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Old Apr 04, 2012, 02:57 PM
When pigs fly rc
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USA, NY, Chester
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were are you in ny?
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Old Apr 04, 2012, 03:52 PM
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Brooklyn, one of the least RC friendly places
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Old Apr 04, 2012, 04:20 PM
When pigs fly rc
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USA, NY, Chester
Joined Apr 2008
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Wow it must be hard to find a place to fly there. Im in Orange County NY which has some open space.
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Old Apr 04, 2012, 05:30 PM
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I'm the author of the linked article about airfoils. When I said "flat bottom" that wasn't including flat plates which are symmetrical. Someplace on the site (I think one of the Model Aircraft Design pages) I specifically state that flat plates are symmetrical.

Now if you're bending one to put camber in it then you're getting an under-cambered wing unless you've applied some type of covering on the bottom to make it flat. Whether you put a covering on the bottom or not, if the foam is cambered you probably see quite a bit of difference between upright and inverted flight.
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Old Apr 05, 2012, 02:16 AM
Assault the sky
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United States, CO, Denver
Joined Aug 2004
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On my cargo plane, first I tried a KFm2 airfoil and then switched to the Armin. The Armin is soooo much better than the KFm2, no incidence angle needed and it flies great. With the KFm2, I needed to either add incidence or fly in a nose-high attitude the whole time.

Also there's something to be said about noise attenuation. It's now virtually silent at full throttle, and it's a twin.
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Old Apr 05, 2012, 07:36 AM
Ed @ Experimental Airlines
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Quote:
Originally Posted by secretspy711 View Post
On my cargo plane, first I tried a KFm2 airfoil and then switched to the Armin. The Armin is soooo much better than the KFm2, no incidence angle needed and it flies great. With the KFm2, I needed to either add incidence or fly in a nose-high attitude the whole time.

Also there's something to be said about noise attenuation. It's now virtually silent at full throttle, and it's a twin.
That's what I like to hear!

Any chance you want to also bring your cargo plane (and some pictures or video) in for the discussion on the foamboard construction thread:
http://www.rcgroups.com/forums/showt...587275&page=14

and/or the parachute cargo dropping thread:
http://www.rcgroups.com/forums/showt...1613883&page=2
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Old Apr 05, 2012, 10:10 AM
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CafeenMan & atone1
Just wanted to clarify - I didn't want to sound "snappy" or disagree with anything said above, I've seen fluid simulations, diagrams, and articles about different airfoils, and I know every single bit can make a difference in a various scenarios. What I was trying to say is that flat bottomed wings that we're making here do work, and work exceptionally well for what they are (easy to build, cheap, light and durable). As Ed mentioned earlier - we're probably getting minor decrease in performance vs fraction of the time that it takes to make these. Nonetheless, you guys have posted great info that I'm sure will come handy in future.


I finally got home before 10pm last night and worked a little on my planes.

First of all, I'm very excited for this small bird -
It will come apart in 3 small pieces. It will be controlled by a Wii nunchuk and main board contains wii plus stabilization system and plenty of other great things.
If anyone is interested , I'll give you a hint - search fmKit.



Also I've put together one of schraut5's designs, thought it would be good for my friend to train with. But this plane turned out to be a little too fast for his likes, so I had to constantly take over controll via trainers port.
30" version, fairly beat up after 2 weeks of use, AUW ~520g . This is my night time parking lot flyer that I'm not afraid to lose or destroy
This is my second plane with KFm2, and while it did perform great, it feels like KFm is not for me.



Here is my miniBaji for night flying that will replace my sloppy 30" wing shown above. I'm planing to hide all electronics inside and make it much lighter than the KFm2 version. Wings are 15" each, and center piece is ~4"
Will try and finish it up tonight

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Old Apr 05, 2012, 03:41 PM
Ichy to Build and Fly.
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United States, FL, Davie
Joined Feb 2011
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Templton,

The progress looks great - Don't forget to post a maiden video.

I started working on a wing at home and will soon post my progress.

But thank you all of you - these techniques opened up a huge potential of making foamies at home and at extremely minimal price ...

Thanks once again.

Mosaic.
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Old Apr 05, 2012, 05:15 PM
<<x USMC
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United States, CA, Burbank
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Originally Posted by rnmosaic View Post
Templton,

The progress looks great - Don't forget to post a maiden video.

I started working on a wing at home and will soon post my progress.

But thank you all of you - these techniques opened up a huge potential of making foamies at home and at extremely minimal price ...

Thanks once again.

Mosaic.

I completely agree, Necessity truly is the mother of invention!!!! I will soon be working on a home brew wing as well.
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Old Apr 06, 2012, 12:01 AM
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templton - you didn't sound snappy to me. I just wanted to clarify that I don't consider a flat plate to be a "flat bottom" airfoil - they are symmetrical airfoils so my comments about flat-bottom airfoils being terrible doesn't apply. Flat plates obviously work well to a point.

The problem with flat-bottom airfoils is that they are incredibly speed-sensitive in regard to trim. I've never gotten one even close to being in trim at all speeds even after multiple changes to wing incidence and decalage.

Flat plates don't have that problem.
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Old Apr 06, 2012, 01:12 AM
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Quote:
Originally Posted by CafeenMan View Post
templton - you didn't sound snappy to me. I just wanted to clarify that I don't consider a flat plate to be a "flat bottom" airfoil - they are symmetrical airfoils so my comments about flat-bottom airfoils being terrible doesn't apply. Flat plates obviously work well to a point.

The problem with flat-bottom airfoils is that they are incredibly speed-sensitive in regard to trim. I've never gotten one even close to being in trim at all speeds even after multiple changes to wing incidence and decalage.

Flat plates don't have that problem.
You know, since I've only flown scratch built planes, with either KFm2 or flat bottomed airfoil, I can't compare to how it actually feels opposed to more proper airfoil, but I usually setup my planes so that I can fly with no hands at full throttle. Also I try to make sure that If I let go of all controls, plane will glide without doing a nose dive. I think all my wings have a bit of reflex or up trim to begin with.

I'm not sure if it's just a problem of flat bottomed airfoils, or if it's a norm, but I always have to add some elevator when I'm below 1/2 throttle, otherwise I might either stall or simply land.

I definitely wouldn't mind having 2 identical planes with different airfoils to compare side by side, but that's too much work just for the sake of experiment, right now it's all about having fun during precious free time
However all of my current projects are based around flat bottoms. I will think on incorporating some curvature into Armin design, while retaining simplicity and strength.

I will upload more pictures of miniBaji tomorrow, it's ~80% done. AUW is 550g with 2.2 battery and since motor is sitting closer to CG, moving battery +- 1/2" is all I need to make it nose or tail heavy. It's not really lighter than KFm2 version as I expected, but maybe it will perform better due to airfoil, or maybe I'll just throw in some crazy prop/motor combo on it

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Old Apr 06, 2012, 08:23 AM
Ed @ Experimental Airlines
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Looking sweet, bro. I can see the refinements happening with each post. All the gear is going inside now. Great stuff!
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Old Apr 06, 2012, 10:09 AM
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yep, I spent a little extra time on this one, even sanded down inside of trailing edge when I was folding the wing.
It turned out a bit too thin to completely hide an average 3S battery, but for the most part we wont see any insides.

Servos are metal gear this time, so I can actually embed them in wing surface and hide wires inside.
ESC and rX are already inside.
The seam between wings and central section will be reinforced and covered with gorilla tape, although it's already pretty rigid.
This time I will add coroplast winglets.


I did make a few very simple ribs to support the shape of center piece and wings around the area where I made cut outs for for the motor. It's very easy to get carried away and get too fancy, but I think for now it's still simple enough. And that's where I should probably stop


Also first picture makes it look like tip cord is same thickness as root, but that's just perspective distortion. I used a piece of pink foam that varies in height from 7/8" to about 1/2"




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Old Apr 07, 2012, 01:51 AM
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More details tomorrow

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Old Apr 07, 2012, 02:47 AM
Assault the sky
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United States, CO, Denver
Joined Aug 2004
152 Posts
looking good
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