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Old Jul 18, 2005, 01:26 AM
Registered User
San Diego Lindberg, California, United States
Joined Jan 2002
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suggestions for a foil for a plank ?

Does anyone have any suggesstions for a suitable flat bottomed foil for a flying plank (no rearward sweep). I don't have a hot wire set up. I plan to just use fan fold foam, so I am limited to simple foils, preferably flat bottomed. Can a plank wing with no sweep, be made to work with a flat bottomed foil. Some elevon reflex is ok.
EP
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Old Jul 18, 2005, 05:02 AM
Proud to eat Kraut ;-)
Julez's Avatar
Germany
Joined Dec 2003
5,203 Posts
Hi!

Most people who construct planks want them to perform well, so they use carefully designed airfoils. These have no flat bottom, so there are no flat bottomed airfoil for this application. At least i do not know one.

As I am sure that you do not want to waste your rare free time with a plane that does not satisfy your expectations, I suggest to you do to things right from the beginning an build hot wire cutting tools. This is really easy, and you will use them often once you have them.
It is better to do things well right now than to do them well in the future, after having some years of frustration.

On my homepage, you will find building advices for a hot wire cutter.

After you built it, use the downloadable PW75 airfoil for your plank.


http://www.extremflug.de/seite028.htm

perhaps use google translate.


Have fun,

Julez
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Old Jul 18, 2005, 07:49 AM
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Germantown, MD
Joined Apr 2005
267 Posts
Thanks for asking the question EP! if you try a plank please post your experienceon how the FFF plank works/doesn't work? maybe you could cut "ribs" of that airfoil and use the FFF as sheeting/covering? maybe this would work and could only take a little more time.

I have looked at planks the last couple of days and was wondering the same thing! I saw a plank called a "Boobie"? named after an Australian Bird and that thing looks cool!

PW75... I'll be checking back here to see what others have to suggest also. I'm off to figure out the Google translate now...thanks Julez.

Jim.
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Old Jul 18, 2005, 08:36 AM
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AeroNut45's Avatar
Australia, VIC, Keysborough
Joined Jun 2004
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Flat bottom airfoil

Quote:
Originally Posted by epkoncept
Does anyone have any suggesstions for a suitable flat bottomed foil for a flying plank (no rearward sweep). I don't have a hot wire set up. I plan to just use fan fold foam, so I am limited to simple foils, preferably flat bottomed. Can a plank wing with no sweep, be made to work with a flat bottomed foil. Some elevon reflex is ok.
EP
Well this photo was taken of me about 28 years ago. This was my third plank. Which was originally designed in the US. It had a 55" span and the fin was sitting right on top of the airfoil. It was very sensitive around the square axis. It was capable of 6 foot loops. But very hard to land. So I redesigned it. Useing a fuzz with the fin behind the airfoil made it a lot tamer. But with that span it only performed well on the slope. So I rebuilt it with a 6 foot span and a fibreglas fuzz. Can't recall what the all up weight was but in some stage I came 3rd in a thermal comp against conventional models.
The airfoil I used was very similar to the one in the pic. It was flat bottom with a little reflex.
AN
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Old Jul 19, 2005, 01:34 AM
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San Diego Lindberg, California, United States
Joined Jan 2002
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pictures of my only attempt at a plank

root chord 7.5"
tip chord 5"
full span elevons 1.5" width
span 48"
clark Y 12% thickness foil
empty airframe 7.6 oz
epp fuse
1/2 thickness FFF for top skin
FFF for bottom skin
6 ribs per side
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Old Jul 19, 2005, 06:56 PM
Striving to Rip the Bring
raptor22's Avatar
San Diego, socal, USA, North America, Earth, Solar System, the Orion arm, Milky way, Universe
Joined Apr 2003
6,320 Posts
Julez is right on here; you usually built a plank to fly well, which means you do not want that flat bottom. Flat bottomed arifoils perform poorly overall, anyways, but are especially bad for planks because you will need excessive reflex

You CAN definetely make it work, but it will not fly nicely. it iwlla slo require a larger static margin (forward CG) because the Cm will shift alot.

I would suggest the PW51 (so a search and you'll find the coords) for an airfoil because it is not hugely complex, and is not hypercritical. If you feel you must go flat-bottomed, maybe a slightly thickened ag03 would work well because it has a relatively low Cm. But even a thickened ag03 will be quite thin for a foamie.

--Alex
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Old Jul 22, 2005, 02:29 PM
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Canada, QC, Gatineau
Joined Jan 2001
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Here's mine, based on the combat Gremlin. Used 1" pink foam carved crudely and palm sanded into a tennis shoe airfoil I did sand some washout and a bit of reflex on the TE. It's 48" WS, powered with an AXI 2820/10. Glides reasonably well with a folding prop.
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Old Jun 19, 2006, 11:53 AM
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Joined Jun 2006
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flat bottom airfoils for plank

I have built several powered planks with flat bottom airfoils and they worked great. I actually found that the Goldberg Vector wing makes a great plank wing if you add 1-1/2"-2" wide elevons. A flat bottom airfoil of about 11-12% thickness with the high point at about 35-40% of total chord and a CG at 17-18% makes for excellent performance. I have flown these in local pylon racing and combat with great success. You cannot believe how tight a flat bottom airfoil makes a pylon turn! Great fun.

jjam
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Old Jun 21, 2006, 09:28 PM
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San Diego Lindberg, California, United States
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more info please JJam

Jjam:
more info on the Goldberg Vector wing ?
What is the span, root chord, tip cord, the planform ?

EP
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Old Jun 22, 2006, 09:51 AM
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Joined Jun 2006
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Vector wing

The vector is an advanced trainer with a flat bottom foam core balsa covered wing.
Stock span 59", constant chord without elevons = 9.75"
I add elevons to bring the chord up to 11" to 11-1/2"
excellent low speed characteristics as well as good top end. No bad habits with a CG of 16-18%.
Buy the wing direct from Goldberg as a replacement.
I have shortened after several combat encounters to as little as 48", but the performance suffers.

Good luck ,

jjam
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Old Jun 22, 2006, 12:28 PM
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San Diego Lindberg, California, United States
Joined Jan 2002
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Carl Goldberg Vector ?

JJam:
I went to the Carl Goldberg url, and I could not find a "vector" trainer nor any other plane called Vector. Is is a discontinued model ? While searching for it, many of the ARF plane's replacement wings are quite expensive . How much was the Vector's replacement wing ?
EP
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Old Jun 22, 2006, 02:39 PM
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Cape Town, South Africa
Joined Jan 2003
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Take a look at http://www.toddsmodels.com and check out the Wing-E. They fly great!

I also hot-wired a wing with a clark-y, got too lazy to put a tail on it, and now it's a plank. Flys great on an Astro 010 16T + 3s 890 LiPo...
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Old Jun 28, 2006, 03:17 PM
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Joined Jun 2006
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Vector wing

I never damaged mine to a point where I needed to replace it. I remember seeing them advertised for about $25.00, but that was a while back. I could make a tracing of the aerfoil though and send it to you. You can make your own or use it as a hotwire template. Let me know.

jjam
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Old Jun 28, 2006, 04:32 PM
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San Diego Lindberg, California, United States
Joined Jan 2002
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thank you JJam

JJam:
No need to trace the foil, I have Profili so I can plot the foil if I know what it is. What is the thickness of your Clark Y ? is it the standard 12% or so ?
I don't have a hot wire jig, so I typically make my wings out of fan fold foam. I cut the ribs out using a paper template, put a piece of FFF for the top and bottom skin, and a CF tube for the spar. I did make a small hot wire jig to slice the FFF to half thickness for the top skin, when I want to save a little weight.
EP
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Old Jun 29, 2006, 03:05 PM
Master of 1 point landing
Naperville, IL
Joined Jul 2005
2,841 Posts
Quote:
Originally Posted by Julez
Hi!

Most people who construct planks want them to perform well, so they use carefully designed airfoils. These have no flat bottom, so there are no flat bottomed airfoil for this application. At least i do not know one.

As I am sure that you do not want to waste your rare free time with a plane that does not satisfy your expectations, I suggest to you do to things right from the beginning an build hot wire cutting tools. This is really easy, and you will use them often once you have them.
It is better to do things well right now than to do them well in the future, after having some years of frustration.

On my homepage, you will find building advices for a hot wire cutter.

After you built it, use the downloadable PW75 airfoil for your plank.


http://www.extremflug.de/seite028.htm

perhaps use google translate.


Have fun,

Julez
Blah blah blah Use the tried and true 4/40 with plated bottom. Works well (4% of chord upward at 40% of chord).
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