Rudder Pedal Spacing - How Far Apart Should They Be?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by wsimpso1, Mar 3, 2019.

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  1. Mar 3, 2019 #1

    wsimpso1

    wsimpso1

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    I have seen everything from pedals only about 1-1/2" between them to 20" between. I went looking and found no ergonomic docs on the topic. Plenty on how far away and which way the pedal should move, but nothing on width between. So, what pedal spacing do you think makes for a comfortable and controllable airplane? Why do you think that works so well?

    In my case, the airplane has a stick between your thighs and I can put the pedals as close as about 3-1/2" and as far as 8-1/2". What have I flown? Mostly Cherokees and Cessnas, but also the J-3, Great Lakes Biplane, Citabria/Decathalon, RANS S6, and a high performance sailplane with a side stick and the pedals barely an inch apart. The only thing that I ever recall irritating me is pedals offset to one side, so yeah the pedals will be straight out in front of the stick. But while I have an option, how close together should they be, and why?

    Billski
     
    Last edited: Mar 3, 2019
  2. Mar 3, 2019 #2

    Hot Wings

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    What style pedals: "T"/"L" tube or plate? Toe or heel brakes? Will you ever be flying in winter boots? If you are building your own I'd make the surface as wide as possible so you can move around a bit to keep comfortable.

    For long drives in autos with no cruise control I've been known to use the left foot on the go fast pedal to give the right a break. If it were me I'd just stand normally and measure the distance between the soles of my shoes and go from there - noting the angle since we don't all have parallel feet.
     
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  3. Mar 3, 2019 #3

    Marc Zeitlin

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    You ask a lot of unanswerable questions :). I'm reading Bill Bryson's "A Short History of Nearly Everything", and in a chapter about quantum mechanics, the penultimate paragraph says:

    "The upshot of all this is that we live in a universe whose age we can't quite compute, surrounded by stars whose distances we don't altogether know, filled with matter we can't identify, operating in conformance with physical laws whose properties we don't truly understand".

    This question reminded me of that. HOWEVER, a short google search turned up this document:

    https://apps.dtic.mil/dtic/tr/fulltext/u2/735315.pdf

    called "Pedal Operation by the Seated Operator", which seemed to me to be a reasonable representation of what a Pilot is doing with rudder pedals in a relatively standard aircraft. There are about 2 zillion references, some of which might even be more applicable, and at least three of the references (34 - 36) are specific to aircraft. The conclusions drawn here are that:

    "... the pedal should be .... in front of the seat..."

    Well.... duh. Given that you've seen pedals that are right next to each other, or far enough apart that you might as well be straddling a horse, it's apparent that pretty much anything will work, to a large extent. Personally, I like my pedals to be about as far apart as my feet are when I'm standing comfortably, and I want them far enough apart so that I can take my feet off the pedals and stretch out my legs between them. This is simple on a COZY MKIV, which doesn't have pedals so much as small pegs. I've got my feet on the pedals on the ground, for the first 3 minutes in the air, for 3 - 5 minutes while landing, and in turbulence. Other than that, I'm more interested in being comfortable OFF of the pedals.

    If I were you, I'd put them 8.5" apart (maybe more, if you can), which is just about normal separation, give or take, and gives enough room to stretch out between them, as long as they don't have sharp edges.

    My $0.02.
     
    Last edited: Mar 4, 2019
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  4. Mar 4, 2019 #4

    wsimpso1

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    Thanks for responding. Pedals are bottom pivoted capital I shape made from 4130 tube. Toe brakes pivot from the top bar of the I. What impact does the pedal type have on how far apart they should be? They are wide enough for my winter hiking boots. No, they probably won't work well with "Mickey Mouse" boots or heavy pack boots. I do not anticipate the need either.

    Wife said "just make them shoulder width". LOL. She does not even mind pedals offset toward center. But you know she has to be a tolerant type, she has stayed married to me...

    I have adjustable pedals, and each pedal has an S tube on the outside of each pair (right side of right pedal, left side of left pedal) to allow fore-aft movement. But I have not built the pedal hanger yet, and can put the pedals close together or fairly far apart. So I was wondering what the collective wisdom might have to say about this.

    Billski
     
    Last edited: Mar 4, 2019
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  5. Mar 4, 2019 #5

    BJC

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    Bill:

    I prefer pedals about shoulder width, like these:
    IMG_2087 (002).jpg

    I thought that I would be uncomfortable with closely spaced pedals, but I have several 5 hour flights with these, and find them comfortable. This airplane has more upright seating, and I can put my feet between and to the left of these pedals. Note that these pedals are relatively wide, so the distance between feet is slightly greater than the distance between the pedals.
    IMG_2089 (003).jpg


    BJC
     
  6. Mar 4, 2019 #6

    wsimpso1

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    Sorry, just inquisitive...

    Yeah, I like that quote!

    And yet lots of airplanes and cars offset the pedals to one side or the other. Wife's RANS S6 and our Cherokee both. A perusal of the space they occupy does not seems to have any pressing reason to not put them straight ahead, but there they are, offset...

    Thanks Marc. I too suspect that pedal spacing is pretty unimportant... It is looking like I will spread them as much as I can, mostly to get thigh clearance for the stick and to put the rudder cables as close to the walls as I can. As for room to stretch out, I am hanging the pedals from a central mount, so the space between pedals is not good for that. I have an adjustment that allows me to slide the whole assembly away from me in cruise, and pull them back to me for footwork again at the end of the flight, so stretching is facilitated.

    Billski
     
  7. Mar 4, 2019 #7

    wsimpso1

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    Thanks Byron.
     
  8. Mar 4, 2019 #8

    Vigilant1

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    Off topic: Today's Dilbert:
    https://assets.amuniversal.com/8c92b0a0f6940136776e005056a9545d
     
  9. Mar 4, 2019 #9

    Mcmark

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    If your stick has a large movement radius will your legs interfere with the pedals close together? Tends to be problematic with long legs and small airplanes. My dad is tall and flew an S1C short fuse. Had to raise his leg and put stick under his knee for full deflection.
     
  10. Mar 4, 2019 #10

    wsimpso1

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    Stick moves 4" from center in both axes, more like two-thirds that at the thighs. Spreading the feet helps with keeping the stick off the thighs...
     
  11. Mar 4, 2019 #11

    jedi

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    Width is widely variable as noted above. The following is not asked but I will tell regardless.

    I like the pedals pivoted from above similar to automotive brake and clutch pedals as this keeps the floor clear and more easily cleaned. Cleaner makes for less and easier maintenance. I have had to replace C 150 rudder pedal bushings because of many years of neglect and grit accumulation.

    Also it is much easier to to retrieve the dropped pencil or cell phone.

    My next great aviation invention will be a seat design that will allow the passenger or pilot to tie a shoe lace without removing the seat belt or having to stand on his head. When Boeing buys the patent I will be "fully retired".
     
  12. Mar 4, 2019 #12

    Topaz

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    FWIW, I tend to find pedals that are a good "foot-and-a-half width" apart or a little more. Say, 8" between the inside edges of the pedals? The tightly-packed pedals made necessary by the nose-cone shape of higher-performance sailplanes somehow make me feel like I'm standing on tip-toes. They work, and you can get used to them, but meh. Just not as "naturally comfortable."

    Since you have a center stick, the other part of the geometry should be that you can still "clamp" the stick with your knees, on those occasions where you find you need both hands free for a short period.
     
  13. Mar 4, 2019 #13

    wsimpso1

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    Hmm, Here is a screen capture of the rudder pedal frame and the pedals without the "S" tubes.

    View attachment Rudder Pedal Assy.pdf

    And here are a couple pictures of the pedals in the cockpit.

    20190304_093746.jpg 20190304_093949.jpg

    The frame is not finished yet... But the plan is to run the frame on a tube above, with a little lead screw and handle on the panel so they can be brought closer or run out of reach for stretch space. The pedals are not "on the floor", but they are bottom pivoted with toe brakes. With them directly in front of the people, there is less room to spread them towards the centerline than towards the sides. Looks like about 5-1/4" between pedals and 5-1/2" for each pedal, plus the retention mechanism and "S" tubes for cable. Even if I hung them separately, there is not much space between pedals for even the wife's Birkies to fit through, but a few turns of the handle and the pedals are out of the way...

    Now we find out how well this stuff plays on HBA...

    Billski
     
  14. Mar 4, 2019 #14

    wsimpso1

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    I wondered. I have flown a high performance glider with the pedals close together, and was not bothered by them, but wondered how that plays after three hours...

    I see that point, but... the stick is about half-way out the thighs and so will not clamp as well as if it were more like between the knees.

    Billski
     
  15. Mar 4, 2019 #15

    davidb

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    I vote for as wide as possible up to shoulder width. Your pedal plate width looks wide enough so your wife could favor the inner edges to achieve her shoulder width.

    I assume your plane has a center console and that doesn’t pose a problem with reaching full stick movement. Bumping your inner thighs isn’t a big deal unless your leg is already pinned against the sidewall or center console. Sounds like you have plenty of room and relatively small stick throw.

    Another thing I would consider is the ability to lift your butt off the seat while flying longer flights. I don’t know your seating position so I don’t know if that will be an issue.

    Edit: now I see the above pictures. Looks nice and roomy. Plenty of floor space to put feet when not on the pedals. Sturdy armrests will be nice.

    Are you planning a single throttle lever in the center?
     
    Last edited: Mar 4, 2019
  16. Mar 4, 2019 #16

    Topaz

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    You could just as easily say, "thighs" as well as "knees". I just mean loosely clamping the stick while you unfold a chart, unpack a sandwich or take the top off a thermos/drink bottle, that sort of thing. If you put the pedals too far apart, that gets to be a little more challenging.
     
  17. Mar 5, 2019 #17

    wsimpso1

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    Left cabin wall. Right seater will have to use "voice command power control". If you want to sleep while the other pilots flies, you have to sit in the right seat.

    Billski
     
  18. Mar 5, 2019 #18

    Marc Zeitlin

    Marc Zeitlin

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    You may want to rethink the throttle/mixture/engine control positioning. Although it is legal to do a biennial Flight Review in a plane that only has "Flight Controls" that are accessible by both the pilot and the instructor, you must also have "Engine Controls" that are accessible to both in order to take a test for a rating. So if you ever want to get a Commercial, Instrument, CFI, etc. certificate and take the test in your plane, you'd need to either have a dual set of engine controls on the right fuselage side, or else put the single set in the middle where it's accessible to both seats.

    If you don't give a crap about taking tests in the plane, then ignore this.
     
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  19. Mar 5, 2019 #19

    Toobuilder

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    I find the narrow pedals of the RV-8 less comfortable than the very wide pedals of the Rocket. I suspect somewhere in between (shoulder width) is perfect.

    Ready to talk about your throttle position yet?
     
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  20. Mar 5, 2019 #20

    davidb

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    I don’t see the ;) so I guess you are serious. Since your airplane seems anything but simplified and otherwise not tailored to just you as the only possible pilot, I have to ask why you would choose to have dual controls but not dual throttle controls. Or, simply put the throttle in the middle. I’ve flown airplanes configured both ways and from both seats and it really only takes a few minutes of flying to feel comfortable and natural with the throttle/stick in either hand and your butt in either seat.

    Instruction, future sale, incapacitation or just both of you being able to fully fly without swapping seats all seem like good reasons to reconsider.
     
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