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Old Dec 06, 2012, 06:51 PM
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Aerodynamic forces on swing-wing Question

I'm designing and building a Large swing-wing 1/5 scale aircraft and I'm trying to figure out what size actuators or servos to use. The question I have is...what type of forces are affecting the movement of the wing....meaning if I had a 30lb actuator pushing the wing forward while the aircraft is moving at 120mph will this be enough to move the wing? Or will there be additional force on the wing which would translate into more weight for the actuator to push? If I'm not being clear please let me know.
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Old Dec 06, 2012, 08:10 PM
the anthropocebo effect
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That is going to require some analysis.

The wing forces are usually resolved into lift (perpendicular to the free stream), drag (parallel to the free stream), and a torque about the wing Mean Aerodynamic Centre (MAC). Depending on the exact situation the wing is usually has an aft force from the drag, but can actually be pulling forward under some circumstances.

The force required to sweep the wing will depend on the wing planform, flight attitude, speed, AoA, the mechanical ratios of the MAC to pivot and actuator to pivot distances, and the friction of the pivot under the flight loads.

There is no simple way to determine if 30 lbs. is enough. Is that a quoted figure, or the actual dynamic force that is available to move something? There can be a big difference between what the manufacturer's quote, which is usually a holding force or torque, and the dynamic force available to actually move something.

If you provide some more details on the wing planform, and how the actuator will be moving the wing, perhaps we could figure out some of the basic forces. I would recommend actually testing the actuator to see how much mass it can lift, to see how much force it actually has.

Kevin
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Old Dec 06, 2012, 08:20 PM
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The bending loads on the wing all go through the hinge. That must be a sturdy fixture so it doesn't bind under load.
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Old Dec 06, 2012, 08:32 PM
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The 30lbs is not a quote figure. Obviously I have bitten off a little more than I can chew here. I will obtain an actuator and a servo to see what works best. I have a NASA research center a mile down the road from me...I have been tempted to ask what would it take to use their wind tunnel. This would give me a lot of answers with this design. Thanks for your response.. I will take some pictures once I get the actuator.
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Old Dec 06, 2012, 09:00 PM
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Quote:
Originally Posted by CFBird View Post
I'm designing and building a Large swing-wing 1/5 scale aircraft and I'm trying to figure out what size actuators or servos to use. The question I have is...what type of forces are affecting the movement of the wing....meaning if I had a 30lb actuator pushing the wing forward while the aircraft is moving at 120mph will this be enough to move the wing? Or will there be additional force on the wing which would translate into more weight for the actuator to push? If I'm not being clear please let me know.
Thrust = drag, so you should be able to get some rough idea what proportion of the drag is due to the wing. How much thrust do you get from your propulsion system. From there, approximate the center of drag for each wing and calculate the moment you need to counter with your actuator. These are all approximations. Or, you could go the other way. Given the span of your wing, what would be the drag required to reach the limit of your actuator. Does this drag make sense?

Mark
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Old Dec 07, 2012, 06:08 AM
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I would use a screw type device - motor loads very low .
the wing would also hold any position desired

The swing wings were really lousy concepts but playing with one could be a lot of fun- the weight of the things was the big stumbling block.
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Old Dec 07, 2012, 12:34 PM
An itch?. Scratch build.
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1/5th scale ?

If that's a F-14 Tomcat, that make it around 150+" span, (over 12ft), and doing 120mph.

Turbine power ?.
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Old Dec 07, 2012, 05:38 PM
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There are roles where a swing wing makes a lot of sense, particularly for low level high speed bombers and fighter-bombers. The list is pretty long here: B-1B Lancer, Tu 22 M, Tu 160, Panavia Tornado, Mig 27, Su-17/-20/-22, Su-24, F111. It's not ideal for pure fighters (F 14 and Mig 23 are the only representatives here, the Tornado ADV was just forced into the role) but it can be advantageous in interceptors operating beyond the visual range. Otherwise, none of these really makes a good dogfighter, but entering a maneuvered fight nowadays means that you already made several mistakes.
An 1/5th scale Tornado or Su-17 should be large, but feasible
An 1/5th scale Tu 160 would be amazing. And could be fitted with a cockpit.
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Old Dec 09, 2012, 08:52 AM
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Originally Posted by richard hanson View Post

The swing wings were really lousy concepts
I must have been wasting my time then.
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Old Dec 09, 2012, 09:07 AM
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I must have been wasting my time then.
Yep, that about captures it.
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Old Dec 09, 2012, 09:11 AM
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I must have been wasting my time then.
The planes were not a breakthru - just a attempt to do the job -If they had been a true improvement -the concept would have continued.
There were lots of lousy fighters over the years - typically the result of not having enough power for the job.
so the developers tried to reduce airframe drag to get the speed desired
Unfortunately we still have some lousy planes - grossly overpriced and unreliable - but what do you expect when the the goal is to drive technology (and profit) with an open checkbook.
I don't see any end to it .
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Old Dec 10, 2012, 01:29 AM
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No one said it was a breakthrough. All airframes are compromises. The Tomcat was built solely as a platform for the Phoenix missile. The sweep (unswept) wings were to reduce air speed for carrier landings (as was the F-111 which McNamara wanted to force on all branches). Anything after was gravy. And the gravy was pretty good. She could definitely reach out and touch someone. Or 6 someones.
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