Insight into the magnitude of forces involved in dogfights during WW2

[Soren]

Insight into the magnitude of forces involved in dogfights during WW2

By 1942 the old WW1 style of dogfighting where one aircraft tries to outturn the other in a prolonged slow speed turn fight was long gone, the speed regimes had moved hugely upward to the point where wing loading no longer was anywhere near being as important a factor as earlier. By 1942 the speeds at which most dogfights were taking place were so high that the lightness harmony of the controls plus the structural integrity of the a/c became the two dominant if not the only factors for achieving success. This is the main reason behind the FW190's huge success against the Spitfire in the ETO and the F6F F4U Corsair's against the Zero in the PTO.

I have chosen to use the FW190 as an example to demonstrate the forces which a pilot of the type had to endure in the high speed, wild confusing dogfights taking place in the mid to late war period.

Lift equation (FW190):

CL * A * .5 * r * V^2 = X Newtons

1.58 * 18.3 * .5 * 1.225 * 112^2 = 222152.045 N

Convert result in Newtons into kgf:

222152.045 Newtons = 22653.2 kgf

Divide result with a/c weight to get Max G:

22653.2 / 4270 = 5.3

Max G at 112 m/s (400 km/h):

5.3 G
________________________________

Using the same equation the Max G at 125 m/s (450 km/h) is 6.6 G, so already at this speed the pilot will be blacking out in a full performance turn.

At 500 km/h which would be the average speed in a dogfight in 1944-45 the G-forces in a max performance turn will exceed 8.25 G's!

At 650 km/h which would quickly be reached in a dive the G-forces the FW190 is capable of pulling are staggering, a massive 13.8 G's! This is way beyond even the structural load limit.


I hope this gave some insight into why the style of dogfighting evolved as it did and why B&Z tactics became dominant in the mid to late war period.

PS: I can add other a/c for comparison reasons by request.

All the best!

 

[Soren]

Here's the P-51D put in for comparison:

1.45 * 21.64 * .5 * 1.225 * 112^2 = 241083.45 N

241083.45 N = 24583.67 Kgf

24583.67 / 4587 = 5.35

Max G at 112 m/s (400 km/h): 5.35 G

So as you can see in terms of instantanous turn rate the FW190 P-51 are very close, it is only in sustained turn rate that the FW190 holds a marked advantage, and this is only at low to medium alt for the Anton. Ofcourse at very high speeds the FW190 will be able to accellerate into a turn allot more quickly because of its much better elevator authority.

 

[Soren]

Bf-109 K-4 Max G at 112 m/s (400 km/h) = 6.4 G
Spitfire Mk.XIV Max G at 112 m/s (400 km/h) = 6.22 G
Ta-152H-1 Max G at 112 m/s (400 km/h) = 6.15 G
Spitfire Mk. IX Max G at 112 m/s (400 km/h) = 7.14 G

 

[davparlr]

Great post Soren! Very informative, I never really thought of this.

I am a bit uncertain regarding your comment

By 1942 the speeds at which most dogfights were taking place were so high that the lightness harmony of the controls plus the structural integrity of the a/c became the two dominant if not the only factors for achieving success.

. While most of the aircraft I looked at that are known as great fighters (American, since the only source on this was the Joint Fighter Conference), all had light and effective controls, it seems to me that the big effort in aircraft design was for more powerful and faster aircraft than the enemy, and not one with lighter controls and stronger airframe. The effort on the P-51H, for example, was to lighten the structure (lower g limits) for speed and maneuverability. Higher speed and more power allow better use of energy management, which, without a doubt, is one of the major factors in successful air-to-air combat. Due to its much higher power, it was much easier for an F6F to maintain airspeed in a turn than an F4F in the same situation.

 

[drgondog]

Great post Soren! Very informative, I never really thought of this.

I am a bit uncertain regarding your comment . While most of the aircraft I looked at that are known as great fighters (American, since the only source on this was the Joint Fighter Conference), all had light and effective controls, it seems to me that the big effort in aircraft design was for more powerful and faster aircraft than the enemy, and not one with lighter controls and stronger airframe. The effort on the P-51H, for example, was to lighten the structure (lower g limits) for speed and maneuverability. Higher speed and more power allow better use of energy management, which, without a doubt, is one of the major factors in successful air-to-air combat. Due to its much higher power, it was much easier for an F6F to maintain airspeed in a turn than an F4F in the same situation.

Dave, the reduction in limit loads on the 51H from D was from 12g to 11g on Ultimate and 8g to 7.4 on Limit Load, which in a turning high G fight was still below the Berger poopy suit capability in 44 and 45.

Your point about power loading is a good one re: energy as the H was nearly 900 pounds lighter and had the more powerful -9 Merlin. It had better acceleration, roll, turn and climb than the D

 

[davparlr]

Dave, the reduction in limit loads on the 51H from D was from 12g to 11g on Ultimate and 8g to 7.4 on Limit Load, which in a turning high G fight was still below the Berger poopy suit capability in 44 and 45.

Your point about power loading is a good one re: energy as the H was nearly 900 pounds lighter and had the more powerful -9 Merlin. It had better acceleration, roll, turn and climb than the D

Indeed. From what I understand the reduction in load factor was to make it similar to the Spitfire. Apparently, the British thought that the P-51 was overdesigned in regards to stress levels.

 

[drgondog]

Indeed. From what I understand the reduction in load factor was to make it similar to the Spitfire. Apparently, the British thought that the P-51 was overdesigned in regards to stress levels.

That is what I believe Schmeud quoted in Mustang Designer - and makes sense.

Having said that, 8/12 is pretty much Aero Structure as practiced today (oops -at least 20 years ago).. NASTRAN and Stardyne type finite modelling make those numbers more consistent (and believable) than the old 'hand hack' methods because these computer models will incorporate realistic deflections and interplay with shear panels, etc.

As to the Brits, they probably were right to focus on more realistic loads based on ACM. Having said that, they experienced a bit of a 'boo boo' in the wing design which had some serious control reversal issues when the wing deformed under high aileron loads... so maybe they went to 8/12 for the spar and torsion box design?? I don't know specifically what they did to fix it.

 

[Soren]

Davparlr,

Regarding my comment on the lightness harmony of the controls and the structural integrity of the airframe being the dominant factors for succes, well usually this was a feature of the faster more powerful a/c over the previous lighter but less powerful a/c. When the FW190 arrived on the scene the Spitfire pilots were at a complete loss as the FW190 ws not only much faster, it also climbed much faster and was unbelievably agile at all speeds, esp. at speeds of 400 km/h and above where pulling lead on one was near impossible without blacking out.

Bill,

The FW190 BF109 were both designed to withstand 13 G's fully loaded, this was the ultimate load limit no doubt, but it is still pretty staggering.

The load limit for the P-51D is 6.59 G fully loaded, now as to the ultimate I don't know but.

The load limit for the Dora-9 fully loaded is 6.9 G.

 

[syscom3]

US fighter pilots had gee suits in which to tolerate the high speed turns.

 

[Soren]

And the German pilots had tilted seats plus heightened footrests, in the end this probably cancelled out the difference with the early G-suit.

 

[syscom3]

And the German pilots had tilted seats plus heightened footrests, in the end this probably cancelled out the difference with the early G-suit.

Not hardly.

 

[FLYBOYJ]

And the German pilots had tilted seats plus heightened footrests, in the end this probably cancelled out the difference with the early G-suit.

It helps but not even close Soren. Take a guy with a tilted seat and heightened footrests and put him against a guy with a g suit at say 7 or 8 Gs. There is no doubt the guy with the G suit is not going to black out first, and this even includes the early USAAF G suits. If it was a matter of tilting a seat back and adding stirrups to overcome blacking out, there's been a lot of wasted money spent in developing anti g technology since WW2.

 

[drgondog]

Davparlr,

Regarding my comment on the lightness harmony of the controls and the structural integrity of the airframe being the dominant factors for succes, well usually this was a feature of the faster more powerful a/c over the previous lighter but less powerful a/c. When the FW190 arrived on the scene the Spitfire pilots were at a complete loss as the FW190 ws not only much faster, it also climbed much faster and was unbelievably agile at all speeds, esp. at speeds of 400 km/h and above where pulling lead on one was near impossible without blacking out.

Bill,

The FW190 BF109 were both designed to withstand 13 G's fully loaded, this was the ultimate load limit no doubt, but it is still pretty staggering.

The load limit for the P-51D is 6.59 G fully loaded, now as to the ultimate I don't know but.

The load limit for the Dora-9 fully loaded is 6.9 G.

Soren the Limit load in the Mustang Manual is 8G at 8,000 pounds gross. You can extrapolate whatever you want from that as it is linear basically.

According to Gruenhagen's "History of Mustang" the Mustang A-D (and K) was 12 Ultimate) and the G,J H and M (Light weigh re-design) were 11 Ultimate at 8,000 pounds - consistent with RAF design doctrine.

US airframe standards and practices in WWII all the way through my own career, at the time NASTRAN and Stardyne became industry standards for Structural and Frequency analysis, used 1.5 limit load (usually at 'yield' for LOWEST single point of stress attaining Yield level), for Design Ultimate and tested analytically if there were discrete 'points of failure' that would fail before 'ultimate' stress point was reached.

Obviously a C-47 flight load limits was 3g positive and 1 1/2 g negative (i think) for normal ops and gross, while the US fighters (exceptions noted) were 8g for nominal (not max) gross weight. Landing loads were considerably higher.

For practical purposes the Manual is right for a 51 after burning the fuse tank over Germany.

I think we have had this discussion before, but I haven't seen anyone including Kurfurst present one LW source specifying limit and ultimate loads for any LW fighter or other a/c.. Have you found a source yet for the above Fw 190 and Me 109 figures?

 

[Soren]

Bill,

I extrapolated the load limit from the 9700 lbs gross weight, which is with an empty fuselage tank. (Simply divide 64,000 with weight of a/c) With a full fuselage tank the P-51D weighed in at 11,000 lbs. So 8,000 lbs is not anywhere near a representive figure, esp. since this is considering that atleast 80% of the internal fuel has been used up, which in turn would mean no return trip. Remember than the empty weight of the P-51D is ~7,400 lbs. Also the P-51's would mostly run on the external drop tanks to the frontline and then drop them to run on internal once the enemy was sighted.

The load limit figure for the FW190 is from the Dietmar Hermann's book on the plane and is the minimum figure for a fully loaded a/c.

What is your source for the 11 G ultimate load limit for the -51 ?


FLYBOYJ,

Is there any proof that these early G-suits helped much in any way ? From what I've heard the heightened footrests and tilted seats did just as much good as these early G-suits. Remember the US pilots were just sitting in what resembled a straight chair by comparison.

Anyway the best way to survive high G's between the early G-suit and the heightened footrest tilted seat is with lots of practice with muscle straining.

Today the G-suit is ofcourse the no.1 reason pilots aren't blacking out above 7 G's, but the design effectiveness is also a good deal different than the early G-suits of WW2.

 

[FLYBOYJ]

FLYBOYJ,
Is there any proof that these early G-suits helped much in any way ?

100% YES - there were extensive tests done at Wright Patterson AFB around 1943 or early 1944 if I remember right. I think the museum there has a whole display of these test and the first implementation of the G suit.

From what I've heard the heightened footrests and tilted seats did just as much good as these early G-suits. Remember the US pilots were just sitting in what resembled a straight chair by comparison.

It didn't matter, again if it was a matter of just reclining the seat and using foot rest a lot of extra "junk" could of been omitted from fighters over the past 60 years...

Anyway the best way to survive high G's between the early G-suit and the heightened footrest tilted seat is with lots of practice with muscle straining. The G-suits are of course the no.1 reason pilots aren't blacking out above 7 G's. The G-suits helps allot.

The physical training (especially leg muscle weight training) is a big part of it. the inclined seat will help but in the end the guy wearing the g suit has a BIG advantage.

 

[syscom3]

Soren, the early g-suits were designed for dive bomber pilots, that had an annoying habit of blacking out after pulling from a dive.

They worked like a charm, and soon found use in the fighters.

 

[DerAdlerIstGelandet]

And the German pilots had tilted seats plus heightened footrests, in the end this probably cancelled out the difference with the early G-suit.

Your proof and source that the tilten seats were better than G-suits please.

The tilted seats and all probably helped but I find it very hard to believe that it was better than a G-Suit, even an early one.

 

[davparlr]

Davparlr,

The FW190 BF109 were both designed to withstand 13 G's fully loaded, this was the ultimate load limit no doubt, but it is still pretty staggering.

The load limit for the P-51D is 6.59 G fully loaded, now as to the ultimate I don't know but.

The load limit for the Dora-9 fully loaded is 6.9 G.

The loaded weight of a Bf-109G is 7480. For 13 "gs" the Bf-109G must be tested to withstand an equivalent of 97240 lbs of force. For the P-51D, if, as you say, has a load limit of 6.59 gs, and, as I remember g limits on aircraft, they are tested to 1.5 times limit load, as drgondog has also said, then the test level must be 9.9 gs. Now the P-51D has a loaded weight of 10100 lbs., so for a load limit 6.59 gs, then it must be tested to an equivalent of 99990 lbs. In other words the aircraft structure of the P-51D must be tested to a higher stress level than the structure of the Bf-109.

 

[davparlr]

Bill,

What is your source for the 11 G ultimate load limit for the -51 ?

This is not surprising at the 8000 lb number. Again, to meet the 6.59 gs at loaded weight, the P-51 must be tested at an equivalent 99990 lbs of force. Dividing this by 8000 lbs, you get 12.5 gs. The 8000 lbs number is obviously a design-to number and is not meant to be any combat weight value.

These g levels are not that far off modern fighter designs where g suits are worn. These numbers are probably over design for the environment in which they fought, which is also probably why the Brits wanted to relax the P-51 specs.

 

[Soren]

Davparlr,

There seems to be something you don't understand;

The load limit of 6.59 G's is for the P-51D at 9,700 lbs, which is with an empty fuselage tank. At 10,100 lbs with full internal fuel the load limit is 6.33 G's.

So this means that the P-51's airframe has a 9.85 G ultimate load limit at 9,700 lbs, and 9.47 G ultimate at 10,100 lbs.

Now as to how mouch force the airframe has to withstand, well what does this matter ?? The a/c which can withstand the most G-forces is what matters. So while the P-51 is able to withstand ~96,000 lbs of force it is also heavier than both the 109 190 and therefore has to cope with more weight for every increase in G-forces.