Armchair Detective Required

[Andy J]

Looking for an armchair detective to suggest a possible reason for a loss of control which occurred yesterday.

 

Model was an old school, high wing 3 channel Playboy with an ~90inch poly dihedral wing. Model was powered by an OS30 2 stroke and it had flown previously without incident about a week ago.

 

Radio, FRSky Horus X10S with OpenTx software, 6 channel Rx  fed from a 6v nimh battery connected directly to the Rx. Battery had been fully charged approx 1hr prior to the flight.

 

So once in the air on its first flight of the afternoon  the model was happily stooging around at approx 100ft at no great distance from the Tx for several minutes. Rudder was slightly twitchy but otherwise the model was fully under control.  Then without warning the model twitched and then immediately entered a vertical dive. At this point the throttle was closed and full up elevator was applied which appeared to have zero effect.  After impact with mother earth I turned off the Tx and recovered the model.

 

Model was implanted in soft earth in a vertical orientation such that the motor was fully buried. Surprisingly the fuselage suffered little damage although the undercarriage was torn off and the prop blades shattered.  The wing which where adjacent to the impact point had suffered the most damage with the outer dihedral ribs on both sides having disintegrated which allowed the TE joint to also fail. LE and main spar joints appeared largely intact.

 

On recovery back at the car the TX was again switched on and certainly the elevator functioned correctly.

 

Did have my mobile phone in my trouser pocket and the Tx antenna was I think in a horizontal attitude.

 

So can anyone explain what may have caused this lack of control and what could have been the reason for a vertical dive?  Attached is the telemetry log to see if anyone can spot any anomalous behaviour. Crash occurred at or around 34:23.

 

 

 

 

 

 

Playboy-2023-02-14.csv

[Denis Watkins]

Sorry Andy,

Your downloaded Playboy csv file is a spreadsheet.

[Don Fry]

Twitchy rudder.

Is that random twitches/no input from you. Or servo wandering in a turn. 

Commiserations, nice aircraft.

[Mike Blandford]

What firmware do you have on the Tx module and the Rx? Do you know if they have "V2" firmware?

 

Mike

[kc]

If the failsafe did not close the throttle and you also closing the throttle and also elevator stick had no effect then it likely it's a battery problem.   A corrupted or loss of signal of any type should cause the failsafe to go to low throttle ( if set properly ) but with no battery power ( or insufficient power) that would not work.    So extensive testing of battery+ switch on the bench plus checking to see if failsafe works is the next step in my view.   Also check the battery charger does actually charge properly.    What is the age of battery?   Is the switch old and could it fail with vibration?  You said the battery was connected direct to Rx - with no switch? 

Edited February 15, 2023 by kc

[Andy J]

51 minutes ago, Mike Blandford said:

What firmware do you have on the Tx module and the Rx? Do you know if they have "V2" firmware?

 

Mike

Mike Tx is 2.3.14-otx

 

RF SW driver was upgraded when using the FRSKy OS to get rid of the un-commanded servo issues.

[Sparks]

I see there is a 6 second jump in time between 34:24 and 40:00 seconds - an interuption in battery voltage to the transmitter?

[Mike Blandford]

Your Rx battery voltage looks very low for a 6v NiMh battery. 5.5V is quite low, and it drops to 5.2V around 31:47. I just checked an old 4-cell 730mAh NiMh battery and I see 5.1V driving Rx, FLVSS and a servo on a servo test mix from the Tx. A well charged 5-cell battery should be showing 6.3V when lightly loaded.

 

Mike

[MattyB]

As per the above suggestions, if you didn’t get an audible telemetry warning and there was no failsafe it’s almost certainly a power supply issue of some type.
 

You will need to do a series of tests, starting with the battery (a full monitored charge and discharge cycle at minimum). If that shows nothing the switch is the next candidate - disconnect it and thoroughly test it in the bench to see if you can reproduce the issue or if there is a high resistance After that it is the wiring loom; check any soldered joints with the wiggle on load, and obviously remove and inspect all the receiver plugs to check for any oxidation or black wire rot. Only then would I move onto the RX itself, although you could also do some range tests with a completely different (known good) loom, power supply and servos so that only the RX is under test.
 

Finally if everything passes those tests do some final ground testing of your full setup before committing it to the air again. The easiest way to do that is to bind the RX to a servo tester model memory that can be set to exercise all the servos simultaneously - this puts lots of load on the flight pack, so should identify a high IR pack or sketchy switch. Someone like this should do the trick…

 

https://openrcforums.com/forum/viewtopic.php?t=2816

 

 

[EarlyBird]

What is A2(V) powering? It gradually drops starting at 7.5 down to 6.0 just before the crash.

[SIMON CRAGG]

I would think a safe bet would be the flight pack. NIMH have a horrible habit of dropping one cell as they get older. One of the reasons I changed Life packs years ago.

 

Before things get too complicated, I would ditch that NIMH pack asap, and purchase a new one or go down the Life road.

 

Hope you find out the cause anyway!.

[kc]

3 hours ago, Andy J said:

Rx  fed from a 6v nimh battery connected directly to the Rx.

That makes me wonder if a switch was actually fitted or not.   If no switch then model may have been on for much longer than the flight?   If no switch why?  

Switches are notorious for intermitant faults perhaps due to vibration or corrosion and they get left in models even when everything else is replaced.  

[EarlyBird]

An extract from the data.

 

Date,   Time,          RSSI,Rx(V),,,               A2(V), R ,Ele ,Thr, Ail  ,S1,6P,S2,EX1,EX2,LS,RS,SA,SB,SC,SD,SE,SF,SG,SH,LSW,TxBat(V)
2023-02-14,13:34:01.050,65,5.3,343.2,0.0,6.8,  1,108,-379,140,146,-1024,1024,0,0,-277,578,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:02.050,75,5.4,343.2,0.0,6.7,  0,   3,-275,-491,145,-1024,1024,0,0,-277,578,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:03.050,67,5.5,343.2,0.0,6.6, -2,-220,-3,-565,145,-1024,1024,0,0,-277,579,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:04.050,71,5.5,343.2,0.0,7.0,  0,-1024,-732,-971,145,-1024,1024,0,0,-276,579,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:05.050,65,5.5,343.2,0.0,7.0, 55,-1024,-887,-984,145,-1024,1024,0,0,-283,578,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:06.050,61,5.5,343.2,0.0,6.7,-55,-1024,-1024,-996,146,-1024,1024,0,0,-274,547,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:07.050,57,5.3,343.2,0.0,6.5,-90,-1024,-1024,-70,145,-1024,1024,0,0,-274,547,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:08.050,54,5.3,343.2,0.0,6.9,-168,-1024,-1024,69,146,-1024,1024,0,0,-274,547,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
2023-02-14,13:34:09.050,54,5.3,343.2,0.0,7.2,  -4,-266, -1024,17,145,-1024,1024,0,0,-274,547,0,-1,1,1,0,1,-1,-1,0x0000000000000000,7.5
 

[Don Fry]

Last time I flew something like this, it used about 50-60 mAh of battery per 10-15 min flight. It had a 4 cell battery (NiCad). It was happy with a 500 mAH cell, for an hour or so of flight, with a calm reserve capacity.
Accept it might have dropped a cell. Accept Life is a better battery.

But a Playboy will be happy on anything, as long as the receiver gets enough to keep it going. I used to roll a fag mid flight. 
Andy, post of 2 hours ago, rudder twitch, what is that? A faulty rudder system, electronic, or mechanical might cause a catastrophic failure when the battery gets overloaded. 

[Andy Gates]

This may help you.

 

Red line is signal strength which is dropping prior to the crash and is at its lowest value just before you had a battery supply failure (green line).

 

The step change in signal strength is also a bit weird.

[Eric Robson]

Yesterday I had the same problem, everything checked on the ground engine fine after take off on the first circuit it went dead stick and I managed to land it ok all checked 2nd flight same thing ran the plane on the ground and after a short time the throttle shut. the cause was the rx battery it showed fully charged but after a while moving the sticks it died. left for a while it showed full charge but under load it drained rapidly. The plane had been stored in the loft since September and was fully charged before flying, the battery was not very old but is a recycle bin job

Edited February 15, 2023 by Eric Robson

[Brian Cooper]

Rx battery. 

Plus, change the switch..... its wiring could be old and suffering from the dreaded black wire corrosion.  

[Cuban8]

1 hour ago, SIMON CRAGG said:

I would think a safe bet would be the flight pack. NIMH have a horrible habit of dropping one cell as they get older. One of the reasons I changed Life packs years ago.

 

Before things get too complicated, I would ditch that NIMH pack asap, and purchase a new one or go down the Life road.

 

Hope you find out the cause anyway!.

Run a five cell Nimh pack (they do have their advantages) and regularly check the cells' performance. A fault will be very apparent if you find a weak/dead cell, but at least the four good remaining ones will have prevented disaster.

Edited February 15, 2023 by Cuban8

[Outrunner]

24 minutes ago, Cuban8 said:

Run a five cell Nimh pack (they do have their advantages) and regularly check the cells' performance. A fault will be very apparent if you find a weak/dead cell, but at least the four good remaining ones will have prevented disaster.

Andy said he was using a 6v battery so it must have been 5 cells....

[Robin Colbourne]

I had a Futaba receiver battery fail in flight. One of the spotwelds failedbetween the tag and the end of the cell, inside the original heatshrink outer covering.  If the heatshrink was squeezed at the ends of the pack, a circuit was made; releasing it, the pack went dead.

[GrumpyGnome]

12 hours ago, MattyB said:

As per the above suggestions, if you didn’t get an audible telemetry warning and there was no failsafe it’s almost certainly a power supply issue of some type.
The easiest way to do that is to bind the RX to a servo tester model memory that can be set to exercise all the servos simultaneously - this puts lots of load on the flight pack, so should identify a high IR pack or sketchy switch. Someone like this should do the trick…

 

https://openrcforums.com/forum/viewtopic.php?t=2816

 

 

 

This may help explain the concept.... https://www.youtube.com/watch?v=OxBFABPli50

 

Very clever - think I'll try that on my ic planes.......

[Andy J]

Thanks for the comments / queries.

 

May have been confused regrading the battery voltage as it is possible that the battery is a 4.8V pack. Don't think I can dig it out of the model to verify as this will require major surgery.

 

The loss of telemetry at time 13:24:34 (and battery volts) is simply because I turned the Tx off and went to collect the model.  As can be seen at 13:40:03 the telemetry recovers when I switch the Tx back on to check if the elevator still functioned which it did.

 

What is strange to me is what would have forced a stable high wing design into a vertical dive.

 

Do notice that at 13:34:06 the battery volts are dropping as the elevator demands go towards full up and then recover as the model hits the earth at 13:34:11 and the elevator demand is removed when I realise all further control is in vain.

 

Don't use a switch on this model as I simply just plug the battery into a floating servo lead connected to the Rx.

[john stones 1 - Moderator]

Clutching at straws, one possibilty is a defective elevator servo.

[Martin Harris - Moderator]

If you’re not sure what battery is in the model, is it possible that any battery charging/checking may have been done incorrectly?

 

A nice scale model was lost at our club due to the owner charging - and checking - a 5 cell receiver pack as a 4cell.  The charger cut off very early as it soon reached the 4S cut off limit and although the checker gave a fully charged indication, during the third circuit of its maiden flight, all control was lost and the inevitable happened. 

[kc]

What does the failsafe do now- does it go to low throttle and does it perhaps go to full down elevator which maybe  caused the nosedive when battery went too low?