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WING ANHEDRAL - 8/5/2012 2:42 PM   
matadco


 

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From: Yukon, OK, USA
Status: offline 		Had a problem on the front wing hold on my 40 size GP Stick. To solve it I cut thw wing in half and attempted to reglue it together. In epoxieing it back I got about 4-5 degrees "ANHEDRAL". From my small aeronotical knowledge, about the size of a pin head, I understand "anhedral" will allow faster roll. "Dihedral" increases stabality in leval flight but what will "Anhedral" do? Just don't know what toexpect or should I recut the wing and start over? This is a project of the blind leading the blind to save an otherwise dinged up old bird.

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RE: WING ANHEDRAL - 8/5/2012 2:48 PM   
Rodney



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Status: offline 		No, anhedral will not make a faster roll but it will help you to fly inverted. It will also make it more unstable in upright flight.

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RE: WING ANHEDRAL - 8/5/2012 6:27 PM   
dbacque


 

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Status: offline 		Dihedral/anhedral has several effects. Dihedral does make a plane somewhat self correcting. In a plane with dihedral, if the plane is banked slightly to where one wing is level, all the lift from that wing is in the vertical direction. The lift vector from the other wing, being at an angle, generates some side force (turning the plane) and reduced up force. Since the level wing has a larger vertical component to it's lift vector, this picks the low wing back up. A plane with anhedral will have the opposite effect. When the plane is in a bank, the anhedral will tend to increase the bank.

Another thing that dihedral/anhedral does is it affects yaw - roll coupling. If you fly a plane with lots of dihedral and apply left rudder, in addition to yawing left, the plane will roll left. In a plane with inadequate dihedral, when you apply left rudder, in addition to yawing left, the plane will roll right.

In some planes a positive yaw - roll coupling is desired. In a well designed aerobatic airplane, the designer strives to get exactly the dihedral that produces no yaw - roll coupling.

How much anhedral will make your stick have bad habits? Like everything else in airplane design, that depends. The best thing to do is to fly it and see how it feels.

Dave

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RE: WING ANHEDRAL - 8/5/2012 7:57 PM   
da Rock



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Status: offline 		Some years back a club member bought a case of ARFs. Yes, a case of ARFs. Hey, it was a good price and he figured a number of us would build them. We did.

Since it was so cheap, I decided to make mine a test case and slapped some anhedral to it. The model was basically an ugly stick that a Chinese mfg had ripped off a week's worth to dump on the market. The quality wasn't there but anything will sell priced cheaply enough, right.

Sounds like I built on purpose what you accidently produced.

It would bore holes in the sky as well as the other ones. Well, actually, it didn't quite. The usual turn most of us fly is done with aileron/elevator. This did as I expected and tried to resist that turn. But I think I was the only one who noticed. It wasn't exactly steady on track when doing IMAC maneuvers. On the other hand, a couple of guys who flew it to see how anhedral flies were of the opinion it flew "exactly like theirs".

Your mileage will obviously vary.

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RE: WING ANHEDRAL - 8/5/2012 8:51 PM   
dbacque


 

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Status: offline 		Rock,

That sounds interesting. What do you mean that it "tried to resist" the turn? Resist the roll or the pull? Should still roll. Should still pull. I would thing that it should only affect yaw - roll coupling and add a slight tendency to drop a lowered wing. How much anhedral did you add? If you were looking to test the the effects of anhedral I'd guess it was more than the few degrees that matadco accidently added.

Like I said, fly it and see how it feels. It's probably fine. Sticks aren't too particular and many have been flown with much bigger problems.

Dave

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RE: WING ANHEDRAL - 8/6/2012 1:44 AM   
matadco


 

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Status: offline 		What occured was when epoxieing the wing halfs together I used the two wing bolts with rubber bands to pull the back halfs together. Guess the rubber band was stronger on bottom than the top. When I attempted to bold the wing down I noticed it dryed with anhedral, about 5-7 degrees I would guess. A stick is really a straight wing anyway. I wasn't sure whether to cut it again and reglue the halves or leave it like it is. About the only thing I know about anhedral is the Pratnor's Curare has about 20 degrees anhedral in the stabs. I really don't know what it does. I build one several years ago and was/is a great pattern ship. Some of our fighter jets had anhedral a few years back. That was suppose to increse the roll/turn rate. Maybe add some positive incedence to off set the anhedral. What about that?

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RE: WING ANHEDRAL - 8/6/2012 12:09 PM   
da Rock



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quote:

ORIGINAL: matadco
Some of our fighter jets had anhedral a few years back. That was suppose to increse the roll/turn rate.



The anhedral in stabs was a method to move the stab down without actually moving where it was connected to the fuselage. Where they are relative to the wing's downwash is important. How their anhedral affects things in yaw is not as important, especially since they're not as significant in area as wings are.

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RE: WING ANHEDRAL - 8/6/2012 12:20 PM   
da Rock



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quote:

ORIGINAL: dbacque

Rock,

That sounds interesting. What do you mean that it ''tried to resist'' the turn? Resist the roll or the pull? Should still roll. Should still pull.


Yup, they still roll however....

When dihedral wings are yawed, what do they do? They roll. When anhedral wings are yawed, which way do they roll?

High wing planes with flat wings (like the stick) still have effective dihedral. Take it away with anhedral, and HAVE some anhedral and where does the wing NOT want to go?

Yeah, the ailerons will drive those drooping suckers into a roll, but they didn't want to do it. The plane wanted to fight the roll and wanted more elevator stick that expected as well.

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RE: WING ANHEDRAL - 8/6/2012 6:28 PM   
Sport_Pilot



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Status: online 		I intentional added anhedral to a 40 GP Big Stick to give it neutral stability.  No more cross control on the ailerons to get a good stall turn.  It rolls faster, but I also cut off the wing tips and the wing tips are simply the square end rib.  Fly's better inverted as well.

I would not correct your mistake.

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RE: WING ANHEDRAL - 8/8/2012 12:00 AM   
Ed_Moorman



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Status: offline 		Unless it's scale, I out anhedral in all my high wing planes. They fly great.
1. Take any low wing plane with a straight wing and dihedral and flip it over. What you get is a high wing plane with anhedral.
2. Generally speaking, 3 things affect roll due to yaw on an airplane. YES, I HAVE BUILT AND FLOWN ALL OF THESE.
a. Wing vertical location: Low wing, mid wing, high wing
b. Dihedral angle: positive dihedral, no dihedral (flat wing), negative dihedral, also called anhedral
c. Sweep: sweep back, no sweep, sweep forward.
3. The following will produce ROLL IN THE DIRECTION OF RUDDER DISPLACEMENT.
a. High wing location (Trainer, Sticks)
b. Dihedral (Trainers, sailplanes)
c. Sweep back (Some pattern planes)
4. The following will produce no roll, given the wing is really at the center of the fuselage
a. Mid wing
b. Flat wing
c. No sweep, straight wing
5. The following will produce ROLL OPPOSITE TO THE RUDDER.
a. Low wing location.
b. Anhedral
c. Sweep forward.

Rules of thumb:
a. High wing location is about equal to 3 degrees of dihedral on both sides (or 6 degrees if you are measuring by holding one side flat). Likewise, a low wing location is about equal to 3 degrees of anhedral.
b. 1 degree of dihedral is about equal to 5 degrees of sweep.


The problem is that most planes have a combination of these. A Stick with a flat wing, like an Ultra Stick, will still roll with the rudder due to the high wing location.

What you are looking for is for the plane to be aero neutral with rudder. No pitch, no roll, just skid. Use 3 degrees each side and your plane will fly a whole lot better. Inside loops will be the same, outside loops will be great and rolls will be more axial. It makes knife edge and 4-point rolls much easier.



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RE: WING ANHEDRAL - 10/13/2012 1:38 AM   
RyanNX211


 

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From: Upper Arlington, OH, USA
Status: offline 		These explanations of dihedral, while often used, are wrong.
http://everything2.com/title/Dihedral+and+aircraft+stability

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RE: WING ANHEDRAL - 10/14/2012 4:11 AM   
charlie111


 

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From: Lynn, MA, USA
Status: offline 		 Dihedral means the wingtips are higher than at the fuselage.Front view it is a very shallow V.This tends to keep the plane level when controls are released!

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