It is well known in the aeromedical community that some fighter aircraft of the WW-1 era were capable of reaching at least +4.5Gz since a phenomenon called "fainting in the air" had been observed and this would be about right for a naïve, relaxed and unprotected pilot pulling sustained Gs. It is also documented that the winner of the 1922 Pulitzer Air Race suffered repeated blackouts and was reaching a speed of over 200 mph and was pulling over +7Gz on the banked 80 degree turns [1].

From these data it is clear that frontline fighters of the mid-1930s must have had at least a +7Gz capability. Fortunately for the pilots prior to the use of anti-G suits these aircraft did not have sufficient energy to sustain that level for an extended period of time. However, from the mid-1920s the value of crouching over and grunting was well known as a means of combating +Gz effects. This maneuver enhances tolerance by shortening the distance from the aorta to the retinas and the base of the brain and was the only anti-G defense used by Luftwaffe pilots during WW-II and was called the alle zusammen sitzgekuerte (the all together sitting posture) [2].

The physiology of G-induced loss of consciousness was not studied systematically until around 1927 when Jimmy Doolittle cited loss of perfusion to the brain as the cause. At the time he was doing research for his doctoral thesis (at MIT) in Aeronautical Engineering while he was stationed at McCook Field in Dayton, Ohio. Flying a late model Fokker fighter equipped with recording accelerometers Doolittle was quantifying the G stresses imposed by air combat maneuvers. His conclusions on GLOC were ridiculed by the contemporary aeromedical community but later validated by it in 1932. The development of the first pneumatic anti-G garment, Cdr. Poppen’s “acceleration belt”, followed ca. 1934 in response to the complaints of dive bomber pilots that their vision was “twilighting” during pull out. The precursor of the modern anti-G suit was the brainchild of an Australian flight surgeon who developed a suit named after him, the Cotton aeiodynamic suit, in the early 1940s.

Obviously pilots of these 1930s aircraft exceeded the usually accepted tolerance limits in steep diving turns but owing to the duration of the brain's blood oxygen reserve (4 to 7 seconds) one can pull any level of G desired without protection as long as it is not prolonged beyond that point. If it is, a sudden and usually disastrous full loss of consciousness occurs without warning.

Definitive data on specific aircraft of this period are provided as follows [3].

Boeing P-26A “Peashooter”: +12/-4Gz
All metal low wing monoplane with non-cantilever wing, fixed gear

Curtiss P-36A radial engine pre-cursor of the P-40: +8Gz
Low wing all metal monoplane, cantilever wing, retractable gear, stressed skin construction

Fiat C.R.32 biplane with Pratt-Warren truss wing braces, fixed gear: +15Gz
Very agile fighter and a favorite of the1930s Italian aerobatic exhibition team. Its successor in 1938, the CR-42, was described in a classified memo by an AAF officer as a very dangerous aircraft because of its high level of agility and high roll rate. It was also heavily armed for its time with two 50 caliber machine guns mounted in front of the open cockpit and firing through the propeller arc.

Boeing P-12 ArmyF4B Navy - a radial engine biplane, fixed gear: +9Gz

Grumman F3F radial engine biplane with retractable gear: +9Gz
Typical “pot-bellied” Grumman design of the period. The FF-1 two place version was heavier and slower and had a 2 man crew and was probably the type used in the movie Dive Bomber.

Comments

These values should be regarded as structural limits and do not necessarily represent values used in operational flying except in extreme emergencies.

The P-26 was Boeing’s first entry into the all metal monoplane fighter business and was very likely overbuilt for that reason. It still used struts and flying wires for wing bracing.

The Fiat CR series biplanes used a truss arrangement instead of the usual more or less vertical interplane struts and flying wires. Head-on this configuration looks something like the letters VOV with the O representing the engine.

References

[1] Foxworth, Thomas G. The Speed Seekers. Doubleday and Co. Revised edition published 1989 by the Haynes Publishing Group. Page 209ff

[2] van Patten, R. E. A History of Developments in Aircrew Life Support Equipment: 1797-1996. 2nd Edition, expanded and illustrated.

[3] Shaw, Robert, President Fighter Command International Assoc. Personal communication.

About the author: R E van Patten PhD vancoax.net