When using 2 engines together with a common power output is
   there a     simple way  to assure that both engines are contributing
   equal power?     I can imagine that one or the other could be
 doing   more work even     though they both are running at the same rpm
   (obviously). I'm thinking     of using 2 of the smaller available
   rotary engines on the    helicopter,  but my question could apply
   more broadly to any engine  type.

        John McEverett
   "is there a simple way  to assure that both engines are contributing
 equal
 power?"
  Same problem exists in EVERY multi-cylinder engine.
  brian gochnauer
  That suggest a simple way to do it is compare EGT's.
  Paul Lamar
  You would probably be much better off comparing CHT's.  EGT's are
 only an imaginary number.  The EGT probe sees about nothing
 interesting 3/4 of the time because the exhaust valve is closed most
 of the time during the intake, compression, and power stroke.
 During the other 1/4 of the time there is exhaust flow.  The
 measured temperature in the exhaust manifold varies according to the
 configuration of the manifold.  Same thing as the problems with
 pressure variability in the intake manifold depending on several
 variables.
  See http://www.sportaviationonline.org/sportaviation/201010#pg89 for
 a nice article on the subject.
  Mark LaPierre
  What exhaust valves? :) We don't have no stinking
 exhaust valves :) Normally people don't install
 CHT's on rotaries with at least one exception but I advocate
 and  maintain it is still a good idea. They just monitor coolant
 temp which is common on both rotors.
  Now for two engines you could monitor coolant temp but
 there could be significant differences in the two separate
 (if used) cooling systems.
  Paul Lamar
 The EGT's in a rotary will have a fairly constant temp reading as the
 pulse
 from one side of the rotor is almost done exhausting, the apex
 seal is  crossing the port. The next chamber starts flowing. If the
 temp probe is  installed just down from where the two exhaust pipes
 from the ports are  joined, the "cylinder" temps are averaged. Then
 the two engines could  be compared.
 Dale Davies

 Usually twin engine aircraft engines are set with matching manifold
 pressure and RPM's plus a slight tweak on the throttles to match the
 revs exactly, ( with constant speed props) , my guess is that if both
 were built and run exactly as a pair the manifold pressure plus EGT's
 would tell the tale?
  John Burey.


Please note John McEverett's original post: two engines with a common
output
for use in a helicopter. This is where the strain gauges and EGT's compared
would get them matched up to both pull an equal load. Obviously, the tune
on
the engines would be virtually identical; both lean or rich of peak.
Throttle
position sensors set up individually to give identical outputs could also
help
in getting them matched, with respect to throttle opening.

Dale Davies

Dale
Thanks for getting the question back on track. Common to both engines a
single shaft output is key. My application is a helicopter, but someone else
might do the same for more power and twin engine reliability on a single
prop. It is done commercially with turbines and I suppose some sort of
torque measurement is used. Each engine would have an over-runing sprag
clutch so if one engine stopped (or was shut down) it would not present a
load to the other. This may be the place incorporate the sensor... as part
of the formsprag. With a belt drive to the common shaft I may be able to use
a tensioning arm arrangement that could sense torque, but this is just an
idea that I have not put much thought into. The overall requirement is: Keep
the engines in balace with minimal parts, minimal weight, minimal
complication, and minimal cost. At the very least I think EGT would work.
About everything I've ever flown has had an EGT gauge to monitor and it does
indicate something, real or not. My interest in doing this for the
helicopter is two fold: 1) allow use of available engines, and 2) provide
the safety of two engines. Thanks for eveyones help.

John McEverett