How good dogfighter was the Mosquito?

[ThomasP]

Hey Drgondog,

re ". . . those loads are Ultimate (Break), the US loading for 'yield' was 8G at specified GW"

I know, hence the words "Ultimate' in my post. But I have had a difficult time finding the 'yield' or 'operational' G limits at design weight for most aircraft, including the Mosquito. The British 'yield' vs 'ultimate' G limit being particularly vague in many cases.

One of my favorite examples of this is the Wellington. Vickers documents listed the 'ultimate' G load as 11 G at 24,500 lbs design weight. Exactly how the weights were distributed in the aircraft so that it would not fail catastrophically at 24,500 lbs under a 10.9 G load I do not know, but it was without a bomb load. In the same chart I referenced up-thread, the "ultimate flight factor" G load for the Wellington Mk X is listed as 4.2 G at 36,500 lbs, but this is with a bomb load. The only vague general operational references for the Wellington that I have found is in the Pilot's Notes, which say:
"
Mk III aircraft:
Take-off and straight flying . . . . . . 34,500 lb
All forms of flying and landing . . . 29,000 lb

Mk X, XI, XII, XIII, and VIV aircraft:
Take-off and straight flying . . . . . . 36,500 lb
All forms of flying and landing . . . 30,500 lb
"
The Wellington was considered quite maneuverable for a bomber, and was using the corkscrew maneuver before the Halifax or Lancaster ever did.

On the other hand, in the same chart the Spitfire Mk IX is listed as having an "ultimate flight factor" of 10 G at 7240 lbs. This is of course 2 G lower than the P-51 which is listed as 12 G at 7836 lbs, but I have never read of an instance where the Spitfire had any particularly problems with maneuvering with any Enemy or Allied aircraft, except in the case of the Ki-43 and A6M. Although there there were numerous instances of skin wrinkling and bent tail sections in the Spitfire after dogfights with these aircraft, most of the accounts I have read were from after the Cotton G suite was introduced into service. According to accelerometer equipped studies/tests, this type of bent tail section occurred at about 10 G.

The sample size was 48x Spitfire and 11x P-51. The max G pulled by any Spitfire in the sample was 10 G and the max for the P-51 was 6.7 G. The average max G was 4.9 for the Spitfire, and 5.2 for the P-51. Damage occurring in the Spitfires was as noted above. (From a different report, P-51s showed less damage after 10 G than the Spitfire, usually just some skin wrinkling and pulled rivets in the wing structure just outboard of the landing gear.)

The sample size was 16x Wellington B Mk n. The max G pulled by any of the Wellingtons in the sample was 3.1 G, with an average max of 2.3 G. There was no noticeable damage due to the G loads.

The sample size was 11x Mosquito F Mk II. The max G pulled by any of the Mosquitos in the sample was 3.9 G, with an average max of 3.1 G. There was no noticeable damage due to the G loads.

So from the accelerometer studies we can figure the Mosquito could handle 4 G instantaneous or more, at least in fighter configuration.

But for the most aircraft, it seems like the 'yield' G limits at the design weight fell somewhere between 50% and 75% of Ultimate G load.

 

[Greyman]

Worth noting on that chart that most US aircraft 'ultimate factors' are just their specification numbers -- not from actual tests.

 

[ThomasP]

True, although I have not seen any significant amount of information that there was any serious problem with the US specification in general. Usually if a US made airframe failed catastrophically it was due to detail problems, like the U/C doors failing to stay closed on the P-51 during high speed and/or high g pullouts for example. Or an airframe losing one or another of its control surfaces as another example. I am sure there were some examples of poor design, but I can not think of any at the moment.

Although there were no instances recorded in the accelerometer tests I reference above, there were at least 5 examples of accelerometer equipped Spitfires losing one or both wings at around 13.75 G. Since this was beyond the 'ultimate flight factor' it is to be expected. But most examples of the Spitfire that broke up in flight were attributed to battle damage and/or fatigue intrusion, leading to erosion of the 'ultimate flight factor'. Again, a certain amount of this is to be expected under the stress of war-time operational conditions.

 

[drgondog]

Hey Drgondog,

re ". . . those loads are Ultimate (Break), the US loading for 'yield' was 8G at specified GW"

I know, hence the words "Ultimate' in my post. But I have had a difficult time finding the 'yield' or 'operational' G limits at design weight for most aircraft, including the Mosquito. The British 'yield' vs 'ultimate' G limit being particularly vague in many cases.

Difficult to find, Yes. The US (USN and AAF) design standards handbooks that existed pre-WWII specified for Pursuit +/- 8G for AoA at Design Gross Weight and a safety factor of 1.5 for Ultimate. 1G Lateral Limit load and most landing gear at 7G.

As you know GW for every American Fighter added weight from Pre-war at alarming rates - which had a correspondng adverse effect on combat design Limit Load G (or 'n')

One of my favorite examples of this is the Wellington. Vickers documents listed the 'ultimate' G load as 11 G at 24,500 lbs design weight. Exactly how the weights were distributed in the aircraft so that it would not fail catastrophically at 24,500 lbs under a 10.9 G load I do not know, but it was without a bomb load. In the same chart I referenced up-thread, the "ultimate flight factor" G load for the Wellington Mk X is listed as 4.2 G at 36,500 lbs, but this is with a bomb load. The only vague general operational references for the Wellington that I have found is in the Pilot's Notes, which say:
"
Mk III aircraft:
Take-off and straight flying . . . . . . 34,500 lb
All forms of flying and landing . . . 29,000 lb

Mk X, XI, XII, XIII, and VIV aircraft:
Take-off and straight flying . . . . . . 36,500 lb
All forms of flying and landing . . . 30,500 lb
"
The Wellington was considered quite maneuverable for a bomber, and was using the corkscrew maneuver before the Halifax or Lancaster ever did.

I would speculate that the 'lower flying and landing GW' is between 'Empty and design GW, whereas the upper limit is Max GW at T.O with manuever limit loads considerably under design GW Limit Load (obvious).

On the other hand, in the same chart the Spitfire Mk IX is listed as having an "ultimate flight factor" of 10 G at 7240 lbs. This is of course 2 G lower than the P-51 which is listed as 12 G at 7836 lbs, but I have never read of an instance where the Spitfire had any particularly problems with maneuvering with any Enemy or Allied aircraft, except in the case of the Ki-43 and A6M. Although there there were numerous instances of skin wrinkling and bent tail sections in the Spitfire after dogfights with these aircraft, most of the accounts I have read were from after the Cotton G suite was introduced into service. According to accelerometer equipped studies/tests, this type of bent tail section occurred at about 10 G.

The sample size was 48x Spitfire and 11x P-51. The max G pulled by any Spitfire in the sample was 10 G and the max for the P-51 was 6.7 G. The average max G was 4.9 for the Spitfire, and 5.2 for the P-51. Damage occurring in the Spitfires was as noted above. (From a different report, P-51s showed less damage after 10 G than the Spitfire, usually just some skin wrinkling and pulled rivets in the wing structure just outboard of the landing gear.)

The P-51D in combat was the Mustang with least margin spread. The 8G limit load as cited was correct for the Mustang I at 1/2 ammo and fuel load (loosely described as 'fighter condition'. While there were improvements made in the form of added thickness to shear panels and doublers to increase resistance to bending loads at high AoA, there were no real changes to attempt to explain the reduction in allowable stresses as the models progessed to P-51B/D.. just a reference in the V-n diagram that the load limits for manuever and Q presented were based on 8000 pounds GW. For a P-51D that basically meant everything but ammo and fuel at TO. Adding those cute extras put GW at T.O. for full internal Combat load at 10, 200 pounds --------->6.27G Limit.

NAA invested much time and money investigating British design practices, particularly wrt to Spit IX, to compare different assumed loading and limits to serve as foundation for Lightweight fighter program XP-51F and G. The changes included reducing Design Limit to 7.5G and Ultimate to 11.25. The P-51H emerged with same loading limits at Design GW - but the design GW for the H was 9600 pounds (same as P-51B at full internal combat load, but 2x50 and ammo increase over the P-51B) - It was a much stronger airframe but the landing gear was designed to Brit standards of 4G, in lieu of US std 7G. Also interesting was Spit IX assumed lateral load = 1g, which was less than the NAA design standard.

The sample size was 16x Wellington B Mk n. The max G pulled by any of the Wellingtons in the sample was 3.1 G, with an average max of 2.3 G. There was no noticeable damage due to the G loads.

The sample size was 11x Mosquito F Mk II. The max G pulled by any of the Mosquitos in the sample was 3.9 G, with an average max of 3.1 G. There was no noticeable damage due to the G loads.

So from the accelerometer studies we can figure the Mosquito could handle 4 G instantaneous or more, at least in fighter configuration.

Instantaneous Manuever Loads are more severe than AoA in most cases, but also in 'most cases' stall occurs in hard breaks, before the airframe Bends. The hardest to predict are the stresses imposed by asymmetrical high G manuever such as a rolling dive pull out.

If I were to guess, the Spitfire V was stressed to higher Limit than Spit IX as the IX was an 'extension' brought about but slapping the added weight of the Merlin 60+ Cooling system increases?

But for the most aircraft, it seems like the 'yield' G limits at the design weight fell somewhere between 50% and 75% of Ultimate G load.

Thomas, I suspect the British airworthy standards and US standards were close same the Design limit threshold for the same materials and same stress analysis/margin approach - and consistent. Fighter/Pursuit had much higher Limit due to Manuever and Q. If I was to attemp to rationalize the original design
Limit Load for discussed aircraft, I would look to the first Production GW at TO for combat load. All subsequent weight growth would detract from the 'new' limit.

 

[GregP]

Hey Drgondog,

re ". . . those loads are Ultimate (Break), the US loading for 'yield' was 8G at specified GW"

I know, hence the words "Ultimate' in my post. But I have had a difficult time finding the 'yield' or 'operational' G limits at design weight for most aircraft, including the Mosquito. The British 'yield' vs 'ultimate' G limit being particularly vague in many cases.

One of my favorite examples of this is the Wellington. Vickers documents listed the 'ultimate' G load as 11 G at 24,500 lbs design weight. Exactly how the weights were distributed in the aircraft so that it would not fail catastrophically at 24,500 lbs under a 10.9 G load I do not know, but it was without a bomb load. In the same chart I referenced up-thread, the "ultimate flight factor" G load for the Wellington Mk X is listed as 4.2 G at 36,500 lbs, but this is with a bomb load. The only vague general operational references for the Wellington that I have found is in the Pilot's Notes, which say:
"
Mk III aircraft:
Take-off and straight flying . . . . . . 34,500 lb
All forms of flying and landing . . . 29,000 lb

Mk X, XI, XII, XIII, and VIV aircraft:
Take-off and straight flying . . . . . . 36,500 lb
All forms of flying and landing . . . 30,500 lb
"
The Wellington was considered quite maneuverable for a bomber, and was using the corkscrew maneuver before the Halifax or Lancaster ever did.

On the other hand, in the same chart the Spitfire Mk IX is listed as having an "ultimate flight factor" of 10 G at 7240 lbs. This is of course 2 G lower than the P-51 which is listed as 12 G at 7836 lbs, but I have never read of an instance where the Spitfire had any particularly problems with maneuvering with any Enemy or Allied aircraft, except in the case of the Ki-43 and A6M. Although there there were numerous instances of skin wrinkling and bent tail sections in the Spitfire after dogfights with these aircraft, most of the accounts I have read were from after the Cotton G suite was introduced into service. According to accelerometer equipped studies/tests, this type of bent tail section occurred at about 10 G.

The sample size was 48x Spitfire and 11x P-51. The max G pulled by any Spitfire in the sample was 10 G and the max for the P-51 was 6.7 G. The average max G was 4.9 for the Spitfire, and 5.2 for the P-51. Damage occurring in the Spitfires was as noted above. (From a different report, P-51s showed less damage after 10 G than the Spitfire, usually just some skin wrinkling and pulled rivets in the wing structure just outboard of the landing gear.)

The sample size was 16x Wellington B Mk n. The max G pulled by any of the Wellingtons in the sample was 3.1 G, with an average max of 2.3 G. There was no noticeable damage due to the G loads.

The sample size was 11x Mosquito F Mk II. The max G pulled by any of the Mosquitos in the sample was 3.9 G, with an average max of 3.1 G. There was no noticeable damage due to the G loads.

So from the accelerometer studies we can figure the Mosquito could handle 4 G instantaneous or more, at least in fighter configuration.

But for the most aircraft, it seems like the 'yield' G limits at the design weight fell somewhere between 50% and 75% of Ultimate G load.

Hi ThomasP.

Out of curiosity only, where did you find these g-studies? I'd really like to read them.

Thanks!

 

[ThomasP]

Hey GregP,

The majority of the info is from an ARC report I posted in another thread:

"Bombers and Agility"

I ran across this report and a couple of others on the subject a few years ago. Unfortunately, my computer crapped out on me a couple of years ago and I lost the copies of some of the reports I had downloaded. As I have not been able to find some of them again, all I have now are notes taken from the reports.

A for instance is the info in my post above about damage to the the P-51. I remember it came from a report, and I noted the info, but I do not know which report it came from as I did not record the report title.

Somewhere, on the internet . . .

There are a couple of memos from the field in the Australia-PTO detailing the use of the Cotton suite, and describe the damage to the Spitfire after dogfighting with the Ki-43 and A6M. I will try to find them again and post them or a link here.

There are NAA and USAAF memos referencing the damage to P-51s due to high G loads, but I have not looked for them since my computer failed. Possibly Drgondog can direct you to them? Otherwise, I will try to find them again.


As an aside, the only concrete info I have on the "ultimate flight factor" vs the 'yield' G load for a UK aircraft is for the Hurricane. As originally designed it was required by the AM Specification F.5/34 to have a minimum "ultimate flight factor" of 10 G, and a minimum 'yield' G load of 75% of the "ultimate flight factor", so 7.5 G in US terms? The first AM DTD Specification No.15/36 for production Hurricanes kept the same "ultimate" and 'yield' G loads. I have read in less authoritative sources that the Hurricane as originally built exceeded this by a significant margin, but have no detailed authoritative technical data. From the chart I reference up-thread, the Hurricane IIC still has a 'ultimate flight factor' of 10.7 G at 7600 lbs, even though that is about 1000 lbs heavier than the original specified weight.

I have always assumed that the Spitfire was built to same requirement, since it was a contemporary of the Hurricane, but I do not have any authoritative source saying so.

This is the chart I have sometimes referenced:



I think this chart is already posted somewhere on this forum.