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Old Sep 24, 2002, 01:51 PM
Arizona Rim Country
Joined Nov 2001
491 Posts
What the Heck it Nasa Droop

I kind of understand the concept, but putting it into practice eludes me. Ron P. did a good job of describing it but still not quite getting it.

I found this article and it helps some. Ron, you got any pictures or diagrams ?

http://www.btinternet.com/~Gpknight/...es/page18.html
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Old Sep 24, 2002, 04:06 PM
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Martin Hunter's Avatar
Kamloops, BC, Canada
Joined Feb 2002
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OK, so it's not a foamie, but it's applicable to your question. My latest wing for my Cessna 180 has droop leading edges on the wings. Here's a shot

Martin
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Old Sep 24, 2002, 07:29 PM
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Kings Park, New York, USA
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NASA Droop

I too had a hard time finding info and understanding what it is it could do for me. Tom Hunt is the one who pointed me onto it.

He inital suggested as a way of adding washout, but i found it also dragged up the airframe of my flying wing without too much pitch change. (Droop does drop nose a little). it also tames the stall by alot.

Not only that, but i incorporated 5 degree negative droop, that i will fool with to see if it can negate washout drag at high speed and perhaps help with inverted flight.

the 180 droop for sure increases lift at slow speeds, but hurts on the top end unless you can retract.

See photo of what i did at:

http://www.rcgroups.com/forums/showt...threadid=63100

I am using a Hitec digital version of the 225 pushing on a cable and actuating a Beckman concealed hinge.

Fool with it as i suggested, if you dont like, just glue them back on. If you have not fooled with Elmers proBond, now may be a good time.

ron parigoris
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Old Sep 24, 2002, 07:56 PM
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Jacksonville, Florida
Joined Aug 2002
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Looks like a fixed-position version of a leading edge flap, or slat, as it's called. The traditional slat allows an increased maximum coefficient of lift as well as an increased maximum angle of attack. Kinda like flaps, only without the decrease in max AOA. Works well at slow speeds on full-size aircraft.

I can only assume the "NASA Droop" is a version of what I have described. At the very least it would increase the camber of the airfoil.
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Old Sep 24, 2002, 08:12 PM
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Upstate NY
Joined Sep 2002
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very similar to 'slats' on the real planes (most huge ones like 777, 747 etc)

GForce
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Old Sep 24, 2002, 08:22 PM
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Fort Walton Beach, FL, USA
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www.cirrusdesign.com

Click aircraft, then features, then wing.
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Old Sep 24, 2002, 08:29 PM
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Yorktown, VA
Joined Oct 2000
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NASA droop concept

Hope I can shed some light on the question. Please forgive the long post.
I was the NASA team leader (now retired) on the project to develop the droop concept at NASA Langley Research Center in Hampton, VA. As part of a program to increase the inherent spin resistance of G.A. airplanes, we tried to prevent stall on the outer wing with a passive, non-moving, low-cost device that would have a minimal impact on performance. After many wind-tunnel tests, trying slots, stall strips, and full-span droop (as in Martin's model), we found that the secret was to begin the droop at the wingtip and abruptly end the droop at a distance of about 40 percent inboard toward the fuselage. The droop was not as exaggerated as some of you are using, in fact it did not cause any noticeable decrease in cruise speed of 3 full-scale airplanes (Yankee, Skyhawk, and Sundowner). In every case, the spin resistance was dramatically increased--when our pilots intentionally tried to spin the airplanes by holding in pro-spin controls for as long as 10 seconds, spin entries were reduced from 70 to 80 percent for the basic airplanes to about 5 percent!

Now, the secret to the concept is the discontinuity. It basically creates a vortex that originates from the notch near stall and sweeps over the wing making the outer wing act like a low-aspect ratio wing (with a very high stall angle of attack) while the inner wing stalls first. In fact, we found that when we faired the droop and removed the discontinuity, each of the 3 airplanes entered spins easier and spun flatter! The real surprize to the engineering community was that the rectangular wings on these airplanes had extensive spanwise flow to the tips near stall, and that the vortex acted like a fence. Today's Lancair and Cirrus airplanes use the droop concept. One word of caution: This concept was developed for wings with aspect ratios of about 7. When you go to higher aspect ratios (as on most gliders) the stall pattern is different and the droop configuration must be modified.

This was a very satisfying project, and we felt we pointed the way to significantly decrease the number of inadvertent stall/spin accidents in general aviation. I also enjoyed working with Dave Robelen, who began his now well-known status as R/C model guru with me back at Langley and flew many R/C models to validate the concept!

Within about 3 months, NASA will be publishing a book I have written --for public consumption--on NASA's contributions to current civil aircraft (airfoils, winglets, crashworthiness, lightning protection, etc.), including the complete story on this program. I'll keep everyone posted on book status. Meanwhile, an outstanding summary of applications of the concept to R/C models is given in Andy Lennon's book "R/C model Aircraft Design" from Model Airplane News--give a look at his chapter entitled "The NASA Safe Wing"!!!

BTW, thanks so much to all of you Forum dwellers for the helpful tips to get me going in this hobby!!

Martin, can you please tell me about the B-17 model hanging on the wall in the photo of your Cessna??

Joe
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Old Sep 24, 2002, 09:57 PM
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Central Illinois
Joined Sep 2002
543 Posts
variable drooping wings

Joe, I found your reply very interesting and informative. I have a question that i think you might be able to help me with. The concept is drooping wings that you can change the angle of droop. I was thinking in this concept that using this wing to control roll instead of alerions. In my thinking, You could control roll with less drag. My question is do you think Changeing the shape of the camber(per say)of the wing to change the high and low pressure to control roll would be as effective as using aleroins. I built a prototypye of this wing and found it to fly and roll but it was extremely sensitave. Droop deflection over 10 degrees in either way was more than enough to get roll from the wing.

And I would also like to see that B17? too Dreamer

Thanks.
David G
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Old Sep 24, 2002, 10:51 PM
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LA County, CA
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Ron, can you post more photos on you NASA Droops, the more the better.
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Old Sep 25, 2002, 09:09 AM
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Colorado
Joined Mar 2000
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Spinner

Thank You, both for your original contribution to general aviation by performing your work, and for chiming in on this forum to provide a brief and clear description of the basics of the results of the work your team performed. One thing that forums like this need more of is a reduction in speculation and a corresponding increase in formal study, evaluation, and engineering.

Thank You.

Scott Winans
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Old Sep 25, 2002, 12:02 PM
Arizona Rim Country
Joined Nov 2001
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Ron P

On your flying wing picture it looks like you've added the droop to the out-baord leading edges. But, from what I've read the Droop should be on the in-board. I'm still just trying to get a better grip on the specifics.
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Old Sep 25, 2002, 12:38 PM
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Kings Park, New York, USA
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Hey pcaffeldt

Where did you read you want to reduce stall speed and thus put NASA LE Droop on inboard of wing?

If you want STOL then more camber and lots of the wing should have Slats or NASA Droop.

I have read about NASA Droop a bit and have not seen anywhere about putting just on the inboard section of wing.

I am using droop for a slight different reason than just keeping the tips flying.

The Tips of my wing stall before the center. Either with low airspeed or pulling Gs, the plane will enter into a spin PRONTO!

I wanted to keep the tips flying to prevent this. When you build a wing, you can prevent by putting in washout. however with too much it creates alot of drag. On an existing wing, it is kinda hard to put in twist. NASA Droop nets as more washout by lowering the LE! It also decreases stall speed a bit, and allows you to fly closer to stall because of the now more docile stall and easy recovery. It also drags up the wing to allow steepier approaches, and ability to bleed airspeed quicker, net you can land much shorter.

You see Lead Edge Cuffs, NASA Droop, Lead Edge slats and flaps and all other to net allow slower flight.

I am shoehorning the NASA Droop:

to act as a means of inducing drag without pitching my flying wing too much (if i had an elevator, adding flaps would work but flaps will pitch a flying wing nose down)

to lower stall speed a bit by effective increasing camber on the outter 12 inches

allowing me to fly closer to stall with confidence because the tips do not stall first. The center stalls first, but even when it does, a wing does not drop anywhere as violent and does not enter a spin very easily. Without droop nose slightly low and banking 45 degrees can cause a tip to stall (slight extra G force, remember holding altitude in a 60 degree bank pulls 2 gs), and a perfect 1 point landing will happen real quick. With droop if you pull too many Gs too slow, it kinda mushes and when you release back pressure it is flying again.

Leaving Droop down slows top speed. You can really feel it. If flying less than 60 MPH, I just drop 1/2 droop and it is a nice thing to fly, over 60 mph, droop up and drag goes away, too high on final with 1/2 droop, put in full droop and drop nose so as to not overshoot.

I also want to fool with the negative droop as a way of getting rid of even more drag at high speed. The wing does have 3 degree washout, and that probably creates drag at high speed, I am thinking that the negative droop will undrag a bit, also may help with inverted flight as washout when upside down is washin which is not a good thing for stalls.

If building a moderate fast wing, you could add more twist in the building stage and blunt the LE a bit and have a wing that handles OK. But at high speeds will be a bit draggy.

On a typical airplane you see flaps on the trail edge. This nets not only more drag, but a slower stall speed for that portion of the wing. It also puts that portion of the wing at a higher angle of attack compared to the tips. so when you stall, the tips will tend to keep flying and help not entering an unwanted spin.

WW2 ME109s had LE pop outs to help with slow and tip stalls. They were speed actuated. If one stuck in the reatacted position, it was far worst than not having in the first place. Many a pilot chose to wire them closed and deal with a known ill slow handeling aeroplane instead of one that may spin RIGHT NOW when going slow, or not.

Ron parigoris
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Old Sep 25, 2002, 01:00 PM
Arizona Rim Country
Joined Nov 2001
491 Posts
Ron, Thanks for your patience

I'm building and flying Zagi type flying wings with electirc power. Tip stall is a problem. I've built some out of solid foam, some out of fan fold foam, and the next one will be out of Correx/Coroplast. I'm fiddling witht the idea of giving the NASA Droop a try as opposed to wash-out of in conjunction with wash-out.

Would I be right, then, in thinking that to add the NASA Droop to a flying wing I would make the changes to the out-board 60% of the leading edge ?
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Old Sep 25, 2002, 01:52 PM
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Kings Park, New York, USA
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Hey pcaffeldt

If you are building from scratch, i would tend towards adding a bit more twist, and or blunting the lead Edge a bit more at the tips (I have good sucess with taper blunting 1/8 inch off a THL 12 inches from the tip). That is if it is going to be stationary droop and you can twist wing.

With Coroplast, yes i think if you taper Drooped 60 or 70% to 15 or 20% chord at the tip it would give you less tip stalling.

Now articulating droop or even ground adjustable (with coroplast, just double stickey tape some thin aluminium and bend to adjust) would be a neat way to go to dial in wing. Once you see how it works, you could just make them fixed in future set at the sweet spot, but my feelings are once you fool with adjustable, you will look foward to fooling with it.

If you do a search on NASA Droop someone posted a pic of a i think coroplast jet looking wing that just bent the LE of the coroplast. Think he said it worked well.

BTW, the only difference between a tric RC 400 wing and a THL wing, is the THL has a bit of NASA LE Droop the entire span of wing. Makes the THL only a bit more draggy, but better slow, and worst inverted. I like the THL. Have sticks that range with AUW of ~18oz to 45 oz on the same wing. At 45 oz it still glides OK, and i blunted 1/8 off the entire span, and taper blunted another 1/8 off the outer 12 inches.

Oh yea, you could always add washout with twisting elevons, especial if wider at the tips.

On my fast and heavy wings, i make elevons a % of chord, and it nets wider at center and narrower at tip. To keep wing area same, i cut TE to accomodate. Now the elevons are thicker at center but the TE of elevons are the same. twisting would not be too effective like this.

I think more efficient to move large surface alot, as compared to smaller a little. Then slow control is good to move the larger surface more!

Bass works well for durable elevons on heavys that need robust elevons that do not flex.

ron Parigoris
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Old Sep 25, 2002, 02:15 PM
Arizona Rim Country
Joined Nov 2001
491 Posts
Ron,

Can you see that look of recognition starting to gleam in my eyes !

What connected most with me in your last comment was the practical application of a thin piece of aluminum sticky taped to the leading edge.

On a 24" wing, from the wing tip inward, what should the length of aluminum be ?
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