Here's a little info on how the 747 handles with a Shuttle mounted on top.

Subj: SCA handling qualities
Date: 07/16/2000 1:37:54 PM Pacific Daylight Time
From: (Gordon Fullerton)
To: (Lewis, Ed) (Dan)



Dan:
The SCA with an orbiter attached, for mild maneuvering, doesn't handle all
that much differently than in the clean configuration. There is a constant
rumbling buffet from the orbiter wash hitting the vertical stabilizer, not
uncomfortable, but always there.

Roll response and pitch response seem about the same. Turn coordination is
affected. With bank angles of more than 10-15 deg, reverse (with the turn)
rudder is required to keep the ball centered.

There is a noticeably greater pitch trim change with power change. When
trimmed on final, which requires a greater power setting because of the
drag, and subsequent reduction to idle during the flare, you must be
prepared for a greater than normal pull force to keep from dropping in.
The biggest effect is of course drag. Typical ferry conditions are at 15000
ft (to keep coolant fluids in the orbiter from freezing), 310 knots TAS,
fuel flow 39000 #/hr. Another way to state it, mileage is about 325 ft per
gallon.

Gordon Fullerton



Here's a PDF version of an old NASA document that discusses the modifications and operations of the Shuttle Carrier Aircraft for the Enterprise glide tests. NASA conducted over 3000 hours of wind tunnel tests on the mated configuration. One point of interest is the higher angle of attack for the Enterprise on the glide tests compared to the ferry flights. The higher angle of attack was needed to ensure the Enterprise cleared the 747's vertical tail on separation.

I have not found any images of the airflow between the SCA and a Shuttle online. It would be interesting to see the interaction between the airflows of the two mated vehicles.