3D biplane wing angles?

[hardlock]

To keep this question simple, Let's say we have a center-line thrust and hor.stab with equal area and no stagger wings w/ symetrical sections.

Basically exactly the same upright or inverted. Now, since this is to be a small area 3D plane, I WANT plenty of drag to keep the speed down.

Normally the wings would be rigged parallel but what if one was to add either toe-in or toe-out so-to-speak to the relative wing angles? Either would certainly add plenty of drag, but which would be better? Toe-in (for wheels) adds tracking stability but for two wings on a 3D plane stability isn't wanted. Toe-out seems logical to me as with some A of A on the top wing if it stalled before the bottom it would want to lower the nose. But again that's adding stability..... :confused:

Any ideas or practical experience on this is greatly needed. Thanks!

[Sparky Paul]

Toe-in/out refers to a lateral displacement in the horizontal plane, not a horizontal displacement in the vertical plane.
The proper term would be incidence.
Having duelling incidences between the upper and bottom wings will result in a lot of drag.. if not bizarre performance, stalling at strange times..

[hardlock]

Any pref. as to positive or negative incidence to each other if I try it?

[Sparky Paul]

Positive incidence will have that wing stall sooner than the reference wing, negative incidence it will stall after..
The plane's response will be different in either case.
You have two wings, upper and lower, with 3 incidence settings (more, the same less)for each to be used in combination.
That's 12 combinations.
What will happen with any of these can't really be predicted.

[Rodney]

Speaking only from practical experience (7 Aeromasters, 2 large Lazy Aces, 1 small Lazy Ace, 2 Phaeton 40's, one Phaeton 90, two Tiger Moths plus a couple others) all flew best with the upper wing at about 1.5 degrees less incidence than the lower and all required some right thrust and some downthrust to fly nicely yet give the manueverability desired for most Radio Controlled flight. Now, all of these have positive stagger, different stagger may effect the results but I've never investigated that.

[Bill Mixon]

To keep this question simple, Let's say we have a center-line thrust and hor.stab with equal area and no stagger wings w/ symetrical sections.

Basically exactly the same upright or inverted. Now, since this is to be a small area 3D plane, I WANT plenty of drag to keep the speed down.

Normally the wings would be rigged parallel but what if one was to add either toe-in or toe-out so-to-speak to the relative wing angles? Either would certainly add plenty of drag, but which would be better? Toe-in (for wheels) adds tracking stability but for two wings on a 3D plane stability isn't wanted. Toe-out seems logical to me as with some A of A on the top wing if it stalled before the bottom it would want to lower the nose. But again that's adding stability..... :confused:

Any ideas or practical experience on this is greatly needed. Thanks!

I have experimented with these configurations on the design in the picture below. I was actually doing it to see what the difference in stability would be, rather than increasing drag.
I tried it with the top wing at +2, bottom at -2 and also top -2, bottom +2. It seemed to fly "differently", but it I could not see any benefit either way, so I went back and set everything at 0. Being this was done on a small plane with flat foam wings it may not be very useful info.
If you want drag add more flying wires and prop for it. :)

[hardlock]

Thanks Bill - Mine is to be a flat plate wing also so besides the drag consideration, I was hoping that changing the incidence of the wings might help the positive/negative pitching transition jerk that these types of wing are known for. I'm going for an ultralight yard version so adding the weight of fat section wings is out of the question. My guess is that a flat plate bi-wing is better in the pitch moment dept. than a mono wing anyway. :)

I used to fly a tail-less bi-wing ultralight (Easy Riser) that had the upper wing at a higher incidence than the lower but was considerably forward (positive stagger?) and it was rigged that way for stability allowing the upper/forward wing to stall first and lower the nose. Similar to the canard concept. Worked great BTW, very stable. Used weight shift for pitch control however. :(

[Bill Mixon]

I was hoping that changing the incidence of the wings might help the positive/negative pitching transition jerk that these types of wing are known for.( Thats what I was trying to do. My thinking was that if both wings were "plowing" through the air at opposing incidences it would smooth out the transition from possitive to negative flight load. I couldn't really tell any difference, that annoying pitch transition issue was still there at higher speeds.

[hardlock]

I just set mine with zero incidence to start. Got it flying pretty well but am experiencing bad adverse yaw with roll.

Are biplanes worse for this than monowings or is it my wingerons that are causing it? I can't imagine 3D foamy bipes dealing with this and still doing what they do so well.

If I add "aileron" differential then it's twice as bad when inverted. If I add a rudder mix then it messes with the rudder balanceing act when doing high alpha manuvers.

Either I'm missing something or this is why wingerons aren't used more?

Here's the planes details, pics and clips if interested:

http://www.rcgroups.com/forums/showthread.php?t=392354

[Ollie]

3D is best for flying slowly. 3D flys on lots of thrust. 3D wants low weight. Streamline 3D is not importment for flying. Lots of thrust over comes weight and drag. The 3D wants lots of control. Any crud airfoil for wing will do for 3D.

[hardlock]

Roger that Ollie - but about adverse yaw?

[Ollie]

You can correct adverse yaw with piloting skill. When the ailerons give adverse yaw correct it with the rudder. That is part of flying the 3D plane well by using piloting skill.

[Ollie]

The main purpose of an 3D plane is aerobatic not a trainer. That means the plane is best set up at almost zero stability! You can't have the cake and eat it too. You have to give up lots of stability to fly a 3D plane well with piloting skill.

[hardlock]

I understand the zero stability aspect of 3D. I have a conventional 3D mono-wing model that flies as expected. Axial rolls are more or less axial with very little rudder needed.

The wingeron bipe however requires almost full rudder IN the direction of the roll to remain axial. Just want to figure out why it does this.

[Ollie]

The induced drag of a wing increses with the square of Cl or square of AoA.

When the roll of the wing, one side reduces drag as the square of the AoA but the other side increses as the square of the AoA. For the extreme changes of the drag of one side compared to the other side. Cdi = (Cl^2)/(AR x pi), AoA is ~ Cl.

Increase the vert. tail area or the length of the tail moment. That will increase the control power with the rudder. It will also, reduce yaw in the knife edge.

[hardlock]

Thanks Ollie, that makes sense. Seems a little short anyway for it's span.