For aircraft with variable-sweep wings, how unstable is it to have each wing in a different position?

Question

Wikipedia presents this photograph of an F-14 Tomcat, with one variable-sweep wing swept forward and the other back:

I was surprised to see that this configuration was possible; much less feasible or safe to fly with. My idle assumption, not being an aviator of any kind, was that this would be extremely unstable and difficult to handle. I would have assumed, given the prior assumption that the aircraft would be unstable, that the wings would have interlocks requiring them to be swept symmetrically, as a safety feature.

Is this photograph of a maneuver that is manageable and safe enough to perform routinely, or would doing this with the wings be an exceptional event or done only for testing? What kind of impact would this have on the aircraft's handling, given a forewarned, experienced pilot?

Answer 1

I was the lead flight test engineer for Grumman on this project. The Navy had experienced a few mechanical failures that resulted in asymmetric wing sweep and this prompted a flight test program to determine the limits of controllability. We determined the aircraft could be flown slow enough where landing was feasible. Flaps were required to lower the approach airspeed to attempt any kind of shipboard landing, meaning both wings needed to be less than 50 degrees sweep. I think three aircraft recovered aboard ship with wings asymmetric to some extent and both forward of 50 degrees. We successfully landed at a field with wings at 20/60 and a fleet pilot eventually successfully landed at a field with a failure to the maximum possible split of 20/68.

Answer 2

This was an intentional test run by Grumman in response to US Navy concerns about asymmetric wing sweep.

From The story of F-14A, Aircraft No. 3, BuNo. 157982

One of these [flight tests] was in response to concerns raised by the US Navy regarding asymmetrical wing sweep. No. 3 is best remembered for photo shown at right. A series of flight tests were conducted from December 19, 1985 to February 28, 1986. Grumman's Chief Test Pilot, Chuck Sewell, conducted several trials with the right wing locked in the forward position of 20 degrees, and positioned the left wing at 35, 50, 60 and 68 degrees of sweep in flight. 60 degrees was determined as the maximum for landing. In the event of an operational in-flight malfunction, Sewell found the aircraft to be acceptable for carrier landings in this configuration.

Evidently it was manageable, and safe enough that carrier landings were permitted with asymmetric sweep. There's no control available for the pilot of the Tomcat to intentionally asymmetrically-sweep the wings in flight, though.

How the handling qualities change I haven't seen reported anywhere. I agree with Robert DiGiovanni that you'd expect additional drag on the side with the extended wing, but the Tomcat has additional options on how to move spoilers and other control surfaces and it isn't clear to me if it can detect and respond to asymmetric sweep or if it's just up to the pilot to do so.

Answer 3

This appears to be a very fancy version of a side slip, which can be routinely performed with many aircraft. Note the ailerons are set to roll left, with the outstretched right wing providing drag to yaw right. It is doing the same job right rudder would do.

Slipping to the left would also be consistent with "raise the dead" thrust asymmetry technique if this was a twin with the right engine out. Slipping to the left puts side force on the tail to counteract right yaw.

I would not do this particular maneuver too slow, particularly in that plane, where spin recovery would be more difficult. But a well trained pilot would be in a safe enough envelope for a few photo shoot takes.