SR-71 Pilot's Operating Handbook

X-Plane SR-71 model by Anthony Booher & Austin Meyer

Handbook by Andy Goldstein - last updated for X-Plane 5.39

Blackbird. Habu. The sled. Call it what you like, the SR-71 is one of the
most extreme aircraft that has ever flown. 40 years after its conception,
it is still the highest and fastest flying jet aircraft ever built. It
stands as one of the proudest achievements of the Lockheed Advanced
Development Facility, the "Skunk Works", headed by Kelly Johnson.


A Brief History

As the cold war settled in after the conclusion of World War II, the United
States government realized that it desperately needed better intelligence
on the military capabilities and activities of the Soviet Union. Most of
the available material had been captured from the Germans and was rapidly
becoming obsolete. Initial aerial reconnaissance attempts with conventional
aircraft brought immediate protests from the Soviets. Furthermore, it was
clear that the rapidly growing Soviet air defenses would soon make such
activities impossible.

The U-2 (also developed by Kelly Johnson) was the first answer to this
problem. Basically a sailplane with a big jet engine, the U-2 was designed
to fly at altitudes above 70,000 feet, where it was believed to be
invisible to Soviet eyes and radar, and invulnerable to their air defenses.
The U-2's very first flight in 1956 refuted the first half of this belief.
Fortunately, the latter half held, but it would only be a matter of time
before the Soviets developed missiles with sufficient range to shoot down a
U-2. This happened on May 1, 1960, ending U-2 overflights of the Soviet
Union.

The CIA and Air Force began to entertain proposals for a U-2 replacement in
the late 1950s. One of these, the A-12, was given a formal go-ahead in
January of 1960. The first A-12 flew on April 26, 1962. Various
configurations of the A-12 were tested not only as a reconnaissance plane
but as a long range, high altitude interceptor. In 1962 the Air Force
ordered its own version of the aircraft for intelligence and ground strike
missions. This model added a second crew member to offload the severely
overworked single pilot of the A-12. Legend has it that it was accidentally
dubbed the SR-71 by President Lyndon Johnson when he announced it in 1964.
(It was supposed to be called the R/S-71.) Rather than embarrass the
president, the Air Force let the name stick.

The SR-71 and A-12 flew numerous missions over North Vietnam, North Korea,
and elsewhere during the mid to late 1960s. Although numerous missiles were
fired at them, none was ever shot down. Only once was one hit by a missile
fragment, with no serious consequences.

The SR-71 is now retired, since its function has been largely taken over by
satellites. Now and again it is pulled out of mothballs for special
missions. We can never be too sure.


Design

The SR-71 bears the classic single-mindedness of Kelly Johnson's aircraft.
Every aspect of its design is directed to flying high and fast, or to the
consequences. Flying at Mach 3 generates a tremendous amount of heat. The
skin of the plane heats up to over 500 degrees F. Pilots could warm
sandwiches by holding them up to the windshield for a short time.

Because of the high heat, every aspect if the plane's design is unusual.
Special lubricants had to be used. The fuel is JP-7, specially formulated
for the SR-71 to have a high flash point but still be usable at high
altitude subsonic flight. A lit match, dropped into a bucket of JP-7, will
go out. The fuel is circulated throughout the plane to cool critical
components and the plane's skin, then is used as hydraulic fluid, and
finally is fed to the engines. The main landing gear retracts into recesses
surrounded by the fuel tanks and the tires are impregnated with aluminum
powder to reflect the heat.

Aluminum fails at such high temperatures. Almost the entire plane is built
of titanium. Ironically, much of this was quietly purchased from the Soviet
Union. All new fabrication techniques had to be developed to deal with the
finicky metal. The wing surfaces are corrugated to prevent warping from
thermal expansion. No sealer could be found that would withstand the heat,
so the fuel tanks are unlined. When the plane is cold, fuel leaks out of
the tanks because all the joints are loose.

The SR-71's fuselage has a pair of chines that run from the nose back to
the wings. At supersonic speeds, the chines provide a substantial fraction
of the plane's lift. In addition, their shape reflects radar signals away
from their source. Between the shape of the plane and considerable use of
radar absorbent materials, the SR-71 was in fact the first example of
stealth technology.

Two J-58 engines power the SR-71. Their design is as unusual as the rest of
the plane. Unlike most fighter engines, they are designed for continuous
afterburner operation at Mach 3. At supersonic speeds, the cones in the
engine intakes create a shock wave that compresses the air as it enters the
engines. The cones can move fore and aft about two feet, and are
automatically adjusted to keep the shock wave just inside the lip of the
engine intakes. A delicately balanced series of shock wave reflections
decelerate and further compress the air until it reaches the compressor
face at subsonic velocity. A series of bypass doors allows airflow into and
around the engine to augment intake air at low speeds and to offload the
compressor at high speeds. The bypass air makes the engine function as a
ramjet, and provides 80% of its thrust at cruise speed and altitude.

A small supply of special fuel, Triethylborene (TEB), is used to light the
afterburners. A shot of TEB raises the temperature in the afterburner to
3000 degrees, which in turn lights the JP-7. The SR-71 carries enough TEB
to light the burners 15 times.

Like the rest of the SR-71, the engines were designed to operate under
extreme conditions. Compare the J-58 to another engine of its time:

                   J-75         J58

 Mach number       2.0          3.2
                   (15 min)     (continuous)

 Altitude          55,000 ft    100,000 ft

 Compressor        250 F       800 F
 inlet temp.

 Turbine inlet     1750 F      2000 F
 temp.             (takeoff)

                   1550 F
                   (cruise)

 Exhaust gas                    3200 F
 temp.

During operation, thermal expansion causes the engines to become 2 1/2
inches wider and 6 inches longer than their cold dimensions.

Alignment of the intake cones is critical. Any perturbation of the intake
flow can result in shock waves or supersonic flow reaching the compressor
face. This causes the shock wave to be expelled, resulting in what is known
as an "unstart". Normal airflow into the engine stops and the engine
abruptly loses thrust. If fuel flow is not immediately cut back, the engine
will rapidly overheat. SR-71 pilots compare the sudden, violent yaw caused
by an unstart to being hit on the side of the head with a baseball bat.


Flying the SR-71

          Note well! The following specifications and procedures apply to
          the X-Plane SR-71 model. Any similarity to the real thing is
          coincidental but greatly hoped for.

The SR-71 is not a "turn 'n burn" fighter. If the F-16 is a Porsche, then
the SR-71 is a top fuel dragster. High, fast, and straight ahead are its
forte. Careless handling at high speed can put you into a spin or tumble
from which recovery is extremely difficult.

At supersonic speeds, angle of attack is limited by the engine intake
cones. Excessive AOA displaces the intake shock wave and risks an unstart.
At cruising speed and altitude, the SR-71's turning radius is about 90
miles. At low altitude and low speeds, its delta wing allows very high
angles of attack. However, there are no flaps or speedbrakes. Careful
planning ahead is always called for.


Specifications and Limits

 Vso    174

 Vs     174

 Vfe    n/a

 Vr     175

 Vto    210

 Vat    190

 Vno    550

 Vne    920

 Mmo    3.2
        (cooled)

 Mmo    2.7
        (uncooled)

 Gpos   7.5 (cold)

 Gneg   3.7

 Gpos   2.8 (hot)

 Gneg   1.7

Maximum Mach number is determined primarily by heat. Fuel cools the wings
and underside of the fuselage. As the fuel tanks drain, they are
pressurized with nitrogen to cool the upper surfaces. If you run out of
nitrogen, the Mach limit drops to 2.7 to avoid overheating.

The 500+ degree heat significantly weakens the titanium structure of the
SR-71, so the G limits are accordingly reduced when the plane is hot.
Breaking the sound barrier at low altitude causes a +4/-2.5G bump, so you
can only so this when the plane is cold. It is safe to break the sound
barrier above 35,000 feet, where there is no bump.


Takeoff Procedure

The SR-71 is not an efficient fuel transport; it is much better to let a
KC-135 do the heavy lifting. Standard operating procedure is to take off
with the minimum necessary fuel, climb to 35,000 feet, and there take on
the fuel necessary for the mission. In real life, before takeoff the SR-71
is fueled with 40,000 lbs of JP-7. There is an extensive runup for each
engine. Between that and leakage, by the time you're ready for takeoff
there's about 6,000 lbs left. X-Plane doesn't model any of this, so just
set the initial fuel load to 6,000 lbs.

There are no flaps. When you're ready, run the engines up to 100%, let the
brakes go and hit the afterburner. Rotate at 175 kt and lift off at 210.
Remember to check for positive climb rate before retracting landing gear!
The SR-71 takes off at a high AOA and has a long nose, so just rotating
lifts you well off the ground.

Stay in a shallow climb to build airspeed, and then pull up to climb at an
indicated 350 kt. Throttle back to level off at 35,000 feet with 250 ktias.
This is where you rendezvous with the tanker. Since X-Plane doesn't model
air to air refueling, just go into the weights and fuel panel and set your
fuel to the amount you need. Note that at maximum weight, you will need
100% N1 (but not afterburner) to hold level flight at 250 kt.


High Altitude Cruise

Once you've refueled, you're ready for high altitude high speed flight.
Engage afterburners and put the plane into a shallow dive. Gently pull out
at Mach 1.2 and start climbing. Maintain 550 ktias until you reach Mach
3.2, then maintain Mach 3.2 until you reach cruising altitude. Make any
significant turns you need to make before climbing. Once you're at
altitude, your turning ability is very limited. At cruise speed and
altitude, the SR-71 has a lot of inertia and only a tenuous grip on the
thin air. Keep a very light touch on the stick and avoid rapid changes in
attitude.

The SR-71 was designed to cruise at Mach 3.2. In real life, excessive heat
is the main limiting factor. Under favorable conditions it can fly as fast
as Mach 3.6, but the risk of unstarts increases. In the X-Plane model, the
engine Mach limit has been set to limit the plane to Mach 3.2.

Maximum level cruise altitude is limited by angle of attack. A 7.5 degree
AOA is considered a safe cruise setting and allows headroom for modest
turbulence and gentle maneuvers. The following table shows cruise altitude
and indicated airspeed at various weights for a 7.5 degree AOA.

 Fuel    Total     KTIAS  Altitude  Fuel Consumption
                                    (approximate)

 80,000  140,000   360    78,700    40,000 lb/hr

 60,000  120,000   335    81,800

 40,000  100,000   303    86,500

 20,000  80,000    275    90,700

 2,000   62,000    238    97,500    20,000 lb/hr

Once you've trimmed the SR-71 for level flight at the proper altitude,
simply let it go and keep an eye on the artificial horizon. The plane will
rise on its own as it gets lighter. The SR-71 can fly higher, but at a
higher AOA that raises the risk of an unstart. Since X-Plane doesn't model
unstarts, you're on the honor system.


The Lob

The SR-71 can fly considerably higher than its level flight limit by flying
in a semi-ballistic arc. Any significant vertical component to its Mach 3.2
speed gives you a considerable amount of upward momentum. This is a good
technique for flying over small areas of heavily defended territory.

The trick to flying a lob is maintaining the correct angle of attack. Watch
the AOA meter carefully through this maneuver. Start in level flight at
60,000 feet at full power with afterburner. Once you've accelerated to Mach
3.2, gently pull up to a 25-30 degree nose up attitude. As you climb,
adjust elevator trim to maintain the 25-30 degree attitude until your AOA
reaches 7.5 degrees. From here on, maintain the 7.5 degree AOA and let the
plane fly the arc. Watch the AOA as you descend. Without occasional nose
down adjustments it will tend to increase as the plane pulls out of the
dive. With a 40,000 lb fuel load you'll peak at about 115,000 feet and
cover somewhat more than 100 miles before you level out.


Landing Procedure

As you approach your destination, throttle the engines back to idle and
descend, maintaining 250 ktias. You'll cover about 200 miles descending
from cruise altitude, and consume about 2000 lb of fuel. Maximum landing
weight is 62,000 lbs. There are no flaps or speedbrakes. Once again,
careful planning ahead is called for.

There's an apocryphal story about an SR-71 re-entering US airspace after a
mission. The pilot contacts ATC and requests clearance to 80,000 feet:

ATC: "It's all yours if you can get there."

Pilot: "Roger. Descending to 80,000."

The SR-71's poor forward visibility makes landings hard. The windshield
center strut would normally completely block your view of the runway all
the way down. In the X-Plane model, the strut has been offset to the right
to simulate the pilot leaning slightly to the left. For reference, the left
edge of the upper artificial horizon is on the plane's center line.

Pick up the localizer about 10 miles out, intercept glideslope and throttle
back to decelerate. Watch the AOA meter - when it reaches 11-12 degrees
it's time to throttle up to maintain airspeed and glideslope. Do not exceed
12 degrees AOA. Your airspeed should be 190-200 kt as you cross the
threshold. Flare it at 185 and gently touch down. Don't bang it down - the
gear and fuselage won't take it. Never let your airspeed drop below 185, or
you'll drag the tail on touchdown due to excessive AOA. (Remember these
airspeed numbers apply to a 62,000 lb landing weight. Try to land a heavier
plane this slow and it will fall like a stone!) After touchdown, hold your
attitude to slow the plane until the nose drops by itself. When the nose
gear is on the ground, pop the drag chute, followed by the brakes.

Even with the offset center strut, forward visibility with the 12 degree
AOA is pretty bad. Switching to the 5 or 10 degree down view helps a lot
but may get you slightly disoriented. The radar altimeter can be a big
help. Set its threshold for 20-30 feet. When you get the "Minimum" warning,
it's time to flare for touchdown. Parallel runways or taxiways are also
helpful visual cues.


Disclaimer

The author is not a pilot and has never even been near an SR-71. All
material in this POH is from various unclassified sources - magazine
articles and books, web sites, and some personal contacts. If you would
like to make corrections or additions to this POH and don't fear visits
from men in trench coats, feel free to contact me at
Andy.Goldstein@compaq.com.


Bibliography

Mach 1 and Beyond, Larry Reithmaier, McGraw-Hill, 1995

Lockheed Skunkworks, Jay Miller, Milton Publishing LTD, 1995

"Blackbird", Flight Journal, Feb. 2000

"The Oxcart Cometh", Smithsonian Air & Space, March 1999

"J-58/SR-71 Propulsion or the Great Adventure into the Technical Unknown",
William H. Brown, Pratt & Whitney, presented 5/18/1981 at American
Institute of Aeronautics, Long Beach, CA.

http://www.fas.org

Numerous web pages. Go find 'em with Northern Light
(http://www.northernlight.com)

"Supersonics: Just Jets, All Audio" - interview with Roger Smith, NASA
pilot, Aircraft Records, 1999
