In the article Doug from Japan recently posted, a "BMEP Gauge" is
referenced, which is actually reading torque from the gearbox.

http://www.gami.com/articles/bttfpart1.php


Shouldn't it be pretty simple to make your own with a strain gauge and PSRU:

http://www.mistral-engines.com/var/ezwebin_site/storage/images/media/images/psru-open/1665-1-fre-FR/PSRU-open.jpg

In that picture, the stationary ring gear could be made free to rotate
against a strain gauge, which through some multiplier according to
gear ratio would give actual prop reaction torque, and with RPM known
power could be calculated just as easily. Do any EMSes do anything
like this this currently? As Doug's article points out, EGT is a
superior way to achieve best mixture, but a power gauge might be very
useful in its own ways.

-Chris

Chris

Yes that is one way to do it but then the stationary gear would have to
be semi retained presenting other design challenges. Since you are
speaking about a PSRU with straight gear you can't take advantage of
the thrusting moment to compress oil in an annual cylinder that would
work if it contained helical cut gears.  Paul has some illustrations on
his website on how this might be done.

Since I have a straight cut gear PSRU, I plan to try a strain gauge as
part of the torsional dampening device before power is feed into the
PSRU.  That doesn't tell me prop power but the PSRU losses can be
measured in the development stage and accounted for. My dampening device
is only six inches in diameter but almost two inches thick and contains
a six metal rectangular shape protrusions nested in hard rubber wedges.
I got the basic idea from a one of the pictures Paul posted several
years ago.   Some where in there between the rubber and hard metal I
hope to insert a strain sensor mounted on a metal plate.  The big task
is not in mounting them it is in calibrating them.  Wireless torque
sensor technology is well developed and the sensor when polled transmits
its data to a circular antennae surrounding the circumference of the
sensors path.   Blue tooth protocol might also work, as well as a brush
and slip ring mechanical contact.   Several companies manufacture small
(watch sized, battery included) packages that are affixed to the
rotating member.

Tracy's PSRU in principle could contain a strain gauge.  I guess it
depends how soft his dampeners are and how much travel the two plates
experience relative to each other. I am not sure if his rubber dampeners
are encapsulated by metal around their outer surface or not.

Doug in Japan

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