Rudder Rigging

[PaulSA]

I am at the stage of fitting cable runs to the rear and would like a couple of questions answered before starting on the rudder.

I have measured the movement of the attach hole on the rudder horn from stop to stop - it is about 4". I have placed the rudder pedals in what looks to be a reasonable neutral position and that is with the horn perpendicular to the attach plate - this seems to give most movement before the geometry starts to get silly. However, the movement at the end of the horn here only seems to be about 2".

Since it is a straight cable connection with no levers or bellcranks, I simply don't see how it is possible to get full movement on the rudder without getting one pedal hard up against the brake cylinder and the other almost flat on the floor!! In any case, as you move away from neutral you start to get diminishing returns as the cosine law takes over.

[Bcone1381]

I hooked up my Patrol rudder cables not too long ago. I didn't put as much thought into it as you did. I just first hooked up my rudder pedals with safety wire instead of the cable so that I could get an accurate pattern for the cables. While the wire was in place, actuated the rudders to full travel with the springs installed to check the rudder pedal position at full travel. It worked out great. I never used a tape measure....just made cable the same length as my safety wire patterns dictated.

Maybe If I describe what I did, it will help.
1) I installed the rudder stops and adjusted them so that the full travel rudder deflection met the Plans parameters.
2) I firmly secured the rudder in the neutral position (I forget if it was Faired it with the Vertical Stab, or if I accounted for 3/4' vertical stab offset).
3) I secured the rudder pedals in the neutral position. (I trusted that the plans showed the pedal position in the intended neutral position and I just sighted them into position, and clamped them there. I did not use any fence protractor or anything....just did it by sight...."That looks about right...")
4) I cut a piece of safety wire that was about 3" longer than the distance between the rudder horn and the rudder pedals.
5) I straighten out the safety wire by clamping one end in the vice, and the other in the vice grips, and whacked the vice grips smartly with a dead blow hammer...it straightens out nicely.
6) I installed and secured the safety wire into the fuselage where the future cable will be threaded....thru all the fairleads, etc. Each end of the pattern wire got a real nice obvious kink where it attaches at each end.
7) I removed the patterns and made up the cables to match them....well I also installed turnbuckles into the cables as well, so that they were positioned behind the aft bulkhead.

[whee]

I ran into a similar issue. See the latter part of this thread: https://bearhawkforums.com/forum/bea...edal-placement

[PaulSA]

I had read that thread but it didn't seem to come up with an answer. I simply can't see how 2" of movement on the horn on the pedal can translate to 4" on the rudder horn. It's easy to position the rudder pedals so you can get maximum movement without geometry issues but it still doesn't seem enough. As far as I can see, the only answer is to rig it all up and if the throw isn't enough, put a hole further in towards the fuselage on the rudder horn.

[Mark Goldberg]

Paul, many Bearhawks have been built like yours. You should get full spec'ed deflection of the rudder with the pedals without any issues. The pedal will kind of hit the firewall at its full travel, but that is by design. Mark

[PaulSA]

Thanks Mark. I wasn't suggesting that it wouldn't work but I just can't see how the geometry allows it. I didn't want to waste time and cable if I had something wrong. I'm not a "look at the plans and fit it together" sort of guy - I like to research and think about it before I commit!

I'll start stringing up and see what happens.......

[whee]

The answer for me was different rudder pedal springs. I never measured the travel of the rudder horn or the pedals. All I know is that the rudder moves 30deg in each direction like it is supposed to and the correct springs keep the pedals from flopping over. The geometry is kinda weird and I don't like it but it does work.

[PaulSA]

OK - problem solved.

I fitted the cables and, as suspected, the geometry wasn't good with the pedals coming almost flat with the rudder hard over. So I had another look at the plans which show a #4 bolt welded to the rudder post as a stop. The QB is slightly different in some areas to the plans and this is one of them. It has a short tube welded in this spot which I assumed was designed to be the stop but, on closer inspection, was exactly the right bore to take a #4 bolt. So I measured the angular throw of the rudder and found it was well over 30 degrees. By putting a bolt in this fitting, it limited it to - exactly 30 degrees!!

I still don't think that the geometry is ideal but at least it works now. I'm still not entirely happy with the return springs I have fitted and will continue looking. They need to be quite short, be heavy duty to give the required return force but soft enough to take a large extension.......

[Bcone1381]

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/6778-rudder-pedal-springs

The link above is a pretty good discussion about the rudder spring.

I am building a Patrol. I ended up fabricating two springs by modifying a hardware store 9 inch long spring that was .750 DIA and had .105" wire. Sounds like the 4 place builders have something similar.

[Battson]

For reference, each kit can have differences around those rudder stops you mentioned. Mine were in quite a different location.

For mines, I needed to file the stops back to get the 30 degrees rudder travel (30 each side of neutral). If I put bolts in the holes, even after the filing, I got much less deflection than I needed.

[JCD23]

Has anyone rigged the rudder cables beneath the floor boards? I realize this would require additional pulleys up near the Rudder Pedals under your feet. I would do this to put in Carbon Fiber FLoor Boards that are 1/4” thick and would interfere with the rudder cables. Any help is much appreciated.

[svyolo]

I wish I had done a little more searching on this before. I just cut the slots in the fabric for the rudder cables. I thought I would double check one last time that all was within spec. I was only getting 22 degrees either side.

No problem, I have an inch of adjustment. I shortened the cables, which brought the rudder pedals aft, which got me to 30 degrees, which I also verified was the at the stops installed at the factory.

Unfortunately the terminals I used at the rudder post couldn't handle the additional angular movement without binding. So I just created more work for myself.

On the 4 place, the forward limit of the pedals is when the brake cylinders contact the tubing at the firewall station. Here is how I would do it next time.

Verify the rudder stops on the fin post are at 30 degrees, if not, fix that first. Mine were exact from the factory.
Push the outboard rudder pedals forward until they contact the firewall tube. If you only have 1 set of brakes like me, temporarily mount one on the other side, outboard.
Set the rudder on the stop, with the pedal on that side at the stop. That length will be the maximum length of the cable on that side. I would make it a little shorter to allow for stretch/adjustment.
If the cable is longer than this, you won't get 30 degrees of travel.

When people ask me what I do for a hobby, I am going to start answering "making things 3 times".

[Bcone1381]

I'd like to fabricate something on my Patrol so the rudder contacts some kind of firewall stop before the tail post stop is contacted.

I often think that if the rudder strikes the stop on the tail post when a rudder pedal is at full travel, then the high pressure on the cable is the main factor in rudder cable wear and tear. The force in this senerio is a function of the speed of the rudder moving and the force that my leg can put on pedals. BANG BANG. The quads are pretty strong muscles. We can put a lot of force on things with our legs.

But if the pedal strikes the firewall or a stop associated with the pedal and the stop at the tail post is not quite reached, then the wear and tear on on the rudder cable is going to be really quite low. Wear and tear might be controlled. We've has some wear issues on rudder cables. and the some Canadians install a pulley on the rudder cable routing to satisfy their certification standards (+3 degree change in direction I think).

[svyolo]

I was going to have them contact on the ground, add a little rubber to the tube at the firewall. I would guess airloads would also stretch the cable a bit.

Hopefully I am not using the rudder stops that often.

[Mark Goldberg]

As you said Brooks - our legs can put a lot of force on the pedals and cable. Bob wants the pedals to contact the firewall about the time the rudder gets to 30 degrees. To keep us from over loading the pedals and the cable. But mostly the pedals. Mark