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Quote:

Originally Posted by UAL T38 Phlyer (Post 1023576)

Since spanwise flow is at the rear-most part of the wing, and local increase in AOA happens there, it will stall root-first. Since this is the aftmost part of the wing, a stall causes a nose-up pitch...generally the opposite of what you want.

The canard can prevent this by stalling and pitching down before the wing reaches a critical AOA, as in the Rutan designs.

Quote:

Originally Posted by tomgoodman (Post 1023681)

The canard can prevent this by stalling and pitching down before the wing reaches a critical AOA, as in the Rutan designs.

Tom:

True, Rutan avoids an aft-wing stall by purposely limiting the amount of "up" lift the canard can generate. This does prevent an aft-wing stall, but also limits the aft-wing from generating anything close to CL-max. This means you need even more wing, or more flaps, to get a reasonable approach or takeoff speed. More wing or more flaps equals more complexity and more weight, which equals more cost. (Both to acquire and to operate). Minor consideration on a homebuilt; more on an airliner.

If the canard (or foreplane) can be made to have a huge range of motion, an aft-wing stall with this configuration could be made recoverable by making the canard lift go to zero, or even a negative value, which would drive the nose (and AOA) down. On all supersonic fighters that I can think of there is an all-moving stabilator (instead of a horizontal stab and elevator), to achieve the required control moment-arms with the large center of lift-ranges generated from approach speed through supersonic flight.

All-moving slabs haven't been used on airliners because, I believe in part, they are more responsive, and would make for a rougher ride in an airliner. This same characteristic makes them perfectly applicable to fighters, where rapid g-onset (and pulling to CL max) is often a necessity.

Rick mentioned fly-by-wire. You don't have to make it that way (as above), but to get maximum benefit from a FSW jet with a canard, you would probably want to. A FBW system would make an all-moving canard stabilator easy to adopt without sacrificing ride quality.

It seems Boeing would make a mistake by introducing a platform to transport category that is "unstable" by design. Airbus avoided doing this with the fbw on the 320 and for good reason.

I also think the canards would be a problem in ground handling.

Quote:

Originally Posted by Bucking Bar (Post 1023305)

OK, can anyone explain why this post was "moved" ?

I put it right back in the Delta RFP thread. It could be relevant.

The design makes a lot of sense, but would be a runway hog.

Maybe a flying saucer is relevant for Delta in the future, but for now, this is merely hangar talk.

Besides, any new airliner from Boeing / Airbus will be used by more than just Delta, or US airlines, for that matter.

When there is a concrete plane for Delta to buy, and Boeing and Delta are ready, willing and able.... then you have a story about Delta.

UAL T38 Phlyer,

Thanks for the explanation. I was curious about the lack of interest in scaling up canard designs for larger aircraft. For transport aircraft, static instability may offer unneeded advantages at the price of unwanted problems.