Variable pitch wing design for a sailplane...

[Quokka]

SWEPT WING VARIABLE PITCH SAILPLANE

Document Type and Number: United States Patent 3561702

Link to this page: http://www.freepatentsonline.com/3561702.html

Abstract: A sailplane is provided in which the line-of-lift of the wing is swept back from the longitudinal elastic axis to give an automatic wing twist with change of lifting force. In operation, a reduction in the angle of incidence from an updraught wind results in a trade of lift for greater forward thrust. An increase in angle of incidence from a downdraught wind results in a trade of forward momentum for greater lift. This is most effective under turbulent air conditions.

...is the bit that I've highlighted in bold type true?

[old,not bold]

Hasn't that patent been held by whichever God one subscribes to for many million years? I'm not an engineer, but to a layman like me it sounds like how a seagull works, when in soaring mode.

[Parapunter]

I'm no sailplane expert, but have flown other types of glider for years & the general rule of thumb is to slow down in lift, to maximise the climb. Makes sense to me.

[Quokka]

But lift?... in a downdraft?

[airfoilmod]

The old F-8 Crusader, although the purpose on that A/C was to improve viz. on short final. Doesn't raising the Angle of Incidence create more Drag (LIFT) assuming the Fuselage keeps its Pitch Angle? That sounds like trading AS for Altitude, Down draft or no. The net gain (loss) of altitude depends on the velocity of the airmass downward. Merely climbing (in an updraft) puts energy in the Bank for later. Or you can gain AS (energy). I may not understand correctly; I have small time in Hang gliders and sailplanes, my motto is Powerless flight is just a negotiation with the airmass, riding the elevator and looking for thermals. It is blessedly satisfying.

[Intruder]

Sounds like the wing is more flexible than "normal," designed in such a way that it dynamically relieves loads on the outer portion when subjected to higher G load in gusts. It may work in principle similar to "active" outboard ailerons on some fly-by-wire airplanes that decrease wingtip loads under some conditions.

I can see the possible advantage of allowing a longer, lighter wing for better overall performance, and a bit smoother ride in turbulence. It might make airspeed control a bit more difficult in turbulence, but that may not be important in context of a constantly changing wing profile...

[airfoilmod]

Newest version of Fly By Wire is automatic Trim. The computer calculates
control inputs needed for "level" (comfortable) Flight, and dinks the control surface before a Human can blink. It does what nearly every pilot tries to accomplish in Turbulence, but fails at. A completely FBW A/C cannot be controlled (hand flown) if the computer crashes, responses are too slow, thinking too long.

But I have a question about this Patented Wing. As I understand it, if the wing reacts "automatically" to load, and compensates by changing Angle of Incidence, what do I do as the Pilot? If I want to ascend in the thermal (updraft), I will have to put excess elevator (up) in to the airframe to counterract the wings insistence on gaining Airspeed. This excess Elevator will create additional Drag, destroying some of Nature's freebie, won't it?

Mr. Quokka, something interesting about the Patent Office: A new idea can be patented if it's new; it isn't necessary that it actually work.

[Mark1234]

quite - I can see (if it all figured out right) how it would help in a straight cruise - a bit like wave powered boats. BUT it would be a PITA thermalling, during pullups and such.

Not to mention the inherent downsides of a swept wing configuration - particularly for a low-speed regime aircraft.

[airfoilmod]

Surfing? I'm not sure about the need for swept wings either. The upside is same wing area with less frontal exposure. Also aftward displacement of shock wave in trans sonic ops (sic). Downside hellish stall speed and low speed handling. No more Super Cub Launches!