This is the STOCK elevator push rod from my Skymaster F-15. I feel that I dodged a bullet here.

On the second flight of the day I noticed that the jet would roll slightly to the right while pulling up elevator. Before the 3rd flight, I re trimmed the Right elevator to match the left. The 3rd flight went uneventful and I packed up for the day.

While unloading my truck, when I took the F-15 out, the right elevator fell to the down position. I thought I may have stripped a servo in transport on the way home. When I pulled the servo cover off, I found the push rod broken in two. This makes sence as to why the trim change.

The way the push rods are set up in the jet is they pull for up elevator. So if this rod was slightly bent were it broke it would pull that elevator to the up position. I really got lucky on this and I replaced both push rods with 6/32 push rods.

Joe Lewis
Kingtech
K-80 and K-140
Owner

That would not have been good. Glad u found that.

Steve,

It looks as if it broke due to you soldering it which caused the cut threads to become weak and brittle. I would suggest that you use loctite instead on the new one. Glad to see you found this on the ground instead of it finding the ground for you.

NICE CATCH!!!!!!

Greg

That is not solder. It is Ca glue. I know there is a lock nut on it but I always put a drop of Ca on the threads for peace of mind.
Where it actually failed was at the threads right after the lock nut.

Joe Lewis
Kingtech
K-80 and K-140
Owner

And this is why I never use the supplied hardware. As matter of fact I wish they would not supply the crappy hardware and lower the cost of the kit.

Joe,

You are a luck man !!! Most guys do not check control linkage's in preflight including myself until my " Incident " .. By God I check them all now !!!! Glad to see it didn't cost you like it did me !!! I had a rod break identical to yours on a Tam F-16 on the elevator.. It too showed itself on the ground when the stab went limp.. I has to be a issue with the rod quality, brittle metal.. Scarey !!!!

Danno

Hey Joe, glad to see you caught that before it bit you!

Also glad to see your up and about!

You need this:

McMaster-Carr Stock Number 1272T12 @$4.85 each, it is stainless steel 3 mm dia. rod in a 1 meter length, also get yourself a 4-40 Die and you can make any length push rod your want that will not break!

The bad/sad thing here is that you should not have to go to McMaster-Carr or anywhere else to retrofit any item as key and basic as a pushrod.linkage/hardware in any of these kits !!! For the most part all of these airplanes we fly look very nice, fly well and so on.. But if you can't count on the critical Guts inside to keep it in one piece and in the air, you might as well throw it in the trash as soon as you take it out of the box... Cause that's where it's gonna end up any way. It's up to the Manufacture to insure quality control on every component of their products.. Unfortunately is comes back to, You get what you pay for.. I can count on less than one hand the Mfg's that fall into that category.And again, It's up to the operator to properly pre-flight the aircraft and look for any abnormalities. But in both of these examples, pre-flight inspection would not have caught the component flaw, and I do not carry an X-Ray machine in my flight box !!.


Danno

Unfortunately structural engineering is not the strong suite of many of the ARF providers, they do however do a heck of a job making them look good!

Just quick note from over the pond!

I never use cut threads on control surfaces for this very reason, all linkages either from stud or rod ends, are cold rolled so that there are no induced weaknesses!

I think that goes for most Rc Jet pilots over here!

I'm glad it happened on the ground, do you think you would have known what caused the problem if the aircraft had crashed?

I'm not so sure, it would have probably put down to radio!

Regards and well done


JT

+1

"Unfortunately structural engineering is not the strong suite of many of the ARF providers"

Exactly. My favorite was when Hangar 9 came out with the 1/4" thick aluminum landing gear that comes in 2 pieces and they have you bolt it to the 1/8 lite ply landing gear plate that is supposed to take all the moment loading from landing. ..But it packs nicely in a box. Which they have you keep for the pieces after the first hard landing. I guess they expected people to pitch it in favor of a one piece carbon/fiberglass gear.

Thanks for all the comments. I am not sure why the rod failed because the first flight there were not any trim changes. On the second flight, I did add the Center line smoke tank tank empty to see how the F-15 would fly with it on. During the flight I thought the trim change was due to the tank. It was only after I landed That I noticed the Right stab slightly higher then the left. The third flight I removed the tank. Only thing I can figure is it was damaged in transport.

Rich,

Thanks for the info on the rod from Mcmaster Carr. I will defiantly be ordering some of the rod. I already have the 4-40 Die.

I agree that we should not have to go elsewhere to replace hardware, but if any of you remember, when we use to build kits, we use to have to buy the hardware separate. I agree the manufactures should leave the hardware out and lower the price.

Danno

I see the pin failed clevis you had. I did replace all of the stock clevises with Sullivan for that same reason. I had read that the stock clevis pin could back out in the direction of the lock, breaking free on the welded side.

Joe Lewis
Kingtech
K-80 and K-140
Owner

Is this hardware ok for use on a modelbau f86d?
Dubro kwiklinks and dubro 4-40 rod , alm post type horns ?
thanks in advance

The hardware looks good. I would NOT use the 4-40 all thread. It is too flexible to make a good push rod. Hanger 9 makes a turn buckle titanium push rods at different lengths.


http://www.hangar-9.com/Products/Def...ProdID=HAN3550



Joe Lewis
Kingtech
K-80 and K-140
Owner

I personally don't use any Plastic clevis' either. Its either the sullivan gold-n-clevis' or a heavy duty ball link ;/ rod end.