--

Here is a strain gauge setup.

TD93A indicator and ZFLA-1-11 foil gage.

The combination indicator and foil gauge is temperature compensated
from
+10C to +100C.

The URL below will take you to the indicator page. On the left side of
the screen you can click on the Strain Gage Series List box. That will
take you to the strain gauge page. The ZFLA-1-11 specs are there
toward
the bottom. From the indicator page, clicking on the Integral Lead
Wire
box will take you to a page that shows the strain gage and wires
already
connected. Just glue the strain gage to the metal under stress, route
the wire, plug it in and you are ready to go.

This web site also lists the appropriate adhesives.

The only fly in the ointment is the need for 60Hz power, which is no
problem for a test stand dyno but would be if you wanted to measure
torque/HP in the air. For in the air measurements a 100W inverter will
serve as the indicator only draws 60W.

The URL for the instrument is;
http://straingage.com/instrument/instrument_sub/TD93A.PHP

Doc Custer
Retired Software Engineer and sometime Audiologist

That is not the only fly :)

The part under stress is this shaft. How do you get the data
out of the rotating strain gage mounted on the shaft to a stationary
signal conditioner?
--
Paul Lamar ...No rotor no motor.

You put the strain gage on a stationary part that is resisting the reaction
force. I am not familiar with the exact setup of the planetary gears. If the
ring gear is stationary, you attach the strain gage to one of the bosses
that prevent the ring gear from rotating. If the planet carrier is
stationary, you attach the strain gage to one of the carrier bosses that
prevent the carrier from rotating.

Doc Custer
Retired Software Engineer and sometime Audiologist

-
Here is a pretty good dwg and some pictures. Mark a suggested position
with xpaint and send it back. The half inch plate behind the thrust
bearing is out as it is subject to complicated forces from the the prop
depending on the pitch or yaw rate of the aircraft. This is the 2.17:1
box. The 2.85:1 ring gear is pressed into the housings and locked
with a few keyways.

I'll also repeat Matt's question. What is wrong with the low cost hydraulic
cylinder
solution? Do you want a electrical signal that can be fed into a computer?
Perhaps and annular load cell would work to measure the helical gear
thrust. Load cells are not low cost.

-- 
Paul Lamar ...No rotor no motor.

Paul

Nothing is wrong with annular hydraulic unit but it is only one way of doing
it.  It is hard to say it is the best.  For pure analog and those that have
the engine nearby the pilot and are satisfied with looking at an analog
gauge then all is fine.  If cost is the deciding factor than yes perhaps
when all R&D is said and done it is probably  the least expensive option.

Perhaps it is easier to intergrate an electrical strain guage into the
engine monitoring system however.  Yes we can put an put a pressure inducer
sensor (type of strain guage) into the hydraulic system, but that is
commiting the cardinal sin of making a reliable design.  IE combining the
failure modes of hydraulic and electrical.

Another reason  perhaps some people like electrical systems better is the
ease of running wire instead of an hydraulic tube. No worry about leaking
seals and joints.  Did I mention there are a few of us that will be running
straight gear PSRUs without a significant amount of inherent thrust:)

Lastly in either case the item has to be made, developed, tested, confirmed
and redeveloped.  Mass produced clutch throw out units verify the concept
has merit and works but it is not the same as designing it to work on
Tracy's PSRU.

Strain gauges on the other hand  have a long and documented use and the
total system though more expensive has more advantages.


I rather like the Land and Sea dyno unit and asked them once if it could be
modified for an aircraft shaft.

I originally thought to put a strain gauge to catch the relative movement
between the flex-plate and the PSRU sun gear drive plate  and send the
signal to a receiver in the housing  via Wy Fi.  The advantage  is at this
location we could also get an idea on what torsional vibrations are
happening if any at different prop speeds. Something that is going to be
more of concern as more of us start to use C/S props. Now I am not so sure
that would be the best location.

I think traditionally for an users wanting to see 'prop HP' there is a
collar that bolts to prop flange.   I wonder why MT props doesn't include
something like this within their electrical adjusted C/S props? They are
already controlling the motor and picking up prop rpm.

Doug Fir

I am all ears if someone can come up with ONE other practical way that works
with Tracy's PSRU. I know the helical gear thrust thing works because that is
what is used in ALL gas turbine turbo prop engines.