Pull-Pull setup on spoilers

[Twizter68]

Has anyone ever set up a pull-pull string system on spoilers?

[BenH]

No, but I use a small diameter flexible-cable-in-a-plastic-tube pushrod system for acutating spoilers from a single servo mounted in the fuse at the wing root. Works great. The cable pulls to open the spoilers and pushes to close them. The modest lengths of cable at the ends which are outside the tube provide a bit of give when pushing the spoilers closed and avoid overloading or stalling the servo.
-Ben

[Twizter68]

Which ones did you use?

[BenH]

Geeze, I built this plane 25 years ago (and still fly it), so who remembers . . . . :)

But I think they are .032" cables in a corresponding plastic tube, as presently made by Sullivan, maybe others.

FYI: I soldered a threaded connector for a small clevis onto the spoiler end, connects to the horn on the servo blade. Soldered a piece of brass tube onto the servo end to make it larger diameter and more solid/durable. These ends insert into EZ connectors on the two servo arms as the wing halves slide onto the fuse. The set screws on the EZ connectors are tightened when the wings are in place, spoiler blades are flush, and servo in the 'spoilers closed' position.

Don't know if this description is adequate, but I could probably post a photo if desired.

-Ben

[Twizter68]

If'n you could, I would be in your debt!

[kwmtrubrit]

I have used two methods. One servo in the centre of the wing (GL wing) with thin (read very flexible) gold-en-rod cable used to operate the spoilers. The other was a servo per spoiler with thin piano wire connecting the servo to the spoiler. If you check out the threads on setting up the pull-pull method on the Fling sailplane tail feathers, you will see how much agro they go through. Setting up a pull-pull on spoilers would be hell in MHO. Of course, you could do the "thread pull up, weight pull down" method too.

Keith

[2motheus]

One of the aggravations of pull-pull is determining how to maintain tension as the geometry changes with control surface rotation. (Search on "Ackerman" for some of the theory behind this.) An easy way to avoid this is to use pull-spring. This is common in Europe, even with the rudder on DLG. Only one side pulls. When the servo moves the other direction a spring moves the control survace to the other side. Even tension is always maintained by the spring. I have successfully used this on both rudder an elevator for a 2m Fling. VERY light! All I use for the "torsion" spring is a piece of (.030"?) music wire with 90-degree bends on each end. The bent ends are embedded in the control surfaces, with the straight center torsion part along the hinge line.

You could do this with spoilers, or use a small rubber band, weight, or magnet to hold the spoiler down when the servo isn't pulling the string to lift the blades.

[OVSS Boss]

Sounds like a real can of worms to get right, when you can set a small servo, HS55 or so, under each and be able to adjust and control throws much more accurately.

JMO, Marc

[Andy W]

I am with Marc - there are very light servos available that will operate all but the largest spoilers (where weight would be less of an issue anyway)..
..a

[Twizter68]

Going to go with the Sullivan's flexrod setup; I have a new wing in build right now, so it'll be getting the rod mod. Thanks for all of the inputs!

[LVsoaring]

I presume the build in progress you're referring to is the Marauder? I'm a big fan of one servo in each wing, but with the Marauder's upper and lower spoilers, the situation gets a tad more complicated. I think just duplicating Merrill's method would be the most time/cost/aggravation effective way to go!

[Twizter68]

Nope; new wing for the Riser; the last one...er...shattered, so I building another one, with some changes in design. Also have to fix the Spirit wings, thanks to a wind shift on landing......

[kwmtrubrit]

Is that a Riser 100 wing? If so what changes are you doing.

Keith

[Twizter68]

Nah, Riser 2M; adding shear webs betwixt the spars, wrapping the spars w/kevlar tow, D-boxing the L/E, changing the di- and polyhedral closer to the Gentle Lady's, and playing with the wingtips.

[LVsoaring]

I used one servo in each wing half on my Riser 100. If you want, I'll try to take a close-up pic for you. Works flawlessly!