Forward swept wing will it turn like a normal three channel?

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Forward swept wing will it turn like a normal three cha... - 4/30/2012 2:47 PM

flyingagin

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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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 2:52 PM

guille2006

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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

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 2:59 PM

soarrich

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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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 3:30 PM

flyingagin

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quote:

ORIGINAL: soarrich

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.

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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 4:38 PM

Shoe

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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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 6:04 PM

flyingagin

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

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 7:09 PM

soarrich

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quote:

ORIGINAL: flyingagin

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

That's an understatement!

You will film it for us, please!

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 7:15 PM

flyingagin

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quote:

ORIGINAL: soarrich

quote:

ORIGINAL: flyingagin

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

That's an understatement!

You will film it for us, please!

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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 8:07 PM

flyingagin

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

This is how I went at it. If this was normal non swept wing, then the cg should be at roughly 30%-33% back from the leading edge, or at or just forward of the spar.

Since the sweep is even (even the big paddle tips) I picked the mid point span wise and on the spar of each panel, and measured straight across to the wing center section. The intersection of that line and the center of the wing span is were I think the cg should be.

There is a mathematically better way of saying what I did. But for the life of me I have no idea how to say it in those terms. Would love to hear some one chime in and correct or concur with my reasoning.

I mounted the engine to the fire wall and laid the wing on top of the fuse. I also laid the tail feathers and boom on the fuse in the location it will be glued at. I then found that balance point and shifted the wing, and checked again. The actual balance point is at the wings center leading edge. It doesn't seem right but I think it is. We are so used to straight wings and balancing at the spar.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 8:16 PM 1 votes

BMatthews

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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.

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RE: Forward swept wing will it turn like a normal three... - 4/30/2012 8:29 PM

flyingagin

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quote:

ORIGINAL: 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.

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.

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RE: Forward swept wing will it turn like a normal three... - 5/1/2012 8:38 AM

BMatthews

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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....

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RE: Forward swept wing will it turn like a normal three... - 5/1/2012 11:40 AM

flyingagin

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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.

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RE: Forward swept wing will it turn like a normal three... - 5/1/2012 6:13 PM

otrcman

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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

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RE: Forward swept wing will it turn like a normal three... - 5/1/2012 11:15 PM

flyingagin

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quote:

ORIGINAL: 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

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

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RE: Forward swept wing will it turn like a normal three... - 5/2/2012 1:42 AM

flyingagin

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

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RE: Forward swept wing will it turn like a normal three... - 12/26/2012 1:36 AM

flyingagin

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It has been a while since I last posted on this thing. Other projects were worked on. And one plane finished and ready for test flight. My building situation became to crowded and cluttered With zero room to put any thing. So getting organized as best as I can in such a small area and cleaned up was the first order of business.

Then I resumed work on this plane. Made a fairing for the back out of $ tree foam board,paper off, to give some stream lining, and improve the looks a bit.

Then installed servos and nyrod linkages.

Put the engine on.

Now the kicker With gear installed I rechecked the balance. OH CRAP OFF BY 10 MILES. The wing has a forward sweep of 7" and with gear in the only place it could physically fit, it really threw the cg off.

Only solution was to cut the nose off. I then taped the engine and battery to a stick and started shifting forward till I hit my balance point. Then made nose extension. Now the cg is spot on at the LE of the wing center section. Wich if measured at the mid span point of the wing puts the cg at the main spar

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< Message edited by da Rock -- 12/27/2012 10:06 PM >

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RE: Forward swept wing will it turn like a normal three... - 1/26/2013 10:02 PM

flyingagin

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Here is an update on this funny wing plane.
I had to redo the tail boom It was to flimsy and extend the nose a bunch, like in a lot to acheive proper balance.

Took it out today to fly. We never even started the engine as it did not range check succesfully.

I will have to replace some gear then will try again.

Hey no poked fun at funny wing. They all seemed rather intrigued by this odd ball, and really want to see it fly.

I will eventually get her in the air. I think while I have this down time with it I will give it a bigger rudder. There was some concern about needing more.

Ken

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RE: Forward swept wing will it turn like a normal three... - 1/29/2013 8:00 AM

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Check the full-size Hansa jet. Interesting design.

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