viperred

What is the point in using diehedral in high wing twins. I've seen some high wing twins with it. Does it just create better recovery/more stability?

Does diehedral on a highwing twin decrease speed vs. a flat wing? Does it increase lift or control?

Anyone that has any thoughts on the subject please jump in.

Paul A.

mulligan

Dihedral on any plane increases lateral stability... when flying upright. There is virtually no penalty on lift or speed. However, control is inversely proportional to stability. When banking, flying inverted, or in general doing anything with the plane laterally, you will constantly be "fighting" the tendency of the plane to return to level. In most cases, though, the effect is not very significant.

The effect of dihedral is additive to the effect of a high wing (which similarly increases lateral stability). There is no difference in dihedral effect between a twin or single-engined plane.

- George

JohnBuckner

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ditto's to what george said but there is another important and viable reason for dihedral in a conventional twin or most particularly a Quad. That is simply to keep the props off the ground in the inevitable sloopy landing or if you are good enough while doing a cross controlled cross wind landing.

John

IWC

planes with dihedral built into the wing are more susceptible to the wind.

IWC

I mean crosswinds

William Robison

My Feedback: (3)

Ed:

Dihedral, in itself, is neither good nor bad. It depends on your design aims.

In full scale high wing planes, there are some few that have a slight dihedral. The Piper Cub series, for example. If you sight from one tip to the other you'll see there's a litle bit.

Generally speaking, the only high wing planes that have enough dihedral to notice are model planes. And they have it to increase their stability. In other words, only trainer planes.

Low wing planes are another matter entirely.

Bill.

calspec

Dihedral will cause a plane to roll when it is yawed. So if you loose an engine on a twin with dihedral it will be harder to control than the same plane with little or no dihedral. But I could be wrong.......

Ed_Moorman

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If you want good aerobatic performance in a high wing plane you will need anhedral. Even a flat wing, like on an Ultra Stick, will cause roll with rudder. I have found that about 3 inches total anhedral (1 1/2 each side) works well on a 40-60 size plane. This is about the same dihedral used on a good low wing plane. Next time your low wing plane is inverted in a cradle for putting the wing on, take a look at the front. You'll see a high wing plane with anhedral.

I think the reason you don't see high wing sport/acro planes with anhedral is that people are terrified of something different. I have had guys tell me the plane would roll over in level flight.

As I recall, a high wing location is equivalent to about 5 degrees of dihedral, but I could be wrong. I also seem to remember that 1 degree of dihedral was equal to about 5 degrees of sweep.

William Robison

My Feedback: (3)

Ed:

Anhedral in not new in this area, as you know.

Bobby is fixing his blue plane again, you need to come over to Holley and fly with us.

Bill.

viperred

I just honestly don't know if I can bring myself to put anhedral design into my wings.. it just seems so radical.. and really I ponder how well it will fly. If bill say's it's good then I trust him lol.. but one thing I really don't like is that it brings the wing tips closer to the ground.. and even on a high wing this isn't necessarily the best thing. It does look pretty darn pimpin to hvae anhedral in the high wing. Have you had good luck with say 2-5% anhedral in high wing's bill? Or what perecentage is best?

Paul

William Robison

My Feedback: (3)

Paul:

It's a lot easier to build a flat wing, and the flat wing will give you a bit of stability.

This is not a bad thing with a twin - Grumman thought so highly of it that they put a remarkable amount of DIhedral in the F7F, and it's a shoulder wing.

If you want to use anhedral, there's no reason you should not. Dragging the wingtips is not an issue, you have the mains in the nacelles, remember? If you tip the plane far enougjh for the wings to hit you have other problems.

Amount? Five degrees isn't really enough to notice, or make much difference in the flying. Go for at least ten, still not enough to have a great effect on the flight characteristics, but enough to look sexy.

Or, as an alternative, an inverted gull wing. Have the wing set with anhedral from the fuselage to the nacelles, and then flat on out to the tips. This would get the center of lift closer to alignment with the center of gravity, and give somewhat the same effect as full span anhedral.

It's really a matter of what you want, and how you want the airplane to look. Doing your own design there is no such thing as "Right" and "Wrong," so long as basic aerodynamics are kept in mind.

Bill.

viperred

okay I think I am going to keep with my straight wing... although appreciate the response and the thought.. may put anhedral on another ship. Definitely gives it a kinda lowrider feel. To bad there aren't more aircraft builders scale and full scale out there.. when did aviation get so darned exepnsive?!?! It shouldn't be.... oh well... thanks buddy....

Paul

Ed_Moorman

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Bill,

I'm at Holly every weekend, only I fly early from 0700/0730 to 0930/1000. Flaps and I don't like the heat in the middle of the day.

I guess I'm going to have to get a Stick or something and make an anhedral twin. I could do 2 TT .46 Pros on a Big Stick 40.

Ed

William Robison

My Feedback: (3)

Paul:

Just thought of a "Cheat" you might like.

Build your tapered wing flat on the board as normal. then when you join the two halves do it with the lower surface flat. This way the upper surface will actually angle down toward the tips. You'll have the look with the still simple straight joiner.

Ed:

I go out in the afternoons to Holly, I suppose if I want to see you there I'll have to get up early.

Bill.

Ed_Moorman

My Feedback: (1)

Bill,

Building a tapered wing flat on the table adds some anhedral to the wing center line, but it isn't enough aerodynamically to cancel out the pro roll due to yaw. You need as much as a low wing plane turned upside down.

Most people are terrified of the unknown. Then they go fly inverted with a 4* and do outside loops and don't realize they are doing the same as a high wing plane with anhedral doing an inside loop. It is also nice to fly knife edge with a Stick without it rolling out.

I have flown so many anhedral planes and dislike the pro roll with rudder, I just modify every thing that does. I don't care what it looks like as long as it flies right.

I am going to have to put together a Big Stick 40 twin with anhedral just to show how a twin flies with anhedral. I guess all the radio will have to go in the tail to balance the engines.

On the wing tips close to the ground, several people have told me that they thing the downward wings pack the air under the plane giving more ground effect and a slightly slower landing. I can't confirm this myself, since I tend to over power and run a heavier engine with a slightly faster landing speed. The Kangke SK/50 shown above (red/white) is made for a .46. I have an OS .61 in it. The 61-size Joss Stick (yellow) has a 1.08 in it.

William Robison

My Feedback: (3)

Ed:

My "Cheat" in post 14 was just to get the "Look," not to get the effect.

Another subject. My Ultrastick 120 flies nicely with a Saito 120, and I just got a Saito FA-80 for another Stick. Would you choose a "40" size for it, or go to a "60" size? Any particular version?

Thanks.

Bill.

Ed_Moorman

My Feedback: (1)

The Saito 80 would be perfect for the 60 size Ultra Stick. A 61 flies it well except for hovering power. Vertical is the only time you get to go full power with a .91.

For a Big Stick, it's a toss-up between the 40 or 60 size. They are considerably heavier that the Ultras. The 60 Big Stick approaches the 120 Ultra Stick for size.

William Robison

My Feedback: (3)

Ed:

Thanks.

Bill.

Robby

My Feedback: (18)

While on the subject of US 120's ...


Ok,, So if a 1.20 flys it well.. And I divide it by two to make a twin,
that would mean two .60's should do well also, yes...? Now, we have
only a small aditional weight, so let's bring that two number to say
.75... Now that UltraStick shoud do very nicely...

Thoughts.?

William Robison

My Feedback: (3)

Robby:

If you apply the "Two-Thirds" rule, you would want to use a pair of 0.80 engines to replace a single 1.20 engine.

But at the same time, since my 1.20 is a four stroke you have another conversion when going to two stroke engines.

So the 0.80s would also be four stroke, and 0.48 two strokes should do just about the same. A pair of 0.60 two strokes should make it a rocket.

Bill.