Wing Frequency measuring app

At 02:42 06 March 2016, JS wrote:
Thanks, Clyde. I know that this measurement is done at every Form Two
inspection where you live.

Until this app, the device was a mark one eyeball, and counting "one,
two,
three, (etc) while looking at some cheap watch. Then doing it again
because
you're sure you lost count! The last bit probably won't change until you
believe the app can count.
Jim


On Saturday, March 5, 2016 at 6:01:24 PM UTC-8, IA DPE wrote:
In order for this to be recorded in the aircraft logbook, it would have
to be a FAA approved measuring device, right?

While I can see some value in knowing this reading, there would have to
be standardization in the measuring device and technique I would think.

20 years ago we could take a video (including a stop watch) at the wing tip

then play it back, in slow motion if preferred. Worked perfectly and it
didn't even require a computer.

Clyde-

Handy little App. Thanks. One suggestion: Put a 10 or 15 second delay from the time the "Start" button is pressed before counting cycles. This will allow the frequency to stabilize before starting the count.

Also, a summary page would be cool. Test time, number of beats.

Definitely worth the $0.99.

Has anyone set up their glider, then measured L and R wingtips, say 10 repetitions from dead stop and looked at the results for consistency?

Can it ever be 'normal' for the L and R wingtips to yield different measurements? How much deviation in successive measurements is acceptable?

Does temperature of the glider affect the measurement?

On Monday, 7 March 2016 02:55:35 UTC+11, Mark628CA wrote:
Clyde-

Handy little App. Thanks. One suggestion: Put a 10 or 15 second delay from the time the "Start" button is pressed before counting cycles. This will allow the frequency to stabilize before starting the count.

Also, a summary page would be cool. Test time, number of beats.

Definitely worth the $0.99.

Thanks for the suggestions; I don't think the delay is necessary since it only averages over the last 20 beats. I am going to change that to a time, rather than a number of beats, since that means a wing at 100 bpm takes twice as long as one at 200 to measure. So I think I'll change it to counting the last 10 seconds or so. It calculates the standard deviation of the beat interval and announces success when that is below .02 for the sample time.

I have some other optimisation ideas to improve the performance on gliders with very flexible wings, which sometimes have a second order vibration going on at the same time.

Clyde

On Saturday, 5 March 2016 08:39:05 UTC+11, wrote:
I have written an app that measures wing frequency - currently available for Android on the Play Store he https://play.google.com/store/apps/d...j.ios.wingfreq.

An IOS version will be available once I jump through the various hoops Apple places in the way.

Video of it in action he https://youtu.be/dBJOBxGWtCQ.

Clyde.

There is absolutely no difference in measured wing frequency whether done on a cradle or main / tail wheel skid or wheel. Try it out before you write otherwise. - Rolf
Rolf

On Sunday, March 6, 2016 at 2:03:36 PM UTC-8, wrote:
On Saturday, 5 March 2016 08:39:05 UTC+11, wrote:
I have written an app that measures wing frequency - currently available for Android on the Play Store he https://play.google.com/store/apps/d...j.ios.wingfreq.

An IOS version will be available once I jump through the various hoops Apple places in the way.

Video of it in action he https://youtu.be/dBJOBxGWtCQ.

Clyde.

There is absolutely no difference in measured wing frequency whether done on a cradle or main / tail wheel skid or wheel. Try it out before you write otherwise. - Rolf
Rolf

So can I assume before you posted that you checked every glider in existence, on every cradle imaginable, and at every tire pressure?

On my Schleicher at least, the builder has called out some very specific jacking points for this procedure.

On Monday, 7 March 2016 09:03:36 UTC+11, wrote:


There is absolutely no difference in measured wing frequency whether done on a cradle or main / tail wheel skid or wheel. Try it out before you write otherwise. - Rolf
Rolf

I have tried it out - and have seen differences. One in particular was 135 on the wheel and 141 on the cradle. That's not a huge difference, but enough to warrant a closer look, so consistency in technique will help avoid false alarms.

Clyde

02:27 07 March 2016, wrote:
On Monday, 7 March 2016 09:03:36 UTC+11, wrote:


There is absolutely no difference in measured wing frequency whether
done
on a cradle or main / tail wheel skid or wheel. Try it out before you
write
otherwise. - Rolf
Rolf

I have tried it out - and have seen differences. One in particular was
135
on the wheel and 141 on the cradle. That's not a huge difference, but
enough to warrant a closer look, so consistency in technique will help
avoid false alarms.

Clyde


Suggest instead of opinion - just use the MM for the glider. e.g. ASG29 MM
para
3.2 gives the support points. MFG data sheet at build gives original
frequency,
MM7.1 requires annual check, MM7.2 requires it after hard landing, gives
tolerance.

Good clear info from Schleicher, which all ties together nicely imho.

And a very nice app from Clyde, thanks. Like a lot of great ideas it seems
obvious
now but you thought of it.

At 07:23 07 March 2016, Steve Thompson wrote:

Suggest instead of opinion - just use the MM for the glider.

A very good suggestion. Did a Twin Astir wing frequency check the other
week, and that was off by 5 compared to the last measurements. Turns out it
somewhat unusually should sit on its wheel and skid (12th item of the
annual checklist in the mainenance manual) not on threstles, with a
specified tyre pressure of 2.5-2.8 bar. Remeasured and it now was bang on.
The way you measure DOES matter.

On Friday, March 4, 2016 at 4:39:05 PM UTC-5, wrote:
I have written an app that measures wing frequency - currently available for Android on the Play Store he https://play.google.com/store/apps/d...j.ios.wingfreq.

An IOS version will be available once I jump through the various hoops Apple places in the way.

Video of it in action he https://youtu.be/dBJOBxGWtCQ.

Clyde.

The easy and revealing part of the test, is to observe the wing tip
phase; in the first bending mode they should be synchronised within inches of each other. A wing lagging in phase would indicated spar or skin damage.
This is probably more accurate than the frequency test.
JMF