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ARG! Control Surface Horns - Help

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Old 07-19-2010, 10:11 PM
  #1  
SeamusG
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Default ARG! Control Surface Horns - Help

Did ya ever think that ya had everything under control - until that is - you realize that you DON'T have everything under control?

I'm reconstructing a ShowTime 50 ARF (there's a thread in the Crash-n-burn forum). Since I was gonna upgrade the original Hanger 9 control horns I threw the original horns out. Makes sense. Aile &Elev standard 1 horn per control surface. Rudd is a pull-pull.

I WASplanning on using the Dubro HDhorns (pic 1) for the Aile and Elev. Well, that is until I realized that I need 2" long 6-32 bolts and the ones provided are only 1 1/2"long - OOPS. Nope, can't find 2" long socket head 6-32 bolts.

So, time to check available nylon horns. See pic 2 (yea, the measurements are very accurate). OOPS (getting a bit redundant don't 'cha think?). The overhang of these hinges is a whopping 3/32". Ineed 3/16" and 1/4" overhang. Drat.

OOPSagain (yea, that's 3). The orignal horns were tightened down so hard that the soft balsa was seriously dented. Little did Irealize that it was necessary to make sure that the face of the horn was perpendicular to the center line of the control surface. Also, during the reconstruction I added 1/16" ply inlays to provide a hard (aka won't compress under pressure) surface to support the horn. But these ply surfaces are at quite an angle to the control surface centerline.

OK peanut gallery, how would you approach selection and installation of control horns?

Btw - though this is a 3D-capable plane my use will be along the lines of a pattern plane - control throws won't be anywhere near the Hanger 9 high rates.

TIAfor your advise
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Old 07-19-2010, 10:32 PM
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Default RE: ARG! Control Surface Horns - Help

Your control surface images still aren't right. The pivot holes should be perpendicular to the hinge point. Not the leading face of the horn.

So, if you have decided on the horn in image one - the clevis/connector hole in the arm that rides up and down the bolt should be perpendicular to the hinge pivot.

The only time this isn't so is if you want to build some Ackerman Effect into a pull-pull system at the hinge point instead of the more usual servo end, or some aileron differential permanently built into the control horns (no one does this with the computer radios available now).



If you are crushing the balsa you can drill it out with a 1/2" bit and then epoxy in a 1/2" birch dowel and drill THAT out for the horn. It won't crush. Alternatively, you can inlay plywood (not "lite ply") but that's more work.
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Old 07-19-2010, 10:41 PM
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Default RE: ARG! Control Surface Horns - Help

Charlie - you just made my point for me. My question is "how would YOU resolve this problem"?

My pic 2 shows what "would" happen if you just plopped standard control horns down on the control surfaces as they currently exist. I wouldn't want to fly the plane if I just bolted those horns on like in the pic.

Please don't assume that I want to use the Dubro stuff. I have a Killer Chaos that needs covering that's just begging for these 'cause the control surface top and bottom are parallel and only 5/8" thick.

What changes to the control surfaces would you make? What other horns would you use? The one in your pic suffers the same problem as the Dubro horns - bolt is way too short.
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Old 07-19-2010, 10:50 PM
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Default RE: ARG! Control Surface Horns - Help

Our local Agway (farm supply store with a garden tractor & chainsaw repair shop) sells hex head cap screws in all kinds of sizes and lengths. 4-40, 6-32, 10-32. Metric, too. I would take the assembly and find a suitably long bolt.

Or, I would shop at a place like Chief Aircraft and get the proper horn for the size model I am building. They come in sizes. ;-) I like the Sullivan offerings over the DuBro, but that's just a personal preferance.





I just assembled an 82" Giant Super Sportster and it had the same type control horns as a .40 ARF . . . just 3X bigger.

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Old 07-20-2010, 06:49 AM
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Default RE: ARG! Control Surface Horns - Help

My personal opinion is do it the easiest way and fly it. The plane is only fifty some inch wingspan. If you are really concerned about the geometry(equal throws each direction, etc.) just compensate through your transmitter set up. On a rebuilt plane(and I've done a few), there are probably going to be other airframe misalignments that affect the plane more than the control surface hinge line being slightly misaligned from the pivot hole of the control horn.
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Old 07-20-2010, 07:57 AM
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Default RE: ARG! Control Surface Horns - Help

I would use this on the rudder:

http://www.shopatron.com/products/pr...=881/101.0.1.1

and I would use standard horns on the elevators. Get them as close as you can to the centerline and you'll never notice a difference - and if you DO, it can easily be compensated for by rotating the servo arm off-center
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Old 07-20-2010, 12:42 PM
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Default RE: ARG! Control Surface Horns - Help

Thx Mike. Dubro has 2 different parts packages that fill the bill. #881 has both the horn(s)and the pull-pull wire / crimps. #880 (at half the price)has the horn(s) only. Since the previous owner didn't double loop the ends of the wire I got the full package.


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Old 07-20-2010, 01:03 PM
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Default RE: ARG! Control Surface Horns - Help

Hey Charlie - I missed your updated post!

What I like about both the Dubro pull-pull package AND Charlie's posted pics of the Sullivan parts is that they both have crowned washers that sit flush against the control surface AND allow for the angle of the control surface. The original Dubro horns pictured early in the thread DO NOT have this feature therefore require a control surface that is flat.

Good information. Thanks.

PS- ANDi like Charlie's suggestion about using a dowel to support these types of horns. I'm thinking that one end could be counter sunk if the control surface is too thick for the length of available bolts.

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Old 07-20-2010, 01:21 PM
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Default RE: ARG! Control Surface Horns - Help

OK- a rookie pull-pull question - how much does it REALLYmatter that the hole of the clevis mount of the horn is over the hinge line? I'm thinking about the condition where it's located behind the hinge line on both sides.
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Old 07-20-2010, 01:30 PM
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Default RE: ARG! Control Surface Horns - Help

Yet another rookie pull-pull observation - I need a servo arm that is the same length as the distance between the control horn attachment holes.

Pftzzz - imagine Bill the Cat coughing up a hair ball the size of a softball and that's how I'm feeling right now. [:'(]
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Old 07-20-2010, 01:38 PM
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Default RE: ARG! Control Surface Horns - Help

You can make your own control horns out of plywood... knotch the control surface for some 3/32 plywood, cut and shape your horn and epoxy in place.

Or, who says you have to use the holes that are already in the horns? Move the horn to where it should be then drill your own holes.
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Old 07-20-2010, 01:47 PM
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Default RE: ARG! Control Surface Horns - Help

The servo arm and the control horn do not need to be the same length.

Also, there is a thing called the Ackerman Principle (Google it) that says you are better off with the control arm holes slightly behind the pivot point to keep the cables from getting too tight
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Old 07-20-2010, 03:07 PM
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Default RE: ARG! Control Surface Horns - Help


ORIGINAL: MinnFlyer

The servo arm and the control horn do not need to be the same length.

Also, there is a thing called the Ackerman Principle (Google it) that says you are better off with the control arm holes slightly behind the pivot point to keep the cables from getting too tight
There was a discussion here on RCU with diagrams that was good if somebody remembers where it is.
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Old 07-20-2010, 03:10 PM
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Default RE: ARG! Control Surface Horns - Help

Here it is: http://www.qmfc.org/school/ackerman.htm
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Old 07-20-2010, 04:37 PM
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Default RE: ARG! Control Surface Horns - Help

Thanks for the link. Em - 1/16" - 3/32" - good to know.
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Old 07-21-2010, 07:11 AM
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Default RE: ARG! Control Surface Horns - Help


ORIGINAL: SeamusG

Yet another rookie pull-pull observation - I need a servo arm that is the same length as the distance between the control horn attachment holes.

Pftzzz - imagine Bill the Cat coughing up a hair ball the size of a softball and that's how I'm feeling right now. [:'(]
Check this thread out for pull-pull schematics:

http://www.rcuniverse.com/forum/m_92...tm.htm#9226186

The schematic that I attach here is just an additional idea to solve the elevator and ailerons, if you want to be precise.
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Old 07-21-2010, 08:44 AM
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Default RE: ARG! Control Surface Horns - Help


ORIGINAL: LNEWQBAN

The schematic that I attach here is just an additional idea to solve the elevator and ailerons, if you want to be precise.
LNEWQBAN- you cheated - you looked in my basement! I've modified the elevators and ailerons as you have shown in your schematic. Each is 5/8" thick which gives me plenty of room for adjusting the horn's "hole height". Each cutout includes a 3/32" piece of ply on both sides. To align the "horn hole"at the hinge line the screw center is 18 mm back from the LE.

Btw - nice color choice on the schematic.

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Old 07-21-2010, 08:52 AM
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Default RE: ARG! Control Surface Horns - Help

ORIGINAL: SeamusG

Btw - nice color choice on the schematic.
I am just trying to learn from your several posts on covering works.
Remember that you were teaching me several tricks on Ultracote not long ago.

How did you cut the recessed holes?
I believed that it could be done with a spade type wood bit.
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Old 07-21-2010, 09:14 AM
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Default RE: ARG! Control Surface Horns - Help

No holes - a slot. Since there were already 3 mounting holes previously drilled through the surface that were filled with finishing resin / micro-balloons putty Iwanted to provide a broader base for more support (don't know if it's needed or not). Ihave this POS Harbor Freight "tablette" saw and used it to make the initial cuts. I followed with a piece of hardwood with #80 grit on one side. Did a decent job. The ply inserts are 22 mm x 28 mm.

Hope it works. Covering is gonna need some attentiion. My current thought are to add some soft balsa blocks at the rear of the openings (easily shaped to conform with the adjacent surfaces). Hey, just practicing for that "perfect" build. Yea - right.


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Old 07-21-2010, 06:01 PM
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Default RE: ARG! Control Surface Horns - Help

FYI- Ijust unearthed the original Hanger 9 hinges for the ShowTime 50. They have a full 1/4" off between the line of holes and the front edge of the horn "foot". All the other horns my box for 40 - 60 size planes have 3/32" offset. Too bad none of my LHSstock Hanger 9 parts.


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