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Old Dec 16, 2012, 06:49 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
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Airfoil and Wash-out.

This in not my area of exrpetise, by along shot, so I could use some help.
I have spent some time searching in reference to wash-out, really didn't find what I was looking for. So it was time to ask.
I am in the plannig stage for a foamy build. I never thought I would get into foamy's, but after seeing the magic that humbertomelo can do with foam, I just have to give it a shot.

I was messing with profili2 this afternoon and came up with this airfoil --it just looked right, nothing special. I was looking for something not overly thick, and still had enough thickness for retracts at 10" out from the root. It works.
The 2-view is just for reference.

Shooting for around 9lb AUW, doesn't need to be overly fast, just a nice stable flyer.

Your thoughts on the airfoil, and suggestions on how many ° of wash-out you think it needs.TIA
Mark
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Old Dec 16, 2012, 07:02 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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I can tell you how much washout and why I use it.
I have used anywhere from 1.5 deg to 3 for my models, I now use 2-3deg washout for my planes the root is set to positive 2-3degrees and the tip is set to 0 degrees. The reason is this gives stability I look for in my models and less than 2 degrees does not give enough stability up to stall. Thanks Keven64.

Eric B.
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Old Dec 16, 2012, 07:28 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
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AirX thanks I had thought somewhere in that area, your root and tip info was a bonus. Just hate to cut the cores and get it wrong, only to have to re-cut them.
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Old Dec 16, 2012, 07:31 PM
EDF rules... :)
AirX's Avatar
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This is just one example that I advocate.
Lots of ways to do it and I am sure more will chime in.

Cheers,
Eric B.
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Old Dec 16, 2012, 09:05 PM
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Iam not an expert...however I have experimented heavily with incident angles and washout, I have found on jets that having 0deg incident on the tailplane and wing both, plus having the fan aligned with the centerline (meaning 0deg also) goes along way to eliminating any adverse pitching with throttle increase or decrease, I have found even 1deg incidence on the wing can cause the plane to "zoom" (pitch up and climb) or nose in when power cuts.
as far as washout I too always use at least 2deg at the tips for turn stability. I have only built and flown one plane that purposely had no washout, it was a P-51 slope ship, my buddy said if I dont put any washout in the wings it will fly way faster...it did..it was nice and fast but was a handful to turn, took a great deal of concentration to to keep it from falling off the wing in turns. I then built another exactly the same but with washout, flew a touch slower but would crank into turns with no worries of tip stall...that one I kept

Joe
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Old Dec 16, 2012, 10:18 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
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thanks guys, seems the more I read up on it the more confused I get.

I even went back and read a thread I started,-- http://www.rcgroups.com/forums/showthread.php?t=1730968 sloperjoe, this might clear things up some. I am still working on the AoI and thrust line part of it.

Although full of info, more than I needed to know---
http://www.rcgroups.com/forums/showthread.php?t=1335029

So at this point, it seems that 2-3 degress wash-out will be ok.

I think for an average person, all we need to know is, what AoI, and how much, if any wash-out. What ever happened to K.I.S.S.?
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Old Dec 16, 2012, 10:23 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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that looks pretty short coupled ,hope wing wont blank the stab.
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Old Dec 16, 2012, 10:45 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
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It has about 10° anhedral each side.
This pic might do.

Take a look at the one hoover or die built.
http://www.rcgroups.com/forums/showp...3&postcount=21
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Old Dec 16, 2012, 11:40 PM
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With that tip like that I would think you would not any. If you have washout then those wingtips will make the plane pitch up. Either make a standard wingtips and 2 degree washout or curve them up into winglets.
That airfoil has a zero-zero CL to alpha so incidence should be set at the desired cruse speed. Did you do any wing planform adjustments? What version of Profili do you have?
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Old Dec 17, 2012, 12:07 AM
Do it Right, the first time!
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p901P901 Actually the real model does have winglets. You can see better photos on their web site. http://adjets.free.fr/adjetsv6GB/index2.htm

I am using profili2 free version.

As to your other questions, I havn't done a thing, because i just don't know what I need to, yet. that's why the questions. this part of a build is my weak spot.


I did mail hoover or die a couple of times on his build. but his work , family, and the up coming holidays have taken all his time. At this point all I have went with is his assurance that it's a great flyer. In my last post there is a link to a pic of his, and he does have the winglets.
I do however appreciate the help.
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Old Dec 17, 2012, 12:08 AM
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I can see that wingtips like that with washout would cause vortexes.
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Old Dec 17, 2012, 12:25 AM
Do it Right, the first time!
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I had read that with winglets, it's crucial that they are dead on, and had not planned on them. If you look at the top view in post #1, I did plan on the curved wing "tips", just not the winglets. How does that change things?

I am not in any rush, so I will wait until I can get further info from hoover or die. Suggestions are still welcome.
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Old Dec 17, 2012, 01:47 AM
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Did some calculations on your wing. If you cruse speed is 100mph using the NACA 1410 it looks like your wing incidence should be 1.77 degrees.
There should be some decalage also or is that a flying stab?. Will stay posted for how hoover or die setup his.

Planform adjustment:

a = a ° + ((18.24 x Cl) x (1 + T)/AR)
a ° = airfoil plot AoA
Cl = Cl at AoA
AR = Aspect ratio
T = Planform adjustment factor.
a = 9 ° + ((18.24 x 1.00) x (1+.408)/3.41) = 16.53°

CL of 1.00 for 16.53° = 1.00/16.53 = 0.0604 per degree

CL=(Lift x 3519)/(p x V^2 x S)
Lift = model's gross weight in oz.
p = density ratio (Minnesota 1500 ft ASL, air density 0.7)
V = velocity, mph
S = wing area, sq in.
Cl = lift coefficient
CL=(144 x 3519)/(0.7 x (100)^2 x 676) = 0.107

Wing Cl = 0.107/0.0604 = 1.77°

NACA 1410 has a 0° zero lift (per plot)

Wing AoA = 1.77°- 0°= 1.77°
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Old Dec 17, 2012, 02:01 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
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That's some fancy calculating. I won't even pretend I know what it all means.

the original model does have flying stabs, but as HOD did, I was just going with elevators. Trying to keep it simple. It was a lot easier to convert all the measurements to this scale, that what the wing set-up will end up being.

Is this a good or poor choice for an airfoil?
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Old Dec 17, 2012, 02:32 AM
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Learned allot from kcaldwel and still learning. Knowing the ideal wing incidence tells you about the washout effectiveness. If you set the washout to the root cord camberline and not by the root incidence then it could be way to much.Too much will effect speed and cause wing drag in turns
The airfoil is fine. Just look at the airfoil plots to see how it performs.
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