"Richard M. Martin" wrote:

There has been lots of e-mail lately about the pro and cons of enlarging the
trailing spark plug hole in rotary engines for aircraft use.  I just
received this attachment from Hayes Rotary Engineering with their views.

Richard

*****************************************************************************
R.E. Enlarging Trailing Spark Plug Hole

I have 27 years experience working with the rotary engine, including full dynometer facilities in
-house.  I am the largest remanufacturing facility for rotary engines in the United States.  
I have worked with NASA, US Energy Dept., US Coast Guard.  I develop single rotary applications 
for pumps and generators and I have worked extensively in alternate fuel for the rotary engine 
which includes natural gas.  Over the past two decades for experimental aircraft only, I have 
successfully opened up the trailing spark plug hole to allow for a TRUE dual ignition system.  
Dr. Michael Seals of Western Washington University, who heads up the Vehicle Research Development
Program for the last three decades and myself collaborated and developed the best running and 
reliability redundancies of a TRUE dual ignition for experimental aircraft.  We have built over 
100 engines with this modification.  We have disassembled and inspected engines after actual 
aircraft usage and found no cracks in the spark plug holes, no pre-ignition, nor destruction of 
rotor housings.

Our findings were conclusive that there is certainly additional blow by when the trailing spark 
plug hole is enlarged, specifically at idle and low speeds.  Understandably aircraft application 
does not rely on idle and low speeds for extended periods of time.  Dr. Michael Seals and myself 
did not find any pre-ignition conditions when ran at higher Rpm's.  After two decades of building
experimental aircraft engine we have not seen any destruction to a rotor housing.  

The importance of this procedure is to have TRUE dual ignition systems, allowing for enough 
engine power if either the ignitions were to fail to be able to land the vehicle safely.

Dr. Michael Seals and myself would recommend that if there is any concerns about enlarging the 
trailing spark plug hole, we suggest to have a switch that if primary (leading) ignition were to 
fail you can turn on the trailing ignition.

Without enlarging the trailing hole there will likely not be enough power to land the aircraft 
safely.  We are troubled with the idea of someone using dual ignition on the leading plugs only.
If a spark plug fouls then there is no TRUE dual ignition.

Thank you
Dennis Hayes
Owner - Hayes Rotary Engin
 
The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2002 All world wide rights reserved.