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Unexplained crash

When a model stuffs in for no obvious reason

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alex nicol18/06/2018 14:21:40
183 forum posts
4 photos

Gents, this ones a bit of a mystery to me. last week I resurrected an old black horse home run, sports aerobatic model, powered by Irvine 53, new gear installed. Funabashi 12z and 2048 pcm receiver, 5 revo's and 2 electric retract units on 35mhz. fully range checked .

off down the runway, slightly premature take off (or so I thought) model got to about 10ft rolled and went in. Initially I put it down to pilot error and tip stall due to lack of airspeed.

This week duly repaired, held it on the ground for as long as possible, smoothe take off with very shallow climb......solid as a rock same as above model rolled on its back and stuffed in.

Examination of the wreckage showed full left aileron. Thing is all the gear checks out, not even the slightest hint of a glitch, also it was a new 6v flight pack. no matter what I do switching on/off etc I can't get anything to twitch or full left aileron to happen........thoughts and ideas please

alex nicol18/06/2018 14:22:40
183 forum posts
4 photos

sorry that should read Futaba 12z ......auto correct lol

will -018/06/2018 14:32:40
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458 forum posts

Reversed ailerons?

Biggles' Elder Brother - Moderator18/06/2018 14:33:41
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Moderator
15748 forum posts
1460 photos

Ok, lets get rid of the obvious things first! I'm sure you have this under control as they say, but just for the record you are 110% certain that the ailerons are working the right way round? I know,...but its worth asking. You wouldn't be the first, or the last, experienced modeller to send a model up ailerons reversed!

BEB

Biggles' Elder Brother - Moderator18/06/2018 14:34:08
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15748 forum posts
1460 photos

Ha! Snap!

BEB

alex nicol18/06/2018 14:37:32
183 forum posts
4 photos

Ailerons were correct......model had just taken off dead straight - no aileron signal given at this point reached about 10ft flicked and in it went......no time to do anything

Biggles' Elder Brother - Moderator18/06/2018 14:45:22
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Moderator
15748 forum posts
1460 photos

Wings straight, unwarped and secure?

BEB

Denis Watkins18/06/2018 14:52:38
3196 forum posts
147 photos

Aileron from the back Alex, lifts the aileron that the stick points too

You say everything is OK, until you put in an input

Double check, like the lads suggest

Edited By Denis Watkins on 18/06/2018 15:01:41

alex nicol18/06/2018 14:54:45
183 forum posts
4 photos

yes, two piece wing with joining tube and locating bolts, impossible not to put in straight. Id flown it before albeit several years ago. When it took off it flew poker straight, the only signal given was a small amount of up elevator to maintain a shallow climb ( circa 20 degrees)

RC Plane Flyer18/06/2018 14:59:05
528 forum posts
20 photos

I see 6 volt pack and retracts had you just put the retracts into up mode ?

alex nicol18/06/2018 15:11:25
183 forum posts
4 photos

hadn't touched the retract switch at this point, although retracts were checked as part of the static preflight check.

With regard to the previous post point, ailerons were and still are correct.......just been to the hut and checked......standing from behind left stick, left aileron up, right down, right stick opposite happens, also part of static preflight checks Aileron extension leads are colour coded with tape, red for right wing yellow for left

Devcon118/06/2018 15:26:15
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1329 forum posts
462 photos

Maybe do a further range check by replicating the position of the model(remains)/tx during the fateful flight. Was the Tx aerial extended for the flights. Can you remember how the Centre of Gravity checked out.

Paul C.18/06/2018 15:29:46
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494 forum posts
115 photos
Hi Alex when you reached the crashed model you inferred that it had full left aileron this should have centered from your transmitter unless you had lost power. Suspect a switch issue especially after a long lay up
Paul.
simon barr18/06/2018 15:36:26
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1010 forum posts
11 photos

Many years ago, I had a similar thing, although still on the ground.... A range check showed that although all was good up to about fifteen feet, after that all contact was lost. A change of Rx crystal solved the problem.

I put it down to a faulty crystal.

Don Fry18/06/2018 15:38:26
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2883 forum posts
35 photos

Another possibility, pointing the transmitter aerial at the model, and lost signal. But that full over servo after crash needs explaining.

Paulo Peres18/06/2018 15:39:08
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89 forum posts
100 photos

Servo with bad electrical connections? A friend of mine lost a DH Vampire EDF on the third flight of the morning as it would suddenly enter a brisk nose down attitude and then recover either by itself or with full up elevator. He would put her flying straight and level, (properly trimmed of course), and no elevator input would be given and it would dive.

Decided to land because of the erratic behaviour but on finals happened again and you know what happens when you run out of altitude... The servo was later checked and performed nicely on the tester... but it kept showing an erratic behaviour. He didn't tear it apart, but it was thrown in the garbage as our best assumption was that some inner connections were failing. All of his next models are safer now!

Engine Doctor18/06/2018 15:39:44
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2080 forum posts
20 photos

A club member had a similar scenario recently . Plane took off rolled without any input and went in . Three crashes and repairs later he spotted the culprit was a broken servo lead causing servo to go full over to the stop . Once the plane crashed and installation was shook up it all worked perfectly . Worth checking servos individually for faults .

Hope you find the culprit as its very frustrating

PS Did you range check with engine running at full power as vibrations can shake any bad connections and show up problems .

Nigel R18/06/2018 15:44:06
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1969 forum posts
366 photos

"Examination of the wreckage showed full left aileron."

Does the model have two aileron servos?

Were both in the 'full left' position?

Are they on a Y-lead, or separate channels?

Was one plugged in to the wrong RX channel?

Assuming correct connections, is there any mixing set up in the TX which could have resulted in the aileron problem?

TBH my first thought was 'dodgy servo'.

alex nicol18/06/2018 15:56:41
183 forum posts
4 photos

Ok I'll try and answer the above

Range, immediately after the transmitter was left at the strip with a colleague, everything forward of the wing te was mangled and the battery disconnected from switch due to impact this and the fact after following a rock steady straight line the model snap rolled left and piled in. each aileron has separate servo's the left was up and the right was down. The way the model reacted it was as if I'd put full left aileron on & full up elevator.

I reconnected the radio gear at crash site and everything centred. I had a walk around the crash site but no glitches at all. A colleague checked everything from the Tx at the pilot stance all was good - I should mention the crash happened at about 150 yards range.

Aerial was fully extended, no other models in the air or switched on

Model was at 90 degrees to the aerial

CG was same place its always been

Receiver doesn't have a crystal, you set the frequency from the Tx - all set ok

New battery & switch fitted - the only thing I can find is the battery connection isn't as positive as I'd like but no amount of wiggling causes any glitching or servo buzzing

Paul C.18/06/2018 16:02:50
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494 forum posts
115 photos
Not familiar with this transmitter does it have a fail safe setting if so how was it set. Running out of ideas now.
Paul.

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