speedracerntrixie

My Feedback: (29)

Sounds like a good plan. remember Bob, we all have our different levels of what we want from this hobby.

countilaw

This thread as gone from describing how slop gets into a bell crank system to just short of calling each other names.

A bell crank system works fine is properly installed. Additional servos works fine too. If you want to stay a purist on old timers that used bell cranks, why not? Why degrade someone because that is their desire.

If you don't agree with their method, us your own d**n method, but don't but degradate someone that doesn't use your system.

I too have been a CEO of a company that supported and supplied the aeronautical industry. I too have built air craft and have been building models for 54 years. But I don't use it to try to prove that I know more about it than someone else.

Brian stated that he liked to use bell cranks in time period projects, and offered a drawing on how to make bell crank installations better. But since some of you think your way is the only way, had to make something out of it and take the entire post out of context.

It's still true today as it was years ago, you can't teach those who don't want to learn.

Frank

longdan

I just love fiddling with a bellcrank setup and watching both ailerons move in opposite directions with one movement at the centre

Woody218

My Feedback: (24)

One of the things that drives me nuts is watching and listening to grown men argue like children over the most trivial *****.

I have used bellcranks, torque rods, flex cable, and dual servos to drive ailerons. All these methods work fine. Do what brings you satisfaction from the hobby. Build and fly what you want to, and to hell with the naysayers!

2.4ghs

My Feedback: (15)

sense you are all on the subject of bellcranks has any of you heard of a idler bell crank?? if so where can you buy them. I have seen them on several big ww1 planes but have never seen one in person. Here is a picture of one

iron eagel

Personally if I wanted to use one servo for two control surfaces I'd set it up with a pull/pull system, a bit more work but by far the best method.

thailazer

Looks like an idler bellcrank is used to terminate push-pull cables; Is that right? Appreciate the photo as I was hoping this thread would yield ideas, photos, diagrams, pros and cons of each system. Things to help a beginner and an old hand as well.

2.4ghs

My Feedback: (15)

yes sir that is true, I am trying to find something like this and I have searched till im green. I tried contacting the person that posted this on scalebuilder but no response.
It is really a neat set up for a push pull set up.

sensei

Here is a link to a manufacturer of very fine products that I have used for years in my giant scale stuff, it is very good quality hardware. Check out the servo trays with idler bellcranks...


http://www.google.com/url?sa=t&rct=j...hk8F8321bgLdIg

Bob

2.4ghs

My Feedback: (15)

Bob that is GREAT, looks like I might be able to use some of this stuff. I am not sure where the guy got the ones on the picture shown as I am scratch building the same type of plane 1/3 scale WW1 sopwith pup.

Again thank you Bob for the great site, lots of great stuff there, love the wire tensioner's

thailazer

Kudos to Bob and 2.4 for bailing this topic out of the "puffy chest vortex" it found itself in occasionally. This is what RCU is all about.... helping each other out.

sensei

If you would like to build your own robust setup like the one in the picture you can start with the main item you will need and here is a link to it.

http://www.aircraftspruce.com/catalo...clickkey=27907

All you will need to do is purchase a some 2024 T3 sheet like .071"-.090" and cut out your arms, drill and assemble, you can find all that you need right from this company. While your in the on line catalog check out the pricing on a 4 X 8 X 1/8 sheet of light ply.

Bob

iron eagel

The pull/pull type of system was used for a lot of full scale aircraft in the old days, using cable and pulleys to route the linkage trough the airframe. I use the Sullivan flexible tubes as the guides for the thin cables that actuate the surfaces. You have to use two control horns for each surface and make sure you are symmetrical to prevent Ackeman but typically the system is lighter and more robust that the bellcrank systems with no slop at all in the control linkages. The beauty of it as far as ailerons is you can use one servo to control both and there is no chance of slop that will induce flutter in the control surface.
Links to information
http://homepages.ihug.co.nz/~atong/
http://web.archive.org/web/200710241.../PullPull.html

2.4ghs

My Feedback: (15)

Hey Bob that is great, I get a family discount from aircraftspruce as my dad was the original founder of the company back in the 60's and sold to Flow and her sons now own it.
I thought they looked familar as my dad built 3 full scale homebuilts back when we lived in Van Nuys CA.
after looking at it, it is a bit over kill for what i am doing, you really don't need to get that carried away. I sure do thank you for the info.

sensei

Yah, that what I was thinking for a 1/3 scale, but this was the type stuff I used in my 70% Staudacher. The Stuff from SWB will work great for just about all modeler needs.

Bob

Quikturn

My Feedback: (12)

I have a TF redbox kit that shows bellcranks for ailerons as well as flaps and look forward to building it that way. I like the idea of using ball links to avoid slop as some people have suggested. It seems a benefit to this setup would be to keep weight (servo) in the center as opposed to having one in the center of each wing.

2.4ghs

My Feedback: (15)

Your right Bob, the swb stuff is going to work much better for this plane, I really think the other way is way to over the top, now like you said 70% yes but a big huge ww1 byplane that might see 35mph on the down line ,
again thanks for the info

ron

BMatthews

Well, I must be one of the odd ones around here.

Whenever I need a complex linkage where it's just not practical or feasable to locate the servo at the tail or in the wing due to the structure being too skinny I always opt for a pushrod and bellcrank arrangement. I've found that it provides me with far less slop than a cable in sleeve and without the heat related expansion/contraction issues with nylong tube in tube flex rods.

I'll often use the steel Qwik Link style connectors for these or "L" bends. Note I do not use "Z" bends as the bend bruises the nylon and results in that slop that you're all worried about. But a snug fitting "L" with the burrs removed fits nicely with zero slop into the typical nylon bellcrank. Then some arrangement is used to keep the "L" from coming out. Methods I've used for that part vary widely.

iron eagel

The method I was talking about is using the brass coated metal cables with a plastic sheathing in a pull/pull configuration, using two control horns for each surface. I think this arrangement can be done with a much lighter weight than control rods and there is no slop at all if done properly.

BMatthews

Any pull-pull arrangement that has a slack removal trimmer will result in zero slop. That's the beauty of it. But they have to be designed so that the "give" on one side matches the "take" on the other. This calls for close attention to getting the control horn holes sitting at exactly 90 degrees to the hinge line of the control surface. And the attachment arm length at the servo and horn must similarly match. Otherwise the pull lines can go slack or tighten and lock up.

Rodney

The arms DO NOT have to be the same length, just do a little sketch on paper. As long as the longest arm does not cause the shorter arm to move past 90 degrees, there will be no problem. With the arms perfectly aligned with the pivot point, one arm plays out as much line as the other reels in and the arm being pulled also has the same reaction. I've been using pull-pull on the bigger models for years and never have a problem of having different length of arms at each end of the lines, in fact, I use this to control the amount of throw, just make sure you do not try to pull the shorter arm past the 90 degree position.

iron eagel

The need for symmetry at each pivot point is a must, or you wind up developing slop or what is called the "Ackerman(sp?) Effect" (good for cars bad for aircraft control surfaces).
Your right it takes some care to get it right but well worth the effort in my opinion. You get a good solid control linkage no slop at all, and it is my understanding that it pretty much eliminates the chance flutter (to a degree you can always over-speed the airframe and the resultant force will overpower the servos themselves). Keeping the guides so the control cables are equidistant from the pivot point is a must so the cable travel is equal at each pivot point as well. And like Rodney say you can vary the length of the control horns at the surface and servo to control travel or mechanical advantage, but perfect symmetry at each pivot point is a must or your going to have slop.
The beauty of a pull/pull setup is you can route the cables around any obstacle or any number of bends you need to get it to where you want it.
I have used it to replace bellcranks used in the old Redboxt Topflite warbirds with success, it is much lighter then using two servos or one with bellcranks outboard for the ailerons.

Rodney

Ackerman is not necessarily bad, in fact a little positive Ackerman is no problem at all. With positive Ackerman you have no slack in the lines when at neutral but the line not being pulled will get a bit of slack as the surface is moved away from center. This is no problem and does not have any bad side effects. Some think that this will cause flutter but it definitely will not. Now, negative Ackerman (where the lines get tighter as moved off center) can be very destructive as it will put undue strain on the servos and hinges of the moveable surfaces. I always make sure that I have a bit of positive Ackerman in all my set ups as it insures no high servo currents or excessive strain on any of the hinges or bearings. The three things that will ruin any pull-pull set us are:negative Ackerman, unequal lengths from the pivot point to the attach point of the line at the moveable surface, to tight a line (you want the lines just taunt enough to have no slack in the lines when the surface is centered).

speedracerntrixie

My Feedback: (29)

Thats exactly what I did on the elevators of my last 2 Lasers. Worked great because the two halfs need to have exactly the same stroke and travel. With ailerons however we do NOT want equal travel so it becomes a very time consuming task to do it mechanically with a single servo.

speedracerntrixie

My Feedback: (29)

Again, this all depends on what you want out of the airplane. For guys flying pattern or a large IMAC airplane in front of a pair of judges will notice a difference if the pull-pull is set up with a little slack. I know I can. It is simply not as presise and I have seen more then a few 40% rudders occilate because the pull-pull was not set up correctly. Bmatthews has it correct, you want to set them up so that you have constant cable tension throughout the travel. Again depending on what your end goal is. Some people are perfectly happy driving a Ford Explorer while others feel the need to own a Range Rover.