Control Horn Break

[Michael Massey]

I just finished my 5 month build of a 10% reduced Legacy (with some cosmetic “liberties” taken on the fuselage.  I am very happy with the way it came out.  My best effort to date.  (Picture below.)   Last week was its maiden flight. It flew extremely well.  The only slight issue that came out of the first few flights is that it needed a very slight flap tweak as the inside wing was a little lower than the outside and when inverted, the opposite was true.  So, tweak the flaps.

I was very careful to cushion the flaps with foam rubber, place ¼” plywood blocks on the flaps over the control horn “tangs” and “C” clamped those in position.  The first tweak did not seem to make a difference, or at least a sufficient difference so I did a second tweak, a little more pronounced than the first.  I heard a very sickening snap and the inboard flap became “limp” as it were. 

After my tears cleared, I removed the flap (those hinges were glued in with CA and were never meant to come out).  The control horn tang was broken at the 90 degree bend.  It was a brand new control horn.  (Below are a couple of pictures showing the break and the same control horn involved.)

Today I will start the agonizing process of trying to get the control horn out of the wing doing as little damage as possible.  One additional problem is that I always glue in brass “hinges” to help hold the control horn in place so getting those out will probably be challenging.

But to the point of this thread, what kind of experiences have some of you had?  I have talked to a few guys and a couple of suggestions came out. 

At least some of the guys, who build their own control horns, first anneal the point where the wire will be bent to form the tang.  Seems very logical and had that been done on the control horn I bought, might have made the difference.  That being said, what if I had annealed the bends on the control horn I bought, before I installed it?  What does everyone think?

As the pictures show, I purchased the control horn from Brodak and have sent them an e-mail about this problem.  I have only had one real experience with Brodak’s customer service and it was very positive.  And to be honest, there is really nothing they can do that will undo the damage.  The cost of the part is not the real issue it is the time and energy that will be necessary to get back to where I was.

[Brett Buck]

I just finished my 5 month build of a 10% reduced Legacy (with some cosmetic “liberties” taken on the fuselage.  I am very happy with the way it came out.  My best effort to date.  (Picture below.)   Last week was its maiden flight. It flew extremely well.  The only slight issue that came out of the first few flights is that it needed a very slight flap tweak as the inside wing was a little lower than the outside and when inverted, the opposite was true.  So, tweak the flaps.

I was very careful to cushion the flaps with foam rubber, place ¼” plywood blocks on the flaps over the control horn “tangs” and “C” clamped those in position.  The first tweak did not seem to make a difference, or at least a sufficient difference so I did a second tweak, a little more pronounced than the first.  I heard a very sickening snap and the inboard flap became “limp” as it were.  

After my tears cleared, I removed the flap (those hinges were glued in with CA and were never meant to come out).  The control horn tang was broken at the 90 degree bend.  It was a brand new control horn.  (Below are a couple of pictures showing the break and the same control horn involved.)

Today I will start the agonizing process of trying to get the control horn out of the wing doing as little damage as possible.  One additional problem is that I always glue in brass “hinges” to help hold the control horn in place so getting those out will probably be challenging.

But to the point of this thread, what kind of experiences have some of you had?  I have talked to a few guys and a couple of suggestions came out.  

At least some of the guys, who build their own control horns, first anneal the point where the wire will be bent to form the tang.  Seems very logical and had that been done on the control horn I bought, might have made the difference.  That being said, what if I had annealed the bends on the control horn I bought, before I installed it?  What does everyone think?

As the pictures show, I purchased the control horn from Brodak and have sent them an e-mail about this problem.  I have only had one real experience with Brodak’s customer service and it was very positive.  And to be honest, there is really nothing they can do that will undo the damage.  The cost of the part is not the real issue it is the time and energy that will be necessary to get back to where I was.

      Tweaking flaps has always made me very nervous, for exactly this reason. I also make my own control horns so at least if it does break, I have no one to blame but myself. I am acutally more concerned about it breaking at the upright, or the upright breaking, but having had some fail during the bend, I can see how you could do it. It depends a lot on how the heat-treating of the upright braze was done.

    I don't know what to say, I have switched to drill rod for the cross-bar in hopes that it will be more satisfactory in terms of hard spots, etc. so it will be less prone to breakage.

    There are ways to adjust the ailerons without having to bend the rod, check out Bob McDonald's "Aquila" article for a clamp block system.

     Brett

[Will Hinton]

I agree with Brett on using drill rod instead of music wire - it's much more tweakable but certainly strong enough to do the job for hundreds of flights.  (Or thousands.)

[Brett Buck]

I agree with Brett on using drill rod instead of music wire - it's much more tweakable but certainly strong enough to do the job for hundreds of flights.  (Or thousands.)

       The problem with music wire is the way it is heated, cooled, and tempered again following the brazing of the upright. Its very easy to get local hard spots that then fail later. SO FAR I haven't had any issues with assembled airplane but I have had them break while testing them post-construction.

    Brett

[frank williams]

It seems to me that drill rod would be very hard and brittle and impossible to bend.  Do you temper it first?

[Brett Buck]

It seems to me that drill rod would be very hard and brittle and impossible to bend.  Do you temper it first?

    Until it is heat-treated, it is quite soft.

    Brett

[EddyR]

I made this repair for a friend and I went in from the bottom. A large hole cut in the bottom will not show from the side. I had to cut one side under the flap horn. This was before ball-links and it was all soldered.

[Dan McEntee]

    I seem to recall discussions about the quality of Music wire going back ten years or more. Didn't Bob Hunt lose a model at the team trials once to a broken solid music wire lead out breaking? I have been bending hooks for one thing or another with thinner music wire and have had it break pretty easy. I think the radius is the critical factor. Not making them too sharp or you really affect the grain structure. This makes me wonder if when one is finished building a control horn, or purchasing a premade unit, that heating the bend until it's blueish will draw some hardness out at that point and make them a bit easier to tweak. The photo of the Brodak unit looks like a pretty sharp bend, and I just have to wonder if it starts there?
   Type at you later,
   Dan McEntee

[Michael Massey]

Brett, thanks for the input.  How do you heat treat your assembly, from beginning to end.

Tx.

Mike

[Tim Wescott]

Man, that hurt just to read about.

One thing I noted, on your picture "006.jpg", it looks like they do a pretty tight radius bend -- you can see that the wire has thinned at the bend, which should not be.

I don't know how much that contributed to the problem, but I use a generous bend on my horns.

[Motorman]

Sorry for your trouble. Better it happened on the ground. You have to bend music wire 45 degrees then move the pliers 1/16th away from the bend then continue bending to 90 to give it some radius. Looks like that wire was bent in a sheet metal break.

Nice colors on the plane, makes me want an orange creamsicle.


MM

[Randy Cuberly]

Wow,
Really sorry this happened.

I will say however that in more than 60 years of doing this I have never seen a horn break like this while tweaking flaps and I typically do this all the time...I use hard points in the flaps specifically to allow it.

I do remember some overhardened music wire that came around about 15 years or so ago and had some break during the initial bending but never after it was formed.  For what it's worth music wire can be annealed by simply heating it until slightly red (the color is important) and then quenching it in water.  It's still pretty strong after that but much easier to bend.  One of the most important things in bending the stuff is to not bend too tight a radius in it.  I think about 2 times the diameter as a rule of thumb should be the minimum inside bend radius.

I do agree with the comment about using Tom Morris Horns...I used to make my own like Brett...Tom's are so good and it takes a lot of work and time to make mine so I'm lazy now and use Tom's.

Definitely use drill rod if making your own.

Randy Cuberly

[bob whitney]

dint think that is quite right .if you heat it and quench it it will be brittle then u need to reheat it to a certain color and let it cool

[55chevr]

If you are hardening steel you heat to the desired temperature. This is determined by red color, then quench.  To temper you heat already hardened steel to an even blue/ash color matching a color chart and then allowing to cool in still air.

[Randy Cuberly]

dint think that is quite right .if you heat it and quench it it will be brittle then u need to reheat it to a certain color and let it cool

OK...but since I do it my way I'll tell you that I've done it about 500 times over the years.
It doesn't fully anneal the material which I don't want to do.  it does soften it and relieve stresses.  It most certainly does not make it harder!!!

Randy Cuberly

[Brett Buck]

OK...but since I do it my way I'll tell you that I've done it about 500 times over the years.
It doesn't fully anneal the material which I don't want to do.  it does soften it and relieve stresses.  It most certainly does not make it harder!!!

  Ron Burn posted a pretty good description on SSW a while back. Getting the temper even throughout is probably the real key, so you don't have hard spots.

     Brett

[frank williams]

I've used some 1/8th inch wire from the metal rack at HomeDepot.  It's not piano wire hardness and will bend more easily, but still has the torque requirements we need for a flap horn.  Piano wire, I anneal but don't reharden.  The silver braze at the post gives enough annealing to allow easy tweeking.  Or  ....... just use TomMorris horns.

[Mike Haverly]

 Having worked in machine shops all of my adult life I can say there is no answer for something as broad a "the steel broke, why?  It, steel, has different characteristics depending on what it will get used for.  Without knowing for sure what material was used to manufacture this particular horn, and, let's face it these are model airplanes, any reasonable manufacturer would do what they can to make a good product but they are not held to account for procedures of a product that was out sourced.  I think most of us know the above already.

    Having said that, I can also say that I have worked with several different kinds of tool steel but never had to deal with the procedures for hardening, drawing, tempering or annealing.  Most companies I worked for had to keep track of what kind of material was used for what and where.  Boeing was very particular and  there were different procedures  used from shop to shop depending the use of the product.  It still interests me so I looked up heat treatment of tool steel.   http://www.speedymetals.com/c-8288-drill-rod.aspx
I have used O1, O2, A2 and W1 from time to time.  As it comes from the source and normalized it is pretty forgiving.  Like Brett said, it is soft and makes little flaky chips when machining.  Get it hard and it is brittle and difficult to deal with.  It can't be bent without breaking after heat treating.

   I started making my own horns quite a while ago, mostly because  the available product appeared to be of poor quality, including some of the vendors here.  I tried music wire, from the hobby shop.  It got hard and brittle and broke easily.  I started using welding rod, such as this: http://www.airgas.com/browse/productDetail.aspx?Category=11&product=RAD64001581  I'm pretty sure that idea came from a Utah modeler.  There are some Canadians that have used it also.  The good news/bad news about this is that it doesn't get hard but is very strong.  If you want hard there is high carbon content rod available like 4130, but again, it becomes brittle and would be a failure waiting to happen, but just like the vendor supplied version may never cause a problem. 
 
   I will never say don't use the vendors, just my opinion.  Like bellybuttons, we all have them.  In any case, I'm sorry to see that happen.

[55chevr]

I was looking at plans for Henk de Jong's Blue Pearl stunt design and I noticed he uses motorcycle spokes for horns and push rod ends.  They are tough and do not fatigue easily.   Just a thought if you make your own horns.  Personally, I find it tough to beat Tom Morris horns. I don't believe in making what you can buy but I understand that some modelers prefer to make their own.