Insight into the magnitude of forces involved in dogfights during WW2

[Soren]

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.

Again why is it necessary to twist what I say ?? I never claimed that the tilted seat heightened footrests were better than the G-suit, just that they about cancelled out the advantage given by the early G-suit. Besides at that period exercise was the best way to withstand G-forces.

 

[Soren]

Anyway getting back on track the point here is that all the fighters above could take G-loads which would black out the pilot quite quickly, and this just illsutrates why a/c-wise light harmonized controls at all speeds plus high perofmance was the dominant factor for success, if these were close however the pilot experience became the absolute dominant factor for success.

 

[FLYBOYJ]

Again why is it necessary to twist what I say ?? I never claimed that the tilted seat heightened footrests were better than the G-suit, just that they about cancelled out the advantage given by the early G-suit. Besides at that period exercise was the best way to withstand G-forces.

Again 100% wrong - tilting a seat back and adding food rest WILL NOT cancel out the advantage of the G suit - even the early ones (which aren't much different from the ones we see today), and I don't care if the pilot was sitting on a milk crate.

I've flown in jets and pulled Gs with and without a g suit and there is a HUGE differance. Again an angled seat will help, but its not cancelling out the advantage, even if the guy in the tilted seat is in exceptional shape.

 

[davparlr]

Davparlr,

There seems to be something you don't understand;

Maybe I didn't understand because you said

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

You didn't define your numbers very well, who would have known you were using an empty tank.

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.

This is true, but then you said

Anyway getting back on track the point here is that all the fighters above could take G-loads which would black out the pilot quite quickly

This is also true and since all of these planes would exceed the pilots ability to perform and were very effective in combat, I scratch my head wondering why we always end up discussing load limits.

 

[Soren]

Davparlr,

I made it quite clear that I extrapolated the 6.59 G figure from a weight of 9,700 lbs, but nevermind cause you obviously missed this, so no point in argueing over it.

As to your last point, well that is alo my point; All of the fighters above could pull G's that the pilots couldn't stand and this at below the normal speed at which dogfighting was taking place by then.

What becomes important in a prolonged dogifght however is the ability to sustain high G's, and here the higher powered FW-190, Bf-109 Spitfire have a significant advantage over the heavier P-51, although unlike the Dora the Anton only has this advantage at low to medium alt. The P-51 was a hottie at high alt, no doubt about it.

 

[drgondog]

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 - the source for the Mustang design loads in Gruenhagen's Mustang and Wagner's Mustang Designer - about Edgar Schmeud.

The former discusses in some depth the RAF design teams dialog with Schmeud and NA engineers in 1942 and early 1943 when the P-51 was undergoing a severe weight analysis for future production versions.

The 11 g target was discussed specifically as one of the considerations to examine to see in US aircraft were a.) over designed, and b.) would point to areas in conventional design of serious concern.

Thus 11g was the design Ultimate for all the Light weight fighters.

The P-51A,B and C was Design limit at 8,000 which was a high (but not max) Gross weight for the 51A, but the 8,000 pound target upon which a 8G limit load kept moving into the normal flight profile, meaning ammo and most internal wing fuel but no fuselage tank (with most of the extra pounds along with heavier Merlin from the P51A)

The F-16 is designed to higher stress limits than the P-51 and the G suits are pushing 9g (I think) which is at the threshold of endurance for a fighter pilot with that G suit in manuever. I don't recall where I pulled the 9g number... but if correct indicates the Ultimate number of the airframe to be well into 13-14G range. Someone else may have a definitive number on this.

IIRC the typical 'high side' of G achievement for un augmented fighter pilot was around 4G? and the Berger moved that peg to 5-6G for limited time?

 

[DerAdlerIstGelandet]

Again why is it necessary to twist what I say ?? I never claimed that the tilted seat heightened footrests were better than the G-suit, just that they about cancelled out the advantage given by the early G-suit. Besides at that period exercise was the best way to withstand G-forces.

Okay then can you please post proof and sources that show that they cancel each other out.

I am sorry but I find it very hard to believe, for the same reasons that Joe has allready stated.

 

[Soren]

A 1 - 1.5 G improvement with the early G-suit sounds very reasonable Bill.

The pressure points, pressure itself and design of later G-suits is quit different from the early G-suits.

The tilted seat heightened footrests helped allot according to the pilots, and according to NACA a 30 degree tilt gives a huge increase in tolerable G.


From here: Physiological Effects of Positive G Forces

"The last method has not effectively been used in military aircraft to any extent to date but which is probably the system of the future. It is reclining the pilot in the cockpit.

Consider a subject sitting erect in the seat of an aircraft. The average distance from his heart to the base of the brain is 30 cm and it takes approximately 24 mm of mercury pressure to raise a column of blood 30 cm in a normal standing environment of one G. It would, of course, take the same pressure to raise a column of blood from the heart to the wrist if the wrist is held at eye level as it takes to de- liver blood to the brain.

In a study in which 250 centrifuge runs were made on human volunteers, it was demonstrated that systolic blood pressure in the radial artery held at eye level was reduced by 32 mm of mercury for every G added to the ± G2 force. Visual disturbances occurred when the systolic blood pres- sure at the base of the brain was reduced to 50 mm of mercury and complete loss of vision occurred when the pressure was reduced to 20 mm of mercury. Loss of consciousness occurred when the systolic pressure at brain level was reduced to zero. This would be equivalent to a five ± G pull, i.e., 5 x 32 = 160, where the blood pressure at the base of the brain would be reduced to zero if the systolic blood pressure in the subject was 160 at the heart level.

These forces were sustained in the study for a period of 15 seconds and the time to recovery unfortunately was not reported. It was noted, how- ever, that under a load of five G's, the systolic blood pressure was reduced by five mm of mercury and the diastolic pressure was unaffected if the head is lowered to the level of the heart. To extrapolate from that information a positive G force in itself would not produce unconsciousness or blackout if the head is lowered to heart level.

Tables 2 and 3 show the time of exposure to ± G loads when pulling from horizontal flight to vertical (Table 2) and from vertical down to vertical up (Table 3) as in an inverted humpty at various speeds from 100 to 300 MPH and at varying G loads from two G's to 12 G's. Table 1 shows blood pressure at the base of the brain with varying seat tilt angles and 0 loads up to 12 G's. Remember that L.O.C"

 

[drgondog]

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.

This is about right for both conditions for the A,B,C,D/K with the A slightly higher with no wing tank and an Allison vs Merlin.

The early B (and RAF Mustang III) had no 85 gallon fuselage tank so these three a/c had higher ultimate Limit loads in context of amount of internal fuel to reach the same 8,000 pounds

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.

Soren just some more thoughts.

In most combat situations the 51 had burned away external and some internal (ie. fuse tank). The max take off weight for no stores on the A was 8200, the B/C was 9000 (with 184 wing plus internal 85 gal tank) and 9540 for D/K. The H was 8500 (with 205 wing and 50 fuse cells)

So if combat was engaged after 'drop' tanks, fuselage tank dry, but all wing fuel and ammo intact - the B was at approx 8500 and the D was at 9,000.. the H in that same conditionwas at 8100

PS the Gruenhagen discussion about 12 and 11 g ultimate load change for the lightweight design is on page 119

 

[FLYBOYJ]

A 1 - 1.5 G improvement with the early G-suit sounds very reasonable Bill.

The pressure points, pressure itself and design of later G-suits is quit different from the early G-suits.

Again, the early pneumatic g-suits aren't much different from the ones today - I've seen both - the biggest difference is comfort and the material used.

The tilted seat heightened footrests helped allot according to the pilots, and according to NACA a 30 degree tilt gives a huge increase in tolerable G.


From here: Physiological Effects of Positive G Forces

"The last method has not effectively been used in military aircraft to any extent to date but which is probably the system of the future. It is reclining the pilot in the cockpit.

Consider a subject sitting erect in the seat of an aircraft. The average distance from his heart to the base of the brain is 30 cm and it takes approximately 24 mm of mercury pressure to raise a column of blood 30 cm in a normal standing environment of one G. It would, of course, take the same pressure to raise a column of blood from the heart to the wrist if the wrist is held at eye level as it takes to de- liver blood to the brain.

In a study in which 250 centrifuge runs were made on human volunteers, it was demonstrated that systolic blood pressure in the radial artery held at eye level was reduced by 32 mm of mercury for every G added to the ± G2 force. Visual disturbances occurred when the systolic blood pres- sure at the base of the brain was reduced to 50 mm of mercury and complete loss of vision occurred when the pressure was reduced to 20 mm of mercury. Loss of consciousness occurred when the systolic pressure at brain level was reduced to zero. This would be equivalent to a five ± G pull, i.e., 5 x 32 = 160, where the blood pressure at the base of the brain would be reduced to zero if the systolic blood pressure in the subject was 160 at the heart level.

These forces were sustained in the study for a period of 15 seconds and the time to recovery unfortunately was not reported. It was noted, how- ever, that under a load of five G's, the systolic blood pressure was reduced by five mm of mercury and the diastolic pressure was unaffected if the head is lowered to the level of the heart. To extrapolate from that information a positive G force in itself would not produce unconsciousness or blackout if the head is lowered to heart level.

Tables 2 and 3 show the time of exposure to ± G loads when pulling from horizontal flight to vertical (Table 2) and from vertical down to vertical up (Table 3) as in an inverted humpty at various speeds from 100 to 300 MPH and at varying G loads from two G's to 12 G's. Table 1 shows blood pressure at the base of the brain with varying seat tilt angles and 0 loads up to 12 G's. Remember that L.O.C"

All fine and dandy - but still gives no indication that an angle seat will cancel out the g suit advantage. BTW the angle of the seat (which is referred as "pitch) has to be factored into the location of the flight controls. A 30 degree pitch is huge - and what Luftwaffe fighter had "pitched" seats????

 

[Soren]

Soren just some more thoughts.

In most combat situations the 51 had burned away external and some internal (ie. fuse tank). The max take off weight for no stores on the A was 8200, the B/C was 9000 (with 184 wing plus internal 85 gal tank) and 9540 for D/K. The H was 8500 (with 205 wing and 50 fuse cells)

So if combat was engaged after 'drop' tanks, fuselage tank dry, but all wing fuel and ammo intact - the B was at approx 8500 and the D was at 9,000.. the H in that same conditionwas at 8100

PS the Gruenhagen discussion about 12 and 11 g ultimate load change for the lightweight design is on page 119

I just used the fully loaded weight with empty fuselage tank for the P-51D, expecting that they ran on external tanks to begin with and on internal on the home trip.

The German fighters were often carrying half full internal fuel tanks, there not being enough fuel to go around. I used the fully loaded weight for all the fighters though.

 

[Soren]

All fine and dandy - but still gives no indication that an angle seat will cancel out the g suit advantage. BTW the angle of the seat (which is referred as "pitch) has to be factored into the location of the flight controls. A 30 degree pitch is huge - and what Luftwaffe fighter had "pitched" seats????

FLYBOYJ,

The LW fighters have pitched seats, around 25 degrees, and the heightened footrests allowed the pilot to increase the pitch of his body even further. The raising of his legs also helps the heart push blood up to the brain.

 

[FLYBOYJ]

FLYBOYJ,

The LW fighters have pitched seats, around 25 degrees, and the heightened footrests allowed the pilot to increase the pitch of his body even further. The raising of his legs also helps the heart push blood up to the brain.

And agree there - I don't know the pitch of say a P-51 or P-38 (I've sat in both). I wouldn't guess they weren't as high 25 degrees but there was a "pitch" there.

Even at 15 degrees, throw a g suit in there and there is a great advantage.

BTW - I sat in "White 14" and I could tell you that seat back was pretty straight.

 

[Soren]

Roger that FLYBOYJ, the FW190's seat has more pitch than the BF109's, far more.

As to the early G-suits, have you ever tried one ? Also is there a study which compares the early G-suit's effectiveness vs not wearing one ?

 

[FLYBOYJ]

As to the early G-suits, have you ever tried one ? Also is there a study which compares the early G-suit's effectiveness vs not wearing one ?

I've seen a WW2 Berger suit, tried on Korean war vintage suits and personally own a CSU-138 that I have used on several occasions. The Berger suit I seen from what I remember was made from "canvas" (possibly something else) and rubber and seemed to have little room to get adjusted when you would put it on. The Korean War suit was very similar to a modern suit and used a nylon material - more "wiggle room' to make it easier to get on. The suit I own is around a post VietNam era suit and had all kinds of zipper and snaps that make it a little easier to put on and adjust, but from the operational standpoint they were about the same in where pressure would be placed on the legs and stomach - the biggest difference I seen from the early suit was comfort and ease of putting it on.

I think you could see that this is an area I'm very "into." Several years ago I did work on a T-33 and the owner and I got his g suit system working so we went out and tested it - this prompted me to buy my own. Additional at the same time I was occasionally getting T-33 and F-4 rides at my full time employer. I went up a few times and was blacked out when we were pulling maneuvers. At later times I used my g suit and it made all the difference in the world.

BTW - not being prepared for accelerated Gs - I blacked out at 4Gs while trying to take pictures in the back of an L-29. One minute we were above the airport in formation - we did a "pitch out" that I was not prepared for, the next thing I know we were on final - out for about 20 seconds.

 

[Glider]

Its interesting but if I remember correctly the first use of an anti G suit was by British Seafires in 1942. They were also used by British test pilots to help them in their analysis of new designs.

I will dig around and see what I can find.

 

[pbfoot]

Its interesting but if I remember correctly the first use of an anti G suit was by British Seafires in 1942. They were also used by British test pilots to help them in their analysis of new designs.

I will dig around and see what I can find.

I think the first G suits were made in Toronto by a gent named Franks who worked under Banting(insulin guy) the RAF used the MK 1 the USAAF and RCAF the MK2 it used water instead of the modern air models

 

[Glider]

Found something that I think will be of interest
Whatever Happened To...?: Catching ... - Google Book Search

 

[Soren]

Does anyone have an exact number on how many Allied pilots wore the G-suit ?

 

[DerAdlerIstGelandet]

All fine and dandy - but still gives no indication that an angle seat will cancel out the g suit advantage. BTW the angle of the seat (which is referred as "pitch) has to be factored into the location of the flight controls. A 30 degree pitch is huge - and what Luftwaffe fighter had "pitched" seats????

I also agree that a tilt seat will make it easier but I would still like to see actual proof that it cancels out a g-suit.