Curved plate sections

[Tom Harper]

Recently I've been able to construct very strong wing panels using 3/16" closed cell foam bonded to 6 ply poster board. The section is a parabolic camber line of 7% (I've used 5-10%). The curvature makes the wing very rigid. 3/16" spruce spars are embedded to 30% of the span.

Curved plate sections are common on indoor models ie McBride B7, but this is a 7 sq ft Norvel .40, very much outdoor model.

The advantage of the curved plate is light weight and ease of construction. I could add a flat plate to the bottom of the curved plate, but I would have to double the curvature to 14% to get the same camber line.

I'm interested in your thoughts. Is there any magic to an enclosed envelope? Is a thin curved plate superior? Are there any published polars?

[nmasters]

Here's the only data I have on a cambered plate. Actually though since the pitching moment is entirely a function of the mean line you can just find an airfoil you like and use its mean line for your cambered plate. Have you tried aluminum tape for spar caps? I haven't tried it on a wing but I have used it to stiffen other things where I don't want to have a noticeable bump or change the thickness. It puts a lot of strength right at the surface and is a lot less fuss than mixing epoxy for carbon.

--Norm

[pmackenzie]

Thickness is good for both bending strength and even more for torsional stiffness.
There is also some correlation between thickness and max Cl.

http://adamone.rchomepage.com/foil_sim.htm


Pat MacKenzie

[Tom Harper]

Norm & Pat,

I agree. I've used the camber line characteristics for AOA and lift. I am curious what the drag implications are. I assume the curved plate is low drag.

[Tom Harper]

Norm,

Aluminum tape - haven't seen it. Sounds good.

This is a no epoxy, carbon rod or CA project. Strictly foam, paper, carpenter glue and packing tape.

[MarkusN]

I agree. I've used the camber line characteristics for AOA and lift. I am curious what the drag implications are. I assume the curved plate is low drag.
A curved plate is low drag, but only for a very narrow range of AOA / design CL. You can easily imagine how the entry angle of the airflow is ideal only for one AOA. The rounded nose of a thick wing is much more forgiving in that aspect.

The advantage of a thick wing besides allowing room for rigid stuctures is in the wider range of CL it can fly effectively. This is only true if Re is large enough for supercritical airflow, though (supercritical concerning laminar separation, not mach number.)

That is where thin wing section such as the curved plate have their forte: very low Re.

[Tom Harper]

Markus,

Thanks for the comments.

The curved plate is a bit cheaper, lighter and easier to build. I'll see how it works out in flight.

[lincoln]

One nice characteristic of a curved plate will be that you won't speed up as much in a dive. As soon as you exceed a certain speed, the drag will go way up. OF course, a lot of pilots WANT to get that speed.

3 1/2% is still a pretty large amount of camber.

Your model may fly like a Pico Stick, which has a similar airfoil.

[Tom Harper]

Lincoln - diving is not an issue with this model. It's strictly AP. Hand launch, level flight, traumatic landing in the rough.

Almost ready to go though, we'll see how it flies.

Tom