Ask the Captain: How can a Boeing 747 carry a space shuttle?

Ask the Captain: How can a Boeing 747 carry a space shuttle?

Question: I’ve always been fascinated at how they could strap the space shuttle on top of a 747 and fly it across the county. How does the extra weight from the shuttle not keep the plane from lifting off, and how does it not disrupt the airflow around the 747 and make it unstable?

— submitted by reader Doug in Indy

Answer: NASA and Boeing have some very smart aeronautical engineers. They calculated that the shuttle could ride safely and securely. They had attachment points built into the 747 to handle the weight and movement of the shuttle. There are extra vertical fins on the tail to help stabilize it in flight.

The weight of the shuttle is calculated like any payload. The 747 produces enough lift to fly and to carry the weight of the shuttle. In this respect it is no different than cargo carried inside the airplane.

The airflow is somewhat different, but the engineers have adjusted it to be stable. The 747 that carried the shuttle is an experimental airplane and may not be as stable as a regular 747, but it served the shuttle program very well.

Q: When a Boeing 747 taxis, do they use an outboard engine to help it turn?

— Steven, Conn.

A: I think your question is whether a captain will use thrust from an outboard engine to assist turning a 747. Usually the momentum of the taxiing airplane is sufficient for the turn. Increasing thrust on large jet engines can cause damage to ground equipment; consequently pilots are very careful about using it during ground operations. It is possible, but it would be rare.

Q: What is the emergency, in-flight, engine restart procedure for a 747?

— Rich, Detroit

A: A 747 engine restart would be like any other jet: Ignition on, starter assist or windmill to increase the rotation to the proper value, reintroduce the fuel. Once light-off occurs, monitor for a normal start sequence.

Q: How much fuel does a 747 carry for a 9-hour flight?

— Ross, N.J.

A: Using this website for the necessary information, a nine hour flight will require approximately 275,000 pounds (just over 41,000 gallons) of fuel. The assumptions are a flat-rate burn of 6,700 pounds per hour per engine, 3,350 pounds per engine for the alternate airport, and 5,025 pounds per engine for a 45 minute reserve.

The maximum capacity for a 747-400 is 379,000 pounds of fuel.

John Cox is a retired airline captain with U.S. Airways and runs his own aviation safety consulting company, Safety Operating Systems.