fxstbi

My Feedback: (3)

A friend of mine is going to scratch build a flat, no airfoil 3D plane using the same design concepts that is used in the small electrics that are so popular today. It will be .100 sized and have about a 55" W/S. Anyone try this in the past and how did it fly? Thanks

longdan

.1 sized with a 55" wingspan for 3D? You don't mean 1.00 size?

fxstbi

My Feedback: (3)

Woops,your right, it would have a Saito 1.00 on it.

Tall Paul

I would expect the 3D capability to be quite limited as the wing will be very inefficient.
The electrics get by with unusually light weight and lots of power.
Your larger plane will be heavier due to the needed stiffness.
An airfoiled wing would be a better choice.

BMatthews

Actually I would expect the 3D ability to be up there. Paul, isn't a lot of the 3D trick range based on being able to push the wing to a stalled condition and then perform post stalled maneuvers?

It will need to be kept very light though. That is the one saving grace on the flat foamies is the lack of overall weight to wing area. It lets the model fly well even when not operating in a post stalled condition.

The big trick will be defining how thick this "flat wing" needs to be for strength and stiffness. It may be well worth using rigging wires off the top and bottom of the presumabley very deep fuselage to support the flat wing. Look at the full scale Eindecker for what I'm talking about.

fxstbi

My Feedback: (3)

Thanks for the info guys. I've seen his plans and the wing will be about 5/8" thick, foam core and sheeted balsa. As it develops I'll post some pictures. Thanks

Yuu

So... what are the section modulus and bending moments associated with that wing? Those flat sheet little foamies are very light, and the moments are low.... so the section can be low too. The Saito 1.00 is pretty heavy, being a four stroker. But then, I've seen a guy stand on a Skat-Cat foam wing sheeted with balsa, and supported on chairs about four feet apart.....

fxstbi

My Feedback: (3)

Section modulus on a foam wing, must be an engineer. (Both of us are engineers too by the way) I know he's not doing any true engineering work trying to design an internal structure to take the loads but we both have allot of experence with model design and are depending on that aspect to work out the details. I know he is using the 1/2" thick blue Dow brand foam and will be using imbedded carbon rods on both sides then sheeting with balsa, that should take care of the bending loads. There will also be an "X" bracing of rods to take the torsion loads. I think the main concern is how the plane will fly in a larger scale with a flat wing. Right now the all up weight looks like it will be slightly over 5 pounds.

Tall Paul

I think the weight will kill you.
My larger foam planes have been poor performers with slab wings.
You're getting out of the "bumble-bees can't fly but they do" Reynolds number range.
The 3D foamies like my eFlite Tribute get a lot of their performance from the prop blast, the props being outsized relative to what you'd use with a glow motor of the same performance.
You won't have that same benefit from whatever you use on the Saito.

BMatthews

Just a thought but I suspect that if the wing spars were done right that you would not require the balsa sheeting and the glue that goes with it. Instead to get a skin you can work with you could look at water based polyurethane and newsprint paper for a sort of paper mache skin. Some testing to determine weights would be needed but the point is that there are options.

dreadnaut

My Feedback: (5)

My thought too. If you are only interested in hanging off the prop, the airfoil is not that important, but structural issues will dictate a built up wing, or some kind of bracing.