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Author Topic: Delimna! Wing design..........  (Read 1804 times)

Offline Bill Little

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Delimna! Wing design..........
« on: August 10, 2010, 03:05:59 AM »
OK, gotta start planning a plane that I have wanted to build since 1963.  No one that i know has done one yet, but that doesn't matter! LOL!!

It is the Cosmic Wind Little Tony.  This will be in the 600sq.in size category, but I am guess and thining right now.

The Dilemma (if it is one):  The LE will be straight, the TE will be swept forward.  I am not concerned about making the flaps work, but I am concerned about this type of lay out.  What concerns should I have regarding straight LE and swept forward TE, since it is basically the opposite of standard practice?

I have built planes with a swept forward TE, but they also have swept back LE.

Thanks, all!
Big Bear
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Offline Bill Little

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Re: Delimna! Wing design..........
« Reply #1 on: August 10, 2010, 02:14:24 PM »
Quote from: Ty Marcucci on August 10, 2010, 10:23:49 AM
I can't believe you of all people are asking this. LL~ Use a Jig.  With your building skills, not a problem. H^^ But with that wing planform, use a thick airfoil. H^^

Hi Ty,

LOL!!  Thanks, but it isn't the construction, it is concerns over any quirks a "design" like that might present in the air. 

Maybe it's a "non issue", but I have never flown a large plane with that set up.  I really liked my old CG Little Toni, but it was flapless, of course.  Just wondering if the lay out would present any issues on a larger airplane in maneuvers.

Thanks!
Bill
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Offline Randy Powell

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Re: Delimna! Wing design..........
« Reply #2 on: August 10, 2010, 02:34:41 PM »
Bill,

Not sure the straight LE will give you many problems (though you will have some CG issues, but those can be adjusted). With a swept forward TE, you do get into problems with induced yaw that will have to be overcome. Last plane I built like this required a much larger rudder and fin than I had originally planed and ultimately a Rabe type wiggly rudder to keep the yaw issues under control. But for all that, once I got it all worked out, it was a really good flying plane.
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Offline John Miller

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Re: Delimna! Wing design..........
« Reply #3 on: August 10, 2010, 02:37:14 PM »
Bill, depending on the scale wing plan, you may find a compromise available. For intstance, the Pathfinder wing is in the ball park as for the size you desire. You can vary the sweep on the trailing edge to approximate the sweep on the scale plane.

It may not be exact, but many semi-scale stunt designs have a bit of fudging going when it comes to wing plan. Many WW2 fighters had relativly high aspect ratios compared to what we generally use in our stunters. As long as you can fool the eye with what appears to be a close copy, you should be fine.

Good luck with your project.  H^^
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Offline Howard Rush

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Re: Delimna! Wing design..........
« Reply #4 on: August 10, 2010, 06:55:42 PM »
I don't know about "induced yaw", but I think Randy's right.  See NACA Report 1098, http://naca.central.cranfield.ac.uk/reports/1952/naca-report-1098.pdf .  Yawing moment due to sideslip is sorta proportional to lift coefficient.  This makes for an instabiliity in tight maneuvers.  I've used a big vertical stabilizer to stabilize this tendency on swept-forward-wing combat planes.  That might work for a stunter, too, if the flaps don't contribute additional perversions.  If you can fix the yaw problem, the airplane should be less sensitive to wind than conventional stunters. 
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Offline Randy Powell

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Re: Delimna! Wing design..........
« Reply #5 on: August 11, 2010, 10:03:29 AM »
Howard,

Picky, pick. Whatever, it creates yaw that has to be dealt with in some way. Greater side area aft of the CG can help to dampen it some.
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Offline Kim Mortimore

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Re: Delimna! Wing design..........
« Reply #6 on: August 11, 2010, 06:22:42 PM »
Bill,
Very cool plane.  With a scale paint job she'll be a looker!   y1  
What do you have in mind for performance vs. realistic scale appearance?  

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Offline John Sunderland

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Re: Delimna! Wing design..........
« Reply #7 on: August 11, 2010, 06:59:09 PM »
I dunno, I cant speak with the same expertise some of these guys can but if you consider what issues say a Twister, Banshee or several other flapped wings with straight LE have going for them vs what the dont...we know how to fix these issues to an extent. However a swept TE has the issues Randy notes here. In this case I would go for simplicity. Wiggly rudders and or big ones seem to be a pain with more problem than gain.

Seems like a trade off on where CG is located or can be located. You will want a more forward CG with straight LE in my guestimation. A big honkin 4 stroke sounds like the ticket for such a venture, modest flaps and stiff stiff stiff surfaces.
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Offline Bill Little

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Re: Delimna! Wing design..........
« Reply #8 on: August 11, 2010, 08:45:07 PM »
Quote from: Kim Mortimore on August 11, 2010, 06:22:42 PM
Bill,
Very cool plane.  With a scale paint job she'll be a looker!   y1  
What do you have in mind for performance vs. realistic scale appearance?  

Hi Kim,

I want to do things along the lines of Ron Burn and Al Rabe.  Keep the outline as close to scale as possible while still retaining top performance.  Ron has really helped me on a project I am doing now, and the Little Tony would be a second build.  Dihedral will be necessary, for sure.  My present project is based off a set of R/C scale plans, but modified for CLPA.  Not much changed to any great degree.

Keith Trostle has also loaned me a set of plans for a Semi Scale plane he had that is VERY similar to the Little Tony.  It has proven to be a great help.

The paint scheme will be 100% Cosmic Wind/Little Tony #3.  ;D  y1

Thanks for asking!
Bill
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Offline Bill Little

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Re: Delimna! Wing design..........
« Reply #9 on: August 11, 2010, 08:47:53 PM »
Quote from: John Sunderland on August 11, 2010, 06:59:09 PM
I dunno, I cant speak with the same expertise some of these guys can but if you consider what issues say a Twister, Banshee or several other flapped wings with straight LE have going for them vs what the dont...we know how to fix these issues to an extent. However a swept TE has the issues Randy notes here. In this case I would go for simplicity. Wiggly rudders and or big ones seem to be a pain with more problem than gain.

Seems like a trade off on where CG is located or can be located. You will want a more forward CG with straight LE in my guestimation. A big honkin 4 stroke sounds like the ticket for such a venture, modest flaps and stiff stiff stiff surfaces.

Hi John,

As tempting as it sounds, I do not have a 4 stroke.  Nor the money right now to get one! LL~  So I will have to make do with what I have. ;D

I think it is worth the chance to see what happens.  I think it will be possible to trim it out, even if it takes a while.

Bill
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Offline EddyR

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Re: Delimna! Wing design..........
« Reply #10 on: August 29, 2010, 08:03:50 AM »
Bill  Having built several Juno's that have the TE swept forward I have found that there is no problem if all the angles are equal. Everything must be right on. Also the plane needs to be set up with no motor or rudder offset. What I am saying is the plane needs to be fyling straight not canted to the outside of the circle. My last Juno,the red one I sold at Brodak had more than stock sweep in the trailing edge so I could get a very thin rib at the tip. The flaps are large on the Juno so it is also important to use a lot less flap movement that elevator. The one I am building now will have a .51 in it. That is a lot for a plane that is only 610 sq". Many people have had problems with planes that have the  trailing edge swept forward.I believe alignment is the reason.All of mine have been I/beams as that is the only way I have been able to keep alignment perfect. If you have a lot more sweep than the Juno then you had better make everthing adjustable. Having two horns on the flaps with adjustable linkage would help.
Ed
Went back in to my old computer to get this picture of the Red Juno. As you can see it has a lot off trailing edge sweep
Ed
« Last Edit: August 29, 2010, 12:45:49 PM by Ed Ruane »
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Offline Chris Wilson

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Re: Delimna! Wing design..........
« Reply #11 on: August 29, 2010, 07:22:21 PM »
I always thought that using a double taper on a wing brought the center of lift more towards the middle of the model or 'under its armpits' and thus made the model more stable and efficient, but suffered in return that slight yaw problem.

But what problem are you going to get here, the TE hinge line angle is not that great but if you want to get all scientific about making things equal in order to minimise any slight errors that may creep in then how would one ever make an inboard wing fly the exact same as an outboard one in all conditions? I doubt that you could, so just accept one benefit for one liability and trim it the best you can.
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