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Old Oct 10, 2009, 12:48 PM
Engineer for Christ
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Snyper - FPV flying wing

Now that I've tried FPV (first person view) flying, I decided to design a better airplane suited for flying with a camera. Paul (happyKillmore) suggested a smaller, more maneuverable airplane, so the Snyper is what I came up with.

The idea is to build a fairly quick and maneuverable platform that can be thrown in the back of a car without dismantling it. It also needs to keep the camera protected and shade it from sunlight. I came up with a flying wing design that I'm hoping will work. This is my first attempt at a 4 piece wing.

The camera will be mounted underneath the wing inside a narrow fuselage. The fuselage will extend beyond the camera lens both to shield it from sunlight, and to protect it in the event of a crash.
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Old Oct 10, 2009, 12:55 PM
Engineer for Christ
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The Wing

The wing is a Gottengen 286 airfoil. This should provide a fair amount of lift. I used blue EPS foam from Lowes and my hot wire bow. The center cut used a 4.5" wide template, while the outer wings used an 18".

Once cut, I trimmed the wings down to add some sweep to the airframe. That should add some stability to the platform and make it a little less sensitive to CG.

Wingspan: 39"
Wing central chord: 15"
Wing sweep: 14"
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Old Oct 10, 2009, 08:20 PM
Wonderfully Wicked
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Is it going to be a flying wing?

Don
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Old Oct 10, 2009, 09:25 PM
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no, silly.
it's going to be a flying pyramid.

geez, just look at the shape.
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Old Oct 10, 2009, 09:29 PM
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OK smarty pants, I did not know if a fuselage was going to be attached and canard thrown in as well. I was asking as a flat bottom airfoil like that is not the best on a flying wing due to its negative pitching moment. Your just agitated because you could not find the flying field today

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Old Oct 10, 2009, 09:38 PM
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Quote:
Originally Posted by The Don
I was asking as a flat bottom airfoil like that is not the best on a flying wing due to its negative pitching moment. Your just agitated because you could not find the flying field today

Don
HA! not true.
all my elipsticks are flat bottom and they fly great.

yes, your right about being perturbed. i drove for over an hour looking.
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Old Oct 10, 2009, 10:20 PM
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I was trying to speak in generalities. A high camber airfoil with a sharp entry and forward high point will have a much higher negative pitching moment then a semi-symmetrical airfoil section will and since it is a flying wing additional reflex will be needed to remove the negative pitching moment out to make it stable. At higher speeds and lower angles of attack the model may act "pitchy" and hunt up and down. Usually the drag from the additional reflex required tends to negate the gain in performance from the high lift airfoil. A lower camber wing has much less negative pitching moment and requires less reflex and behaves better at lower angles of attack. I am not saying flat bottom will not work on a flying wing just that there are better alternatives. The Ellipstik does have a flat bottom but also a lower camber and a rounded leading edge as well.
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Old Oct 10, 2009, 10:37 PM
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Quote:
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The Ellipstik does have a flat bottom but also a lower camber and a rounded leading edge as well.
and as you explained....it can be VERY pitch sensitive.
ask me how i know.
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Old Oct 10, 2009, 10:42 PM
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That is why I have not covered that one I got from you. I want to modify the bottom of the airfoil a little. It won't take much to change it but it will fly a lot better through the whole speed range.

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Old Oct 10, 2009, 11:01 PM
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it wouldn't be to difficult. i've thought about it once or twice. i think a single spar maybe 3/8 to a 1/2 in. high opposite of the front main spar would be more than enough to give it an airfoil.
on yours, it would be very easy since the battery box is on the inside. you'll only have to come up with a way to access the door.
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Old Oct 10, 2009, 11:02 PM
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That is exactly how I was thinking of doing it.
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Old Oct 10, 2009, 11:42 PM
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Fuselage made

I made the fuselage out of 1/8" balsa sheeted to blue foam. I will need to sand it up and hollow out the chamber for the camera and electronics.

I threw this a few times and noticed the severe pitching. It is going to need some reflex in the trailing edge to counter act it for sure. However I use this exact same airfoil and set up on my Super Flea and it flies well, so I don't think it is going to be too much of a problem. I also still need to round over the wing leading edge which will help a lot. It is still rough cut. Also the Extended nose moves the CG forward so hopefully it won't need too much reflex when it's all done.

So far the entire airplane is 4.9 oz. I don't know what the covering will add, but I'm guessing an AUW around 28 oz with the camera, transmitter and GPS on board.
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Old Oct 11, 2009, 11:06 PM
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I changed my design a little bit on Don's constructive criticism and made an undersection for the wings. I used a USA 49 airfoil for the underside to help with the severe nose down of the Gottengen airfoil.

I melted out a trough for a carbon spar in the bottom of the upper wing half. I filled this with a Gorilla/Wood glue mix and allowed it to expand a bit before placing the carbon spar inside the trough. I then trapped the spar insude using the lower wing parts. To join the upper and lower wing parts I used 3M super 77 adhesive.

This wing is incredibly stiff, but unfortunately a little heavy now. It went from 4.9 oz with the fuselage to 8 oz It looks like I'm going to be closer to 28 oz when I'm done.

-Alex
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Old Oct 11, 2009, 11:23 PM
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Alex,

I think you are going to be happy with that. Looks good! The ritewing I had glided forever and had a semi symmetrical airfoil close to this one posted below. But as you get close to 130 mph even that starts to tuck on you at high speeds. I am curious to see if after you fly your new wing if you notice a difference or not.

Don
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Old Oct 12, 2009, 07:50 AM
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Alex, at 28 oz with the Ultrafly B/6/15 1500kv outrunner you're looking to use, I think it's really going to be on the heavy side. I typically use that motor on my 14 oz planes and it's got plenty of power. On accasion, I've loaded up my 14 oz planes with bomb-bay doors and remote ignitors and a camera. That added about another 10 oz to the AUW. It flew like a dog... I think that bipe had a wing area of 383 sq in. What's your guess on the wing area of your Snyper?
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