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Unexplained crash

When a model stuffs in for no obvious reason

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alex nicol18/06/2018 16:03:31
183 forum posts
4 photos

Apologies if I don't answer in time, suggestions are coming in thick and fast.

To Nigel R, no Y lead, one servo on each aileron colour coded leads from receiver red for right & yellow for left. aileron operation checked after the wing was attached and again at take off. Sifting through the wreckage left wing servo was fully up & Right fully down. I assumed this is the way it went in as the battery lead disconnected on impact - hard to tell what the other servo's were doing as the fuselage above the wing was mangled

alex nicol18/06/2018 16:05:49
183 forum posts
4 photos

To Paul C,

Yes it does have a fail safe but it isn't set

Martin Harris18/06/2018 16:17:25
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8015 forum posts
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I'd put my money on a servo or wiring problem.

Some years ago, I was flying one of my models and during a roll, I had a massive glitch and the model stopped responding meaningfully - much stick waggling and I found myself the right way up but with a model rolling and diving for no reason...

Until I realised that things were stable with some up elevator and left aileron deployed. I made an immediate landing and walked up to the model - at which point all became clear. The right aileron was sticking up. Taking the wing off revealed that its connecting lead was half out at the receiver - contrary to my normal installation procedure, I'd made a very neatly laced form of the wiring and the combined weight of the cables had acted on the slightly tightest connector (the right aileron) easing it out under various g loads.

The point here is that had I not managed to recover control (it was a close run thing) in time to avoid spreading ply and balsa over the field, after picking up the wreckage I would have been convinced that I'd had a radio problem.

Martin Harris18/06/2018 16:18:27
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Posted by alex nicol on 18/06/2018 16:05:49:

To Paul C,

Yes it does have a fail safe but it isn't set

Naughty!

Devcon118/06/2018 17:03:07
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1329 forum posts
462 photos

Did it feel like you had any form of control like trying to correct the roll for example.

When you say it snap rolled did it look like the elevator gave an uncommanded input as well.

Could somebody else have been using a 35Mhz set.

I'd check the true performance of the battery pack under a load test.

Might be worth checking for any unnoticed damage to the integrity of the Rx aerial lead.

Curious to check what happens at the Rx and servos if you simulate a failsafe by turning off the Tx, I know you said a failsafe wasn't set but wonder what the setup defaults to.

Edited By Devcon1 on 18/06/2018 17:05:05

fly boy318/06/2018 17:35:08
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3333 forum posts
11 photos

Hi, many years ago using 35mhz peg system, a fellow flier returned my channel peg to the board for me to use. This's I did, but inadvertently he had left his Tx on. Wrote off my model. It happens. Cheers

Martin Harris18/06/2018 17:48:43
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8015 forum posts
203 photos

Or the beginner setting up his model in the pits using the peg for "channel 60" because it said 35.060 on the crystal - while I was flying on 66...

Percy Verance18/06/2018 18:34:12
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7099 forum posts
142 photos

fly boy

My radio manufacturer got round that senario by offering a system (on 35mhz) which scanned the airwaves prior to transmitting a signal and wouldn't allow your transmitter to emit an rf signal if your channel was already in use, so the crash you had wouldn't have happened......

If only all 35mhz sets had it, then pegboards may have been little more than ornaments. It would have saved many models..........

And this system would have helped in your scenario too Martin.....more so if the dimwit had it in his tx.

 

 

 

Edited By Percy Verance on 18/06/2018 18:43:52

kc18/06/2018 18:35:20
5636 forum posts
164 photos

Someone else on the same frequency 2weeks running causing the same crash seems unlikely. More likely some other cause. Suspicion should fall on anything that could cause the ailerons to jam or anything that could cause the aileron lead to loosen ( catching the throttle or elevator linkage perhaps? or the switch? ) But both ailerons going wrong whilst on separate leads suggests it's battery or switch related ( battery sliding back and disconnecting seems worth checking ) If the switch or anything is a bit old check for Black Wire Corrosion ( on red wire too)

Frank Skilbeck18/06/2018 18:38:36
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4179 forum posts
98 photos

When it rolled in, did it roll to the left, or was the full left aileron you trying to stop a roll to the right?

BTW if your plane has a failsafe it is a CAA requirement that the failsafe is set to stop the plane from flying away, on a power plane that means engine stop or reduce to tickover.

Edited By Frank Skilbeck on 18/06/2018 18:40:42

Biggles' Elder Brother - Moderator18/06/2018 18:41:49
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Posted by alex nicol on 18/06/2018 15:56:41:

each aileron has separate servo's the left was up and the right was down.

That is beginning to sound like a radio problem. If just one servo was effected it could be a servo problem, but both, whilst not impossible, is not likely. More likely is the aircraft thinks it received a signal for left aileron?

BEB

Percy Verance18/06/2018 18:46:17
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7099 forum posts
142 photos

Odd you say that BEB. I very recently swapped out a wing servo in my Easystar because it developed a *twitch* at neutral.

alex nicol18/06/2018 19:11:22
183 forum posts
4 photos

Gents, thanks again for your input.

I've tried to summarise all points raised

What I can add is there was no radio interference from the field, as there were only two of us present at the time and the other Tx while on 35mhz is on 84, mine is on 76.

battery pack was fully charged and good a prior power cycle ensured 2hrs plus at a 1amp load.(6v 2500mah)

the switch was new

the receiver was new, first time in a plane Pcm 2048

the reason for full left up aileron and full right down was battery disconnected on impact.....no input from stick

the plane was only about 10ft up when it flicked, no time to react (or even add an expletive or two) and no other input given other than a very slight amount of up elevator to maintain a 20degree climb angle

absolutely no sign of servo glitches or buzz

range check carried out engine stopped, post crash range check carried out from pilot stance to crash site approx 100-150 yards tx ariel fully extended Rx Ariel run from Rx through top of fus to fin

cannot simulate anything untoward, tried wiggling all plugs connections......not a peep

individual aileron servos on separate channels 4 & 5 ( colour coded extension leads ......impossible to mix or plug in wrong Rx slot) left hand aileron fully up and right hand fully down

I'm completely stumped

Paul C.18/06/2018 19:18:39
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494 forum posts
115 photos

I am beginning to think that you next move should be to get the tx and rx checked out by futaba service agent just to be sure nothing is amiss. Not sure who they are these days but I am sure someone here will supply details, less cost than crashing another model and will give you confidence.

Paul

alex nicol18/06/2018 19:23:41
183 forum posts
4 photos

Hi Paul,

I'm inclined to agree with you, if for no other reason than to rule it out

Chris Bott - Moderator18/06/2018 19:31:14
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Alex how many others fly on 35MHz at your club? Do you successfully fly other 35MHz models?

It sounds to me like there's a chance you have an interfering signal at that point where the glitches happened.
Maybe be a microwave link crossing the field or an electricity pylon with an arc running across an insulator?
RC Plane Flyer18/06/2018 19:39:48
528 forum posts
20 photos

Radio Check Have heard Mike Ridley mentioned on here many times

kc18/06/2018 19:46:30
5636 forum posts
164 photos

35Mhz radios have not been sold for some time so it must be fairly old now and it's debateable whether it's worth spending money on having it serviced. With good 2.4ghz radios available at low prices it might be better to spend the money on a new set.........

Martin Harris18/06/2018 19:49:04
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8015 forum posts
203 photos

Which way did it roll when it went in?

John Muir18/06/2018 20:50:01
357 forum posts
1 photos

This has to be down to either the transmitter or receiver as both aileron servos got a 'go left' command at the same time. If the transmitter is in regular use with other aircraft and the same thing hasn't happened with them, then it's the receiver. Can't even pretend to know what the fault might be that could cause a spurious command on two channels though. If you only use the transmitter on this plane these days, then it might be the transmitter.

Only one other thought: you said the failsafe wasn't set. What if it was, but just not as you would have meant it to be? So a simple loss of signal might produce full aileron. In which case maybe a dodgy receiver aerial that loses its connection when it's vibrated. Or do I have an over active imagination?

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