 1,900 RPM, with a blast now and then to 7,500 RPM. Street plugs that must remain un fouled at 1,900 RPM run high nose temps. Is that the plug you want in the airplane at more than full throttle for hours on end?

How long could you drive a 95 twin turbo RX-7 at full throttle on the street, before you were killed or a cop stoped you?

Best power, and highest cylinder temp is just a hair rich of peak EGT.

For a long climb-out, perhaps a bit richer (better lubrication for the pre mixers) and some fuel cooling and slightly better sealing would be better. At cruise, instead of just less throttle, stay at full throttle and lean well lean of peak EGT

Lower total power output just like the lower throttle setting, but less heat and lower fuel consumption as well.

The "Oh crap!!! What was that??" fuel setting should include richer fuel flow for better sealing and some fuel cooling.

Just my opinion. I could be completely wrong.

Lynn E. Hanover