I read about "Park Bench" ailerons being used on high speed A/C during the 1930's.

What are they, what do they look like, and what A/C may have used them?

And worse yet, is they any scaleability in these such taht they can be used on a model A/C?

Wm.

Never heard of them.... and can't corrupt any I have heard of to that phrase..
There's the Northrop Gamma style, which could be considered to resemble a "park bench" back rest... they're raised up from the aileron surface itself, similar to a modern spade device, but much more span.
No current images of a Gamma in my library, but I have seen some somewhere..
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Sometime later that same day..
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A link ...
http://www.angelfire.com/va2/aerodrome/alpha/gamma.html
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An image..notice the caption at the site...

The ailerons on the Gamma are the park bench types.

And I'm not sure why you want to use them other than for a scale model. Even the later Gammas switched back to conventional ailerons IIRC.

Lots of drag, act like deployed spoilers ALL the time. Not much to recomend them I'm afraid.

Seems to me, Northrop and one other small time A/C constructor of the early 1930's were mentioned as using them. I know very few A/C had them, but did not know of any advantages. I could see some disadvantages due to hanging out there with an exposed hinge point.

Any theories as to what they were to do differently than common
ailerons?

Wm.

Yep, the Northrup Gamma. Don't know about the other one.

Perhaps they were attempting to avoid the patent that Curtiss had on conventional ailerons? Would it still have been in force at that time?

or

The Cunningham-Hall A/C of the early 1930's used them, plus a ducting of airflow within the wing. I understand there is one on display at Amherst.

Was wondering the effectiveness of all this.


Wm.

You got to remember back in the thirties there was a lot unknowns about aerodynamics and a lot of experimenting going. The first few versions of the Gamma had the park bench ailerons. The ailerons were mounted above the wing instead of in the wing. The later versions of the Gamma had conventioal ailerons.
The JU87 Stuka had simular ailerons except they were mounted below the wing.

This sort of aileron would still be operating in freestream air when a normal aileron may be in separated or stalled air on the wing. I would guess they'd keep working down to very low speeds. That's just me looking at 'em and supposing.

Glen Curtiss team did these to bypass the Wright Bros wing warping .
right?
The theory is nice but mechanically they are a mess.
If it were me -- I would have designed a wing with movable top bottom surfaces which could slip to form necessary contour for best lift and or bank.
Maybe someday a material will be invented which makes this goofy idea possible
Like all aircraft design - the early stuff was based on materials available and power available.
The Curtiss Flyers were never going very fast so the mechanics of the setup were possible using a pivot and wires and pulleys.
Just think what he could have done with an AO540 and molded carbon fibre---

The skin friction causes the air near the wing's surface to slow down.
The slowed down layer of air is called the boundary layer.
The boundary layer builds up thicker when moving from the front of the airfoil toward the wing trailing edge.
And the slower we fly, the thicker boundary layer becomes.

If I'm not mistaken, the Kitfox homebuilt uses those Junkers type ailerons.

Adam One's drawing is an elegant explaination of the theory that the Park Bench designers thought was true. I think, in fact, the design was not good because - short of airflow separation - the freestanding ailerons were not as effective as conventional ones, which affect pressure distributions on the much larger areas of the wing itself.
At least the freestanding ailerons below the wing make more sense than the ones above it.
A good example of how a rear surface effects the flow far forward is the aerodynamics of tailgates on pickup trucks. Most people think removing their tailgate will lower the vehicle's total drag but usually this will increase it. Another good example is how a rear spoiler can actually affect radiator flow at the vehicle's front - something I have witnessed in the wind tunnel.
Allan

rear spoilers on new cars are simply purty ups --like much of the pick up truck "trick" stuff.
As you have likely seen in tunnel test - if'n you want the car to stick n go fast --- then clean up the belly drag and pressure problems - but you can't sell that idea to the typical buyer -
For his time - Glenn Curtiss was simply brilliant -coming up with the movable panels .
(I think it was his idea )

Some rear spoilers on cars do help in terms of lowering the CD. Probably all of them help in terms of creating down force for handling. Whether they are worth the money they cost and the weight penalty (which certainly doesn't help mileage) would depend on the vehicle. Porche 911s are terrible without the spoilers. Their rear surfaces droop off too fast and the air separates way up without them. The Audi TT was dangerous on the Autobahn before they fixed it with a rear spoiler. The VW beetle could be greatly improved with a proper rear spoiler (not the silly little automatic lip at the top of the backwindow on their "sport" model).
When Ferrari first came up with the lip type spoiler on the back of their LeMans car years ago, everybody said it was just a "fix" for handling problems - until the windtunnel tests showed that it actually lowered drag too.
The belly flow on modern passenger cars is unimportant. A front airdam keeps the air from going under there in the first place and is easy & cheap. I know there is a Lexus ad where they turn the car over on a spit and babble about the dimpled undersurfaces but the improvement of that kind of thing is absolutely miniscule, if it is even measurable.
When I started in the industry, car aerodynamics were terrible so there was much to improve. Now the public is used to rounded surfaces, flush glass and high rear decks so much aero testing is aimed at handling issues and wind noise.
Allan

Does that stuff have any real effect on handling at the around-town speeds we are *supposed* to be going? I mean, autobahn is one thing - but you shouldn't be doing too much "handliing" there. I just think it's almost all about marketing - since a car's life is almost all spent at speeds where these things don't do much.

If you drive a lot at highway speeds it may be worth it, but for 55 and under, probably not. I believe a properly designed car will already have pretty good aerodynamics and the only separate "add on" part that is worth it economically is the cheap rubber front airdam because it has to be close to the ground to work and you don't want a permanent part of the body down there to possibly get torn off.
On the other hand, the more passion there is in the auto market for cool looking stuff, the more job security for people like moi. I ain't retired just yet.
Allan

On my 65 corvette pro street we monted an air speed sensor to the bottom of the the car. With the car as low as legal 3 inches clearance at rest, It showed an air speed of only 37 mph under the car at 202 mph measured in the clocks.At this point the nose valence is almost touching the ground. Surprisingly rear downforce was greater with the rear spoiler at only 25 degrees from horizontal. This was measured with shock travel data. Raise the rear spoiler and the car lost mph. This is probably a idiosyncrasie of this particular car but it shows you cant assume anything when it comes to airflow. It does what it does and what may seem an obvious truth my be negated by other unseen factors.

I guess I said things a bit wrongly -
The belly drag and pressure comment referred mostly to stuff far dirtier than the present line of disposable cars.
I live near Bonneville Salt Flats and my passion was racing for many years. (starting in 1954).
Cars like my full size Chev van really have dirty bellies.
A belly tanker has a clean (but salty) belly ----
The spoilers I scoffed at are the 200 mph stuff on a 100mph sedan.
Is is amazing tho -at how clean come of the new stuff really is -and the lack of wind noise in even the lower priced offerings is really notable.
I remember the KAMM back stuff from earlier times - which sure turned out to be an effective (tho homely ) fix.
Having sold cars - I know first hand that you can get a lot more milage out of showing off the kooool spoiler than talking about flat floorpans etc.

The sole reason for employing "park bench" ailerons is to permit the use of longer flaps. Park bench ailerons are much less effective than normal ailerons, since they act, largely, as little independent surfaces, very much like the ailerons that were mounted between the wings on some very early biplanes. A trailing edge aileron acts in concert with the wing surface ahead of it, changing the lift coefficient of the entire surface, and thus producing vastly higher rolling moments in relation to its surface area. The full span, underslung, slotted ailerons used on some of the Junkers designs, and on the Fieseler Storch were far more effective at providing good lateral control near stall, as well as acting as landing flaps, and consigned park bench ailerons to the dustbin of aeronautical history.

To add to what Rotaryphile (what does a rotaryphile know about airplanes anyway :-) said - and to disagree with what adam_one said - if you take wind tunnel data on rolling moment due to aileron deflection, Clda, it is constant over a fairly large range of angles of attack and 0 to 20 degrees of aileron deflections. Only when the wing is partially or totally separated does the effectivness go down. There isn't a boundary layer effect at any practical flying speeds.

How much was the wing chord during your wind tunnel tests? and which was the lowest airspeed?
Friction and the Reynolds effect result in an approximately ½" thick boundary layer toward the rear portion of a 4 to 5 ft. chord wing designed to fly at low speeds e.g. S.T.O.L.
A conventional aileron would thus have about 2 degrees of deflection with very little control effectiveness.

You're assuming that the control surface deflection must be larger than the boundary layer thickness before much force is generated but that is not true. The boundary layer is not some kind of vacuum within which nothing happens. It is AIR, just like the freestream air except slower moving, and is fully capable of transmitting forces.
Allan

But since the AIR is slowed down within the boundary layer, it reduces the control surface effectiveness, especially during take-off and/or landing approach when the airspeed and AOA may be near stall.
Also in those circumstances the conventional aileron that moves upward is acting in the disturbed flow from the wings upper side, whereas the one that moves downward increases the drag, which may lead to adverse yaw.
The "Junker" aileron/flaps type are often used on aircraft designed for STOL.

You are combining the effects of boundary layer and separation. The fact that the boundary layer slows does not matter, since the boundary layer touches the freestream. It just acts as if the aileron is a little thicker. However, there is often separation right at the trailing edge, at virtually all but diving conditions, that could cause a control deadband you refer to. However, blaming it on boundary layer is wrong. You need to have separation for that to occur.

I think you’ve misunderstood...
First, I referred to a boundary layer of about ½” causing reduced conventional aileron effectiveness at about 2 degrees deflection on the wing mentioned above.
The air within the boundary layer has almost the same speed as the wing itself so its impact on the control surface is much less compared with the free stream.

Then, in the next paragraph, I added a further advantage of the “Junker’s” aileron. [8D]