11-04: Elevator Rod End Bearings

In a previous post i trial fitted the elevators, and found that the leading edge of the elevator was rubbing on the HS elevator mounting brackets.

Based on the RV7 manual, i elected to wind out the bearings to 7/8" from the spar face, in order to stop some of the rubbing (in addition to some massaging of the leading edges themselves) and i contacted Van's to get some assistance as to how far out i can wind the rod-ends, to make sure i was doing the right thing (newbie paranoia i think - in the end i had to work it out myself!).

RV 7 Build Drawings

Below is the email i sent to Van's - in essence seeking approval to wind out the bearings to the same distance as the RV7:

I have finished the elevators and I’m trial fitting them as per page 11-02.

I set the rod end bearings accurately to 13/16 from the spar face, and the leading edges were rubbing against the HS hinge brackets between 20-30 degrees nose up. There was no rubbing nose down.

I removed the elevator and reshaped and flattened the leading edge a little with a rubber mallet. I reinstalled and it was better but still just rubbing approaching -20 and +25.

I have managed to get it not to rub by backing out the rod ends a turn and a turn and a half. The rod ends are now at 7/8 outboard and 29/32 inboard. At these settings there is no rubbing until -30 and +40 - which I think is good. (They are slightly different to even the gap at the counterbalance skin).

I’m just worried about the number of threads showing out the back of the nutplate.

Can you advise what is the maximum distance the rod end bearings can be taken out to?

I note the RV7 has the same rod end and nutplate - I don’t know if the thickness of the spar and spar reinforcement plate is the same but perhaps you would know this?

  And here is the reply from Sterling:

I am afraid I do not have a max tolerance for this measurement. I can however say this assembly can be treated the same as a nut/bolt combination meaning if you have one or more threads protruding through it is acceptable. The trouble here is that without a borescope it’s a little difficult to see this.

On quick inspection I believe the parts build up in the 14 is thinner as they do not have the forward E-00001 doublers.

So where to next?

I decided to check on the RV7 manual and parts list, and work out what parts made up the build up where the rod ends were installed, and calculate the total thickness:

RV7 Parts list

E-610PP - Hinge Doubler - 0.063"

E-702 - Elevator Spar - 0.032"

E00001A - Front Face Doubler - 0.063

TOTAL: 0.158"

I then compared this to the RV14:

E-00902-1 - Elevator Spar - 0.032"

E-910 - Hinge Doubler - 0.063"

TOTAL: 0.095"

So the RV14 is 0.063" or 1/16" thinner than the RV7, with the same nutplate and the same rod end. 

Get out the calculator...

The RV7 plans ask you to set the rod ends at 13/16 (same as the RV14), but give a maximum value of 7/8":

On the RV7 - this presumably means, that with the rod end set at the maximum 7/8", and with a material thickness of 0.158", there would be the required one thread showing out the back of the nutplate. 

On the RV14 therefore, with the same nutplates and rod ends, but with 1/16" thinner material, the rod ends could be wound out 1/16" more than the maximum permitted by the RV7, which is 7/8". 

So doing the maths: 7/8" + 1/16" = 15/16", or 30/32". 

Given this, i marked my ruler and wound one rod end out to 30/32". 

Borescope time

Here is a picture of the back of the rod end, wound out the 30/32":

Note: the blue paste is Boelube from installation of the rod ends.

As you can see there are ZERO threads showing out the back of the nutplate!!! 

Meaning?

This means two things:

1. This is not an acceptable distance for the RV14, and i will need to wind the rod ends in a little, so i achieve at least one thread out the back of the nutplate. 

2. With regard to the RV7, where the material is an additional 1/16" thicker, if a builder set their rod ends to the maximum distance of 7/8", the end of the threads would be 1/16" inside the end of the nutplate. (this doesn't sound right to me!). Please send me a comment if you think i have made an error here (a highly probable occurrence!)

Final decision

So moving forward, i wound the rod end in a full turn and had another look at the end of the rod end:

This seems to be a much better situation. I then measured the distance i ended up with:

As you can see above, it is about 29/32". I ended up working on 28/32", which is 7/8" as my final decision, and then checked all the remaining 3 rod ends to make sure they were showing one thread:

Conclusion

This was an interesting exercise. I the end, i have finished up with elevators which do not rub at all, and i am happy that the rod ends are at the correct distance for my aeroplane. I hope i have made an error in my calculations regarding the RV7, or i have missed something. Overall i am surprised that Van's didn't publish a maximum value on the RV14 for the rod ends, especially since Step 4 of 11-03 (where you are drilling the elevator horns) they ask you to wind out the rod ends - but how far is too far?

11-03 Step 4:

"NOTE: Verify the minimum distance from the Horizontal Stabilizer Rear Spar web to the Elevator Torque Tube is 1 5/8 [41.3 mm] as shown in Figure 2. Readjust the Elevator rod end bearings as necessary to achieve this distance prior to drilling." 

Anyhow, moving onto the aft fuse!