A Preface to Planes with Pronated Pilots
The pilots did not sit; they lay on their bellies.
Almost all types of aircraft that are in operation today (fixed-wing airplanes, helicopters, motor gliders etc.) have pilots in the seating position. However, the first heavier-than-air, powered aircraft had a pilot in the prone position, in other words, lying in the stomach-down position. This was later changed to the classic seating position by the Wright Brothers themselves, and the design was adopted thereafter.
After WWI, the fundamental concerns that hindered smooth flight were solved with improvements in design, material science and manufacturing technology. Aircraft were then structurally sturdier, more efficient and had better airworthiness than the first few aircraft. More agile and sharper manoeuvring aircraft required that drag-reduction and measures to counter the effects of g-force on pilots need to get refined.
What is the g-force and how is it significant?
The g-force, or gravitational force, is a type of inertial force experienced by a body when the magnitude or direction of its velocity changes in a very short interval of time. One instance where the g-force can be experienced is in a giant Ferris wheel. As you go up in the wheel, the blood from the upper part of your body flows downwards to the legs due to the upward g-force experienced, causing light-headedness. While coming down in the wheel towards the ground, the downward g-force drives blood from the lower part of the body to the head. There are limits to both positive and negative g-forces that can be tolerated by a human being. The g-forces experienced in a Ferris wheel or a roller coaster are well within the tolerable limits for most people. However, this is not the case with fighter pilots.
The g-force experienced by a fighter pilot can be both positive and negative. When blood quickly flows from the head to the legs, the heart pumps blood faster and harder to ensure sufficient blood supply to the brain. If the cardiac and the vascular system do not meet the demands, then the pilot’s performance starts to degrade, causing temporary loss of vision, black-out/red-out, unconsciousness, and even death (in extreme cases). It was observed that when the pilot is in an inclined position, there is a lesser burden on their cardiac and their vascular system to pump blood to the brain. It allows the pilot to withstand higher magnitudes of g-forces. Therefore, the pilot can significantly reduce the radii of turns or increase pull-up/pull-down acceleration. The maximum g-force that the pilot can cope with before losing consciousness is tabulated as follows:
Multinational companies, student groups, and the defence sector of various countries began designing aircraft with pilots in the prone position. The concept started to gain attention once more in the 1940s, after it was abandoned by the Wright brothers at the beginning of the twentieth century. The Akaflieg Berlin B9 and the Akaflieg Stuttgart fs17 were the first among many prone-pilot aircraft. They were developed by students to investigate the advantages of having the pilot in the prone position. These, and other similar aircraft, successfully demonstrated that having prone pilots indeed reduced the frontal area of the fuselage, thereby reducing drag, and helped the pilot sustain the effects of higher magnitudes of g-forces.
How is engineering a prone-pilot aircraft different from engineering a seated-pilot aircraft?
Certain design aspects had to be into account during the development of prone-pilot aircraft. One of these was the furniture required to support the pilot and enable his functioning. Couches, armrests, chin rest, and feet support are a part of this furniture. The control stick and the foot pedals cannot be designed and integrated into the system the same way as they are done in a conventional seated-pilot aircraft. If there is more than one pilot on board, then the space and controls for the other pilot must also be planned out. The change in the overall weight and location of the centre of gravity of the vehicle must be considered since they can influence its stability in the air. In addition, temperature control, oxygen supply, independent communication system with the ground station etc., are all required to be provided. Hence the cockpit layout of a prone-pilot aircraft is noticeably different compared to that of a conventional seated-pilot aircraft.
Another crucial consideration in the design of prone-pilot aircraft is the emergency and escape system. Unlike in seated-pilot aircraft, an ejection seat cannot be used to vacate the prone pilot; a wholly different escape system is needed for emergency evacuation. Consider the case of Gloster Meteor F8 ‘Prone’ Pilot. The fuselage of the standard Gloster Meteor Mk. 8 was further elongated ahead of the nosewheel bulkhead to house a couch, controls and instruments for the prone pilot. Here, the seated pilot uses Martin-Baker Mk.1 ejection seat to vacate the aircraft conventionally. The prone pilot vacates into the airstream by sliding off the couch downwards.
How was the flying experience for the prone pilots?
Some of the drawbacks mentioned by the pilots who gained first-hand experience at flying these distinctive aircraft were redressed in subsequent prone-pilot aircraft that were built. The observations include the following:
- Initially, the prone pilots tended to misjudge flight speed and had higher reaction times. These drawbacks were mitigated with time and practice.
- Some pilots reported that flying for long hours in the prone or semi-prone position was much less comfortable. It also placed restrictions on head, neck and shoulder movement, hampering constant vigilance. In the 30 March 1956 issue of the Flight magazine, Royal Air Force test pilot C.M. Lambert, who flew the Gloster Meteor Mk. 8 in prone position, recalled being strapped in as being “in the trussed chicken state”.
- Prone pilots also noticed that it is difficult to see the wingtips during landing and taxiing without releasing the safety harness and raising the head.
- Having a transparent lower cover for the pilot improved downward visibility without much strain, which is necessary during landing.
- In a fully prone position, the arms are almost in level with the shoulders; and this made seeing forward and controlling the aircraft’s attitude slightly unpleasant. The Horten brothers used a semi-prone position in Horten flying wings, where the upper body of the pilot was at 30° from the horizontal. Therefore, the pilot did not need to turn their neck upwards, as much as in the prone position, to look forward.
Will the prone-pilot aircraft make a comeback in the future?
Some of the prone-pilot aircraft that were successfully contrived never witnessed actual service, while some of them did not even make it through flight tests. Today, pilots flying in prone position can be spotted in hang gliders. Hang-gliding is a popular air-sport, wherein the harnessed pilots are suspended from the airframe below a wing made of sailcloth. The attitude of the hang glider is controlled by shifting the pilots’ weight as they lie prone. However, in the case of hang gliding, a bad heads-first landing can also be fatal to the pilot. A supinated pilot, who lands feet first, has more chances of surviving a crash in a hang glider. Rigid-wing hang gliders Millennium and Utopia, and gliders Swift and Swift Light, among others, have pilots in the supine position. Therefore, the supine position is another prospective alternative to the seated or the prone position.
At present, the drawbacks associated with having pilots in prone position outweigh the advantages posed by the same. Anti-g suits have sufficiently advanced that pilots can withstand higher g-forces in the seating position itself. However, we cannot rule out the possibility of applying this concept in the future. Since the design has proven to offer some advantages, such as reducing the frontal area of the fuselage and withstanding higher g-loads, the idea cannot be declared to be completely unavailing. From flight tests up to this point, it is clear that while the concept alone proves to offer advantages, its efficacy in fully-functioning aircraft still needs to be developed. Some possible instances in which the prone position may be used, in my opinion, are hypersonic space flights, advanced bombers, and high-speed reconnaissance aircraft.
References:
