1 year, 4 months ago
Why did the SR-71 Blackbird leak fuel and how was this overcome?
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M$1 Answer
The seals on the fuel tanks of the SR-71 were purposely built a fraction to small in order to compensate for the expansion that occurs due to heat build up of supersonic speeds.
The SR-71 had an offically stated speed of mach 3+.
This seal leakage was a known factor when the aircraft was built.
The fuel tanks in the fuselage and wings only seal once the plane is airborne and up to operating temperatures. Had the seals been designed to fit tight when the aircraft was at 'rest' then they would blow out and fail once the plane reached operating temperatures.
The JP-7 fuel which was used in the SR-71 has an extremely high flash point so there was very little danger of fire with the plane on the tarmac.
Standard procedure for the SR-71 was to take off with a minimal fuel load and then approximately 7 minutes after takeoff rendezvous with an airborne tanker and top its tanks up.
A full load of fuel would give the plane a 2,500 mile range.
Maximum takeoff weight of the airplane is 170,000 lbs. and without fuel, the aircraft weights 60,000 lbs.
-quote-
Developed for the Air Force in the early 60's as a high altitude, high speed strategic reconnaissance platform, the SR-71 is the world's fastest and highest-flying production aircraft. Also known as "The Sled", the SR-71 is capable of flying at speeds in excess of 2200 mph (Mach 3.5+) and at altitudes beyond 85,000 feet and has the ability to fly over 2,000 miles without refueling. At operational altitude and speed friction between the air and airframe generates so much heat that the SR-71 will expand by as much as 11 inches. As a result, the Blackbird's elastic fuel cells, which also serve as heat sinks once airborne, leak heavily on the ground and so the SR-71 is only loaded with sufficient JP-7 to get to refueling altitude where it takes on a full load before climbing once again to its operational altitude. Once at cruising altitude, fuel flow is automatically regulated so as to maintain the aircraft's center of ballance.
-end quote-
A truely remarkable aircraft.
http://www.youtube.com/watch?v=-1250fZuhUg
Sources:
http://tech.military.com/equipment/view/89725/sr-71-blackbird.html
http://www.sr-71.org/blackbird/sr-71/
The SR-71 had an offically stated speed of mach 3+.
This seal leakage was a known factor when the aircraft was built.
The fuel tanks in the fuselage and wings only seal once the plane is airborne and up to operating temperatures. Had the seals been designed to fit tight when the aircraft was at 'rest' then they would blow out and fail once the plane reached operating temperatures.
The JP-7 fuel which was used in the SR-71 has an extremely high flash point so there was very little danger of fire with the plane on the tarmac.
Standard procedure for the SR-71 was to take off with a minimal fuel load and then approximately 7 minutes after takeoff rendezvous with an airborne tanker and top its tanks up.
A full load of fuel would give the plane a 2,500 mile range.
Maximum takeoff weight of the airplane is 170,000 lbs. and without fuel, the aircraft weights 60,000 lbs.
-quote-
Developed for the Air Force in the early 60's as a high altitude, high speed strategic reconnaissance platform, the SR-71 is the world's fastest and highest-flying production aircraft. Also known as "The Sled", the SR-71 is capable of flying at speeds in excess of 2200 mph (Mach 3.5+) and at altitudes beyond 85,000 feet and has the ability to fly over 2,000 miles without refueling. At operational altitude and speed friction between the air and airframe generates so much heat that the SR-71 will expand by as much as 11 inches. As a result, the Blackbird's elastic fuel cells, which also serve as heat sinks once airborne, leak heavily on the ground and so the SR-71 is only loaded with sufficient JP-7 to get to refueling altitude where it takes on a full load before climbing once again to its operational altitude. Once at cruising altitude, fuel flow is automatically regulated so as to maintain the aircraft's center of ballance.
-end quote-
A truely remarkable aircraft.
http://www.youtube.com/watch?v=-1250fZuhUg
Sources:
http://tech.military.com/equipment/view/89725/sr-71-blackbird.html
http://www.sr-71.org/blackbird/sr-71/
You can leave an optional "tip" with Mahalo's virtual currency, Mahalo Dollars. If you are asking a difficult question that might require some research, or if you'd like a wide variety of feedback, a higher tip often leads to more answers to your question.
M$
Thanks Shadowbear for a very comprehensive answer. As a young boy I saw the SR-71 at the 1974 Farnborough Airshow in England. I remember them announcing its arrival over the PA system and then saying that there would be a slight delay as the aircraft had "overshot" and was currently turning around over Sweden :) I subsequently saw it on static display at the airshow. It's certainky one of the most beautiful aircraft I've ever seen.