• SR-71 Blackbird

    Just Flight SR-71 Blackbird for FS2004

    By Andrew Herd (28 May 2006)

    The Lockheed SR-71 shares the distinction with Concorde of being a plane that looks like it belongs to the future despite being part of the past. In common with the supersonic airliner, the SR-71 looks as if it is doing Mach 2 even when it is sitting on the ground, the difference being that Mach 2 doesn't even represent a fast cruise as far as this most potent of all spy planes is concerned. Only a handful of pilots (known as 'habus' in the Air Force) flew the SR-71 and every one of them marked it as the high point of his career. I guess it isn't surprising in a plane that can fly from New York to London in only a couple of hours.

    The origins of the SR-71 design lie in Lockheed's earlier spyplane, the U-2. Clarence L. 'Kelly' Johnson was the designer and chief architect of both and only three years after the U-2 had flown, he reasoned that effective countermeasures would be developed against it and began work on a replacement. This aircraft would be a radical departure from the already radical principles behind the U-2 and would fly higher and faster than any plane before it. In 1959, Lockheed got approval to go ahead and build five A-12 hulls, as the new design was known, and first flight took place in 1962. A total of 15 were built for a highly secret CIA program code-named OXCART; the pilots selected to fly it having to meet a requirement of 1000 hours in 'century' series fighters and 2000 flying hours in total before they could even begin training. The reason? The A-12 explored the very limits of what was then known about the physics of flight. A couple of hulls were built as ultra-high speed M-21 target drone carriers and a further Blackbird variant, the YF-12, was intended to be a high altitude interceptor, but the idea was shelved due to cost over-runs. The most numerous Blackbird variants was therefore the SR-71, with 29 A series hulls completed, 2 Bs and a single SR-71C - eleven of the As and one of the Bs were lost in crashes, but none due to enemy action, although there were some near misses.

    Some idea of the technical problems that had to be solved before the SR-71 became operational can be gained from looking at the issues surrounding the camera system, a payload which was lay at the heart of putting the plane in the air in the first place. At altitude, the outside air temperature usually hovered around -45 degrees F, but friction in cruise heated the skin around the camera bays to something like 450 degrees F, yet when the plane slowed and descended to refuel, the cameras ran the risk of freezing. There were so many critical systems on the SR-71 that cooling air was at a premium, so the cameras had to make do with being air conditioned by a 200 F draft, which was the coldest air available. Now turn your mind to the technical problems caused by the speed the plane was travelling. The cameras exposed 9 inch frames and the optics had to be able to cope with the fact that the lens was moving at something like 3000 feet per second. The specialised focal plane shutters used took between 0.1125 and 0.225 seconds to expose a frame, during which time the SR-71 would have travelled between 371 and 742 feet. In order to prevent blurred images, the SR-71 had to be fitted with a highly specialised camera mount that moved backward the precise rate needed to cancel the forward motion of the aircraft as each photo was taken - and all of this had to be done with very basic computers and 1960's vintage electronics. Fuel temperature was another issue, as the tanks heated up to around 300 degrees, far beyond the point at which JP-7 vapor is liable to ignite. The solution was to pump nitrogen into the tanks as they emptied and the supply of liquid nitrogen became the limiting factor in the duration of SR-71 operations, given that many missions involved mid-air refuelling on at least one occasion. And the tanks weren't even the hottest part of the plane, the windshield could reach 700 degrees; hot enough for crews to use it to warm up their tube feeds - and some parts of the wings were said to top 3000 F, all of which meant that the length of the plane could increase in flight by up to a foot.

    However, the most famous problem associated with the SR-71 was a phenomenon known as 'unstarts'. This was only a risk after the plane flew supersonic and was caused either by air pressure inside the engine inlets becoming too great, or the 'spike' in front of the intake sliding too far aft. The spike was there to position the supersonic shock wave inside the inlet throat and to slow down the airflow, as turbojets cannot 'breathe' supersonic air and it was programmed to move backwards and forwards according to the aircraft's speed. The spike on its own wasn't enough, so a set of computer controlled bypass doors were fitted around the inlet to dump excess air that tended to pile up at that point, and if either those or the spike lost the plot (to complicate matters, if the spikes weren't in line within 1/10th of an inch with each other, controllability problems were liable to occur), the engine and afterburner would very suddenly flame out. A flame-out is bad enough at normal speeds, but at Mach 3 the effects were compounded by the huge increase in drag associated with the unstarted engine, the resulting yaw and roll being so bad at times that the pilot's head would smack hard against the canopy. On average, unstarts occurred every third flight, but sometimes things would go so badly wrong that the problem would happen again and again - the only solution being to descend and fly subsonic, creating an easy target for enemy fighters. Given that SR-71s frequently flew over hostile territory, this was an ever-present worry for the crews and indeed the writing appeared on the wall in 1986, when six MiG 31s subjected a Blackbird to a sustained missile attack which the crew were lucky to evade. The plane was withdrawn from operations in the early '90s, replaced by satellites.

    One final point of interest was the SR-71's stall, or rather the lack of it. Typically, deltas don't stall, they just 'depart from controlled flight', a feature which was compounded on the Blackbirds by the lack of any high lift devices on the wing, or of a stall warning indicator. Pitch the plane any more than 8 degrees up when it was supersonic and a rapid loss of lift would be followed by a completely uncontrollable pitch up, recovery from which was said to be impossible, the only solution being to eject. Add to this the fact that the planes were sometimes flown at night at altitudes of up to 80000 feet, in a cockpit that wasn't well designed for night flying, and in a hull that didn't approve of being banked beyond 35 degrees, and you have something of a handful.

    The Just Flight SR-71 Blackbird was developed by Pilot's - well known for their Boeing Clipper - and will install on any 1.7 Ghz or better PC, as long as it has at least 512 Mb of RAM, a 64 Mb video card and 300 Mb of hard disk space. The product is supplied in a DVD-style box, which contains a CD, a 20 page set of pilot's notes and a color flyer for other Just Flight Products. In addition to the SR-71, the CD gives you the the opportunity to preview a wide variety of other Just Flight products, as well as giving you the choice of installing 32 bit or lower quality DXT3 textures for the plane.

    Installation is over before you know it has got started, leaving you with a choice of seven different SR-71s, in - as the blurb has it - any color you like, as long as it is black. The choice is between three different 9th reconnaissance wing aircraft, a NASA plane, a hull preserved at Duxford in the UK, and a couple of others. No indication of which model of SR-71 is depicted is given, nor is there any history of any of the planes; which isn't surprising really, given the great secrecy surrounding the project. That appears to be that, as no start group program is created and there are no PDFs hidden in the plane folder. If you can't find the aircraft using the FS2004 aircraft selector, just look under 'Pilot's'.

    A total of seven pages in the manual are dedicated to telling you how to fly the sim, most of which is devoted to explaining the panel, so don't expect too much hand holding when you decide to take to the air. Such information as can be gleaned from the documentation was enough to tell me that takeoffs are possible at gross using as little as 50% throttle and that the approach speed is 250 knots, slowing to 175 for final. Dumping speed in the real SR-71 down was quite an art, by the way, as it lacked flaps and was designed to give the least air resistance possible, so descents had to be planned well in advance and airbrakes and a landing parachute was used, but even then, a landing roll of at least 6000 feet was expected. SR-71 bases had an emergency barrier similar to the ones you see on carriers, just in case of overruns.

    The visual model is about as eye-catching as you can expect an all-black plane to be and has all the usual animations, including an opening cockpit and a braking parachute - as you can see from the shots, it looks fantastic in flight. If you load the plane with more than 50% fuel, it drips out, just like the real ones did. In view of this and the high security surround the project, SR-71s were rarely operated from 'normal' air force bases and if they were, they were parked well away from other aircraft.

    The 2D panel is best described as an FS98/2000 hybrid, but nearer to FS98 than 2000, as you can see from the screenshots. The layout is a compromise between reality and convenience of operation in FS2004 with a large 'navigation display' positioned just to the left of the lower center which definitely wasn't a standard fitment on real Blackbirds. The manual says that Pilot's have included this to make the plane easier for beginners to navigate and this statement sets the flavor of the sim - this is a high speed addon for people who are new to simming. Real SR-71s had a TACAN receiver instead of the navigation display and lacked such a sophisticated autopilot; in fact the panel of a real one was filled with gauges very different to the ones seen in the 2D panel of this simulation, especially because the SR-71 engines were hybrids between a turbojet (below 2000 mph) and a ramjet above that figure. I guess a 'real' layout would send most newbies screaming for the hills, so you can understand Pilot's rationale in making everything as simple as possible to operate. One interesting omission is the periscope which SR-71 pilots used to inspect the fuselage and wings - a feature which would have been fun to use in the sim.

    Experienced simmers are likely to be a little disappointed with the virtual cockpit, which more or less duplicates the layout of the 2D panel, but adds non-functional graphics depicting the autopilot and interphone panels lying below the pilot's right arm, and the UHF translator under his left. Quite a few of the gauges in the main section of the panel are also bitmaps, many of them too blurry to make out properly - and where these sit next to working gauges, the contrast is obvious.

    The flight model is impossible to comment upon, given that there are tantalisingly few accounts of what an SR-71 was like in the air. However, in keeping with Pilot's philosophy of keeping everything simple, the addon is forgiving as far as handling is concerned, as long as you don't try to operate it from a runway less than 10000 feet long. It climbs like a rocket and my standard departure involved firewalling the throttles and pointing the nose at the moon, as you can see in the screenshot above left. One gotcha for newbies is the approach speed, which is fast compared to anything else you are likely to have tried in FS2004, the lack of flaps meaning that the only way to lose speed in a hurry is to raise the nose, which doesn't exactly do wonders for the view ahead, which is limited to begin with, since SR-71 pilots weren't expected to be looking out and flew on instruments pretty much the whole time. Setting up a stabilised approach on the ILS with an acceptable rate of descent and some power on is the only way to be sure of a safe arrival - just make sure that you don't have too much fuel remaining, as the V-speeds will be


    fairly meaningless otherwise. Deploying the braking chute needs judgement, as it won't put in an appearance unless the wheels are rolling and the plane is doing less than 175 knots, as far as I can tell. The big challenge is flying the Blackbird high and fast, because the gap between the stall speed and never exceed speed becomes quite small at extreme altitude and when you consider that even a 1 degree change in pitch at Mach 3 results in a fairly impressive rate of climb or descent, together with an accompanying increase in airspeed, your will learn to become best friends with the autopilot.

    Verdict? From an beginner's point of view, Pilot's have done a good job at making a very complex aircraft simple enough to have fun with. That being said, just about anybody who enjoys the idea of flying high and fast might take a look at this addon, because it offers a rare opportunity to explore the limits of Flight Simulator, without having to suffer any of the hardships that real SR-71 pilots had to go through, like having your head banged on the cockpit side panels by those unstarts. Have fun.

    Andrew Herd
    andy@flightsim.com

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