Push Pull tube interfearance

[birddog486 21]

I'm building a C model Avid and I'm not sure if I should worry about this or not,,,At the rear push pull tube where the forked connector attaches to the elevator horn,, The through bolt hits the frame so the elevator can only deflect nose down approx 15 degrees or a bit less. Not the 17 degrees Avid states in the manual.

Travis

Edited 14 Jun 2012 by birddog486

[EDMO 1078]

I'm building a C model Avid and I'm not sure if I should worry about this or not,,,At the rear push pull tube where the forked connector attaches to the elevator horn,, The through bolt hits the frame so the elevator can only deflect nose down approx 5 degrees. Not the 7 degrees Avid states in the manual.

Travis

HOLY MOLY! Got to go check my magnum manual, although yours is a different model.

I have never heard of only a 7 degree down elevator - most all planes that I have delt with have about 17 to 20 down and as much as 40 up elevator. Are you sure about that figure? Could it be a misprint?

I'm sure that an Avid builder can answer your question, but it sounded so far off from what I have seen, I had to ask.

Now, I reread your post, and you said nose down - I was talking about trailing edge down. Are we on different parts???

ED in MO

Edited 14 Jun 2012 by Ed In Missouri

[birddog486 21]

HOLY MOLY! Got to go check my magnum manual, although yours is a different model.

I have never heard of only a 7 degree down elevator - most all planes that I have delt with have about 17 to 20 down and as much as 40 up elevator. Are you sure about that figure? Could it be a misprint?

I'm sure that an Avid builder can answer your question, but it sounded so far off from what I have seen, I had to ask.

Now, I reread your post, and you said nose down - I was talking about trailing edge down. Are we on different parts???

ED in MO

Sorry to scare you Ed. It should have read 15 and 17. Not sure why the one wasn't working.

[EDMO 1078]

Sorry to scare you Ed. It should have read 15 and 17. Not sure why the one wasn't working.

Thanks for the correction - My heart has not slowed down tho - My Magnum manual index referred me to Chapter 5, step F........Would you believe it - the Turkeys did not put that page in my book - mine ends with step E!!!!!!!!!!!

you probably will never use that extra 2 degrees, but the bolt binding is really a concern to me - There should definately be some safety concerns there - hope you find a fix for it.

Can you bend something to get it to clear?

ED in MO

[BryceKat 125]

Travis,

2 degrees would be unnoticable, just make sure it isn't going to damage the assembly. Bryce

[akflyer 1427]

Are you using the pan head bolt back there with the short nut? Mine would hit if I put it in one direction, but not the other. I dont remember what side I had to put my nut on though.

[dholly 718]

I don't recall how my Mk-IV was, but if your Avid C is anything like my KF3 was, that damn clevis bolt only has about one short and curly clearance to the frame and is a real biotch to replace. I ended up burning a hole in the fabric with a pointed soldering iron to get a screwdriver on it. I just did my my KF4 for annual, it's got a little more room but not much. I believe the nuts went on the pilot side in both instances. Is your interference with the correct hardware? In any event, I would go thru the effort to eliminate all interference.

[birddog486 21]

The problem was with a standard bolt and not a pan head, I'll give that a try tonight and get a pic or two.

[dholly 718]

FWIW, the notes from my last KF3 annual show the replaced hardware as:

(1) AN23-15A Clevis Bolt - Elevator Horn to Elevator Push/Pull Control Tube Rod End

(1) AN364-1032 Elastic Stop Nut - Elevator Horn to Elevator Push/Pull Control Tube Rod End (new p/n MS20365-1032)

[akflyer 1427]

FWIW, the notes from my last KF3 annual show the replaced hardware as:

(1) AN23-15A Clevis Bolt - Elevator Horn to Elevator Push/Pull Control Tube Rod End

(1) AN364-1032 Elastic Stop Nut - Elevator Horn to Elevator Push/Pull Control Tube Rod End (new p/n MS20365-1032)

I dont know that I would use a lock nut on that connection. Standard practice is, if it is subject to rotation, use a cotter key! Doug, I think your correct that the nut is on the pilots side.

[dholly 718]

I dont know that I would use a lock nut on that connection. Standard practice is, if it is subject to rotation, use a cotter key! Doug, I think your correct that the nut is on the pilots side.

Yes, conventional wisdom would suggest that. However, I assure you those are straight out of the KF3 manual and the KF4 is the same. Reason being (my thought) is that the bolt itself is NOT subject to rotation. The nut (and clevis head) is snugged tight against the elevator horn which in turn is held tight against the Heim rod end bearing. The Heim rod end bearing body then does the rotating around the captive bearing. All of my planes had elastic stop nuts in that location, not castle nuts with cotter pins. Just be certain to replace that clevis bolt regularly (ask Joey about that). FWIW, Kitfox calls for mandatory replacement of the (AN3-15) Elevator Idler Bellcrank to Fuse Mounting Bolt at the front Elevator Push/Pull Control Tube Rod End at every annual condition inspection. Might be a good idea for an Avid C mixer too...

Edited 14 Jun 2012 by dholly

[birddog486 21]

I'm using the first builders manual for a mk4 and it wasn't specific on the type of bolt for that connection. I had a standard AN3 and a castle nut in there and it hits on both tubes as the push pull tube is pulled forward.

I dug through the manual for the model-c and it says to use an AN23-10. Using the cap head bolt is closer to going through but the nut and protruding threads still make contact and it looks like it could be possible for that bolt to get wedged between the tubes if the elevator was forced down by the pilot or a hard landing.

Im thinking I'll just use the standard bolt and castle nut and live with the reduced nose down pitch.

Travis

[dholly 718]

I'm building a C model Avid and I'm not sure if I should worry about this or not,,,At the rear push pull tube where the forked connector attaches to the elevator horn,, The through bolt hits the frame so the elevator can only deflect nose down approx 15 degrees or a bit less. Not the 17 degrees Avid states in the manual.

Travis

*WARNING*

When I read your original post, it seemed to me that your primary concern is with the elevator deflection, not the nut and bolt contacting the frame. With all respect, I think you have that backward. A few less degrees of down elevator than called for in the manual really is inconsequential, you won't miss it like up elevator deflection on your landing flare, but any stress inducing metal on metal wear points have the potential to be much more consequential.

In my opinion, there should be absolutely -zero- binding of your flight control systems, and certainly no metal on metal contact interference anywhere. My manual goes so far as to state that very specifically. As you noted, your situation is a significant safety issue on a critical part, that does not sound like something to simply live with. I would continue trying to find the nut and bolt combination that fist without contact. It has to exist because the plane was not designed to have such bolt and frame interference. Clearly, Kitfox (and maybe Avid too) used the clevis head bolt and short stop nut combination at this location because it is the minimalist hardware that would still provide the strength, security and clearance required without binding. Big bolt heads and big castle nuts are not required.

A couple of thoughts, that elevator push/pull tube to elevator horn clevis bolt is made to be drawn tight against the Heim rod end bearing, ie. you might need to squeeze the elevator fork horn together to do that which, in turn, might reduce your clevis bolt length requirement ever so slightly. Or, perhaps a slight bend of the elevator fork horn towards the clevis head side is necessary to add just enough clearance on the short stop nut side. In any event, you still need the correct length clevis bolt because it's so tight in there that only one size off is a show stopper. One full thread on the outside of the stop nut is all you need. The only alternative I see is to weld stop tabs to your fuse to take the hit from the incorrect nut and bolt, but then, that circumvents the system design.

Even though it is a royal PITA with so little clearance when done correctly, I would urge you to work towards a proper solution. I got so frustrated replacing that damn bolt on both my Kitfoxes (spent HOURS on each!) that I actually had to walk away and come back a few days and beers later. If your Avid is not covered yet, better get it right now because it's 10x the fun after the wrapping is on!

I think I better go let the dogs out now...

[Av8r3400 1179]

Amen, Doug.

[akflyer 1427]

Amen, Doug.

X2

Any potential binding in the control surfaces needs to be dealt with now. If you are planning on any short field work, or rough gravel work, you will want every degree you can get of down so you can get, and keep your tailwheel in the air ASAP. I wish I had more down when I am on wheels!

[EDMO 1078]

Amen, Doug.

I will join in on the "told-you-so" chorus.

This is the time to listen to the advice so wisely given.

Don't ignore the WARNINGS, and have a big "OH SHIT" later on when you learn your mistake.

ED in MO

[birddog486 21]

I'll get a picture of the location so you can see the problem area. There is no Heim Rod end bearing on this end of the push pull tube. This location uses a Fork end. With a standard AN bolt and castle nut installed they provide a stop against the frame at 15 degrees down elevator. In reading the forums apparently the MK4 avid tubes were widened in this area but the early Avids were this way?

I may just cut the tubes off and change the way this is setup but I'd like to hear from other Avid owners that have experience in this area.

Opinions are welcome though BTW this is a nose dragger

Travis

Edited 15 Jun 2012 by birddog486

[birddog486 21]

The bolt is loose in the pic but when it's tightned it still contacts in the same way. using a pan head bolt isn't the answer either which is what The early Avid manual recommends.

Travis

[dholly 718]

Well I can solve some of the mystery. I went [way] back into my Mk-IV construction log and found a pic of the elevator horn and connector on the end of the push/pull tube. The Avid set up is different than the Kitfox 3 and 4.

The Kitfox has a Heim rod end bearing on the end of the P/P tube that goes between two elevator horn tabs and uses a clevis bolt with short nylock stop nut. The Avid has a single elevator horn tab and a simple clevis rod end on the P/P tube. It does use a castle nut and cotter pin. I put pics of both up, just be aware that my Avid pic isn't going to equate exactly with your C model, because one of the Mk-IV improvements was a wider fuselage and different tubing at that exact area.

Now that I see just what your issue is, I would have to question whether your control rigging is installed and set correctly throughout. Have you made all your final adjustments? If so, I would go back and double/triple check everything 'cause something sure ain't right.Maybe someone else has an idea?

Edited 15 Jun 2012 by dholly

[akflyer 1427]

I would be hitting it with a torch and warming it up real good then tweaking those tubes a bit to give me good clearance. I will look at mine when I get home on the 27th and see if I can get a good pic of that area to see how mine is in that area. I know it is tight, but I also know it fits!

[EDMO 1078]

The early KFs had the fork end on the elevator rod - Use a clevis bolt or grind a bolt head, or whatever it takes to eliminate any binding. This is a shear bolt setup, so the head matters little, except to keep it from falling out. I would think that a clevis bolt would solve your problem.

IMO: A locknut is plenty good since there is little, if any, rotation involved.

A washer and a cotter pin in the end of a clevis pin would be safe for this location, if clearence demands it.

Good Luck, and really hoping you find a good fix for this.

ED in MO

Edited 16 Jun 2012 by Ed In Missouri

[dholly 718]

The build manual Leni posted up is for a C model I think. That drawing shows an AN23-10 bolt and AN416-R4 thin check nut at the P/P to elevator clevis. If that's what you use it should fit assuming everything is rigged properly, not so sure I'd be reaching for a touch quite yet.

[EDMO 1078]

Travis,

After flapping my yap, and voicing concerns about any binding bolt or control, I finally looked at your photo.

This does not look like a "binding" situation, rather, it is an interference like you first stated, and maybe not as dangerous.

Rather than bend things, although that is propably feasible, can you adjust your P/P to make things right, and let the tubes be a travel stop?

Other options may be there too - but have to be thought about first.

Best wishes on your fix.

ED in MO

P.S. After thinking some: Conclusion is that you dont need that 2 degrees as much with a nose dragger, so, if no binding, I would just let it go, as is.

ED in MO

Edited 17 Jun 2012 by Ed In Missouri

[SuberAvid 617]

That space is really tight; I didn't have any issues with the fork /clevise cvontacting my tubes on my MK IV but I have a clevice pin in mine and not a clevise bolt. You might try that since the head of the clevise pin is very thin and the cotter end just requires one washer behind the cotter pin so it makes this the thinnest way to go. The shank of the clevise pin is the same as a clevise bolt and that is the wearing surface so it is just as strong as the clevise bolt.