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- #861
Wow that is interesting and a bit counter-intuitive. Do you know why thinner air or higher altitude made G more risky / damaging for the airframe? Is that just a matter of the TAS?
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Wow that is interesting and a bit counter-intuitive. Do you know why thinner air or higher altitude made G more risky / damaging for the airframe? Is that just a matter of the TAS?
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- #862
I had no idea about the extent of this either. And look how tough the Tempest is. I think WW2 planes were a bit more heavily built than modern fighters. Most modern fighters (with certain exceptions like the A-10 and the Su-27) don't even have armor any more. Carbon fiber and so on is much lighter but not quite as strong by weight. I think?
I admit I'm out of my depth here so forgive me if I'm wrong about that.
DarrenW
Staff Sergeant
I was too, but that's what Greyman's reference states. Maybe he can give us some more details regarding these stats....
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- #864
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- #865
I think there was different ways to measure this - the limit, then there is a guarantee like 50% or 100% - a 100% guarantee on a 6G limit means 12G effectively, whereas a 50% guarantee on a 6G limit is 9G. Or something like that.
Hello Slaterat,
On the assumption that "Less than 2 seconds" in this case means around 1.5 seconds:
The roll rate would only be about 60 degrees per second which is quite poor performance and this is not even at high speed.
Just for a performance comparison:
The early P-40 (Probably Tomahawk) had a peak roll rate of 135 degrees per second at 350 MPH IAS.
At 200 MPH IAS, roll rate was around 75 degrees / second
At 300 MPH IAS, roll rate was around 115 degrees / second
(from AHT graph)
The Merlin P-40 seems to be a lot slower for some reason.
(By reputation the P-40 had a pretty good roll rate.)
At 200 MPH IAS, 84 degrees / second
At 300 MPH IAS, 83 degrees / second
(my read of the graph)
Thanks for the data, Greyman,
I wonder what the operational limits actually were because at least for the US types, these are the maximum loads above which the wings are expected to fail. Typically, the US aircraft as originally designed could tolerate up to 8G without permanent structural damage but that limit drops as aircraft weight inevitably grows.
Hello Schweik,
Thanks for the listing of turning times.
I would have thought there would be an advantage for the Soviet Yak fighters, but they look pretty close to even. I am very surprised the lightened Yak-1 did not show a more consistent advantage.
- Ivan.
Close. At higher altitudes you generate less lift for a given airspeed and sustain it for less time due to engines making less power.
Also expect that the G limits posted above are probably ultimate design loads or where structural failure is to be expected.
Twice that I know of Eagles at Eglin pulled over 11 G's and flew again. They were fairly new at the time. I've also seen 10 G's force a wing change. Max allowable in the Eagle is 9 down to about 6.5 depending on speed and altitude (positive G's).
Cheers,
Biff
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- #868
Well one of the Yak 1s said it turned in 17 seconds which is very fast indeed. The test shown were mostly done at 1,000 ft and at I forget at what speed. It's probably different at different altitudes and speeds without a doubt.
It's also odd that the Hurricane had such bad turn times since most people say it out turned most of the other planes listed. So who knows there could be issues with those tests.
So I wouldn't take it as definitive proof it's just a data point.
From what I read one of the traits of the Yak which isn't that easy to quantify is that they did not lose speed much in a turn (or as much) having small wings they had a lot less drag. So they could turn and keep turning. If that makes sense.
Schweik / Gents,
There are two types of steady turns. The sustained, usually accomplished at higher speeds, which will be measured in degrees per second or time for a complete 360. This turn is your fastest 360 but the circle is larger.
An example of when to use this one if you are being bounced from behind and you have time to turn, meet the attack and sustain or maintain energy/ airspeed.
The second turn is a radius turn, meant to makea smaller or smallest turn circle.
Use this one if your trying to get someone out of your chili or to get into someone else's or bring your nose to bear for a gunshot.
This is the cliff cliff cliff notes version as there is an encyclopedia Britannia worth of discussion on turning fights.
Cheers,
Biff
wuzak
Captain
wuzak
Captain
Perhaps because the P-40F had 6 guns and armour?
Though the roll rate of the P-40F is shown to be superior at 200mph IAS.
There were no other specifics on that time to roll rate for the Typhoon. In other time to roll tests at the A&AEE, for what ever reason, they tend limit the application to 1/4 aileron.
Other testing at A&AEE, previously posted by me, the Kittyhawk's ailerons were solid at 460 IAS, whereas the Typhoon still had good aileron control at the same speed.
No more granularity in the data unfortunately.
I did copy down figures from destruction tests of the Spitfire I, Hurricane I and 109E. Those are much more detailed.
eg Spitfire I (design factor 10.0) 6,200 lb:
High incidence condition
no permanent set at 10.0 G
no serious effect below 11.5 G when rivets begin to fail
collapse by fracture of main spar at 12.3 G
Low incidence conditionno effect other than waving skin up to 9.0 G
collapse by failure of skin attachment at 12.0 G
DarrenW
Staff Sergeant
DarrenW
Staff Sergeant
BiffF15 is right on the money. In my Hellcat example, the TAS at 30,000ft is about 130 mph less than it is at 10,000ft, while the "safe" positive G load is only about half that found at the lower elevation. Reduced lift had to play a big part.
Shortround6
Major General
Most US fighters were designed to have an ultimate 12 G load, that is point at which they figured there would be permanent structural damage.
This ultimate load was actually a safety factor as they were trying for an 8 G load in flight.
G loading was relatively primitive at the time as was testing for metal fatigue in general.
G load tests were often done by suspending the aircraft (or it's wing) upside down and piling on (or hanging) sandbags/weights until they reached the desired "test weight" which, while better than not testing, is hardly reflective of the dynamic loads imposed by flying. One reason for the 50% safety margin.
Now days it is done in specially constructed jigs using calibrated hydraulic jacks on large aircraft, Small planes (small manufacturers still do the old way)
Since just about every aircraft known to man gained weight somewhere along the design/development process the actual G loading went down. The Mustang was good for 8"G"s in service (12 Gs ultimate) at 8000lbs, since flying a Mustang at 8,000lbs meant you were seconds away from running out of fuel or oil you had to make allowances. 8 times 8,000 is 64,000. If the Mustang is grossing 9000lbs you divide 64,000 by 9,000 and get 7.111 There is actually a chart in the manual that explains this.
Please note that armor has nothing to do with aircraft strength. in fact it is a liability. Very few aircraft used armor (IL-2 and siblings excepted) as structural components. Most armor has little or no bend unlike some structural members than can bend/deflect and return to "normal" after the load is removed. Armor is either going to permanently bend or break. Granted it may no do so until something else has already broken.
However for some of these load/stress limits to work the weight has to be evenly distributed over the structure. Too much weight in one location can break the structure even if the total weight is less than the ultimate load. B-17s needed to fill the outer wing tanks in order to get close to the max gross weight. Running several thousand pounds below max gross but having all the weight in the bombbay and inner fuel tanks put too much bending stress on the wing.
The designers/engineers were learning an awful lot about structures and stress during this time and even a few years could mean major changes under the skin.
There were different ways that some of this was measured or different allowances made from country to country so trying to compare the English G load levels to the American ones is not strictly accurate for example.
Pilots tolerance to G load is rather variable. I will defer to the people on this board who are actual pilots but I believe it is somewhat time related. As in a pilot may be able to tolerate 6-8 Gs for a few seconds without totally blacking out but trying to stay conscious at 4-5 Gs for 30 seconds may not be doable?
Just throwing numbers out. feel free to correct. You also had varying degrees of greying out before total blackout.
Many dive bomber pilots routinely blacked out during pull outs from dives but since the plane was climbing (or about to ) in a pretty much level attitude when the blackout occurred the pilot had time to recover (both consciousness and the airplane). A pilot trying to pull 5-6Gs in a turning dog fight only a few hundred feet above the ground doesn't have that luxury.
This ultimate load was actually a safety factor as they were trying for an 8 G load in flight.
G loading was relatively primitive at the time as was testing for metal fatigue in general.
G load tests were often done by suspending the aircraft (or it's wing) upside down and piling on (or hanging) sandbags/weights until they reached the desired "test weight" which, while better than not testing, is hardly reflective of the dynamic loads imposed by flying. One reason for the 50% safety margin.
Now days it is done in specially constructed jigs using calibrated hydraulic jacks on large aircraft, Small planes (small manufacturers still do the old way)
Since just about every aircraft known to man gained weight somewhere along the design/development process the actual G loading went down. The Mustang was good for 8"G"s in service (12 Gs ultimate) at 8000lbs, since flying a Mustang at 8,000lbs meant you were seconds away from running out of fuel or oil you had to make allowances. 8 times 8,000 is 64,000. If the Mustang is grossing 9000lbs you divide 64,000 by 9,000 and get 7.111 There is actually a chart in the manual that explains this.
Please note that armor has nothing to do with aircraft strength. in fact it is a liability. Very few aircraft used armor (IL-2 and siblings excepted) as structural components. Most armor has little or no bend unlike some structural members than can bend/deflect and return to "normal" after the load is removed. Armor is either going to permanently bend or break. Granted it may no do so until something else has already broken.
However for some of these load/stress limits to work the weight has to be evenly distributed over the structure. Too much weight in one location can break the structure even if the total weight is less than the ultimate load. B-17s needed to fill the outer wing tanks in order to get close to the max gross weight. Running several thousand pounds below max gross but having all the weight in the bombbay and inner fuel tanks put too much bending stress on the wing.
The designers/engineers were learning an awful lot about structures and stress during this time and even a few years could mean major changes under the skin.
There were different ways that some of this was measured or different allowances made from country to country so trying to compare the English G load levels to the American ones is not strictly accurate for example.
Pilots tolerance to G load is rather variable. I will defer to the people on this board who are actual pilots but I believe it is somewhat time related. As in a pilot may be able to tolerate 6-8 Gs for a few seconds without totally blacking out but trying to stay conscious at 4-5 Gs for 30 seconds may not be doable?
Just throwing numbers out. feel free to correct. You also had varying degrees of greying out before total blackout.
Many dive bomber pilots routinely blacked out during pull outs from dives but since the plane was climbing (or about to ) in a pretty much level attitude when the blackout occurred the pilot had time to recover (both consciousness and the airplane). A pilot trying to pull 5-6Gs in a turning dog fight only a few hundred feet above the ground doesn't have that luxury.
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- #877
Being able to withstand G loads was another of those rare skills (like marksmanship in general, or deflection shooting specifically, or a knack for riding a stall) that some pilots used to their advantage. Greg Boyington and the Australian Ace Nicky Barr both had developed personal techniques of 'bearing down' to withstand G load. Boyington was a wrestler and Barr was a rugby player, which apparently contributed to their having the right kind of (thick, muscular) necks for that business.
I think in later periods they started teaching this but I don't know when.
I think in later periods they started teaching this but I don't know when.
Hello Schweik,
That Yak-1b (predecessor of the Yak-3) was the lightened Yak-1 I was referring to.
Note though that its times were not consistent.
They probably all started out at cornering speed.
I believe BiffF15 already gave a pretty good explanation of the difference between turn rate and turn radius.
The British tended to be interested in Turn Radius. The Soviets tended to be interested in Turn Rate.
Consider this: One fellow flies a Fokker Eindecker with a stall speed of around 40 MPH and can make a 360 degree turn inside a 200 yard circle. He is flying so slowly that a full 360 degree turn takes about 30 seconds.
The other fellow is flying our venerable P-40 and can make a full 360 degree turn in 22 seconds but needs 700 yard circle to do it.
Which fellow turns better?
(The numbers are all invented, so I don't know if the physics actually fits together, but I think it still makes a good enough illustration.)
I believe that other factors may also be masked here such as how good the initial turn rate is. If a fighter bleeds speed at a higher rate, it will not show up as well here because although its initial turn rate is the same, it can't sustain it for as long before it gets down to stall speed while pulling G.
Note how the P-40M has a better time than the P-40E?
The P-40M weighs more and has exactly the same wing and I don't think the longer tail is going to change things.
That idea actually doesn't make much sense.
A smaller wing does have less Parasitic Drag but because of the smaller area is going to need more Angle of Attack to lift the same weight and that would cause Induced Drag to be higher. Parasitic Drag tends to influence maximum speed while Induced Drag tends to influence how much speed is lost when pulling G.
Instead I would look for lower weights and wing loading, wing planform and differences between the 2200 series airfoil of the P-40 and the Clark-Y of the typical Yak fighter.
- Ivan.
I have almost nothing on WWII G resistance but there is this bit from a report on a liaison visit by two Central Fighter Establishment members to various USAAF and USN stations late 1944:
"G" Suits
The Berger type "G" suit, operated by air pressure on the calves, thighs and abdomen, was worn by the CFE representatives while undergoing tests in a centrifuge chamber. The majority of personnel available for the trials had been able to withstand no more than 4 "G" without the suit and the Department were disturbed by the fact that both CFE representatives reached 6.5 "G" unassisted. Wearing the suit both blacked out at 6.5 "G" and this is explained by the fact that the suit is extremely uncomfortable and therefore counteracts the natural resistance which some pilots develop. As a result of discussion it was agreed that whereas the suit would be valuable to those pilots whose threshold was about 4 "G", the discomfort caused would not be compensated for by the gain of 1.5 "G" by pilots whose threshold was more than 5 "G".
"G" Suits
The Berger type "G" suit, operated by air pressure on the calves, thighs and abdomen, was worn by the CFE representatives while undergoing tests in a centrifuge chamber. The majority of personnel available for the trials had been able to withstand no more than 4 "G" without the suit and the Department were disturbed by the fact that both CFE representatives reached 6.5 "G" unassisted. Wearing the suit both blacked out at 6.5 "G" and this is explained by the fact that the suit is extremely uncomfortable and therefore counteracts the natural resistance which some pilots develop. As a result of discussion it was agreed that whereas the suit would be valuable to those pilots whose threshold was about 4 "G", the discomfort caused would not be compensated for by the gain of 1.5 "G" by pilots whose threshold was more than 5 "G".
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- #880
Ivan1GFP said:
Well, most of the P-40 variants generally had a lower wing loading than most of the Yak variants. Big wing with a large wing area.
Aside from wing loading, power also makes a difference - the P-40M may have had a better (quicker by time) turning circle in their test because they flew it at a higher power setting.
Most of the M-105 powered Yaks (except the Yak 3 with a more souped up 105PF) seem to have similar power to mass ratios as P-40s, so long as the latter were flying at moderately high power settings, i.e. 57" Hg or 60" Hg etc. which they were capable of at all the altitudes combat normally took place on the Russian Front (up to about 10,000 ft). The VK-107 powered Yaks were considerably zippier of course.
As for the rest of it, my main sources aside from whatever hard data gets posted here or WWIIAircraftPerformance.org are pilot accounts and operational histories. The latter report that the P-40 out turned all the other modern fighters in Russia and the Med (German, Italian or Russia). In Russia only the older I-16 or I-153 etc. would out turn it. I already posted one Soviet pilots account that the P-40 could "easily out turn" a Yak 7 - I don't mean just turn time I mean getting on the other aircraft's tail.
As for
P-40E is .14 hp / lb at 42" (1,150 hp) and .17 at 56" Hg (1,470 hp)
P-40K is .16 hp / lb at 51" (1,325 hp) and .18 at 60" Hg (1550 hp)
P-40M is .13 hp / lb at 51" (1,200 hp) and .15 at 57" (1,360 hp)
P-40N** is .15 hp / lb at 51" (1,200 hp) and .17 at 57" (1,360 hp)
These are from Wikipedia so cut me some slack if there are mistakes:
Yak-1B is .19 hp / lb (M-105PF / 1,180 hp)
Yak-7 is .16 hp / lb (M-105 / 1050 hp)
Yak-9D is .17 hp / lb (M-105 / 1,180 hp)
Yak-9U is .21 hp / lb (VK-107 / 1,500 hp) - 1944
Yak-3 is .22 hp / lb (VK-105PF / 1,300 hp) - 1944
Per the above, only the rather 'tepid' P-40M* is too sluggish to compete. The V-1710-81 etc. can make 57" up to 8-10,000 ft. V-1710-39 or -73 are a little lower than much. Not not talking about heavy duty overboosting which is available down below 2,500 ft. By 1944 the Yaks are clearly pulling ahead but in 1942 or 1943 the P-40s look competetive (just as Golodnikov noted). Also keep in mind, unlike in the tests I posted where they indicate 6 guns, the Soviet pilots mentioned routinely taking one pair of guns out of the P-40 which would also improve wing loading, acceleration and roll rate a bit more.
I'm not saying the P-40s were better mind you. Soviet pilots generally still preferred the Yak due to "higher combat speed" whatever that means precisely and better climb rate and vertical turn performance. The P-40 had the much higher dive speed, stronger build and heavier armament. All I am saying is that they were clearly comparable and not 'second rate'
* P-40Ms would handle and fly better at higher altitudes 10-15,000 ft of course lol
** This is the lightened early P-40N
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