A Review of Chuck Yeager's Letter of Testimony on the Budweiser Rocket Car

by Don Baumea

The purpose of this review is to encourage the reader to reevaluate a document that has been used to support the Project S.O.S. (Speed Of Sound) claim that Stan Barrett drove the Budweiser rocket car to a speed exceeding Mach 1.

Photo by Cole Coonce On December 17, 1979 Stan Barrett was strapped into the cockpit of the Budweiser rocket car waiting to make a final run in an attempt to be the first person to drive a land-bound vehicle faster than the speed of sound. Previous trials exposed shortcomings in the basic design of the car. The propulsion system was unable to develop enough power to accelerate the vehicle to a speed high enough to establish an official FIA or FIM sanctioned World Land Speed Record, which at that time stood at 622.

Hal Needham and the team must have reckoned that the rules for land speed racing were in fact obsolete and did not apply to their project. In the team's estimation the general public would not be able to distinguish a peak speed run from an official World Land Speed Record. If the general public accepted their logic and claim of being the first to exceed the sound barrier on land, it could be expected that corporate sponsors would pay a great deal of money for the chance to ride with history. The team in fact, claims a World Land Speed Record, while the Mach 1 event is a purely aerodynamic or atmospheric related phenomenon. Their approach has generated arguments that may rage for quite some time and it is not the author's desire to debate it here. The only issues of critical importance are: did this car reach and exceed Mach 1; and is there evidence that can support such a claim?

On that cool December morning, Stan Barrett and the Budweiser rocket car were ready to answer the skeptics. With the aid of an additional rocket engine, Stan blasted away on his bid for a place in automotive history.

The final determination of the vehicle's top speed during the run has been disputed primarily because of the methods used to calculate the speed, and its extremely small margin of success. Although there were spectators and members of the press present for the run, it was up to the Project S.O.S. team to provide the final judgment as to the outcome of the run.

This verification process was unique to this project in that at no time previously has any team ever been allowed to determine whether or not they were successful. Only impartial officials should make the final determination of speed.

In the final analysis, it is important to note that even after further evaluation of the data, which proposed three new and different projected velocities, all of which were rejected and the original preliminary estimate 739.666 miles per hour was proclaimed as the final speed.

Bonneville photo by Cole Coonce The International Hot Rod Association was represented and acted as the officiating organization for the event. It has never been proven that the IHRA had the ability to independently set up the necessary timing and recording equipment, collect, calculate and interpret the raw data for a supersonic aerodynamic event. In the loosely-organized, worldwide community of land speed racing enthusiast, there is a general consensus which states that the Project S.O.S. team and the IHRA teamed together to capitalize on a narrow yet potentially profitable opportunity. If the IHRA sanctioned the first supersonic run for a non-specified distance, this event could then serve to give the IHRA much prestige over the primary official organizations, which chose not to participate because neither recognized the speed trap distance of 52.8 feet, as did the IHRA rather conveniently. The IHRA, being compensated by the Project S.O.S. team, had nothing to lose and literally everything to gain if Mach 1 was achieved. The decision to base their project's success on accelerometer data is unprecedented.

Equally unprecedented was the wait for the report on the speed, which came nearly eight hours after the run. Then came the team's verdict. A preliminary investigation of the run data was interpreted, indicating a high degree of probability that the car exceeded the speed of sound by achieving a velocity of 739.666 miles per hour, or Mach 1.01. No sonic boom was heard however. This speed was estimated from data supplied by a radar system that had initially reported the speed at 38 miles per hour, as it had tracked a large truck off in the distance, away from the track that the rocket car had used.

The press received the team's verdict with mixed enthusiasm. Some chose to accept the claim while others rejected it. To this day, virtually all further published references to this event which claim the sound barrier had been broken can be traced to these few initial reports.

Credibility is very much like a line of credit: if someone extends it to a person, then it is quite likely that others will follow suit. It is most interesting to note that even the press, at times, believes that what it reads must be true.

About one month after the run, the Project S.O.S. began distributing a letter written by Brigadier General Charles Yeager, enclosed in this review, to further lend support to their claim. The release of this document has been universally regarded as a public relations maneuver on the part of the team to further lend his credibility to their assertion of a Mach 1 run.

The original interpretation of the run data was not producing the result the team had expected, since the results were ultimately ambiguous. Records of all kinds often generate controversy as a byproduct. This dispute of the Project S.O.S. claim is important because it represents a very unique event. Once it has been done, it will be recorded in history forever.

The author of this review has the opinion that the Budweiser rocket car did not achieve the velocity that is claimed by the team.

Mr. Yeager's singular proof of evidence is the fact that the vehicle's rear wheels came off of the ground at the rocket car's terminal velocity. It is the author's opinion that the car did achieve a very high velocity, while Stan Barrett drove most skillfully and fearlessly. In a 1987 telephone interview, Stan Barrett vividly recalled that the car was beginning to go divergent (turn off-course) as the rear wheels touched down, slightly off the center line track created by the front wheel, and that, in his estimation, the margin of time remaining until total loss of control of the vehicle resulted could be measured in milliseconds. The author honestly wishes that this fearless man had achieved the claimed speed. Yet the records that are available clearly indicate that the speed that the car reached is unknown in terms specific enough to grant a claim of Mach 1.

This review will focus on this aforementioned letter, and will pinpoint problems that the author has with various assertions within it.

The following is a direct transcript of that document.

January 10, 1980


It is quite obvious that the Hal Needham, Budweiser rocket car exceeded the speed of sound because of the rear wheels leaving the ground as the car achieved top speed.

As the car approaches .9 to .94 Mach number, very strong shockwaves will form on the nose, the tail and the wheel struts. When the car goes supersonic, the shockwaves which formed on the nose at lower speeds will move to the rear of the car. Evidentially the chocking effect of the shockwaves under the car, as they moved to the rear, lifted the rear of the car off the ground. I observed the track of the rear wheels on the supersonic run and the rear wheels were off the ground for 650-700 feet. A photo taken at the trap shows the rear wheels off the ground about 10 inches. Since the rear wheels weigh about 100 lbs. each and were rotating between 7-8000 RPM, they acted as gyros to keep the car from turning, directionally or laterally.

Having been involved in supersonic research since the days of the XS -1 rocket plane, which I flew on the first supersonic flight on October 14, 1947, there is no doubt in my mind that the rocket car exceeded the speed of sound on its run on December 17, 1979.

(Signature of Charles E. Yeager)

Charles E. Yeager
Brigadier General USAF, Retired

Overall, Mr. Yeager asserts that the car achieved Mach 1 because the rear wheels lifted. He adds several seemingly-reasonable conclusions that he makes based on his extensive experience, which was afforded to him through the exclusive privilege of piloting the world's first supersonic aircraft. His experiences certainly must have opened many doors for him, and it would seem to be a fair assessment that he must have also had a great deal of exposure to an entire range of supersonic research material, facilities, and personnel. When his letter is read with this preceding assumption it is easy to accept the conclusions he makes. The author does not make these assumptions at all because his personal experience in aerospace, as well as the automotive racing field, has demonstrated to him that, although an individual may posses great knowledge or experience in one general area, it is almost always the case that an individual is not as informed or experienced in other fields of endeavor. Clearly, the activities associated to aerospace research and the pursuit of a land speed record are vastly different endeavors, not only in objective, but also in methodology.

Mr. Yeager says it (the Mach 1 claim) is quite obvious because the rear wheels left the ground. Many people are not aware of research that was conducted by Jim Reisbeck at Boeing Aircraft who developed a principle and application in aerospace where a symmetrical airfoil with a given weight and a specified velocity demonstrated buoyant lift, which is to say, the airfoil reached a stabilized height above the ground plane relative to its physical properties as opposed to the normal aerodynamic lift associated to this type of airfoil. The exposed portion of the rocket car's wheels do in fact represent the essential elements of that shape. The result of this research was the definition of a type of height stabilized flight which is the result of pressure lift that is generated because of the interaction of the ground and the airfoil. The rear wheel assembly has an aerodynamic fairing that left exposed a substantial portion of the wheel to the high velocity air during its final run. The wheels have a machined knurled surface which would have contributed to higher air pressures which would have had force vectors applied predominantly upward.

Many people who have studied this project miss one unique detail of the three-wheel design. The two rear wheels present more potential lift due to the combined area of both wheels which are, in the case of the Budweiser rocket car, individually the same width as the front wheel. As an analogy, imagine three water skis that support a vehicle which is balanced at its middle. The rear skis would rise up on plane before the front due to the unequalized lift, front to rear. With the car, moving the center of gravity toward the rear would help equalize this effect but it would reach a practical limit eventually because aerodynamic forces constantly build as the vehicle accelerates toward the transonic speed range. Also, the vehicle was liquid-fueled, and had demonstrated an aft center of gravity which would have shifted forward slightly while the overall weight was dropping incredibly quickly. Between both propellant sources, solid and liquid, the vehicle lost 1,560 pounds of weight, which represents a 28.8% loss in a span of 19 seconds. As the lift forces climbed higher, the car got lighter. Now the front wheel did not levitate because a small set of wings, mounted far forward of the center of gravity, were used to push down with sufficient force, while no such device was used to provide any down-force at the rear of the car. The wing provided much leverage, as revealed in the front suspension load cell data.

Another detail that bears noting is the location of the solid-propellant JATO booster rocket. Its location was above the center of gravity, and its line of force contributed lift above the center line of the vehicle, in the vertical plane. The auxiliary booster was ignited and burned for only 5.5 seconds before all thrust ceased at the vehicle's top speed.

Another lifting source was very likely caused by the cockpit canopy due to its shape and location far aft of the center of gravity. Normally, a windshield profile, as found on most cars, will generate a definite high pressure region at the lower base of the windshield and a very low pressure area at the forward roof line. The author has demonstrated in a wind tunnel to his satisfaction that this condition also existed on the rocket car. But of major difference is the feature of the rocket car's half-conical windshield design, which has a very small surface area at the front for the high pressure air to act upon, whereas the upper portion of the canopy does in fact have a sufficiently large area to allow the low pressure air to act upon. In this case, the overall airflow results in a slightly forward lifting force, however not enough to lift the rear wheels alone.

Over the course of many interviews with on-site witnesses, the author believes that the rear struts, which were fabricated from round tubing and faired with sheet metal trailing edges, were also a significant source of lift at the rear of the vehicle. Witnesses claim that these fairings were installed with their trailing edges noticeably lowered which would have clearly met the requirement for generating significant lifting force. These witnesses were very specific in their descriptions of this particular detail. In his final report (AIAA Paper 81-0219, dated January 12-15,1981) Ray Van Akin also states, "This configuration was thought to reduce drag while not likely to generate much lift. As mentioned before, however, the rear wheels experienced a period of being airborne." If he was able to eliminate this as a source of lift, he would have stated it. The author therefore believes that the true reason the rear wheels lifted is because several events converged at the same time to create a combined total lifting force which acted upon the rear of the vehicle. These forces, by themselves, probably would not have been enough independently to cause the rear wheels to lift. As Mr. Van Akin alludes, these forces were overlooked in the design phase because they were not deemed large enough to calculate.

It is highly unlikely that the wheels lifted for the reasons Mr. Yeager claims. No portion of his letter provides reasonable explanation of the cause of the lifting rear wheels at the vehicle's terminal velocity. The many converging events which occurred, as documented by onboard data acquisition systems, clearly record maximum thrust levels being reached at the point of lowest vehicle weight. It is worth noting that the rear wheels settled abruptly upon the termination of thrust of the booster rocket without any momentum effects observable, as would be generally expected given the rate of deceleration the car exhibited.

Mr. Yeager states that, "as the car goes supersonic the shockwaves which formed on the nose at lower speeds will move to the rear of the car." In reality, a shockwave should attach to the nose, but only when the vehicle actually achieves Mach 1, not at lower speeds as he indicates. The bow shock would then remain attached to the nose thereafter while other shocks of different types may migrate to some degree. In reference to his claim that it will move to the rear, perhaps it is time for him to go back to flight test school to brush up on the basics. When an aircraft reaches a higher Mach number, the shock will lay back (become a more acute conical or wedge shape) around the nose and other locations. For certain types of shockwaves there is slight rearward movement, but nowhere near as much as he suggests. And certainly, shockwave migration or geometry sweep increases do not happen significantly at Mach 1.01. The shockwave on the nose is very much like a slightly conical dish, approximately 170 degrees (at the velocity that is claimed) which would emanate away from the vehicle in all directions. The sweep geometry can vary slightly, but not even close to what Mr. Yeager proposes.

Jim Reisbeck's research did not account for, nor did it fully investigate, transonic effects, which can be present at speeds substantially lower than Mach 1. In the case of the final run, which occurred early in the morning when the air temperature measured a brisk 20 degrees F., the conditions did exist which would further encourage the formation of very localized shock fronts directly ahead of the exposed portions of the wheels, front and rear. In fact, published photographs clearly show the formation of these local shocks which finally stabilized approximately five to eight inches away from the tread surface, as would be entirely expected for this type of physical arrangement. At no time (in the very clear photos) did the shock front emanate away from the local flow field of the wheel or the car. Mr. Yeager speculates (note his use of the word, evidentially) how the shockwave will have developed and choked causing the rear wheels to lift. Five-time world land speed record holder Craig Breedlove truly experienced transonic chocking effects in his Spirit of America Sonic 1 jet car at slightly under 600 miles per hour, which caused the front wheels to lift and then stabilize at a specific height. He was not supersonic at the time. It is worth drawing attention to Mr. Yeager's conjecture, which is what it most definitely must be, because there has never been any mention of wind tunnel testing by the designer, Bill Fredricks. In fact it is widely known that the Budweiser rocket car is in fact a repainted version of his prior LSR project, The SMI Motivator and not a new vehicle specifically built for an assault on the sound barrier. The SMI Motivator was essentially an eyeball-engineered vehicle and no documentation exists suggesting otherwise.

How can he know the precise shockwave formation characteristics of an untested and unverified design other than by pure speculation? Perhaps Mr. Yeager is referring to a well known research paper which studied the supersonic viability of an other vehicle named The Blue Flame, which was the official world land speed record holder in 1979. Though a model was fully tested in a wind tunnel by qualified personnel, it did not precisely represent every detail of its successful full-scale counterpart. Their widely-published research photographs clearly depict the formation of a shockwave strongly present and attached to the nose of the model, with the specific geometry that is typical for the velocity tested. No shockwave has ever been seen on the Budweiser rocket car at the expected locations in any published photographs, further evidence that the vehicle did not achieve Mach 1. At no time, in any currently available photographs, is there any evidence that a shockwave is present or forming at the nose of the car. The author believes that the reason for this is because the car did not even achieve Mach .9, because that is the only explanation that can create a local shock in front of the wheels but not at the nose of the vehicle. A disturbance on the surface of the lake bed would have betrayed the presence of the bow shock.

The author has never seen nor heard of any type of vehicle or aircraft that does not demonstrate a shockwave either ahead of or attached to the nose when at a velocity equal to or greater than Mach 1. Critics are curious how Mr. Yeager would propose to explain this amazing violation of transonic/supersonic aerodynamics. A transonic shock condition is the only explanation. It is a situation where local airflow conditions meet sonic requirements. Though away from this local environment where the conditions are dramatically different, the conditions that cause the formation of a shock do not exist. Blunt objects are great shapes for demonstrating shock up conditions. The wheel/ground plane environment does fit the general requirements.

The rear wheels have long been argued to have stabilized the car after they lifted off the surface of the dry lake bed. Who would dare dispute Mr. Yeager's assumption in the face of his observed opinion? The gyroscopic forces are substantial indeed. It bears noting that this explanation went completely unchallenged, that is until recently when famed speed king Craig Breedlove returned to the world of officially sanctioned high speed record racing with his third and final Spirit of America jet powered racer. To the horror of all who witnessed, Craig lost control of his car when he ran into a 15 mile per hour crosswind at a speed nearing 675 miles per hour. He was attempting to set a new officially sanctioned world land speed record. Evidence exist that Craig would have reached nearly 800 miles per hour within the measured mile if the run had been uninterrupted. During the crash, Spirit rolled onto its left side and continued on, making a 90-degree right turn. The gyroscopic effects of his wheels, which were very close in weight and size to the Budweiser rocket car's wheels, were no match to the forces that act upon the vehicle's body at those high speeds. These two vehicles are very different in design, yet the gyroscopic forces are nearly identical. Such is the power of aerodynamic forces at speeds approaching the speed of sound. Craig has been quoted in several interviews after the crash that the rear wheels were beginning to get very light and in fact had began to lift slightly. Certain questions concerning Mr. Yeager's understanding outside the realm of aerospace come to bear with some relevance in the light of these and many other facts regarding the entire Budweiser Project S.O.S. effort. Again, the author provides the possible explanation that Mr. Yeager was provided information which appeared to be correct without personal analysis and confirmation. He may have been regurgitating information that he believed was true then.

An interesting item is the nose mounted pitot tube for measuring the vehicle's air speed. Other than one minor mention of its data in published reports, this sensor is left out of the whole picture. The reason for this can only be guessed at by the author. It may be noted that given all of the other areas that the team neglected to calculate for it is quite possible that they did not anticipate the extreme vibrations that would be transmitted to the pitot tube from the vehicle's interaction with the bumpy track. In aircraft applications these devices work predictably and are quite reliably. On the car, its readings may have been too erratic to have provided reliable data. Yet the Mach 1 event is an aerodynamic event and this device was the only instrument on board that could have captured the dramatic pressure shifts at the nose of the vehicle as they occurred. Instead the team resorted to accelerometer data to verify the final speed.

What then is the value of having a celebrity who provides testimony which should provide approval and validation of a claim if he is out of his element? One interesting point that has been made by critics is that, although everyone accepts that Mr. Yeager was the first man to pilot an airplane in excess of Mach 1, there is never any mention of what documentation exists that proves he achieved this great feat. The author does not doubt the claim that he is the first. He does make this point to demonstrate how easy it is to claim something without ever having to provide the evidence or documented proof, nor require it to become convinced. This does not apply to Mr. Yeager as it does to all of us who have perpetuated his incredible story without any evidence other than the Air Force says he did. Something to think about. It was the Military who told the world that Mr. Yeager broke the sound barrier first. I wonder if Mr. Yeager would be able to look at the Bell X-1 data, perform the apparently complex calculations, and arrive independently at the conclusion that he broke the sound barrier? Would Stan Barrett be able to verify the claim similarly? I do hope the Military was able to solve these calculations in less than eight hours back then. The author speculates that Mr. Yeager was quite comfortable in his endorsement because in essence the Military did the same for him. That may be the way it gets done in the Military, but here in the civilian world we rely upon independent verification which is provided by a sanctioning organization. His argument might incorporate the idea that nowhere in automotive racing and sanctioning organizations is there a qualified group capable of setting up, recording and rendering an accurate finding of the results because of the extremely technical nature of supersonic aerodynamics. The Budweiser team paid their people to perform this vital function, though it appears they may have overpaid if the results are any measure. Any organization can hire qualified experts. The issue is impartiality and accuracy.

The author acknowledges that Mr. Yeager acted in good faith without any intent to deceive the public. It is very difficult to imagine anyone endorsing this claim which rightfully should stand on its own merit without celebrity endorsement. Any record is exactly that, a matter of record. It reflects that there is specific qualified evidence that proves the claim and this evidence is recorded in a format by regulated officials for the express purpose of proving that the claim is based on fact and not speculation. Any record that requires an endorsement by a celebrity is doomed, because this type of endorsement is in direct opposition the whole record process.

On a final note, let us again be reminded that the goal of exceeding Mach 1 on land is in fact an aerodynamic event, one that is transient in response to subtle changes in atmospheric conditions. It is not so precise an event that anyone should expect to easily claim victory while attempting to do so at a speed so close to its mathematical demarcation line, as the Budweiser team had tried to do. Any competent aerodynamicist would have been able to establish a network of sound recording devices appropriate for the conditions that would have captured not only the signature of the passing shockwave, but the velocity as it passed from station to station. The results would then be easily viewed on an oscilloscope so that it could be compared to the expected pattern the Budweiser rocket car would generate, based on wind tunnel evaluations. Microphones could have been placed above the track by being suspended on a wire, should there be any ground attenuation effects which may not have been foreseen.

ThrustSSC and the shock wave Shockwaves are visible to the naked eye. Sandia National Laboratories have published several photographs of aircraft at Mach 1 that clearly demonstrate in exquisite detail every single shockwave that that you would ever hope to see. Most people have never seen a shockwave because the requirements are specific and are generally not present when viewing supersonic aircraft at speed. However, when the conditions are right it is easy to view the phenomenon. The primary requirement is that an appropriate background must be available to allow the shockwave to distort thereby showing itself in full three dimensional form to the naked eye. The Budweiser rocket car had the proper background and lighting. It is an absolute fact that the shockwave, if present, would have been captured on film. The camera geometry was good. The camera location was very good. It just did not happen. In the opinion of the author, the Budweiser rocket car failed to generate any evidence that can be used to validate the Mach 1 claim.

The Mach 1 event was to be recorded over a distance of 52.8 feet. At the speed the car is reported to have achieved, so many critical measurement errors potentially exist that literally only a slight rise in air temperature alone could invalidate the claim, in addition to the problems of using radar over such ridiculous distances.

It has been claimed on the basis of a preliminary analysis of radar and accelerometer readings that the car exceeded Mach 1. Yet in a published report on the reported Supersonic Run, author Ray Van Akin states throughout that other detailed and exhaustive studies have been performed on the data and that extensive analysis were required to arrive at a conclusion. One such conclusion was that "For all intents and purposes, we have achieved a probability or confidence level of one that the vehicle exceeded the referenced speed of sound." If the event should happen very close to the limiting boundary between subsonic and transonic regimes where no absolute determination can realistically be made with certainty, it would be fair to expect that the Mach 1 event should not rely upon probabilities. The language of probabilities and data smoothing techniques, confidence testing and so on permeate the report's text. In an event such as the Mach 1 event, the reader should understand that it can and does exist outside of the realm of probabilities and data interpretations. So fragile is their proof, that after many years of research, the author is unable to find any evidence whatsoever that can establish the validity of the Project S.O.S. claim.

It may be quite obvious to Mr. Yeager, and he may have had no doubts in his mind at the time of his endorsement. Still, it is a shame that his endorsement did nothing to quiet the critics. He should have realized that the Mach 1 event will always require that the documentation be the final endorsement, not a poorly-written letter by a figure from aviation's pioneering past. It is also quite obvious to the author, and he has absolutely no doubt in his mind, that Mr. Yeager knows considerably less than he should about supersonic aerodynamics and endorsements. (However, the author really liked him in the movie The Right Stuff. That was a great cameo scene at Pancho's.)

Finally then, we come to the one piece of evidence that is for critics, a critical blow to the Project S.O.S. claim. The speed and all of the previous claims are based on the accelerometer data. The author has reviewed the strip chart recording of the actual run and it clearly records several major spikes in the data, which indicate a very erratic thrust output. There is a great deal of noise present as well.

All of the accelerometer readings from other sources in the vehicle have substantial noise, but the Mach 1 claim is built on the forward vehicle acceleration data, and it is quite a mess. The author and other critics do not support the Mach 1 claim because the data does not clearly support such a claim, and this is consistent with the assessment of Mr. Van Akin, who, in the author's opinion, does not truly know if Mach 1 was exceeded, though he believes it did.

A final indictment comes from the curious fact that Mr. Needham has not consistently challenged publications when articles contrary to the Project S.O.S. claims are printed. What we do have is a few individuals who have discovered that editors of various non-automotive publications will gladly print their letters of rebuttal when the Mach 1 claim is challenged in the course of other articles on the subject of land speed record racing. After all this time and energy, their best defense is now played out in the editorial comments section by obscure individuals, who without any documentation or proof, try to convince others to believe as they do purely because they say the Mach 1 event happened. Sometimes they succeed. If it were my project, I would not let it be defended in this way, unless I knew I could not prove my claim and I felt that these individuals could do a better job than I could. Defending is not proving.

One final point that must be addressed is the fact that several major land speed record programs exist currently, and it was the stated goal of the Thrust SSC team to exceed Mach 1 for the first time ever. How would a Project S.O.S. supporter explain how so many millions of dollars could be raised and many major corporations be enlisted if a definitive answer on the subject of the Budweiser rocket car were not reached? Their verdict exceeds opinion by the widest margin: it just did not happen, period. And by the way, they have bet millions on it. Would Mr. Yeager be so inclined to gamble with his own money? It is an interesting idea, their millions versus his opinion. One man versus many corporations.

The "Budweiser Rocket Car Episode", as it has come to be known, will be an important chapter in the history of land speed record racing. It is a terrible shame that the Budweiser team did not achieve Mach 1, not only for Stan Barrett, but for everyone that loves the world of speed.