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Old Jun 25, 2009, 08:50 PM
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FF DLG airfoil advice?

Hello my name is Jon I have mostly been trolling this wonderful site and studying its contents top to bottom. My main interest is free flight discus gliders but I also plan to scratch build a few R/c DLG's as well in the future. I have recently started learning to cut foam cores for my free flight discus gliders and I am able to find answers to 99% of the questions I have on the proccesses invloved by searching and studying this site, it is a very useful tool!

To get to my question, I am looking for an airfoil to use for my gliders and would like to hear some peoples different opinions of what airfoils would be best? The wing is 1 meter in span with polyhedral, tips appx. 3"-4" wide and a root width of 5"-6". I have been considering the Zone airfoil, the Ag-04 series, the Ag-12 series, the Ag-16 series and the Ag-455 series. I dont know where to start and I am very open to any ideas, I appreciate any advice.
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Old Jun 25, 2009, 09:43 PM
Unshaven yokel
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Portland, Oregon
Joined Oct 2007
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Why free flight? Although pretty neat to make one, the RC guts only add an ounce.

Then again, you can make a more streamlined fuse, or go without one and just add a ball of weight to the front of a boom with a wing pylon mount if you don't have the RC guts.
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Old Jun 25, 2009, 11:42 PM
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Free flight models are what I enjoy the most it is where my roots are, we are a small but dedicated group. I like R/C as well and have even built a small 28" R/C DLG. I realize this is not the freeflight forum but the similarities between the two are numerous. Any thoughts on airfoils?
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Old Jun 26, 2009, 12:19 AM
Unshaven yokel
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If you suck at cutting foam, then I'd use AG36 because of it's tolerance for error.

Otherwise, I'd use AG16 for floaty awesomeness
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Old Jun 26, 2009, 05:36 AM
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Hi Jon

You will be sure to get great advice on the SFA forum, where they have a few specialist FF DLG pilots.

http://www.smallflyingartsforum.com/...?board=Gliders

Richard
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Old Jun 26, 2009, 09:07 AM
But I am learning
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You have to consider that fact that the newer foils (ag455 and zone) have the reflex already built into them. It starts at the 70% chord length. I doubt that this is desired in the FF world.

Good Luck, Brian P.
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Old Jun 26, 2009, 04:44 PM
Grumpy old git.. Who me?
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Aberdeen
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For free flight the R/C airfoils you mention are unlikely to be optimum. For starters at least some (if not all) of the airfoils you list are designed with flaps in mind which free flight obviously dont have. Also R/C need a wide flight envelope allowing good penetration to fly back from down wind and to hunt for thermals.. A free flight model just needs simply to be optimised for low sink rate.

You may be best looking at airfoils used on rudder/elevator 'floaters'?

Steve
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Old Jun 26, 2009, 05:20 PM
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You may want to look at some of the posts from our resident FF hand launch expert, like this one.

Randy
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Old Jun 26, 2009, 06:42 PM
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Quote:
Originally Posted by JonSayre
To get to my question, I am looking for an airfoil to use for my gliders and would like to hear some peoples different opinions of what airfoils would be best? The wing is 1 meter in span with polyhedral, tips appx. 3"-4" wide and a root width of 5"-6". I have been considering the Zone airfoil, the Ag-04 series, the Ag-12 series, the Ag-16 series and the Ag-455 series. I dont know where to start and I am very open to any ideas, I appreciate any advice.

Jon,

Like you, I have done a bit of reading in the reverse on the SFA forum. The differences between our airfoils and planes as compared to those TLGs of Jim Buxton, Lee Hines,Tim, Stan H, or Bruce Kimbal, etc are that F3K type planes have to vary their performance windows for different tasks. They must penetrate upwind, launch high then float using changes in airfoils by flaperons, they tend to be able to be ballasted, and must slow down for fast relights. FF gliders, as is my opinion, and perhaps others here, need to mainly launch high, float, but most of all they must be able to be trimmed so that they can recover from stalls. F3K ships tend to have their CGs set to give neutral dive tests, and this is not what you might want for TLGs to pull out.

Now when you look at the Zone, Ag45 series, they are drawn with reflex, and this generally helps with bagging. The AG12 and the AG16 are presented in their high lift setting and need to be bagged in a bed. You woudl have to experiment with the flap angle if you intend to use them in a non-moveable flapped wing.. The Ag04/08 series tend to be flatter airfoils like those used in FF designs. In my opinion, and having flown it on my DLGs, the AG16 is the better of the airfoils for floating. It carries weight well and has a broader AOA range, which might be more useful for a FF design. The Ag12 is nearly identical to a flapped Zone. My simple comparisons of them on Compufoil show them nearly identical for the first 40% or so, and then they differ slightly in camber and thickness. I know a DLG pilot at Poway who has been using the AG12 for years and has done well. If you add flaps to the Ag12 to reflex it, it becomes the Zone as drawn in its reflexed orientation. The AG16 also has a better performance graph at the lower Reynolds numbers, while the Zone and Ag45 series tend to loose it altogether. With what little I understand for narrow chords, i. e. below 4", these are not much better than a typical flat bottomed shaped airfoil. (BTW, I will take the heat for my opinions because I think differently than the other designers that use them.)

But all that does not matter. The Ag16 is a slight bit thicker, and this would lend itself a better narrow chord and stronger wing. Bagging a Ag16 with say 0.6 oz FG at 45/45 with CF spars as in F3K , perhaps 0.020", would give you a very strong and light TLG. You might tyr slicing and embedding 0.003" CF sheet vertically in the foam to prevent bending. this is really strong and I use that method for my stabs on my DLGs. That is how I am looking at doing one of mine after building one of Stan Buddenbohm Bug kits. I think the plane Jim used at the Nats is already on it's way in the composite direction. What was his airfoil? Are you asking these question having attended the USIC/AMA NATS 2009 contest?

I was thinking of using the Ag16 on my new ships because while I can't launch high, I could use the floating power of the airfoil. Besides, I do not think anyone has used an Ag16 on a SG type plane because everyone thinks it is too draggy for launch.

I hope this helps. Are these all "my" secrets????

Chris
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Old Jun 26, 2009, 08:46 PM
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Thanks for the responses everyone, I think I will just end up experimenting with the Ag04, the ag-18>ag19, and the ag-27. I may build the same exact wing with the three different airfoils and just see what they do. Your responses brought up a few points that I have not thought about so I am glad I asked!
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Old Jun 26, 2009, 10:39 PM
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Jon,

From an old hlg flyer, nice to have you here

Are you aware that Mark Drela is an old indoor hlg flyer, and once held the national record? Mark is very approachable, and I'll be that if you dropped him a PM, he might have some insights.

I didn't understand if you were going for indoor or outdoor hlg. My somewhat dated experience in hlg led me to believe that launch height is better than floatability. Indoors, once you can get to the ceiling, then float is king. Outdoors, I'm not so certain. I'd be tempted to look at low drag airfoils. The discus launch is going to really help your altitude.

I've watched a guy at 60 acres in Seattle flying his bird. Really impressive. Keep us informed. And think about Dr. Drela.
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Old Jun 27, 2009, 01:06 AM
agnotology
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Joined Jan 2007
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Quote:
Originally Posted by Thermaln2
The Ag12 is nearly identical to a flapped Zone. My simple comparisons of them on Compufoil show them nearly identical for the first 40% or so, and then they differ slightly in camber and thickness.

Chris
Chris,

Good observation! A flapped AG12 is basically identical to the Zone 52 in shape and performance, at least from some quick Profili runs. I'll have to try XFLR5 later.

Kevin

Kevin
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Old Jun 27, 2009, 02:33 AM
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Joined Feb 2009
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Yes, there are many of us who are FF'rs, heres a link

Quote:
Originally Posted by JonSayre
Free flight models are what I enjoy the most it is where my roots are, we are a small but dedicated group. I like R/C as well and have even built a small 28" R/C DLG. I realize this is not the freeflight forum but the similarities between the two are numerous. Any thoughts on airfoils?
Hi Jon,
I am glad to see you joining in.

Rc DLG has a lot of inactive/active FF'rs so you are in the right place.

Check out J. Buxtons build for a std hlg and you will see it is incredibly simple airfoil using wire cut foam, CF, and other non-wood parts.

http://www.smallflyingartsforum.com/...num=1243130737

Then check out this, it is right up our alley -

http://www.rcgroups.com/forums/showthread.php?t=840763

the 1m spanned 'Mimi' airfoil is almost flat, with conventional balsa and micro rc gear. He emailed me the plans and Office Depot printed the PDF plans full size for 3$ = my next project.

BTW- i was out in Perris,CA last weekend and talked with Lee Hines and Stan Budenbaum and it was a delight to see their f1a's and 'tlg's flying. It recharges the battery to see where it all began and how wonderful it is to see a model trimmed up to fly by itself. Stan B. uses a micro-servo to activate a Remote DT feature on one of his tip-launched gliders= cool stuff.

take care, john s. (ex-f1b/p30)
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Old Jun 27, 2009, 10:20 AM
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I have spent quite a bit of time over on small flying arts, some of my builds are posted over there.


This is the airfoil Mr. Ishii Mitsura designed and used on his record setting indoor TLG.



I have been using an airfoil similar to Stan Buddenbohm's as well as a conventional solid balsa airfoil. I am just trying to think outside the box a little bit.
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Old Jun 27, 2009, 09:16 PM
Throw a glider!
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Columbus Ohio
Joined Mar 2007
413 Posts
Good Question Jon

Jon and I are both kind of jumping around between SFA and RCG. Discus launch has changed our world, and you RC guys have a jump start on us big time in that skill set.

It is kind of funny; the RC guys are saying to look at FF style foils. Conversely some of the FF guys beat me up for using a "simple" FF foil in my indoor gliders rather than a complicated Drela section since I hotwired it.

The answer is probably somewhere between, but we have yet to prove it. Typical wood FF foils tend to b simple so that the wing section can be shaped reasonably constant. The idea is that there is more performance gain to an airfoil that is of constant section that is all working at the same speed than there is in the few percent you gain from a complicated airfoil like a Drela that would be impossible to carve uniformly over the entire span. I think that is sound reasoning.

Now that some of us FF guys are making foam wings we can experiment with a more complicated section and try to gain those extra few percent. As many have pointed out though the RC foils are designed to for a different task than FF, as range is a primary design goal.

It is a very interesting time in FF glider developments. If anyone has never seen it flown up close, stick around after the AMA RC glider Nats till Thursday, which is when FF HLG flies. It would be worth seeing.

Attached is the glider I used to win the Indoor FF Nats with this year, and a picture of the simple FF airfoil used, a Buddenbohm catapult glider section.

Jon, the Ishii foil may be a good choice for us. I am getting templates lasered to laser cut for an outdoor model for the NATS.
~Jim Buxton
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