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Old Sep 03, 2004, 09:55 PM
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Buzz_Man's Avatar
United States, GA, Powder Springs
Joined Dec 1999
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Plank With "Clark-Y-ish" Airfoil?

Hello - some place I read where "just about any" airfoil will work with a plank flying wing - would a flat bottom airfoil, similar to a Clark Y work?

What about dihedral, if it's possible to use a flat bottom wing?

C/G will still be ~30% of constant chord with a plank?

I'm familiar with most of the pros of planks, what are the cons?

Seems like one of these could be created in just a couple of hours.

Thanks,

Buzz
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Old Sep 03, 2004, 11:21 PM
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Central Illinois
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Ha Buzzman. Choose your foil shape on the performance envelope you desire. A ClarkY is an excellent shape. Also a flat bottom really helps in the construction. Pinning the ribs down to the board makes leveling a brezze. Sweeping the wings back helps enough with stability so dihedral is usually not needed but(I learned that from Ollie). You can easilly enough. No law says you cant but it will change things. Do you have a spreedsheet for calculating cg math wise? there are several online calcs if yo do a search and il send you the copy of the one i have if you need it. Its in xls format.
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Old Sep 04, 2004, 06:55 AM
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Buzz_Man's Avatar
United States, GA, Powder Springs
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Quote:
Pinning the ribs down to the board . . .
I don't use this method - here's the last wing I created - bottom is "flat enough". BTW, I've also figured out how to "fix" the trailing edge to be "single ply" thickness which isn't shown in this photo:

(link to foam wing construction)

Quote:
Sweeping the wings back helps enough with stability so dihedral is usually not needed . . .
Sweeping & dihedral add time to the process - being somewhat of a mathemetician (mathmajician, is more like it), I am inherently lazy and don't wanna do something if the result isn't blah, blah, blah. Plus, there's something ugly-beautiful in the straight plank wing. It's almost like the plane is saying "Oh yeah? Well then, try me!" (using the voice from the talking hat in Harry Potter's movies). I have opted to toss on two angled fins instead of one vertical in the center. Maybe I could add a swept wing - that would almost be as easy.

Actually, a fellow modeler gave me the motor/gearbox/prop I want to design around - also, I want something that'll fly in my backyard - something I can toss off the 14 foot tall deck which is just outside my kitchen door. Here's the drivetrain (& I realize this'll be a slow flying plank):

Speed 300 gear drive with 11" prop
2100 3 cell lippo's (the only batteries I have avail)
2 HS-55's for elevons

So, I was thinking about something in the 36" range with a nearly flat bottom wing to haul around the 5 oz battery.

Covering & c/f spar will be omitted . . . who needs 'em? Impacts are much more entertaining & violent without that stuff. I guess I could spray paint some artwork on the thing but my goal is to have a two hour wing - from first cut of foam to tossing it off my deck - two hours tops. I think it can happen - I'm going for it!
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Old Sep 05, 2004, 08:18 AM
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Lake Macquarie, Aust.
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You need tonyo to chime in and show you his "zipper" plank wing. I'm pretty sure it is flat bottomed and from his reports flies very well. It is actually held together by a real zipper

2 hours from "go" to "go" COOL , just make sure you post it here!
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Old Sep 05, 2004, 12:39 PM
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Clark Y-ish......

Ding-dong!
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Old Sep 05, 2004, 12:44 PM
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Toledo Express, Ohio, United States
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plank

rcm has plans for a couple of plank flying wings.
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Old Sep 05, 2004, 03:47 PM
Crikey never leave beer behind
steve wenban's Avatar
Mt Annan Sydney Australia
Joined Dec 2003
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I only build and fly planks I prefer eppler sections over clack y but if you want to see photo's here's our hompage
http://swenban.rchomepage.com/ and its not a commercial site lol
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Old Sep 05, 2004, 05:13 PM
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I've just found the link to the post about the Zippy if anyone wants to take a look.

http://www.rcgroups.com/forums/showthread.php?t=250921
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Old Sep 05, 2004, 05:17 PM
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United States, GA, Powder Springs
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First of all, thanks everyone for the great info!

Quote:
I only build and fly planks
That's respectable. Who needs a stinin' fuselage anyway? (ha)
Quote:
I prefer eppler sections over clack y
How do I get a template for an eppler airfoil? I only chose a "pseudo-clark y" because I know about what it looks like and I know how to build one very easy using the encyclopedias (we got all of them at a yard sale for $2)

Quote:
rcm has plans for a couple of plank flying wings.
I tried two Google searches and ended up lost. Can I get some help with this one?

There's something beautiful about the simplicity and efficiency of a plank - I find planks intriguing.

Thanks a whole bunch,

Buzz
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Old Sep 05, 2004, 05:18 PM
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Oh - one more thing - is dihedral with a flat-bottom (or similar) wing necessary, desireable or should be avoided?
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Old Sep 05, 2004, 05:32 PM
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North-East England
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You've not heard about Profili? How many Eppler's would you like? 100, 200? How about NACA and any others you can think of. This program has at least 2000 sections. It's a superb tool to have. You can download a simple version or buy the full one (and unusually, it's worth it!)

Look for some reflexed ones and build the stability in. MH52 is good.

http://www.profili2.com/
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Old Sep 05, 2004, 06:21 PM
Crikey never leave beer behind
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Mt Annan Sydney Australia
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here's a link to any section you want
http://www.aae.uiuc.edu/m-selig/ads/coord_database.html
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Old Sep 05, 2004, 07:00 PM
Crikey never leave beer behind
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Mt Annan Sydney Australia
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dont need it

Quote:
Originally Posted by Buzz_Man
Oh - one more thing - is dihedral with a flat-bottom (or similar) wing necessary, desireable or should be avoided?
I wouldnt use it on a plank that really where the name comes from flat as a plank you really dont need it but if you are using a high degree of taper in the wing I would suggest about 2 to 3 degree's of washout at the tips. dont worry to much about finding a wing section with reflex in the section as it can be acheived with raising the elevons
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Old Sep 05, 2004, 09:06 PM
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United States, GA, Powder Springs
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Quote:
I wouldnt use it [dihedral] on a plank that really where the name comes from flat as a plank you really dont need it . . .
Thanks - that'll save building time. If it's truly a two hour plane, then I guess I could build a zillion different wings with various airfoils - I want to start out with the slower airfoil for two reasons: 1 - I'm just getting back into r/c and blah, blah, blah; 2 - I want to test the lifting capacity of a plank for aerial photography considerations.

Happy flyin' & for the United States folks, happy Labor Day,

Buzz
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Old Sep 05, 2004, 10:39 PM
Enjoy Life B4U Die!
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United States, GA, Powder Springs
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Here's an idea I had for a plank - the airfoil is sort of based on the Zagnutz shape, 36" x 9" (including 1 1/4" for elevons). The pod below the wing houses the lipo battery - does it seem like using an HS-55 for each elevon would work, or do I need to use larger servos like HS-81's?

Again, my plan is to design something that flies well with a total of two hours of building.
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