Induced Dihedral

[acrojack202]

Hi,

Can anyone explain 'induced dihedral' ? I believe it is related to wing leading edge sweep, but not sure how. I've heard the term used, but not being an aerodynamicist, never understood it.

Jack

[Pro1Foam]

Not sure, but i think a "induced dihedral" with "a little faster than i should have" wall that bent my wing tube. LOL

Sry had to add that, Now back to the question at hand......

[tommy321]

I've never really heard this term used, but a quick search of google seems to find that people are using it to describe either:

a) dihedral caused by the airflow pushing a flexible wing upwards. Like a kite, or a paper plane.

b) dihedral effect caused by some design feature other than dihedral. Dihedral improves an aircrafts lateral (roll) stability. So if you add something else that also has this effect, once could think of it as induced dihedral. However, I haven't really ever heard of the term "induced dihedral" being used this way - it's at least not very widespread in aerodynamics literature.

Tom

[acrojack202]

Tom,

That's consistent with what I recall. The discussion had to do with rolling characteristics of a pattern plane that was popular around 1980, called the EU-1A. It was a large plane (for that time) with a fuselage reminiscent a F-4 fighter and dramatically swept wings and a low aspect ratio. It rolled like it was on a wire. It had some other less than desireable features like that big wing blanking the elevator; in a vertical downline, you may not have elevator response unless you added power to get some prop wash. Many experiments with stab position and anhedral.

At any rate, the conventional wisdom had it that the wing sweep was responsible for roll stability and it was referred to as " induced dihedral ". That's the only time I've heard the term. In retrospect, I think the great rolling characteristic may have been due to a low moment of inertia about the roll axis due to both the sweep and low aspect ratio. At any rate, it was a great plane.

Jack

[tommy321]

Yup... Sweepback gives you lateral (roll) stability. I've always just thought of it as independent of dihedral. I teach a groundschool for full scale pilots, and the three sources of lateral stability we teach are:
1. Dihedral,
2. Wing Sweep,
3. Keel effect.

Keel effect is easy to visualize. On a high wing aircraft, most of the weight is in the fuselage, which is beneath the wing. When the aircraft is banked, the low fuselage acts almost like a pendulum (or the keel of a boat) trying to right it back to level. This is why high wing aircraft typically have less dihedral than low wing aircraft.

Sweepback is a little tougher to visualize working. If you picture a delta winged aircraft, when the aircraft gets into an uncommanded bank, it will begin to slip towards the low wing. Slipping towards the low wing will cause the incoming air to hit the low wing's leading edge at closer to a right angle than the high wing. The high wing will see the incoming airflow at a very acute angle. The low wing, seeing more direct airflow will start to create more lift, and will tend to raise the low wing.

Tom