Top model control horn installation

[ahdofu]

Well after a 6-month hiatus I'm back on putting together my Indian V glider and have a question. The control horns, as supplied by Top Model, are small pieces of hard fiberglass like material (see pic below). The manual is cryptic but the installtion appears to suggest that one cuts a slot inside the control surface, inserts the horn and glues the horn in place. The horn itself does not have much of a surface area for the glue to stick to. The whole thing looks too flimsy to me but being my first glider, I may be overreacting. Anyway do these things fail or are they trouble free? Also what do you use for glue? CA or epoxy?
Thanks,
Matt

 

[Konrad]

The process is fine. Do make sure that you remove the covering about 1mm all around the horn. Mask about 1.5mm to 2mm around the horn. then make a 2mm epoxy fillet around the horn. (This stabilizes the horn and seals the covering. Before the epoxy sets remove the mask and allow the epoxy to flow onto the covering a bit.

CA is too brittle and will crack and fail at sometime in the life of the ship.

P.S.
Make sure the clevis pin hole is over the hinge line (@90°).

 

[ahdofu]

Thanks Konrad. Is 5-min epoxy good enough for this purpose or does it need to be a longer cure epoxy?

 

[Konrad]

NO! I don't like 5 min epoxy for anything! Now with foam safe CA I don't even like 5 min epoxy for field repairs. 5 min epoxy isn't very stable. Just what you don't want on a control feature and one with limited contact area. I'd like to see 15min or 30 min with some Cabosil mixed in for stability. Cabosil isn't needed but is nice. If you have some fine milled glass filler that would also work well.

 

[ahdofu]

Thanks. What about the servos? They're to be glued as well. The manual suggests that epoxy be used which is annoying to me. Do you still use the same epoxy as before? Out of curiosity do folks ever find the need to replace servos on a glider?
Matt

 

[Konrad]

Top models supplies urethane foam blocks (P/N 2-4) to be glued to the top skin to hold the servo captive, they are glued in with epoxy (I guess 5min would work ok, lots of area and it will be stronger than the blocks).
I would add a dab of silicone adhesive with some dental floss imbedded (to act as a cut wire should it be needed) to the contact side of the servo, just to keep the servo from falling out.

For the fuselage servo tray I’d use real epoxy 30min and even think about using some 2oz glass cloth across the joint. (Yes my landings are that bad)!

Servo life is low on gliders. Not from vibration issues but rather gear train failures, as we land on the belly, often resulting is contact with the control surfaces.

 

[Wayne]

To give you an idea, I prefer that style control horn on most anything except maybe a depron plane (thin foam sheets). They work great. I have used a wide array of glues and epxies and all have been fine for this task. I actually like to use epoxy as it makes a nice fillet to distribute the load past the cut area. Never had an issue.

 

[Konrad]

I don’t know if I’ve mentioned this before, I see a few Gotcha in the manual.

First,I don’t like to make a solder extension on the servos. This make replacement of the servo a pain. I like to use plug in extension that I then tie some dental floss (unwaxed) as a safety keeper.

Second, the manual shows two configuration of how the tail boom is seated in the fuselage pod. Top Models wants the front end of the boom to be seated on the hatch relief boss (1A + 1B =0). (See detail on page 4). That means that there will be a slight v shaped gap going aft. Make sure to fill this space with epoxy.

 

[ahdofu]

Konrad,

Hmm... I am glad I asked this question. The kit provides wooden blocks that are glued to the servo tangs. The wooden blocks are then glued to the surface and that how the aileron servos are mounted. The kit does not have any urethane foam blocks. Is this a generic foam that can be found at any hardware store or is Top Model the only source?

I could not quite follow how the dental floss trick works. I gather the floss goes in between the servo and the foam. If you want to remove the servo, you pull on the floss and that cuts through the silicone glue. Also if the foam gives and the floss remains attached to the wing, then the servo won't fall out. Do I have it correctly understood?

I thought about using a servo extension but couldn't as the holes for the servo wires are tight. Finally ended up soldering the wire. Once I am done with the winds, I'll follow up with the fuselage.

Matt

 

[Konrad]

OK, My Top Models blocks have all been urethane (wooden would be fine). Do not glue the servo to the blocks. Glue the blocks to the inside of the top wing skin (remove foam as needed). With "special glue" glue servo contact side to inside of top wing skin. Embed dental floss as cut wire in this glue.

Dental floss safety is to keep the connectors from unpluging.

The servo connector are designed to be de-pinned. Just lift the retention tab and pull out the contacts.

Mefisto build (BLEJZYK)

Yes, that was an error I made, no key for the back of the slip on nose cone. I had to adjust with some tape. Lesson learned. Looks super nice, glad you got the glue to cure. I remember gluing on the nose on mine, that is a big step!

forum.alofthobbies.com

 

[ahdofu]

Thanks Konrad. Since the servo is being glued directly onto the skin and not the blocks, then why even have the blocks?
Matt

 

[Konrad]

Rotational support. With the blocks you don't need to use much special glue. (This is a big plus if you have ever tried to cut a servo free). But to your point there are many, many ways to anchor the servo to the wings. With a bit higher class of glider I like to use servo mounting trays/frames.

Servo Frames

High quality servo frames that work great. Makes for easier servo replacement, and bearing mounted trays greatly reduce play in the servo for better centering and

alofthobbies.com

 

[ahdofu]

Konrad,
In examining the servos I see that they also come with screws. Is there a reason for not using screws to install the wing servo as opposed to glue? I figure the servo can be screwed to the wooden blocks and the wooden blocks would then be glued to the wing surface. May be this setup is too flimsy. Thoughts?

 

[Konrad]

That's fine. But how are you going to remove the screws should the servo need to be replaced? Most of us use wing servos. these have the mounting tab properly oriented for mounting in a wing.

 

[ahdofu]

In this case there is barely enough room to use a small phillips driver bit with a needle nose pliers to tighten/loosen the screw.

 

[Konrad]

This is suppose to be a hobby not a source of frustration! This is why we have wing mounted servos with the mounting flange rotated 90°. Unfortunately this feature is market at a higher price point (it is well worth it). There are some servo brands that do supply a 90° bracket in the nominal 9 gram class of servo.

KST X08H Servo - 2.8Kg (38.88 oz in), .09-sec - Wide Voltage

KST's new tiny alloy servo, the X08 is just 8mm wide and weighs just 8 grams, but it packs a real punch!

alofthobbies.com

Emax ES3352 Thin Digital Servo - 2.8Kg (38.88 oz in), .10-sec - 12.4 Grams

Emax delivers a quality thin wing servo with a great price!

alofthobbies.com

 

[ahdofu]

Yes I should have gotten the KST servo now that I see the installation challenge. The Emax servo pretty good too. Sigh ... it is certainly not my first time to have regrets afterwards.

 

[Konrad]

There really isn't too much wrong with the glued in system as shown by Top Models. Just don't use too much "special" glue. KST are great, but to my mind too good for a plane like the Indian V. Save the budget for the next (first) high performance glider.

 

[ahdofu]

Out of curiosity what should be my next high performance glider?

 

[Konrad]

You'll need to tell us what you are looking for. Fly the Indian V, see what she does or doesn't do for you, and then we can give you some direction towards your next soaring machine.