Some SR-71 statistics & facts

[C-117]

So how fast does the SR-71 really go?

The fastest published speed of the SR is Mach 3.5. There are several factors that limit the speed of the SR, one is the shock waves generated by various parts of the plane, at around Mach 3.6- 3.8 the shock wave off the nose of the aircraft narrows enough to go into the engine, while there is the inlet spike (which slows the air to subsonic before it enters the engine), the shock wave bypasses the spike and causes the engine to flame out. Second is the heat generated by the plane moving through the atmosphere, even titanium has it's limits, and the heat generated by the SR brings the fuselage to the brink. In a Lockheed Skunk Works study to see how much money and development it would take to get the SR to go faster than it's designed top speed 3.2- 3.5, the designers discovered (among other things) that the metal divider between the windshield was heating up so much above mach 3.5 that it was affecting the integrity of the windshield, and at that point they had stretched the glass technology to the max! So Mach 3.2 to a max of 3.5.

The design Mach number of the SR-71 is 3.2 Mach. When authorized by the Commander, speeds up to Mach 3.3 may be flown if the CIT limit of 427 degrees C. is not exceeded. Crews have reached 3.5 Mach inadvertently, but that is the absolute maximum anyone is aware of.

How high does the SR really fly?

The SR doesn't fly quite that high, the highest altitude attributed to the SR was 100,00 ft (18.93 miles), all the U.S. Air Force and Lockheed admit to is above 80,000 ft. The SR-71s engines require a sufficient quantity of air in order to operate. The maximum altitude limit is 85,000 feet unless a higher altitude is specifically authorized. Crews have inadvertently reached 87,000 feet, but no higher.

So what does it cost to fly the SR-71?

There are lots of numbers floating around about how much it costs to fly the SR, figures over US$100,000 an hour to fly the SR-71 are realistic, and one photo could cost up to a US$1,000,000. The figures are all over the place, it's especially hard, because you can figure it so many different ways....do you include Tanker support, flight proficiency ops - SR "B" model and T-38 -, and numerous other expenses. Figure it as what it actually costs to fly the airplane itself, no training, tanker support, etc. and numbers come to around US$38,000 per flying hour. The costs can be lower to a rock bottom price of US$27,000 per hour if the annual flying time gets above 300 hours total. So, the actual cost is probably somewhere in between 38 and 27 thousand US an hour.

"The SR takes off with almost dry tanks"

Well not exactly empty, the SRs tanks hold 80,000 lbs. of fuel, the SR-71 usually takes off with 45,000 lbs. of fuel on board. Not what folks would call almost dry! The SR takes off with either 45,000 lbs., 55,000 lbs., or 65,000 lbs. of fuel. Almost all flights were refueled by KC-135Q's (now "T"), there are a few exceptions though... one was called the "Rocket Ride", which were flown from Kadena AB, Okinawa and then on to Northern Korea, on 65,000 lbs of fuel. The only SRs that launched with a full fuel load were the test flights from Palmdale, CA.

Cheers!

[Vonsmalhausen]

that's what i call an Extreme Machine :cool2:
saw one flying a display some years ago @ Chievre, a sight you NEVER forget :mexwave:

[MD-11]

Almost all flights were refueled by KC-135Q's (now "T")

Look here
http://www.airliners.net/open.file/223229/M/

[C-117]

Right - the KC-10 had a limited run refueling the SR. Great pic!

Here's another bit of trivia. The SR-71's initial designation was RS-71. When the then President of the U.S. Lyndon Johnson made the press announcement and responded to subsequent questions to the media about the Blackbird - he mistakenly reversed the designator to SR. Lockheed changed the designator instead of reversing what the President said...!

[L-1011]

Why can't the SR-71 take off with full tanks? Are it's engines not powerful enough

ciao,
TriStar

[C-117]

The Blackbird needs to be flown fast enough to expand its structural components to 'fit' prior to an aerial re-fueling before it can take on
a FULL fuel load. Also, no sense wasting fuel (tanked - increased takeoff weight) when at least one inflight refueling evolution is in the plan.

[L-1011]

Thanks C-117

Indeed it's a good reason !

ciao,
TriStar

[OompaLoompa_12]

Guess What... My Gramps was a navigator on the SR-71.

[regi]

Despite its unique features, the entire SR-71 program was halted after all.
Satelites have taken over the photography role. And there was no combat role for the SR-71.
As you mentioned: quite expensive pictures.
The big difference with satelites and the plane is that a photo shoot target knows exactly the pass over time of the satelites, but doesn't know if the pictures are taken. The target usually knows it when a plane has come over its soil , so it knows it is watched specifically.

[MD-11]

No comment

[bigjulie]

Good drawing MD-11

[AirSmetten]

Hellow

The SR-71 was idd an Extreme Machine and luckely I saw it in the air one time during its Final display @ Nellis in '97.

The sight of those enormous burners kicking in is crazy 8)

There are some details incorrect in the first post I'm afraid.
The cone in the engines has a quite different function of those you find back on Mirages,F111,F104,...etc. For those aircraft your theory is correct and it's function is idd slowing down supersonic airflow to subsonic airflow to keep the engine running.But the SR-71 is a very special plane so the engine cones also have a different function(but no panic they also slow down the airflow for the engine) The second function of these cones ,for the SR-71 the most important, is that they create a major pressure interval. Because of this it is possible to use the 'turbo-ramjet' propultion to create and maintain such high cruise speeds.So in fact the SR71 uses ramjet-type engine with a normal turbine engine build inside it.At Sealevel and subsonic speeds the conventional turbine engine produces 100% of the trust , when the SR-71 flies at Mach3+ speeds and at extreme altitude these conventional engines produce only 30% of the total trust.

The use of ramjet technology makes the Blackbird possible to fly much higher than onter aircract.At these altitudes the air density is very low so drag also reduces. Because of this cruise efficiency (miles/gallon) is also much higher.

For those who not believe it :
The chief technical advantage of the SR-71 is the special turbo-ramjet engine. The engines intake area is a large cone which can be moved in and out to regulate the amount of air going into the engine. Thus at high altitudes, the turbojet begins operation very similiar to a ramjet. In fact this increases performance to such a degree that the SR-71 currently holds the absolute world class speed record, at 2,193.6 miles per hour and a level flight altitude record of 85,069 feet (set in July of 1976) . Obviously its ceiling is higher that the 85 thousand feet when not pushing for maximum speed.

The SR-71 is fueled with JP-7, a high temperature fuel, which is also part of the heat transfer capabilities of the airframe. At operational speed, the temperature along the back of the aircraft rises to 511 degrees farenheit, the temperature along the engine nacelles around 1,050 degrees, and the engine exhaust area at about 1,500 degrees. Fuel rises to 320 degrees C. A single SR-71 is reported only to fly a total of 200 hrs per year.

http://www.milnet.com/sr71h.htm

Greetz
Rick

[chornedsnorkack]

Hellow

The SR-71 was idd an Extreme Machine and luckely I saw it in the air one time during its Final display @ Nellis in '97.

The sight of those enormous burners kicking in is crazy 8)

There are some details incorrect in the first post I'm afraid.
The cone in the engines has a quite different function of those you find back on Mirages,F111,F104,...etc. For those aircraft your theory is correct and it's function is idd slowing down supersonic airflow to subsonic airflow to keep the engine running.But the SR-71 is a very special plane so the engine cones also have a different function(but no panic they also slow down the airflow for the engine) The second function of these cones ,for the SR-71 the most important, is that they create a major pressure interval. Because of this it is possible to use the 'turbo-ramjet' propultion to create and maintain such high cruise speeds.So in fact the SR71 uses ramjet-type engine with a normal turbine engine build inside it.At Sealevel and subsonic speeds the conventional turbine engine produces 100% of the trust , when the SR-71 flies at Mach3+ speeds and at extreme altitude these conventional engines produce only 30% of the total trust.

The use of ramjet technology makes the Blackbird possible to fly much higher than onter aircract.At these altitudes the air density is very low so drag also reduces. Because of this cruise efficiency (miles/gallon) is also much higher.

For those who not believe it :
The chief technical advantage of the SR-71 is the special turbo-ramjet engine. The engines intake area is a large cone which can be moved in and out to regulate the amount of air going into the engine. Thus at high altitudes, the turbojet begins operation very similiar to a ramjet. In fact this increases performance to such a degree that the SR-71 currently holds the absolute world class speed record, at 2,193.6 miles per hour and a level flight altitude record of 85,069 feet (set in July of 1976) . Obviously its ceiling is higher that the 85 thousand feet when not pushing for maximum speed.

Well, I kind of doubt the drag is reduced by air density as such.

After all, SR-71 at merely 3 Mach has to support over 98 % of its weight by lift. Which means it cannot climb on steady level flight to altitudes where the air would be too thin to support its weight. And if it is in air thick enough to give lift, it is also in air thick enough for drag.

How does the lift/drag ratio (which defines the required thrust/weight ratio) of SR-71 at Mach 3 compare with the lift/drag ratio of, say, a Concorde cruising at Mach 2,0?

[AirSmetten]

hi again
For those who interested here you can find a Reconnaissance Profile of a regular SR-71 sortie with the specific altitudes flown.

http://www.sr-71.org/blackbird/diagrams ... rofile.php

Here I have a sketch off the cone system:






And chornedsnorkack , I don't think your question is properly defined. L/D is associated with angle of attack. Generally speaking, L/D increases with angle of attack up to stalling angle of attack. The maximum L/D will be reached around of the beginning of stall. However, the conclusion is based on the condition that flight speed is less than sound.

Super-sonic flight is dramatically different from sub-sonic. According to 2-D linear classic aerodynamic theory, except for additional drag, the thickness and curvature don't generate lift in supersonic flowfields. This is totally different from sub-sonic. This is why all supersonic aircraft are thin and sharp, especially for the wing. Only angle of attack can create lift. One thin flat plate is a perfect supersonic shape.

For supersonic flight, actual flight angle of attack is very small. The aerodynamic loads (both drag and lift) sharply increase due to shock wave and because the load is proposional to (speed)^2. Very little angle of attack can provide enough lift to overcome the gravity. In supersonic flight, lift is not a demand. To overcome drag is every thing, very very important.

For supersonic flight, L/D is not important. The reasons are (1) design theory is totally different from subsonic. The major thing is to reduce drag D with proper pay-volume. (2) L/D will increase with angle of attack. Supersonic aircraft will never reach the stall/flow separation angle, value of which is significantly higher than subsonic (about 12 degrees for subsonic). Before reach that angle, the aircraft would have already been structurely destoried by too much number of gravity.

[chornedsnorkack]

hi again
For supersonic flight, actual flight angle of attack is very small. The aerodynamic loads (both drag and lift) sharply increase due to shock wave and because the load is proposional to (speed)^2. Very little angle of attack can provide enough lift to overcome the gravity. In supersonic flight, lift is not a demand. To overcome drag is every thing, very very important.

Er, perhaps at low supersonic flight.

At every speed under Mach 25, some lift is needed to carry a part of the aircraft weight, and at lower speeds the most part of the weight.

All aerodynamic loads decrease with the air density. No matter how fast the plane flies, below Mach 25 it is possible to climb to the altitude where the thin air will not support the aircraft weight, no matter what the angle of attack.

You must keep the lift. It would be easy to decreast the drag by making the wings shorter, or thinner and narrower, to the point of having no wings at all, or by decreasing the angle of attack to zero. But those things cost lift, obviously. Which is needed below Mach 25.

For supersonic flight, L/D is not important. The reasons are (1) design theory is totally different from subsonic. The major thing is to reduce drag D with proper pay-volume. (2) L/D will increase with angle of attack. Supersonic aircraft will never reach the stall/flow separation angle, value of which is significantly higher than subsonic (about 12 degrees for subsonic). Before reach that angle, the aircraft would have already been structurely destoried by too much number of gravity.

If you are flying in sufficiently thin air, you will find that it is impossible to pull +1 g no matter how great the angle of attitude. Obviously, it has to be possible to reach stall angle without structural failure in a craft flying supersonic in sufficiently thin air.

[smokejumper]

The SR-71 actually (just like the Concorde) grew in length when it heated up in flight. I believe that the SR-71 actually lengthened about 0.5 meters (18 inches) in length, while the Concorde elongated about 0.2 meters (6 inches) - at least that's what I recall. When fueled on the ground, the SR-71 actually leaked fuel onto the tarmac; once it took off, the plane topped off its tanks from a RC-135Q and then accelerated to Mach 3 where it lengthened and the tanks properly sealed.

The RC-135Q was a modified RC-135 that was only used to refuel the SR-71. The fuel was a special high boiling point, very low volatility fuel (remember that standard JP-4 will boil off at low pressure or high altitude), that was difficult to ignite. I remember once that an engineer threw a lighted match into a standing pool of this fuel. In the mid-1960's, I worked for Mobil Oil. We manufactured a special fuel (521C) that was delivered solely to Pratt and Whitney and the Air Force. It was assumed that it was for the SR-71 engines, although no one really knew.