anh

Photos of hang gliders that illustrate how billow contributes to the net geometric anhedral of a swept wing

This page last updated August 31 2005

Jim Norton flying at Dog Mountain WA, #1--note how we can see the top surface of the near wingtip and the bottom surface of the far wingtip. There's nothing like a Falcon for demonstrating how billow contributes to a wing's net geometric anhedral.

Jim Norton flying at Dog Mountain WA, #2--Again, note how we can see the top surface of the near wingtip and the bottom surface of the far wingtip.

Jim Norton flying at Dog Mountain WA, #3--Note how we can see part of the underside of the far wing, near the tip, due to billow.

Dan Tyler launching at Detroit Lake OR--again we can see part of the underside of the far wing, near the tip.

Dwayne Hyatt flying at Peterson Butte OR, #1--again we can see part of the underside of the far wing, near the tip.

Dwayne Hyatt flying at Peterson Butte OR, #2--even with this topless high-performance glider, we can see a large part of the underside of the far wing, near the tip, due to billow.

Dwayne Hyatt launching at Peterson Butte OR, #2--in this view of this topless high-performance glider, enough billow is present that we can easily see top surface of the near wingtip, though all of the rest of the wing is showing its underside.

Pilot launching at Peterson Butte OR, #1--with this Falcon it is very clear that billow is contributing to the wing's net geometric anhedral--note how much of the top surface of the near wing is visible. On the ground the trailing edge is being held up by the luff-line, but in flight it will billow in much the same way.

John launching at Peterson Butte OR, #1--the way that billow contributes to the wing's net geometric anhedral, and the "M" shape of the wing as a whole due to billow, are both very visible in this photograph. The large amount of top surface that is visible on outboard portion of the near wing, and the large amount of bottom surface that is visible on the far wingtip, all make it obvious that this wing will have a significant amount of net geometric anhedral. This photo also shows that due to billow, the inboard parts of the wing are creating the opposite geometry--creating a dihedral effect, or decreasing the wing's net geometric anhedral--but the roll torque generated by these inboard areas when a sideways airflow component is present will be relatively small in comparison to the roll torque generated by the more outboard areas.

John launching at Peterson Butte OR, #2--this view emphasizes the washout built into the wing--note the very large angle between the tip strut and the keel tube--and note the top surface that is visible on the outboard portion of the near wingtip.

Pilot landing at Packwood WA--on this single-surface trainer, the wing nearest the camera is giving a dramatic demonstration of how billow contributes to the wing's net geometric anhedral. Note how much of the top surface of this wing is visible, near the tip.

Ken Dawe's Swift at Packwood WA--the lowered flaps create a dihedral effect (increasing the net geometric dihedral or decreasing the net geometric anhedral). A very close look at the photo will reveal that the top surface of the far flap is visible, and of course the bottom surface of the near flap is visible. A key point here is that the flaps are hinged along a swept hinge line. Lowering the flaps creates an effect that is opposite to what happens when billow raises the trailing edge of a swept-wing hang glider. Here, a sideways airflow blowing from the observer toward the glider would tend to strike the bottom surface of the near flap and the top surface of the far flap, creating a roll torque away from the camera. In the real world there would never be this extreme degree of sideways airflow but this dihedral effect will be present to some degree even if there is only a slight sideways component in the airflow. Extending both spoilerons on the top surface of an aircraft with spoilerons would have the opposite effect, creating an anhedral effect, if the spoilerons were hinged along a swept hinge line.

ATOS at Oceanside OR--the ATOS's flaps create the same dihedral effect as do the Swift's flaps: we can see the top surface of the far flap, and the undersurface of the near flap, just as we can see the undersurface of the near side of the V-shaped tail. Of course neither the flaps nor the V-tail create much roll torque in the presence of a sideways airflow, because they act at a relatively short moment-arm from the CG.

This little RC Rogallo trike has no droop in the leading edges in relation to the keel, but the very large amount of billow obviously gives the wing a large amount of net geometric anhedral--note the large amount of top surface that is visible on outboard portion of the near wing, and the large amount of undersurface that is visible on the outboard portion of the far wing. Despite this, the extremely swept leading edge of the delta wing will also tend to create a strong dihedral effect when a sideways airflow is present. In fact, this little RC model was the only flex-wing aircraft I tested that ended up having a net positive coupling between yaw and roll at most angles-of-attack, indicating that the swept or delta wing shape was actually dominating over the large amount of net geometric anhedral created by the billow. The aircraft's yaw-roll coupling was explored both with a rudder (ground-adjustable only, and positioned both above and below the keel in different trials), and with a ribbon streamer to increase the drag of one wingtip, with consistent results in each case.

Up to "Photos of hang gliders and models to illustrate how billow contributes to the net geometric anhedral of a swept wing"

Copyright © 2004 aeroexperiments.org