Spring return on spoilers

[wadeg]

Can anyone comment on the reliability of having a spoiler actuated by cable with a return spring? This was used on the Maupin Woodstock and on other homebuilt sailplanes. I have concerns about cable-actuated spoilers that rely upon the spring to return them. If a spring fails while the spoiler is deployed, I forsee the airflow pushing the spoiler aft but the negative pressure over the wing keeping it deployed/open. Anyone know of failures of the springs in such a case?

Opinions based on other control systems using cables and springs might be helpful too.

[steveinindy]

Anyone know of failures of the springs in such a case?

I recall a case of inadvertent deployment here in Indiana several years ago (probably early 2000s) involving a glider but I don't remember much in the way of specifics. I would think that a design with more than one spring (example: one on either side of the spoiler) would reduce the risks of a failure substantially. That is the approach used in my current project.

[WLIU]

For certificated airplanes, the airplane must remain controllable if one spoiler sticks in the deployed position. So the design can include redundancy in the actuation mechanism to reduce the incidence of the failure of a part causing an asymetric spoiler deployment or retraction, but the design process should also provide for the aircraft remaining controllable if the spoilers malfunction.

Spoilers do not have to be large to have a large effect. I have a C-182 with Precise Flight electric spoilers. They are about 12" wide, one on each wing, and my rate of decent almost doubles when they are deployed. I will note that they hardly ever deploy or retract exactly at the same speed. That results in the airplane making a little wiggle when extending or retracting the spoilers. Note - The spoilers create turbulence and they are NOT ahead of the ailerons. If they were, you would feel the disturbed flow through the control yoke/stick, and the disturbed airflow could possibly be a flutter input. The more inboard location also reduces the lever arm that a stuck spoiler can work through and helps with keeping the airplane controllable if one were to stick.

Hope this info helps.

Wes
N6234A

[Kiwi ZK-CKE]

Ever thought of using push - pull cables (e.g Morse / Teleflex / Cablecraft)?. They are very unlikely to break - especially for something only used a few cycles per flight and they are double acting. I'm not sure sure of your exact application, but they may be worth considering. The entire control system on my aircraft uses them, and they work well in that specific application.

[tonycondon]

At least some of the Schweizer 1-26's use top only forward hinged spring return spoilers. I think the D & E models went to top & bottom spoilers similar to the 2-33.

My Cherokee II also has spring return spoilers. I've never had a failure of the spring although I did have the actuating cable get hung up on the root rib once during a landing, so I ended up landing with one spoiler about 3/4 deployed and other closed. It was hardly noticable.

At high speed (80 mph +) in the Cherokee II the spoiler gets sucked out slightly, I can't tell other than being able to see it. I don't know how far they would get pulled out if there was no spring, but i doubt it would be too far.