>>> 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
<http://straingage.com/instrument/instrument_sub/TD93A.PHP>
<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.
>
> --
> Paul Lamar ...No rotor no motor.
>
> Here is the high buck way of doing it. I still can't figure
> a way of getting it in Tracy's psru.
>
>
http://www.memagazine.org/backissues/membersonly/oct00/features/torquetake/tor
<http://www.memagazine.org/backissues/membersonly/oct00/features/torquetake/tor>
> que.html
>
> Paul Lamar ...No rotor no motor.
>
Paul
Sixteen years ago I invented a chair that moved in relationship
to the
virtual image the viewer was seeing in their LCD goggles. You can
imagine
being on a roller coaster and hearing 3D holophonic sound
through the
headphones. In short Panasonic picked up on the project and
patented the
control system but decided not to include it in their massage
chair
line-up.
Too real. Made the average person throw up. Not so good for a
relaxing time
but pilots should love it though. Panasonic Corp. develop the
method of
imbedding within the audio/visual data on the DVD, the movement
control
signals to drive the electo-servo motors of my 3 axis chair.
Call me crazy and someone with the electrical engineering knowledge
please
jump right in here and correct me but for a method of measuring
engine or
prop torque perhaps the following is food for thought..
DVD drive optical readers are now very very cheap and small
right? Also
easy to burn in simple data on a track in an exact location. Let
assume for
argument sake we burn in a digital mark say '01' on a track out
near the
outer edge of two DVD discs. They are now identical. These
lightweight CD
plastic discs can be mounted apart, one on the prop flange and the
other on
the sun gear shaft support plate. Both areas are ventilated. We
now have
at least 14" of shaft twist length in which to measure the
difference.
The rest is calibration. At rest both readers must be showing the
disc in
the same position. In operation the arrival of the inner data
number
near
the sensor can is the reference point and so gives us engine rpm.
The prop
flange point of arrival gives us prop rpm. As power increases the
outer prop
flange disc will take a longer period to arrive at its sensor
position.
The difference in time is what we are interested in. We know the
diameter
of the mark location on the disc, software can calculate the
difference in
angle between the two and a simple processor can drive the works to
calculate the torque and Prop HP.
Another way would be to put the second unit on the rear of the
engine so we
could measure it across the engine to get engine torque. We could
also throw
away the magnetic Hall sensor and encode a few more different
numbers on the
same track, say '010" and "0101" of our reference disc
pertaining to
timing
mark positions.
Challenges : Keeping the disc clean and sensor in the proper
position
unaffected by vibration. Calibration - torque wrench????
Flying with a torque meter equipped C/S prop can be helpful.
Doug Fir
Putting a DVD track on the input shaft and one on the output shaft
of Tracy's gear box won't work as the input shaft rotates 2.85
times the
output shaft. The DVD track would have to go inside the box on the
planet
carrier. I don't think it would survive the heat and hot oil
environment.
Putting a DVD track on the nose of the e-shaft and one on the out
put side
I don't think will work as there are two sources of torque on the
e-shaft and not one.
Namely the front rotor and the rear rotor. How would one
calibrate it?
It might work.
This is also not cheap. My guess is a $100K R&D program minimum.
I am still waiting for some one to come up with something cheaper
and simpler than the annular hydraulic cylinder and cheap pressure
gauge.
--
Paul Lamar ...No rotor no motor.
Interesting idea.
The absolute relative position between the two sensors/marks is not
critical - just that you have a precise way to measure the timing of the
passage of the marks. Not a big deal with a microprocessor.
It doesn't have to be a DVD nor even a piece of plastic. DVDs burners
work by using a laser to make marks in a metalic substrate. The
poly/vinyl is just there as an optically transparent carrier for the
metal. As such, this system doesn't need to use DVD parts. A laser
could be used to directly engrave useful marks on a piece of aluminum
(or whatever).
I envision laser engraving a ring of markings around each end of one of
the shafts (the longest one that's carrying torque). Shine a
laser/light-diode combo at the marks. Use a small microprocessor to
keep track of the timing between passage of the marks. You'd be able to
diagnose problems like a single weak apex seal if you wished - by
measuring torque throughout the system rotation.
The CD/DVD players have a very sophisticated method of adjusting the
focal length of the optical system (besides the x-axis) - the better you
can focus on the surface, the smaller the feature size you can resolve,
the more information you can store. It might take a fair amount of
analysis to figure out how good you need
_this_ system to be.
Calibrate it once on a dyno - prop-shaft driving the dyno instead of the
e-shaft. Or, bolt a drum of a known (large) radius onto the prop
shaft. Attach a rope to one point on the outside of the drum. Remove
the spark plugs from the engine. Hang a weight onto the end of the
rope. Engage the starter and allow the drum to reel in the rope while
the torque meter takes data...
I don't know if this is any better than the throw-out bearing system,
but it's very interesting.
Regards,
Matt-
Those lasers are going to have to work INSIDE Tracy's psru bathed in
240 F hot oil.
GOOD LUCK! :)
Paul Lamar
Well, there is that... :)
The other problem with all strain gauge systems is that they work best
when something in the system is flexible enough to provide a deflection
large enough to measure readily. When dealing with torsional dynamics
which may lead to harmonic excitation, adding flexible things should be
done very carefully..
Regards,
Matt-
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