Flap cables rubbing

[svyolo]

One of the gotchas that might be easy to miss, is the 0 degree flap setting, the pushrod needs to be resting (pulled actually) up against the pad on the tubing. If it isn't, or one side isn't, you can adjust the flap pushrod to zero, but in flight, with air loads, it might go farther up, past zero. Result - heavy wing.

I didn't realize how much force the flap springs would impart to the mechanism. You cannot properly adjust the cables without all 4 springs attached - not 1 or 2, but all of them. Which makes adjusting them (and making them) much harder. There is a lot of torsional flex in the torque tube. I ended up pulling the cable off of the pulleys, and sometimes removing a pulley, rather than remove the springs to adjust something.

The springs are also a bit hard to install and remove. I used pieces of 100# fishing line to pull the spring aft onto the arm, pulling the line straight back through the hole in the aft spar.

I will try tonight to come up with the actual procedure used to do all of this.

[svyolo]

The little voice in my head has been whispering "electric flaps" over and over.

[Nev]

Very interested in your thoughts on electric flaps......

[Battson]

Don't walk toward the light, Nev!

[Bcone1381]

Help me understand the difficulty with the flap adjustment. I might be wrong, but you may be over thinking it. From what I am thinking....

1) In the Flaps UP position, the springs force the flap pushrod against the rubber bumper. So, No adjustment is needed. The flap cables might even be a bit slack when the flap lever is in the UP position. I don't see a need for any adjustment.

2) When I pull the flap lever with a small mis-adjustment in the lengths of the cable that attach each flap to the Flap Junction Plate, no big deal. The Flaps are connected to each other via the tri-angle shaped plate. So the load on each flap will be equalized by the plate shifting slightly one to equalize the tension in the two cables and thus equalizing the flap travel. Plans call for a turn buckle on each of those cables. I adjust the turnbuckles so the junction plate remains centered.

One adjustment you might want to look at is how far the flaps travel down when the handle is in the FULL down position. If it travels past the point where Bob designed it to be, it may cause a load in the structure above the design considerations. I set my flap cable tension so distance between the rear spar and the inboard flap lever in the fully deployed position meets what is called out for in the plans.

[svyolo]

During the adjustment, I could get one side down on the stop, and the other one looked like it was down, but wasn't. I could only tell by looking through the hole in the rear spar. The side that wasn't "up" all the way still had spring tension, which was carried all the way through the system. Both sides, from the view from the access cover, looked up. Both sides had identical cable tension.

If you adjusted both flap pushrods so that they were zero at this point, it would look correct on the ground. But in the air, only one side would be "against the stop". The other could move up past zero a little bit with air loads. Top side of the wing is low pressure. It might get sucked up a degree or two, against cable tension, which is light at this point.

Right now, with flaps at full, I have about 38 lbs of cable tension on the upper cables. With the flaps retracted, it is about 17 and both pushrods are up against the stops.

But at one point, I had the same tension readings, with one pushrod on the stops, one about a 1/4" off of it, and the springs on that side were keeping about the same tension on the whole system. I assumed both were on the stops, but one side was not.

BTW I am not using tension readings for anything other than information. I just wanted to see how much it was.

[whee]

The little voice in my head has been whispering "electric flaps" over and over.

You just made my puke in my mouth a little🤮😉

[Bcone1381]

During the adjustment, I could get one side down on the stop, and the other one looked like it was down, but wasn't. I could only tell by looking through the hole in the rear spar. The side that wasn't "up" all the way still had spring tension, which was carried all the way through the system. Both sides, from the view from the access cover, looked up. Both sides had identical cable tension.

If you adjusted both flap pushrods so that they were zero at this point, it would look correct on the ground. But in the air, only one side would be "against the stop". The other could move up past zero a little bit with air loads. Top side of the wing is low pressure. It might get sucked up a degree or two, against cable tension, which is light at this point.

Right now, with flaps at full, I have about 38 lbs of cable tension on the upper cables. With the flaps retracted, it is about 17 and both pushrods are up against the stops.

But at one point, I had the same tension readings, with one pushrod on the stops, one about a 1/4" off of it, and the springs on that side were keeping about the same tension on the whole system. I assumed both were on the stops, but one side was not.

BTW I am not using tension readings for anything other than information. I just wanted to see how much it was.

What would happen if the cable tension was zero when the Flap Handle stowed while the flaps are removed from the wing? Both flaps pushrods will rest on the rubber bumper. Now install the flaps, and adjust the rod end bearing so the flap positions are equal.

In flight, the cable tension and the flap position is self adjusting. (via the flap cable junction tri-angle) The the tri-angle move towards the higher loaded flap and releases some of its load.

Issue #2. When I installed the flap cable system on the Patrol, I had to release all cable tension when the flaps were UP to prevent the Flap Handle from moving the inboard flap arm beyond a point that would result in 40 degrees. The distance between the Inboard Flap Arm cable attach hole and the rear spar should meet the plans when the Flap Handle is fully deployed. Because of my experience, I wonder if your flap handle is pulling the flaps too far down with a flaps up 17 pound cable preload.

My procedural recommendation to set the flap cable tension is to
1) Remove the flaps from the wing.
2) Loosen cable tension via the turnbuckles so that slack exists and so the Flap Pushrods rest against their rubber bumpers.
3) Pull the Flap Handle to Full Flaps.
4) Adjust each turnbuckle so the Inboard Flap Lever position meets what is called for in the plans. (as Indicated on the Patrol Plans below with red arrows.)

Mission complete. No cable tension meter required.


Screen Shot 2019-04-17 at 8.20.11 PM.png

[svyolo]

That is exactly what I did initially, but then I went back and verified if the pushrods were resting firmly on the bumper. At first they appeared to be, but looking closer, and measuring the distance from the spar to the pivot bolt, one was off the bumper slightly. I could not see it from below, only from the hole in the rear spar from behind the wing.

A very minor error in the length of the cable at Flaps 40 is a very small angular error. As the flaps retract, the angle of the cable gets much more acute, and that same amount of linear error becomes a much larger angular error.

I got better results by using the resting position on the bumper as the "index" for adjusting the cables. I wanted a little tension on it while I was adjusting to make sure all the slack was taken up in the pulleys, which are small in diameter.

Then pull on full flaps and make sure they are the same.

Anyway that worked for me.

[AKKen07]

Hey folks I need some help please. I am clearly missing something, and probably something obvious, but I am very much missing it. When the flap lever is in the forward/down position (flaps up) the flap cable coming from the flap lever going aft, immediately contacts the gear strut attach point. Then proceeds back a few inches to contact the bolt in the elevator bellcrank (maybe because it is displaced by the strut attach pt.)
A couple of notes:
1) the rigging is not complete - wings are not even out of the crates yet. But I don’t see how it would change this since the cables will only be under more tension in the same pulleys etc.
2) my kit’s flap lever is constructed slightly different than Bob’s drawings. It’s hard to explain but it places the attach point about 1/8” closer to centerline than it would otherwise. I put more details in the pictures below to explain. This may be normal in the kits but it may not be?

[Mark Goldberg]

Ken, I will call you later to discuss. Mark

[Steve W]

I wanted to update on my use of the swaged ball/fork ends l initially installed three years ago and mentioned on this thread. I thought this would be a better rig than a shackle and thimble. I was very wrong.
I recently assembled the plane at a local airport preparing for its final inspection. I was surprised to find the cable assembly was too stiff and the ball didn’t pivot at all in the fork. The cable was being forced hard against the pulley at full flap. Today I replaced both cables with a shackles and thimbles. The shackle should allow the thimble pivot enough to better align the cable with the pulley.
After tensioning the cables, the assembly was much better and was quite pleased with the results. I wanted to mention this because there were some interest from others. The ball end and fork didn’t work for me.
By using a shackle, I was able to just clear the rear spar attach fitting. I had to flatten the press ridges on the nico sleeve, it was that close.

[alaskabearhawk]

The ball will not pivot in the fork under load and it shouldn't have to.

[jaredyates]

Thank you for taking the time to follow up here!

[RatherBFlying]

AKKen07 how did you end up resolving your interference? I have the same issue. My flap cable rubs against the lower elevator bellcrank bolt when flaps are fully retracted.

[AKKen07]

I’m afraid it’s still a work in progress. Put that task off until later. Soon, hopefully.

[RatherBFlying]

007DD11C-ADF9-490C-8215-9E180714CB18.jpg I solved my flap cable / elevator bellcrank interference. I found that my bellcrank was actually off center a small amount towards the passenger side, aggravating the interference. I removed about 3/16 of an inch from the pilot side of the bellcrank pivot tube and cut a spacer to fill in the gap on the passenger side. This moved the bellcrank back to center, or a little closer to the pilots side of center and left a small gap between it and the flap cable.

Edit: I noticed this thread was in the quickbuild section, I should note that my project is a scratch built.

[AKKen07]

I’m glad that’s all it took! On to the next puzzle