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Unexplained crash


alex nicol
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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)

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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

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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

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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

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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

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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.........

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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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I've been flying at this site for over a year with no issues. no glider clubs anywhere near.

if I switch the tx off nothing moves on the plane, I also unscrewed the Ariel and walked out of range.....nothing glitched. got a couple of little buzzes but no real control surface movement when I screwed the Ariel back in. Had the model under observation by a colleague as I did the walking

I haven't flown anything else since this happened as I don't want to risk it.

I have an old precedent fun fly airframe which I'm thinking of knitting out with a good known receiver, servo, battery comb to see what happens.......fail safe will be set

if it goes ok then it'll be process of elimination. just for info switch and aileron extension cables are in the bin as a precautionary measure. I'm tempted to toss the whole suspect set, but it's really irking me not knowing the cause

thanks again to all that contributed, if I ever find out I'll post the details

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Hi Martin, separate channels, no y lead.

Further update, after plugging everything in on the bench, all worked fine. left it all switched on and did 5 minute interval quick stick wiggle checks, first couple went ok then the elevator servo was unresponsive, I picked the servo up and the base was absolutely roasting. hasty power off ensued servo in the bin. nothing's glitches remaining servos working fine, continuing to test

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Posted by alex nicol on 18/06/2018 22:27:41:

Hi Martin, separate channels, no y lead.

Further update, after plugging everything in on the bench, all worked fine. left it all switched on and did 5 minute interval quick stick wiggle checks, first couple went ok then the elevator servo was unresponsive, I picked the servo up and the base was absolutely roasting. hasty power off ensued servo in the bin. nothing's glitches remaining servos working fine, continuing to test

That servo that got hot, was probably putting a high load onto your receiver / battery which caused the receiver to brown out or the electronics to mis-behave.

I reckon you may have just found and fixed your problem.

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