Not a good description, and this may not be the right fourm for this, but here goes anyway

We had a guy at the field a couple days back with a discus launch glider. Every thing state of the art. What caught my attention was the controls. He used kevlar cord through the boom with a rod as a bearing on the end and a 180 turn to pull pull elevator and pull pull ruder. Very clean and not much to cause drag.

What really got me going though was the ailerons. The servos were mounted in the wing so the axis of the servo output was on the cord line. The servo was mounted at about 45 degrees to the hinge line. There was a little coupling between the output shaft and a rod that ran to the hinge line and had a bend in the end that tucked into a pocket in the aileron. There was nothing in the airflow at all. He told me the name of the setup, but like a lot of things it was gone by the time I got home. I'm scratching my head about the geometry of the pocket and bend. He claimed some guys arer using the same type setup on 1/4 scale and larger.

Any links to explain this stup? The Geometry, ETC.

Thanks
Don

I belive that this is what you are looking for.... http://www.irfmachineworks.com/rds/




(edited so that link would work as a link)

Jackpot. Exactly what I was looking for. Do you have any experience with them? I'm rebuilding a 1/3 scale Laser 2000 and I was wondering how they would work on it.

The mind is running amonk right now. Two standard size servos on each aileron, and three mini's on each elevator half. Maybe stick the the pull pull on the rudder with the pair of servos I now have..

Thanks again for the link. Time to do some home work.

Don

i love the idea. the less visible controls the better. i need to buy a set just to check them out. i had forgot about this idea.

Don, I do not have any flight experience with them, but I had designed another set of wings (using the same concept)for my giant protege. However before I could complete the wings, my protege had an untimely contact with terra very firma...There is a build thread on RCSCALEBUILDER.COM where the concept was used in a UHU 219 (I believe). so you may want to check it out. I will try and provide a link later....

Well it is later and here is the link that I was telling you about. http://www.rcscalebuilder.com/forum/...N=1&TPN=10 study the pictures and text and you will be surprised at how easily they can be utilized...

It's a slick system but tight mechanical tolerances are required to avoid free play in the surfaces. Also it's much more tedious to adjust the control surface throw. if you want less than plus or minus the full servo wheel angle. What you need to do is alter the bend in the activator wire where it crosses the hinge line. But that means extracting the wire by some means which pretty much implies that you have really good access to the servos and activator wires. It may even require that you can remove the control surface via extracting the hinge pins.

It's a very slick system but as I hope you can see it comes with its own baggage that complicates the use of it.

hmmm. interesting point. one might want to make a mock up 1st before burying this system in a actual project.

Access to the page is denied

Just join and then you can see it. For what it's worth though, there are a lot of missing photos in that link. Lots of good infor also.

Don

A very, very good idea. And as you've seen now that you understand the concept it would not be hard at all to make these up in your own shop. And a mockup to play with and test different angles on the knee bend of the activator torque arm would really help.

indeed, i have seen a thread somewhere where the builder machined his own parts.

and as for joining rcsb or better yet donating annually there makes for a ton of quality reading. there is some magnificent work going on over there.

The RDS system is great for a sailplane, but for your Laser you want something more robust and easier to install. Check out the Durant Direct Drive system: http://www.durantdirectdrive.com/

Bterry, having never installed either type, I think the RDS would be easer to install, and would be less visable. Ican't imigane trying to cover the plane with the durant direct drives. Changing a serov would require the removal of the control surface. These are just my observations from looking at the site. Seems that one of the model magazines ran a How To on a similuar setup in the last year or two. One of the negatives was the bulge in the surface for the servo. With the RDS, the servo can be moved back to the fat part of the wing or elevator. I'm not sure Iwould use them on the rudder, but given enough meet in the rudder, it may be possible. The Laser 2000 only has a 3/8" thick rudder and elevator. Tying to hide servos in it woudn't be easy for either system.

Thanks for the link anyway.

Don

You may be able to get away with using the RDS sytem as long as your "rotating activator rod" is of sufficient torsional stiffness. Think of how much a 5/32" torsion rod landing gear on a trainer will flex for instance. On a typical .40 size trainer with 1/8" or 5/32" wire landing gear with a cross-fuse width of about 4" will easily deflect 15-20 degrees without too much force. I fear that using such a system on a larger aerobatic plane will lead to problems as the twist in the system will tend to "soften" the control response. The amount of twist in the RDS rod will be linear with the length of the rod, but will increase with the third power (cube) of velocity. Given enough speed, your surfaces may not deflect at all.

I am worried you will have flutter with the RDS system. If you use a carbon fiber torque tube setup instead of a simple wire you may be able to eliminate it. However remember you are building a plane with maybe 20% of the wing area (wing + aileron), nearly half of the total horizontal stab area (stab + elevator), and well over half of the vertical stab area (fin + rudder) is a movable surface. Sailplanes have control surfaces that are a significantly smaller portion of the total surface area, AND they only deflect a few degrees, while a Laser could experience up to 45+ degrees of travel (less for an IMAC setup of course).

I am contemplating building a 40% Laser myself, and will likely use the Durant system on the ailerons. For the rudder I will us a pull-pull cable system (which is scale, btw) and on the elevators I will use direct pushrods. It would be very easy to rig up a pull-pull system for the elevators as well, driven by an internal bellcrank attached to the elevator joiner.

Personally speaking I love to see innovation in our models. I greatly enjoy watching a single development system (such as Mr. Harley Michaelis' RDS control actuators) create a total paradigm shift in the state of our art. I would love to see it work in your case, but just realize that using a stock system may not be sufficient for your needs you will likely need to greatly upgrade the strength of the system.

For what it is worth, one problem I see with the Durant system is the decrease in resolution when using smaller control throws. For instance when I only want 15* or so of throw, the servo moves only 1/3 of it total throw and the resolution (number of discrete steps) is cut by 1/3.

They are great for 3D setups however.

I'm not sure the flexability will be an issue. True the wire landing gear flexes a lot, but it is a different than a tortional flex. I saw some articles on the setup and some load testing. THey came up with a tortional twisting of something on th order of 0.015 degrees, for all practical purposes, zero. This was with the loads of 100mph on a large surface, The servo is really the weak link, not the rod.

They also stressed the need for a snug fit on the pocket. The bend in the rod is the limit of the angular travel of the surface. There is also reference to a mecanical advantage from the system, requiring less servo strength.

I think you would be somewhat in the same boat as the durand method in that it would be all but impossible to change the mecanical advantage to give more or less throw. It woud requre a different bend and a different approach angle.

The rods they sell are "hardened and tempered" I'v see reference to the rod ends silver soldered into steel tubing for weight reduction. There is a lot of test bed engineering to be done before I comit a 33% to useing them.


The Laser I have is a Laniar kit. There are four servos under the horzontial stab, two set up as a pull pull for the rudder, and one on each elevator half. A lot of weight aft.

Don

I don't know if I'd run those things in a 33% plane. There are these things, I can't remember the name, but you put the servo in the trailing edge of the wing (or stab) but ahead of the aileron and you attach the servo arm to the control surface. It's a direct linkage control system. It was in the AMA Mag like 1.5yrs ago. Maybe someone has more info on it than I do....but it seems to be the best way of doing it something like that.

I had totally missed that part or read it and it didn't register.

There's no way I'd use either the angled wire in a box system or the Durant system in your case.

The biggest reason is the issues of installing either one in a rebuilding situation. Either systems would require major work and demolition to incorporate into an existing plane and for no actual flight benifit. Add to this the need for a very high degree of accuracy with either system to ensure that the servo axis lines up spot on with the hinge line or that the bend on the torque activator lines up dead on the hinge line axis. You just do not need that sort of extra concern in a rebuild. During new construction it wouldn't be so bad since it would be easier to arrange assembly jigs and measure alignment more easily. But on a rebuild you're not going to have a good way to ensure that amount of accuracy in the placement of these systems.

And frankly it's just more work to cut into an existing model for this than it's worth. Neither of the systems give you any advantage other than a visual one for neatness. And both bury the servos in a way that makes adjusting or replacement a total PITA. On a model of this size external horns on the underside of the model are all but invisible anyway. If the model uses surface mounted servos and you're just looking to tidy up the installations just lower the servos deeper under the surface so just the output arms are exposed. Just putting the bodys of the servos under a hatch or patch of covering material will make things look a LOT cleaner but still allow ready access to them for servicing. A far more sensible compromise all around in my opinion. Especially given the opportunities for damage to the servos from pushing around such large surfaces or if those surfaces should suddenly be leaned on by an external force. I don't fly the big stuff like these but it seems to me that burned out servos and stripped gear trains would not be all that uncommon on these models.