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« on: October 21, 2010, 02:33:14 PM »
rcfoamcrafters
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Hi Guys....I'm getting ready to draw up one of the jets below on a piece of foam for another pusher jet. I haven't decided which one yet, but I like the forward swept wings (something I don't have.


Question...Does forward swept wing aircraft need canards? If so, can they be fixed?

Airflow over a forward wing moves toward the center of the aircraft rather than to the outside as it would with a swept back wing. Would this be the reason for canards?

Let me know....Wayne


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Tech Question...Forward Swept Wings
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« Reply #1 on: October 21, 2010, 04:28:04 PM »
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The SU-47 is missing in the image! I too am an addict of forward swept wings, made a little prototype of the SU-47 and will be constructing a full profile EDF jet the following month..
About your canards!
If you are planning to construct a jet that will do smaller loops or take shorter radius turns! then you will need canards.
If no, then you can opt for the fixed ones!
At high speed as when your canards move forward up, your ailerons will have to move up too, this helps in making smaller loops and turns!
This is according to my experience!
Someone may have a better picture..

Regards,

Dorwin
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« Reply #2 on: October 21, 2010, 04:44:04 PM »
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OK Dorwin, that makes sense. So if I'm not concerned about a tight turn radius, the canards can be fixed? If they are fixed should there be any angle of attack or just be at 0 degrees?

That wasn't a complete list of fighters, but I thought it had some interesting designs. I want to do the Su-55, but right now I'm finishing up another F-4D Skyray. They look great in the air. I should have it out for it's maiden in a few hrs. Just need to let the paint dry and get my electronics on it.

Thanks...Wayne

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« Reply #3 on: October 21, 2010, 07:51:32 PM »
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hi rcfoamcrafters,

If u ant quick loops the it requires cancard to move. but i made 21" Su-47, which had elevators as well as aileron. i hooked left aileron to left elevator and same for right, and believe me, while doing level flight if i give full up elevator it just nose up and flips down, like 360 turn at one place, its wonderful and i dont have canards moving. you can check my post at

http://www.rcindia.org/electric-planes/scratch-built-biofoam-su-47-20-wingspan/

but if u have canards then it should be properly sanded so that it should not create turbulence/drag for main wing
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« Reply #4 on: October 21, 2010, 11:59:44 PM »
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I'm thinking about building the Su-55. It's not actually a forward wing, but looks cool with the canards. I was going to leave them fixed for the time being and see how it flies. I'm getting kind of old for all that high speed flipping stuff. I'll stick with speed in a straight line, and fly it upside down back to me. Being serious, I think since I build without plans and draw out my own, it would be best to fix them until I get the bugs worked out (cg, balance, trim, etc.) then if it's a good fly I would probably make them function. So you would just Y wire the left, and  Y wire the right so each side works together?

Thanks for the info....Wayne
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« Reply #5 on: October 22, 2010, 06:14:05 PM »
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Just wanted to clarify, that these fighters or the image altogether aren't the actual aircraft. I think it's an image from a game, but never the less it has some interesting designs that can be incorporated into our hobby. If the winds not blowing today, then I'm going to maiden my new F-14D, then come back home an start drawing up and building the Su-55. I'm still going with 1/2 Dow board, but I'll see in what area I can lighten up in and try to give it 400 watts (2700KV/w a 6x4) and see what happens. All of my planes so far, come out under 700 grams.

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Re: Tech Question...Forward Swept Wings
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« Reply #6 on: October 22, 2010, 09:52:21 PM »
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Wayne,

Forward swept wings (FSW) are a killer on the structural strength of the wing and that's why they are so rare. They are superior in performance compared to the conventional straight or swept back wing. In FSW great stress comes on the wing tips and consequently on the whole wing causing breakaway/structural failure. However, having FSW does not mean you require canards. In fact the inflow of air towards the center of the wings in FSW (which is the main reason for their superiority over conventional wings) also has no reason to have canards. Canards are great for greater maneuverability and in modern fighter aircraft have the additional advantage of having another lift producing surface compared to the conventional tailplane which produces a downward force to balance the four forces i.e lift vs weight and thrust vs drag. Of course most modern aircraft having canards and FSW are 'unbalanced' i.e continue to pitch up as alpha (angle of attack) increases and the lift vector shifts behind the C of G and consequently require a Fly By Wire (FBW) with computers keeping the aircraft stable.

This is not true for model aircraft which are stable i.e lift vector is kept ahead of the C of G.

Regards
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« Reply #7 on: October 22, 2010, 10:58:41 PM »
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Verma ,

Very educational and technical post that even I can understand. Many of the model aircraft we build are from designs of FBW type aircraft if you will, and we need to determine a flyable C of G either by experiment or trial and error and in some cases if we are not quick enough or have the area to do it in, leads to disaster. Glide tests, dropping on a mattress etc, can get you close, to a balance point but does not mean that will be a flyable C of G. I think I would pass on building a FSW design 44" long with say a 36" weighing in at a couple of pounds. On the small/lighter side of the scale, it could be fun to experiment with and get into that next level of flying skill like some have already done and enjoy flying, but I don't think it would become my favorite plane or everyday flyer.

Thank you for this great reply...Wayne

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« Reply #8 on: December 12, 2010, 02:34:48 PM »
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Lift vector Behind CG, I thought was stable and conventional. Relaxed static stability means CP moving ahead and close to cg and sometimes moving ahead of it. unstable is is when CP is ahead of CG. that's how Lift weight couple is nose down and thrust drag is nose up couple.

Verma...Kermode is a better place to start.
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« Reply #9 on: December 12, 2010, 03:24:48 PM »
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This is not true for model aircraft which are stable i.e lift vector is kept ahead of the C of G.

Think of  it this way, at stall when the lift reduces, verma's model will continue to pitch up because weight vector is behind lift vector.

Listen to what the Old Timer "bogey" says, (and all over nasa of course).

http://forums.x-plane.org/index.php?showtopic=46015
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« Reply #10 on: December 13, 2010, 09:49:16 AM »
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Thanks for correcting me Augustine. It is as you said lift vector should be behind C of G for an aircraft to be stable.
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