RAF & Sparrowhawk steering

CLS447

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Joined
Oct 30, 2003
Messages
6,324
Location
Reading, PA
Aircraft
Air Command 503 & Air Command SxS /EJ2.5
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Aprox 400 gyro
While redesigning my nosewheel & steering system on my SxS AC, I have been comparing notes with the RAF & SH's system.

Today I went to see Larry B.'s new machine & made an eye opening discovery.

What actually turns the nosewheel on these machines?

When the right pedal on the pilots side is pushed, the rod on the left passenger's pedal pushes back on the steering "knuckle". How does this happen?

Well, the rudder cable from the R pilot pedal is pulled, this rotates the rudder & pulls back on the left pass. pedal which then pushes on the Knuckle & turns the wheel. And visa versa.

I guess you all knew that! I just didn't realize the the stresses of turning the nosewheel were actually on the rudder cables!

Obviously it works fine, but if one were to lose a rudder cable, you would also lose your nosewheel steering.

No big deal, but with all this stuff about crimping & bungee cords on the pedals it just makes me feel better about having push/pull teleflex cables!

My system I am building on my AC is different in the aspect that my nosewheel is in front of, not behind my pedals, like the RAF.

I will have it so that when I push the pilot right pedal my steering rod
will directly push the steering knuckle to the right. When I push the pilot left pedal the movement will be transfered to the passenger left pedal via the connecting rod & then directly push the knuckle to the left.

The rudder cables are an entirely different thing. I could lose steering but still have rudder control or lose rudder & still have steering. Or I could just smash into the ground & lose everything!

If you lose one rudder cable , you could still use the rudder with the push/pull cable. (heel/toe).

No big deal , just a recent observation that I have never heard anyone talk about before. Thanks
 
I didn't mean to knock their system or upset anyone just was hoping to hear some other opinions.... pro or con.

Does anyone have anything to say about it ... even if it's "shut the hell up"?

Another thing about both systems, Is it true that you can tighten the steering by tightening the 3/4" nylock nut beneath the knuckle? How tight do you guys like to make it? Or do you like 0 friction on the nosewheel? C'mon anybody!

These are important subjects to me right now.
 
Personally I like zero friction on the nose wheel and I like it directly linked to the rudder pedals. I have heard many disagree with this type of system for various reasons but I would be happy to challenge anyone to a centreline tracking contest on take off and landing, and in any wind conditions, with this system. Both students and genuine pilots found it very easy to use. If you are worried about breaking a cable, link the two pedals together. However, no amount of redundancy will make up for poor workmanship.
 
Thanks Tim, maybe we can get this dicussion going,

I just always assumed the RAF was directly connected to the nosewheel. Then I found out that it is actually the rudder cable that really does all the steering.

If they would use springs & nuts on the other side of the knuckle rod ends, then it would be a push/pull rod setup. I wonder if this would be an improvement or not?

Has anyone tried this? Then even if a rudder cable was disconnected you could still steer the nosewheel. This would also relieve some of the stresses placed on the cables. Hmmm....
 
Chris:

The RAF steering is directly off the rudder pedals. Threaded rods are connected to a pitman arm which is solidly connected to the nosewheel shaft.

The rudder cables control only the moveable rudder.

I'm like Tim...I like it and have had no problems.


Cheers :)
 
Harry , unless your setup is different ,you better get under that dash & have a closer look! When you push the pilot side right pedal, Does that pull on the pitman arm or does the left passenger side push on the arm.

If you answered left side push, then what makes that side push?

Maybe the one I am looking at is set up wrong. The SH we are working on is not that far yet. I will definitely have to refer to the manuals.

Which side of the pitman arm rod ends are your springs on....front side or back side?

Get me straight on this ,could you Harry?
 
This is a schematic......

This is a schematic......

....out of the Raf consruction manual. I added the rudder cable info myself.

When you push on either of the right rudder pedals the nose wheel is steered via the springs, and the rudder cables are direct from the pedals. The spring idea is good only if you have a decent trailing nosewheel, but a cable failure will allow a lot of "non pilot input rudder" to one side.

Centering springs back at the rudder end is the best scenario to allow for rudder cable failure.

Aussie Paul. :)
 

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Thanks Paul, then Larry's is set up correctly .

OK, then from those pics, tell me , do those rods push rearward on the pitman or pull forward on the pitman?

If they push rearward against the springs, How then by pushing on the pilot side right pedal,does this steer the wheel to the right?
 
A little confusing isn't it............

A little confusing isn't it............

Thanks Paul, then Larry's is set up correctly .

OK, then from those pics, tell me , do those rods push rearward on the pitman or pull forward on the pitman?

If they push rearward against the springs, How then by pushing on the pilot side right pedal,does this steer the wheel to the right?



They push rearward on the pitman arm Chris.

I am sure that it relys on the rudder cables to to pull the left pedal back and so push the pitman arm rearward. :confused:

Aussie Paul. :)
 
Chris, me lad...with all due respect...I don't have to take a closer look under the dash of my RAF, as you suggested...I built my RAf and have maintained it and have flown it for 7 years now. :D

There are no centering springs for the rudder/rudder pedals on the RAF. I believe the two small springs you have reference to, are installed on the rods to the pitman arm. These springs are installed fwd. of the arm and the rod end bearing. These springs are compressed on the initial installation and adjustment of the rods...to maintain the the left offset of the nosewheel steering. The purpose of these springs is also to maintain the space between the adjustment nuts.

I'll try to describe the rudder pedal setup. The rudder pedals consist of two separate, square steel tube welded assys. One pedal assy has the pilot's L/H pedal and the passenger side L/H pedal; the other pedal assy. has the R/H pedal for both positions.

When the pedal assy's. are bolted down, the pilot's R/H pedal has a rod attached from the low corner of the pedal to the pilot's side af the pitman arm. The passenger side of the L/H pedal has a rod going to the passenger side of the pitman arm.

So; if you can picture that setup, you will see that when the pilot presses the R/H pedal, he in fact pulls forward on the pitman arm and the nosewheel and the rudder deflects to the right...and vice versa.

Centering the rudder, in flight, is by foot pressure of the pilot. I have the Snider Rudder Anti-Servo Tab installed on my RAF and it works fine.


Cheers :)
 
Harry, Let's work through this together, peaceably.

First of all I believe the spring are there to absorb sideway bumps on the nosewheel & for landings with rudder inputs, also.

Now for a couple of basic tests.... If you remove the nylock nuts on the end of the allthread rods, does it still steer exactly the same?

2. If you disconnect one of the rudder cables does it still steer the same?

3. If you do both of these things, I think that the rod will just pull right through the rod end on the pitman arm & fall to the floor without ever moving the wheel or the opposite pedal.


Since you are performing an annual on your machine , this would be a perfect time to check those points anyway. Lube cables , inspect crimps, lube pedal to cable pivot points, check nosewheel for slop & so on & so on.

I am curious to see if adding springs on the back side of rod end also wil work/help.

Your response would be helpful. How about you Stan F., since you two are obviously the only people who fly RAFs or at least the only ones who post! Oh & aussie Paul !
 
Not quite right Harry....

Not quite right Harry....

Chris, me lad...with all due respect...I don't have to take a closer look under the dash of my RAF, as you suggested...I built my RAf and have maintained it and have flown it for 7 years now. :D

There are no centering springs for the rudder/rudder pedals on the RAF. I believe the two small springs you have reference to, are installed on the rods to the pitman arm. These springs are installed fwd. of the arm and the rod end bearing. These springs are compressed on the initial installation and adjustment of the rods...to maintain the the left offset of the nosewheel steering. The purpose of these springs is also to maintain the space between the adjustment nuts.

I'll try to describe the rudder pedal setup. The rudder pedals consist of two separate, square steel tube welded assys. One pedal assy has the pilot's L/H pedal and the passenger side L/H pedal; the other pedal assy. has the R/H pedal for both positions.

When the pedal assy's. are bolted down, the pilot's R/H pedal has a rod attached from the low corner of the pedal to the pilot's side af the pitman arm. The passenger side of the L/H pedal has a rod going to the passenger side of the pitman arm.

So; if you can picture that setup, you will see that when the pilot presses the R/H pedal, he in fact pulls forward on the pitman arm and the nosewheel and the rudder deflects to the right...and vice versa.

Centering the rudder, in flight, is by foot pressure of the pilot. I have the Snider Rudder Anti-Servo Tab installed on my RAF and it works fine.


Cheers :)


From the schematics I posted you can see that the compression springs are there for 2 purposes. The main one is to keep the 2 degrees left nose wheel position, the second being to keep some pressure in the cables.

If the nose wheel was a trailing design the the springs would also allow self aligning of the nose wheel to the direction of travel if the nose wheel touched the ground.

Harry, the right rudder pedal does not pull the pitman arm, the left pedal pushes the pitman arm.

Chris I will have a look and see what having another spring behond the piman arm would do. I might just have to get some all thread and springs to try it.

Aussie Paul. :)
 
Thanks Paul. I did another test with Larry the other day.... I had him hold the pedals centered. Then I grabbed the nosewheel & twisted it left & right. The spring allowed it to move without the pedals moving. I figured that this was for some sideways shock absorbancy.

When setting up the nosewheel, Is the pitman arm installed perfectly perpendicular with the nosewheel or is that where the 2 degrees left is applied?

Or is that done with the rod adjustment alone?

Why is the 2 degrees left used ? And would that be with the pedals centered?

I am really trying to understand why RAF decided to push the opposite side of the pitman using the rudder cables, when they could put the springs on the back & actually pull the pitman directly, without the rudder cables. Those rods would be stronger in tension than they are in compression.

I know that the pitman arm rodends are 3/8" but they are used with a side load. It has recently been dicussed that they are only designed for tension/compression.

I believe the Sparrowhawk is exactly the same. If it needed improvement, I figured SH would have done it. If it ain't broke don't fix it, might have been the thought.
Or maybe there was no thought used at all....just copy it.

I can tell you that there are more parts to the SH setup... mostly in the addition of bronze bushings installed in the pitman arm so the 3/8" rod ends swivel freely. Not a bad idea after examining the RAF setup where the rod ends are tightened directly to the pitman. The rod end itself did not swivel at all.

I have been told that SH is changing their rudder cables over to an exposed system with pulleys....I wonder why? I know it was a real pain bending the guide tubes and routing the rudder cables through the keels.

I sure am anxious to here Harry's thoughts & findings. How about you Stan?

I know that for me this was a bit of an eye opener!
 
Chris: The two degrees left nosewheel setup is due to the fact that some right rudder is being held on takeoff. This tends to keep the nosewheel more straight with the runway as is leaves the surface. If the nosewheel did not have this 2 degree offset to the left..and was straight...then when the nosewheel came off...the right rudder would turn it right a little..and if it came back down on the runway,...then the nose of the RAF would be pulling right.

Stan
 
As far as I know the current plan is to change to external cables over pulleys on the Sparrowhawk. David and I did this mod to my machine quite a while back and I have been lobbying for it. I have found the pedal pressures to be too high to suit me with the stock setup. I have sent pictures to many of my SH customers showing this, but if any others would like them, I will be glad to send.
 
Aussie_Paul said:
Harry, the right rudder pedal does not pull the pitman arm, the left pedal pushes the pitman arm.


Aussie Paul. :)

Touche' Paul...my brain fart...I was sittin' here at the keyboard trying to visualize the pedal effect on the pitman arm and got screwed up. Thanks.


Cheers
:)
 
Chris:

You got it. I'm too old to do anything other than peaceably. :D

To answer your queries:

A. Sideway bumps? :confused:

1. Sure does.

2. Sure does.

3. Nope...L/H maybe; R/H no...per my setup. I think your simulating a rudder
cable failure?!

Adding springs aft of the pitman arm...mabe/maybe not help what...
centering the pedals? I don't have space to add any springs, aft of the
pitman arm anyway.

As Stan said, the left offset was to...as RAF factory stated...to help the
low time RAF pilot to compensate for the torque on takeoff. An experienced
pilot would not need the offset.

On the ground, the offset does help on L/H turns but hinders R/H turn
radius quite a bit.


Cheers :)
 
Harry said....

Harry said....

Touche' Paul...my brain fart...Cheers

Not a problem Harry. Now I don't feel so alone!!!! LOL :D

Aussie Paul. :)
 
Why not make it simple and light Chris and make it a castoring wheel and use indivdual wheel braking for steering.
 
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