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Scram

Wingtip repair

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Scram

Never having done a surface repair on a wing before, I'm wondering on what is the best method.

I have 200g/m2 carbon and laminating epoxy available as well as glass cloth.  The tip has been repaired before by a previous owner.

The tip is essentially straight with some small protrusion somehow on the top side.  The rear spar at the crease point is crushed and is separated further down (up?) the wing but I can cyano that.

20190117_113853.thumb.jpg.9172bed419db39ba3f7b9ec55eae5bd1.jpg20190117_113837.thumb.jpg.0fd0970270c6f934937ca1e887470bbe.jpg

20190117_114114.thumb.jpg.71436ba225817e93001baf5437170b33.jpg20190117_114048.thumb.jpg.532eee0be892bbd57856f76839cebc22.jpg

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isoaritfirst

Easy way,

stuff the broken area with dry carbon tows, allowing them to seperate when you push them into place.

Push them through the break hole or through the TE. 

spread them out like cobwebs inside the broken area.

When all in place carefully flood the area with cyano and after a short time kick it to stop any further movement. But allow it some time to wet out the carbon befor you do that.

 

Result should be a solid web of inner support. (providing your wing (foam) doesn't react to cyano.....)

 

Once solid patch the hole with a small amount of body filler.

 

More elaborate method

Cut out the damage and make ply of carbon cloth using 2 or 3 pieces. set at under pressure and keep warm. biase the weave.

fit the replacement piece in with butt joints and cyano, you can add support pieces underneath but not necessary.

run a trickl of epoxy over it to fill any very small cracks and give a area that can then be sanded back to flush fit the surfaces.

No inner strength needs be added. 

 

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Scram

Thanks Mike.

I like the simple solution.  Think I would do well to remove the tip aileron section so then I can replace the crushed rear spar section after infilling with carbon tows.  I think the foam may be cyano safe as we poured some in at the slope and the foam is not melted.

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isoaritfirst

Just fold it back out of the way

 

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Scram

Followed Mikes "simple method" advice.  Now have a much stronger wing tip.  Just needs some paint now and stick the tip aileron back.

20190119_114606.thumb.jpg.8d4836e9f849fa2ec7c6657bfab88dca.jpg

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Scram

Seems like I was fortunate in not flying my Crossover last Saturday.   🤔

During structural strengthening work done on it this week the left aileron servo proved to be duff.  It will work for a few cycles and then ceases up, getting hot.  Could have been difficult!!

I had it out and cleaned up all the gears but the problem is not there.  Fortunately I have a new one.

I'm wondering about one of the flap servos which sits there going:  yoing-yoing-yoing-yoing.........

as if it is hunting for centre. ????

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Kyri

Great work on the wingtip, looks excellent. I liked reading this thread as there are lots of ideas and  tips for a very common problem, good to see the outcome as well.

Regarding the servos. I had issues with some servos that I got in a used plane (so already had years of use in some cases). On two occasions, I found a servo stop working - fortunately, at home. If it happened in the air it would have been interesting. In my case there were two causes, one of them was a worn out motor, (the brushes weren't even there, but I wonder if the motor ever had brushes or just the copper spring against the comm). The other was a burnt component on the board. I managed to get hold of a couple of replacement inners (motor plus board) as the gears were ok. It is worth keeping the gears from the one you took out. 

For your flap servo depending on what it is, you could check the pot, which might be dirty, I don't know if you can access the track and clean it. 

It might be best just to change it out if in doubt, its a nice plane!

 

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Scram
45 minutes ago, Kyri said:

Great work on the wingtip, looks excellent. I liked reading this thread as there are lots of ideas and  tips for a very common problem, good to see the outcome as well.

Regarding the servos. I had issues with some servos that I got in a used plane (so already had years of use in some cases). On two occasions, I found a servo stop working - fortunately, at home. If it happened in the air it would have been interesting. In my case there were two causes, one of them was a worn out motor, (the brushes weren't even there, but I wonder if the motor ever had brushes or just the copper spring against the comm). The other was a burnt component on the board. I managed to get hold of a couple of replacement inners (motor plus board) as the gears were ok. It is worth keeping the gears from the one you took out. 

For your flap servo depending on what it is, you could check the pot, which might be dirty, I don't know if you can access the track and clean it. 

It might be best just to change it out if in doubt, its a nice plane!

 

Thanks Kyri.

I will certainly keep the gears.  Not yet sure if I can get further inside these servo's - MKS DS6125mini.  They were expensive servo's - not sure I can get another though I have not looked yet. 

EDIT:  Looks like the likely replacement is even more expensive:   MKS HBL6625mini at £120 each ..........  aaaar!!

EDIT2:  Looks like the less costly HV6130 would be a direct swap into the RDS servo frames.  Only £66 each  🤔

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Kyri

Mine were MKS's too, exactly the same servo's.

As I have learned, they are powerful servos and known for this type of thing. If your flap servo is the same then you are getting an early warning and should swap it - an alternative that I have found is the kst DS135 at £23 from hyperflight, the geartrain is not quite as tight as the MKS but not bad at all, especially for the price. Different output spline but maybe you can make them work?

regards

Kyri

 

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Scram

B***er!!

The other aileron servo has just failed too!!

Thanks for the suggestion Kyri but I might be in a pickle there.  The plane is arranged with RDS linkages and the servo frames and actuating link are specific to this servo which is no longer available  😪

As you say the KST DS135 looks suitable.  I have contacted Hyperflight to check if it's a straight swap . . . . . . or not ??  Not enough dimension details shown.

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Kyri

The output spline is different, but you should be able to get the rds attachments for it I am sure? 

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simon_t

Just remember if you replace the 6125 with a different servo, that servo will have a greater travel - the 6125s have less rotary range for the same stick movement as most other servos (including 6130s)

Simon

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isoaritfirst

Have you made the surfaces stuff during repairs. 

Your servo problems sound like they are working too hard. 

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Scram
On 19/01/2019 at 16:28, Kyri said:

The output spline is different, but you should be able to get the rds attachments for it I am sure? 

Cheers.  I will try.  I suspect the only likely source will be Aer-o-tec, the plane maker ??

23 hours ago, isoaritfirst said:

Have you made the surfaces stuff during repairs. 

Your servo problems sound like they are working too hard. 

No.  surfaces are all free and the first one removed still locked when out of the wing.   However . . . . . . . .

. . . . . taking the first one out I found the wires were glued to the spar  :ermm:

. . . . . when I took the second one out, the back (front wrt the wing LE) was glued in with cyano.  I must have been too liberal running that pesky thin cyano in to reattach the rear spars.  It goes anywhere that stuff if you's not careful  :frantics:

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But having dismantled the 1st servo, there's no sign of cyano penetration inside

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and on the second one, there's no sign of cyano anywhere near the casing joints.

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Could fumes get in and damage the pot, I wonder?  Does not seem very likely as the pot seems to be well sealed in.

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I will have to try the servo on the tester again, in this dismantled state and if still duff, I will see if I can get the pot out but I've got little expectation of being able to clean it.  As the servo doesn't work anyway I've nought to loose.

EDIT:  Taken servo 2 apart, cleaned gears and tested motor without anything.  NO GOOD.  Intermittent operation and with watt meter in circuit found it would draw up to almost 4A doing nothing but get hot!!  So that's a dead one.

The 1st servo though, on reassembly seems to operate perfectly on the servo tester, in oscillating mode I cannot stop the output shaft rotating with an arm on, by hand.

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Scram

Decided to replace all servos with the KST DS135 minis, and bought some replacement arms from Ober, the original RDS supplier.  Bit horrified at the cost of these just 4 arms/shafts: €65.88 but it is still the least cost way to get this plane safely in the air again.  It's a bit too battered to justify maybe £400+ on replacement MKS gear.

I was warned by Ober that the output gear position is different by 0.1mm!!  Oh dear, I don't think that will cause a problem  😉

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rwhitt

These MKS minis need to be regulated, when they first came out they were getting fried and MKS recommend using the MKS sbecs to keep the voltage down.

If you havn't ordered already...there is another possible option 

Russell

 

 

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Scram

Thanks Russell.  I'm only running 4.8v from 4 cell NiMH so it's not that. 

Most likely too many duff arrivals.  :frantics:

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rwhitt
10 minutes ago, Scram said:

Thanks Russell.  I'm only running 4.8v from 4 cell NiMH so it's not that. 

Most likely too many duff arrivals.  :frantics:

Ah 😆👍

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Scram

The replacement RDS rods to fit the KST servos arrived the other day - very quick delivery from Germany.  However, I was a bit perplexed to find the steel parts with the bend were separate from the alloy parts so I have to fix 'em myself.  How to get them the right length?

I know the servo is supposed to be able to slide a little in the mount and this is to allow for the box in the surface effectively moving backwards and forwards a little.  Somewhere there is a video showing this.  But how should I allow for this?  I put the old rods in place and moved the aileron to see how much movement and where it occurred. The movement was very little so if I make the new rods the same lenght as the old, I should be near enough.

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The old rods have the shorter alloy part and the steels are being secured using Araldite Standard epoxy (24h)

Before fixing these I installed each servo in the wings but found they were held tight by the clamps, particularly the rear one (actually the one nearer the wing l/e) which proved to be a little thicker than the ones on the MKS servos. So I made shims to go under the clamp.  I also had to file the corners of the alloy mount which would bind inside the clamp.  Finally, I had to fit the RDS rod on the servo in place in the wings to ensure all would be free as the location of the output gear is 0.1mm different.  No problem on 3 of the servos but the last one became very stiff so I had to relieve the mount a little to free up the servo.

Just waiting for the Araldite to go off now.

I found also that the KST servos go in opposite direction to the MKS and I'm sure I will have to do some setup revisions to the Taranis program.  Will I be ready for Saturday??  :ermm:

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Brett82
1 hour ago, Scram said:

Will I be ready for Saturday??  :ermm:

I hope so...

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