flyingagin

Will it turn like a normal three channel plane?
I scratch built this wing about 15 years ago and just dug it out again. It was built for an wieght caring contest. The wing is finnished other than some covering trim work. But I never finnished the oroginal plane, Due to moves etc. So the wing is all that is left
When I built this wing I discussed it with other club members, and the one big question we came up with was " would it turn correctly?" It is for a three channel plane, rudder,elevator, throttle.
Specs
polyhedral
The span is 54" STRAIGHT ACROSS TIP TO TIP
The root chord is 8"
The tip chord is 10"
The tips are actually 9" each in span by 10" chord for a total 180sq"
The center section panels are 20" x 8" (x2) for 320sq".

I am currently building the rest of the plane as just a simple box fuse from the wing trailing edge foward and an arrow shaft boom to cary the tail feathers.

guille2006

Thanks God you have a good dihedral there; anywa you'll need a BIG rudder to counter the yaw poor stability of that wing.
So: enlarge the rudder to increase yaw stability and shold be fine.
Hope it helps

soarrich

My Feedback: (98)

Cool wing, I think it will turn. What was your reasoning for going to larger tips. I understand the sweep forward, but not the larger tips.

flyingagin

It was originally built for a wieght carring contest. At the extreme wieght the small .25 sized planes were carring even a very gentle resulted in the plane starting a side slip, that was not always recoverable. Not so much as a stall or tip stall but slideing sideways. Most were airleron planes modified to carry the lead box.

So I went with polyhedral and the big tips (almost PADDLES?) to help pull the low wing up. I reasoned any side ways airflow in a slip would catch that big tip and push it back up before the slip got out of control.
We all thought it was tottally wierd but worth a shot
.
At a contest max of 500sq" the .25 powered planes managed to lug almost 12 lbs around the pattern. Or make one whopping big crash crater in the ground.

The wing has never left the ground yet.

I have the tail feathers and boom done. Starting the fuse. Balance is going to take a rather longish nose to get the cg correct.

I have to double check my numbers but I calculated that the cg should be at the wings center section leading edge due to all the foward sweep.

Shoe

I think what you want to know is: in what direction will this wing want to roll in response to sideslip? Forward sweep will normally make a wing roll in the opposite direction that dihedral (or polyhedral) will. The question is: which geometric feature will overpower the other? I think this is pretty easy to answer... hold the wing into the wind and give it some sideslip. Which direction does it want to roll? Is the magnitude of the roll tendency comparable to what you would feel for other designs? If the wing ends up high-mounted, that will also tend to add some roll tendency in the same direction as the polyhedral.

flyingagin

I am thinking the first flight is going to be interesting.

soarrich

My Feedback: (98)

That's an understatement!

You will film it for us, please![X(]

flyingagin

Yes
I may need the video just for future laughs
I think I will slowly add power until it gets airborn then test how it responds to rudder while low and slow.

flyingagin

I just did a double check of were I think the cg should be.

BMatthews

The amount of dihedral you have will more than make up for the destabilizing effect of that fairly low sweep angle.

An old rule of thumb I've seen printed is that a thirty degree sweep is equivalent to around 5 degrees of regular dihedral. So the effective anhedral effect of the forward sweep will only cancel out a couple of degrees of your polyhedral angles. That will leave more than enough to get a nice roll response from your rudder.

flyingagin

Awsome.

I will still treat the test flight very carfully till I see how well it responds. Crashing from very low and slow will leave bigger pieces to pick up.

But what you say makes perfect sense. I have heard the rules of thumb dihedral also.

I am still glad I built it the way I did. It has been the source of lots of discussions ever since.

BMatthews

Well, it does look odd what with the big "paddletips" and sweep forward look. You're obviously keen for attention from others at the field....

flyingagin

It was origainally designed for a weit carring contest.
We (some club member and I) thought the wings forward sweep would possibly be slightly more efficient.
Polyhedral eliminated a servo, and ailerons (three channel plane). A very small weight savings. It was also thought the polyhedral would help with turns over standard dihedral. At the extreme wing loading the planes had a tendency to start a slide side ways and then rather spectacular impacts with the ground. Hence the big tips (paddles?). They are 2" wider than the rest of the wing. We thought they would improve turn stability at the extreme wing loadings and help (push??) the low wing back up.
I was originally going to name it “CARGOYLE”, for cargo and gargoyle. A pun on the looks and function.

otrcman

As long as you are worrying about your swept forward wing, here's another concern: Wings of that configuration often have trouble with structural divergence. Speed and wing loading are your enemies in this respect. As you increase your wing loading the problem could become more pronounced. The two symptoms of divergence are unusually rapid roll response to gusts or rudder input and (worse) actual wing failure.

I can see from the photos that the leading edge is sheeted. That will help to make the wing stiffer in torsion. Is it also sheeted on the lower surface ? And did you put shear webs on the spar face to structurally connect the upper sheeting to the lower ? All that will help to make the wing more resistant to twisting and therefore structural divergence.

Dick

flyingagin

Thanks for the input Dick

Wing failure was a concern when I designed it. I was fortunate to be friends with a structurall engineer at the time (fellow club member). I consulted him a lot on it.
Top and bottom are fully sheeted. Both top and bottom spars are capped with monofilament carbon fibre, both sides of both spars. I think they are also Bass wood 1/4 x 1/4. I found a unused peice of of sparring in my wood scrap box. And man are they strong. Also there is full span vertical sheer webbing between the spars (glued full face to the back of both spars.
I would really hate to get hit in the head with that wing, it is pretty darn strong. No idea how much it weighs, but it seems reasonably light.

Also the engineer had run some speed calculations on the cargo planes. He figured they would max out in level flight at 35 mph and have a stall speed of maybe 30-32 carrying a winning weight load. Obviously that just aint much margin. You barly can get off and sustain level flight. Oh and there was only 300 ft from release till wheels off the ground or you had the flight disqualified. A lot of stall thuds at the 300' mark. the first turn was just nasty. you had to clear the fence. Well at least you did not have far to walk with your trash bag.

To get the most out of the stock engines 10% nitro we were 11x4 wood props were the only thing that had a chance.

I am going to use a large diameter low pitch prop on this thing (speed will not be this wings friend), and throttle management.

Ken

this is going to be fun as long as I don't get laughed off the feild

flyingagin

Ok here are a couble of pics. I am just holding the parts together for effect.

flyingagin