When at their neutral position the space for extension springs between the rudder pedal attach point and the fuselage anchor point on my 1550 V-Max is only 4 inches. To achieve the 30 degree rudder deflection specified either side of center the cables must travel about 2 inches laterally each way from their neutral position at the rudder horn. To keep some spring tension on the cables at all times that means an extension spring would need to measure 2 inches at rest to 6 inches fully extended. Checking the McMaster-Carr extensive chart I find there is no such extension spring ... twice the at rest length is the maximum stretch for extension springs.
The plans specify no particular spring ... other than it will have to come from the hardware store. Can any V-Max builder share with me how they handled this dilemma?
The sole purpose of the springs is to keep the pedals upright when entering the a/c. The location is not critical as long as they allow full deflection..
Since the springs are totally nonfunctional why not leave them off?
Good question. I'm beginning to think they may be more trouble than they are worth. By placing the springs with a simple cable loop the pedals would always be right where you left them.
They could be left off but because of the flexible rudder cables they will fall forward when you exit the a/c and make it inconvenient when you enter it.
They could be left off but because of the flexible rudder cables they will fall forward when you exit the a/c and make it inconvenient when you enter it.
Mongte
That's true, but I was wondering about replacing the springs with a short closed loop cable. (I haven't learned how to post photos but can probably draw a mental picture.) On the forward side of the pedal replace the spring with a short cable connected to the pedal the same way as the aft cable(s) are connectes on the other side.. On the fuselage replace the eye bolts where the other end of the springs would attach with small pulleys. Run this short cable through the pulleys and attach the other end to the other pedal in the sams way. The result is a fixed length cable loop forward of the pedals which works with the aft cables to form a closed control system. The pedals will then always be vertical within their normal range of travel. The aft cables will also be easier to tension using the turnbuckles because the adjustment will not be made against a spring.
Keith and I have been exploring this method. Has anyone else utilized a closed rudder control scheme as an alternative to the admitedly almost useless springs?
Of course you could. But, why add useless weight and complexity to your plane? Sounds like a solution in search of a problem.
My Eindecker has the same type rudder pedals with no springs or anything else. Not a problem.
That's fine if you're comfortable with it. I would not be. Actually the cable loop is less complex than the springs, but it may add a couple of ounces weight.
Rubber bungees instead of springs? Just a though, but it represents the least deviation from the plans and would be inexpensive to implement (but would need to be replaced with each conditional inspection).
At first I agreed with texasbuzzard that it was a great idea, by then the A&P half of my brain kicked in. With the cable loop, there is the (remote) possibility that some FOD (a pebble from your shoes, that missing pen, rogue screw/bolt, a mysterious acorn, etc...) could get caught in the pulley and jam your rudder pedals - and that normally sucks. It's also another lube point, and another cable to inspect (in a crappy location for either). If a bungee/spring breaks, you would have to apply some pressure to the pedal to counter the pull of the unbroken bungee on the opposite pedal.
I just see the spring/bungee (or just floppy pedals) option as the one with the fewest opportunities for a bad day.
IMHO, Ironnerd is accurate in his assessment of risk of cable getting jammed.
If no spring or other device is used, like Radfordc suggested, the issue may be, what happens if both feet have to be taken off the pedals momentarily in flight ? With feet off them, if pedals fold fully flat forward, then how do we pick it back up without contorting your body ? This may be a very unlikely scenario, but Murphy's law may apply. Otherwise, I would have gone with what Radfordc suggested.
I have discussed this at some length with wjnew37 off-forum, because we both were trying to install a pulley system. The single pulley closed loop that I installed ( picture below ) has some drawbacks. Since there is a change of direction of the cable at the pedals, there is some sideways load being transferred on to the pedal hinge, which in turn restricts free movement of the pedal. It still works OK, but there is slight friction from the rudder pedal hinge.
I have tightened the entire cable loop so there is no slack at the rear/front portion of the cables. Alternatively, we could keep some slack in the whole closed loop, so that when we keep the feet on the pedals, the slackness transfers to the front loop. Then the sideways force on the pedal hinge can be eliminated, enabling free movement of the pedals. The only drawback with this arrangement is that in flight, a slightly loose cable is moving around forward of the pedals, though still passing through a pulley. A slack forward loop may be more susceptible to getting caught / jammed, and also, it is easier for a slack cable in the front loop to slip off the pulley..
If the springs' job is only to keep the pedals from falling fully forward towards the pilot, why not put a mechanical stop to the pedal so it does not fall forward all the way, but the mechanical block still enables full freedom of movement through the full arc of deflection of the rudder and the pedals. One crude depiction is given below.
I have always been uncomfortable with the hardware store spring scheme shown on my 1550V plans. As explained to Keith all my flying has been done in tri gear aircraft where the pedals are connected to a steerable nose wheel. In effect that is a closed control setup because the steering rods and nose gear act like the cable and pulley setup being discussed. An open control system is a foreign idea to me. Probably all GA aircraft ... and my other Experimental ... utilize closed control systems. (I have flown the Grumman Tiger with a free wheeling nose wheel, but it did not have a "disconnected" rudder.) Because of the limited space between the V-Max pedals and firewall a cable and pulley system may not be possible, but I will probably try it. If it is not possible I will take the suggestions to have nothing at all ... as uncomfortable as that is.
The bottom line is that a closed control system is smooth and solid ... feet on pedals or not ... and a bullet proof pulley design is not that difficult. Maybe Dave (Cooper) if he sees this will give me a steerable nose wheel option when he gets to the tri gear Epic. The 1550-V is apparantly the only Minimax that does not have that option. (An old dog needs an old trick.) That would solve this problem for me , as well as several others. My first plane was a Tri-Pacer with steerable nose wheel and a simple hand brake. Worked great!
Why not have the closed loop complete with centre pulley, but instead of using cable from one pedal to the other, get a large width pulley, then use 1/4" thick bungee instead of cable? That way, if the pulley jams there will still be stretch in the bungee to allow the pedals to work. It should also be cheaper to make, and easier to install and calibrate, as you don't need to be exact with the cable length. A simple reef knot on the bungee at each end will allow you to set up the amount of default tension you want in the system. Furthermore, bungee doesn't rust, so wouldn't need oiling, and if it breaks then it's simple and cheap to renew.
This topic has appeared several times in this board, and will probably appear several times in the future.
For what it's worth, here's my take.
Firstly, the rudder control system as designed is already a closed loop system. Forward deflection of one pedal results in equal & opposite deflection in the other. Adding a cable between the pedals does not change this.
Secondly, as has been said, the springs simply stop the pedals flopping rearward while you're out of the cockpit. When I'm seated in the flying position, I almost physically can't remove my feet from the pedals, as there's nowhere to put them. So once you're ready to fly, failure of the springs would not even be noticed until you get out after landing.
I share the concern that a cable between the pedals could potentially snag. It will also detract from the feel of the pedals ( I wear very thin-soled light sneakers for flying, in order to get maximum feedback from the pedals. I'm pretty sure a cable would damp some of this 'feel').
Again as has been suggested, it is easy to arrange bungee cord to get sufficient length to operate over the required range. The other way to do it using springs is to arrange the positioning of the ends of the spring to make use of 'efficient' & 'inefficient' arc (this is how you get differential aileron travel): a constant deflection on the pedal can translate to a varying extension in the spring. In this way, you can make the spring pull most to keep the pedal forward when it's upright, with its effect diminishing to almost nothing at full pedal travel in either direction. Sounds more complex than it is in practice: just doodle with pencil & paper & it will become clear.
In summary, I believe another cable linking the pedals gives potential for jamming and detracts from feel. It also adds weight & complexity, in an area which is very hard to inspect. With a little thought, both springs or bungee will work to keep the pedals in place with maximum simplicity & reliability, and minimum weight.
But as with the rest of the build, it's your plane, & your decision. That's one of the major plus points of building your own.
Which way do y'all suppose the pedals will fall without the springs?
I'm thinking they will flop aft in the direction of cable tension, and that if the hinges are installed per blueprint, they will not be able to fall flat on the floor. You'll just have to slide your toe under the pedal and lift into position (radfordc let me know if I am going in the right direction here).
It seems to me that wjnew37, just wants his rudder pedals to be more like the pedals he is used to in other planes. I also agree with radfordc that this is a solution is search of a problem. It is wjnew37's plane, and if he wants to make a few changes, I'm cool with that, but I'm not sure the reward is worth the additional effort, weigh, and complexity.
As Keith1100 points out, such a system can actually introduce new problems. Keith1100 , have you consided turning those bolts around so the heads are up, instead of down next time you are down there?
ironnerd, you're right. I am probably just more comfortable with a system that has served me ... and others ...well thru the years. I suspect though the GA industry had a reason for doing it the way that has served me well.
A "closed control system" is one that provides feedback to the operator. With springs, or nothing at all, If the pilot's feet are on the pedals and applying force it is a closed system because the pilot receives feedback on its operation. Conversely if fthe pilot's feet are not on the pedals it is an open system and the pedals can collapse. The springs will prevent the collapse but that is a convenience ... not a requirement ... so the springs can be left off altogether if desired. I'm just more comfortable not having to fish around for the location of the pedals.
Which way do y'all suppose the pedals will fall without the springs?
I'm thinking they will flop aft in the direction of cable tension, and that if the hinges are installed per blueprint, they will not be able to fall flat on the floor. You'll just have to slide your toe under the pedal and lift into position (radfordc let me know if I am going in the right direction here).
My rudder pedals don't flop either direction. The rudder cables provide enough support to the pedals to keep them upright at all times. Without springs in the system there essentially is no tension on the rudder cables until you actually put your feet on the pedals.
I agree that if you take your feet off the pedals in flight you might see some movement in the rudder circuit....but you would need to be a midget to be able to get your feet off the pedals. My Eindecker is worst case...all moving rudder, no vertical stabilizer...and there just isn't any problem flying.
My rudder pedals don't flop either direction. The rudder cables provide enough support to the pedals to keep them upright at all times. Without springs in the system there essentially is no tension on the rudder cables until you actually put your feet on the pedals.
I agree that if you take your feet off the pedals in flight you might see some movement in the rudder circuit....but you would need to be a midget to be able to get your feet off the pedals. My Eindecker is worst case...all moving rudder, no vertical stabilizer...and there just isn't any problem flying.
Ah-hah! I forgot that the cables are cables and not yarn. They still have some rigidity even when "slack". Sounds like it's really just a preference issue, which is part of the attraction of Experimental Aircraft.
I actually like that the rudder loop is "open". Steve Wittman used to say "Simplicate, and add lightness" (which he borrowed from William Bushnell Stout), and this is a nice example of Simplicating something. For my plane, I'm thinking Rubber Bungees or no pre-tension - we'll see.
Which way do y'all suppose the pedals will fall without the springs? I'm thinking they will flop aft in the direction of cable tension, and that if the hinges are installed per blueprint, they will not be able to fall flat on the floor.
Ironnerd, you caught me there. Yes, the pedals fall toward the aft of the airplane. But I was referring to the pedal itself. The front side of the pedal faces the aft of the airplane.
Since the entire cable is stretched and taut, some amount of loading is coming on :
The front pulley Rudder pedal hinges Rudder horn ( which transfers the loading to the rudder hinges ) Tail wheel steer hinge
I will keep watching the above 4 locations to detect any signs of undue wear / failure.
For front pulley, at first I ordered a 2 inch aircraft pulley, but while rigging it, realized that it is not supposed to take the load caused by the stretched cables. That aircraft pulley was meant for routing an aileron cable etc where the cable is tight , but is not stretched that hard. So I ordered another stronger steel pulley. This heavy duty pulley has a sealed and greased ball bearing, and has much higher load rating. So there is no need to grease the pulley shaft. Also I changed the shaft that came with the pulley with AN-5 bolt and lock-nut from ACS.
I found a couple light duty springs in Autozone that worked quite well. The heavy duty spring supplied in the kit was to stiff for the short length required for the V-max. B-👍
I found a couple light duty springs in Autozone that worked quite well. The heavy duty spring supplied in the kit was to stiff for the short length required for the V-max. B-👍
Thanks, Brian. I have been curious how you handled the pedal springs on your V-Max. I have admired your work for a long time and really appreciate your input.
That's true, but I was wondering about replacing the springs with a short closed loop cable. (I haven't learned how to post photos but can probably draw a mental picture.) On the forward side of the pedal replace the spring with a short cable connected to the pedal the same way as the aft cable(s) are connectes on the other side.. On the fuselage replace the eye bolts where the other end of the springs would attach with small pulleys. Run this short cable through the pulleys and attach the other end to the other pedal in the sams way. The result is a fixed length cable loop forward of the pedals which works with the aft cables to form a closed control system. The pedals will then always be vertical within their normal range of travel. The aft cables will also be easier to tension using the turnbuckles because the adjustment will not be made against a spring.
Keith and I have been exploring this method. Has anyone else utilized a closed rudder control scheme as an alternative to the admitedly almost useless springs?
That would work, and I have thought about that too, except I would put a spring in the middle of the short cable, instead of a adjusting turnbuckle. I saw a box of used 3/4" phenolic pulleys at Sun-N-Fun for 3.50 each (NO bushings or brackets) which I thought was a little steep for used crap! But I kind of wish I had them now!! Here's a link on Amazon for a some pulleys <https://www.amazon.com/Sava-CB.....ds=1%2F16+pulley>
Also, I know you mentioned you were going to have 2" of rudder travel in each direction, why don't you just mount the spring attach point lower on the rudder pedal? It won't need to travel 4" then. You can make an angle bracket out of scrap AL laying around and it might even stiffen up the plywood rudder pedal.
Scott, There would be no spring or turnbuckle in the short loop. It would be a fixed length cable. (See Keith's photos above.) Tension on the closed system would be set by adjusting the rear turnbuckles ... that is one of the advantages. Your suggestion about moving the spring attachment is interesting. If it turns out springs are my only choice I will consider that.
I have been flying with my system for over 8 years with no issues. Really, the short cable and pulley up front are just doing essentially what the springs do. There is very little tension on the cable and it is not a necessary or critical part of the main system. It basically just allowed me to avoid hassles with springs and tensions. At first I worried a bit about having the cable wrap so far around the pulley (it really shouldn't wrap more than 90 degrees), But it has been a non-issue. I have never even lubed the pulley. Hell...you just don't move the Max's pedals and control surfaces very far anyway. The most extreme movement seems to be in the ailerons, but that's an illusion, because your legs block any extreme side-to-side movement in flight. The most extreme pedal inputs you will ever likely introduce is when taxiing around. In flight the pedals actually move very little.
Have I not read somewhere on this site about someone using spring loaded hinges? Now wouldn't that eliminate ALL the above listed "It might get jammed, hard to maintain & lubricate, hard to adjust..." issues? It would be a hardware store of course & wouldn't have the benefit of going through an FAA certificate process BUT, if they make (spring loaded hinges), it seems like another good option. Anything (could) jamb/break). The old Murphy's Law thing , But I think one could tell if they were holding it in hand if it were built to a level of satisfaction they would be comfortable with. Just did a Google on the subject....Looks like there are LOTS of choices. No pulleys, no external springs or spring length to worry about. I would be looking in that direction if I were contemplating a design change to the issue of holding my pedals back with some amount of tension. What say you guys? See any you like the specifications of? Which (might ) you pick? P.S. Am I missing some MAJOR, OBVIOUS reason that this is NOT a good idea? I can't imagine that almost ANY of these spring hinges is of any lower quality than what you might be picking up at your local HW Store OR what TEAM might be shipping in a hardware package??????????? HMMMMMM TTT
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