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Aug 26, 2018, 08:05 PM
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Wings break OFF.....


Well that was a first, in any aircraft I have owned......
Yet another way to add to the long list of ways that a model aircraft can crash - or try to.

I don't flt the Mig-29 aggressively at all, so far. Just very leisurely 'airshow circuit patterns', with some Rolls or a Loop here or there.
Maybe must as well I never have or do!!

On Saturday I was flying the Mig around and then went through a large loop, into an exit Roll, then a long banked turn to come beck into an upline of a loop to go into a Split-S, which effectively is the same as having done a loop instead anyway. You have just rolled over 180deg and done the loop down-line the other direction.
It pulled out into level flight and I banked shallowly to come back more to my direction, and some very short time from the move to level and bank there was a "BANG" noise, which I right away knew was the sound of "something reasonably strong being broken apart". In that split second all you can do is watch the aircraft motions to try to work out what has happened physically...and what is GOING to happen aerodynamically! With a notable 'Bang' it is likely to be quite un-aerodynamically sound and head for a crash! LOL

The Mig skewed off aside - leftwards I think - and dived at a medium/high rate. Natural pilot instinct is to correct for those un-commanded motions, and I COULD control it to some degree. Very quickly I got it to climb, but it has a severe roll to one side (left?) and I needed a lot of Roll correction for that.
Quickly I found I needed a LOT of AoA for it to not lose altitude. Maybe 25deg to 35deg. But apart from difficulty keeping it under fair control, I COULD fly it onwards and I immediately brought it around to land. And successfully did.....

As it was coming around to land I could see one wing was 'notably too small'.... a huge part of it had broken off!
As I walked towards it on the ground and got closer, I could see that BOTH wings had broken off huge pieces!!

I expect the arcing out of steep descent - down-line - of the Split-S is where the forces were too high and at least fractured the foam to be ready to complete breaking off that little bit later.
I do very large and smooth arcs for loops and split S's, so there are not much force anyway. Not versus many videos you see of other people flying models around madly like blow-flies! But anyway, it must have been enough to break the wings! I can't think of any other possible reason, such as a bird strike.... LOL

The wings broke DIAGONALLY, from the rear root outwards, on an angle/path that goes out past the end of the main spar (6mm CF tube).
The Mig wings are quite thin really and I guess the "FlyFly Foam" is not dense enough construction to be as strong as truly required. It FEELS quite strong when flexed, but it is not truly strong enough...... not for 'normal' flying around, of 'calm' smooth loops.... and certainly not if you really threw it around like a full scale Mog-29 can be!!

One wing has a "compression dent" where the foam breaking away made it all compress lie a dent.
The other wing has a DENT further inboard on the remaining wing portion (not the broken piece) and WHAT would have caused that in that place? it was not marked, dented, when it took off! I don't think either wing break portion could have GOT to that position to dent it. That interesting dent is what made me think of a POSSIBLE bird strike, and the shock of impact got the wing stress and breaking underway.
It doesn't seem likely.... but is possible.

So now I will repair that and move on to the FIBERGLASSING of the entire Mig. Though, of course, I will also add another form of STRENGTH to the wing, across those diagonal break paths. Two full span spars per wing, one to run parallel to the leading edge angle and near the leading edge (25mm aft of that?), and then another similar angle one well back in the wing and that will finish at the rear end of the wing tip. Then the fiberglassing over it all....

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Aug 27, 2018, 09:37 AM
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Thread OP

Wings break off - video


Mig-29 Fulcrum - FlyFly Twin 70mm EDF - Wings break off (4 min 9 sec)
Aug 30, 2018, 09:30 AM
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Wing repairs, and Ailerons


I replaced the large foam damaged areas with balsa wood fill ins. Then filler and sanding....


I was also adding Ailerons so I cut those off and fit some 3D printed Servo Boxes for their servos.
The Ailerons will use specially designed and 3D printed hinges. Fully "sealed" radiused Aileron and Wing mating faces - so there is no gap in the Aileron to Wing join ever.


All work on the Wing that I want to do can be done without worrying about the stock finish as it is going to be WBPU/Glassed anyway.
eg: Running servo wires in grooves.... the repairs.. the extra spars that will be added....


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Aug 30, 2018, 09:38 AM
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Extra Wing spars


I added a pair of 4mm carbon fiber tube spars per wing. One runs parallel to the leading edge angle, 50mm back from the leading edge. The other runs a shallower angle, but more rearwards in the wing - aft of the main 8mm spar.
Fitting these was just a 4mm wide slot added under the Wing and then using PolyUrethane glue to glue and 'fill' them in. With a number of small Epoxy 'blob' points also done so that it is all locked in solid quickly (5 minutes) whilst the PU glue takes hours to expand and set.
The PU glue refills the majority of the foam slot, and then the rest is just filled with filler.....


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Aug 30, 2018, 09:45 AM
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3D Printed Aileron Hinging


I 'mapped' the Mig-29 Ailerons into 3DSMax to design the hinging system. Then extending those to form the 'Wing' area near them too. This was to get the correct thickness and slope/tapers of what the 3D printed pieces will replace in the removed foam for them.

The Aileron 'face' is 180deg rounded, and a matching face for the Wing is also made - but it has a 0.4mm greater Radius, plus only 160deg which means the "Aileron" will always be 'sealed' to the Wing, for any angle it ever moves to. the 160deg is to allow the Aileron to be able to move to 45deg or so before its outer surface will ever hit the Wing face/edge and be prevented from any further angle. For any travel of +40deg to -40deg, or so, the seal/gap is almost indiscernable (0.2mm region).
The hinging is via a pivot rod that runs the entire Aileron span and out into the new Wing hinge piece. 3mm CF rod used for that. This forms a rock solid, zero freeplay, pivot/hinge result.
The two 3D printed pieces are made up as a complete assembly and then epoxied into the Wing which is cut out to match what they will replace. Then the Ailerons are attached to the Aileron Face portion of that.
3mm CF 'pegs' are used also, to 'skewer' into the Wing and the Aileron, so the pieces are not just a flush face epoxied on - they are also skewered/embedded into the foam to assure they will never come apart or off!

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Last edited by PeterVRC; Aug 30, 2018 at 11:05 PM.
Oct 01, 2018, 06:34 PM
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Thread OP

Repaint


I am not totally sure why I repainted it in a Green/Grey camo scheme....
I always really wanted a Grey/Grey version of the Mig but seeing I was repainting an Me-262 in Green/Grey I decided it looked good and would be better visibility then Grey/Grey too. So I did that. It looks good, and there is even actually at least one Air Force that have a similar Green/Grey scheme (Arabia or something!) - and even an odd Russian one in pics here or there - so it will do fine. I will just use the original FlyFly decals still - unless I think they are too crappy (plasticky) and then I will vinyl cut some of my own if need be.


The underside will all be a Light/Med Grey, but I can't do that until I finish the Aileron servo wiring runs in the wings.
I also will add a CF rod (or two) in each fin, as they are quite thin and flimsy and might be the next thing(s) to break off in flight all by themselves one day!



Once all the painting is done, and the decals, it will then be covered in WBPU/Fiberglass.


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