In a report submitted to the "Journal of the British Interplanetary Society", in London on the 1st of February, 1947 and subsequently published in June of the same year, entitled  " INTERPLANETARY FLIGHT: IS THE ROCKET THE ONLY ANSWER?", written by A. V. Cleaver, has this to say (see pages 135-136)

...The same is true of the even more obviously fallacious proposal of. W. Bull, an American inventor, who also made some early rocket experiments. His idea is shown in Fig. 2 and described in reference (6), ( referring to the popular science article in 1935); at any instant there may be a positive upward force (f1 - f2), but the net impulse over the whole period taken to bring both masses to rest back at the central position (o) is zero.

Apart from the fundamental fallacies in such schemes, it is evident that anyone submitting such ideas for space-ship propulsion can have no conception of the power expenditures involved. The thrust horse-power even of [the] V.2 at "all burnt" was over 600,000; this quantity is, of course, the product of thrust and velocity of flight in appropriate units, so for a 100-ton projectile accelerating at 2g. effective, the figure would be about fifty million horsepower by the time escape velocity was attained! These figures illustrate the absurdity of even searching for a solution which involves the use of rotating or oscillating machinery in a primary role; they also serve to emphasise the inescapable and entirely fundamental difficulty of the task which we are attempting, by comparison with any past engineering achievement.

While Cleaver is correct in his assertion that the net impulse in Bull's device sums to zero over a complete cycle, he does overlook three important facts.

First, the idea of averaging the net impulse over complete cycles hides the fact that a useful translation of the device actually occurs. It does not necessarily follow that the device returns to its initial position at the end of any cycle. Indeed we do not for the present consider (or are even interested!) in the problem of returning the masses to their initial positions. This is crucially dependent on the ability of Bull's device to both dissipate the kinetic energy of impact at one end (possibly by some heat exchange mechanism with the outside environment) while improving its transfer at the other.

Second, it is force which causes acceleration in masses not impulse.  Impulse is a measure of the instantaneous transfer of momentum, and it is conceivable that momentum can be influenced without causing a change in the velocity of a test mass, by any means which will allow an exchange of mass to occur while maintaining a constant velocity. This may or may not be significant according to other factors. (see the discussion of Davis' mechanics in the 'evidence' page).

Thirdly, note that Bull makes no claims that his device can operate in a continuous cycle, (although he conjectures as to the possibility), in his writings. Indeed further experimentation may, in all probability, lead to a conclusion that the 'one-shot' nature of the cycle is not amenable to 'closure' and thus relegates the device to the pile of interesting but useless scientific curiosities.

Most physicists and engineers, at this point of the discussion, retort "...but we can simplify the argument if we just consider the dynamics of the centre of mass of the system of masses comprising the device and by the laws of conservation of momentum and energy arrive at the only possible conclusion..." But that is just the point. The kinetic energy of impact is inelastically transformed into heat and other random internal stresses, (i.e. a dissipative process), so we cannot, in all fairness and honesty, quote and subsequently proceed to uncritically use these conservation laws to unequivocally deny the possibility of the existence of any interesting effects.

May I be so bold , in light of modern theories of zero-point-energy and other such stuff, as to suggest that perhaps we don't realise just how little is known about such cross transformations of energy and concomitant interactions in even simple systems. But then you hear "...but we can track the dissipation of energy in all its forms, and I bet it all balances." Sure, I agree. But until we establish beyond all experimental error, that this is indeed the case, then I remain to be convinced, one way or the other.

It is usually not very difficult for scientists to separate the important ideas and developments from those that employ, as Cleaver (1957) would say, "... a style of pseudo-scientific gobbledy-gook which has been worse than meaningless."  These reports, "...with their facile employment of meaningless jargon...", "... obviously emanate from people who realise that there is a good technical "story", possibly even a very important one, but who do not have the facts to write it up properly and who furthermore, to put it bluntly, have not the faintest idea what it is really all about."

Cleaver should be given credit for the level-headed approach he adopted in the evaluation of the various proposals at the time. An attribute which was in short supply among the engineering fraternity of the period, who I'm sure would have loved to have a say but could either not bear to risk exposure or perhaps were not genuinely interested in such matters. Nonetheless, Cleaver had the presence of mind to recognise, and the self confidence and assurance, to assert something which should be crystal clear even today:

If any anti-gravity device is ever to be developed, the first thing needed is a new discovery in fundamental physics - a new principle, not a new invention or application of known principles, is required.

The truth of this statement is clearly not recognized by many journalistic writers [on "electro-gravitics."] The simple fact is, that at the moment, we do not know whether gravity nullification, reversal, or control of any kind, is possible or not. New fundamental knowledge might show that it is. On the other hand, it might place the whole concept in the same class of scientific absurdities as perpetual motion machines, or Well's Time Machine for travel into our own established past; like them, it might violate some fundamental natural law of physics or logic. New knowledge of the sort required might come from theoretical researches in the more abstruse realms of mathematical physics, or from a more or less accidental experimental observation. Both these avenues have, in the past, led to fundamental scientific discoveries.

Arthur C. Clarke once conveyed to Cleaver a discussion he had had with a " well-known American science journalist in New York ", regarding reports of  the involvement of some leading American companies ( who hold military contracts) and their research efforts into "anti-gravity" and "electro-gravitics". Clarke was assured by the journalist, "...that the whole business was a case of Much Ado About Nothing, started by a bunch of engineers who don't know enough physics."

Today we can regard this statement as uninformed opinion, perhaps even an outburst of bravado, on the part of the unnamed journalist, given the calibre of the scientific credentials and clout these organisations possessed. Companies like Glen L. Martin (today Lockheed-Martin), General Dynamics Corporation, (whose chief scientific consultant was Dr. Edward Teller), Princeton Institute for Advanced Study, the University of North Carolina (Dr. Bryce S. De Witt) and many others. In fact it is not so easy to discount these reports, as the journalist may have tried to convince Clarke at that time. For example, the March 1957 issue of Aviation Week, under the heading 'Pure Research Group Investigates Gravity', has this to say:

New York - Gravity must be understood before it can be controlled, Welcome W. Bender, RIAS (Research Institute for Advanced Study), Baltimore, Md., told a recent chapter meeting of the Institute of Aeronautical Sciences, Bayshore, L. I.

Anti-gravity in the sense of devices which repudiate or circumvent the pull of gravity is out of the question at this time, the vice president of the Martin Co. pure research subsidiary said. Inventors who talk of levitation gadgets don't appreciate that we have only superficial understanding of the mechanism of gravity.

Unlike many other fields where creative engineering techniques are being applied with continuing success, Bender indicated that the understanding and control of gravity phenomena may take the whole careers of dedicated scientists of the Newton and Einstein breed before the groundwork has been laid so that the problem can be defined and attacked by engineers.

At RIAS, less than a half-dozen scientists are hacking away at our "sea of gravity ignorance."

However, while Bender's summary is true, it is equally true, that a complete understanding of certain physical phenomena is not absolutely necessary in order for us to benefit from the technological development and exploitation of the effects of that phenomenon. This is exactly the situation in the case of the electromagnetic field. While we have a strict and accurate (as far as we can tell), mathematical formalism or description of the electromagnetic field in Maxwell's equations, we are far from any realistic physical interpretation of the concept of an electromagnetic wave. For example, our complete lack of understanding of Young's double-slit, single-photon, self-interference effect, in terms of a plausible physical processes.

Returning now to the subject of Inertial Propulsion. The number of U.S. patents granted to date on both IP and FDP schemes is relatively small, around a hundred or so, with the earliest, probably that issued to Sverre Quisling, of Madison Wisconsin, under the description 'Propulsion Mechanism', dated Jan. 14, 1930, No. 1,743,978. Without going into detail Quisling's mechanism, requires, beyond any doubt, static friction (during the inactive part of the cycle) in order to prevent 'roll-back'. The similarity with Dr. Farral's inertial drive mechanism (1966) is rather good. The latter being an improvement to the basic idea. In fact Robert Clough, Jr. published some do-it-yourself instructions for a similar easy-to-build  working model in Popular Mechanics magazine under the title 'Mysterious Walking Box' (1963).

One of the latest U.S. patents, awarded to a William Kunz (1999), goes under the name 'Centrifugal Propulsion System', (as if centrifugal force were real!).   These patent disclosures make wonderfully interesting reading, if you're of a technical bent and don't mind the legal jargon. Although many patents contain references to earlier patents, I sometimes wonder if any of the patentees ever bother to actually read the existing claims of others. For the most part, after having meticulously read and re-read the most interesting ones you kind of get the impression that they really don't.

Under these circumstances therefore, it never ceases to amaze me, (given the rule that patents can only be issued on demonstrably workable ideas), how the U.S. government continues to allow the award of a legal document (patent) so unscrupulously. Is this a government scam? Perhaps Don Lancaster is right when he says that patents are not worth the paper they are printed on. I agree.

Now, I'm not condemning the notion that a possible physical effect may one day be found, just don't expect to read about it first in the letters patents. It won't be available for everyone to read for a dollar-eighty per copy!

Everyone should approach, with extreme scepticism, the notion that the weight of existing patent claims constitute some sort of de facto proof of   the existence or validity of the concept of Reactionless Propulsion. A notion which has yet to be demonstrated. There is no value in taking such an attitude.

What follows, is some tantalising evidence that, in my personal opinion, should be investigated thoroughly (if it has not already been done).

H.D. Kellogg, reports 'Experiments in Gyro Thrust', in the May 1967 issue of  'Experimental Mechanics' journal:

At Yale University in 1963, and now continuing at Drexel Institute of Technology, investigations into a phenomenon of gyro-thrust action are being carried on. A Sperry laboratory gyroscope, mounted on a platform free to rotate about  a vertical axis, will develop a space-thrusting action exceeding forty times the mass of the gyrowheel. Applied impulses which tend to change the gyro gimbal's axial orientation, will generate a reactive force that propels the entire system angularly in space.
Gyro-technology teaching does not take note of this gyro-thrusting action and has almost denied that the system's acceleration from rest and its accumulated momentum technically exists. The spinning gyrowheel appears to transmit a thrust generated by gyro-inertial forces, sufficient to move the vehicle system without suffering any change in the spin rate of the wheel. It is as though the wheel itself idles through the thrusting process, the energizing force reacting against the wheel bearings.
Gyro-thrusting appears to be a process free from any mass ejection, unlike rockets. When different balancing loads are placed on the platform, vehicle rotation rate changes, until a finite load limit is reached, above which the force that provides the spatial traction breaks down.
Work on gyro-thrust is being carried on by H.D. Kellogg under a Sigma Xi Research Grant for Gyro-Thrust Measurement, under auspices of the Physics Department of Drexel Institute of Technology.


Subsequently, two years later (in the May 1969 issue), this announcement was  followed by another titled, 'Monitoring Gyroinertial Displacement-force Induction':

Instrumentation-gyrodynamics principles do not apply to the mechanics of a gyro thruster. Three-year experiments at the Physics Department of the Drexel Institute in Philadelphia have established the momentum induced into a loaded carrier by action of energized gyroscopic force-couples. Displacement forces, developing inertial traction in excess of 100 times the gyrowheel mass are registered.
Momentum-induction measuring apparatus in the photo establishes specific gyro-thrust capacities. In the usual mechanics-of-rotation formula (Lt = Iw), applied impulse torque (Lt) is derived from energizing spring at right which tumbles gyrowheel axis through 50 degrees of arc in a fractional second, when triggered. Induced carrier momentum (Iw) includes platform, load cartons, and affixed gyro mass. The suspended system's developed speed of level revolution (w) and total momentum (Iw) is indexed by stopwatch readings. When additional torquing springs are applied, there is little or no corresponding gain in the generated system momentum. All tests show that excessive impulse force is rejected by specific limits of gyro-thrust action.
Positive force-attitude controllers for space vehicles can now be devised, eliminating adverse saturation effects in reaction wheels and avoiding the mass exhaustion of jet thrusters hitherto used. The "Gyrothrust" measurements also point up new principles involved in devising captive-mass linear space drives for propelling aerospace vehicles.

Both articles include photos of the experimental set up.

There is little else to add to this evidence in the way of commentary. Either the results obtained by Kellogg are erroneous or they indeed do exist. In Jan. 1961 Kellogg filed his claim for a U.S. patent (No. 3,203,644) which was eventually granted in August 1965, fully two years before the first of the two announcements was made in 'Experimental Mechanics'. A formal analysis of the gyrodynamic thrusting effect referred to by Kellogg was sought in the literature without success. Similar research carried out in England by Prof. Eric Laithwaite, (the inventor of the linear induction motor), during the late sixties leading up to the present (Laithwaite died recently), has led to further supporting evidence independent of the work of Kellogg. For further information see the bibliography section.

One more comment is in order before we move on. I'm not sure if NASA has adopted the use of on-board gyroscopes to maintain (or to change), a satellite's orbital or axial orientation with respect to earth's surface. We can find this idea in the book 'Interplanetary Flight' by Arthur C. Clarke, first published by Harper & Row (1950):

The problem of spaceship manoeuvrability is one of some importance, but it has seldom received any quantitative discussion. There are only two basic ways of altering the attitude or orientation of a body in space - by tangential jets, or by gyroscopes or their equivalent. The rotation produced by jets is permanent: since the body is in a vacuum and no frictional forces are acting, it will retain indefinitely any spin given to it. Jets would therefore be used to neutralise any unwanted rotation: they would hardly be used to change the attitude of a non-rotating ship. Gyroscopes or flywheels would be more suitable for this purpose, since they could move a body's axis from a position of rest in one direction to a position of rest in another.
If one imagines a massive flywheel at the ship's centre of gravity, both bodies being initially at rest, then since the total angular momentum of the system must remain constant, spinning the flywheel in one direction will cause the ship to rotate in the other. This rotation will continue as long as the flywheel is kept spinning, which would require very little power, and it could be stopped at any position by bringing the flywheel to rest again. Since the moment of inertia of the spaceship might be a hundred thousand times that of the largest practicable flywheel, its turning speed would be correspondingly smaller, and in extreme cases it might take several minutes to make a large movement of the ship's axis...

However please note that this effect differs from the gyrothrust effect reported by Kellogg in that gyrothrust results from a sudden change of the angular momentum vector. In Kellogg's own words: "Any rotating mass if torqued in a manner which changes the pointing direction or orientation of the spin axis in space, (i.e. involves rate of change of acceleration), can be referred to as a gyrotorque system." In contrast the action described by Clarke does not involve any forced changes in the direction of the angular momentum vector of the gyroscope, only its angular velocity.

The schemes considered thus far have intentionally been simple mechanical  systems (i.e. those which do not contain a great deal of linkages, multiple rotating or gyrating parts etc.) The more complex the mechanism the greater the effort required to analyse and validate its operating characteristics. And therefore engineers are much less likely to voluntarily agree to embark on a protracted analysis. Much less when there are unusual claims involved. For this reason engineers usually like to "break-up" a complex machine (or other systems), into its basic constituent elements, and proceed to analyse these. As a result, a loss of "signal" may occur especially when the claimed effect may be rather minute and possibly rely on some special "synergy" between  its sub-parts. This may be reflected in the old adage that "The whole is greater than the sum of its parts".

Finally, there exists in the literature an interesting claim of a scheme for inertial propulsion which contains no moving parts! For this reason it may be worth while reviewing it here since it is perhaps unique among the known proposals. The idea appears in the September 1979 issue of The Physics Teacher, under the title 'A Self-Propelling Mechanism', proposed by Lewis Epstein, Director of Research, Baus Optics, Inc., and Physics Department, Louisiana State University, New Orleans, Louisiana:

We are all familiar with mechanisms purported to violate the first law of thermodynamics, and some of us have even made acquaintances with mechanisms purported to violate the second law of thermodynamics, but have you ever met one which purports to violate Newton's first or second law? The mechanism about to be described is intended to accelerate without the application of external force or the ejection and loss of reaction mass. The mechanism does require energy to operate.
A sled- or railroad-mounted prototype of the mechanism will be outlined; however, its immediate adaptation to space craft is apparent. The mechanism is truly the essence of simplicity. (Perhaps this is why it has not been previously noticed.) It consists of a water bucket with a hole punched in its side close to the bottom. The jet of water squirting from the hole impinges on a splash plate and then falls into a collecting basin. If desired, the cycle can be closed by a pump that lifts the water from the basin back into the bucket.
Since the prototype is railroad-mounted, only horizontal forces are of concern. Were the bucket not punctured, there would be no net horizontal force on it, since the horizontal pressure exerted by the water at any point on its side would be nullified by an equal but counter-directed pressure on the opposite side of the bucket. Punching a hole in the bucket upsets this balance. If a hole of effective area is opened at the depth where the water pressure is P, the balance is upset by an amount PA, representing a net force Fb pushing on the inside of the bucket opposite the hole. So we have an elementary rocket.
Now we must consider the force, Fs, of the jet impinging on the splash plate.  Off hand Fs would be expected to counteract the reaction force, Fb = PA, on the bucket. Let us see. In accordance with Torricelli, if energy is to be conserved, the velocity, v, of the water squirting from the hole must equal the velocity that a body would obtain when falling freely from the height, h, of the water surface to the hole. Whence:

                                 v = gh.

Now, if the water has density, , its pressure at the depth where the hole was punched must be:

                                  P = gh

and thus:

                                  P = v


                                Fb = vA.

The counter force against the splash plate must be the time rate of change of the water jet's momentum as it strikes the plate. To make things simple, the plate is covered with a screen, so the water will not rebound. The plate then simply absorbs the momentum in the jet. The mass of water impinging on the plate during a time, t, must be vAt and its momentum must be vAt. The time rate of change of this momentum is vA and accordingly the force against the splash plate is:

                                Fs = vA.

So it turns out that:

                                Fs = 2Fb.

The force on the splash plate does not just counteract the reaction force on the bucket, it overwhelms it by a factor of two, and we must conclude there is a net force on the whole mechanism. The mechanism is compelled to accelerate in the direction of the splash plate.
What consequences this may foreshadow for interplanetary travel cannot be known. What consequences this may have on a prelim examination are even more foreboding.


Director of Research,
Baus Optics, Inc.,
Physics Department,
Louisiana State University,
New Orleans, Louisiana 70118

(The diagram is omitted.)

This is certainly one of those occasions where the whole business really is "much ado about nothing". Here Epstein has made the common error of making a pronouncement about an area of study outside of one's specialisation without first checking with an expert in the field, (presuming Epstein's usual area of interest is optics.)  However Epstein can be forgiven for this oversight since the correct explanation is not covered in most undergraduate physics courses on fluid mechanics. Thus he would not have been aware of this. In fact I distinctly remember asking my fluid mechanics professor about coefficients of efflux. His reply was that we would not be covering the topic, as "... it is of interest mainly to hydraulic engineers...", and thus physicists would be spared the details.

The correct explanation can be found in volume II of 'The Feynman Lectures on Physics', 40-7 to 40-8. I will quote briefly, the relevant parts:

... At the top of the tank the pressure is p0, the atmospheric pressure, and the pressure at the sides of the jet is also p0. Now we write our Bernoulli equation for a streamline, [such as the one shown in the figure]. At the top of the tank, we take v equal to zero and we also take the gravity potential to be zero. At the speed vout, and   =  -gh, so that

                          p0 = p0   + vout -  gh,

                                     vout  =  sqrt(2gh).

This velocity is just what we would get for something which falls the distance h. It is not too surprising, since the water at the exit gains kinetic energy at the expense of the potential energy of the water at the top. Do not get the idea, however, that you can figure out the rate that the fluid flows out of the tank by multiplying this velocity by the area of the hole. The fluid velocities as the jet leaves the hole are not all parallel to each other but have components inward toward the center of the stream - the jet is converging. After the jet has gone a little way, the contraction stops and the velocities do become parallel. So the total flow is the velocity times the area at that point. In fact, if we have a discharge opening which is just a round hole with a sharp edge, the jet contracts to 62 percent of the area of the hole. The reduced effective area of the discharge varies for different shapes of discharge tubes, and experimental contractions are available as tables of efflux coefficients. If the discharge tube is re-entrant, [as shown in Fig. 40-8], it is possible to prove in a most beautiful way that the efflux coefficient is exactly 50 percent.

In other words, these effects, (coefficients of efflux), are due to viscous, frictional losses. If we take the coefficient of efflux into consideration then we get Fs = (2Fb)/2 or Fs = Fb, which brings us more into line with the expected outcome. (Perhaps these frictional forces may be minimised by using super-fluid-Helium as the working medium ?)

To conclude this section. There are far too many complex schemes in the literature, to consider even attempting an evaluation, let alone thorough analysis, of each individual scheme. There are simply not enough of the right, qualified people, with the required resources. Perhaps it is just as well that NASA and other government and non-government organisations (including universities) get involved in this effort. I will continue to keep an eye on all future developments, and other  efforts, with great interest, and to continue to update this site as time permits.

Neither ignorance nor complacency should be allowed as an excuse to hinder progress toward a better understanding of nature. We really do need to find out whether there is any substance to these far-out ideas. Our survival as a species may ultimately depend on some new principle which will lead to better, more efficient, ways to leave our world - if the need should ever arise.