Hollow molded sloper build Q's - RC Groups
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Apr 27, 2003, 04:02 PM
Registered User
Mattebox's Avatar

Hollow molded sloper build Q's

Iím finally getting around to putting together my 2M hollow molded sloper and had a couple of questions.

1. Whatís the general consensus on gluing servos into the wing? I was planning to reinforce the wing skin with a CF patch and then gluing the servo in with 5 minute epoxy and Cabosil, but Iíve heard that some people use RVT silicone. I want the servos to be in there solid, but still be able to be removed (if needed) without damaging the wing skin.

2. The wing has four servos but is 2 pieces. Since I donít have a center panel I canít wire everything up to a single D-sub connector to mate to a wire harness in the fuse. Each wing panel will have to have its own combined aileron/flap connector. Whatís a good, small 4 or 6 pin connector (polarized and locking preferred) that I can use for this purpose?

3. The plans call for the flap horns to be on top (for the bottom hinged flaps) but there is no cutout through the wing for this. I hate to have to cut through the wing so is there really any great advantage to having horns on the top of the flaps? Does it affect servo performance or flap deflection (Iím hoping to get to 60 or 70 degrees. With top mounted horns the servos will be pushing instead of pulling when deploying the flaps but I thought pulling was the better condition for the servo?

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Apr 27, 2003, 07:20 PM
Registered User
1. If your wing skins are pretty soft add a carbon patch like you said. It all depends on the servo when it comes to installing in the wing. If your uing a good quality metal geared servo I'd glue them in with 5 min epoxy and micro ballons. Make sure you sand the servo/skin and clean with rubbing alchohol. The more micro ballons you use the easier it is to remove the servo. If your using plastic geared servos I'd shrink wrap them in because more than likely you will be yanking them out more than once to replace the gears. I wouldn't use silicone!

2. 4 pin Deans or the 6 pin Multiplex plugs work great for auto connecting wing panels.

3. flap horns on the top make for a less slop flap linkage. It's very easy to do and there is less drag since the linkages are in the wing. Just use a Dremel!

What model are you working on? It's too bad this forum is 99% foam
Apr 27, 2003, 07:21 PM
Scale Nerd!
Wight's Avatar
Servo fixing:

There was a good article about this in Quiet Flyer International (QFI) a UK title. (Now merged with an electrics title, and a poorer mag for it.) While recognising the silicone was good in the sense of extracting servos later, the problem pointed out was that if a servo loosened on a hard arrival, you had no way of bonding it back slopeside as the only thing that'll stick to silicone is more silicone. The method a lot of UK racing guys use, (and which I've tried several times with excellent results) is to wrap the body of the servo in tape, then epoxy it in place. The servo is just as solidly secured, however if you have to remove it (stripped gears for example) you just slit the tape, peel it open and lift out the servo. Some servos (volz) come with optional ply mounts for fixing into wings. Definitley reinforce the skin. Some people make up a balsa "rib" to bridge the top and bottom skins each side of the servo mounting area. If you're going to DS, that mightn't be a bad idea. (My only moldie is an F3J ship so I didn't bother with the "ribs")

Wing servo plugs:

Multiplex do a 6-pin connector, which they also use for their electric motors/speed controllers, etc. (Using 3 pins per lead in that application) They are polarised, gold plated, and work fine.

Multiples also do a wing lead set that includes two 5-pin gold palted connectors. Again these have polarity. These are designed to be fixed in the root of the wing and the root of the fuselage. When you push the wing on, the connector automatically connects. If your wing is this of this type I definitley recommend them. I've used them in 4 different models and to be honest in any situation that I can use them I will. Makes rigging/derigging VERY hassle-free.

Horns on Top
This is to do with the geometry of the hinge being on the bottom. The further away the pushrod connection is from the hinge line, the less aerodynamic load is transfered to the servo. Good old law of the lever!
Apr 28, 2003, 12:19 AM
Registered User
Mattebox's Avatar
Thanks for the info guys. I'm working on a Valenta Swallow (although ironically I just finished an XR foamie wing the other day).

I'm using HS-85MG's on the flaps and nylon geared HS-85's for the ailerons and v-tail. I'll also probably put a hardwood spacer block between the servo and the carbon spar to make the servo extra secure.

I've heard of those Multiplex connectors but I was hoping someone might know of something comparable from an electronics supplier like Mouser.

As for the top flap horn, the reason I'm hesistant to do it this way because I'd have to cut through a carbon subspar (or something like that) at the hinge line. It is normal to do this? Also, having the horn further away from the hinge (on top) increased the leverage and reduces the slop, but this is usually at the expense of deflection travel. Do you think I'll still be able to get 70 degrees of flap with this setup?
Apr 28, 2003, 07:06 PM
Scale Nerd!
Wight's Avatar
Regarding the horn on top, if they say do it that way, I would. See http://www.f3x.com/zenith/zenithbuild.htm for an example of how to set up a top-driven surface. (flaps in this case too.) You need to have the horn set up at a very shallow angle to get the flap angle you need. I have this aircraft (called Corrado in Europe) and I agree it's fiddly to set up. I had to cut a half-channel in the trailing edge "spar" (wood in the Corrado) to let the rod/clevis pass through. This should make no real difference to the strength. If you can get away with just a small hole, even better. (By the time you break the wing due to this material being removed, the flap will have LONG separated in flutter, especially if it's bottom-mounted.)

I'd go top-mounted horns, definitley. It might be a pain, but it's worth it. BTW I know how you feel r.e. cutting through the top surface. I remember being absolutely terrified drilling the holes for the horns in the surfaces. Talk about a "one chance only" situation!

r.e. servos, buy the absolute best you can afford. There's no point in having a really good airframe without the servos to go with it. Take time with the linkages, make sure they're absolutely slop-free. Metal horns, clevises on threaded rod with locking nuts, etc. (Ball-links are suppossed to be best, I must admit I've never tried these....) A really well-fitted molded glider is the ultimate flying experience from a pure performance point of view...