Wing sweep for a dihederal effect.

[Butch777]

I've read that wing sweep adds a dihederal effect and seems to work good on flying wings.
Does the sweep need to be trailing edge as well as leading edge to get this effect??
Does a delta wing have a dihederal effect because of the leading edge sweep?
I'm working on a light weight, EPP pusher, twin boom type and don't want too put a long nose on it, or heavy batt in it, to get the C/G right. I want to use it for training on windy days, so I think a bit of sweep will help me with the C/G and make it a bit more stable, but I want to keep it a slow flyer as well.
Any thoughts?? Thanks, Butch

[raptor22]

Sweep will add dihedral, but its alot lower drag to just add dihedral in the first place. It works well on wings, because they can have the tendency to dutch-roll if you add too much dihedral. The other nice thing is that it works upside down as well.

The important thing is that the 25% chord part is swept. However, you need alot of sweep to get much effect, so unless you have a low AR delta, you probably are going to need some TE sweep as well.

--Alex

[Sparky Paul]

For your plane, sweep will help put the c.g. aft of where it would be on a straight wing, as you surmised.
For slow flight, a light weight plane is better than playing with the aerodynamics.

[lowdive]

maybe pick up a stryker fuse for $20 and cut it down to the shape you want... you can add your booms to it, too. the stryker design by itself is great in heavy winds.

[Butch777]

Thanks Guys,
I built a EPP windy day flyer that seems to do real well. I call it a slo-cat. I took a Slofly wing and reduced the sweep a bit, added a tail boom and a half fuselage. At 6ozs flying, with a 12oz thrust CustomCDR single, I fly it in front of my house in over 10mph gusty winds. With large ailerons, that have lots of differential and a good power system, Its very responsive. It will climb stright up, loop in 6ft and turn in 8ft. It can be caught by hand real easy. Of course I've bounced it off all the trees, light poles and cars around.
So what I'm trying to do in a trainer is to incorperate the basic slo-cat design, but cheaper and a little more floatie. Using a GWS IPS motor, less sweep and a bit more wing area is the way I thought to go. What do you think?? Butch

[Sparky Paul]

About all that would need is a thicker airfoil to fly slower.
Everything else looks OK.

[fhhuber506771]

Looks and sounds like a winner already. (going to post plans? :D )

For a trainer version, you'll want the controls less responsive, but thats just changing the linkages for less throw. (or dialing in expo on a computer radio)

Longer booms and a bit more wingspan would be another way to go. More wing area and a higher aspect ratio allows slower speed (more efficient and lower wing loading) The wings could be clipped to match your current design when the student gained ability to handle a faster roll rate. ;)

There's several directions you could go in making that into a sporty looking trainer...

[BMatthews]

Wing sweep is a poor substitute for dihedral. I read somewhere that it requires something like 30 degrees of sweep to get the same restoring effect as only 5 degrees of dihedral.

You see, with dihedral the yawing results in a shift in the angles of attack for the wings on either side with the leading wing going more positive and the trailing wing going less positive than in non yawing flight. With the flat but swept wing you're relying on the apparent span shifting as seen from the front with the leading wing appearing to be longer and the trailing wing appearing to be shorter. The span and area shift is no where near as effective at shifting the lift as the angle of attack shift is and that's why it's far better to use dihedral.

[Sparky Paul]

The rule of thumb for sweep is 15 degrees equals about 1 degree of dihedral.
The sweep on the model illustrated could be augmented by a degree or two of dihedral for extra stability, but looking only at stability and ignoring handling results in a plane which can't turn.
A light airframe, a thick wing, and the sweep with added dihedral should do what he wants, without resulting in a goofy looking plane.
If it looks goofy, it will fly goofy. :)