I've been thinking again, and you know how dangerous that can be.     One of the major problems with my Jenny project was mounting the bellcrank and feeding the flying and (predominately) the pull test loads into the structure, while trying to keep a scale cockpit area.

I've been thinking about the possibility of going to a control handle with an RC stick on it for pitch control and using a system like Clancy's for the elevator as well as the throttle.  One of the advantages for scale would be that the elevator servo could be placed somewhere more convenient than in the cockpit where the bellcrank is usually located.  Another big change would be one wire to carry the flying loads and a small coaxial or spiral wrapped ground line.  The flying wire attachment could be anywhere convenient to the structure, not necessarily in the fuselage, though it would still need to be near or on the vertical CG.  I'm considering using an RC-car transmitter handle and using the auto speed-trigger for the elevator and the wheel for the throttle. Clancy's encoder would be substituted for the RF transmitter in the handle.

An added advantage for those so inclined would be some variation of the auto-stability being proposed for stunters. Perhaps a line-pull based system that rolls the model out if the pull drops off, using active rudder and aileron.  I could use that in the Jenny for sure. Control of the model wouldn't depend on line tension anymore.  Regardless of your feelings about the purity of U-control, such a system could potentially save some nice models.

Anyway, nothing on paper yet, and I would have to build a plane to test the system.  Maybe this coming year.

John

No, actually the problem was solved for the Jenny, but the bell crank is partly visible.  Keep in mind, in this case, the pull test is 50lbs, so there is a big load to deal with.

The real problem is for future aircraft, TBD, where the issues are likely different.  The loads must be routed into the structure in a way that can be accomodated and still give smooth, bind-free control, etc. The point is that there are more approaches out there than linkages and pulleys. And yes, for the Jenny, I did think about turning the corner with pulleys and attaching the leadouts to the scale elevator cross bar, but pulleys large enough to give smooth control are a worse problem than the bell crank to hide.  The pulleys have to take the pull test loads as well as the control anchor point.  The result for what I did do is a compromise, but in sport scale the cockpit interior is not judged, I just want it to look scale for my own satisfaction.

For a precision scale project, the requirements are more stringent and the interior appearance is important. The flying wire attachment and the control actuation need not be linked, so perhaps there are two easier problems rather than one difficult one.

John

From the general regs:

2. General. A Control Line model is flown on one or more steel wire line(s) or metal line(s) of equivalent strength, attached to the model in a manner providing aerodynamic control of the model’s elevation through manipulation of the control surfaces during flight. Such manipulation of control surfaces, and any other of the model’s operational features, may be accomplished by mechanical means, by electrical impulses transmitted through the line(s), or by any other control system that does not interfere with the control of any other model or present a safety hazard to competitors or spectators.


John

WOW!!  I have been there there and done that.  What I know about all this it is legal for AMA. It is not legal for FIA. I have an EXTRA 300S with a Saito 120 4C (big ship).  I have a 6 channel controll handle for it.  The controll handle sends a signal down the line for ailerons, rudder, smoke, and throttle.  The elevator up-down controll is still through a conventional two line system with handle.  The only difference is that the bell crank is linked to a pot on a servo driver, not the elevator.  The servo driver drives two servos for the elavator (300S has a split elavator).  This in fact acts as a power assist for elavator control. This is important when at low throttle.  All you need is enough line tension to run the pot.  Works great.  Advantages are easy to hook up.  Servos provide muscle to overcone pushrod drag. Works with low line force.  Disadvantage is more stuff to go wrong.  Also weighs more. You need a big battery on board to run all of the electronics.  With this setup I can do a pre-flight for the judges.  Waggle ailerons, rudder, etc.  I can steer on the ground for taxi manuvers.  SO far I have not had a system failure.

Picturs shows the boat load of servos. Not shown are the two servos in the wing.  It also shows the control head that goes on the handle.

I too had thought of a chest harness with a cable between the aircraft and harness to handle the centrifugal force.  All functions would come from a gutted RC control box held in both hands RC style. The box would talk down the a twisted pair of wires supported by the teather cable.  You could actually do slack line maneuvers. It would fly like a RC that is limited by a 60 ft pair of lines.

For what its worth John, as scale judges we are instructed by the rules not to downgrade forany intrusion the controls make to the models lines.

And I think you may fight an uphill battle with controling pitch by RC even if it is in the lines, but do it as you see fit.

Could be an issue getting the control rate such that the pitch control has the right gain for the model: there's still something for us mechanical guys to work out.  There are a bunch of different servos out there though, and the problem is not much different than the control rates and resolution required for landing an RC plane.  I guess it's time to do more concrete planning and try it out.  My crashed Vector might make a good test bed. I already own most of the other stuff.

I'll keep ya'll posted.

Control rate is not a problem.  As it turns out the elevator pretty much tracks the handle.  Scale aircraft generally don't fly a stunt pattern.  Loops and wing overs maybe.  If you think about it elevator movement is quite slow for scale flight.  Amount of throw is controlled same as in RC.  You change the length of the servo arm and the length of the elevator horn.  And of course the spacing of the wires at the handle.  If you are going to drive the elevator with a stick controll at the handle it still won't be a big deal.  Move the stick and adjust the length of the servo arm and the length of the elevator horn till you get a reasonable elevator throw.  The other cool thing if you also have throttle you can always land if thing are not right.

Actually, I didn't intend to sound like I was complaining about the pull test. It is a requirement that must be dealt with. 

The  Jenny weighs 10.3 lbs, and its actual in flight pull is about 7-10 lbs, so no harness required.  I've never considered using a harness to hold a model, I think that I wouldn't let myself in for anything that would pull that hard. It's easy to calculate approximately what the pull would be ahead of time and adjust your speed/weight target accordingly. At that weight, it falls within the 5G pull test range, giving 50 lbs. 

John, thanks for your comments about the controls. I never found it difficult to get to a good set up when flying RC, so don't think it would be too hard for U/C. All the usual things apply, a straight model, correct CG in all axes and one should be able to reach a viable set up with some testing. As you say, with throttle, you can always slow down and land.

John

I just had a brain wave. 

I know that you're looking for an electronic solution, and I know this isn't it.  But with all those wires and struts that abound in a Jenny anyway, you could bring the control lines to a bar (essentially the bellcrank, only disguised) in the rigging, and bring push-pull elevator cables off of the bar, have it all hanging out in the breeze, and maybe not have it look that bad!

Note that this is idle poofery -- challenge me to do it, and I'll say "when I build a Jenny".  Then I'll say "when I build my second Jenny".  Then you'll notice that I predominantly build fast things for control line, and you'll feel cheated.

One of the things I like about U/C is the direct touchy-feely of the handle in my hand.  I do away with that reluctantly.  What I've been thinking about here is a way to solve some of the more difficult packaging problems with various scale planes.  I think John has proven it's a viable way to try.

John

I buried the bellcrank in the wing of my Spacewalker and built a raised ball link to protrude just enough to allow the pushrod wire to skim along the surface of the wing.  The cockpit floor hid the wire neatly.