Frequently Asked Questions!

Welcome to my FAQ page. Here are some of the questions I have been asked about the SR71, Stealth technology and other topics.

Topics

How fast does the SR71 Really go?
Are stealth Aircraft Invisible to radar?
How high does the SR71 fly & do the pilots get Astronaut wings?
Does the SR71 take off with empty fuel tanks?
What causes the SR71 engines to stall?


How fast does the SR71 Really go?

The USAF has never really admitted to a true top speed, but most experts agree that the top speed of the SR71 is Mach 3.5. This is because of two simple reasons. First the glass in the windshield and second the engine spike

The windshield limit the SR71's top speed because its glass would begin to melt at speeds higher than Mach 3.5. The glass technology was, in 1964 when the Blackbird was made, at the highest they had the capability to make. Glass technology has not changed that much in since then when it come to handling the temperature variations that the SR does at high altitude and speed.

The other main reason it cannot go faster is because even though the engine spike moves to slow down the super-sonic air (so the engines don't unstart) to sub-sonic speeds, it can only do so up to a certain point. This point is around Mach 3.5 and depends on altitude and other atmospheric conditions.

In effective and safe speed tests the USAF will not usually fly faster than Mach 3 and if the weather cooperates they are allowed to go to Mach 3.2. But every once in a while pilots have reported inadvertently going Mach 3.5.
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Are stealth aircraft invisible to radar?

Easy answer is no! Why is a better question. First you need to know how radar works. Radar works by using a transceiver send out a radio wave at a certain frequency. When, and if, that wave hits an object, the part of the wave that hit the object is returned to the wave's source. The amount of radar energy returned tells the operator how big, how many, and most of the time what that radar wave hit.

Stealth technology works on the principle of not only scattering that return wave and absorbing as much of that radar energy as possible. This will diminish the radar return to practically nothing, but a small amount of energy is still returned. For instance, the B-2's radar signature is said to be the size of a small birds. For a plane that size, that is a very little radar energy return. So while stealth aircraft are not invisible to radar, they blend in so much and the signature is so small that it just ends up looking like ground clutter or small animals and are ignored, until of course something blows up.
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How high does the SR71 fly & do the pilots get Astronaut wings?

The highest released altitude that I have heard of is about 86,000 feet. The reasons for this are the same as the top speed question. Another reason is the fact that while the SR71 uses special fuel it is still uses jet engines. Jet engines need air, especially high thrust jet engines like the Blackbird's.

SR71 pilots don't get astronauts wings, why, because to get astronaut wings you must fly, at a minimum, 264,000 feet. 87,000 feet is much lower than this.
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Does the SR71 take off with empty fuel tanks?

No, the SR71's fuel tanks are not empty when taking off. The SR71 takes off with anywhere from 45,000 lbs to 65,000 lbs of fuel out of the possible 80,000 lbs it can hold. It will then, soon after takeoff refuel and go on its mission. There have been a few time a Blackbird has taken off with a full fuel load, but all during flight tests.
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What causes the SR71's engines to stall?

The SR71's engines can stall or unstart during supersonic flight rather easily. These are caused by shockwaves coming from off the plane entering into the engine. This shockwave will stop the engine cold. Most of the time the engine restarts quickly, but a good portion of the accidents the Blackbird was involved in are due to engine unstarts.

The SR71 does has airspikes in the engines that automatically move in and out to stop the shockwaves from entering the engine. This fixes the problem most of the time. In fact without these spikes (designed by Ben Rich of Skunk Works) the Habu couldn't fly at all. A few Shockwaves still can get through, but it doesn't cause too much of a problem.
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