What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

elevator pushrod problem

WingsOnWheels

WingsOnWheels

Well Known Member
I am rigging the elevator an ran into a problem. The forward (small) pushrod is contacting the top of the hole in f-605 before the elevator stops. I could make the hole slightly larger, but the rod is at a point it will hit the underside of the floor at the extremes of its travel. I double checked my measurements and the bellcrank and contol stick weldment, both are where they should be. I will call Vans tomorrow, but is this a common issue, or has someone else run into this problem?
 
Make sure the belcrank aft of the baggage compt is positioned correctly. It should be vertical ( relative to the fuselage level ref.) when the elevator is neutral.
 
RVDan said:
Make sure the belcrank aft of the baggage compt is positioned correctly. It should be vertical ( relative to the fuselage level ref.) when the elevator is neutral.
Click to expand...

It is. The pushrod touches at both the forward and aft extremes, so i can't adjust it out.
 
Don't know about the six, but on the 7, the sticks are not vertical with a neutral elevator. They are actually quite forward. Drawing shows maybe 30 degrees tilt from straight up and down.
 
Last edited:
Same for the -6, the stick is forward when the elevator is neutral. The only thing I could think of is that the bellcrank pivot point is located wrong. The stick doesn't change the contact point in the rear much. Any pics of where the rod contacts?
 
The pushrod is contacting where it passes through f-605, The rear spar bullhead. There are no clearance issues at the bellcrank. Since it is contacting in both dorections ( up and down elevator), it isnt a neutral point issue. I measured the weldment to make sure it was correct, no issues there. This is a later fuselage kit, there have been a few places where vans changed to rv-7 parts that dont quite work. I not sure if there have been any changes in this area, ill have to consult my old vs new plans.
 
Last edited:
I had the same problem on my -6A. Van's suggestion was to trim until there was no binding. I didn't need to remove much - perhaps 1/16th of an inch - and filed out the tooling marks.
 
Enlarge the hole, just don't cut into the carry-through strap. Hopefully you got the strap low enough on the bulkhead to give you room.
 
Thanks for the replies. I spoke to Ken at Vans on Monday and he said I could trim more from F-605 and could also trim a little from the yoke on the control stick weldment to keep it from hitting the rod end at full up elevator travel.

I did a little bit of trimming last night and played with the pushrods some more. Since the hinge point for the control sticks is off-center, I bought myself a bit of clearance by making the sticks more vertical in neutral.

At this point I can solve the binding at F-605 and at the rod-end. However, I find that the pushrod break the plane of the floor buy ~3/32" at full down elevator travel.

If there are any RV-6 building that happen to have there floor center cover open for maintenance, could you send me a picture showing the position of the control stick weldment at full forward and full after travel? Also, could you let me know how much clearance you have to the floor at full down elevator travel?

The place where I have an issue is where the seat slopes down from F-605 and then goes flat before sloping up to F-604. Here is a quick MS paint drawing to show the issue.

2cid2za.jpg
 
I didn't see it called out specifically in previous posts and may have missed it, but are the elevator stops (F-611B spacer for down limit, F-612B angle for up limit) in place? Assuming those are in place, do you get full travel of the elevator or full travel "and then some"? Full travel without the stops is significantly more than it is with them installed as you probably know.
 
Last edited:
ChiefPilot said:
I didn't see it called out specifically in previous posts and may have missed it, but are the elevator stops (F-611B spacer for down limit, F-612B angle for up limit) in place? Assuming those are in place, do you get full travel of the elevator or full travel "and then some"? Full travel without the stops is significantly more than it is with them installed as you probably know.
Click to expand...

The stops are all in place. The down stop is about .5 degrees short of Max, and the up stop is about 2 degrees short of Max. If I have to, I could change the down stop closer to minimum and that may eliminate the problem. However, I shouldn't have to do that unless something else is wrong. To note, I have an RV-7 tail. I am going to measure tonight to see if the elevator control horns are the same from the RV-6 to the 7.
 
WingsOnWheels said:
The stops are all in place. The down stop is about .5 degrees short of Max, and the up stop is about 2 degrees short of Max. If I have to, I could change the down stop closer to minimum and that may eliminate the problem. However, I shouldn't have to do that unless something else is wrong. To note, I have an RV-7 tail. I am going to measure tonight to see if the elevator control horns are the same from the RV-6 to the 7.
Click to expand...

That seems like a great next step. I have an -8 vertical on mine but the normal -6 horizontal. Something is oddly different here - looking forward to hearing about what you find!
 
Trim it

ChiefPilot said:
I had the same problem on my -6A. Van's suggestion was to trim until there was no binding. I didn't need to remove much - perhaps 1/16th of an inch - and filed out the tooling marks.
Click to expand...

I just checked my fuselage... looks like I trimmed almost 1/8 upwards and about 1/16 on the lower side of the hole.

The trimming almost, but did not, touched the 1/8 bar cross piece.
 
az_gila said:
I just checked my fuselage... looks like I trimmed almost 1/8 upwards and about 1/16 on the lower side of the hole.

The trimming almost, but did not, touched the 1/8 bar cross piece.
Click to expand...

I already trimmed the hole in F-605 quiet a bit. Ken @ Vans said that I could take more, but since the control rod is breaking the seat plane, it won't do me any good.

I just can't figure out what I may have screwed up. The Control column supports are mounted to F-604 per the plans. there is littl room for error in the bellcrank without edge distance issues.

Do you recall how much up and down deflection you have at your elevators. If less than Max, what was the limiting factor?

Thanks,

Edit: What drives me nuts on this whole thing is that my build is dang near done. All I have left is fairings, pants, wingtips, a little cowl work, and paint. I didn't anticipate a major problem with the controls.
 
Last edited:
WingsOnWheels said:
I just can't figure out what I may have screwed up. The Control column supports are mounted to F-604 per the plans. there is littl room for error in the bellcrank without edge distance issues.
Click to expand...

Have you checked to see if there is a slight bow in the push/pull tube, and it is installed with the bow upward? That push/pull tube is a bit of a bugger to get installed.... you might have bent it very slightly while doing so.
The simplest check would be to just unbolt both ends and rotate it 180 degrees.
 
Is your pushrod too short?
My pushrod rod end will almost hit the spar web with the stick in aft position.
Here is my thinking, and Scott, Gil, and others far more in the know here than I, poke some holes in this, frankly, this gets my brain a little fuzzy;

A longer push rod would shallow out the vertical travel.
I would not be concerned about weldment and bellcrank geometry or reference to each other as long as I could get full travel without any over center of the bellcrank, which would be nearly impossible given the clearances through the tunnel.
Of course a longer push rod here, means a longer push rod between the bellcrank and the elevator.
I built mine per the dimensions called out on the plans. I barely met minimum thread insertion on the rear pushrod for the rod ends, but I made it. I looked at building a new forward pushrod, but came into this exact problem you are having and realized if I shortened it to get a little more thread insertion in the back, I would be introducing other issues, like the bellcrank hitting the back of the baggage bulkhead, or perhaps the pushrod hitting the floor?
 
The problem i have with the forward travel of the pushrod is that the rod end contacts the inside of the yoke on the control stick weldment. Ken said i can trim a little material away from that area for clearance. That is limiting my control adjustment. A little more tweaking it may work out, but it will.still be very close.
 
WingsOnWheels said:
The problem i have with the forward travel of the pushrod is that the rod end contacts the inside of the yoke on the control stick weldment. Ken said i can trim a little material away from that area for clearance. That is limiting my control adjustment. A little more tweaking it may work out, but it will.still be very close.
Click to expand...

Colin - I do remember having to do this, but it wasn't quite enough before I was uncomfortable taking more material away. Is it now hitting on the shoulder of the threaded insert in the pushrod? I ended up filing a chamfer in that shoulder just at the point of contact.. I did not have to file much and I felt comfortable with this modification and did not feel it affected the overall integrity of the part. However, modifying a part like that is a personal decision and choice. Just telling you what I did.

PS - I believe it was Ken who told me about trimming away some of the yoke, many years ago. He hangared his 6 near mine, and was kind enough to take me flying in it and helped me with advice on my build many times. He would know.
 
Last edited:
WingsOnWheels said:
The problem i have with the forward travel of the pushrod is that the rod end contacts the inside of the yoke on the control stick weldment.
Click to expand...

This starts to become a problem when you adjust the control sticks to be more vertical at neutral... vs angled fwd as they are supposed to be. You are inducing this problem with your adjustments compensating for the other problem.
 
RV-6A - what I remember

WingsOnWheels said:
The problem i have with the forward travel of the pushrod is that the rod end contacts the inside of the yoke on the control stick weldment. Ken said i can trim a little material away from that area for clearance. That is limiting my control adjustment. A little more tweaking it may work out, but it will.still be very close.
Click to expand...

Collin - I had to go back out and review my forward elevator tube travel to remember some details. 1) I also filed away a tad from the control tube elevator yoke (fwd end of elevator tube) mainly because the straight and very sharp edge would indent the top of the rod-end. Minor clearance added but any contact is smoother now. 2) the elevator tube under the seat pan tunnel cover is very close to touching, 1/16" clearance but the motion on the tube is almost vertical (not horizontal) at that point of stick max fwd. 3) without the control stick boot retainer, MY control stick moves forward further, ALLOWING the tube to come up that high. (Normally this would be restricted by the elevator stops, or the boot retainer. My elevator is currently OFF.) 4) I vaguely remember that the control stick was supposed to be (5degs ?) forward and not absolutely vertical when setting up the travel. Will research the manual for that detail.

I recently found that the rivets on the aft end of the elevator tube snagged the edge of the aft baggage compartment bulkhead hole. Discovered while reviewing the pitch servo motion. Had to adjust the spacers on the bellcrank, and will file the hole edges slightly.
 
If all else has been tried...

RV 7 & 9 models have a raised cover in the centre tunnel area. What say you copy something similar to gain your needed floor clearance? Don't make it too high if you have manual flaps though.
 
RViter said:
Collin - I had to go back out and review my forward elevator tube travel to remember some details. 1) I also filed away a tad from the control tube elevator yoke (fwd end of elevator tube) mainly because the straight and very sharp edge would indent the top of the rod-end. Minor clearance added but any contact is smoother now. 2) the elevator tube under the seat pan tunnel cover is very close to touching, 1/16" clearance but the motion on the tube is almost vertical (not horizontal) at that point of stick max fwd. 3) without the control stick boot retainer, MY control stick moves forward further, ALLOWING the tube to come up that high. (Normally this would be restricted by the elevator stops, or the boot retainer. My elevator is currently OFF.) 4) I vaguely remember that the control stick was supposed to be (5degs ?) forward and not absolutely vertical when setting up the travel. Will research the manual for that detail.

I recently found that the rivets on the aft end of the elevator tube snagged the edge of the aft baggage compartment bulkhead hole. Discovered while reviewing the pitch servo motion. Had to adjust the spacers on the bellcrank, and will file the hole edges slightly.
Click to expand...

The clearance you to the floor sounds pretty similar to mine. Based on the responses to this thread it seems I am not the only one with this issue and it just needs to be worked out. I was concerned that I had made a mess of something down the line or it was related to my change to the RV-7 Tail. I can buy myself another 1/8" of clearence if I buy new F-633 L&R (the brackets that connect the weldments to F-604) and drill the holes closer to the top.
 
rvbuilder2002 said:
This starts to become a problem when you adjust the control sticks to be more vertical at neutral... vs angled fwd as they are supposed to be. You are inducing this problem with your adjustments compensating for the other problem.
Click to expand...

I agree completly, but at this point I don't see any other options. If I set the control stick neutral to 5 Degrees forward, the pushrod doesn't clear the floor at full forward stick travel. I think the reality is that the design max down limit for the elevator (while also having max up) is not possible without modification to the control. Looking at the plans even, the geometry doesn't work out. It is unlikely that full down elevator will be used by 99% of RV'rs, The better option may be for me to limit down travel closer to Min than Max. That may eliminate the need to make modifications.
 
Last edited:
WingsOnWheels said:
The stops are all in place. The down stop is about .5 degrees short of Max, and the up stop is about 2 degrees short of Max.
Click to expand...

Chapter 15 gives the travel limits of Max 30/25 (Up/Down) and Min 25/20 (Up/Down). There are no issues with going with the minimum limits and it aids in avoiding control components interfering with structure. You will typically only hit these deflections when taxiing and it could be a WILD ride if you hit them in flight.:eek:

Try limiting the UP stop by a few degrees and see if that eliminates the interference issue. It's pretty easy to simulate this.
 
WingsOnWheels said:
I agree completly, but at this point I don't see any other options. If I set the control stick neutral to 5 Degrees forward, the pushrod doesn't clear the floor at full forward stick travel. I think the reality is that the design max down limit for the elevator (while also having max up) is not possible without modification to the control. Looking at the plans even, the geometry doesn't work out. It is unlikely that full down elevator will be used by 99% of RV'rs, The better option may be for me to limit down travel closer to Min than Max. That may eliminate the need to make modifications.
Click to expand...

Something must not be right with the entire assembly...there are too many -6s flying which don't have this problem.

Is the bellcrank installed correctly, right side up? Is it the correct control stick weldment? Etc.

Find the root cause of this interference...the plane certainly wasn't designed to be as you describe.
 
RV7A Flyer said:
Something must not be right with the entire assembly...there are too many -6s flying which don't have this problem.

Is the bellcrank installed correctly, right side up? Is it the correct control stick weldment? Etc.

Find the root cause of this interference...the plane certainly wasn't designed to be as you describe.
Click to expand...

I will check some more measuements on the weldment. I did check that the horn was the right length, but that was it. The bellcrank is positioned per plans. Ken mentioned that filing the yoke a bit is a common mod. I think i need to adjust the down stop a bit. I would rather limit down travel than up if i have to pick one.
 
RV7A Flyer said:
Something must not be right with the entire assembly...there are too many -6s flying which don't have this problem.

Is the bellcrank installed correctly, right side up? Is it the correct control stick weldment? Etc.

Find the root cause of this interference...the plane certainly wasn't designed to be as you describe.
Click to expand...

Well, yes and no. Every 6 is different, not like the pre punched kits. I built my wings but was one of the early QB fuselages. I had many discrepancies from the plans to the actual built fuselage, especially in and between the area of the center section and baggage bulkhead. I had a lot of compromises with rear baggage side panels, wing sweep, etc....but she still flies fast and true. A credit to the conservative design of the product.

It does not take a lot of change in this area to start introducing problems. However, it all can be worked through, one way or another as evidence by the shear number flying. Some of us just had or have a little more fiddling to do, and this area seems to be one of them, at least it was for me.
 
After messing with everything again last night it looks like I can make it work but I would have to limit elevator travel to minimum both up and down (25 / 20) rather than what I have right now (27.5 / 24.8). With this being an A model, I was hoping to maximize up travel so I could hold the nose off as long as possible.

Before I make any changes though I am going to find the root cause of my issue. Also last night, I pulled out the plans and drew up the basic floor, F-604 and F-605 structure in CAD. I also added all the geometry for the control system components from the stick to the elevator all exactly matching the plans. My next step is to model the elevator travel I have on the plane and see where my results differ from the CAD model. Assuming there is a delta, I'll start to measure every component until I figure out what happened.

And in case anyone is wondering, I don't believe any of this was caused by switching to the RV-7 tail. The elevator control horns for the RV-7 are an RV-6 part number and at quick check the measurements appear to match the RV-6 plans.
 
Very timely Colin ... I am getting close to do the push-rod install and look forward to hear what you find out ...

Good luck !
 
I miss real drawings.

WingsOnWheels said:
After messing with everything again last night < snip >
Before I make any changes though I am going to find the root cause of my issue. Also last night, I pulled out the plans and drew up the basic floor, F-604 and F-605 structure in CAD. I also added all the geometry for the control system components from the stick to the elevator all exactly matching the plans. My next step is to model the elevator travel I have on the plane and see where my results differ from the CAD model. Assuming there is a delta, I'll start to measure every component until I figure out what happened.

< snip >.
Click to expand...

Yes -this is what I do from time to time to really understand what is going on and why. Having real dimensions, lengths, center, clearance, and angles is invaluable for really building an RV. I do it in pencil, but, the result and understanding is the same.

I miss real drawings.

Please share your result, it is an interesting issue.
 
Ok, I have put all the required structure and control system parts into CAD for analysis. The data I loaded is all directly from the most current set of plans I have. I have not compared it to the very old set I also have, but some of those drawings do have revisions in the current version.

Here is a overview of the drawing I made. For control neutral, I assumed a 5 degree forward cant of the control sticks, and that seems reasonable. I did not include any aileron control parts on the drawing, so that is why the control stick look funny. The square at F-605 represents the per-plans vertical dimensions of the pushrod cutout.

The fuchsia lines represent the control system with Max (25 Deg) down elevator deflection.

7V3nZk.jpg


The area circled above is shown in more detail in this image. The green line is the top of the seat rib. The fuchsia lines are the pushrod width and centerline. You can see that the pushrod is breaking the plane of the seat pan/seat rib top.

VsQ3jD.jpg


Here is the system again with Max (30 deg) up elevator. This is based on the same neutral point as the down elevator example.

hUeen2.jpg


And a closeup of the highlighted area.

YrMhvM.jpg


You can see that the control rod is one again interfering with the seat pan. However, less so than the down travel limit. For max Up elevator the overlap is 0.063". For max down elevator it is 0.127". Changes to the neutral point could improve one or the other, but not both.

My conclusion is that it is not possible to reach max up and down elevator deflection with the RV-6 control geometry per plans.

The next step is to see what is the max possible deflection without the noted interference.

It seems where I went wrong was to make my elevator stops before completely rigging the elevator controls. I should have left the stops long and trimmed them once I had everything set up and could make appropriate adjustments. For my RV, I need to make new up and down stops to something less than max deflection, but no less than minimum. Based on what I have seen already I think I will have to remove around 5-10 degrees of total elevator travel, but that is just a guess at this point.

I would really like to know how much up/down travel some completed RV-6s have for comparison purposes. Are builders generally ending up with something close to Minimums?
 
Was just about to cut the hole in F-606, good timing.
Very interested to hear what travel others have on their flying rv-6's
 
JonJay said:
25/30 on mine
Click to expand...

Thats very interesting. I wonder how your installation differs. Did you have to remove any material for clearance at the forward rod end. Id really like to know how much clearance you have from the pushrod to the floor, and how far from the top of f-604 to the top of f-633 ( the pivot blocks for the control weldment).
 
I have been trading pictures with Don in Fl, he is getting near full up/down travel as well with no issues. From the pictures, his setup look the same as mine.

Back to the drawing board again. Im not sure what is different.
 
Mine looks exactly like what is shown on dwg. #40 .
Clearance to the seat pan is not an issue, not really even close. Weird.
 
Is it possible that your seat ribs are from an RV-7?
The seat pans were lowered for the -7 and -9 to increase headroom.
 
Colin,

You used 5 degrees for the stick angle, but as I read it, the easier method is to make the drive horn (Detail A in the picture) vertical when the system is in neutral position.

This is what the plans seem to show.

controls_zpsccb2ae38.jpg


If you change the stick neutral angle, does it help? My scan is different from the green neutral lines in your CAD drawing.
 
Last edited:
I have a -7, not a -6, so I don't know the details of construction on a -6 and how they differ, but...

Are the F-633 control column mounts positioned correctly (impossible to do on a -7 due to pre-drilled locations, but maybe not on a -6??? I don't know if they're pre-drilled or not).

Just a thought, and it may not even be possible to mount them too hight, don't know. Just thinking out loud.
 
az_gila said:
Colin,

You used 5 degrees for the stick angle, but as I read it, the easier method is to make the drive horn (Detail A in the picture) vertical when the system is in neutral position.

This is what the plans seem to show.

controls_zpsccb2ae38.jpg


If you change the stick neutral angle, does it help? My scan is different from the green neutral lines in your CAD drawing.
Click to expand...

Ill recheck my stick angles in the cad drawing, maybe i messed something up there.

In my actual installation, i have played with all sorts of neutral points. The closest in have to clear is with the sticks vertical at neutral. But that still leaves me with a bit of a problem at full down elevator.

The only place i can fimd room for error it at the f-633 vertical position. I mounted mine withe with mounting hole 1/2" from the top edge, but on of the pictures i saw from someone with no issue, it looks like theirs was closer to 3/8". That may be all it takes to make the difference.
 
Mel said:
Is it possible that your seat ribs are from an RV-7?
The seat pans were lowered for the -7 and -9 to increase headroom.
Click to expand...

I dont think so, but ill check my ribs to be sure. I think there are other differences as well, like the shape of the lightening/aileron cutout. Mine has the traditionl round cutouts.
 
RV7A Flyer said:
I have a -7, not a -6, so I don't know the details of construction on a -6 and how they differ, but...

Are the F-633 control column mounts positioned correctly (impossible to do on a -7 due to pre-drilled locations, but maybe not on a -6??? I don't know if they're pre-drilled or not).

Just a thought, and it may not even be possible to mount them too hight, don't know. Just thinking out loud.
Click to expand...

None of those parts are prepunched on the -6, but the position called out one the plans is specified as approximate. I think moving these lowers is my best bet for a fix.
 
WingsOnWheels said:
None of those parts are prepunched on the -6, but the position called out one the plans is specified as approximate. I think moving these lowers is my best bet for a fix.
Click to expand...

LOTS of work (IMHO). Again, take a look at a 7 or 9 model & see how the factory delt with this clearance issue in later designs. Copy the center tunnel cover used in these models & trim the seat pan accordingly. The structure is virtually the same these models as in your 6.
 
Ralph Inkster said:
LOTS of work (IMHO). Again, take a look at a 7 or 9 model & see how the factory delt with this clearance issue in later designs. Copy the center tunnel cover used in these models & trim the seat pan accordingly. The structure is virtually the same these models as in your 6.
Click to expand...

Putting in new F-633 l&r shouldn't be a big deal. Four bolts all together. I did check last night and i can remove the section of the tunnel cover under the flap motor assembly and it will do the job, but i would rather address the root cause if possible.
 
I did another quick check with my CAD model. If I move the F633 down just a little bit, it solves all my interference problems. So that is my plan. I'm going to double-check a few measurements first just to be sure. If that all checks out, I'll spend the $70 for new parts and be done with it.

Thanks everyone for your help. Having the pictures from other builders definitely helped clear things up. I'll report back once I get the new parts installed.
 
I had a look at my two F633 - I have the pivot point for the stick assembly - 1.062" down from the spar top bolts .. How does that compare with your cad model layout ?
 
Dimensions

JanRV6UK said:
I had a look at my two F633 - I have the pivot point for the stick assembly - 1.062" down from the spar top bolts .. How does that compare with your cad model layout ?
Click to expand...

Interesting, the plans show 1.25 inches down from that bolt hole - but does use the term approx.

IIRC the angle came cut to length from Vans with the stick pivot bearing already installed so the builder had little control over the 1 3/4 dimension shown in the plans.

I'll measure mine...

UPDATE

Mine measured 1.28 pivot to upper bolt hole.
 
Last edited:
I had a another look and re measured ... I have 1.107 to the bolt hole centre ... and then I have 0.611 from the bolt centre to the top the bracket ....
 
You must log in or register to reply here.
Back
Top