Pitch sensitivity in flat-plate airfoils.

[Butch777]

I'm always trying to make a slowflying, outdoor, maneuverable, EPP pusher, for flying in small areas and in some wind.
I came up with a modified Flying Wing I call a Boomer, useing the EPP WildWings wing cores and some others.
The airfoil is simi-sym, about 2/3s above the cord line.
The 31", 7oz WW Boomer will float for 40ft with a good toss and will fly in front of the house in the street, with trees, cars and poles and survive.
It flys very well and many people fly them now and are happy with them.

I tried to build a smaller version, to go slower and fly in tighter spots.
I built a 18", 2.5oz, using a LPS motor and a Combat Pocket Wing for the wing core. Even at 2.5ozs, it was fast and flew good in 10mph winds, but wouldn't slow down enough.

So I built a 18", 2.4oz, flat-plate, wide cord airfoil, using 10mm EPP sheet and sanding a ClarkYish airfoil into it. I used a 5g outrunner on it. It flys ok in calm weather, but is real pitch sensitive the wind.

I'm thinking, that because the cord is so wide, it amplifys the pitch sensitivity. So I think I need a thicker airfoil, maybe a built-up, using EPP sheet. Would a ClarkY-ish be ok or should I try more of a semi-sym, like the WildWing has??

Like I said, the goal is a EPP pusher, small slowflyer, that will do well on windy days.
Any help would be appreciated, thanks, Butch

[BMatthews]

On its own the chord doesn't mean a thing. But when you combine a rather wide chord with an extremely short tail moment arm and a very modest tail size you have a good recipe for pitch problems. It's the overall model design that is at "fault" and has nothing at all to do with JUST the wide chord. What the wide chord does is make the rest of the factors inadequite to deal with the issues.

You can limit the issues by adding a bit of reflex to the ailerons to make it act more like a plank style flying wing and by running with a rather forward CG placement at around 25 to 28% at most back. Do that and it'll perk right up and fly right.

[HugePanic]

did you try a KF-profile-wing???
(search for Kline vogleman here at the forum)

lots and lots of people build they foamies with that airfoil....

[bwalt822]

moving the cg forward reduces pitch sensitivity. You just have to be sure to have enough tail incidence or reflex the ailerons to overcome the subsequent pitch down moment.

Or you could increase tail area and or tail moment arm

[JetPlaneFlyer]

It will always be very difficult to make a model that can fly very slow AND cope well with wind/turbulence. To fly slowly the main requirement is very light wing loading... Unfortunately light wing loading also results in a model that will be effected badly by any gusts and turbulence.

Steve