Anti-G suit with pressure regulator

Inflating a fighter-pilot's anti-G suit to the correct pressure is facilitated by the pressure regulator design. Using Preview Control, the movement of the control stick is used to predict what the G-force on the aircraft will be in the time ahead. A computer determines what pressure is needed in the suit to safeguard the pilot at that G-force. The size of the air-flow aperture in the regulator is defined by overlapping windows in the housing and rotor of the regulator. The rotor is moved to give the correct overlap by means of a servo motor or stepper motor, which positions the rotor in response to the computer output. The very fast, stable, response of the regulator to the computer input enables the suit pressure to follow the G-forces predicted by Preview Control with great accuracy.

BACKGROUND OF THE INVENTION 
This invention relates to anti-G suits, of the kind used by pilots in high 
performance aircraft. A modern fighter aircraft is capable, as a 
structure, of withstanding the forces associated with carrying out 
manoeuvres up to about 15-G. However, even with the best of conventional 
precautions to protect the pilot, the pilot undergoes such physiological 
problems as blacking out at about 10-G. Under normal conditions, the pilot 
starts to suffer G-force-related problems at 6- or 7-G. 
It is conventional practice to equip a fighter pilot with an anti-G suit, 
in which inflatable bladders are secured around the pilot's legs. A sensor 
senses the G-force on the aircraft, and inflates the bladders to an 
appropriate pressure. The pressurised bladders serve to prevent blood 
pooling in the pilot's feet, whereby the blood is prevented from draining 
from the brain, and causing blackout and the other physiological problems. 
Conventional anti-G suits add about 1-G to the pilot's tolerance of 
G-forces. 
The designer of the anti-G suit is faced with the following considerations. 
A first problem is that, if the suit is inflated/deflated too slowly, the 
suit might actually harm the pilot, by trapping blood in the lower 
extremities. 
A second problem is that the suit should not, for physiological reasons, be 
pre-inflated to a pressure higher than that dictated by the G-force, for 
more than a few moments, since that might seriously affect the pilot's 
blood pressure, and hence his capability/comfort level. 
A third consideration is that it takes about half a second to one second, 
after the pilot has actuated the control stick to call for a change in 
G-force, for the G-force actually to come onto the aircraft. It takes the 
conventional anti-G suit and pressure regulation device about another 
half-second to a second to inflate the suit to the correct pressure as 
dictated by the new G-force on the aircraft. This speed of response is 
only acceptable if the aircraft changes G-force slowly, and if a second 
change in G-force is not commenced until the first change has been 
completed, and the suit inflated. Of course, in a fighter aircraft, the 
pilot may be changing his demands of the aircraft several times a second. 
It may be noted that there are two components to the time it takes to 
effect a change in the pressure in the suit. First, the pressure regulator 
has to be re-set so as to admit a flow of air into, or out of, the suit; 
in particular, in the regulator, the size of the aperture or orifice 
through which air flows into or out of the suit has to be changed, and 
this change takes a measurable time. Secondly, there is the component of 
time that it takes the air actually to flow into or out of the suit. It is 
these two components in aggregate which take the second or half-second, as 
referred to. 
With the conventional manner of controlling the inflation of the anti-G 
suit, it was not really worth reducing the suit-inflation time. If the 
suit inflation time were, at great expense, reduced below half a second, 
say, it would make little difference. For occasional changes of G-force 
(ie changes spaced more than about 2 seconds apart) the conventional 
pressure-control system could keep up. For more rapid changes in G-force, 
the suit pressure could not begin to change until after the G-force was 
established, which swamped any such minor gain in the suit-inflation-time. 
It is known, however, that it is possible to predict the G-force that will 
be present in the aircraft in about one second's time. That is to say: 
although it takes about a second after the pilot actuates the control 
stick for the G-force to actually come onto the aircraft, it is possible 
to compute, more or less immediately after he has actuated the control 
stick, what that G-force will be. Therefore, it is possible, at least 
theoretically, to set the pressure in the suit according to that predicted 
G-force, rather than to the actual G-force already established on the 
aircraft. If this is done, the second or half-second that is used up in 
inflating the suit can run concurrently with the second it takes for the 
G-force to build up. Thus, the suit can be inflated, ready, by the time 
the G-force comes on. 
The system of adjusting the suit pressure not to the actual G-force on the 
aircraft, but to the G-force that will be appearing on the aircraft in one 
second's time, is called the Preview Control system. The system yields 
marked advantages over the conventional system, because inflation of the 
suit can be initiated a sufficient time before the G-force comes on for 
the suit to be inflated to the correct pressure to support that G-force. 
Improvements in the pilot's tolerance are predicted to be as high as 2- or 
3-G extra, especially in cases where the pilot is requiring rapid changes 
of the G-force. 
As mentioned, with the conventional suit-pressure control systems, there 
was little to be gained by reducing the time taken to actually inflate the 
suit. By contrast, with Preview Control, any saving in the time it takes 
to inflate the suit, instead of being just of marginal interest, will now 
be very useful. When the G-force on an aircraft changes, it does not 
change according to a smooth linear ramp function, but rather in a more 
complex fashion: slowly at first as the control surfaces on the wings etc 
are adjusted; then rapidly; then slowly again as the new G-force is 
approached. If the suit can be pre-inflated in less than one second, there 
will be an improvement in the accuracy with which the suit pressure will 
be able to follow this pattern of change of the G-force. 
It is emphasised that there is nothing that can be done, outside of a total 
re-design of the whole concept of fighter aircraft, about reducing the up 
to one second it takes from the time the pilot actuates the control stick 
to the time the G-force comes on. (This period is not stated as a fixed 
constant: of course, the greater the desired change in G-force, the longer 
the period will be. The period of up to one second is stated as being 
typical of the time it takes, from the moment the pilot starts to actuate 
the control stick, in practice and in a real aircraft, for a substantial 
change in G-force to become established in the aircraft.) 
However, it is recognised that, with development work, there is something 
that can be done about redesigning the suit and its inflation system, to 
reduce the time it takes to inflate the suit. But the key step forward of 
Preview Control is that the suit starts to become inflated, not after the 
G-force has become established in the aircraft, but a half second or up to 
one second earlier than that, ie as soon as the pilot actuates the stick. 
The present invention is concerned with combining a pressure regulation 
system into a Preview Control suit inflation system, which will permit the 
pressure in the suit to be changed, accurately, and with stability, in 
appreciably less time than the half to one second that such inflation has 
conventionally taken. 
A number of approaches to the pressure regulation requirement will now be 
discussed. 
First, it should be noted that the pressure regulation requirement is a 
most demanding one. The time it takes to change the G-force, and therefore 
the maximum time that can be allowed to change the pressure in the suit, 
if Preview Control is to work at all, is one second. If the suit pressure 
can be changed faster than that, so much the better: the time saving can 
be used, not to change the suit pressure too soon ahead of time, but to 
make the changes in the suit pressure follow the changes in the G-force 
more accurately. 
The nature of the aircraft and its relation to the suit should be borne in 
mind in this context: consider, for example, if the suit, in order to 
perform its function, had to change its pressure very quickly (say in 
one-fiftieth of a second) no pressure regulation system could ever keep 
up, and high-performance anti-G suits could never be established. If, on 
the other hand, the aircraft were such that five seconds were available 
for changing the suit pressure, it would be so easy then for the pressure 
regulation system to keep up that virtually any type of regulator would 
serve. 
It is recognised, as an aspect of the invention, that the time taken to 
change the pressure in the suit can be reduced down below half a second, 
which is very worthwhile, or even less, by the arrangements as described 
herein. It is recognised that this order of magnitude of a reduction is 
exactly what is required to convert Preview Control of anti-G suit 
inflation from a theoretical desideratum into a practical reality. 
Again, it is pointed out that the time taken to effect a change in the 
pressure in the suit is in two components: the time to change the aperture 
opening in the regulator, plus the time to transfer the air into, or out 
of, the suit. In Preview Control, a computer on the aircraft is supplied 
with signals not only from the pilot's actuation of the control stick, but 
also from sensors which indicate, among other things, the aircraft's 
present G-force, the cockpit pressure, and such factors as the aircraft's 
altitude, speed, weight, and many other factors that affect the prediction 
of the G-force. The computer calculates the ideal pressure in the suit 
needed for the pilot to tolerate that G-force. 
The invention provides a comparator, which makes a comparison between this 
ideal pressure that will be required in one second's time, and the 
magnitude of the pressure as it now is, as derived from a pressure sensor 
in the suit, and calculates the rate at which air must be admitted into 
the suit (or released from it) in order for the suit pressure to be at 
that ideal value when that G-force comes on. 
The comparator computes how much inflation-air, or rather how great a flow 
rate of inflation-air, should be admitted into the suit. The pressure 
regulator therefore must be of the type that is able to receive a signal 
from the comparator, and to respond to such signal by automatically 
opening the aperture in the regulator to the appropriate size of opening. 
One type of pressure regulator that might be considered for use with 
Preview Control is the type based on a solenoid-operated on/off valve. 
With such a regulator, the computer is programmed to energise the solenoid 
when the valve should be open and de-energise it when the valve should be 
closed. This simple type of pressure regulator is adequate, however, only 
when the changes in G-force are well-spaced apart (eg more than two 
seconds apart). This type of regulator may be termed the solenoid on/off 
regulator. 
Suppose, as an example, that tests have shown that the ideal pressure for a 
particular G-force in a particular suit should 6 psi. Now, in order to 
inflate the suit from, say, 3 psi to 6 psi, it is necessary to turn the 
regulator off at about 5 psi, because otherwise, if left open, the 
pressure would be still rising when it reached 6 psi, and the pressure in 
the suit would overshoot. Turning the incoming pressure off at 5 psi so 
that the pressure just settles to 6 psi is something that can be 
programmed into the computer. If the change is from 5 psi to 6 psi, 
equally, the cut-off at 5.8 psi, or as required, again can be programmed 
into the computer. But these values are empirical, and depend on the 
computer "knowing" both the start pressure and the final or aimed-for 
pressure. Therefore, if the aimed-for pressure should be changed before it 
has been reached, ie by the pilot having again actuated the control stick, 
then the computer/regulator combination cannot possibly keep up, and the 
pressure in the suit will be awry, perhaps wildly so. With an on/off-based 
pressure-controller, the more the pilot requires a change in G-force 
before an earlier change in G-force has been completed, the more 
unpredictable the action of the regulator will become. The simple on/off 
solenoid type of pressure regulator therefore depends on the computer 
starting from a situation where the G-force and the pressure were in 
synchronisation, that is to say, the pressure in the suit was at the ideal 
pressure as required for that G-force. The computer cannot be allowed to 
start a new computation when the "start" pressure for that computation 
pressure has not yet reached correspondence with the G-force. Therefore, 
the simple solenoid type of pressure regulator cannot be used when the 
pilot requires rapid changes in the G-force. 
Another conventional type of pressure regulator includes a spring that acts 
on a valve member. The pressure in the suit also acts on the valve member, 
so that, if the pressure in the suit is too low, the spring drives the 
valve member open, admitting more pressure into the suit. As the suit 
pressure increases, the valve gradually closes, thereby reducing the flow 
rate into the suit as the ideal pressure approaches. This type of 
regulator therefore has a built-in protection against overshoot: that is 
to say, the valve aperture becomes smaller as the pressure differential 
becomes smaller. 
This type of regulator may be termed a balance-spring-against-pressure type 
of regulator. 
If this type of regulator were selected for use with the anti-G suit, the 
size of the opening through which pressurised air passes to the suit would 
not be controlled, or not controlled directly, by the computer. The 
computer would control the force on the spring, and the size of the 
opening would be determined by the force on the spring as balanced by the 
pressure in the suit. 
In order to provide that the opening is large when the difference between 
the spring and the suit pressure is large, the designer would be 
constrained to give the spring a low stiffness rate; ie the designer 
provides that the spring moves a substantial distance for each unit of the 
difference. But if the spring is of a low stiffness rate, the spring is 
floppy, and the regulator is thus able to hunt and overshoot and be 
otherwise unstable. 
On the other hand, if the designer of a balance-spring-against-pressure 
type of regulator makes the spring rate too stiff, then the size of the 
opening will not change much for a given unit of difference, and in that 
case the regulator will lack the sensitivity required for it to open wide 
when the difference is large and open only a little when the difference is 
small. 
If he were to use the balance-spring-against-pressure type of regulator, 
therefore, the designer would be forced to compromise between a high 
spring stiffness rate that gives too little sensitivity, and a low spring 
stiffness rate that promotes instability. It is recognised that this 
compromise cannot be met with a balance-spring-against-pressure type of 
regulator, when it comes to pressurising a practical anti-G suit in a 
practical aircraft, when the pilot is calling for the G-force to change 
for a second time before a first change has been completed. So, in the 
cases of both the solenoid on/off type of regulator and the 
balance-spring-against-pressure type of regulator, as just described, the 
regulators simply cannot be made to keep the suit correctly inflated to 
the correct pressure, when the pilot is calling for rapid changes in the 
G-force on the aircraft. It is not a question of increasing the size of 
the pipes and valves: even with the components of optimum sizing, the 
compromise between sensitivity and controllability cannot be met. 
An aircraft anti-G suit has pockets which have a total capacity, typically, 
in the five to ten liters range. The suit is pressurised to a maximum of 
about ten or twelve psi. The material of the pockets is resilient to a 
certain degree, so that the volume of the suit increases as it is 
pressurised. With these parameters, changing the pressure from 3 psi to 6 
psi in half a second, accurately, and with stability, is a most demanding 
task. The task is made doubly difficult if the required or aimed-for 
pressure should be changed before the initial aimed-for pressure has been 
reached. It is recognised that conventional pressure-regulation systems 
are not equal to the task. 
It is recognised that Preview Control of the pressure of an anti-G suit 
however can be made to work, provided the suit pressure is controlled by 
the pressure regulation system as described herein. The benefits of 
Preview Control, provided the pressure can be properly regulated, can be 
expected, it is aimed, to be that the maximum G-force the pilot can 
withstand can be as high as 10-G. Even more important than the maximum 
G-force is the fact that the pilot can withstand rapid changes in G-force, 
and can withstand rapid rates of change of the G-force. 
In the invention, the pressure regulator has a fluid-flow aperture 
connecting a pressure source with the suit, in which the aperture is of 
variable size. The regulator is such that the valve member of the 
regulator can be held at the partially open position. 
In the invention, the size of the aperture is changed very rapidly, and yet 
with stability. One preferred manner in which the rapidity-stability 
requirement might, in the context of the invention, be numerically 
defined, is proposed as follows. 
In the preferred definition, the time taken to effect a stable change in 
the size of the aperture is the time taken from the moment of initiation 
of the size change until the moment the change is stabilised to the new 
opening size, and is stabilised thereto with a deviation error from the 
required new size of less than one tenth of the magnitude of the change. 
In the invention, it is preferred that the time taken to effect such a 
stable change is so rapid that the time interval between these two moments 
is less than about 100 milliseconds. 
It is recognised that one of the keys to making Preview Control work is to 
provide a controlled force to change the size of the aperture opening in 
the pressure regulator very quickly. There are limits to what can be done 
to reduce the actual air flow rates into and out of the suit pockets, 
since the pockets are a little elastic, and there is a limit to how fast 
air can move through passages and pipes, whereby the inflation time of the 
suit, from opening the aperture to the suit being inflated (and the 
aperture reduced to zero) is quite long: of the order of 300 or 500 
milliseconds. The invention lies in getting the aperture valve-member to 
change its size in a controlled and stable manner in a much shorter time 
interval than that. 
The invention lies in recognising that a progressively-opening valve member 
(ie the member that opens/closes the regulator aperture), and a powered or 
active servo-system to power the valve member between openings, will 
provide the required degree of rapid yet stable response. A passive system 
for opening the valve-member, where the opening force comes from the 
pressure itself (as in the conventional spring/piston regulators) cannot 
have the quick, stable response required. A designer can vary the size of 
the opening by providing a bank of on/off valves, and switching in more or 
less of the valves. But on/off valves cannot be cycled on/off rapidly, ie 
slamming rapidly from fully open to fully closed, and expect to have a 
long service life. 
It is recognised that the valve member can be made to move to the new 
opening size of the aperture rapidly if the valve member opens the 
aperture progressively, and if a powered servo-system is provided, which 
powers the valve member to the new opening size. 
The invention reduces the time it takes for the pressure regulator to 
effect a rapid but stable change in the size of the aperture. As a result, 
it now becomes very worthwhile also to reduce the time taken for the air 
to flow into and out of the suit. Once the invention is in place, careful 
attention to pipe sizes, etc, can be expected to pay off in sharper 
control of the suit pressure. 
The reduction in the time taken to effect a stable change in the aperture 
size means that the changes in suit pressure can be accomplished in 
markedly less time than it takes for the G-force actually to come on to 
the aircraft. Advantage can be taken of this reduction in time to make the 
suit pressure conform not just to the changes in G-force, but to different 
rates of change of the G-force. It may be that the ideal suit is one that 
exactly follows the changes in G-force as they come on to the aircraft, or 
it may be that having the suit-pressure slightly anticipating the upcoming 
G-force gives better pilot performance results. The point is, the 
invention permits either to be tried: the prior art pressure regulators 
were so unresponsive that it was hardly possible even to experiment with 
such determinations. 
Exemplary embodiments of the invention will now be described with reference 
to the accompanying drawings, in which:

DETAILED DESCRIPTION OF THE DRAWINGS 
The structures shown in the accompanying drawings and described below are 
examples which embody the invention. It should be noted that the scope of 
the invention is defined by the accompanying claims, and not necessarily 
by specific features of exemplary embodiments. 
FIG. 1 shows a series of sensors 2, which are set up to detect the various 
parameters on which the pressure in the receptacle 3 should depend. A 
computer 4 receives the signals from these sensors, and, using formulas, 
algorithms, empirical relationships, and the like, as previously 
programmed, makes a computation as to what pressure, under the 
circumstances, the receptacle 3 should be at. The computer then issues an 
appropriate voltage or other form of output signal to an actuator of a 
pressure regulator 12, which adjusts the pressure regulator to supply the 
desired pressure to the receptacle 3. 
In the case of an aircraft anti-G suit, the sensors 2 may be set up to 
detect present G-force on the aircraft, present suit pressure, altitude 
and speed of the aircraft, position of control stick (which determines 
what the G-force will be in, say, half a second, or one second), and so 
on. 
The computer 4 responds to the values of the parameters, and computes a 
figure for the desired pressure. This computation is done by the computer 
more or less immediately. If the parameters are varying rapidly, the 
computer changes the output signal for the desired pressure, which is 
again done more or less immediately. 
No matter how fast the speed of response of the computer, for the 
receptacle 3 to be correctly pressurised at all times requires that air 
must be fed into and out of the suit with great response, rapidity, and 
accuracy. 
FIG. 2 is an assembly drawing of the pressure regulator 12. The regulator 
is provided with a pressurised air supply, at inlet port 14, and an 
exhaust at exhaust port 16. Air at the regulated pressure is present in 
the pressure tube 18, which is connected to the pilot's anti-G suit. It is 
the task of the regulator 12, when the suit pressure is too low, to admit 
air from inlet port 14 into the pressure tube 18, and when the suit 
pressure is too high, to transfer air out of the pressure tube 18, and 
exhaust the air from exhaust port 16. 
The regulator 12 includes a rotor 20. The rotor 20 is housed inside a 
hollow sleeve 23. The sleeve 23 is clamped or otherwise fixed into the 
housing 25 of the regulator against rotary or other movement. 
The housing 25 is formed with annular grooves, which are disposed radially 
outwards from inside the interior of the housing. The grooves are an inlet 
groove 27 and an exhaust groove 29. The inlet and exhaust ports 14,16 
communicate with these grooves. 
The rotor 20 is provided with inlet windows 30 and exhaust windows 32, 
which correspond to the inlet windows 34 and exhaust windows 36 in the 
sleeve 23. When the rotor is turned clockwise from a centralised 
equilibrium position, the inlet windows 30 in the rotor start to lie over 
the inlet windows 34 in the sleeve. The number of degrees of angular 
movement of the rotor 20 is a measure of the size of the aperture thus 
created. The exhaust windows 32 in the rotor do not move over the exhaust 
windows 36 in the sleeve when the rotor rotates clockwise. 
Similarly, when the rotor rotates anti-clockwise, the exhaust windows 32,36 
overlap and the inlet windows 30,34 remain closed. 
The magnitude of the aperture or orifice created by the windows sliding 
over each other determines the rate and velocity of flow of pressurised 
air from the inlet into the pressure tube, or from the pressure tube to 
exhaust. 
Once pressure in the pressure tube has reached the desired value, the rotor 
resumes its centralised or null-position, where both the inlet and exhaust 
windows are closed. 
The rotation of the rotor 20 is effected and controlled by means of a 
stepper motor 38, the armature of which is coupled to the rotor 20 via a 
coupling 40. The coupling 40 is effective to transmit only torque between 
the armature and the rotor, thereby relieving the rotor of the effects of 
any slight misalignment with the armature. 
It may be noted that nothing in the mechanical structure of the regulator 
12 is set by, or depends on, the pressure in the pressure tube 18. In 
particular, it may be noted that the windows lie over each other in an 
open or closed position entirely in dependence upon the electrical setting 
of the stepper motor, and not at all in dependence upon the pneumatic 
pressure in the pressure tube. In conventional pressure regulators, often 
an aperture-closure-member is acted upon by the pressure in the pressure 
tube, whereby as the pressure rises, the pressure urges the closure member 
to reduce the aperture. This is not the case in the present design, where 
any pressure in the pressure tube, or in any other part of the regulator, 
has no effect on the orientation of the rotor. 
It is important, from the standpoint of speed of response, accuracy, and 
reliability of the regulator that there be as little friction as possible 
between the rotor 20 and the sleeve 23. Preferably, the rotor is made of 
stainless steel, and the sleeve from a bearing-material compatible 
therewith. 
It is important that the fit of the relatively moving parts on each other 
should not change even if temperature and other ambient conditions should 
change (as they do, in aircraft). The designer preferably would avoid the 
use of plastic materials for the sleeve or rotor, therefore, since plastic 
materials are often not so dimensionally stable under extreme variations 
in the environment. 
The rotor and sleeve are in a journal-bearing relationship, and because of 
the design of the regulator there is very little side or radial loading 
between the rotor and the sleeve, and it is recognised that air bearings, 
comprising a trickle of air supplied at the inlet pressure, will suffice 
to hold the rotor and sleeve apart. Accordingly, passages 43 are provided 
in the housing 25, which conduct air from the inlet port to air-bearings 
45,47. 
The air bearings 45,47 are hydrostatic, in that they are supplied with 
pressurised air throughout operation of the regulator, and so long as the 
regulator is supplied with pressurised air. 
Air bearings leak air, and the leakage may track its way to the exhaust 
port, and also into the pressure tube. However, this can usually be 
ignored; if the leakage causes an increase in the pressure in the anti-G 
suit, the sensors and the computer will detect that, and will open the 
exhaust window to maintain the desired suit pressure. 
The magnitude of leakage of air from the air bearings 45,47 is not large, 
since the air bearings comprise such a very small clearance between the 
rotor and the sleeve. However, the designer might wish to see to it that 
such leakage is minimised. In that case, seals may be incorporated into 
the design. 
It is preferable to avoid elastomeric seals between the rotor and the 
sleeve, because elastomeric seals add rubbing friction and introduce 
hysteresis, and are liable to fail. A labyrinth seal is preferred for 
minimising leakage of air from the air bearings. A labyrinth seal may be 
provided by forming many small grooves in the outer surface of the rotor, 
as shown at 67 (FIG. 7). 
The amount of leakage through air bearings increases with pressure. 
Therefore, it may be found that even at the null-position of the rotor, in 
which the pressure in the suit is being maintained constant, a small 
compensatory movement of air into or out of the suit will be required. The 
system will automatically signal the need for such small 
equilibrium-maintaining air-flows. The magnitude of the air-flow needed 
will vary with the pressure. 
The stepper motor 38 may be subject to slippage and other errors, whereby 
the angular position of the armature of the motor for any given input 
signal may vary over time. A magnet 50 is attached to the rotor, to assist 
in periodic re-alignment and re-orientation of the rotor. 
With the window arrangement as shown, the rotor would step through about 90 
degrees clockwise to fully uncover the exhaust window, and the same 
anti-clockwise to uncover the inlet window. An appropriate number of steps 
would be around ten steps for the 90 degrees, ie the stepper motor 38 
should be the kind which has at least forty steps or more per revolution. 
Proprietary stepper motors generally have far more available steps per 
revolution than forty. That is to say: there is no difficulty in selecting 
a stepper motor which has the required sensitivity to operate as 
described, 
The rotor 20 is constrained in the housing against any other mode of 
movement except rotation about the cylindrical axis of the rotor. As such, 
the rotor is not affected by the G-force experienced by the aircraft. A 
linearly-moving, or sliding, component in the regulator, by contrast, 
would be affected by such G-forces, which would affect the accuracy and 
controllability of the regulation. Also, the angular momentum of a rotor 
about its cylindrical axis is much less than the linear momentum of a 
slider of corresponding size. 
The inlet windows and the exhaust windows are each divided into two half 
portions, which are situated in diametric balance on opposite sides of the 
rotor. Therefore, when air flows into or out of the windows, the momentum 
of the flow does not give rise to a reaction to one side or the other. If 
the flow were to take place only through a single window, the resulting 
reaction force would be transmitted to the air bearings. Air bearings 
perform best (at least at low rotational speeds) when subjected to only 
nominal radial or side loads. 
It may be noted that the momentum of the flow does not tend to carry the 
windows with it: that is to say, the windows are neither pushed open nor 
pushed closed by the flow of air, no matter how vigorous that flow. In the 
design as described, the opening of the windows is virtually completely 
neutral as regards susceptibility to the effects of any forces other than 
the forces transmitted to the rotor from the stepper motor. Therefore, the 
stepper motor is not required to deliver much by way of overcoming 
spurious forces and resistances, and can be set for light, yet positive, 
fast, response. 
In order to provide a good circumferential length of window, the inlet 
windows and the exhaust windows may be at two different axial locations as 
shown. If all the windows were at the same axial location, especially 
since the windows are divided into half-portions, each window would have 
to be circumferentially quite short. The two half portions of the one 
window can be spaced or staggered axially, which allows for even more 
circumferential length to the windows, if desired. The designer will incur 
little penalty by extending the axial length of the rotor so as to 
accommodate axially-staggered windows. 
It will be noted that the windows in the rotor extend through the walls of 
the rotor, which are thin. Therefore, the length of the flow-restricting 
pathway is short. When the window is just open (ie almost closed) for 
example, the short restricted flow aperture is backed by wide open zones. 
This again makes for fast, positive, controllable, response. If the window 
were long, ie long in the direction of flow of air through the window, 
then especially when the window was almost closed, it would take a 
non-negligible lag time for the small flow of air to become established 
into or out of the interior chamber of the rotor. In the described design, 
the rotor walls are enabled to be thin because the outlet to the 
receptacle comprise the hollow interior of the rotor, and therefore the 
windows communicate directly with the output passage. The fact that the 
rotor is a thin-walled tube is therefore a preferred feature of the 
invention. 
The low-inertia, balanced, rotor as described, can snap to a new angular 
position quickly, and can stop accurately at the new position. Such a 
rotor has little angular momentum, and is not significantly vulnerable to 
overshoot or other instabilities. By feeding the output to the receptacle 
directly from the hollow interior of the rotor, and placing the windows in 
the cylindrical wall of the rotor, both the increase and decrease of the 
pressure in the receptacle can be handled with the same positive, 
controlled, accuracy. This is important in a fighter aircraft, where, 
during combat, the rotor can be expected to be in constant motion, 
accelerating, stopping, reversing, and stopping again. 
It may be arranged that the windows overlap and uncover each other in a 
more advantageous manner than if the windows are basically rectangular as 
in FIG. 2. FIG. 5 shows triangular overlap of the windows, which provides 
a more linear relationship between air-flow-through rate and the angle of 
orientation of the rotor. 
FIG. 6 shows a regulator of somewhat different design. Here the rotational 
orientation of the rotor 60 is set by a (conventional) 
rotary-variable-displacement-transducer (RVDT) 63, rather than by the 
magnet and sensor as in FIG. 2. Rotation of the rotor is controlled by a 
servo motor 65. The servo motor 65 and the RVDT 63 together serve to move 
the rotor 60 rapidly, but with great stability, to new orientations as 
required according to signals fed into the RVDT and motor. As the 
requirement for re-orientation of the rotor arises, the RVDT measures the 
error between the actual orientation of the rotor and the desired 
orientation, and provides a signal corresponding to the error; this signal 
is used in the usual negative-feedback loop to drive the error to zero. 
FIG. 7 shows the rotor 60 in more detail. The grooves 67 for the labyrinth 
seals for the air bearings may be observed, along with pillows 68 and 
pockets 69, which serve to enhance the performance of the air bearings. 
The rotor is formed with a nose 70, which interacts with a limiter 72 to 
limit the angular movement of the rotor. 
The rotor 60 is provided with through-holes 74, which serve to equalise 
pressure either side of the main structural wall 76 of the rotor. Thus, 
there is no net pressure acting to load the rotor in the axial sense; if 
such axial loading were present, thrust bearings would be needed to react 
the axial force. 
The hole 78 (FIG. 6) serves to receive a peg, by means of which the rotor 
60 can be accurately aligned rotationally with the body of the regulator, 
when setting up, and when checking the alignment of, the rotor. The hole 
78 is plugged during normal operation. Similarly, the hole 80, through 
which electrical leads to the servo-motor 65 are passed, is sealed during 
normal operation. 
A coupling 83 ensures that no spurious misalignments can be transmitted 
between the servo motor 65 and the rotor 60. Similarly, a coupling 85 
isolates the RVDT 63 from the servo-motor. 
It will be understood that in the systems as just described, the item that 
is under control is the size of the aperture in the pressure regulator. 
The computer issues a signal stating how wide open the aperture is to be 
at a particular instant. The computer carries out the calculation based on 
empirical formulas; for example, that xx psi pressure differential 
requires zz sq cm of aperture opening, as an empirical relationship. As 
the air flows in, to equalise the pressure, the formula indicates that a 
smaller opening of the aperture is now required. (The empirical 
relationship is not necessarily mathematically simple: for example, it 
might be appropriate in some cases for the aperture opening to depend, at 
least in part, on the rate of change of the pressure differential.) 
It is not essential that the aperture opening be updated in a smooth, 
step-less manner. For example, it may be appropriate for the required 
pressure differential to be determined periodically; in that case, the 
aperture is kept at the last opening-setting until the next update. In 
fact, in that case, the aperture, instead of remaining static during the 
period between updates, may be set to change, between updates, according 
to some pre-determined formula which anticipates what the next opening of 
the aperture, following the next update, may be expected to be. 
One further consideration in the case of high performance fighter aircraft 
is the pilot's breathing. It has been found that pilot performance is 
improved in high G-force manoeuvres if he is supplied with 
positively-pressurised air for breathing. For safety's sake, however, it 
is preferred, if the pressure of the breathing air is to be increased 
substantially, that the pilot be provided with a constraining jerkin 
around his chest to prevent inadvertent over-inflation. 
It will be appreciated that such a jerkin should not take the form of a 
tight band constricting the pilot's breathing at all times, but should 
take the form of a band of variable tightness, which is applied only when, 
and to the degree, necessary. 
In fact, it is recognised that the Preview Control system as described, can 
be used not only to inflate the pilot's anti-G suit, to prevent blood 
pooling in the lower extremities, but can be used also to control the 
inflation of the pilot's chest jerkin, Whereby positive pressure breathing 
can be safely and comfortably resorted to. The control requirements are 
very similar, although naturally the empirical relationships are 
different. 
FIG. 8 is a block diagram showing a generalised version of the whole anti-G 
suit control system, in which the pilot's movement of the control stick is 
converted into a corresponding pressure in the anti-G suit (and in the 
chest-jerkin). 
The stick movement and the rest of the aircraft parameters are fed into the 
preview control computer 90, Which uses the data to compute what the 
G-force on the aircraft will be half a second or a second ahead (this 
period depending on, among other things, the type of aircraft, etc). The 
preview control computer issues an output signal 92 corresponding to that 
predicted G-force. 
The preview control process may be carried on continuously, whereby the 
output signal 92 is being continuously and step-lessly updated, or may be 
carried out in discrete steps, at intervals of, say, 100 milliseconds, 
whereby the signal 92 is step-updated at those intervals. 
A calculation is next carried out, to determine what the suit pressure 
should be to best protect the pilot from that G-force. This relationship 
between suit-pressure and G-force is determined beforehand, empirically, 
in tests on pilots under controlled G-level conditions. As a result, the 
predicted G-force signal 92 becomes a pressure signal, P-preview 94. 
Meanwhile, pressure sensor 96 in the suit is providing a signal 
corresponding to the present suit pressure, P-now 98. Comparator 103 
produces a signal corresponding to the difference 105 between P-preview 
and P-now. In other words, the comparator 103 determines how much 
inflation (or deflation) of the suit has to be done. 
Another calculation is now carried out, to determine what the size 107 of 
the aperture opening in the pressure regulator should be in order to 
change the pressure in the suit by that amount. This relationship between 
pressure difference and aperture size again is empirical, being determined 
beforehand in tests under controlled conditions. The aperture should be 
opened as widely as possible, bearing in mind the need to keep the 
pressure from overshooting the desired value. 
The signal 107 corresponding to aperture size is then fed to the powered 
servo system 109, which actually turns the aperture opening/closing means 
110 (ie the rotor in the regulator), thereby adjusting the aperture size. 
As the suit becomes inflated the pressure sensor in the suit changes its 
signal 98, which sets up a change in the size of the aperture 107 in the 
regulator. When the suit is fully inflated, the aperture closes. 
Before that happens, the pilot may have changed the control stick, 
initiating a change in P-preview. This might require the aperture size to 
inflate (or deflate) the suit to the new pressure. 
In some cases, the pressure sensor 96 in the suit may not be responsive 
enough. In that case, more sensors may be included in the suit, positioned 
at strategic locations. Not just the sensor readings, but the 
relationships between sensors can then be used to determine patterns off 
airflow, which can be used to give a more accurate indication of what the 
size of the regulator aperture should be. 
With the pressure regulation system as described, it now becomes worthwhile 
to increase the responsiveness of such things as the suit pressure 
sensors, since, with the elimination of other sources so error, such 
things are now contributing significantly to whatever delays and time lags 
still remain in the system. 
The preview control system, and associated facilities, as described, 
produce a signal corresponding to the desired aperture opening size, more 
or less immediately the pilot moves the stick. It is a main feature of the 
invention that the regulator aperture is actually manipulated to that 
desired size also more or less immediately. Thus, it may be regarded that 
as the pilot moves the stick, the rotor in the pressure regulator 
instantly moves to the required new opening that will inflate the suit to 
the new pressure. In other words, there is a virtual instantaneous, ie 
lag-free, correspondence between the pilot's movement of the stick and the 
opening and closing of the aperture in the regulator. Now, the only lag in 
the system is the suit itself. When the indicated pressure difference 105 
is at a maximum, and hence the aperture 107 is wide open, a typical G-suit 
pressure regulator will produce a flow rate into the suit corresponding to 
a reduction in the pressure difference of about 20 psi per second. As the 
desired pressure is approached, and the aperture starts to close, the rate 
of increase of suit pressure becomes much slower. 
It can be helpful in some cases not to keep preview control operational all 
the time. At times when the pilot knows there is no prospect of high-G 
manoeuvres, he may switch off preview control, thereby preventing the 
build-up of whatever cumulative errors there may be in the system. In 
fact, it is beneficial if the pilot can carry out controlled G-force 
manoeuvres, using the G-force sensors on the aircraft, whereby he can 
"train" the preview control system to reproduce accurately the best 
relationship between G-force and suit pressure.