flyrotary@lancaironline.net Mailing List Archive

From my understanding, when aluminum expands, it expands in all directions and when it cools it contract in all directions. Unfortunately, with the rotor housing firmly clamped between the side housings it is not able to expand in that direction but will readily contract during cooling. If the temperature had been high enough to cause a high rate of expansion then cooling will require an equal rate of contaction thus leaving a rotor housing samller in one dimension.

----- Original Message -----

From: Ed Anderson

To: Rotary motors in aircraft

Sent: Saturday, July 17, 2004 12:55 PM

Subject: [FlyRotary] Re: 11th test flight

Dale,

Not being a rotary engine mechanic, I only know that one of things that you were to check for after a case of "overheating" was "shrinkage" of the aluminum rotor housing. I never heard an explanation for why this supposedly happened but the thing you were to check for was the width of the housing. There were minimum specs which if below supposedly rendered the rotor housing "Bad". I do know that when I took my first engine apart after overheating it to the point that the inner coolant seals failed, I measured and found one of my housings right at the limit - now it may well have been at that point before I ever ran the engine as I did not measure it before hand.

The only thing I could ever think of that might cause this (assuming it was caused by overheating) is that we have 17 of those big bolts holding that pancake together which compress the rotor housing between the iron housings. If it go hot enough supposedly that clamping pressure could cause the aluminum to weaken sufficiently to partially collapse the housings coolant chambers and reduce the width of the housing. But, that was just my take on it.

Now with the later engines I have not heard about this shrinkage problem - so whether it was an "old wives tale" or there was some substance to it that has been overcome by better castings/alloy , I really do not know.

Ed

Thanks Ed, I value your insights.

I know that seal chatter was an early development problem with the wankel, but thought that Mazda had pretty much made it a thing of the past with modern materials, geometry, and springs. I did not realize that this was a temperature dependent problem, that we still had to deal with.

Also, not quite sure what you mean re: "shrinkage of the aluminum rotor housings"? It can't shrink with heat. By this do you mean that, that having exceeded some elasticity limit, the aluminum cannot return to it's original specs upon shutdown once it has been overheated? Wouldn't it thus be oversize? Please explain ... this sure sounds like an "engine killer".

Thanks,

Dale Smith

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