Some repair work on the Push Pull

The Push Pull is now 10 years old. Quite an age for a Depron lightweight.

It was built to specifically test the effect of flaps. They are in two sections, occupy 2/3 of the span, 40% of the wing chord and the aft section descends to 90 degrees.

The hope was that by hinging the flap so near the spar it would reduce the nose down trim when the flaps were fully deployed.
By using counter rotating in line props there should be little or no torque effect. In addition being on the centre line should largely keep the prop wash inline with the tail plane and elevator regardless of the flap setting.
The motors are Emax 2805 3000kv turning 5x3x3 from a 2200 mAh 2s. It uses my 35 Meg Futaba as that is the only Tx I have with a knob to work the flaps rather than a switch.. With such huge flaps they can only be applied proportionally as the air speed declines.
After quite a bit of trial and error adjustment (and repairs!) it eventually ended up flying really pretty well.
However at the last outing (I had intended to take it to the DVMFC open day) on test one flap servo functioned very intermittently. In doesn't fly so well with only one flap working. :woohoo:
The problem was the electrics were always a bit of a sardine can and of course all fully built in. It was going to a 'moot' point whether attempting the repairs would in effect wreck the airframe.
This gives a flavour of the cut outs required to be simple to extract the servo.
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At least the reason for the servo failure became clear.

It was actually like that in the wing.:ohmy:
Note the twin flap links. The one on the inner most arm hole works the first flap to give 45 degree at full deflection. The other link gives the full 90 degrees. It took quite a bit of fiddling to get it to work and even more to ensure both left and right flaps moved equally together.
So far so good.

New servo installed and tested.

The next step is to get both servos "Y" connected to check that both sets of flaps still move in the same way over their full range.
Followed by the tricky job of replacing all the cut outs on what is quite a highly stressed Depron structure. :ohmy:

The flaps now work as intended along with the other control surfaces but the motors don't work! :woohoo: Actually they both just oscillate suggesting the ESCs have failed. I seem to remember on the last flight one motor was a bit reluctant to run smoothly.
To get at them required still more of the wing pylon to be cut away.

A true 'sardine' arrangement with both ESCs wedged adjacent to each other, totally enclosed so no cooling. It is perhaps not too surprising they failed. It does seem odd that they both failed at the same time.
Two new ESC ordered from China through Amazon so it could be a while.

Could be esc failure, but it could also be that one of the wires from the esc to the motor has disconnected, so the motor has no rotational reference.

Yes indeed.
The first job is to extract the ESCs in such a way as to leave the motors connected. Everything is soldered there are no connectors in the motor wiring.It It should possible to test if there is a bad connection.
To be honest I cant remember how the motor are fixed. The 2805 uses a 'drum' mount so once all the Depron streamlining is removed it should be possible to get them out if necessary.

The Push Pull has been hanging on the wall in this state for just over a year.
 
With the current rather gusty and wet conditions I took pity on it and finished off the repairs. Horrible job as the wing pylon was internally damaged almost beyond repair
It now looks like this.
 
I really should have scrapped it but its flight characteristics with its huge 2 section flaps fully extended are at the very least "interesting"!
 
The counter rotating push/pull props remove all motor torque effects which is an vital attribute at the slowest flight speeds.

Did you find why the motors wouldn't run? I don't recall you mentioning it since I suggested that you check all three wires were connected from esc to motor.
Did your Chinese speedo's arrive?

The new speedos are in.
The reason the props would not run was simple. I was using a very old 2s LiPo for testing. Use a new 2s and they ran perfectly. Obviously the high amp starting pulses were drawing down the volts to a point where the ESCs just gave up!
However there is still a problem in that the flap servos in particular oscillate a bit when the motors are running but are perfectly still when the motors are off. I fear the ESCs are just too close to the Rx (actually right up against it!!) and it is a 35 meg after all.
If I can summon up the interest I should really build a new fuselage with a better internal layout. 

I was watching a bit of the women's tennis at Eastbourne yesterday afternoon when a particularly loud plane flew over quite low which I recognised as likely a Merlin. It was indeed a Spitfire. Interesting the cameraman also noticed and never mind the tennis he focused on the plane until I guess the producer told him to get back to the job in hand!       

I guess the cameraman found the tennis as excitng as I do!

Were you looking for this Simon?
 

Yes indeed.
I tried searching "Push/Pull" and nothing found . Obviously I should have used "Push Pull"