F-35 and Airshows

Discuss the F-35 Lightning II
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marsavian

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Unread post12 Nov 2019, 23:10

wrightwing wrote:
quicksilver wrote:So, are you saying (in comparison to the C) that the A sustains more G at the same flight conditions, or are you saying that although it sustains a lesser G number, it does so at a slower airspeed thereby producing a higher str?

You understand the term (And difference) sustained turn rate (i.e. the max number of degrees per second that can be sustained) vs. sustained G at X velocity/altitude, right? STR refers to degrees per second, not the Gs being sustained. ITR refers to the maximum instantaneous degrees per second (again, not Gs.) These numbers are generally referring to sea level performance, not M.8/15k feet at XYZ weight. To use some real world illustrations, the F-16 is an STR/rate fighter. The F-18 is an ITR/radius fighter much the same way the F-35A is to the F-35C.


Spurts has modelled the two variants and he gives the technical reasons why the A cannot sustain the same rate as the C and it is due to higher wing loading causing the induced drag to be 20% higher (3rd link).

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wrightwing

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Unread post13 Nov 2019, 00:09

quicksilver wrote:
wrightwing wrote:
quicksilver wrote:So, are you saying (in comparison to the C) that the A sustains more G at the same flight conditions, or are you saying that although it sustains a lesser G number, it does so at a slower airspeed thereby producing a higher str?

You understand the term (And difference) sustained turn rate (i.e. the max number of degrees per second that can be sustained) vs. sustained G at X velocity/altitude, right? STR refers to degrees per second, not the Gs being sustained. ITR refers to the maximum instantaneous degrees per second (again, not Gs.) These numbers are generally referring to sea level performance, not M.8/15k feet at XYZ weight. To use some real world illustrations, the F-16 is an STR/rate fighter. The F-18 is an ITR/radius fighter much the same way the F-35A is to the F-35C.


STR is a consequence of G performance in a given configuration and weight at a given set of flight conditions. The program chose to use a certain set of flight conditions to make a comparative assessment; apples to apples if you will. In that official comparison, the C was/is the better performer in STR. We don’t know how that comparative performance might change if we alter the flight conditions. However, what we do know from pilot comments Is that the F-35A is a radius fighter as it generally suffers in comparison to other fighters in sustained performance (reference John Venable’s Heritage report from a few years back). Anecdotally, (from public reports) it accelerates like a Viper and points like a Hornet. It’s not a rate fighter.

Here’s the link to JV’s report — https://www.heritage.org/defense/report ... concurrent

It's a rate and radius fighter, which has been said by a number of.pilots. It has similar STR to F-16s.and superior ITR to F-18s. The C just happens to have superior ITR to the A. We're talking past each other. I'm not talking about sustained Gs. I'm talking about how many degrees per second each model can sustain vs how many degrees per second each can achieve instantaneously. These numbers don't correlate to max available G, max sustained G, or minimum radius turns.
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wrightwing

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Unread post13 Nov 2019, 00:13

marsavian wrote:
wrightwing wrote:
quicksilver wrote:So, are you saying (in comparison to the C) that the A sustains more G at the same flight conditions, or are you saying that although it sustains a lesser G number, it does so at a slower airspeed thereby producing a higher str?

You understand the term (And difference) sustained turn rate (i.e. the max number of degrees per second that can be sustained) vs. sustained G at X velocity/altitude, right? STR refers to degrees per second, not the Gs being sustained. ITR refers to the maximum instantaneous degrees per second (again, not Gs.) These numbers are generally referring to sea level performance, not M.8/15k feet at XYZ weight. To use some real world illustrations, the F-16 is an STR/rate fighter. The F-18 is an ITR/radius fighter much the same way the F-35A is to the F-35C.


Spurts has modelled the two variants and he gives the technical reasons why the A cannot sustain the same rate as the C and it is due to higher wing loading causing the induced drag to be 20% higher (3rd link).

viewtopic.php?p=394678#p394678
viewtopic.php?p=394723#p394723
viewtopic.php?p=394725#p394725



Again, this isn't a discussion about Gs but degrees. Turn rates are about °/second, not Gs. As for the particular discussion in the link, the F-35A at 3i didn't have it's full envelope. At 3F it's capable of 9G with full fuel and internal payload. Not 7G at 60% fuel.
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quicksilver

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Unread post13 Nov 2019, 00:29

:doh:

Are we talking past each other or do you not understand?
Last edited by quicksilver on 13 Nov 2019, 00:33, edited 1 time in total.
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marsavian

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Unread post13 Nov 2019, 00:31

Spurts was basing his calculations on 3F/absolute limits.

sprstdlyscottsmn wrote:Don't get hung up on G. The F-35C will have the best turn rates at operational conditions, both ITR and STR. Being 7.5G means it puts less stress on the pilot to have that agility. 9G will only be available to the A at airshow altitudes or supersonic speeds at operational altitudes. At 0.9M and 30,000ft, with 60% fuel and an A-G internal load, the F-35A is limited to just under 7G. It can't make enough lift to reach 9. Meanwhile an F-35C with the same conditions can reach 7.5G down to about 0.83M.
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Corsair1963

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Unread post13 Nov 2019, 01:21

The F-35B/C limit the G to 7/7.5 to extent their service lives. Not that they can't pull more G....
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element1loop

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Unread post13 Nov 2019, 04:12

One vaguely wonders why spinning around in small circles is a tactically significant thing to do when USAF has not been in a gunfight in 46 years, or about 2-generations of fighter aircraft already?
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wrightwing

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Unread post13 Nov 2019, 06:10

marsavian wrote:Spurts was basing his calculations on 3F/absolute limits.

sprstdlyscottsmn wrote:Don't get hung up on G. The F-35C will have the best turn rates at operational conditions, both ITR and STR. Being 7.5G means it puts less stress on the pilot to have that agility. 9G will only be available to the A at airshow altitudes or supersonic speeds at operational altitudes. At 0.9M and 30,000ft, with 60% fuel and an A-G internal load, the F-35A is limited to just under 7G. It can't make enough lift to reach 9. Meanwhile an F-35C with the same conditions can reach 7.5G down to about 0.83M.

The A has demonstrated 9G/50° AoA/M1.6 at full internal payload and fuel (not at 30,000ft of course.) That was part of opening the 3F envelope. Sustained G at various weight/speed/altitudes is another matter, as is the difference between °/second turn rates, minimum radius, max G, etc.... Each of those are maxed out at different airspeeds/altitudes. But one last time, turn rates are measured in degrees per second, not Gs.
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marsavian

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Unread post13 Nov 2019, 06:22

But one last time, turn rates are measured in degrees per second, not Gs.


Everyone is fully aware of this so it did not need stating once nevermind the numerous times you did. Gs however are indicative of turn rates at the same altitude and speed. The F-35C has the best STR of the F-35s which has been stated by the military, test pilots and backed up in theory by Spurts calculations. Its ITR can also be superior but not at the same speed and altitude when the 9g limit of the F-35A should prevail.
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quicksilver

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Unread post13 Nov 2019, 12:59

“I'm talking about how many degrees per second each model can sustain vs how many degrees per second each can achieve instantaneously. These numbers don't correlate to max available G, max sustained G, or minimum radius turns.”

Actually, they do, but not exclusively. For example, a high alpha pedal turn can (in certain situations) ‘move the nose’ at very high rates, but they are very low G maneuvers (obtw, the Rafale guy describes being in one in the hushkit interview on the other thread).

What you seem to be talking about is what we used to call a ‘turn rate plateau‘ — ie, the rate of nose movement a jet can ‘sustain’ (for a limited period of time) from a starting position/condition to a ending position/condition where you have either killed the adversary, or you have to change the geometry of the fight, or/and you gotta get some energy back. You can go to an em diagram for many jets and ‘trace’ them in a fashion.
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Unread post15 Nov 2019, 12:53

element1loop wrote:One vaguely wonders why spinning around in small circles is a tactically significant thing to do when USAF has not been in a gunfight in 46 years, or about 2-generations of fighter aircraft already?


No argument here, as I think even PCA will compromise on this metric (for more fuel, sensors and weapons). However, those small circles may come in handy when dodging SAM's or AAM's for that matter. USAF has since the days of the F-15/16 always had tight turners, and since those days been absolutely dominant. The domination has occurred mostly because of superior radar, weapons and training but turning tight was always in the mix.

Giving that up (or at least minimizing it) is going to be something that's very difficult for USAF leadership to come to grips with. Witness well, the F-35. Had to do it all, and in doing so some design compromises occurred. Yet, its ITR is absolutely scary along with clean F-16 like STR.

It's still there, almost 20 years after GW1 saw USAF Eagles turning tight with Mig-25's (and to a lesser extent), 29's...
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quicksilver

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Unread post15 Nov 2019, 14:02

“Giving that up (or at least minimizing it) is going to be something that's very difficult for USAF leadership to come to grips with. Witness well, the F-35. Had to do it all, and in doing so some design compromises occurred. Yet, its ITR is absolutely scary along with clean F-16 like STR.“

:bang:
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charlielima223

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Unread post15 Nov 2019, 14:22

element1loop wrote:One vaguely wonders why spinning around in small circles is a tactically significant thing to do when USAF has not been in a gunfight in 46 years, or about 2-generations of fighter aircraft already?


On the F-22 Raptor ep of TFPPC, the host tells of his experience with an F-22 where the F-22 ends up giving him a "face shot" during a 180 left to left pass where the F-22 actually turns into him.

For those real physically close CAS situations, it offers quicker follow up passes... one of the many things the A-10 is known for.

I akin it to a cars 0-60 performance. Everyday driving you're not thinking about it. Really what (most) people think about for an everyday driving is fuel efficiency and payload/passenger space. Yet when there are those times when you have to accelerate pass a slow driver or onto the express way, the ability to accelerate quickly comes in handy.
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Unread post15 Nov 2019, 20:24

mixelflick wrote:GW1 saw USAF Eagles turning tight with Mig-25's

What's this account?
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Unread post16 Nov 2019, 00:29

Just watched F-35 Demo at Aviation Nation 2019

Not bad
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