We've been using the same Veco control horn design for 70 years.  The only innovation I know of is the slider adjustment, and it is a poor design.  Its main vice is unwanted adjustment sliding—that destroyed another good stunt plane today. It's also heavy, has to be disassembled to adjust, cannot be adjusted accurately or repeatably, and is cumbersome to disassemble and reassemble for a takeapart plane.  The only improvement I can think of beyond some cool ones Derek Moran did is to print a set of slot fillers so a setting can be repeated and so the thing won't slide in flight.

Proposed requirements:
Lighter than the steel contraptions we're using
Input arm length irreversibly adjustable (can't slip)
Input arm length infinitely adjustable
Input arm length repeatably adjustable
Accommodates or, better yet, incorporates ball link functions
Retains arm length setting when disassembled and reassembled
Can be hinged accurately to a stabilizer
Have a hinge with no more friction than a 3/32" rod rotating in brass tubes
Connects two elevators unobtrusivey.

Anybody have any ideas? 

Howard,

Sorry to hear that a plane was lost. That is always terrible.

There are some plausible arrangements, but your list of design goals is very demanding. Usually, you can design things that are simple, lighter and reliable--but with few features (in the case of an elevator horn it would sacrifice adjustments and disassembly), or you can increase the weight budget and start adding functionality. True for full-sized planes and toy airplanes too. That said, if cost was not the driver, then some more intricate machine work can be done and better metals used. I don't think this is the place for anything plastic or composite.

I am reminded of the throttle linkage on the '42 Ford tractor....at least for your "easy to disassemble," and goes back together with the same adjustment.

Dave

Having said that composites are not a good choice for an elevator joiner, what would a composite joiner/horn look like? Here's a sketch of a non-take-apart-but-adjustable-radius unit. It would take precision fabrication because you NEED the dovetail groove unless you add more fasteners. And it has to be a really close-fit dovetail.

The isometric does not show the details of the horn or even include the arm. At that point I was still scratching my head and deciding if the joiner even needed the arms that engage the surface. I decided no, so then it was worth playing with the other details.

Not my favorite, but if ya just gotta have carbon to make it ProStunt, then....

This is the control horn from one of my Canards.  It is inspired by RC Aileron posts.  It needed to be adjustable and trimmable while hidden in the nose with no access.  It will work equally well on an elevator.  The post is a threaded shaft that passes through the elevator pivot but is not attached.  Top and bottom washers soldered to the post keep it in place but allow it to turn using a hex driver through the bottom.  This gives you throw adjustment. Centering adjustment is done at the flap end using the standard opposite thread pushrod.  I build all of my planes with the pushrod exiting the bottom of the wing with a hatch for access.

As Dave suggests, the problem with fixing it at the elevator end is weight. The obvious solution is a jackscrew so you can both easily adjust it, and also not be so prone to slipping. But it is always going to be heavier, and cutting away the fuselage to give access makes it less rigid, right in the critical area where it needs to be rigid.

  To reveal how far I am lagging behind the standard, I just used the old "multiple holes" method until fairly recently, which I occasionally used and then put right back to 1:1. Only my 2006 and 2020 airplanes had a slider horn. I have used it exactly *once* and the next step in trimming is to put it back to 1:1 as it started. I have altered my flap dimensions multiple times. So while it is a useful trim adjustment if you are doing something completely new, in fact, it is not something that needs fiddling on a regular basis, and in my case, it is only a temporary adjustment until I can alter the size of the flaps so I can put it back to 1:1.

  I think the answer, at least for electric, is to put the adjustment at the flap horn end, instead of the elevator end. This puts the extra weight near the CG rather than the tail, where it just kills you. You don't want to do this with IC models because if you do, the fuselage will fall apart pretty quickly from vibration, but you can put a pretty big hatch or extend the existing hatch back to the hinge line to give access on electric. That way the jackscrew doesn't not cost you ounces on the nose.

Note this is just like a Yatsenko Shark; you can't adjust it or do anything with the elevator horn, and you have to take the fuselage apart and look from the front to even see it. Unfortunately it doesn't allow much adjustment at the front end, either. This is pretty consistent with their approach, and as it happened with me, once I figured out what to do with the flaps, I didn't need much ratio adjustment either (or neutral, for that matter).

  Until then, having been very close witness to both major incidents that I know about - Jim Aron's 20-pointer pancaking itself at the NATs (which was repairable with extreme measures - like cutting the entire nose off and putting on another one) , and Chris' potential 20-pointer in Napa yesterday (which does not appear fixable in any practical way) -  be very careful to check the hardware pretty frequently. It *can* happen to you.

In Jim's case, it used the "single screw" that both held the ball link and slider. The ball bore directly on the horn upright, and the force of tightening the screw spread out the fork until it (presumably) let the ball come loose and slide to the bottom/"slow" end of the fork, which didn't give enough turn to pull out of the outside square.

  In Chris' case, it had a washer between the ball and horn upright, and the screw just loosened up - and then did *exactly the same thing*, it slipped to the bottom of the fork, right at the first corner of the outside square. I don't know about Jim's case, but Chris' nut was brass, which is prone to "creep" and has a low coefficient of friction against both the screw and upright. I don't remember if either case had a lockwasher to keep tension on it even if it backed off a little, which would give more time to catch it getting loose before it gave up completely.

    A really simple safety measure would be like Howard says Derek suggested - stick something in the slot as a filler to prevent it from sliding at least in the bottom, which is the dangerous way for it to slide. This can be just an another slider with a screw through it, cut to the right length to fill up the slot at the current adjustment setting. Or even just glue it, and break the glue loose. Since there is no load on it, it can be almost any material and use a 2-56 screw or glue and you would just have to remove it, and make a new one to jam up the slot.

    I note that the real evil is that when the slider slid to the end of the slot, it was too slow to pull out from 45 degrees. That suggest that the slot is far too long - you will never need to adjust it to the point you can't do a 45 degree loop. If you are making your own, unless you are doing something pretty crazy or wildly experimental, you only need a tiny bit of adjustment (mine is set to 1" nominal and I have moved it about 1/8" total experimenting with it), so just don't make the slot so long.

  Going forward, I am either going to make my adjustment with a jackscrew arrangement at the CG for electric, and go back to the "multiple holes" system for IC. For tomorrow's flying session I am just going to check the screw and stuff a piece of "Sterling-grade" balsa in the slot and glue it into the slot to jam it with Ambroid. Ambroid because I can easily clean it off later. This pending me making a new permanent "jammer" (probably spruce with a 1/64 ply backer and wrapped with thread, and slobbered with Ambroid.

    Brett



 

Howard,

Why do you want to use a ball link in the elevator horn? There is no need for multiple-axis movement, or whatever you call it, between flap- and elevator horns.
Ball horn takes more space (sideways), and when I look at the rather flimsy looking
slotted horns, the asymmetric variable load is yelling for something to get loose at some point.
In my own take-apart models I always used a home-made dural fork-thingy and a separate hardened steel pin that stays in place with a piano wire clip. I think it has lower friction and better long term stability than what a ball link would have.
I must think about the adjustable horn length, the filler blocks idea sounds good.
can you give some dimensions (horn length, fuselage inside width, amount of adjustability you need...), and I'll think about it. L

Quote from: Lauri Malila on April 08, 2026, 12:45:16 PMWhy do you want to use a ball link in the elevator horn? There is no need for multiple-axis movement, or whatever you call it, between flap- and elevator horns.

  Agreed and I do not use a ball link for that, either. I use a bent wire with a spring keeper (although it is nearly impossible to get it loose even without the keeper due to clearance). This is mostly for clearance purposes.  My slider is a separate steel block with the usual tenon and a screw that just keeps the block from sliding (hopefully...). Steel because it doesn't creep, and separate because I just need a 3/32 hole (1/8" hole through the steel and a 3/32" ID tube for a bearing.

    I have a ball link at the flap end so I can screw the entire pushrod in or out to adjust the relative neutral, and there is plenty of space for it there.

   I think mine is maybe a bit more secure than Jim's or Chris', but it is definitely not immune to the same issue.

    Brett

Here is the machined 6061 aluminum slider that I use on the my elevator horns. This method prevents the slider from getting jammed sideways in the slot and/or spreading the slot.   

I have a couple of different ideas that are just slight variants of the current design -  but I will have to draw them tomorrow, all this model flying (now that I am free to do it anytime) demands a good night's sleep. Think about a linear rack with a pin, and a set of vernier holes to put a screw in.

    Brett

Quote from: Dave Hull on April 07, 2026, 11:47:37 PMThere are some plausible arrangements, but your list of design goals is very demanding.

That's why I asked you guys, and I was pleased that those who I hoped would respond did.

Good point that the place the pushrod attaches need not be the same place the adjustment happens.

Quote from: Brett Buck on April 08, 2026, 12:16:03 PM...it is only a temporary adjustment until I can alter the size of the flaps so I can put it back to 1:1.

Quote from: Brett Buck on April 08, 2026, 12:16:03 PMI think the answer, at least for electric, is to put the adjustment at the flap horn end, instead of the elevator end.

I had only considered changing elevator control horn radius, but Brett points out that the airplane response comes from several parameters, including flap size, flap-elevator control horn radius, and elevator control horn radius. Putting the adjustment mechanism weight at the flap control horn is obviously better, but I would never have thought of that.  That he can pick a combination that gives the arbitrary flap:elevator deflection ratio of 1:1 is pretty cool.

Quote from: Brett Buck on April 08, 2026, 12:16:03 PMIf you are making your own, unless you are doing something pretty crazy or wildly experimental, you only need a tiny bit of adjustment (mine is set to 1" nominal and I have moved it about 1/8" total experimenting with it), so just don't make the slot so long.

Another obvious point I hadn't thought of. 

Quote from: Brett Buck on April 08, 2026, 12:16:03 PMGoing forward, I am either going to make my adjustment with a jackscrew arrangement at the CG for electric, and go back to the "multiple holes" system for IC. 

Now that you're retired, you won't have time to maintain both a fleet of IC airplanes and a fleet of electric airplanes.

Quote from: Lauri Malila on April 08, 2026, 12:45:16 PMWhy do you want to use a ball link in the elevator horn? There is no need for multiple-axis movement, or whatever you call it, between flap- and elevator horns.
Ball horn takes more space (sideways), and when I look at the rather flimsy looking
slotted horns, the asymmetric variable load is yelling for something to get loose at some point.

Good question.  I guess I use it for pushrod length adjustment, which could be done at the other end of the pushrod, although the other end is less accessible in my airplane.  You are correct about the multiple-axis movement. Paul Walker has been telling me the same thing. Ball links can freeze and hurt one's stunt score.  I hadn't thought about the asymmetric load, but your forked thing or Ken's canard thing would be better.   

Quote from: Lauri Malila on April 08, 2026, 12:45:16 PMcan you give some dimensions (horn length, fuselage inside width, amount of adjustability you need...), and I'll think about it. L

I could have before getting all these new-to-me ideas, but now it will take me some time.

Quote from: Brent Williams on April 08, 2026, 08:09:56 PMHere is the machined 6061 aluminum slider that I use on the my elevator horns. This method prevents the slider from getting jammed sideways in the slot and/or spreading the slot.   

I had forgotten this one.  Yes, you or Gordan sent me some. 

"That he can pick a combination that gives the arbitrary flap:elevator deflection ratio of 1:1 is pretty cool."


Ah, Howard--yer killin' us!

Quote from: Brent Williams on April 08, 2026, 08:09:56 PMHere is the machined 6061 aluminum slider that I use on the my elevator horns. This method prevents the slider from getting jammed sideways in the slot and/or spreading the slot.   

   Hi Brent;
   Got a photo of the other side to show attachment to the pushrod? I like the socket head (2-56") and flat washer, but need to see the aluminum block for clarity

  Thanks!
  Dan McEntee

Quote from: Dan McEntee on April 09, 2026, 11:08:52 PMHi Brent;
  Got a photo of the other side to show attachment to the pushrod? I like the socket head (2-56") and flat washer, but need to see the aluminum block for clarity

  Thanks!
  Dan McEntee

I use a 4-40.  The ball link is sandwiched between the two washers. 
Eliminates many of the possible problems

Quote from: Brent Williams on April 10, 2026, 10:41:43 AMI use a 4-40.  The ball link is sandwiched between the two washers. 
Eliminates many of the possible problems

 I very strongly suggest you add a star lockwasher to your stackup, that will give it some tension even it backs off and reduce the tendency to spin entirely free.
   
     Brett

Quote from: Brett Buck on April 10, 2026, 12:18:32 PMI very strongly suggest you add a star lockwasher to your stackup, that will give it some tension even it backs off and reduce the tendency to spin entirely free.
   
     Brett

Thanks Brett, I will do that.

Edit:  added a photo

I have one of those aluminum channel retainers I got from either Brent W or Gordan  D.  Very clever and simple idea.  Kudos!!

I made a small upgrade and installed a steel blind nut into the aluminum channel retaining it with JB Weld.  I torque the screw hard and would rather react that load with steel threads.

One thing I do on the Tom Morris control horns is to ditch the brass tubing and make my own tubes with a bigger inside diameter. The brass K&S tubing just doesn't have enough clearance for freedom of movement imho.

MM

Quote from: Motorman on April 15, 2026, 07:50:40 PMOne thing I do on the Tom Morris control horns is to ditch the brass tubing and make my own tubes with a bigger inside diameter. The brass K&S tubing just doesn't have enough clearance for freedom of movement imho.

Especially with the bent rod