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Wing Stagger on a Biplane

Old 11-28-2009, 11:12 PM
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hillbillynamedpossum
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Default Wing Stagger on a Biplane

Im playing around with some FFF and already built and crashed a 24" biplane....it was a lot of fun. I know this is a silly question, but why are the wings staggered on a biplane. It seems like every bipe Ive ever seen had the upper wing about 1/3 to 1/2 the width of the chord forward. Was this just so the pilot had better visibility? Is there some aerodynamic benifit to this?

Just Curious...
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Old 11-28-2009, 11:42 PM
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gramps2361
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That is a good question possum I don't have the answer, but I am looking forward to the replies. Just looked it up it is for aerodynamics here is a link.
http://wiki.answers.com/Q/Offset_arr..._biplane_wings
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Old 11-28-2009, 11:48 PM
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Posumm here is another site that gives some more in depth info.
http://findarticles.com/p/articles/m...n8799373/pg_2/
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Old 11-29-2009, 01:38 AM
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Wow Gramps thanks...That second article was very imformative. I think the bipe I build tomorrow will be ortho....whatever....no stagger. Im thinking small sponsons or wire skids and no landing gear. I had a few troubles with bending my gear so....to heck with landing gear, leave em off. I might save a half ounce in the process.

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Old 11-29-2009, 01:52 AM
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Ya I never knew why myself till you asked just took it for granted that's how it's suppose to be. Glad to be of help hope your next one works out.
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Old 11-29-2009, 02:19 AM
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Yeah, I might do a build thread If this one turns out ok

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Old 11-29-2009, 02:33 AM
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Hope you do a thread ya seem to be building quite a bit. I have 2 bipe's now a hobbylobby waco and a balsa arf tiger moth. I love flying these 2. Went to a auction last weekend and got a sig minibipe 25.oo bucks I am going to start this plane sun a gas to electric build unless the weather changes then I will be flying. Fell in love with the biplane they look great in the air and on the ground.
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Old 02-22-2010, 06:46 PM
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The second linked thread were good but the real reason why biplanes have stagger was somewhat lost in the text. The WikiAnswers page is plain wrong (now corrected).

They have stagger so the pilot can get in and out of the cockpit and/or so his field of vision is kept as clear as possible.

If you imagine a typical WWI biplane with no stagger then the top wing would move back until it was above the cockpit opening and the pilot would be unable to get in. Even if he was a gymnast and so could squeeze in he would be unable to see upward. You can't simply move the cockpit back to fix the problem because that would result in the plane being tail heavy.

For an RC model this is not an issue so you dont need any stagger, unless you think it looks cool

Steve

Last edited by JetPlaneFlyer; 02-22-2010 at 07:25 PM.
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Old 02-22-2010, 10:59 PM
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The major exception to the upper wing being forward is the Staggerwing Beech, or D-17. In the Staggerwing, the lower wing was forward so the landing gear would have an easy place to retract. Of course it was a cabin biplane, so entry was made via a door.
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Old 02-23-2010, 06:25 AM
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Rabitcreekok,

My understanding was that the Beech 17 had reverse stagger mainly for the exact same reason that 'top entry' cockpit biplanes have positive stagger.. i.e. field of vision. If the top wing was level with, or forward of the lower wing then the pilot would have had no upward line of sight.

The lower wing being forward did then provide somewhere to mount the landing gear but i doubt that was the main reason for selecting reverse stagger.

Steve
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Old 02-23-2010, 03:59 PM
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Originally Posted by JetPlaneFlyer View Post
Rabitcreekok,

My understanding was that the Beech 17 had reverse stagger mainly for the exact same reason that 'top entry' cockpit biplanes have positive stagger.. i.e. field of vision. If the top wing was level with, or forward of the lower wing then the pilot would have had no upward line of sight.

The lower wing being forward did then provide somewhere to mount the landing gear but i doubt that was the main reason for selecting reverse stagger.

Steve
I must confess, Steve, that the visibility factor seems to be the stated reason for the negative stagger, according to all the information I could find.

However, in my 50+ years of exposure to general aviation, I had always heard that the landing gear was the reason for the change.

In fact my Dad did a total restoration on a basket case Staggerwing for my brother, including a total rebuild of the wood in the cabin and he told me the landing gear was the reason for the negative stagger. I really did not make it up. I actually still have the old framework from the cabin, stored up above in my hangar.

Oh well, I an never too old to learn that I am wrong.

Thanks, Steve.
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Old 02-23-2010, 06:06 PM
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Maybe your old man was right and the online stuff (and me) wrong?.. More likely though that both landing gear and visibility was a factor. It's arguable which was the greater influence on the designer, i dont suppose anyone can be 100% sure what was in his mind when he layed it out.

Steve
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Old 02-24-2010, 01:47 PM
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To my understanding, with one wing on top of the other, the low pressure area on top of the lower wing is negated by the high pressure on the bottom of the upper wing. Moving the upper wing forward gets that area ahead of that low pressure area of the bottom wing, increasing the lift. Distance apart makes a big difference too.
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Old 02-24-2010, 05:14 PM
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Originally Posted by flypaper 2 View Post
To my understanding, with one wing on top of the other, the low pressure area on top of the lower wing is negated by the high pressure on the bottom of the upper wing. Moving the upper wing forward gets that area ahead of that low pressure area of the bottom wing, increasing the lift. Distance apart makes a big difference too.
Thats not the reason, or at least it's not that simple. The lowest pressure area on a fifting airfoil is actually on the top over the first third of the airfoil chord (see attached plot). The rear top part of the airfoil is usually at close to 'normal; atmospheric pressure.
If your understanding was reality then the last thing you would want to do is move the top wing forward, right over the lowest pressure area of the bottom wing. Reverse stagger where the top wing is set back would be the norm.

Wings do interfere with each other in that the flow circulations fields interact with one another, so yes large seperation is desirable, but stagger really makes little difference to this unless the stagger was so extreme that you would end up with a tandem wing layout.. even then the flow fields still interfere.

Steve
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Old 02-25-2010, 12:05 PM
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I thought turbulance might be a factor, between the wings and the horizontal tailplane.
I think I've read something about the top wing been forward in aerobatic aircraft for better performance in a loop.
I don't know how many WW1 aircraft were capable of doing a loop but I think that it's a debted topic to perform a loop or immelman turn in WW1 aerial combat.
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Old 03-21-2010, 02:00 AM
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There is another reason for stagger - the slot effect.
As a biplane with conventional stagger approaches the stall the top wing tends to influence the airflow over the lower one with the result the top wing will actually stall first. This means a more gentle "partial" stall and thus a reduced risk of entering a spin. An important characteristic as spin recovery was by no means certain for many WW1 types.
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