The North American XB70 Valkyrie

Exploring high altitude flying at supersonic speeds.

This piece is a further treatise on high speed flying and perhaps it is instructive to look at this facet of flight and aerodynamics in conjunction with the XB70 as it explored exactly this area of aviation.

Some while ago, I built a 1/72 scale model of the Valkyrie which was made by Italeri. It was problematic in the sense that the wing sections were difficult to properly assemble and then place onto the fuselage. Large gaps became evident, all of which required filling and finishing and took at good deal of time. Final painting in white took nearly three bottles of acrylic paint and some periods standing in my garage where I keep my “heath robinson” spraying booth. On the plus side, the finished article, which is sizeable, turned out not to be too dreadful with the possible exception of one of the decals which folded itself into a small and irretrievably crumpled mass. The resulting “U S Air Force” insignia isn’t readable past the “For,” which is irksome. Decals will do that if you aren’t careful.

I have written briefly about the history of North American Aircraft in the past and I would direct you to my article on the P51d Mustang for some further detail on the company itself, suffice to say that throughout its ongoing lifespan the company has developed high performance aircraft and gained a considerable reputation for operating at the limits of what is possible in relation to speed and endurance. The XB70 was no exception to this as we will see.

It is the case with all experimental aircraft that the history is longer and more convoluted than one might perceive at first glance. The XB70 started with the 1954 publication of a general operational requirement for an, “Intercontinental Bombardment Weapon System Piloted Bomber.” This jauntily named requirement was intended to replace the B52, then in operation and suggested an operational lifetime of approximately ten years from 1965 to 1975. It turns out that various (unnamed) contractors had collaborated in the conceptual stages for several years before the GOR was issued, however when the requirement was issued, the aircraft it sought was given a project name of “Weapon System 110A.”

Of the initial six contractors who expressed interest in the project, (or who had worked on it before the issue of the GOR- this is not clear), only two decided to present proposals- North American and Boeing. After review, it was decided to allow the further development of WS110A on a research and development basis. This appears to have meant that entry into service of any aircraft was far from certain, but that further pre-contract award works would be necessary from each manufacturer before a contract would be let. Moving forward to December 1957, North American were awarded a contract for phase 1 development, the first operation of which was to produce a full scale mockup of the proposal, although work to complete that was halted in early 1958 as further questions appear to have arisen relating to the configuration of the aircraft which seems to have been occasioned by funding restrictions- a repeated problem in such projects. Notwithstanding that, the original plan was to procure 65 B-70 bombers for the US Air Force- a large number by any measure.

As is almost invariably the case, the requirements for the project continued to change. The phase 1 development was for one “air vehicle,” and a full scale mock up aircraft at a contract value of approximately $74 million dollars (for a period of around one year). This was not an inconsiderable sum even by today’s standards. Later in 1958, North American was approached to build a second aircraft and a corresponding contract was raised for a further $120 million dollars.

What has become known as “mock up” aircraft are often the subject of of some questions. In fact they are most often produced to allow fatigue testing of an airframe and other components, so in effect such a model is a production piece that is not intended to fly. It is useful to study aircraft components on the ground in order to discover as far as possible how resistant they are to the stresses and strains of flight. This is better than the alternative of an aeroplane “mowing along” at mach 2.5 and then suffering an unexpected failure- something which fatigue testing might have discovered.

Simultaneously to the commencement of the mockup build, General Electric made an initial run up of the proposed engine, a J93 unit of which six would be required for each aircraft. Also at about this time, the overall project requirement changed from two to three aircraft in the development prototype series.

The mock-up build was completed on schedule in February 1959, despite the earlier delays. Following this, the usual development inspections were carried out on the aircraft which resulted in some changes taking place. Notable ones amongst them were a shortening of the front fuselage by around thirty inches and changes were made to the fairings on the upper fuselage which resulted in around 16,000 pounds of extra fuel storage- quite a significant change in the latter case. In point of fact, 761 requests for changes were made in the period from February to April 1959.

Things were looking good for the project for a short while, but in October 1959 the funding constraints started to have an impact. The initial requirement for twelve air test vehicles (ordered as “YB-70” in 1960 under plan W27 R), was reduced to ten and then reduced to one single unit and the prototype aircraft set aside for fatigue testing being earmarked as a flying trial aircraft. Much of the ancillary work was continued on the aircraft systems, but the most visible change in the project was the reduction in workforce from 20,000 people to 7,000. In September, an order was issued to redirect the work on the project to the production of 11 YB-70 variants in addition to the single XB-70.

So, work continued throughout 1960 with development on various aspects continuing. The many required technical drawings, (more than 200,000 in fact) were completed, however it was in 1961 that the project was curtailed to a much larger extent. Cost reductions in the defence budget, coupled with the rapid development of guided missile technology were cited in the presidential message delivered in March of that year. In short, longer range missiles with big payloads would be brought into service more quickly, could be deployed more rapidly than manned bombers which would have lower survivability owing to short range anti aircraft guided missiles. The nett result was that, rather than bring the XB70 into service in numbers, the currently planned aircraft would be deployed as a test bed for the development of a bomb navigation radar, which I assume was somewhat similar to the original Canberra “blind bombing radar” device. The project was reduced to three aircraft as a result, perhaps with the underlying thinking that a Mach 3 bomber could still quickly be developed if a need was seen for it.

(I have often wondered why the term “missile” was used at all. A modern day missile is a highly effective and deadly way of dealing with airborne threats and, because of its capability, should perhaps be better named, “hittile.” I’ll get my coat).

Assembly of the first aircraft (XB-70A) began shortly after this along with work addressing further problems with fuel tank sealing which seems to have been an issue from quite early on in the program. This resulted in the development of a polymer sealant specifically to overcome the problem. Other changes were made on the fly in the next three years which included the removal of the additional air intakes which would have improved the ability of the aircraft to fly in poor weather conditions. Doing so further lowered the development cost and was done (I suspect also) because it was not anticipated that an experimental aircraft would fly in anything but good weather conditions.

The final assembly was completed early in 1964 followed by roll out of the first XB70 which took place on 11 May, some three years after the budgetary cut-backs which led to the program reduction. The media attention was significant and some 100 staff members and VIPs from various contractors involved in the project attended the event. The first flight took place around 4 months after this and lasted just over one hour. The planned speed of Mach 1 was not reached owing to a problem with the retraction of the undercarriage and there was a further problem with two tyres bursting on landing, but despite this the aircraft came to a halt without incident.

Between September 1964 and mid 1965 the flight program progressed without too much in the way of difficulty until just after the roll out of XB-70B, the second test aircraft. A structural failure of the starboard wing tip of the XB-70A caused parts of the apex of the wing to enter the air intakes and damaged two of the engines, however landing at Edwards AFB was possible and was accomplished without any real problems. Any landing you can walk away from is a good one. Meanwhile, XB-70B completed its first flight and reached mach 1.4 and an altitude of 46,000 feet.

It looked as if things were proceeding very nicely after the XB-70B completed a 33 minute flight at Mach 3 during a two hour sortie and with much of the rest of that flight completed at over Mach 2, but on 8 June 1966 disaster struck. The XB-70B was travelling in formation with several aircraft (Northrop F5 “Freedom Fighter,” F104 “Starfighter,” F4 “Phantom,” and T38 “Talon”), for publicity photographs for the purpose of promoting the General Electric company who provided engines for all of these aircraft. The five aircraft flew what might be described as a fairly tight formation for around twenty minutes before the Starfighter appears to have started breaking formation. The report states that Joe Walker’s aircraft, for reasons that are not fully understood, moved to a point just underneath the Valkyrie’s Starboard wing tip, where his tail plane struck the slightly downward canted wing apex. This caused an upward pitching motion to the Starfighter and it is believed that wake vortex patterns around the Valkyrie caused the smaller aeroplane to be drawn upwards and over the top of the larger aircraft. This motion removed much of the Valkyrie’s starboard vertical tail fin and all of the port side unit.

The Valkyrie was seen to continue flying for a short period whilst the Starfighter was consumed in flames killing the pilot. Test pilot Al White, whom I understand was the pilot with control in the Valkyrie is said to have reported that little effect was felt from the initial collision. Several seconds later, the Valkyrie went out of control, rolling and yawing simultaneously at which point Al White ejected. He was injured by the ejection process as his arm was caught in the clamshell which was supposed to enclose the pilot when ejecting.

Carl Cross, who was flying in his first mission on the XB-70 was unable to leave the aircraft due, (it is suspected) to a problem with his ejection seat and perished when the Valkyrie struck the ground in a flat attitude. Much has been surmised about the reasons behind the accident and subsequent crashes, but the outfall of it was that two exceptionally fine pilots died as a result and one of the only two XB70s was destroyed.

The remaining XB70 (bureau number 62-0001), now rests at the National Museum of the Air Force in Dayton, Ohio where it can be seen at close quarters. I imagine that it is a truly impressive aeroplane measuring, as it does, 193 feet in length and some 30 feet high at its tallest point.

There are many notable features about the Valkyrie but the one that is perhaps the most notable is the extended nose which places the flight crew some 65 feet forward of the point where the wings meet. This position makes ground movement more difficult as the undercarriage is sited some 80 feet behind the pilot. The other factor is exactly how high above the ground the pilots are - the lower part of the crew entry door is nearly 17 feet off the ground- that is approximately first floor level if you think about it.

From an aerodynamic perspective, the Valkyrie deployed some interesting features. Most noticeable would be the canards. These are horizontal stabilisers that sit forward of the mainplane and provide stability and trimming control in the pitching plane. It should be noted that the elevators were incorporated into the rear control surfaces in the form of “Elevons,” which is a similar configuration to the SR71. Stability and lift at high altitude was accomplished by the use of variable tilt wingtips, which were often canted down to an angle of 65 degrees. This created a passage of higher pressure air between the tips, thereby creating lift. The downward sweep also stabilised the aircraft in the yawing plane, (ie, horizontally from side to side). This principle was known as “compression lift,” and was quite different to the SR71 use of vortex lift from the chines, (canards in all but name), which created lower pressure above the mainplane.

The initial flight research program was completed in August 1966 and was followed by further trials and flight test programs researching sonic booms, (I suppose that they found out that sonic booms are very noisy and that chickens don’t care for them), and also into structural dynamics. The remaining Valkyrie left Edwards AFB for the last time in February 1969 bound for Wright Patterson AFB where it was placed in the museum I mentioned earlier and has not flown since then.

The Valkyrie is another example of engineers finding solutions to practical problems in aviation, a task that continues to this day. It is sixty years ago that the Valkyrie took its first flight and it was designed by people at North American Aviation whose most complex quick calculation tool was probably a slide rule, (an example of which you can see above). In these days of computers and models it is likely that engineers could not have surpassed what North American Aviation’s boffins were able to achieve at the time. Not bad for a mechanical device eh?