Rudder cable adjuster

[svyolo]

Anybody try using a #MS21259-4RH and threaded fork to adjust the rudder cables? Much lighter than a turnbuckle. Nicer looking and probably slightly lighter than a nico press and metal plate with adjusting holes.

[svyolo]

They make them in RH and LH threads. Use one of each on each end of a control cable, and the whole cable could function as a turnbuckle body? There is a hole for safety wiring.

Aircraft turnbuckles are heavy.

[Archer39J]

When I look at MS21259 rev J the spec says a min breaking strength of 2,000 lbs. If I recall correctly the primary turnbuckles are all 3,200lb.

[PaulSA]

Am I missing something? The rudder controls aren't "closed loop" and don't require tensioning. As I understand it, the springs on the rudder pedals are there to stop them falling down. On the VANS aircraft (where the pedals are hinged at the top) the cables are loose.....

[Archer39J]

Am I missing something? The rudder controls aren't "closed loop" and don't require tensioning. As I understand it, the springs on the rudder pedals are there to stop them falling down. On the VANS aircraft (where the pedals are hinged at the top) the cables are loose.....

They're just for additional adjustment, otherwise you'd have to get your cables and springs exactly the same. Some omit them, some add them. They're not called for in the plans for what it's worth. I chose to put them behind the cargo bulkhead.

See this for more discussion: https://bearhawkforums.com/forum/bea...ckle-placement

[Bcone1381]

Anybody try using a #MS21259-4RH and threaded fork to adjust the rudder cables? Much lighter than a turnbuckle. Nicer looking and probably slightly lighter than a nico press and metal plate with adjusting holes.

I am sure that you know that the part referenced is for swaged cables. Swaged cables look real nice. I use turn buckles with cable eye ends attached to a cable thimble like Dave B.

Spruce will make up swaged cables. My concern was getting the cable lengths exactly right, and depending on them to duplicate it. But if you can get the lengths right who needs a length adjustment?

[Archer39J]

I used the ACS pre-fab swaged cables for my tail wires, they do look quite nice. I couldn't see using 2,000 lb rated hardware on the rudder cables being a problem, it's not like you're going to ever produce anything close to that with your own two legs. But there is a safety factor and some design considerations I'm sure I'm ignorant of. Also provided you can find fork hardware that will give you the cable rating. Running it by Mark or Bob would be prudent.

[svyolo]

I will run it by Bob. I heard he doesn't use turnbuckles,or very few. I think I could get by with 1 on 1 side of the ailerons, and maybe one more on the elevator.

[Battson]

Am I missing something? The rudder controls aren't "closed loop" and don't require tensioning. As I understand it, the springs on the rudder pedals are there to stop them falling down. On the VANS aircraft (where the pedals are hinged at the top) the cables are loose.....

People have snapped the rudder horns off a Bearhawk on a few occasions, by pressing hard on the rudder pedals. So they aren't under constant tension, but they do need to be strong and adjustable in an ideal world.

[svyolo]

On the rudders, I would use no turnbuckles. LH and RH threads on each side. Install the cables untwisted and natural. Adjust them loose so they are very close on each end. After that, adjust each front and back the same amount to keep from twisting them.

Elevator Maybe use a TB on one side. Or maybe not. Get it close with the cable, and tension with the TB.

It might take slightly more time to get the adjustment right, but it might also save 1-2 lbs. But maybe not. I think safety wiring 2 swaged ends might be easier than 1 TB.

[Battson]

Getting the right pedal angle correct is very important for them to work properly. The pedal angle is completely dependant upon the rudder cable's exact length. Not to mention your adjustment of the centre pedal position.

In my case, it took days and hundreds of dollars of wasted cable to get the pedal angle exactly right, without turnbuckles. Those "adjustable" steel bars were too coarse for my liking.

Then when something minor changed with my pedal geometry, I was faced with doing it all again. But instead, I added short turnbuckles and it took 15 minutes instead, first try. I immediately realised the folly of trying to leave the turnbuckles out.

Remember, even pre-stretched cables can loosen over time - the cable eyes on the end change shape as they get pulled on, particularly if you have a tendency to lean on the brakes hard. This has a bigger impact than I first expected.

To save a fraction of a pound, you might prefer to pack a light lunch instead

[svyolo]

Or skip lunch, for 6 months in my case. LOL.
I was wondering about rudder pedal position as well. And all the other controls. I have all the rudder, elevator, and trim cables nicopressed on one side, and cut long.
I will use those and the turnbuckles that I already bought until I get it to the way I like it. But once I get it right, later I think I will try to replace them with swaged ends. Swages are also a lot stronger than nicopresses if I remember right.

I will check again, but I think I added up all the turnbuckles and they weighed about 2 pounds. I have an old sailboat lifeline turnbuckle (much nicer than the AN ones) and they weigh half of what the AN weigh

[svyolo]

I bought a couple of fittings including a MS21259-4 stud, MS665 threaded fork, and MS20667-4 swaged fork. I am pretty sure I will use at most 2 turnbuckles on my 4 place. If I use two, 1 will be in the middle of the two aft aileron cables in the cockpit, and 1 on one of the elevator cables.

You only get about +/- 1/4" of adjustment with a turnbuckle. The MS21259 and MS665 it looks like you could get up to +/- 7/16". Almost double for less cost and weight.

Rudder cables, 1 swaged fork, and 1 threaded fork and stud per side.
Elevator, 1 turnbuckle and one swaged fork on one side. One swaged fork and one threaded stud and fork on the other.

Aileron, aft cables 2 swaged forks on each side, with a turnbuckle in the middle. Long front cable, one swaged fork, one threaded stud and fork per side.

I am also going to experiment with trying to tension the cables with just the threaded stud/fork. It is only 30lbs of tension. If I can tension them properly, and still get the pin/bolt in with only 2 hands, I won't have any turnbuckles.

The only challenge will be properly measuring the length of the front aileron cables. Going through 3 pulleys per side will require measuring with an actual piece of cable. I will probably use one piece from the stick, pull it tight and mark it at 1 specific rib location. Then attach it to the aileron bell crank, pull it tight, and measure to the same rib.

If I do it right, there will be no safety wired terminals, or nico press fittings with sharp edges in the cockpit.

[Bcone1381]

I find it hard to believe my turnbuckles only have a 1/4" of adjustment, but I am often wrong. How did you come to that conclusion?

A nice way to get a dead accurate cable length is to fabricate a pattern for your cables using safety wire. When the wire gets removed from the can of safety wire it will look like a worn out slinky. Put a pair of vice grips on one end, and the other end in a vice and whack the vice grips a couple of times with a dead blow mallet. It will be straight as an arrow. Feed the straight wire thru the path the cable will travel, and then bend the ends around where your termination hardware will attach. When you remove the wire, take care to protect those ends.

[svyolo]

Safety wire (or any wire) would work fine for a straight run, but I doubt it would work well to measure the cable for the forward aileron loop. The cable goes through 3 pulleys, and I am guessing the different radius caused by the different diameter of the wire vs cable might make for too much error. It might be close enough. Just a guess.

The spec for aviation turnbuckles is a maximum of 7 threads difference. I believe it is allowed 3 threads outside to 4 threads inside, per side of the turnbuckle. I measured 7 threads on the specified turnbuckles and it is only 1/4". So each turnbuckle, in the size specified, can only allow a range of adjustment of 1/2", or +/- 1/4".

Not much adjustment, for the weight, expense, and complexity of the turnbuckle. Instead of 2 on the aileron loop, I would prefer 1 (or none) to adjust tension only. I would also have one of the threaded studs with a threaded fork. Those seem to have almost double the adjustment range of a turnbuckle, for a lot less complexity and weight. If I can figure out a way to accurately tension without a turnbuckle, I won't use any turnbuckles. It might be difficult on the ailerons as the only place with a lot of access is overhead in the passenger compartment. The wings will be closed, and the only other place to work is through the small access panels.