Xplorer flap horn repair

[Gary B]

Ye olde broken flap horn problem!

 

During one flight at the F3J Nationals I was rapidly running out of slot time with way too much height so me being me I stuffed the nose down instead of accepting the overfly and less risk of damage.

 

I always know when the landing has been a tad heavy because the canopy slides off forward!

 

As my reactions are not the quickest the flaps were still down as it hit the ground, inertia did the rest and poor 'Dora the Xplorer' had to be retired for the rest of the day with a broken left flap horn.

 

Looking at it at home the horn had sheared flush with the flap and I've been worrying about it and scratching my head since, knowing that I would have to fix it at some point over this winter.

 

In a fit of enthusiasm I dragged the wing panel out of the box today and stared at it long and hard! The main option I had been thinking of was drilling and using a stud extractor ('Easy Out' as they are sometimes known). I've done this many times on full-size aircraft but this is only a 3 mm diameter part, the chances of drilling an accurate hole and finding a small enough extractor were slim.

 

Another option was creating a screwdriver slot on top of the broken bit, not easy either but I went for this method. A razor saw got me nowhere so I used a Dremel with a cutoff wheel to form the slot which worked with very little damage to the flap skin.

 

Another worry (I worry a lot!) was whether the horn had originally been fitted with threadlock/cyano etc, I tried moving the other horn and it moved fairly easily so things were looking promising.

 

Sure enough the broken horn moved using a jeweller's screwdriver (applying pressure to prevent chewing the new slot in the soft brass) and my heart lifted! Yay!

 

Fitted a new horn and replaced the other side as a precaution then rigged the glider to check surface neutral and full down deflection which just needed a tweak of the sub-trim to get it back to where it was.

 

I would advise against using threadlocker on these horns as it would have made the job 10 times harder, if not impossible. 

 

So pleased I think I might give 'Dora' a clean and polish!

 

Should be piccies below (I blended the munched flap wiper BTW), cheers.

 

 Gary

 

 

 

 

 

[Austin]

Well done Gary, thats reason I don't glue the horns on my models 

[satinet]

did you get a hunski at least?

[Gary B]

Yup, now we know!

 

I'm sure some manufacturers' instructions recommend threadlocker, they can't turn at all as long as the link is connected, spose you could get a little bit of slop but I would live with it.

 

Must give a shout out to Wixy and his RCmetalbitz for throwing a pair of horns in my direction at the Nats, still owe him a couple of beers!

 

GB

[Gary B]

I think so Tom, if not it was in the high nineties with a nanosecond to go! Still got thrashed though, need to tune my winch up for less time on the line.

 

Strangely I had to swap to my battered Pike Superior and started flying like I knew what I was doing!!

 

[isoaritfirst]

Agree with all of that - no stud locker.

If threads are a bit sloppy and if like me you have an aversion to slop, adding a dab of paint to the threads may be a way forward

[John T]

Another method is to use a Pritt Stik glue, as this tends to go off slighty when applied yet should still come out when required.

 

Pritt Stick is also good to secure carbon rods in place on elevators etc...again will come out with moderate force

[Peter]

As a long time expert at making clumsy landings I can recommend this method for extracting broken horns:

 

1. Estimate from the horn geometry where it would exit the bottom skin of the flap if the hole went right through.

 

2. From this point on the bottom drill a very small hole (about 1mm dia) until the end of the broken horn is felt.

 

3. Insert a small probe (wire, small drill, very small screwdriver etc) and push the broken horn out.

 

4. If it is stuck in with epoxy, loctite, paint or anything else then warm the broken brass end of the horn with a very small soldering   

iron. It just needs to get warm enough to soften the adhesive so about a minute is usually enough then push from the bottom again.

 

5. Bingo, broken bit out, hole still the same size and all the repair work needed is to insert a new horn and the fill the tiny hole in the bottom of the flap. A small bit of balsa is good for this because it is easy to remove for the next time the horn is broken!

[Gary B]

Ah, that would work on a Tragi Cluster (the horns are threaded but glue into plain holes I think), the Xplorer has metal threaded female inserts built in to the flap structure so they have to be unscrewed.

 

I've bent and broken the link rods before so I upgraded the links with Wixy's stainless parts and it looks like I've moved the weak point to the horns!

 

Think I'll take the overfly option next time!

[EssexBOF]

I was plagued by this on the Shadow I use. Now I make sure the horn is not tight on the thread when installing, by running an M3 tap down the thread. Plus I now use plastic kwik links so if I am slow in getting the flaps up, the kwik link goes and just have to screw on a knew one. They take normal flight loads no problem.

Now use this method all the time

[Gary B]

That's an interesting idea.

 

The servos must be tough because I've never stripped any gears.

[EssexBOF]

That's an interesting idea.

 

The servos must be tough because I've never stripped any gears.

 

 

Yes they are Turnigy 712Gs, never had a problem with them since changing over to them, just broken horns

 

I used a slightly different method to extract the broken horn in drilling a 1.5mm hole down the middle and then tapping in an old 5 sided broach from my old toolmaking armoury, into the hole and unscrewing that way.

[Gary B]

Haven't heard 'broach' for a while, my dad was a miller and turner.

 

Kind of reamer?

 

I meant my servos when I mentioned gear stripping, they're Graupner HVS 930 BB MGs.