Sig 4 star 40 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 06-02-2010, 11:59 PM   #1
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Sig 4 star 40

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Getting ready to cover a 4 star 40, but I feel the wing is a little flimsy. Just wondering if it would be worth putting 1/32 or 1/16 balsa across the whole leading edge span for strenghth and to keep wing straight. Any input would be great. Has anyone done this and if so how did it effect the plane if any.

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Old 06-03-2010, 02:41 AM   #2
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Re: Sig 4 star 40

I did it on a 4*60 only for appearance. It complicated the wing root area. I don't think the 4*'s need it for strength. I've seen lots flying with the ribs showing under plastic on the LE.
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Old 06-03-2010, 05:31 AM   #3
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Re: Sig 4 star 40

The covering will add a lot of stiffness to the wing so I wouldn't worry about it.
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Old 06-03-2010, 08:02 AM   #4
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Re: Sig 4 star 40

While it's not required, a real benefit would be that your airfoil between the ribs ahead of the main spar would be true. As it is, the covering sags so the wing is thinner there.

After you've build the wing is not a great to time to make the mod. You'll now have sheeting which is higher than the tops of the ribs behind the spar. To fix that problem, you would have had to either lower the tops of the ribs in front of the spar or add cap strips to the ribs and a trailing edge cap to maintain the proper, identical height for the covering overall. Otherwise, there will be a step where the LE sheeting ends.

It's easy to change before you build the wing by simply cutting down the ribs ahead of the main spar and increasing the depth of the leading edge cut outs by an amount equal to the thickness of your sheeting. Then you won't even need to add any cap strips and your overall wing dinesions will be identical to what they would have been had you not made the change.

Perhaps an easier solution at this stage would be to add a false rib midway between every two existing ribs. These would only go from the leading edge to the main spar. That will certainly strengthen your wing and provide less sag in the covering with negligible weight gain. You could add two, equally spaced, in each rib bay to increase the effect.

If you look at a lot of WWI biplane wing designs, you'll see the false rib technique used. A perfect example is the Sopwith Pup. BUSA does that on their 1/3 size model of it as well.

In any case, the easiest thing is to just leave it alone. You'll find the wing plenty strong enough and no adverse aerodynamic effects as designed. Those planes work great just the way they are. Mods will satisfy your inner purist and help to distinguish your 4*40 from everyone else's bird.
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Old 06-03-2010, 09:39 AM   #5
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Re: Sig 4 star 40

Kinda depends on what you're covering it with. Good quality covering like Ultracote would give it plenty of strength. With lighter material like Monokote it might be worth beefing up the structure...I don't find you can get it as tight. Not sure about dope, no experience there. Good luck.
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Old 06-03-2010, 09:47 AM   #6
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Re: Sig 4 star 40

I built my 4*40 a number of years ago as per the kit plans, It has taken it's share of bumps and has stood up well. I don't think there is a strength problem with the 4*40 wing. I used Monocote to cover it.
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Old 06-03-2010, 09:51 AM   #7
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Re: Sig 4 star 40

I've built a 4*60 and covered it with sig aerocote no mods to the wing and no structural problems after 2 seasons.
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Old 06-03-2010, 11:15 AM   #8
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Re: Sig 4 star 40

I have an old mid star 40. I assume it is pretty much the same wing. Put that one thru heck and back, and stood up very well.Covered with ultracoat, and no problems with the wing or how it flies.
happy flying
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Old 06-03-2010, 12:35 PM   #9
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Re: Sig 4 star 40

I like the sagging cover effect on my 4*40 wings and the wings are stiff enough after the application of the iron on covering.

The 4*40 was designed as a 40 size plane and it flies happily w/ the OS40FP.
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Old 06-04-2010, 08:38 AM   #10
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Re: Sig 4 star 40

I had a 4 star 40 some years back, built it as per the plans never had any issues with the wing, covered it with monocote I believe . Flew it with an OS .40 SF with a tuned pipe, was a nice flying plane. I happened to stall it while coming in for a landing one time and pretty much did it in.
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