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Nick in Flap Pushrod

B

Bikeman55

Member
Hi everyone,
While working on my RV 7A today (I didn't build it) I noticed a nick in one of the hexagonal flap pushrods. It looks like a mark from a tool, and is fairly deep on one of the the hex corners. The rod is not rubbing anywhere, its a definite ding from something. Should this be replaced?

Thanks in advance for the input!
 
Ding

If you think it will polish out, do that. The hex are an "RV 9" part that many used on the RV 7's. Also cheap enough to just replace. :)

Note: I did see one RV7A with the flap drive arm not tight enough in the blocks and it would work itself from side to side... something to also check.
 
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Flap Push Rod

I had an original tubing push rod with manual flaps break on short final.
The aircraft rolled 90 degrees before I could retract the flaps and land.
In my opinion a damaged flap rod should not be taken lightly.
We have the Avery Hex replacement rods installed now.
A very important safety modification with minimal cost.
I would not fly with the original tubing.
 
A pair of hex pushrods from Avery is less than $20. Cheap insurance.

I replaced the stock round aluminum pushrods on my RV-6 because one had been rubbing slightly against the fuselage opening. It was a very quick and painless repair for a lot of peace of mind.
 
You guys have me freaking out. Is this the flap rod you are talking about changing to? Is it for the -9 models too? I don't think it is, but I may not remember correctly.
http://www.averytools.com/prodinfo.asp?number=4660

What is the problem with the standard issued flap rod? Al's experience is not something I want to happen to me. I know Im not half the pilot he is! I know you can't take the risk out of everything, but if this is something that has happened more than a couple times, for the money, Im willing to make a change. Thanks for the info.
 
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Mike, was that the one that went down just over the highway near Cambridge? The one I am thinking about I thought was a BD-5.
 
I also replaced the stock flap pushrod, however, I'm not sure using the standard pushrod is a cause to freak out. I'm not aware of any significant problem with their use.

Frankly, your flap pushrods should be a standard check on every preflight. It's not hard but the key is what you would do IF you found a problem.

To the original question, if you have a critical flight control with a potential problem, and you're moved to ask what you should do about it, you probably already know the answer.
 
Flap Rod

To clarify the original rod was manufactured by the builder from a piece of aluminum tubing in accordance with the building manual. The builder used a drill to increase the hole size to allow the tubing to be tapped with a 1/4-28 tap. That did not leave much material left to withstand the environment flaps see in use. I was very lucky as I really did not realize at first why the aircraft rolled. I simply reversed what I had done (retracted the flaps) which allowed me to regain control and land. Of course the affected flap dropped down upon landing. We would have been grounded if a kindly soul had not helped us purchase a tap locally to make a field repair. I was totally unaware of the Avery replacement hex material prior top our incident.
 
What Bob said....

As info, there are thousands of RVs with the round tubes which had to be tapped by the builder to accept the rod ends. In my opinion, the hex rod gives builders a sense of comfort because they didn't have to drill and thread a tube. However, if, like in your case, the hex rod is damaged, it's easy and cheap to replace. Just replace it. It's more important that you have and keep high inspection standards. That's what Bob Collins was driving home.
 
With questions like this, you can answer them yourself with a question. "Do I die if it breaks?"
 
Another option used by many of us is to replace the tube with a 4130 steel tube, tapped to the appropriate thread. The weight increase is negligible and you no longer need to worry about it rubbing on anything - the other thing will always wear away first....
 
rockwoodrv9 said:
Mike, was that the one that went down just over the highway near Cambridge? The one I am thinking about I thought was a BD-5.
Click to expand...

No, the one I was talking about was a jet, (BD 10 based as I recall), happened at Minden NV. Happened in the pattern, rolled the plane into the ground, IIRC.

There was a BD 5 crash here, but I recall it was an engine failure??

Different crash.
 
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Ironflight said:
Another option used by many of us is to replace the tube with a 4130 steel tube, tapped to the appropriate thread. The weight increase is negligible and you no longer need to worry about it rubbing on anything - the other thing will always wear away first....
Click to expand...

This is exactly what I did in 1990. I was not comfortable with the aluminum pushrod supplied with the kit.
Remember, flaps are the only control surface that are deployed into the wind and stay there. There is quite a load.
 
Mel said:
Remember, flaps are the only control surface that are deployed into the wind and stay there. There is quite a load.
Click to expand...

Maybe I missed something, have any of the stock push rods ever failed?

The same engineers that designed the airframe designed this part. If we are "uncomfortable" with this part, what else should we question, the Vertical Stab? Oh wait,.......:D

Sorry for the thread drift, but we have people citing accidents that not only had nothing to do with this part but had nothing to do with flaps.
Now we have trusted people saying they are uncomfortable with a part that has been in wide use for many, many years.

I trust your judgement Mel. If there is a problem, all of us using the stock part should know about it.

PS - I would absolutley have used the Avery part had they been available when I built my 6 for the simple reason it would be one less part to fabricate....
 
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JonJay said:
Maybe I missed something, have any of the stock push rods ever failed?
Click to expand...

Yes, see next paragraph from post 4.

Alschief said:
I had an original tubing push rod with manual flaps break on short final.

The aircraft rolled 90 degrees before I could retract the flaps and land.

I would not fly with the original tubing.
Click to expand...


JonJay said:
Sorry for the thread drift, but we have people citing accidents that not only had nothing to do with this part but had nothing to do with flaps.
Click to expand...

I am the one citing a crash, and it was due to a single side flap failure.

I made it clear it was not an RV, but did address the issue of what a single side flap failure will do. Simply put, it can kill you pretty quickly----or at the minimum really get your attention.

As Mel says above, "flaps are the only control surface that are deployed into the wind and stay there". And, consider that virtually the only time flaps are used is close to the ground. If you lose a single flap control, the plane will want to roll, and the circumstances of the timing and extension of the flap at the time of the failure will determine how hard the roll input is, and if it is something the pilot has the time and altitude deal with.
 
Mike S said:
Yes, see next paragraph from post 4.






I am the one citing a crash, and it was due to a single side flap failure.

I made it clear it was not an RV, but did address the issue of what a single side flap failure will do. Simply put, it can kill you pretty quickly----or at the minimum really get your attention.

As Mel says above, "flaps are the only control surface that are deployed into the wind and stay there". And, consider that virtually the only time flaps are used is close to the ground. If you lose a single flap control, the plane will want to roll, and the circumstances of the timing and extension of the flap at the time of the failure will determine how hard the roll input is, and if it is something the pilot has the time and altitude deal with.
Click to expand...

Fair enough. This has been hashed out before, shocker I know,;
http://www.vansairforce.com/community/showthread.php?t=84307&highlight=flap+push+rod
 
They have been tested...

As a result of builder concern, the flap pushrod design specified in the plans was tested many years ago.

Testing was done to failure, which occured Waaaay above the normal load that these parts would ever experience.

Over the years I have heard of a couple of instances where people had problems with these parts.
In every instance I can think of, there was another factor involved...
deep gouge caused by rod rubbing on fuselage opening... pushrod had been bent to keep it from rubbing on fuselage opening... etc.
 
All the force on the flap pushrods are in compression. If there's a defect in the wimpy thin round aluminum ones, it could bend over and suddenly give you the dreaded asymmetrical flap deployment scenario with little or no warning. The extruded hex pushrods are much beefier, and nice to get a wrench on to hold them while tightening the jam nut on the rod end bearings. The 4130 steel ones of course, are going to be the strongest you can make. When I helped my friend build his RV-8 a few years ago, we made his out of 4130. When I replaced mine, I didn't have any more 4130 tube lying around and I needed to order some other stuff from Avery anyway, so I just bought a set of the hex aluminum ones from them since it was convenient.
 
So Van's is offering a hex pushrod, which appears to be what I have. Are they the same ones made by Avery? If not, what is the difference between them? And what length do I need for an RV7?
 
Bikeman55 said:
So Van's is offering a hex pushrod, which appears to be what I have. Are they the same ones made by Avery? If not, what is the difference between them? And what length do I need for an RV7?
Click to expand...

Avery has them pre-cut... sized for the "7". Call them up and order a new set. :) The length is stated on their website.
 
I agree 100% !

Alschief said:
I had an original tubing push rod with manual flaps break on short final.
The aircraft rolled 90 degrees before I could retract the flaps and land.
In my opinion a damaged flap rod should not be taken lightly.
We have the Avery Hex replacement rods installed now.
A very important safety modification with minimal cost.
I would not fly with the original tubing.
Click to expand...
 
Ironflight said:
Another option used by many of us is to replace the tube with a 4130 steel tube, tapped to the appropriate thread. The weight increase is negligible and you no longer need to worry about it rubbing on anything - the other thing will always wear away first....
Click to expand...

That's what I did when I was putting my RV3 back together after I bought it
less engine and disassembled. The alum just looked too thin after it had been
drilled and tapped. Like you said the 4130 can't weigh that much more.

JM
 
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