Warning: Elevator Horn Failure on Brodak P-40 ARC

[Steve Kocher]

The weld connected the vertical control arm to the rod on the elevator control horn broke in flight on my Brodak P-40 ARC.  I was attempting the horizontal square eight when I lost elevator control pulling out of the "coffin corner" leg of the outside square.  Fortunately, the failure occurred after the aircraft had made the rotation from vertical to near horizontal.  I was able to level out inverted using flaps only.  Boy, was that close.

I flew out the flight inverted by maintaining full down.  The inverted landing after running out the fuel only resulted in a broken needle value. 
I examined the horn after landing.  The weld had broken allowing the arm to rotate around the horn without moving the elevator. 

I purchased the P-40 last fall.  The airplane had about a dozen flights. I notified Brodak via email of the problem.

Steve Kocher

[Louis Rankin]

Steve,

I was fearful to read your post because I did not want to learn of the demise of such a good looking P-40 (Steve's P-40 is the best I have seen, hands down!).  I am glad you were able to save it.  Next time put some Tom Morris controls in your ARC project!!!!!!!!!!!

Come out and fly with us this weekend.

[Wynn Robins]

got a picture of the P40??  if it is the best one around I'd like to see it.

[Jim Oliver]

Same thing happened to the elevator horn of my Top Fright Score.  It happened on the last corner of the
Square Eights, so fortunately I recovered sorta level.  The elevator was stuck at about 10 degrees down for the rest of the flight.

Jim

[Steve Kocher]

Louis is a bit too kind.  Here a couple of pictures of the P-40.

Steve.

[Louis Rankin]

See, I was right.  Best ARC P-40 I have ever seen!!!

[Bill Little]

That one IS very nice, Steve!   What's the powertrain?

[Steve Kocher]

It's all Brodak.  Brodak .40 for power.  Finished with all Brodak dope, of course.

Initially, I was concerned that a .40 would not be enough engine.  But, the Brodak .40 has more than enough power.  In fact, I have been flying on 62' (eyelet to eyelet) lines, but I need to go to 64' to get the lap time down.

Steve.

[Paul Taylor]

Steve,
Where do you fly? Maybe we can come an watch?

Glad to hear you got it down with minor damage.

Paul

[Paul Smith]

I've never quite trusted these gizmos.

Sure, Tom Morris and some other suppliers make heavy-duty hardware that works.

But in general. they're an engineering nightmare. 

Torque is transmittted through a 3/32" or 1/8" rod.  The force is attached to the surface of the rod, thus the lever is only 3/64" or 4/64".

Depending on the size of the flippers, the load has a moment of 1" to 1.5". 

Thus, the rod is operating at a mechanical disadvantage between 24-to-1 and 32-to-1.  So if there is one pound of force on the flippers, the rod/horn  joint will feel 32 pounds.

This is why I favor a plain U-rod and a nylon horn on the outside flipper.   If you want a front row score, buy a Morris horn for $8.  If you just want to fly a Top Flite Score, do it my way for next to nothing, and have easy adjustment to boot.

If you're just trying live with an existing ARF, you could abandon the stock wire horn in place and bring the pushrod to a stout outdoor nyon horn.

[Jerry Bohn]

Bummer to have that happen to a good looking plane like that.
Thats one reason I would like to see some ARF/ARC's made in USA.
Welders Wanted: Apply in Hong Kong China to "ARFs Am Us", .39 cents per hr. 12hr days.
Why by an ARF/ARC and rebuild it when it's new? Might as well build kit especially profile.

[Paul Smith]

So true !

The other question is: why use a full-body control horn on a profile model?   The whole pushrod is outdoors, so why try to hide the horn (and lose the whole rig in the process)?

[Steve Kocher]

I have been contemplating how to replace the control horn.  I think that I will remove the horn from the rod and place a nylon control horn on the elevator.

The question that I have is how do I reinforce the elevator.  It is a built up elevator and there is only a small balsa tip where the horn can be attached.  I am thinking about using a strip of plywood on the bottom.  Should I include a strip of plywood on the top, as well?  What size plywood should I use?  Is there a better choice?

I want a bulletproof control system, but I also want to minimize the effect on the appearance of the aircraft.  Any suggestions will be welcomed.

To answer Paul's question, I was flying with my father in Shreveport, LA. at the time of the mishap.

Steve.

[Bob Reeves]

I would just fix the broken control horn and not re-engineer the elevator control system. However I have an OA outfit and could braze it in less time than it would take to find a plastic horn.

[Steve Kocher]

I don't do any welding.  I try to stay as far away from heat and metal as possible.  Can the horn be re-welded to the rod without first removing it from the elevator? 

[Rudy Taube]

I don't do any welding.  I try to stay as far away from heat and metal as possible.  Can the horn be re-welded to the rod without first removing it from the elevator? 

Hi Steve,

Like you, I am "metal challenged". I would not bother with trying to repair your broken horn. Just go with your idea to use a separate horn attached to the EL. We use them all the time in RC, and they hold up well under more stress than our CL flying will give them.

You are correct, you will need to reinforce the attachment area. 1/16" (1/32" may be enough, but I use 1/16") ply that extends at least 1/4" beyond the horn mount is enough. We use a dowel inserted into the balsa in our EL on our 35% 30 lb planes, we then put the ply over the top and bottom and drill through the whole thing to insert the metal bolt that becomes our adjustable control horn. This may be overkill for our small CL planes, but it is the most bullet proof method! ;-)

 Yes, no matter which horn you use, you should use one ply on the top and one on the bottom. With some hard balsa in between (if you don't use a dowel). There is no need to crush the wood, just snug tight is enough into the plastic screw plate, or blue Locktite if you use the metal unit.

Make sure you use a LARGE R/C horn that is made for .60+ size planes. the standard ones are not up to our task. Here are some possible horns:

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXD936&P=7

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXD937&P=7

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXDCU2&P=ML

Good luck with your fix.

Like others have said, your P-40 is beautiful. You are right up there with Mark's beautiful P-40. I love my ECL P-40, but I wish it looked as good as yours. :-)

Regards, 

[taildragger-j3]

I'm with Rudy 100%. The nylon horn will do a more than good job. I've used them on everything I've built in the past 10 years, and had not one failure. (except from the pilot, of course)

[Bob Reeves]

I don't do any welding.  I try to stay as far away from heat and metal as possible.  Can the horn be re-welded to the rod without first removing it from the elevator? 

Wouldn't attempt to weld or braze it with it still on the airplane but I sure might take a stab at soldering it. Again, I have the equipment , supplies and experience to do it and make it hold. All you really need is a fairly large soldering iron, couple of heat absorbing clamps, flux and solder.

Haven't seen the P-40 control horns but if they are the wire wrapped control horns I have seen on other ARF's they are soldered (not welded) in the first place. The design (with the wire wrap) is sound as long as the soldering job was good, sounds like whoever soldered the one in yours didn't get it clean or hot enough. If you were closer To Tulsa I would be happy to solder it for you.