WW II airframe G limits

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Barrett

Senior Airman
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Feb 9, 2007
Western United States
I've looked and looked online but do not find documented figures. Thought that the BAE test reports would include some info but apparently not.
A couple of sites show "the" P-51 at 8+ and 4-.

I knew a double ace who said he pulled 9 or 10 fighting a 190 and flew home with his hemorrhoids...

Noted this thread from 2010: Maximum G Loading evaluations...

Most often it appears that threads begin with pilot G tolerance ("One size fits all," right?) and a few cite 1944-ish G suits, which provided about 1 G extra tolerance. Considering that most WW II VF came in several flavors, it stands to reason that some variation existed. It'd be interesting to see the difference between "the" Spitfire and "the" Seafire, for instance.

Do not recall seeing a G meter in a 109 or 190, FWIW.
 
And another weight dependent number arrives and of course bombers had different limits to fighters. There is North American Aviation newsletter which explains why the P-51D with its additional fuselage tank and wing-mounted racks should not be taken above 6.5G, while the P-47 could cope with up to 9G.

From the RAF specification F7/30 reproduced in Spitfire by Morgan and Shacklady

The strength of the main structure when carrying the specified load (Fixed and removable military load of 660 pounds plus fuel etc.) plus 100 pounds shall not be less than as specified hereunder

Load factor throughout the structure with the centre of pressure in its most forward position 9.0
Load factor for wing structure with the centre of pressure in its most backward position in horizontal flight 6.0
Load factor in terminal nose dive 1.75

Inverted flight
Load factor at incidence corresponding to the inverted stall and with C.P. at 1/3 of chord 4.5
Load factor at incidence appropriate to steady horizontal inverted flight and at the maximum speed of horizontal normal flight 4.5

(details on landing gear)

DTD publications and A.P.970 and A.P.1177 referenced.

The wing is to be sufficiently rigid to withstand satisfactorily any torsional or other loads which may be encountered during service operations.

Ribs (both mainplane and tail unit) are required to develop, on test, factors 20% greater than those specified for the aircraft as a whole.

The RAF had the "Canadian Frank's suit promised to enhance blackout thresholds by up to 2.0 G, the Admiralty acted first. Entering service in October 1942, the FFS Mk II was dispatched aboard HMS Furious. The carrier's Supermarine Seafire pilots praised the suit's effectiveness in combat against Vichy French Dewoitine D.520s over North Africa the following month, as part of the Allies' operational imperative to assert overwhelming air superiority during Operation Torch. After that it was withdrawn from use over enemy territory" (until it could be employed in numbers).

Aviation Physiologist Nic Green has noted that as early as 1940, "It was known that a Spitfire or Hurricane would break up at +12Gz, and sustain damage above +9Gz": N. D. C. Green, "The Fight against G," Royal Air Force Historical Society Journal 43 (2008): 70.

Peter Hobbins publication on the RAAF (Cotton) G-suit. Hobbins, P. (2020). Engineering the Fighter Pilot: Aviators, Anti-G Suits, and Allied Air Power, 1940-53. Journal of Military History, 84(1), 115-149. Accident Conscious: Accounting for Flying Accidents in the Royal Australian Air Force during the Second World War. War in History, 28(3), 608-634. Also an Article in Aviation heritage V48 no 2

Pilots had different resistances to G force with 6G the general limit, one of the ideas was a suit to give consistent resistance to around 6G, the suit designs could get to 10G which raised issues about the airframe strength. G meters and stall warnings were required. One test pilot remarked he would prefer to be conscious if the aircraft was disintegrating. The RAAF decided to impose a limit of 6.5 G.

The RAAF had the Cotton suit,
20 October 1941 protection limit found to be 9G, later "As the secretary of the Australian Advisory Committee on Aeronautics remarked, "It is evident that, if the suit is going to be used with present designs of fighters, the old basis of fighter design strength will have to be dropped." "

13 April 1942 Robertson and Arthur conduct first blackout tests with CAAG suit in Hurricane V7476 at Mascot; seat collapses on Robertson at 8 G.

4 November 1942 AMEM report 145. Kittyhawk. A report has been received that buckling occurred on the tail plane when an acceleration of 9.7G was recorded.

9 June 1943 First Spitfire Vs begin to be fitted with CAAG equipment for 452 Squadron.

8 July 1943 CAAG immediately called 'zoot suit' by 452 Squadron pilots.

9 July 1943 Four of first six converted Spitfire Vs reach 452 Squadron for testing.

Air conditioned ready rooms needed when wearing the suit.

7 September 1943 Two CAAG-equipped Spitfire Vs joins combat with Japanese fighters; pilot of EE734 appears not to have been wearing suit but apparently pilot of LZ845 was, as its wings were strained.

21 June 1944 Three spiral dives were made maintaining 6G for 15 seconds in each without any sign of blackout or discomfort.

G suits tended to reduce fatigue and could be useful keeping the wearer afloat after ditching.
 
Hi Barrett,

The chart that comes immediately to mind is the V-n Diagram, sometimes called a V-G Diagram. I show one here representing a P-51 Mustang at 8,000 pounds gross weight. I drew this one from a flight operating guide illustration.

P51 Load Limits.jpg


You can draw a V-n Diagram for almost any situation ... IF you have the data. Unfortunately, it isn't readily available for most aircraft, let alone for most aircraft that were combat aircraft back in WWII. This one also doesn't show the areas where you can survive, but only with structural damage. That is shown below. This is not for any particular aircraft ... it shows the components of a V-n Diagram.

5-55_edited2.jpg


Again, the issue is being able to get the data. Any single diagram describes only one situation. If the altitude, atmospheric pressure, temperature, or weight changes, the diagram changes.

I'd love to collect these in one place for various fighter aircraft from WWII, but have only seen one for the P-51D airplane at 8,000 pounds. I'm pretty sure they exist somewhere, but they have done an excellent job of eluding both my grasp and my sight.

Best regards,- Greg
 
Again, the issue is being able to get the data. Any single diagram describes only one situation. If the altitude, atmospheric pressure, temperature, or weight changes, the diagram changes.
Or there is some aileron or rudder input, or the aircraft is climbing or descending, or any one of a hundred other things...
 
Mr. Horikoshi helped the Planes of Fame restore our A6M5 Model 52 that still flies with the original engine. I see it every weekend.

He said then it was a 6.0 g airplane with a 100% safety factor at design weights.

That is 6.0 design limit and 12.0 g ultimate failure limit. The design weight included fuel, oxygen, guns, fire extinguishers, and ammunition for a normal loadout. Can't recall if he mentioned the limits with the drop tank. I'll ask.
 
I've looked and looked online but do not find documented figures. Thought that the BAE test reports would include some info but apparently not.
A couple of sites show "the" P-51 at 8+ and 4-.

I knew a double ace who said he pulled 9 or 10 fighting a 190 and flew home with his hemorrhoids...

Noted this thread from 2010: Maximum G Loading evaluations...

Most often it appears that threads begin with pilot G tolerance ("One size fits all," right?) and a few cite 1944-ish G suits, which provided about 1 G extra tolerance. Considering that most WW II VF came in several flavors, it stands to reason that some variation existed. It'd be interesting to see the difference between "the" Spitfire and "the" Seafire, for instance.

Do not recall seeing a G meter in a 109 or 190, FWIW.
Around 1974 my father obtained full blueprints of the Bucker Jungman. Purely for novelty, a few engineers at Air Canada ran a stress model (this was a lot of work to load up n the wing and other structures). They came back with +9/ -6 G endurance and rupture was well above but to forget those numbers. My father began to build the aircraft but was deported for espionage at maybe 15% completion.
 
MANY thanks to all, guys. Much appreciated.

I thought I had the SBD-5 figures from the restoration my family did in the 1970s but apparently that data went with the airplane to the Marines and then (currently) USAF at Wright-Patterson. I knew several SBD pilots who seemed approximately agreed that a 9-G dive recovery was fairly typical, depending on release altitude. Some suffered from the effects long afterward.
 

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