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Model vs Trees

Failure of something!

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Chris Walby24/01/2019 15:59:39
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955 forum posts
228 photos

Hi,

Okay I had a Cougar IC (old and second hand one) which maiden last week in the windy conditions and was okay.

Today all seemed alright (pre-flight checks etc) but on the first/last flight it took off and I circled around okay (just mooching on 1/4 throttle).

Tried a bit quicker with a down wind roll, but it seemed to be delayed (roll rate was okay once it go going), tried it a couple more times plus a loop and it was okay.

Went to roll to inverted and nothing....no control (throttle to idle)

I was thinking RX battery, explains why it didn't go to throttle cut/loss of signal

Or the RX switch, open circuit when aileron servos + elevator were applied, but would the throttle not stayed higher than idle?

Could be the RX, loss of signal...it did fly nice and level until it hit the tree tops, but I have throttle cut set and had been flying further away so that does not add up.

Any other ideas before I commence the post mortem on the bench?

cougar vs tree.jpg

PS I might have done more damage getting it out of the tree although the wind did most of the work.

alex nicol24/01/2019 16:18:15
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285 forum posts
13 photos

Hi Chris,

To be honest this is probably one of the worst things to happen as in all likelihood unless it's something really obvious you will never be a 100% sure and it'll take a bit of time to rebuild confidence in your radio gear. Personally I'd scrap everything in the plane Rx, switch, leads, battery and servo's.

That said if curiosity gets the better of you I'd be inclined to check all connections, switch and battery lead for -ve lead corrosion.

I had a similar issue where a model just stuffed in for no apparent reason, diagnosed a faulty switch, used the gear with a new switch in another airframe and promptly stuffed that in as well. I concluded the original switch whilst definitely faulty may have been damaged in the crash and wasn't the root cause. I put all the sevo's on a tester and let them cycle and after a couple of minutes the elevator servo got very hot and failed........full flight pack got binned.

Good luck with whatever you decide

Chris Walby24/01/2019 16:29:33
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955 forum posts
228 photos

Cheers Alex,

I think you are right, they were all old servos that had been standing around a long time including the switch.

Probably try the RX out in one of my very low cost Depron self builds and bin the rest.

Just like to know why...

Nigel R24/01/2019 16:34:32
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2986 forum posts
472 photos

gut feel, power problem of some kind, slow roll response preceeding total fail, not even failsafe happening, says low power to me, although I am unfamiliar with the RX you have installed and what its behaviour under low power is

cycle the servos for a 1/2 hour for confidence in them, should be an easy win

then proceed back up the chain

test the switch under load, same with the battery, plenty of cable waggling to try and reproduce a possible mechanical fault in the wiring

do the same for the battery

Denis Watkins24/01/2019 16:43:15
3814 forum posts
54 photos
Posted by Nigel R on 24/01/2019 16:34:32:

gut feel, power problem of some kind, slow roll response preceeding total fail, not even failsafe happening, says low power to me, although I am unfamiliar with the RX you have installed and what its behaviour under low power is

cycle the servos for a 1/2 hour for confidence in them, should be an easy win

then proceed back up the chain

test the switch under load, same with the battery, plenty of cable waggling to try and reproduce a possible mechanical fault in the wiring

do the same for the battery

Nigel is always in the right ballpark Chris

But be assured, a perfectly OK preflight checked cell can fail the next time up.

I reckon more than 95% of inflight failures are Rx supply

SIMON CRAGG24/01/2019 17:30:34
404 forum posts
6 photos

I think most of us have had that sinking feeling!

Apart from all the good ideas so far:

What was the RX battery spec?

Rolling down wind is always going to be a slow affair.

Have you checked all the plugs / sockets for any sign of corrosion?

Did you complete a decent range check?

I could think of loads more, but please let us all know if you found the cause.

Hope this helps.

Martin Harris24/01/2019 18:11:46
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8741 forum posts
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Posted by SIMON CRAGG on 24/01/2019 17:30:34:

Rolling down wind is always going to be a slow affair.

Why?

The only difference is the amount of ground covered during the manouevre - the roll rate will be identical.

My money would be on a failing battery from the description - have you checked it yet Chris?

Edited By Martin Harris on 24/01/2019 18:17:07

alex nicol24/01/2019 19:07:07
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285 forum posts
13 photos

Hi Chris,

What happened is the $64,000 question. Rx check in depron airframe sounds like a good idea. It's the not knowing what caused it that drives me daft. Thing is if it was a bad connection simply unplugging and plugging it back in could be enough to clear the fault.

When it happened to me the second time I had a bit of a strop and cut all the cables off (mainly to remove the temptation of reuse) and threw the whole lot in the bin in disgust

As you've probably guessed it still annoys me to this day

Paul C.24/01/2019 20:46:00
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583 forum posts
139 photos

20181211_130316.jpg20181211_124420.jpgHi Chris, I put my money on a dicky switch as the failsafe did not kick in. I recently had an encounter with a tree fortunately it was all down to me 😂 the only excuse I have is that as the leaves have fallen off I thought I was well this side of it. Totally obliterated the airframe and new head required for the engine, good job we had a long pole on site.

20181211_123315.jpg

Braddock, VC24/01/2019 20:56:16
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1626 forum posts
76 photos

Paul, probably the engine out of balance, it's only got one prop blade...........devil

SIMON CRAGG24/01/2019 20:58:58
404 forum posts
6 photos
Posted by Martin Harris on 24/01/2019 18:11:46:
Posted by SIMON CRAGG on 24/01/2019 17:30:34:

Rolling down wind is always going to be a slow affair.

Why?

The only difference is the amount of ground covered during the manouevre - the roll rate will be identical.

My money would be on a failing battery from the description - have you checked it yet Chris?

Edited By Martin Harris on 24/01/2019 18:17:07

No it wont......suggest you read up on yer aerodynamics fella!

Paul C.24/01/2019 21:07:26
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583 forum posts
139 photos
Posted by Braddock, VC on 24/01/2019 20:56:16:

Paul, probably the engine out of balance, it's only got one prop blade...........devil

😂 I did find the other blade at the time but had to go back next day to find the receiver battery, you just got to love trees 😨

Paul.

Martin Harris24/01/2019 21:56:14
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8741 forum posts
214 photos
Posted by SIMON CRAGG on 24/01/2019 20:58:58:
Posted by Martin Harris on 24/01/2019 18:11:46:
Posted by SIMON CRAGG on 24/01/2019 17:30:34:

Rolling down wind is always going to be a slow affair.

Why?

The only difference is the amount of ground covered during the manouevre - the roll rate will be identical.

My money would be on a failing battery from the description - have you checked it yet Chris?

Edited By Martin Harris on 24/01/2019 18:17:07

No it wont......suggest you read up on yer aerodynamics fella!

I believe my understanding of basic aerodynamics is quite reasonable. Rather than me doing research which I believe won't alter my opinion, would you care to illuminate me as to why the roll rate will change? Please don't try to tell me that the airspeed will change between level flight at a constant throttle upwind and downwind...

Chris Walby24/01/2019 22:27:34
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955 forum posts
228 photos

The bench post mortem has (I believe) found the issue.

Only change from last week when I flew it, where connected the RX battery, put the wing on and off I went was to chance a connector on the already installed switch to a JST (as that's what's on my battery).

Now my money was on the switch, but no as playing around I found I had not pushed one of the connector pins fully home. It only needs to be back 2 or 3 mm and its an intermittent connection. Pushed it fully forwards and it locked in the connector.

It was a little odd as the servos twitched before the RX went into failsafe which gave me the clue and with the connector "fixed" I can't get it to do it again.

PS Thanks for all the suggestions, now where did I leave the wood glue!

Nigel R24/01/2019 23:16:56
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2986 forum posts
472 photos
Nightmare! At least you found the root cause. Live and learn.
SIMON CRAGG25/01/2019 00:52:34
404 forum posts
6 photos
Posted by Martin Harris on 24/01/2019 21:56:14:
Posted by SIMON CRAGG on 24/01/2019 20:58:58:
Posted by Martin Harris on 24/01/2019 18:11:46:
Posted by SIMON CRAGG on 24/01/2019 17:30:34:

Rolling down wind is always going to be a slow affair.

Why?

The only difference is the amount of ground covered during the manouevre - the roll rate will be identical.

My money would be on a failing battery from the description - have you checked it yet Chris?

Edited By Martin Harris on 24/01/2019 18:17:07

No it wont......suggest you read up on yer aerodynamics fella!

I believe my understanding of basic aerodynamics is quite reasonable. Rather than me doing research which I believe won't alter my opinion, would you care to illuminate me as to why the roll rate will change? Please don't try to tell me that the airspeed will change between level flight at a constant throttle upwind and downwind...

I'll leave it there. Life is to short for petty point scoring. Safe flying fella.

Martin Harris25/01/2019 01:14:30
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8741 forum posts
214 photos

Quite right Simon - but it's not about points scoring.

From my best guess in the absence of any feedback from you, this appears to be directly related to a rather widely held misconception regarding flight into wind and downwind which I believe is in everyone's interest to understand.

We can agree to disagree if you like but one of us is wrong - and if it's me, I would certainly like to know why, rather than being rather condescendingly referred to aerodynamic textbooks with no explanation.

Levanter25/01/2019 07:38:08
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880 forum posts
436 photos

The aircraft is flying in a mass of air and doesn't know whether it is moving upwind or downwind, or across wind for that matter. If you think about it how can it? if there is wind, this mass of air is moving relative to the ground and therefore when the aircraft is being observed from the ground (rc pilot) it looks like it is going at different speeds but that is relative to the fixed point (ground) and not the moving air mass.

Taken to extreme and the windspeed is greater than the airspeed and the aircraft can appear to stand still or even go backwards! But we all know that is "impossible" in aerodynamic terms zo we readily accept the concept of a headwind. Same thing applies to currents and tides when sailing. It also explains the common and infamous stall on the downwind turn.

So Simon, I think you are being deceived by appearances and Martin is in fact perfectly correct and his explanation was spot on. It is an important subject.

Levanter

Piers Bowlan25/01/2019 09:22:35
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1826 forum posts
44 photos
Posted by Paul C. on 24/01/2019 20:46:00:

20181211_130316.jpg20181211_124420.jpgHi Chris, I put my money on a dicky switch as the failsafe did not kick in. I recently had an encounter with a tree fortunately it was all down to me 😂 the only excuse I have is that as the leaves have fallen off I thought I was well this side of it. Totally obliterated the airframe and new head required for the engine, good job we had a long pole on site.

 

20181211_123315.jpg

Sorry to hear of your loss Paul. A very nice looking model of Peter Miller's Cap 20L- or at least it was. I did the same as you when I thought my glider was flying towards me in front of a tree and was very 'surprised' when it just stopped in the branches! Depth perception is deceptive but if it was easy there wouldn't be any challenge.

Edited By Piers Bowlan on 25/01/2019 09:24:53

Chris Walby25/01/2019 09:39:52
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955 forum posts
228 photos

What surprised me was the noise as it hit the upper branches, a real crack that could be heard clearly around the countryside (if there was anyone else to hear it).

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