Rudder Pedal Placement

[alaskabearhawk]

The plans have the axis of the rudder pedals being 4 inches from the center of the front lower firewall tube. In Eric's info he said that Proto II had the pedals 5 inches from the firewall. I checked my email archives and there is quite a bit of conflicting information for the placement of the pedals. From what I gather, they should be per plans. But with the rudder horn being extended to 3 1/2 inches are there any issues with pedal travel? I'm assuming with the longer horn too much travel isn't an issue, but I want to have enough. Thoughts?

[Battson]

The pedals do travel a fair way, but it's not an issue provided you place the pedals exactly in accordance with the plans. I tried several other placements, and you can open yourself up to problems if you deviate from the plans.

Here's a video of what happened if I moved my pedals out of spec.. http://www.youtube.com/watch?v=n_uk9o2N2zQ

[alaskabearhawk]

That was a clear video and informative, but where did you have your pedals when you did this? Do you remember the measurement? That was exactly what was talked about just over a year ago. Here's the narrative and Kevin Deutcher's fix:

"A couple weeks ago I tried to bring to your attention a possible problem that results from locating your rudder pedals further aft than what the plans show without moving the attach point for the master cylinders aft also. Basically, you can end up with an "over center" brake pedal that is difficult to get out of a "locked" position of full pedal. The geometry of all this has to be right.

FYI - the plans show the rudder pedal assy to be 4" aft of the center/bottom firewall tube. If you placed your pedals close to the four inches, this should not be a concern for you. But if you moved the pedals aft intending to be able to reach the rudder pedals better (if you are shorter), then this is important.

Attached are two pictures. One shows the brake pedal locked in an over center condition. The other picture shows a super simple fix to prevent it from happening by placing a clamp to limit travel somewhat of the brake pedal.

This was investigated by scratch builder Kevin Deutcher in Phoenix who takes an engineers approach to investigating and solving problems. Bob Barrows reviewed what Kevin came up with and thought it was a good easy fix. Thanks Kevin for your time and effort. Mark"

Attachment(s) from Mark Goldberg

http://groups.yahoo.com/group/Bearhawk/attachments/folder/1279853062/item/2019879594/view

There were other emails that I saved that seemed to contradict this somewhat. If you went with the 4 inches and it's worked without any issues, that's what I need to know.

[DesertBearhawk]

After watching the video, which was very good at showing exactly the issue is, my first thought was to place a stop on the pedal just as suggested in the above post. The clamp is a simple fix, I would have welded something to achieve the same thing but I am one to complicate things!

[alaskabearhawk]

Ok...so nothing definitive about rudder pedal placement? Plans show 4 inches, Eric Newton said in his build manual that Proto II had 5 inches. Wayne Massey mounted his at 5 inches. Anyone have an actual measurement that works without any geometry issues?

[Mark Moyle]

Another way to prevent cam over of the toe brakes is to move the master cylinder mount points closer to the rudder pedal assembly. A long as the toe brake fulcrum is a greater distance from the master cylinder mount the toe brake will never cam over. Mark M Sent from my iPad using Tapatalk HD

[whee]

I'm installing my pedals and rudder cables and ran into a little issue. Might be kinda hard to explain. With the cables properly adjusted when one pedal, let's say the left, is pushed to full left rudder the right pedal lays at such a steep angle that when right rudder is applied the pedal can lever over so your pushing the pedal into the floor. I know, hard to explain. Anyone else run into that issue.

[jaredyates]

Is the problem that the right rudder pedal is ending up "face first" on the floor, aft of the pivot point? When you say "properly adjusted," what does that mean? Can you post a picture showing the pedals in the problem configuration?

[Zzz]

In my opinion, the problem is being solved the wrong way. The problem, as I understand it, and discussed with Battson at the time I was locating my pedal assembly to drill, is this:

The rudder pedal not being depressed rotates away from the firewall, and if the same brake pedal is simultaneously depressed too far, will trip over-center where the master cylinder attaches to it. This allows the master cylinder to cam in place like a chair-back leaned against a door knob. In order to remedy this situation, one would have to reach down and pull up on the brake pedal to pull it back over center of the cylinder.

Just took a quick video as my Bearhawk is in my garage: https://www.youtube.com/watch?v=dF6NGosgbfw

Sorry Battson, no time to add Doobie Brothers.

This is clearly a safety issue, as 1) no one wants a stuff rudder pedal, and 2) no one wants a brake stuck on. However, I question the practical situation where this might really occur. It seems a primed and properly bled brake line wouldn't allow such a deep compression of the master cylinder in the first place, though the further the rudder pedal rotates aft, the less the cylinder must depress for this to occur.

Current solutions address placement such that the rudder pedals bottom out against the firewall, but I think the solution is to weld a stop on the backside of the brake pedal arm itself, which bottoms against the rudder pedal, limiting the brake pedal travel. One could simply reshape the attach bracket that is already being welded on there to extend down and provide the stop.

Just my opinion of course, sitting here at my desk with only mind main and memory to serve me.

[whee]

Is the problem that the right rudder pedal is ending up "face first" on the floor, aft of the pivot point? When you say "properly adjusted," what does that mean? Can you post a picture showing the pedals in the problem configuration?

Yes, the right peddle ends up face first on the floor. Properly adjusted is the cable length is such that at full deflection in each direction the master cylinders don't quite touch the firewall. I'll see if I can get a picture.

I've messed with it a little and set the floorboard in place. I don't think is as much of a concern as I thought but I still don't like it.

[Mark Goldberg]

Do you have brake fluid (5606) in the master cyls. If not, they will behave differently when filled.

I am not sure I understand the issue either. With the pedals located properly with 5606 in the master cyls and rudder pedal springs attaching them to the firewall - I do not see there is any issue. If you try to locate your pedals further aft - the geometry gets screwed up and things can happen. Mark

[whee]

Perhaps I should have started a new thread. My issue isn't with the brakes caming over and locking the pedals. My problem is the shallow angle of the pedal that is not being pressed but when it is pressed to go the other way it is over center and goes the wrong direction.

The springs do pull it the correct direction but I'm not sure I have the self control to let the springs act first when things get squirrely on the ground.

[jaredyates]

Interesting. When you are at the stop, how much deflection are you getting at the rudder? I haven't looked at mine from that angle in a while, but I think the resting/neutral position has the vertical part of the pedal much closer to plumb. To put it another way, I think my rudder cables might be longer than yours. The pedals on mine definitely don't do that. Does your pedal geometry match the upper left part of plans page 27, both in the forward/aft location of the pivot, and the neutral angle of the pedals?

[Battson]

Mine are capable of doing this too, but it was worse when I had the dimensions wrong, and when I had springs which were too weak / too long.

In reality it has never happened operationally.

Jon, I think your springs are fractionally longer than what I have (not saying mine are perfect - they aren't - but that's my only reference point.) It's also possible that your rudder cables are shorter than mine too.

All the brake hoses plugged into the pedals also change the feel of things a bit, as does the tailwheel connections and the springs in the tailwheel chain too. They make a big difference to how the pedals feel.

And another thought... you only use full travel when you are taxiing or landing. In that case, your feet are on the pedals and your toes are up above the brakes. That changes the geometry of your pedal-body interface quite a bit.

[whee]

My rudder stops are set at 30* in each direction per the plans. Currently, in that video, I lengthened my cables so that the arms on the pedal torque tubes contact the side fuselage tubes just before the rudder horn hits the stops. This allows the pedals to stand up as far as possible but I don't like it, the rudder horn needs to hit the stop first but shortening the cable to make that happen will make the situation worse.

The pedal assembly is from the factory and matches the plans. The pivot point in the plans is 4" from the firewall, mine is set at 4.75". If I move the pivot point forward to 4" then if have to angle the pedals further aft so I could get full travel at the rudder before the torque tube arms hit the fuselage tubes. I didn't realize the drawing shows the neutral position of the pedals but I see it now. I'll check to see how close mine are.

Battson, What dimension did you have your pedals at when you had it wrong? Mine are wrong, by 3/4", but moving them forward would make things worse.

I am going to get shorter springs which will help but even so during an exciting landing things could go terribly wrong. As I explained above, I can't make my cables any longer and still get full rudder travel. I actually need to shorten them about one turn on the turnbuckles.

I can't remember where I like my feet when landing. When I raise my feet on the pedals so my toes are above the brakes I can't move the pedals very far before I start apply brakes, my ankles just don't bend like that. I really struggle with toe brakes and when flying Mel's BH I missed the heels brakes in my Luscombe immensely.

But, as mentioned, I don't know that this is an issue operationally.