Garfield and company looked into this in some detail and concluded
exactly what you have. He located a reasonble cost rf unit (a few
hundred $) and planned to incorporate it into a short bolt on prop
extension so it could be moved from engine to engine. (I understand that
adding an extension is not ideal physics but I consider it a workable
plan.) An IR or laser LED was also discussed to beam the info down the
centerline of the shaft.

Anyway, I would plunk down $1000. in a heartbeat for such a plot,
probably more. Otherwise it will take me a couple of years to accumulate
a couple of hundred hours to gain confidence in my engine system. Your
location would be a factor. Multiple tests to let me tune the dampers in
my psru might be desireable. Even a single test to tell me what (if any)
rpm to avoid would be well worth $1000. in my opinion.

Yes I think you could recover your costs. No I don't think you could
make an ongoing business of it for a lot of reasons.

An under $1,000. unit such as Garfield envisioned that I could rent (or
build) would be wonderful. Even better would be releasing the details
into the public domain. A user group would spring up quickly.

My experience is that very very few people understand how important this
is. Many might benefit hugely as combinations of common engines, psru's,
flywheels, and props became known good (or avoid) combinations.

Ken

Dan Horton wrote:
RAH Gang,
Have not posted here in a while. Hope all are doing ok.

I'm considering the purchase of some very expensive equipment for
the live measurement of torsional vibration. The methods are industry
standard; apply strain gauges to the shaft, connect to a telemetry
radio transmitter, beam the signal to a receiver, then output to a
variety of analysis/recording devices.

The typical result is a plot of vibratory torque amplitude by RPM.
Any critical (resonant) RPM range is obvious. The point is to
determine vibratory behavior and loading while the airplane is safely
tied to a post. Unacceptable vibratory torque amplitudes are cause
for a redesign. This sort of work is a big part of what you pay for
when you choose a certified engine/propeller combination.

The homebuilt world has a lot of interest in alternative engines,
propeller speed reduction units, etc. To date, very few are subjected
to actual measurement. The usual program is to fly it and hope it
doesn't break. If it doesn't break in 50 hours or so, the builder
declares it to be a success. If the builder is also a vendor, the
next step is an advertisment in Sport Aviation. There are obvious
shortcomings to this system.

RAH is a great place for opinions, so I would like to hear yours.
The questions a

(1) Would individual homebuilders pay money to have their
self-designed engine/drive systems checked for torsional amplitudes,
determination of frequency, etc? If yes, how much money would it be
worth to an individual builder?
(2) Would homebuilders eventually demand evidence of such testing
from vendors to the experimental market? Or is it likely that the
average homebuilder would never become aware of the need for such
testing?

Please, no soapbox stuff. This is not an invitation for another
debate about "certified vs auto conversion" and the like. This a more
of a market survey. Is there a market for a currently unavailable
service that would make the use of experimental engines and drive
systems safer?

Thanks,
Dan Horton