Control column installation and bearing stiffness (page 29-05 step 7)

iamtheari · #1 09-24-2018, 08:13 PM

I got the bottom fuselage skins riveted together tonight and proceeded to install the control column. There is almost no play when one side's hardware is installed so I do not think I need any shims. But when the hardware is torqued to spec, the bearings seem rather stiff. It moves smoothly without binding, but it resists movement and will easily hold itself in position against gravity. How freely should the control column move?

RV-14E · #2 09-24-2018, 08:51 PM

You may need to try different combinations of washers/shims to eliminate bearing load. I believe there ought not be a change in friction as you torque the nuts. Shim with care.

If it's any consolation, as I look at my time lapse from when I completed that task on 4-Jul-15, it took me 3 hours to find the right combination. I obtained very smooth movement in both axes with no noticeable friction. It was frustrating but worth the time invested. It's best to do this now when access is so easy.

Not everyone's will be the same as mine, however my ultimate washer stack ended up being two NAS1149F0363 on the left inboard and single 363 and 332 washers on the left outboard (top image). The right side had two 363 washers with a single F-14146A shim (sandwiched between the washers so it won't contact anything) on the outboard side and a single 363 with the same size shim on the inboard side (bottom image).

iamtheari · #3 09-25-2018, 07:41 AM

Thanks. I'll spend my weekend in that tedium, I guess, since it'll be worth it. My concern is that the bearings themselves are not working correctly but I don't know how to differentiate that from misalignment of the control column, nor how to fix them if they are sticking.

Tom Martin · #4 09-25-2018, 07:57 AM

The RV 14 is a wonderful example of how new technology has improved the design, and quality of parts. I do have a concern about this particularly part of the airplane in terms of maintenance. If those bearings are ever to be replaced it is going to be a major job. The "bearing" holders are riveted to the fuselage and if I were to do it again I would use screws to fasten these parts to the airframe. This would allow you to easily remove those parts to replace the bearings. Airplanes can last a long time and 20 or 40 years down the road those bearings will need to be replaced.

iamtheari · #5 09-25-2018, 08:08 AM

Quote:

Originally Posted by Tom Martin

The RV 14 is a wonderful example of how new technology has improved the design, and quality of parts. I do have a concern about this particularly part of the airplane in terms of maintenance. If those bearings are ever to be replaced it is going to be a major job. The "bearing" holders are riveted to the fuselage and if I were to do it again I would use screws to fasten these parts to the airframe. This would allow you to easily remove those parts to replace the bearings. Airplanes can last a long time and 20 or 40 years down the road those bearings will need to be replaced.

I wonder if I would be better off drilling those rivets out and re-engineering the bearing bracket mounts now, before I install the side skins and age an additional 20-40 years. I'm 36 now and, if there's a tedious job that must be done, I'd rather do it now than in retirement.

kbalch · #6 09-25-2018, 08:29 AM

As always, be careful with any reengineering, particularly of the "eyeball" type. If Van's hasn't OK'ed a change and you don't have the experience to do the math yourself, then any structural deviation from plans (including substituting screws for rivets) is a bad idea, even when it seems obvious that it'll work fine in a given situation.

Be aware, too, that any such deviation from plans is a likely focal point for future legal action by a new owner (even should you document and fully disclose all such deviations, which you're absolutely going to do, right?) or his estate's attorney.

I build with the intention of enjoying the plane (or car, bike, etc.) for a few years and then selling it and moving on to the next project. I couldn't possibly care less about maintenance issues 20-40 years down the road. Your mileage, of course, will very likely vary.

rvbuilder2002 · #7 09-25-2018, 08:40 AM

Quote:

Originally Posted by iamtheari

I got the bottom fuselage skins riveted together tonight and proceeded to install the control column. There is almost no play when one side's hardware is installed so I do not think I need any shims. But when the hardware is torqued to spec, the bearings seem rather stiff. It moves smoothly without binding, but it resists movement and will easily hold itself in position against gravity. How freely should the control column move?

As freely as as it does when only one side is torqued up.

The fact that it tightens up is an indicator that you do need shims.

Any noticeable friction at his point in the system will have an influence on flight characteristics. Most notably... pitch stability, and the ability for the airplane to return to trimmed flight after even a slight upset.

iamtheari · #8 09-25-2018, 08:44 AM

Quote:

Originally Posted by rvbuilder2002

As freely as as it does when only one side is torqued up.

The fact that it tightens up is an indicator that you do need shims.

Any noticeable friction at his point in the system will have an influence on flight characteristics. Most notably... pitch stability, and the ability for the airplane to return to trimmed flight after even a slight upset.

Thanks. I'll loosen one side at a time and see how that goes. I agree that any friction between my hand and the control surfaces would be best to avoid. My main concern is whether I somehow messed up the bearings themselves when sandwiching them into the bracket assemblies.

rvbuilder2002 · #9 09-25-2018, 08:46 AM

Quote:

Originally Posted by Tom Martin

The RV 14 is a wonderful example of how new technology has improved the design, and quality of parts. I do have a concern about this particularly part of the airplane in terms of maintenance. If those bearings are ever to be replaced it is going to be a major job. The "bearing" holders are riveted to the fuselage and if I were to do it again I would use screws to fasten these parts to the airframe. This would allow you to easily remove those parts to replace the bearings. Airplanes can last a long time and 20 or 40 years down the road those bearings will need to be replaced.

I have been working on RV's for almost 30 years now (and work on the oldest side by side RV flying

) and have never had to replace one of these bearings.
If the control column is shimmed properly so that there is no side load on the bearing, and they are lubricated occasionally, they will last. That is the main reason that even though design effort is typically made to make things reasonably maintainable,maintainability was compromised in this instance because it is unheard of to have one of these bearings fail.

rvbuilder2002 · #10 09-25-2018, 08:47 AM

Quote:

Originally Posted by iamtheari

Thanks. I'll loosen one side at a time and see how that goes. I agree that any friction between my hand and the control surfaces would be best to avoid. My main concern is whether I somehow messed up the bearings themselves when sandwiching them into the bracket assemblies.

These bearings can tolerate no side load without there being a large increase on friction.
That is the reason for the emphases on using shims and it is likely the cause of your friction as well.