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Old Jan 28, 2007, 08:57 PM
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Any way to get a 15:1 glide ratio out of a 12" span glider?

I've heard of it being done before, but haven't found any specific information on picking super-efficient ultra-low RE airfoils, planforms, etc. Should I try a super thin, cambered solid balsa wing like the indoor glider guys use? What about using a slight "concave-up" camber towards the TE, to reduce the chances of a separation bubble? Various aerodynamic websites have helped, but I think this goal is like a needle in the proverbial haystack. The whole point is to make a super-efficient indoor slope glider that can fly off the air flowing around my hands, head, and body.
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Old Jan 28, 2007, 10:33 PM
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"Any way to get a 15:1 glide ratio out of a 12" span glider?"

No.

"The whole point is to make a super-efficient indoor slope glider that can fly off the air flowing around my hands, head, and body."

Yes. It has done it with a model for about 50 years. Just made it very, very light enough for a very, very low sink speed and slow walking air speed. Use a 8-1/2" x 11" paper for a slope "hill" and make the wind by slowly walking in your hand. Outline the wing with 1/64" square light balsa and cover it cover with microfilm. Just don't sneeze near the fragile model.
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Old Jan 28, 2007, 11:44 PM
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Quote:
Originally Posted by Ollie
"Any way to get a 15:1 glide ratio out of a 12" span glider?"

No.

"The whole point is to make a super-efficient indoor slope glider that can fly off the air flowing around my hands, head, and body."

Yes. It has done it with a model for about 50 years. Just made it very, very light enough for a very, very low sink speed and slow walking air speed. Use a 8-1/2" x 11" paper for a slope "hill" and make the wind by slowly walking in your hand. Outline the wing with 1/64" square light balsa and cover it cover with microfilm. Just don't sneeze near the fragile model.
Indeed, and I think the number you care about should be the minimum sink rate, rather than glide ratio. And of course low airspeed, too.

Is there any data on the minimum sink rate, for either holding a piece of paper or only using airflow around the head?
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Old Jan 29, 2007, 02:06 AM
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Free flight models and indoor models typically have about a 6:1 to 3:1 glide ratio due to many factors.

I agree that light weight and the resulting low sink rate is what you want.
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Old Jan 29, 2007, 04:04 AM
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http://www.rcgroups.com/forums/showt...+along+gliders

I think this is what you may have heard about
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Old Jan 29, 2007, 08:17 AM
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"---airflow around the head?"

Politicians, around the world, are famous for airflow out of mouths and warm gas (thermals) from other body orifices.

Doctors use equipment to measure breathing.
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Old Jan 29, 2007, 09:17 AM
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As others have suggested, L:D is not the critical factor here, rate of descent and glide speed are much more important. I have done exactly as you describe with a number of small models, some built up, some foam. I would start by trying a flying wing out of the thinnest foam you can find, and use a sheet of cardboard, say around 11x17 or slightly larger, as your slope for starters. Once you get used to the performance and handling, graduate to smaller and smaller pieces until your forehead is enough. The first time I saw such a model flying, Rob Romash of Estes was flying a scale rogallo wing hangglider with a hollowed balsa pilot. It was the coolest thing I had seen to date.

Thayer
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Old Jan 30, 2007, 10:27 AM
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Thanks for the suggestions; however, based on my own tests, a low sink rate/ flight speed by itself is NOT enough for forehead sloping. Why? Low flight speeds mean very little air is deflected around my body, thus the low sink rate is matched by an equally low updraft; the glider barely flies (off my forehead) as a result. I've done plenty of flying w/ a board, and with just my hands; I'm just looking for ways to make "forehead sloping" easier and more consistent. If there's something even better than the MacCready Air Surfer planform, I'm all ears (haven't found anything better to date)

As far as glide speed being critical for walkalong gliders; true, but only within the context of someone keeping up with it and controlling it (from what I've experienced). I've experimented with "runalong gliders"; one of them weighs 9.3 g on a 10" span, and I must go almost all-out to keep it going. For precise "mind control" (sloping off of forehead) I agree, slower is better (for control) as long as the L/D doesn't drop off precipitously.

If you want slow and low sink rate , try condenser paper tumblewings; they're the slowest things I've flown, period. (<1 mph flight speed, 7-8"/sec sink rate typically). The low L/D makes them entirely unsuited for forehead sloping, unfortunately.

Again, thanks for the suggestions; a stick-and-tissue/film plane seems to be the way to go.

P.S.
I had heard of indoor sloping over the past 35 years, but 50?! Who did it before the MacCreadys?
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Old Jan 30, 2007, 03:21 PM
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Rob's Rogallo was condenser paper covered. I have no idea what its glide ratio was, but it wasn't much. Basic FS Rogallos were often as low as 4:1. While his sail was a more efficient shape, it did not have the benefit of a high Reynold's number. Less than normal walking speed was plenty.
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Old Jan 30, 2007, 06:04 PM
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Quote:
Originally Posted by yoyoML
Indeed, and I think the number you care about should be the minimum sink rate, rather than glide ratio. And of course low airspeed, too.

Is there any data on the minimum sink rate, for either holding a piece of paper or only using airflow around the head?
I made a mini Air-Surfer clone and flew it off my forehead (barely). Its sink rate was around 9" or 10"/sec. If you plan on flying a walkalong glider using a board, 1 to 1.5 ft/sec sink rates should be acceptable. If you don't mind jogging or running, you can go even heavier and faster with the expected higher sink rate.
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Old Jan 30, 2007, 07:23 PM
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Flyingwingbat1,

I did a crude calculation and I think I see what you’re getting at. Sink rate is (D/L)*Vo and the slope lift is Vslope*sin(gamma). Where gamma is the slope angle, Vslope is the person’s walking speed and Vo is the flight speed. In this case Vo=Vslope so:

sin(gamma) = D/L

This means you want max L/D for the minimum slope angle needed to sustain flight at (any) given walking speed.

For fun I “built” a condenser paper floater which is simply a piece of ½”x1/8” condenser paper. I released it and, sure enough, I couldn’t get it to sustain altitude in ridge lift because I kept running into it (i.e. poor L/D=0). I was able to maneuver it around the room quite easily by blowing on it! Have you considered a walk-along thermal-soarer that uses “hot air”?


Steve
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Old Jan 30, 2007, 08:42 PM
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If you want a condenser paper "floater" that can actually be flown, here's what to do:

1. Cut out a rectangular strip of c-paper, approximately 1.5" x 3/8", or any other CLOSE dimensions giving a 4:1 or a 4.5:1 aspect ratio.

2. Snip off the corners, thus "rounding" them, sorta like the cut-off corners of a stop sign.

3 Fold up the last 3/16" of each end of your rounded rectangle, forming endplates. Try to fold them perpendicular to the main horizontal section. Your little "aircraft" will still be floppy at this point.

4. Here's the trickiest part. Bend down the 1st 25% of the chord to make a downward-pointing "LE", then bend UP the last 25% of the chord for an upward-pointing "TE" The folds should measure about 45 degrees off the horizontal section. If you can, make the TE fold (as seen with the "wingtips" up) a bit steeper than the LE, this'll help it spin smoother.

5. Now the tumblewing should be stiff enough to fly. Hold it high by the TE, then try to "flick" it, sending it into a spin. Descent angle is about 45 degrees, and you'll have to hold the board nearly vertical to keep it going. It took me far longer to type this than it does to actually make one (only 5 minutes, and that's only due to c-paper's delicacy. Regular tissue tumblewings take maybe 2 minutes to make.

Quote:
Originally Posted by mlbco
flight at (any) given walking speed.

For fun I “built” a condenser paper floater which is simply a piece of ½”x1/8” condenser paper. I released it and, sure enough, I couldn’t get it to sustain altitude in ridge lift because I kept running into it (i.e. poor L/D=0). I was able to maneuver it around the room quite easily by blowing on it! Have you considered a walk-along thermal-soarer that uses “hot air”?


Steve
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Old Jan 31, 2007, 08:50 AM
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Steve,
Your design is an autogyro but not a glider.

Copy nature's maple seed but larger and lighter. Make the wing outline with 0.02 Dia. carbon with weight of 0.2 gram! Use the carbon rod about 30" long and bend it into tear shape. Put about 0.1 gram weight on the apex.
http://www.goodwindskites.com/merch/...lidroundcarbon
Cover the wing with 0.000059" mylar.
http://www.modelresearchlabs.com/pricelist.htm

It spins around the weight near the apex.
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Old Jan 31, 2007, 09:53 AM
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Quote:
Originally Posted by Ollie
Steve,
Your design is an autogyro but not a glider.

Copy nature's maple seed but larger and lighter. Make the wing outline with 0.02 Dia. carbon with weight of 0.2 gram! Use the carbon rod about 30" long and bend it into tear shape. Put about 0.1 gram weight on the apex.
http://www.goodwindskites.com/merch/...lidroundcarbon
Cover the wing with 0.000059" mylar.
http://www.modelresearchlabs.com/pricelist.htm

It spins around the weight near the apex.
I think mlbco's design is more a bit of fluttering paper, vs an autogyro, at least from his description anyways (Could you clarify, mlbco?).

Can you easily keep the "mylarseed" up by blowing upward on it, Ollie?

I tried "sloping" a genuine maple seed once; no luck at all, it would need some decent, measurable L/D to work well.

Can you keep the "mylarseed" up by blowing upward on it, Ollie?
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Old Jan 31, 2007, 11:24 AM
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Ollie and flyingwingbat1,

My condenser paper experiment was not a tumble wing, but more like a parachute. The L/D was essentially zero (pure vertical descent) and therefore it can not be slope soared. The same would be true for a maple seed, unless you cyclically vary the blade pitch to induce forward flight, or have a stable fuselage below it with offset CG. I have built many maple seed models, some 3 feet in span. I've also built many McCutchen-style motorized versions from 10" to 5 feet in size. An optimized rotating wing has an effective drag area equal to its swept circular area. If you just want to test an idea involving low sink rate, it's simpler to build the appropriate sized "parachute" than fool around with an autorotating system. The maple seed makes sense when resources are limited (i.e. you can't easily grow a full sized parachute) and you want to get a low sink rate for seed delivery. Regardless, it will need L/D>0 to stay in front of a slope. Maple seeds can (and often do) catch thermals which greatly enhance their dispersal.

Steve
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