TT2

My Feedback: (13)

I'm looking for opinions on double truss control horns. I'm getting ready to have a bunch of these cut out for a kit that I'm producing with sheeted foam wings and tails. It seems to me that they have several advantages...mainly that a hard point is not required and they may be installed after the surface is sheeted and covered. I plan on fabricating them out of 3/32" G10 fiberglass. I have designed them to extend to the center of the hingeline when using 3/8" balsa stock for the hingelines, be exactly 1.25" vertical from the center of the hingelines, and drilled for 4-40 thru bolts to accept a Neslon ball link. I will most likely offer these, and 3", 4", 4.5" and 5" double truss rudder horns separately from the kit.

All in all I think they are a much better system than some of the other commercial large-scale horn offerings. Am I missing anything? Opinions?

-Tom

the-plumber

I used the Nelson double-truss hardware until he stopped making it, and started making my own. I use the same gage 2024-T3 aluminum, ball bearings, etc.

Double truss is ideal because it eliminates the rotational vector associated with conventional off-set connections - all vectors are on the centerline of the fitting.

If you don't plan on installing hard points, what do you think will transmit the control horn load to the flight control surface, the _sheeting_ ?

Or did I miss something ?

mglavin

My Feedback: (31)

Sounds like Tom wants to use a double truss control horn verses a double truss servo arm Fred. As long as the control arm is fixed in or to the wood bevel stock I wouldn't have a problem with this idea. Simply gluing into the foam may suffice though.

I like the double truss stuff too. From a mechanical and or structural perspective there is nothing better IMO.

TT2

My Feedback: (13)

The front of the embedded horn section would be in full contact with the back of the beveled hingeline stock...the hingeline stock would remain uncut. The embedded part would carry through to the bottom sheeting. The resulting surface area of the embedded assembly would be greater than a normal hardpoint, plus the added benefit of contacting the hingeline stock and BOTH sheeting surfaces...not just the bottom.

Click on pictures for full size:

[link=http://home.centurytel.net/rcstuff/edge_540_50cc/images/horn_01.jpg][/link]

[link=http://home.centurytel.net/rcstuff/edge_540_50cc/images/horn_02.jpg][/link]


The sheeting is blue, the foam core white, the hingeline stock green. The purple would be lite ply with matching lightening holes. I've seen people screw or 'pin' these types of assemblies together (and I've done it also on big horns) but I can't imagine the shear strength of good ol' thick CA being exceeded without ripping the entire assembly out of the surface anyway. If you installed them with polyurethane glue they'd be PLENTY strong yet much lighter than other options.

Obviously you lose adjustability, but who needs it? If you used a 1.25" horn you'd have 1:1 mechanical advantage...if you needed to decrease throw / increase mechanical advantage, go in on the servo arm holes. You shouldn't ever increase throw / decrease mechanical advantage by decreasing the control horn length / increasing the servo horn length (resulting in a mechanical advantage of LESS than 1:1) anyway, right?

The solid model shows the assembly being flush with the outer upper skin. For appearance sake you could remove some material from the assembly and backfill the slot with balsa, then sand smooth to the upper surface for a truly invisible installation.

Let me know what you think. If I had a bazillion of these things made they would be less expensive than anything else available.

-Tom

the-plumber

Looks like a plan to me.

Photo shows a 2024-T3 double truss horn embedded in the 5/8" ash half-round L/E on the aileron of my 33% Extra 230, during construction.

Robart hinge pins are recessed into the L/E at the radius, just like the prototype. I'd have to rip that aileron apart for those horns to fail. APITA to build, but about the strongest horns I could come up with.

TT2

My Feedback: (13)

Nice. I'm trying to reduce the PITA factor by supplying these things pre-fab. Aluminum (2024 or 7075), G10, or carbon fiber are all good candidates for a material.

-Tom

xtreem3d

My Feedback: (1)

http://www.dreamworksrc.com/catalog/...29e75c02c1f4f0

just thought i send it to you. pretty sure you can cut them cheaper but WTH,
steve
ps. where is osborn , MO ? i'm in st. louis.

Diablo-RCU

My Feedback: (1)

The only issue I see with this setup for ailerons is that if the servo is mounted upright, then the link going to the aileron horn will change angles and bind in the horn. If the servos are installed on the side, there is no binding problem.

TT2

My Feedback: (13)

xtreem3d: Thanks for the link...interesting. Don't get me wrong, they are nice, but...$6 an arm? I was thinking more along the lines of $10-$15 for two elevator, two aileron, and a rudder horn. Osborn is about 50 miles north of KC.

diablo: A ball link should be used between the horns and will allow for linkage deflection with upright-mounted servos. When sandwiched between the horn plates, a nelson 3/16" ball link will deflect about 20 degrees total. This should be enough to compensate for any changes in geometry. A 1/4" ball link allows for much more deflection. Either could be used...it's simply a matter of how far apart the horn plates are spaced.

-Tom

mglavin

My Feedback: (31)

Why not use the servo hatch access panels like those from J&B, the servo is mounted on the side. I have them installed in several GS aerobat models. Haven't used anything else since discovering them.

jbaccesspanels.com

TT2

My Feedback: (13)

SHAMELESS PLUG ALERT!

Or, if you want the best, you could use the ones from [link=http://www.fiber-lite.com]fiber-lite[/link]. 0.050" Carbon fiber...enough slot for 3D throws...cheap too. Definitely catching on in popularity...sold a BUNCH this week.

-Tom

mglavin

My Feedback: (31)

“Best” is simply in the eyes of the beholder IMO. I once fabricated my own hatch doors; they look to be exactly as depicted on the FiberLite site. While these are nice they require more labor, component fabrication and heat cycling to form fit them. The JB stuff is a complete kit, no fabrication and it utilizes a CNC wood receptacle and hatch door which allow for a distinct and sharp parting edge. These can also be contoured easily with a sanding block if need be. On all but small empennages with large couture changes they work fine. 3D throw is not an issue either.

Might I suggest the receptacle for the hatch door as JB utilizes for your products. I think you'll find there well suited for foam and balsa sub-structure. Composite or molded structures would require another approach, albeit similar.

TT2

My Feedback: (13)

I see your point. I may consider a surrounding plate that would be permanently mounted to the surface. That would speed up installation, but really it goes pretty quickly as it is once you have the process down.

Back to the horn subject...how do you feel about G10 as opposed to carbon fiber or aluminum? The G10 would bond easier with CA to the wood spacers for quicker assembly...much cheaper also.

-Tom