In June 1963, Popular Mechanics took a closer look at the controversial B-70 supersonic bomber. Two years prior, President John F. Kennedy cancelled the program due to its perceived inability to penetrate enemy air defenses, like the Soviet Union’s SA-2 Guideline surface-to-air missiles. Instead, the platform transformed into a test bed for supersonic flight as the XB-70A Valkyrie, which created a lot of useful data regarding Mach 3 flight.
The big jump in aviation—from the present to the future—takes place this summer with the testing of America’s newest, fastest, costliest bomber.
The B-70 (actually the XB-70 for “experimental bomber”) is a weird-looking airplane unlike any that ever flew before. More sophisticated than a space capsule, it is designed for effective operation in the searing temperatures of 2000 miles per hour.
And it was, long before its first flight, a controversy.
Its critics say we don’t need bombers any more, that the ICBMs have taken over and, besides, the B-70 is old-fashioned even as an airplane. Counter-punching, its advocates inquire when are intercontinental missiles going to have a bomber’s reliability?
Besides, they say, there’s no guarantee that a next war would be one of nuclear suicide. They say there are non-nuclear weapons that can be “delivered” cheaper by bomber than by rocket. As for the B-70 being out of date, this can be said of any aircraft by the time it is built; research certainly hasn’t stood still since the B-70 design was finalized.
One side says that a single ground-to-air missile can kill a B-70, the other side talks of new electronic counter-measures that would divert or kill the anti-aircraft missile.
Depending on who wins, only three prototype B-70s may be built.
One thing is sure. The B-70 is the big jump, the big breakthrough, that allows aviation engineers to talk positively of supersonic passenger transports. All the major problems of 90-minute coast-to-coast air travel have been or are being solved in the B-70 program—how to insulate passengers and crew so they won’t incinerate from aerodynamic heating, how to keep the landing tires from cooking, the windshield from melting, the fuel tanks from exploding. The research that went into the B-70 provides the answers to all these questions.
Even such a “minor” question as whether a pilot can land his craft safely is being solved. (Due to the 180 feet or so of fuselage and the nose-high landing attitude required by the delta wing, the pilot in the cockpit is still 40 or 50 feet in the air at the time his main gear contacts the runway).
The B-70 has a delta wing and a long fuselage projecting forward from the wing, with two small “canard” control surfaces just aft of the cockpit. The plane is about 180 feet long and its wing is about 125 feet wide. (Pinpointed dimensions were secret when this was written.) Its wing tips can fold down for greater efficiency when flying supersonic in the thin air of 70,000 feet. It lands at about the same speed as today’s jet fighters. Its crew works in a shirt-sleeve environment of 85 or 90 degrees, some 15 degrees warmer than would be agreeable in a passenger transport. It was built by North American Aviation for the U.S. Air Force.
The prototype is powered with six General Electric J-93 afterburning turbojets that were designed as part of the B-70 project. Each engine develops in excess of 30,000 pounds of thrust. The engines have air-inlet ducts of variable geometry, and the shape of the ducts can be changed at high altitude to compress the thin air better. This reduces the amount of power needed to drive each engine’s compressor. The turbine blades are of a new steel alloy and can operate at higher, more-efficient temperatures than previously were practical.
The B-70 has been called a “steel airplane,” and so it is to a considerable degree. A new technology was developed especially for this program, for manufacturing stainless-steel honeycomb from thin-gauge material. The honeycomb is used in wing surfaces and other areas where aerodynamic heating is greatest. Even thick aluminum sheets would lose strength at the speeds the B-70 is designed to fly. Some structural members that require high strength and light weight are of titanium. Aluminum is used in areas not subject to high temperatures.
Across-the-board developments required for the B-70 include high-temperature tires that withstand 360-degree temperatures for four hours, an electrical system (including motors and generators) that operates in temperatures approaching 600 degrees, and a 4000-p.s.i. hydraulic system using a high-temperature fluid and permanent, brazed fittings.
More than 14,000 hours of study in more than a dozen high-speed and lowspeed wind tunnels have been devoted to the B-70 project. It was from these studies that the canard-delta planform was selected as being the best for the B-70’s purposes, yet this unconventional canard-delta shape was found to have inherent problems that called for still more wind-tunnel time.
One such problem was the loss of stability that occurs at low speed and at the high angles of attack required at landing or take-off. In these nose-high attitudes, the nose and the canard surfaces create air vortexes that flow back and envelop the vertical stabilizers, reducing or eliminating their steadying effect and thus reducing pilot control. The best solution has been to increase the size of these vertical tails and to locate them where they are least affected by the unstable air.
No one could afford to test fly an aircraft like this one without knowing ahead of time how it is going to handle, how best to control it. Flight simulators have been built by National Aeronautics and Space Administration for this purpose, for working out the best pilot procedures under both normal and emergency conditions. NASA did the basic research for the B-70 and is now doing the same for the SST (supersonic transport) which NASA is now beginning to call the SCAT (supersonic commercial air transport.)
One of NASA’s simulators is a typical cockpit for the pilot, in front of which is a motion picture screen showing the image of the threshold and runway lights of an airport. The lighted picture changes in angle and attitude according to the way the pilot handles his controls, just as it would during an actual landing.
Another simulator, a cage that rides up and down the side of a building like an elevator, is used for testing a pilot’s ability to make smooth landings while his cockpit is still many feet above the surface of the runway.
Another research device, called a five-degrees-of-freedom simulator, resembles a big centrifuge. The pilot’s cage, or cockpit, can move up or down, yaw, rotate and perform all the motions of flight. The flight characteristics of the design that is being studied are cranked into the centrifuge by a computer and the pilot then simulates an actual flight.
With this device the best flight profiles are worked out ahead of time, including the angle of climb-out and its length of time, the most efficient altitude at which to boost to supersonic speed and how to handle emergency situations. A typical emergency concerns the violent yaw that would occur when supersonic if an outboard engine should fail. The reason the B-70’s engines are clustered close to the airplane’s centerline is to minimize the effects of an engine-out.
As with the B-70, there is real controversy on whether the U.S. wants a Mach-3 airliner or can afford it. Why not settle for a Mach-2 machine, as the French and British are reported to be doing, with some U.S. assistance?
True, it’s easier to build a 1400-mph craft than one that travels 2000 m.p.h. The slower craft can be built of aluminum and with standard techniques. But the word “aluminum” tells the story. The speed limit of this very popular metal is just about Mach 2.4. Above that velocity it loses much of its strength from the heat of speed. Thus it has no “growth potential.” It’s a dead end.
U.S. aerodynamicists argue, “Now that the B-70 is showing the way, it’s silly not to make use of it. We can leapfrog direct to a Mach-3 airliner and still have a potential for even faster transports if we ever need them.”
Setting our sights on Mach -3 will be tremendously expensive. Development of the triple-sonic airliner may run to a billion dollars for the first one and perhaps $20,000,000 a copy, after the billion is spent in research.
To operate economically, an airline might have to charge $1000 or $2500 for a round-trip across-the-country flight. The planes would fly empty.
The Federal Aviation Agency is studying this. In a report due late this month it probably will say: 1) Yes, national prestige demands that we build Mach-3. airliners even though their cost can’t be justified on economic grounds, and 2) Uncle Sam will have to pick up most of the check for a commercial transport.
Parallel to the FAA study, NASA is conducting a feasibility study of four proposed planforms for SCAT. One is a canard-delta comparable to the B-70, one a tailless delta with no canard, another a delta with a separate tail aft of the wing, while the fourth has a variable-angle wing that sweeps forward to about the same configuration as present jet transports for subsonic operation, then folds back into delta shape for faster-than-sound flight.
NASA has asked two aircraft companies to evaluate the designs from the standpoint of relative costs, relative weights. This information, due back in November, will guide NASA in deciding into which of the four designs its research efforts should best be put. There is still a long way to go: NASA also is studying rudders of various size, variously twisted and warped wings for highest aerodynamic efficiency, engines in separate pods and, in one version, folding wingtips similar to those of the B-70. One spokesman says the final design for SCAT could be started two years from now. On that basis, it could be flying in 1970.
Apparently noise is going to be an unavoidable accompaniment to the supersonic era. With all its afterburners turned on, the B-70 will make an ear-shattering roar on take-off and climb-out. Even at altitude its supersonic boom will startle people on the ground. But the engineers are saying that the supersonic airliners won’t be as bad, that they won’t use afterburners or even duct burning, that their noise at take-off will be no greater than our present jet transports.
Today, NASA is studying the effect of supersonic overpressures on nearby aircraft in flight. What this means is: “Will a sonic boom created by one aircraft hurt another airplane that is nearby?” It is said that an adjacent airplane will receive only a slight bump, nothing serious.
Military or civilian, any aircraft traveling faster than Mach-1 creates a shock wave, a sonic boom. Can anything be done to minimize this nerve-shattering noise? So far the answer is nothing.
Once upon a time, piston-engine aircraft used to cart us across the country in eight hours, plus. Then, a short five years ago, the jets chopped this time to five hours, or less. That was really travel – ing, it seemed at first, but now experienced air travelers are becoming bored with the tedium of the five-hour ride. They can hardly wait to go supersonic!