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Unexplained crash

When a model stuffs in for no obvious reason

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Biggles' Elder Brother - Moderator18/06/2018 21:05:15
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Posted by Martin Harris on 18/06/2018 19:49:04:

Which way did it roll when it went in?

I understand it went left, under full left aileron Martin.

BEB

Chris Bott - Moderator18/06/2018 21:23:58
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Oh I meant to ask in my previous post. If failsafe isn't set, what happens when Tx is switched off? Do the ailerons go full left, by any chance?
Denis Watkins18/06/2018 21:34:37
2812 forum posts
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Don't rule out the glider guiders Alex, Are there hills nearby that gliders use, as their crystals are even numbers like yours.

On the patch, we use odd number crystals, and the lads on the hills use even numbers

Just so as we never clash on 35Mhz

alex nicol18/06/2018 21:51:36
84 forum posts

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

Martin Harris18/06/2018 22:09:19
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I missed the info that it rolled left which was in one of your later posts. In the interests of clarification, were the aileron servos connected to separate receiver channels or did you use a Y lead - apologies if I've missed the answer to this too!

alex nicol18/06/2018 22:27:41
84 forum posts

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

Gary Manuel18/06/2018 22:31:35
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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.

alex nicol18/06/2018 22:39:18
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I'm hoping that's it, but I'll keep testing for a bit to make sure............I've got time on my hands to put my home run jigsaw together )

Chris Bott - Moderator18/06/2018 22:45:46
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Sounds extremely plausible, Alex.
Don Fry19/06/2018 06:40:12
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Alex I did that, wrote a 25 cc petrol OD off. Tested the bits. Then wrote a plan built 80 powered machine. I never got the the bottom of it. Bin the bits.

AVC19/06/2018 07:25:53
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Posted by Gary Manuel on 18/06/2018 22:31:35:
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.

This servo is probably part of the answer, specially if you are using NiMh batteries, as the discharge rate is relatively low so that servo was probably taking all the juice of the battery.

But I still think that you should double (or triple) check the F/S, because a loss or reduction of power in itself shouldn't result in full left ailerons, especially when using two separate channels. The 12z has two types of F/S, signal F/S (standard) and battery F/S. Check if the set up is different for the battery one, especially for channels 1 and 6

RC Plane Flyer19/06/2018 07:30:07
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Hi again we're all the servos rated for 6 volt use ??

AVC19/06/2018 07:56:39
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Are the servos Hitec by any chance?

Itisme19/06/2018 10:10:33
29 forum posts
18 photos

Just a thought, i recently lost a plane in a similar way, take off as usual then suddenly rolled to the left. A friend watching said i stalled it (had that plane for about 18 months so i thought that unlikely). On inspection i found that all servos but the elevator servo worked correctly, the elevator would quickly go to full throw up (radio on low rates) then slowly return to centre in jittering steps.

alex nicol19/06/2018 10:58:39
84 forum posts

all thoughts welcome.

the week prior it did a very similar thing and I thought id taken off prematurely and tip stalled. after repair a week later and being very mindful of last weekI kept it on the ground and got max speed before taking off and also kept the rate of climb at a low angle (about 20 degrees)

this time it came off the ground as if on rails, recommended engine is 40-45 2s, I had an Irvine 53 on an 11x6 so no lack of power. I was approaching the point where I was thinking about making a gentle 90 degree left turn. Before any control input was given model was on its back and contact was made with terra firma........it happened in a blink no time to react

alex nicol19/06/2018 11:00:12
84 forum posts

Hi AVC

yes, rudder and elevator were HiTec servo's

alex nicol19/06/2018 11:04:09
84 forum posts

Hi Don,

the bits will most likely have a future date with the bin........the only thing stopping me at the minute is the desire to get to the root cause.

AVC19/06/2018 11:15:22
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Thanks Alex. I'm a great fan of Hitec servos but in my experience, when there have a electrical problem (and I have had a couple or three of them...) they tend to drain the battery very quickly, faster than other servos.

Have you checked the battery F/S in the radio?

John Muir19/06/2018 11:24:58
348 forum posts
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I once had some DYS servos which had a fault that caused electrical feedback to the receiver and made other servos connected to the receiver glitch. I replaced an aileron servo on an old plane with one and the rudder went mad. I thought the old rudder servo had gone defunct and replaced that with another DYS which only made all the servos start playing up. I figured it out on the ground luckily but if your rudder servo has developed an issue that causes something similar, maybe just when it gets hot or when vibration loosens a component, that could explain the left aileron command.

Don Fry19/06/2018 12:10:42
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One thought that keeps coming back to me is a plane what has been range tested, tested mechanically, and has then done the same thing twice, at the (more or less), same range, and orientation to the pilot.

I struggle to see any other cause than a loss of signal issue

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