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From: Brent Regan <brent@regandesigns.com>
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Subject: Re: L-IV Choice of Engine
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Ted asks:
<< Is there an instrument that can be attached to the engine somewhere 
that will measure frequencies to assess likely nodes of "don't run there?"
 >>

The short answer is no.

Imagine a rod with an accelerometer mounted half way down its length. 
Excite the rod at its second harmonic and the accelerometer  will see no 
acceleration or displacement as it is sitting on a "node". If the rod 
were 360mm long the nodes are at 0mm, 180mm and 360mm with the points of 
maximum displacement and acceleration at 90mm and 270mm. These will also 
be the points of maximum stress, unless the ends or the rods are fixed, 
then the maximum stress will be at the ends.

Someone experienced in these matters and with a detailed knowledge of 
the engine system would be able to put some accelerometers on the engine 
at various locations and use a spectrum analyzer to determine the 
vibrational energy distribution versus frequency and then connect a 
shaker to the engine and see what "buzzes", but this is a lot closer to 
art than science.

In response to my comment <<< After more than 100 years, the prime mover 
of choice still has a piston, rod and crank. There may be a reason for 
that.>>>

William observes: <<< The piston engine was invented first.>>>

True, but the Wankel engine first ran February 1, 1957,  54 years ago. 
Actually, to be accurate, Wankel's pure rotary design DKM 54 (Rotor and 
housing rotated) ran on that day. Froede's epicyclic configuration, the 
KKM 125, what we now recognize as the Wankel engine, first ran on July1, 
1958.

If the Wankel engine is superior it has had plenty of time and 
opportunity to prove it. I have a collection of rotary engines including 
ones for model aircraft, powered hang gliders, snow mobiles, lawn mowers 
and race cars demonstrating that the Wankel has been exposed to all 
these markets yet has failed to dominate any of them.

In the last 50 years entire industries based on new technology have come 
and gone. While I love the round motor it is hard to reconcile the claim 
of rotary superiority in an environment where significantly better 
technology quickly conquers the market.

The Wankel may be the better engine, just not better enough.

Regards
Brent Regan