RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, BANGALORE
ANNEXURE-II
PROFORMA FOR REGISTRATION OF STUDENT FOR DISSERTATION
1. NAME OF CANDIDATE AND ADDRESS
DR PARUL GOEL
INSTITUTEOF AEROSPACE MEDICINE, INDIAN AIR FORCE
VIMANAPURA PO
BANGALORE—560017
2. NAME OF THE INSTITUTE
INSTITUTE OF AEROSPACE MEDICINE
INDIAN AIR FORCE
VIMANAPURA PO
BANGALORE—560017
3. COURSE OF STUDY AND SUBJECT
DOCTOR OF MEDICINE [MD] IN AVIATION MEDICINE
4. DATE OF ADMISSION TO THE COURSE
02 JUN 08
5. TITLE OF THE TOPIC
TO STUDY EFFECTS OF Gy ACCELERATION ON +Gz TOLERANCE
6. BRIEF RESUME OF INTENDED WORK
6.1 NEED FOR THE STUDY
"It is not the resistance of material which limits the aerobatic performance of the artificial bird, but the physiologic resistance of man, who is the brain of the artificial bird" (Bleriot, 1922) [1]
The 21st century fighter aircraft and their capability for rapid onset, high-sustained acceleration has lent a new urgency to Bleriot's observation. By redirecting engine thrust in flight ie Thrust Vectored Propulsion (TVP), increased aircraft manoeuvrability can be achieved [2]. This TVP enhanced manoeuvring has been termed variably as ‘Super Agility’ (SA), ‘Super Manoeuvrability’(SM) and ‘Enhanced Fighter Manoeuvrability’ (EFM) [3]. SM refers to the capability of an aircraft to maintain controlled flight at speeds below that of the airframe stall speed. Current aircraft employing aspects of this technology include the Lockheed Martin F-22, some versions of the F-15, F-16, F-18, the Mikoyan- Gurevich MiG-35 MFI, Sukhoi-Su-37 and the Su-47 [4]. Others are X-31, Su-35, Rafale, Gripen, Eurofighter, and MiG 29 [2]. These capabilities include multi-axis accelerations with unprecedented angular velocities and accelerations around all three principal axes of the aircraft.
Thus, SM capabilities of aircraft would result in newer physiological challenges to the aircrew. SM aircraft could manoeuvre to produce sustained acceleration in X and Y axes, a situation that pilots are heretofore not subjected to. This exposure in X and Y axis may then be followed by a sudden, rapid onset, sustained Gz.
Literature is limited about the tolerance to High Sustained Gz (HSG) immediately following Gy acceleration.
Some studies have indicated that +Gy acceleration in conjunction with +Gz can enhance tolerance [13]. Other workers have found performance decrements and impaired orthostatic tolerance [16, 18, 21]. During Gy acceleration blood supply to the brain is not directly threatened because of the relatively short vertical hydrostatic column that exists in this orientation. Yaw axis acceleration is also seen to reduce baseline baroreflex mechanism by 30% [6]. Considering above facts it is hypothesized that prior Gy acceleration exposure may alter +Gz tolerance.
In addition to the physical effects of lateral and sagittal accelerations the vestibular effects of a fast changing acceleration vector may also result in significant effects on the autonomic system, which, in turn, may result in altered orthostatic and G tolerance. This has been discussed below.
Detailed studies are required to assess such changes and effects. These will require the availability of facilities to simulate acceleration in all 3 axes as well as the availability of sophisticated and accurate physiological monitoring and recording systems. These facilities are available at Dept of Acceleration Physiology and Spatial Orientation at Institute of Aerospace Medicine Bangalore.
6.2 REVIEW OF LITERATURE
The cockpit of a combat aircraft poses a stressful environment with multiple stresses mainly, high work load, fast changing scenario, multiple tasks and information overload. SM aircraft will subject pilots to multiaxial accelerations. There is thus a need to study the effects of such multi-axial acceleration on humans.
While +Gz will probably be less than current aircraft, and of shorter duration, it may be more frequent. Gy exposure, now rarely experienced, will become frequent during pointing and escape manoeuvres.
SM aircraft give the pilot the capability to redirect their engine thrust and change their velocity vector at will, thus gaining advantage over other aircraft. If the aircraft has both vertical and lateral thrust vectoring, pilots can pitch or yaw their aircraft dynamically. This will cause acceleration in X and Y axis which may be followed by HSG exposure. Modern aircrafts are capable of very high G onset rates 6-9G/sec. Literature is presently scarce on these physiological aspects of multiaxial acceleration.
This thesis is an attempt to understand the effects of multiaxial G stresses on human body.
Super Manoeuvrability
Dr. WB Herbst of West Germany first coined the term Super Manoeuvrability in 1980 at Messerschmitt-M Boelkow-Blohm (MBB) following research conducted in the 1970s [2] .
Herbst and his group conceived the idea that controlled flight was feasible at high angles-of-attack (AOA) corresponding to airspeeds below the stall speed [7]. Multi-axis manoeuvring in SM aircraft is made feasible by a series of factors such as thrust-weight ratio, TVP, an electronically monitored control system and unique aerodynamic features especially a negative stability margin [8].
The provision of canards offers additional control movement and thus allows the AOA to reach very high values. With the AOA increased to very high values above those for maximum lift, the aircraft is able to manoeuvre in less air space in significantly shorter period of time and by directing thrust vectoring control system in longitudinal and lateral planes; it is capable of significant excursions in Z, X and Y axes.
High AOAs during PST allows unprecedented manoeuvring potential that could include the ability to quickly “point” the nose of the aircraft at an adversary while maintaining complete control.
By redirecting the thrust vector into the yaw plane, it would be possible to introduce a lateral “pointing” [2]. It also helps in improved capabilities for reconnaissance, missile avoidance, high altitude operations, short take off and landing, auto manoeuvring, stealth and safety [4]. SA plays a role in breaking missile or laser lock-on with manoeuvres such as flicks or translations.
As an example of the physiological consequences of SM flight the Herbst manoeuvre is being described. The Herbst manoeuvre consists of an abrupt pitch-up to a high AOA in the PST envelope followed by a 180 degree yaw leading to a nose-down inverted attitude and low airspeed. Recovery then allows the aircraft to reverse direction within a very short turning radius. The pilot would start the Herbst from +Gz, experience increased +Gz of short duration due to pitch, and experience additional increased +Gz due to aircraft decelerating profile drag.
Then, depending on entry speed, seat back angle, and time at high AOA, the pilot would experience 0 Gz or -Gz before +/-Gy begins during the yaw phase. If stable velocity is achieved prior to yaw, the pilot would experience +1 Gx (gravity) [2].
High-agility flight gained popular attention at the 1989 Paris show when the Russian Su-27 demonstrated a manoeuvre that became known as the Cobra manoeuvre [8].
A subsequent version of the Su-27, the Su-37, has fully independent, fully moveable thrust nozzles for each of its two engines. The Su-37 demonstrated superior agility that included backward flight during post-stall loops [9]. An additional manoeuvre, the ‘hook’ - or sideways Cobra, was introduced using the Su-35 [10].
The magnitude of yaw induced Gy would vary with the distance of the cockpit from the centre of aircraft rotation [11].
PREVIOUS STUDIES SO FAR
Albery WB [2004] studied multi-axis acceleration environment on the Dynamic Environment Simulator gimballed centrifuge. Relaxed, unprotected subjects were exposed to lateral (±1, ±2 Gy), transverse chest-to-back (+1, 2.5, or 4 Gx), or back-to-chest (-1 Gx) sustained acceleration. Positive G (+Gz) acceleration was then added beginning at 1.0 Gz by gradual onset (0.1 Gz · s-1) until the subjects lost nearly all of their vision. Baseline +Gz-only relaxed tolerances were measured before and after all combined Gy/Gz and Gx/Gz exposures. Heart rate, percent cerebral oxygen saturation, and cerebral blood volumes were collected during each exposure. Adding moderate transverse (+Gx) acceleration significantly reduced +Gz tolerance. Adding moderate lateral Gy significantly increased +Gz tolerance [13]
Hershgold performed some of the earliest Gy research, exposing humans to ±6 Gy on a human centrifuge and X-raying their chests during the exposures. He used a restraint suit with full torso, head, and leg support.
One subject had an episode of bradycardia and profuse sweating while all subjects reported aching and tugging sensations in their chests. The dependent lung displayed an increased density while the superior lung was blanched [14]
Popplow et al exposed centrifuge subjects to ±1.5, 2, and 2.5 Gy combined with either +1 or 2 Gz for 30 s on the Dynamic Environment Simulator (DES) centrifuge at Wright-Patterson AFB, OH. They found a small, but definite, reduction in percent arterial oxygen saturation (%SaO2), even with low levels of Gy/Gz. They also observed that the +Gy/Gz exposures were subjectively more painful for the subjects than the -Gy/Gz exposures. [16]
More recently, Lyons et al. investigated the human consequences of agile flight, interviewing several test pilots who have flown thrust-vectored aircraft such as the X-31 and experimental F-15 and F-16 aircraft. Although the X-31 was fully manoeuvrable in the pitch and yaw axis, it was principally studied in the pitch axis.
The yaw axis (±Gy) was not extensively studied during the X-31 program. None of the X-31 pilots interviewed believed the combined axes of acceleration posed a specific G tolerance problem, although potential spatial disorientation problems were identified.
Van Patten[1982] A group of AFTI/F-16 Project Test Pilots was subjected to sustained and oscillating lateral accelerations ranging from 1 Gy to 2 Gy in 0.25 Gy increments while performing complex tracking tasks.
The acceleration environment was produced by the AFAMRL's human centrifuge, the Dynamic Environment Simulator. This investigation revealed the possibility of potentially hazardous inadvertent and inappropriate control cross coupling resulting from the acceleration environment. Throttle pitch pointing, rudder, and roll inputs were the most notable. Useful information was developed concerning pilot fatigue from multiple, sequential exposures to Gy. [17]
Multi-axis acceleration induces unusual vestibular stimulation, which can affect the G tolerance through vestibular generated cardiovascular responses. The cardiovascular effects of coriolis cross coupling were highlighted by Sinha et al. They found that the vestibular cross coupling caused an impairment of sympathetic activity resulted in vasodilatation, thus impairing orthostatic tolerance [21]. Urschel et al demonstrated that high angular acceleration of the head about the yaw axis reduced the baseline baroreflex mechanisms by 30%. These findings provide support for the influence of vestibular system on sympathetic outflow in humans and are a concern for G tolerance in the pilots flying supermanoeuvrable aircraft [18].
Limited research by Van Patten at the US Air Force indicated the Gy acceleration generates problems of head support and limb mobility [2].
Human Centrifuges
The human centrifuge offers the promise for ground-based super manoeuvrable aircraft simulation. Gimballed centrifuges, those with an active cab and fork, can produce accelerations in several axes while turning. The clever centrifuge programmer can reproduce most agile aircraft manoeuvres in terms of angular velocities, transient accelerations, and sustained accelerations by mapping the six degrees of freedom motion of an aircraft to the four degrees of freedom provided by a centrifuge. When coupled with a wide FOV visual system, the simulation can be very compelling [2]
The High Performance Human Centrifuge at IAM, IAF Bangalore possesses high rates of onset of Gz at 10 G/s and active motion in all three axes viz roll, pitch and yaw. The centrifuge has been manufactured by AMST GmBH Austria and has been installed in 2008. It possesses a wide field of view of 120 deg and has the facility for monitoring 32 channels of physiological parameters.
The present study intends to analyze the effects of multi-axis manoeuvring. This study has been done to understand the in-flight acceleration environment, to which the aircrew of a supermanoeuvrable aircraft is exposed. This knowledge will be useful for aircrew training, aero medical evaluation and research
6.3 AIM OF THE STUDY
The aim of this research is to measure the effect of lateral +Gy acceleration on +Gz tolerance. The hypothesis is that +Gy acceleration prior to +Gz acceleration would reduce +Gz tolerance. A level of 0.05 is selected to define statistical significance.
OBJECTIVES OF THE STUDY:-
a) To determine the relaxed tolerance of human volunteers to +Gz acceleration.
b) To subject volunteers to Gy acceleration followed by +Gz acceleration.
c) To determine whether there is a change in the relaxed tolerance of human volunteers to +Gz acceleration following exposure to Gy acceleration.
d) To determine whether the results are statistically significant.
7. MATERIALS AND METHODS
Subjects: - Asymptomatic healthy, human male volunteers without any disease or infirmity. . A baseline ECG will be taken for all subjects to rule out obvious cardiovascular pathologies. Subjects will be instructed not to consume alcohol 12 hours prior to the run and to avoid smoking on the day of the experiment. It would be ensure that the last meal is taken at least 1 hour prior to the experiment.
Inclusion Criteria
Normotensive
Age group 20-35 years
Males
Exclusion Criteria
Any Disease or Infirmity
Sample size:- 20 Subjects
Equipment
High Performance Human Centrifuge at IAM.
9G for human use and 15 G for material testing.
Onset of acceleration is at the rate of 13G/sec (instantaneous) and sustained at 10G/sec. It has active gimbal control to simulate G in all three axes.
Arm is 8m in length.
It can be controlled by the operator as well as the pilot from inside the gondola.
Sample Size: - 20 subjects
Design of the study :- It will be a repeated measure (within subject) design wherein each subject will be evaluated twice, during assessment for baseline relaxed ROR +Gz tolerance as well as the same with additive Gy. This is a prospective interventional cross over study.
Experimentation: - The study will be conducted in high performance human centrifuge (HPHC) installed at IAM Bangalore. Initially subjects will be briefed about the run and an informed written consent will be obtained. The baseline level for the +Gz exposure will be +1.4Gz. Relaxed G tolerance will be measured using ROR (Rapid onset run) at 1G/sec. Peripheral Light Loss (PLL) would be taken as the end point of the runs. The minimum washout period between two runs would be five minutes to allow heart rate and blood pressure to settle down. In the subsequent exposure, the subject would be exposed to 2Gy and followed by a combined exposure of 2Gy plus Gz to his relaxed tolerance. In case the subject does not have PLL at his Gz level of his original relaxed tolerance, the Gz would be increased gradually at the rate of 0.1 Gz/s till PLL is achieved. Results of these two runs will be compared and analysed using statistical methods described below.