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Oct 03, 2012, 02:11 AM
SINK HAPPENS !!!!
EeleyEagle's Avatar

Steves Hurricane


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Oct 03, 2012, 02:35 AM
Entropy is happening!
Jim.Thompson's Avatar

Crash analysis.


I'm still trying to figure out what caused the crash of my plank on the last Monday. I've explained the basics of what happened in post #2324. Unfortunately, no one else saw it happen and it was all over in an instance.
I've spent the day working with an aviator friend and explained the sequence of events to the best of my recollection.
His suggestion is that it was a high speed stall!
Now I don't know much about "high speed stalls", so cannot argue. However, I'm more willing to find some fault with my flying rather than put the loss down to equipment failure or some other airframe fault etc.
The receiver still works and was still bound! I did not receive any telemetry beeps suggesting that I still had RF link till out of sight down the slope.

Anyone able to provide some insight here? I fly on very low rates, sometime too low to pull out of sticky situations at low altitude.

Puzzled.........

Jim.
Oct 03, 2012, 03:21 AM
by ZIPPER
ZIPPER's Avatar
It could be that your servos aren't strong enough and are stalling anger high loads.
Or there is some up and down movement in the hing, when under high loads the elevon is moving up and down along the hing instead of pivoting up and down.
I've had it happen on a wing at speed.
Oct 03, 2012, 03:46 AM
Secret clown business
gizzo's Avatar
Thats funny you mention that Glenn. My Diode has been behaving badly and i figured out it was the hinge getting sloppy and the elevon not moving, not moving, not mov....moving ALL the way. New hinges made it sweet.
Oct 03, 2012, 04:01 AM
Crikey never leave beer behind
steve wenban's Avatar
Thread OP
Quote:
Originally Posted by EeleyEagle
That launch looks a lot more scary than it actually was
Oct 03, 2012, 04:05 AM
Crafter of flying plugs
Owen Hedger's Avatar
Quote:
Originally Posted by steve wenban
That launch looks a lot more scary than it actually was
I remember it being precisely that scary Steve. I was some way up the slope and was waiting for it to reappear, or not.
Oct 03, 2012, 04:13 AM
Just Toss It !!!
MATIN's Avatar
I was scared!!!
Oct 03, 2012, 04:20 AM
Bogan of distinction
Stehl's Avatar
Jim, +1 to the servos stalling and being ineffective at speed.
Or maybe your balance weight/ batt shifted ?
Oct 03, 2012, 04:35 AM
Crikey never leave beer behind
steve wenban's Avatar
Thread OP
nah I knew it was ok as soon as I got the nose down and got airspeed
Oct 03, 2012, 04:39 AM
Entropy is happening!
Jim.Thompson's Avatar

Stalled servos.


[QUOTE=mams1;22900187]Jim, +1 to the servos stalling and being ineffective at speed.
.................................QUOTE]

I strongly suspect that Glenn (and your) suggestion is the real reason for the crash. Servos stalling. Just to remind you, the plane was a four servo plank: after a very short while, it started to sort of wobble in the roll axis as if the servos were not operating equally as they should have with the elevator stick being pulled back slowly.
Not the battery/nose weight moving. It was well secured and the plane was in full dive attitude.
I also doubt if the hinges were allowing the surfaces to move vertically, but there is some doubt about that. Lets say it was possible, but not likely.

Thanks Glenn and Stehl!

Jim.
Last edited by Jim.Thompson; Oct 03, 2012 at 04:40 AM. Reason: inclusion of italics
Oct 03, 2012, 04:41 AM
Auzzie built planks
timbuck's Avatar
+1 on servo's if you can exclude RX/TX problem.
Did you have Kevlar or silicon hinges ?.
.1 If it was a control surface problem it would have come up , as in how the plane was handling.
.2 high speed stall... Only happens banging a hard turn at speed and then applying to much reflex to the TE , stopping the lift.
.3 CG to nose heavy...wouldn't have been flying as good as it was ripping around the sky.
.4 CG to tail heavy.....same as above. But could induce a flick or pitching rotation....and would have recovered after got speed again , also in a near vertical dive , would have tucked badly.
5.
Servo's ???? I have an near identical crash with servo's that basically didn't move controls at speed...
In a dive across the sky fast but not a steep dive. I would run out of elevator at speed....BUT if I just leaned on the elevator a bit , as it would climb and slow down , I would gain elevator back.
Servo's just wouldn't lift control surfaces at speed. The day ended with a vertical dive that had zero control of anything.

Servo's are my bet.

Tim
Latest blog entry: More colours
Oct 03, 2012, 04:43 AM
Just Toss It !!!
MATIN's Avatar
Jim

In addition to all the other causes for the crash, please consider the following:

Some "unusual attitude" situations are unrecoverable, no matter how experienced the pilot is.
This is true of models as well as full scale.

Matin
Oct 03, 2012, 05:00 AM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by timbuck
+1 on servo's if you can exclude RX/TX problem.
Did you have Kevlar or silicon hinges ?.
.1 If it was a control surface problem it would have come up , as in how the plane was handling.
.2 high speed stall... Only happens banging a hard turn at speed and then applying to much reflex to the TE , stopping the lift.
.3 CG to nose heavy...wouldn't have been flying as good as it was ripping around the sky.
.4 CG to tail heavy.....same as above. But could induce a flick or pitching rotation....and would have recovered after got speed again , also in a near vertical dive , would have tucked badly.
5.
Servo's ???? I have an near identical crash with servo's that basically didn't move controls at speed...
In a dive across the sky fast but not a steep dive. I would run out of elevator at speed....BUT if I just leaned on the elevator a bit , as it would climb and slow down , I would gain elevator back.
Servo's just wouldn't lift control surfaces at speed. The day ended with a vertical dive that had zero control of anything.

Servo's are my bet.

Tim
Tim,
The hinges were silicone. The servos were cheap chinese Corona 939mg. (I'm ashamed to admit!). Such a heavy, fast flying plank like it was deserved better I now realise.
As for the CG questions in point 2 & 3, I'm very confident that the CG was optimum. Pismo Jim also flew it and trimmed it out - he confirmed it was flying very well.
I don't know what you meant in point #1 ?

I have the moulds and will be building at least one or two more. What servos would be suitable? Any suggestions?

Matin,

I take your point! However, on further reflection and after reading all the above, I strongly suspect the servo explanation, at least for this crash.

Jim,

wiser for the experience.........
Oct 03, 2012, 05:12 AM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by steve wenban
That launch looks a lot more scary than it actually was
I was standing fairly close to the edge at the time and thought it looked quite ok. I would have been concerned it you hadn't let it drop to gain airspeed.

Jim.
Oct 03, 2012, 05:16 AM
Bogan of distinction
Stehl's Avatar
Arie used 939's in his bitzer and it went 140something DS'ing a small zone(lotsa G's).
It must have been one hell of a dive?
Or maybe one servo clapped out and dropped voltage to the others?


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