B

Bob Axsom

Well Known Member
During the annual I jacked the front of the plane up to check the breakout force and it was fine (I guess it settles in after you tighten it three or four times) but I did notice some play in the strut itself. I traced it back to the bolt in the engine mount/nosegear mount weldment. It was not detectable with the nosegear on the ground.

Bob Axsom
 
Bob, I've heard that is quite common. However, can you somehow measure the amount of play - maybe fore/aft distance at the axle nut? We're talking hundredths of an inch, right? Maybe 1/64th?

Best,
Doug
 
No I tightened it up

It was not a great deal of movement but it was quite noticable down at the end of that long arm when I was pulling on it with the fish scale. There is probably some settling over the years since I installed it and maybe it didn't like all the times the breakout force got low and it shook so violently. Once I tightened it down again there was no noticable play. Just another thing to check at the annual.

Bob Axsom
 
Make sure it's not nyloc

The nut specified in the kit is a nylon locknut that's not even heat rated. And it sits, what, about 8" above the exhaust stacks?

I struggled with bad nose gear shimmy for a long time before it finally dawned on me to replace that nut with an all-metal lock nut. It used to loosen about every 30 hours. I could tell it was loose when the shimmy reappeared. But on my last annual it was just starting to get some movement, about 140 hours after replacing the nut. I was disappointed that even the metal nut had loosened, but at least it's better than before.

To answer Doug's question -- it depends on how long you let it go. It eventually wallows out the hole. Mine probably moves 1/32 if the nut isn't tight -- which translates to a big movement at the bottom of the leg (1/4" or more). I've thought about reaming it to the next larger size.

One other thing -- I suspect it would help a lot if I was better at holding the nose off on landings. Any castoring nose wheel is going to shimmy a little if it's moving too fast, and any shimmy helps loosen that nut. Unfortuanately, my home field is a (narrow) 9-27, so I'm usually touching down in a 10-knot crosswind. It's hard to keep the nose off when you need the brakes to stay on the runway.
 
Mine is the Nylon AN365

I do have exactly the condition you describe. Thank you very much for sharing this information. I just got the cowling back on after replacing the alternator field connector yesterday evening. I think I will add a split type lock washer the next time I have the cowl off. You know, a cross bolt through the mount and the strut might help the problem as well. Big job!

Bob Axsom
 
The problem of the nose gear strut working back and forth is more significant than it may seem. After about 200 hours and around that many landings, I wanted to inspect my nose gear strut. It took about 3 or 4 hours to remove it, owing to this problem. The gear leg had worked back and forth enough to raise a burr on the gear leg and on the bolt itself, which made removing the bolt almost impossible. The gear leg was also very difficult to remove once the bolt was out.

At initial assembly, I didn't like this play and replaced the standard AN bolt with a close tolerance bolt. In my particular assembly, it was not possible to tighten this bolt enough to prevent the play (IIRC, it took several times the rated torque of the bolt to even begin getting friction).

I filed a small fillet in the nose gear bolt hole, to minimize the effect of a sharp edge dinging the bolt, and this has fixed the problem. I took the nose gear strut out again at about 650 hours with no problems.

I highly recommend removing all gear legs every couple years, as failure to do so may result in not being able to remove them at all. There is some galling that happens on the pressure points (against the sockets) on the main gear legs. And yes, this is with copious amounts of thick grease applied.

Alex Peterson
N66AP RV6-A 722 hours
 
I'm at your time point #1

I assume the bolt hole you relieved the edges on was in the strut and not the mount or did you do both. [I realized that you might have actually added a fillet on the outside of the mount - could you clarify that for me?] From your description I assume the close tolerence bolt was installed after the 200 hour observation. Do you happen to have the part numbers of your replacement hardware? I have the uncomfortable feeling this is going to become a significant maintenance issue over time.

Bob Axsom
 
Last edited:
Bob,

I added the fillet on the outside of the gear leg. A fillet on the inside of the mount would be good also, but tough to do. A fillet on the outside of the mount would simply make the airplane a little lighter.

I don't have the hardware callout here, but look for the same basic size/length of AN bolt and get a few of the close tolerance bolts. A say to get a few, but there will be a size distribution and you might pick the best fit. It isn't the close tolerance per se, but the fact that the close tolerance bolts are slightly larger than the standard AN bolt. I had the close tolerance from the beginning, as when I was working on building the plane, I would often use the motor mount as a pull to get up from the floor. When I did this, I often would hear the click as the strut went from one position to the other.

Alex Peterson
N66AP RV6-A 722 hours
 
Extreme dynamic forces

Bob Axsom said:
During the annual I jacked the front of the plane up to check the breakout force and it was fine (I guess it settles in after you tighten it three or four times) but I did notice some play in the strut itself. I traced it back to the bolt in the engine mount/nosegear mount weldment. It was not detectable with the nosegear on the ground.

Bob Axsom
Click to expand...

There are a number of places on an RV where you can expect extreme dynamic forces including of course the interface of the gear legs and their mountings. I noted on my RV7A that Vans specified a .311 drill (or alternatively a 5/16 drill) to size the hole in the gear leg and associated mount. Well it is absolutely positive that a standard AN bolt through a drilled 5/16 hole in that location will not be "snug". And in this location, as well as the nose gear (and also the rear wing spar to fuselage connection) you really want "snug" bolts.

If a bolt is not "snug" in these locations then it will eventually wear and deform the surrounding metal resulting in an even looser fit...and so on.

The best way to get a truly snug fit in these locations is to drill the holes undersize and bring them up to snug in steps with an adjustable reamer.

Producing a less than snug fit in these locations cannot be compensated for by simpling torquing up the bolt to remove movement by friction. This only works until the first landing. And the problem is that the smallest amount of looseness at the bolt results in quite a lot of movement at the wheel. I personally believe that much of the wheel shimmy that builders report (on the mains and on the nose) starts at the loose bolt at the gear leg to mount interface.

If the bolt in these locations is not "truly snug" I recommend the hole be drilled out with an adustable reamer and an .016" oversize NAS bolt be installed. The best way to do this is to bring up the hole in steps and test fit the bolt at every step (because there is always some dimensional variation in every diameter bolt). In the end the bolt should be a "tap in" snug fit just like the bolts that attach the wing spars to the 704 bulkhead. That's the fit that you want on the gear legs as well.
 
Last edited:
How about replacing the bolt with a threaded taper pin? In the old days that was a fairly common fix for slight misalignment or hole elongation in the RV-3 and -4 main gear leg sockets.

Hawkeye Hughes
 
Good ideas all

I can see I'm going to have to expand my personal experience envelope once again but that's what we buy into when we decide to build a thing as complex as an airplane.

Bob Axsom
 
taper pin?

REHughes said:
How about replacing the bolt with a threaded taper pin? In the old days that was a fairly common fix for slight misalignment or hole elongation in the RV-3 and -4 main gear leg sockets.

Hawkeye Hughes
Click to expand...

I'd never heard of a "taper pin".

I found these links at Spruce:
http://www.aircraftspruce.com/catalog/hapages/an386taperpin.php
http://www.aircraftspruce.com/catalog/topages/reamers.php

So how do you do this? I guess you just carefully ream the hole until the right number of threads stick out the other side when you insert the pin?

It lists a nut and cotter pin for each size. Is that a normal castle nut? Can you order the version without the hole and use a standard AN lock nut?

It also mentions an AN385 but there's no page for it. What's the difference?

It would sure be nice to get the right stuff the first time. That reamer is over $40! That's a 1/4" bolt, right? So we'd need the #3 reamer (1/4-28) and an AN386-3-WHAT?? How the heck do you pick the 2nd number? How do you specify the length of the pin?

This sure looks like the correct way to fix this if we can figure out the details.
 
Do you think a "color" (?) of Locktite would help at the INITIAL (new) installation?

YOur opinion, please...

Don Gray
N17QB 7A in progress
 
Loose Nose Gear

I had this same problem on my -6A. Noticed it during one of my first few hour checks. A call to Van's and they gave me the name of a supplier near them (Columbia Aircraft Hardware maybe?) that sold close tolerance AN bolts. As I remember, it was even a tighter fit than a NACA bolt. Had to put it in dry ice to get it in. Never noticed it loose again though!
As others have said, your mileage may vary!!
Bill Waters
 
Taper Pins

Tapered fasteners were used in the F-4 Phantom II and probably a lot of other high strength no motion allowed applications. These high strength demand assemblies get very sophisticated with no bungling tolerence for getting the full benefit. I think one needs to develop good understanding of the theory and the critical application parameters before trying use these sophisticated fasteners in their airplane. Close tolerance bolts is an easier to understand concept and is probably easier to apply but we know that is a conjested area to work in. I don't think the loctite approach will do any good at all - this seems like a design compromise for ease of assembly that is subject to metal yielding over time such that what is tight now will not be tight 200 flight hours from now. For now I plan to leave mine as is. The next time I remove the cowl I plan to add a split lock washer. When I pull the engine, I expect to make a change to the installation. If Lycoming keeps going as is that may be a lot sooner than I would like.

Bob Axsom
 
Taper Pin Size

jonbakerok said:
I'd never heard of a "taper pin".

I found these links at Spruce:
http://www.aircraftspruce.com/catalog/hapages/an386taperpin.php
http://www.aircraftspruce.com/catalog/topages/reamers.php


That's a 1/4" bolt, right? So we'd need the #3 reamer (1/4-28) and an AN386-3-WHAT?? .
Click to expand...

The "Thread Size" listed in the Spruce table DOES NOT indicate the size of the hole that the pin is intended to go in. Different sized pins within a range will use the same size threaded tip to mount the washers and nut. I believe that the "D" value listed for the pin is the diameter of the narrow end, and is generally very slightly larger than the starting drill hole size. For example the -3 pin in the table (Minimum diameter .317) would be used with a 5/16" bolt size, (nom .3125"), starting point.

Hawkeye
 
Once you see the way a taper pin would be used, it is reletively simple. You match the reamer you buy to the first dash number in the part number of the pin you chose. You choose the pin by the grip length (Same as the grip on the current bolt, or SLIGHTLY more) and desired diameter. Then you ream your current hole until the grip of the pin just protrudes through both holes, and put your nut on an torque it up, maybe with a washer. If done right, it should be a lot nicer, long term solution to the problem than close tolerance bolts.
 
REHughes said:
How about replacing the bolt with a threaded taper pin? In the old days that was a fairly common fix for slight misalignment or hole elongation in the RV-3 and -4 main gear leg sockets.

Hawkeye Hughes
Click to expand...


Some-one please correct me if I'm wrong (I'm sure they will) but the gear leg to mount requires a snug fit on both sides of the gear leg. There will not be enough bearing interface to prevent deformation under load if the taper pin is only snug on one side of the gear leg. To get a snug fit on both sides you need a parallel fastener.

Incidentally it is a myth that an AN close tolerance bolt is always larger in diameter than a standard AN bolt. It is in fact simply tighter in its tolerances. Because standard AN bolts have a much larger tolerance it is in fact possible to get them with a larger diameter than a close tolerance bolt (they vary more both up and down).

Furthermore if the gear leg bolt is not very snug it means that there is reduced interface between the bolt and the surrounding metal. This increases the pressure on those areas that are touching and results in deformation. A snug fit in the first place is the way to go.

I recommend a variable reamer for the job. Best way to get a really tight fit. A little more expensive but, hey, we're building aircraft.
 
Why wouldn't it be tapered on both sides?

Bob Barrow said:
To get a snug fit on both sides you need a parallel fastener.
Click to expand...

Why wouldn't it be tapered on both sides?

I wish we had someone who has done this to draw a picture and give details, because it sure seems like a simple solution. It seems like you would get the same benefit as a close tolerance bolt without really having to ream a perfect hole and mess around with frozen bolts and all that. And if it ever loosens up, you just give it another turn.
 
Okayyy, I've never seen a nosewheel setup on an RV-A, but what I anticipate it to be would be one tube inside of another tube, so here is my drawing:
picture1.jpg

Seems like the perfect application of the taper pin to me.
 
osxuser said:
Okayyy, I've never seen a nosewheel setup on an RV-A, but what I anticipate it to be would be one tube inside of another tube, so here is my drawing:
picture1.jpg

Seems like the perfect application of the taper pin to me.
Click to expand...

Are you proposing that the hole in the mechanism be drilled out with a tapered drill to match the tapered pin. That's what your drawing seems to show.
 
Well, that'd be what I'd be suggesting, but again, I've never actually looked at a nosegear setup on an RV up close, so I can't guarantee it would work fine, but it should if I understand where it's located right. This is at the top of the nosewheel tube, where it fits into the engine mount right?
 
Tapered Pins

Bob Barrow said:
Are you proposing that the hole in the mechanism be drilled out with a tapered drill to match the tapered pin. That's what your drawing seems to show.
Click to expand...

Bob, I think I know where some confusion might be coming from. With your Aerospace background you are probably more familiar with some of the Huck-type or Hi-Shear tapered fasteners that would only go into one side of a flat or tubular assembly, but the type of tapered pins referred to here (AN386) will indeed go all the way from one side of the outer tube to the other.

Once the nose gear leg is inserted into the retaining barrel and aligned, a pilot hole is drilled from one side to the other. Then the correct size tapered B&S reamer is inserted in the hole and a constant tapered hole is created all the way from one side to the other. The ideal final size for the tapered hole is achieved when the tapered pin can be inserted all the way through, and the smooth part of the narrow end extends about 1/16" past the outer barrel surface. A special contoured washer and nut provide fixation and torque to pull the tapered pin tightly into the hole to remove all relative motion between the assembled elements.

I have an early RV-3 that employs tapered pins running through the front and rear steel spar splice plates on either side of the wing spar butt ends and the 300 bulkhead. Van later changed to Close Tolerance Bolts for this assembly, but I am sure it was on the basis of reducing the difficulty for the builder, rather than achieving a higher level of engineering performance. There is just NO motion in a properly done tapered pin joint, and they would seem to be highly desirable in certain high-force-cycle areas such as the tailspring anchor, and I assume the nose gear rod attachment.

regards,
Hawkeye
 
REHughes said:
Once the nose gear leg is inserted into the retaining barrel and aligned, a pilot hole is drilled from one side to the other. Then the correct size tapered B&S reamer is inserted in the hole and a constant tapered hole is created all the way from one side to the other. regards,
Hawkeye
Click to expand...

Thanks Hawkeye, that's what I find most delightful about the internet email groups...I can always learn something, and I love learning things (particularly about aviation!!!). There is probably real merit in the tapered pin for this application but as another lister has noted the drilling/reaming preparation may be beyond many builders. On another point: the tapered pin would probably be a whole lot easier to remove if necessary. It's obvious that many builders have trouble removing the AN bolt after flying for a while.
 
Let me know if anyone finds a source for the tapper pins and reamers that are the right size for this job. I searched for quite a while a few months ago for this very fix on my 9A. I could find the reamers but couldn't find the right size tapper pins.
 
You must log in or register to reply here.