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Rudder Springs

Bill.Peyton

Bill.Peyton

Well Known Member
Ok, here is what I am trying to do. I would like to have springs attached to the rudder cable ends to help in protecting the rudder from wind and to also eventually develop a rudder trim system similar to the piper aircraft. I test installed two rudder return springs which attached at the base of the Pilot Right peddle and the Co-Pilot Left peddle. The spring is attached at the other end to a bracket on the side of the tunnel next to the firewall. The issue is, now there is tension on the cables at all times, it is amazing how much friction the cables have as they thread there way from the front to the rear of the aircraft. The lack of pulleys really shows. My concern is the rudder cables will eventually wear right through the snap bushings. I am now looking at strategically installing pulleys in three different locations to get rid of a lot of the binding a wear issues.

For those of you flying, have you ever inspected the snap bushings for wear?
Has anyone else tried a return spring arrangement?
 
I don't think there will be enought force to return the peddles and protect the rudder with the small springs and short lever arm. I had looked at this system before, Thanks
 
Have not thought about springs but...

I have thought about installing a phenolic friction block setup on each side of tunnel encapsulating the rudder cable. For those long climbs tighten the left block. For those long descents tighten the right block. For parking for more than just fuel or a quick bite to eat tighten both blocks. I will probably do it after flying. Possibly a good winter job.

Also on the bushings vs pulleys. Our Blackhawks had cables ran over phenolic pulleys all the way to the tail rotor gearbox where they connected to dual hydraulic cylinders(primary and backup). Very little friction in that set up but very heavy too. Angles were much greater than on our RV, so it was a requirement.

You might also be able to run them through pieces of 1/4" thick phenolic. Lubrication of plastic bushings with some boelube may help keep the friction down. Fly over and I'll give you some 1/4" phenolic. I have plenty left after making my own terminal blocks.

Just about finished with panel wiring, then I'll be getting it up on the gear soon. Work picks up when the temps are above 85F.
 
I don't know if springs are a viable solution for the gust lock issue, but I can tell you that the snap bushings in my RV-6 look almost new after 10 years and 750 or so hours. Even if they wear out after 20 years, replacing them is cheap and easy. I can't imagine that pulleys would be a better solution if you use cost, weight, and complexity as your metrics. Beyond that, the pulleys would probably need more maintenance than the bushings will.
 
And if you think that wear will be a problem, a smaller bushing will snap into the existing bushings. Just split them with a razer and slip them over the cabal and press into place.

A piece of tubing split on one side and tapered on one end will push out the smaller bushing if you ever need to replace it.

Like Mel said....... this is not a problem. And drag on rudder pedals are not a problem compared to aileron drag.
 
Adding the springs seem to be adding problems

I don't want to start an argument on this so just think of this as a caution. I wouldn't do it. As others have said the existing design is wear free on my RV-6A after 7 years also. The springs load up the system and lead to the need for other changes. I use two inverted square "U"s with ~3" legs made of 1/8" piano wire on each side of the rudder in holes in the rudder stops and the rudder horn. They are so solid that if you accidently leave them in on takeoff you have a fixed rudder. If you have one on one side only it can be overcome by you or the wind but not on both sides. When our plane was parked on the ramp at St. Simons Island, GA a couple of months ago the wind blew the tail one way and the breakout force on the nose gear was exceeded, the main gear went over my special 3/4" aluminum angle chocks and the plane was sitting askew to the limit of the tail tiedown rope but the rudder remained locked as straight as an arrow.

Bob Axsom
 
This is why this forum is great! I wasn't sure on the bushings, but it sounds like they are a non-issue. I still like the idea of centering springs. I don't like the idea of always having to put blocks in the rudder or a bar on the peddles for just a short time. I have read several posts regarding rudder damage and personally seen two different 10's with dented rudders from contact. Today I went out to my Archer to see how hard it is to move the rudder from the rear. It is amazing how stiff the springs are and yet, I have never felt like I was pushing on a spring.

Wayne, I just got my aircondx installed in the workshop. 2.5 tons should keep it cool this summer! Ill pick a good weekend and give you a call and swing by.
 
Last edited:
Bill.Peyton said:
Today I went out to my Archer to see how hard it is to move the rudder from the rear. It is amazing how stiff the springs are and yet, I have never felt like I was pushing on a spring.
Click to expand...

You were not just pushing on a spring, the rudder on a Archer is connected to the steerable nose wheel. Don't expect to flip the rudder side to side with the nose wheel on the ground.

With springs connected to the rudder pedeals on an RV, you will not feel them during normal use. But they will coushion the effect of side loads when tied down. And with less flat surface for the wind to push against, your RV might not shift from It's tie down spot.
 
Actually, the rudder pedals on a Piper Archer are connected to a hydraulic piston/damper which penetrates the firewall and the springs are connected to the damper on one side and the nose wheel steering on the other. The dampers allow you to overcome the springs and the force of the nosewheel when it is in contact with the ground. The trim mechanism is hooked to one side of the torque tube through a lever. It applies additional spring tension only to one side, which offsets the dual springs in the engine compartment. It really does work very well, although I am sure there is a lot of weight involved with the whole system.....
 
Bill, IMHO the best rudder gust lock is a 2 pin device at the rudder itself.

It involves a 3/16" hole in the rudder arm and another in the rudder stop at the fuselage. Its about as stone simple as can be and works - only tried to taxi one time with it installed before the red flag was added. :)



Uploaded with ImageShack.us
 
I installed centering springs from the pilot right side and the copilot left side forward to the fire wall. Works great. It keeps the rudder from flopping in all but heavy breazes.

Gary Specketer
 
Another option

Here is an option in case none of the others appeal to you.
I had a flap actuator assembly left over from a previously owned RV-8.
Seemed to be a solid mechanism to make a trim system out of it while I am waiting for paint to arrive.
The actuator has 5" of "brute force" linear displacement and can handle a substantial spring to effect left or right rudder movement.
The left side has the spring fixed and only the right side is actuated back and forth. The concept is not new except maybe for the use of the flap actuator.
The cost is probably less than installing a servo and tab on the rudder and it keeps the rudder clean.
Additionally these 2 sprinds will keep the rudder from flopping around in the wind.
This RV has not flown yet but I am confident it will work but may need a few spring adjustments before it works perfectly.


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Ernst, thanks for the photos. I think your system may work, my only suggestion is that you use the proper clamps for the control cables, the clamps you have used may cause a kink in the cable. What you need are .125 inch couplings, just like would be used to attach an autopilot bridle. They consist of 2 pieces which both have 2 parallel grooves and are about 1" long, both cables pass through and get clamped in between the two halves. Go to this link and look on page 14. http://www.inetefb.com/Documentation/Cirrus/AMM/pdf/22-11.pdf
 
N427EF said:
Here is an option in case none of the others appeal to you.
I had a flap actuator assembly left over from a previously owned RV-8.
Seemed to be a solid mechanism to make a trim system out of it while I am waiting for paint to arrive.
The actuator has 5" of "brute force" linear displacement and can handle a substantial spring to effect left or right rudder movement.
Click to expand...

To me, that's more than it needs. A heavier motor, heavy springs, and associated fittings. The rudder DOES require "brute" force. Yet a simple light servo, as used in the elevator or ailerons, can do the same trick, by moving a small rudder tab. Simple, light, and all the adjustment one needs.

L.Adamson ---- RV6A
 
That's kind of the conclusion I have come to also. Some light springs with a TA-12a servo on one spring is all it should take
 
I doubt the 1.2" travel would be enough with RA servo

when connected to springs. The 20 lbs of operating thrust may be sufficient unless you had to use a lever to increase the travel, which it may not be then. I used those cable clamps on my grape arbor cables and yes they do kink the cable. Like Bill, I would use the aviation equivalent. Good engineering otherwise. Plenty of thrust and travel with that setup. Just would not be able to install it in mine due to GRT AHRS in that location and Aux bat on right side.
 
Bill, I will definitley change those clamps, just did not have any on hand
and don't know what they are called.

I am not trying to convince anybody that this is a better design than the servo activated trim tab which is probably the most gentle solution for trim.

I can tell you from experience that a TA-12 Ray Allen Servo will not do the job. We tried the same idea on our RV8's and that servo even with a lever arm could not move the rudder.
What I have is certainly a bit overkill but as I pointed out I already had the
flap actuator and tried to put it to use.
The installation is also less invasive than hacking up the rudder and making accomodations for a servo.
The spring loaded rudder is also a plus.
 
Same for me Ernst.

No way was I going to cut a hole and add weight to my rudder unless it has been tested by Van's or equivalent. Yes, many have that mod. As we've seen, all it takes is 34 kts over Vne, 109 over Va to ruin your day. I prefer to keep my margins as high as possible for that one bad piloting day I may have. I would have never thought losing a rudder/vertical stab would cause loss of control.
 
N427EF said:
The installation is also less invasive than hacking up the rudder and making accomodations for a servo.
Click to expand...

It's no more of a hack, than the servo & hinge tab in my right aileron. It's even Van's approved..

Works very well too. And other pilots prefer it over their bias spring setup.

L.Adamson --- RV6A
 
I agree with you Wayne. I did speak with Vans regarding the trim tab mod and how it might affect the rudder balance. I decided not to make the mod. to the rudder, but have not ruled it out. I would rather have a solution that would help the stabilize the rudder from wind damage, keep the cables tensioned and also provide rudder trim. I did a temp. hook up of the springs from the rudders to the firewall. I really did not like the feel on the pedals. The springs cause the cables to really drag through the snap bushings, it's like pushing down on the left rudder while using the right rudder. I realize the the RA servo will not pull the spring, my plan was for a third spring just for the trim. It really only has to move less than an inch. I have been experimenting with some pulleys and rollers in two areas in the -10 that have several pounds of pressure on the snap bushings (with springs installed). The 10 is unlike the rest of the fleet, it's made to cruise not for aerobatics and boring holes in the sky. I am willing to accept a little less feel for a lot of convenience, I just haven't come up with the total solution at this point, but no rush here.
Bill
 
How about a manual trim system with a mixture cable,pulley and a spring??

Bill, Go to Tim Olson's site under modifications and look at my test version of a trim system. It uses a venier mixture cable to set rudder trim. I have a spring that allows for rudder pedal travel at all times.really easy to do. I refined the system with a traditional mixture cable after completing a proof of concept with the system pictured on Tim's site. 400 hrs and works fine, also works as a gust lock by pulling up the cable to pull the right rudder pedal down then install a converted extendable painting pole to push down on the left rudder pedal. It works great. Just another way to approach it.

Take a look see,
Don Orrick
N410JA
 
Take your time...

research, test if possible, weigh the advantages vs disadvantages then build it or go back to the plans and keep truckin'. I heard from many guys before I started that if you want to finish quick stick to the plans so that is what I have been doing for 99% of the plane. Nothing wrong with making improvements as long as we know how it may effect something else later like "flutter". No boring holes in the dirt either. Aerobatics look like fun but my stomach as well as the wife/kids could not stand it. Hoping for some more sunny days. We had a mostly sunny day today. More rain starting tomorrow. Not condusive to flying is it.
 
Don, I can't find the link in Tim's site. Do you have a link?

Wayne, The mods take too much time don't they! I have been using the crappie weather for shooting approaches. We had some good 700 foot ceilings in light rain the other day. It keeps you current and comfortble when you have the real thing. I ahve been spending too much time building and not enough time flying!
 
Been there, done that, doesn't work.

What is needed is a system that relaxes the tension on one spring while the other is extended, like the manual aileron trim system that Van's provides.

It takes some head scratching to see why a fixed bias spring coupled with a variable bias spring system does not work. The clue is that when one spring is pulled on by the servo, the opposing spring is extended so that both springs end up being the same length, thus providing equal and opposite force. The rudder neutral position will change on the ground, but there is not enough differential force to have any affect during flight.

Trust me on this one. I flight tested a system with a fixed bias + variable bias and it had zero effect even with the fairly stiff springs that I used. I think very strong springs would work, but not with a RAC servo.

Vern

Bill.Peyton said:
That's kind of the conclusion I have come to also. Some light springs with a TA-12a servo on one spring is all it should take
Click to expand...
 
I can't find the link in Tim's site. Do you have a link?

Bill,
Go to building tips, under that look for cool mods, in the cool mods look for rudder trim.
Don
 
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