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Matt6461
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Altitude of the static 6g maneuver?

Sat Apr 02, 2022 1:31 am

Wing strength is tested so that the wing can withstand a static 6g pull-up at MZFW.

I recall reading recently that this was tested at 20,000ft altitude pressure and, now that I think of it, that makes sense: it's hard for a fighter aircraft to pull 6g's in the stratosphere, let alone a big airliner. The wing stalls before this happens, meaning you have to keep descending before it's possible to pull 6g's. Can anyone point me to the regulations governing the 6g certification test?
 
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Matt6461
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 1:44 am

...the FL20 testing level is probably related to needing to avoid mountains? I.e. you have to be able to pull out at 6g's over the Andes or Himalayas? But I guess if you're directly over Everest you're screwed. Something to think about on my next trip to those parts. Probably part of the reason a lot of flights go around the Himalayas. Also explains better something I never quite understood - why flying "The Hump" to China was so dangerous in WW2. Max cruising level for a laden WW2 planes was in the mid-20's; if you hit a strong up/down draft off the mountains you probably don't have the static altitude maneuver room to recover before losing a few thousand feet and...
 
Woodreau
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 2:01 am

FAR 25 is the starting point for certification of transport category aircraft in the US
 
Flow2706
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 7:05 am

Airliners are usually certified for +2.5/-1gs (this number comes from a regulation as well but I’m too lazy to look up the exact reference now), not to +6. So the test has to be performed up to 2,5 x 1,5 (safety factor) = 3,75g. For obvious safety reasons this test is not performed inflight but on the ground in a specific test rig where the wing is pulled up with a crane.
 
kalvado
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 8:10 am

Flow2706 wrote:
Airliners are usually certified for +2.5/-1gs (this number comes from a regulation as well but I’m too lazy to look up the exact reference now), not to +6. So the test has to be performed up to 2,5 x 1,5 (safety factor) = 3,75g. For obvious safety reasons this test is not performed inflight but on the ground in a specific test rig where the wing is pulled up with a crane.

Is that for MTOW or MZFW? I suspect 3.75 x MTOW and 6x MZFW are closer together. Or maybe 6x MZFW is 2.5 MTOW for some specific type, and nondestructive test may be done in flight?
As for fighters, if I remember correctly a just under 10g requirement (not sure at what weight) is limited by pilot, not by (actually stronger) airframe.
 
gloom
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 9:03 am

kalvado wrote:
As for fighters, if I remember correctly a just under 10g requirement (not sure at what weight) is limited by pilot, not by (actually stronger) airframe.


Correct. Most fighters are rated +9/-3 g I believe, and this is indeed human factor limited.

Once pilot is removed from equation, most current jets would be able to reach double digits, differing between types and specific frames. For those being gen4+ (4.5 or 5, so anything beyong Mig29/Su27, or F15C/F16C/F18C), we're talking estimation between 12 and 15G.

Cheers,
Adam
 
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Matt6461
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 9:59 am

gloom wrote:
kalvado wrote:
As for fighters, if I remember correctly a just under 10g requirement (not sure at what weight) is limited by pilot, not by (actually stronger) airframe.


Correct. Most fighters are rated +9/-3 g I believe, and this is indeed human factor limited.

Once pilot is removed from equation, most current jets would be able to reach double digits, differing between types and specific frames. For those being gen4+ (4.5 or 5, so anything beyong Mig29/Su27, or F15C/F16C/F18C), we're talking estimation between 12 and 15G.

Cheers,
Adam


6+g even at 37,000ft though?

I guess with thrust vectoring air density doesn't matter? I may be stuck too much on WW2 fighters...
 
CosmicCruiser
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 12:54 pm

Matt6461 wrote:
.... Probably part of the reason a lot of flights go around the Himalayas. Also explains better something I never quite understood - why flying "The Hump" to China was so dangerous in WW2. Max cruising level for a laden WW2 planes was in the mid-20's; if you hit a strong up/down draft off the mountains you probably don't have the static altitude maneuver room to recover before losing a few thousand feet and...


If I may comment on flying the hump. A good book to read is Dick Coles War. Cole was a pilot on the Doolittle Raid but after crashing and being rescued he was assigned to "fly the hump." The biggest challenge to the Hump pilots was the total lack of good weather info and the rate at which the weather changed. They were not usually above all the mountains and usually in the clouds. Rapid and dramatic wind changes would put them well off course and often resulted in contacting the side of a mountain. Many guys made their own maps and tried to wag their courses as they saw fit. Check out the book.
 
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zeke
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 4:52 pm

Matt6461 wrote:
6+g even at 37,000ft though?


I think you maybe are confusing the aerodynamic wing loading with the structural ultimate load. I am not specifically aware of anything to do with 20,000 ft except that is the normal FAR 25 limit for flap use.
 
RetiredWeasel
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 8:43 pm

gloom wrote:
kalvado wrote:
As for fighters, if I remember correctly a just under 10g requirement (not sure at what weight) is limited by pilot, not by (actually stronger) airframe.


Correct. Most fighters are rated +9/-3 g I believe, and this is indeed human factor limited.

Once pilot is removed from equation, most current jets would be able to reach double digits, differing between types and specific frames. For those being gen4+ (4.5 or 5, so anything beyong Mig29/Su27, or F15C/F16C/F18C), we're talking estimation between 12 and 15G.

Cheers,
Adam


I'd take issue with that. The fighter aircraft can be designed to take more g's than the pilot can take, but that means adding strengthen materials and weight. GD designed the F-16 to handle 9's (+ some margin) because that's the max what most pilots can sustain. Pulling more can cause structural damage to the aircraft. Ask any pilot who over g'd a fighter and he'll tell you the flight surgeon doesn't come out to exam your body, but maintenance has to do an over-g inspection on the aircraft to make sure nothing broke.
 
RetiredWeasel
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 8:44 pm

RetiredWeasel wrote:
gloom wrote:
kalvado wrote:
As for fighters, if I remember correctly a just under 10g requirement (not sure at what weight) is limited by pilot, not by (actually stronger) airframe.


Correct. Most fighters are rated +9/-3 g I believe, and this is indeed human factor limited.

Once pilot is removed from equation, most current jets would be able to reach double digits, differing between types and specific frames. For those being gen4+ (4.5 or 5, so anything beyong Mig29/Su27, or F15C/F16C/F18C), we're talking estimation between 12 and 15G.

Cheers,
Adam


I'd take issue with that. The fighter aircraft can be designed to take more g's than the pilot can take, but that means adding strengthening materials and weight. GD designed the F-16 to handle 9's (+ some margin) because that's the max what most pilots can sustain. Pulling more can cause structural damage to the aircraft. Ask any pilot who over g'd a fighter and he'll tell you the flight surgeon doesn't come out to exam your body, but maintenance has to do an over-g inspection on the aircraft to make sure nothing broke.
 
RetiredWeasel
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 8:45 pm

Delete Duplicate
 
RetiredWeasel
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Re: Altitude of the static 6g maneuver?

Sat Apr 02, 2022 8:47 pm

gloom wrote:

Correct. Most fighters are rated +9/-3 g I believe, and this is indeed human factor limited.

Once pilot is removed from equation, most current jets would be able to reach double digits, differing between types and specific frames. For those being gen4+ (4.5 or 5, so anything beyong Mig29/Su27, or F15C/F16C/F18C), we're talking estimation between 12 and 15G.

Cheers,
Adam


I'd take issue with that. The fighter aircraft can be designed to take more g's than the pilot can take, but that means adding strengthening materials and weight. GD designed the F-16 to handle 9's (+ some margin) because that's the max what most pilots can sustain. Pulling more can cause structural damage to the aircraft. Ask any pilot who over g'd a fighter and he'll tell you the flight surgeon doesn't come out to exam your body, but maintenance has to do an over-g inspection on the aircraft to make sure nothing broke.
 
gloom
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Re: Altitude of the static 6g maneuver?

Mon Apr 04, 2022 7:13 pm

RetiredWeasel wrote:
The fighter aircraft can be designed to take more g's than the pilot can take, but that means adding strengthening materials and weight. GD designed the F-16 to handle 9's (+ some margin) because that's the max what most pilots can sustain.


The point you raise is valid, but not completely adequate. Two drawbacks for additional strengthening are resulting from heavier, more expensive frame, and are: higher fuel burn and less maneuverability. Both by a small margin (weight is only a part of equation), and higher cost is also acceptable. With that in mind, +9 is considered max for long time acceleration. For short periods, to avoid missile seekers, fighter pilot would use more than 9g. I know of at least two frames officially allowed to reach +10. Tested and certified. And then there's all vast area of "non-certified, but built with extra/better materials/construction/joints/whatever". If any from a type would sustain 10g, I'm quite sure many of the type would a couple more. And many probably have had...

Cheers,
Adam

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