Airplane flap control
Airplane flap control
(OP)
I am working on a project regarding general aviation aircraft. I need to deploy a device, very similar to flaps, on the airplane. For safety reasons the Flaps must be able to return to their original position if any system failure were to occur. In other words the actuators holding power must be low enough for wind resistance to close the flaps as a fail safe if the system were to malfunction or occur an electrical power loss. Right now the best thing I can come up with is a common ball screw linear actuator. Is their any better commercial available options, possibly something with a magnetic clutch?? I will need one for each side of the plane and weight is a significant factor.





RE: Airplane flap control
can't any sort of power assist (electrical, hydraulic) be neutralised (eg with a CB) so that it won't lock down in a failed case ?
then have a manual retract. look into what they do with landing gear, ie manual extension in th eevent of a hydraulic failure.
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RE: Airplane flap control
A motor with an arm and a link ought to meet your requirement. Can your ball screw be back driven? Can it be reliably back driven after it gets dirty?
If your actuator must work continuously against the airflow, then it is equivalent to or just plain is a solenoid. It will consume power, all of which will be converted to heat, all the while your device is deployed. Is this acceptable?
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JHG
RE: Airplane flap control
You might have a concept of "closed" in your mind, but a dangling thing in the air stream with no positioning forces from an actuator acting on it has no way to read your mind.
It will go to the position where the aerodynamic forces are neutral at the moment. And that position will change with airspeed, angle of attack and probably a few other factors.
RE: Airplane flap control
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RE: Airplane flap control
Good practice would include fabric gaiters over the exposed portions of the screws to protect them from external contamination, and to limit the spread of internally generated contamination. Gaiters don't weigh a lot. Ordinary ballscrews do. Aircraft may use hollow and/or nonferrous ballscrews, which are not otherwise common.
I recall examining a reactor control rod drive (some decades ago; they may be different now) comprising a roller screw, the nut of which was split on an axial plane, and spring loaded and hinged so the rollers would be pushed out of engagement on power failure, allowing the control rod to drop, scramming the reactor. I think the magnetic field of the drive's motor pulled the nut halves together, so the nut and screw were engaged so long as the motor was powered up. It was relatively simple and sturdy, and definitely not flight-weight, and definitely not affordable by ordinary mortals. I'm not aware of anything similar produced for commercial applications, but it may provide food for thought.
Speaking of which, it should be possible to build a clutched linkage, e.g. using trailer brake (electro)magnets run at reduced power to grip a flat ferrous surface (you need a pulse of higher power to pull them in at startup), interposed between some kind of actuator and the linkage to the flap itself. Startup would also have to include some procedure to align the parts, e.g. by letting the flap drop against a stop (or be driven to a known position by weak springs) and driving the actuator to the corresponding position before engaging the clutch.
Mike Halloran
Pembroke Pines, FL, USA
RE: Airplane flap control
RE: Airplane flap control
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RE: Airplane flap control
RE: Airplane flap control
RE: Airplane flap control
what is a CB? .. the landing gear solution would be ideal, but I am trying to keep the system as simple as possible and i think it would add too much weight.
RE: Airplane flap control
One of those might be exactly what you need, or one of the manufacturers might be able to make a special for you.
RE: Airplane flap control
What you need to consider is whether the actuator failure mode where your flap defaults to some neutral position is actually "fail safe". If the flap defaulting to a neutral position due to an actuator failure creates a condition where the aero balance of the aircraft is rapidly upset, it may cause the pilot to lose control. In this regard, it may be safer to have an actuator that can maintain its position in the event it loses power.
RE: Airplane flap control
Best to you,
Goober Dave
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RE: Airplane flap control
"CB" = circuit breaker, so that if your electrical system jammed, you can take control by disabling the electrics.
this is going to be a complicated mechanism, with your assured retraction requirement. airloads, inertia loads, may not be sufficient to retract the "flap" so you need to design in a primary extension/retraction mechanism, including a feature to disable it in the event of a mishap, and a secondary retraction means (and if you're particularly paranoid a third retraction means).
if think MJ's idea is a good primary means, if it includes a locking feature. alternatively a doubling acting hydraulic/electric actuator (with a locking feature). then you need the secondary retraction means, maybe this is where you spring can come into play ?
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RE: Airplane flap control
Sorry, but I think that's an absurd requirement. You cannot possibly compensate for all failures. All designs are compromises amongst competing requirements. For example, you could possibly design some sort of, say, triple failure tolerant mechanism, but it might be ridiculously expensive, weigh too much, and eat up too much volume. Therefore, you must allow for some failure that ought to be as unlikely as possible.
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RE: Airplane flap control
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RE: Airplane flap control
But even assuming only single failures, there are still tons of possible single-point failures that could not all be mitigated. For the desired electrical actuation, the control could potentially be stuck ON, which requires some sort of watchdog, and a secondary disconnect like stacked drivers driven with independent circuits. So, right off the bat, the circuitry complexity is doubled just to handle this one failure.
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RE: Airplane flap control
RE: Airplane flap control
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RE: Airplane flap control
Flap controls driven by independent mechanisms on small aircraft make me nervous, how do you reconcile one side failing and the other side not?
There have been instances of un-commanded roll rates on small aircraft, when a push rod has failed on a manual centrally driven system, yet alone a system with separate servos.
B.E.
You are judged not by what you know, but by what you can do.
RE: Airplane flap control
RE: Airplane flap control
B.E.
You are judged not by what you know, but by what you can do.
RE: Airplane flap control
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