Already in 1951, a mere half decade after Chuck Yeager first broke the sound barrier in his Bell X-1, the world was gearing up for the new reality of supersonic warfare. Air superiority as a significant tactical advantage on the battlefield was well-established during World War II, itself only half a decade in the past at the time this article in a 1951 edition of Air Trails. The learning curve was steep but the progress fast on how to build and fly aircraft operating beyond Mach 1. Crazy phenomena like aileron control reversal came as a surprise to engineers and pilots on the bleeding edge of that technology, and were major issues that need to be dealt with and mitigate. Here is a wee bit of early history on the supersonic warplane development.
By R. G. Naugle
We have a new breed of fighters coming out - and going up - supersonic interceptors! These fast-climbing, sky-rocketing meteorites will flash through the midnight sky in short bursts of supersonic speed to slash and tear at high-flying enemy bombers. Fleets of reserve craft will stand by on the alert, crouching on airport ramps ready to scream off in near-vertical climbs.
The U.S. is developing a new breed of interceptor to deal with high-flying enemy bombers that may try to attack American cities.
We've never had interceptors before. They're purely defensive weapons and we've never needed them. We've always carried the fight to the enemy's homeland with bombers and general-purpose fighters modified to do the particular job. Some carried drop tanks and escorted bombers over long distances, and then fought off the enemy's defending interceptors over the target. Others, operating by themselves, carried a small arsenal of rocket projectiles, cannon and guns on tactical strikes to break up the enemy's ground defenses, transportation and communication systems.
We still need such fighters - penetration fighters, as they are now called. But modern war, like modern football, requires two teams, offensive and defensive. One team to score on the enemy, another to prevent him from scoring on you. We must still have penetration fighters, but we now need and will soon build a huge fleet of East, goal-line defending supersonic interceptors to prevent enemy touchdowns on the North American continent.
Speed and ceiling of bombers now equal those of fighters since both, in the practical sense, are held back by the sonic barrier. For example, the F-86 and B-47 are not only similar in general design but both have about the same top speed and maximum altitude capabilities. Both fighter and bomber can now closely approach the speed of sound with their thin sweptback wings and jet power, and both can achieve stratospheric altitudes undreamed of during World War II. And herein lies the rub - for fighters must chase, catch and shoot down bombers.
This means we must have supersonic interceptors, for not only must they fly faster than the speed of sound to overtake fast modern bombers, but they must also do so in order to regain their maneuverability at extreme altitudes! This is not generally appreciated. But a simple chart shows it quite clearly.
It is the chart of speed versus altitude that positively defines the limits any subsonic airplane must fly within. We know that an airplane must fly so fast to stay in the air - the normal low-speed stall. On the other hand, a subsonic airplane cannot fly faster than its critical Mach number - some fraction of the speed of sound. "Buffeting" occurs in both cases, a breakdown of airflow over the wings and the sudden loss of lift. Therefore these limiting speeds are called the "buffet boundaries." If these speeds remained the same at all altitudes a plane could fly as fast and have the same maneuverability at high altitudes as it does near the ground. But they do not remain the same.
The stalling speed tends to increase with altitude while the critical Mach speed tends to decrease with altitude - thus squeezing the flyable speed range together until, at some altitude, the stalling speed equals the critical Mach speed. The altitude at which this occurs is sometimes called the "altitude barrier" since an airplane cannot fly any higher than this. The airframe as a heavier-than-air machine can no longer support itself in the air and fly as an airplane above this point. Power is not a factor. While considerable power is required for a plane to approach its altitude barrier, more power will not allow it to go any higher.
We see immediately how maneuverability is affected. The speed range at any altitude - that is, the gap between the stalling speed and the critical Mach speed - defines the maneuverability, the tightness of turns, the number of G's that can be pulled in maneuvers; and it is maneuverability that counts in fighter attacks. This then is the graphic picture all subsonic aircraft are confronted with, and we can see pictorially how both the B-36 and the B-47 baffle fighters.
The B-47 rides along the critical Mach speed line and challenges any subsonic fighter to catch him. The B-36 flies slower - but it goes higher, up into the corner near the altitude barrier and sits there - forcing the fighter to come on up and fight him on his own terms. The B-36's maneuverability is gone, but what is more important, so is that of the attacking fighter. Only if the fighter can fly at supersonic speed can he catch the fast B-47 type bomber; only if he flies supersonic can he increase his speed-range and regain his maneuverability at extreme altitudes to attack B-36 type bombers.
The present-day interceptor, like the F-94C shown here, is only a stepping stone toward the full-fledged bomber-killer, agile at stratospheric heights and deadly with its rockets and electronic sights.
Let's see how this picture looked to Group Captain "Car's Eves" John Cunningham, Chief Test Pilot of the de Havilland Aircraft Co. of England, when he set his world's altitude record of 59,492 ft. in a specially modified stripped-down Ghost-powered de Havilland Vampire. (Each wing-tip had 8 ft. extensions.) At 59,000 ft. he could only fly at speeds between 125 mph indicated (about 400 mph true) and 150 mph indicated (about 465 mph true). If he flew slower than 125 indicated, he'd stall. If he flew faster than 150 indicated, he'd exceed his critical Mach number. He was sitting close to his altitude barrier and didn't have quite enough power to reach it - where theoretically, he could fly at only one speed. As it was, he could only pull a theoretical 1.4 G maneuver, a gentle turn. The slightest over-control would cause him to stall out.
Cunningham couldn't possibly have fought that day. Had a bomber been sitting at 59,000 ft., Cunningham himself would have been shot down from the more stable gun-platform on the bomber, able to train its guns on him at will. For we must remember that up to now fighters must point to where they shoot - and this means maneuvering.
This instance then, shows why interceptors, the goal-line defenders of our cities, must be supersonic craft. For when they smash through the sonic barrier, they not only smash through the altitude barrier as well, but regain their original low altitude maneuverability. They can thus successfully chase, catch and attack the bomber and force him to fight his way through to the target.
Our "90" series of penetration fighters approach in performance what interceptors must do. The sweptwing Lockheed F-90, for example, with, afterburner added to its two Westinghouse 3,000 lb. axial-flow J-34 engines, is reported to be able to fly supersonically and to get upstairs - probably within 5 minutes. This 13-ton goliath was designed for penetrating enemy lines and has the built-in range to escort bombers. However, with less fuel, it can skyrocket to altitude at fantastic speeds. The only ready-to-go interceptor we now have is the straight-wing Lockheed F-94-similar in appearance to the two-seat TF-80C trainer. The nose is extended to pack in the required radar gear and an afterburner is added to the J-33 engine to shoot it into the stratosphere in a matter of minutes. However, it is distinctly a subsonic airplane and is intended only as an interim model until true interceptors can be made available.
Another modified service type is North American's sweptwing F-93A - a modified F-86 with a Pratt· & Whitney J-48 engine and afterburner installed. Flush inlets on the side of the fuselage leave the nose section clear for radar equipment. The '93 therefore vies with the F-94' as an interim interceptor, but only the prototype is in existence at the present time.
Several of the "80" fighter model experimental series could also be used as interceptors. These are the huge 13-ton giants designed specifically as penetration fighters - fast long-range fighters for penetration into the enemy's homeland for either bomber escort or tactical operations against ground defenses. McDonnell's sweptwing Voodoo F-88 is a rip-roaring fast-climbing meteor powered with two Westinghouse J-34-W-34 engines. The second prototype and production models will have afterburners installed, boosting its already impressive performance considerably. The F-88 is a companion design to Lockheed's F-90.
Chart of Indicated Airspeed (AIS) versus Altitude for various Mach numbers.
Northrup's straight-wing F-89 Scorpion, while originally designed as an all-weather fighter, carries two jets with afterburners and is equipped with the necessary radar equipment to spot and chase high-altitude bombers. Its rate of climb with afterburners undoubtedly places it within the required 5 minutes to 40,000 ft. category. It is already in production and being delivered to the Air Force.
We see then that only those fighters with afterburners can be classed as interceptors. True interceptors, now on the drawing boards, will probably have rocket motors added as auxiliary sources of power, since their power is unaffected by altitude. Jet engines, you remember, lose all their thrust at about 67,000 ft., and at 50,000 ft. have only about a fifth of their sea-level thrust. That isn't good enough.
The Navy has several fighters with the performance to be classed as interim interceptors against B-29 type bombers. The Chance-Vought twin jet F7U-1 Cutlass with afterburners is a standout contender since, like all carrier borne craft, the wing loading is moderate, allowing better maneuverability at altitude. McDonnell's twin jet Banshee is another fighter with better than average high-altitude performance. However, it is not sweptwing and is without afterburners-both requirements for high-performance interceptors. It too has a low wing loading and excellent performance at the 40,000 ft. level.
The true nature of the interceptor emerges. It will have a great amount of electronic and radar gear aboard, it must be supersonic, it will probably make its attack from the rear since several attacks can be made, and it will use small supersonic rocket missiles - probably with target-seeking devices and proximity fuses. They will outrange the enemy bomber's rear turret cannons.
Such rockets were used briefly at the very end of the last war. The Germans had their R.4/M supersonic rocket missiles. They were unguided, weighed 7 3/4 lbs. when fired, carried 1.1 lbs. of warhead, and had a maximum velocity of 1,800 ft. per sec. - Mach 2.0 or 1230 mph. Used only during the very last days of the war, six experimental Me-262's each equipped with 48 such missiles once hit a raiding party of B-17E's, destroyed fourteen and returned to base without a single loss. That's the kind of interceptor superiority we must have now.
Such an interceptor must hit 40,000 ft. in less than 5 minutes and 50,000 in less than 10. It must be capable of going to at least 60,000 ft. with sufficient maneuverability to turn inside a subsonic bomber. It must have a combat radius of at least 500 miles and carry complete night-fighting radar equipment. It must have auxiliary power-auxiliary rocket motors for rapid climb and supersonic speed at extreme altitude.
And we need them now!
Posted December 7, 2014