What post stall maneuvers can F-35 perform ?

Discuss the F-35 Lightning II
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optimist

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Unread post20 Jan 2019, 11:33

garrya wrote:That look like the start of a tail slide maneuver
Apparently this is how it could be used in combat:
2AB38D65-33FA-42F2-8A23-6A9EB4F9ADB6.jpeg

download/file.php?id=29404&mode=view


Gee that's an old tail slide chart. HMD cue and HOBS = a high probability for blue to kill red at the very beginning.

The late 1980's cobra was promoted as a way of cutting the arc in a circle fight, again obsolete now.

Of course this is a proven move and still relevant :)
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garrya

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Unread post21 Jan 2019, 04:43

For the record, I was wrong about the cobra maneuver that F-35 performed
sprstdlyscottsmn wrote:Let's break the Cobra maneuver up into three phases. The Pitch Up, the Pitch Down, and Energy Recovery.

Pitch Up: This phase of the maneuver is about the control authority in pitch and the ability to generate a pitch rate relative to the local airflow (i.e. not indicative of a turn rate) high enough to exceed the stabilized AoA. This phase doesn't really give a rat's a$$ about going up, down, sideways or anything. If you want to nitpick then the easiest way to do it would be wings level inverted so that gravity can help you move the CG in the direction you want. The standard airshow Cobra is at low altitude (dense air) with gravity fighting the initial pull (when the controls have the most bite) more than the end of the pull. Once you are past 90 AoA in an airshow cobra gravity is helping to hold the nose up relative to the horizon (not the plane up from the ground, just the nose) because the center of gravity is behind the tail surfaces. In the Testing Cobra shown in the F-35 video, gravity is not helping or hindering the initial pull, but it is hindering the end of the pull (the area around 90 AoA). The thing to note here is that the controls were able to generate the needed forces in thin air.

Pitch Down: This phase of the maneuver has more to do with inherent stability at ~90 AoA than anything else. In the Airshow Cobra, gravity is pulling the plane either straight down the tailpipes or even over the back. The plane has to generate drag at the tail to pull the tail back, pulling the nose down. In a fully stable plane even the wing drag will pull "beneath" the CG of the plane and lower the nose. In a neutral or unstable design the wing drag will have no or even slightly negative impact on returning the nose to the proper position. The tail is much farther from the CG so it has a larger impact even with less drag force. In the Testing Cobra gravity is keeping the speed up but it is not "helping" to pull the nose down in an unstable design like the F-35. The wing drag and forward fuselage drag are more or less balancing the gravity, it is still up to tail drag to impact the pitch moment. In both cases, the AoA is reduced through zero and into a negative value briefly.

Energy Recovery: This phase is very straightforward. The Airshow Cobra is using the high engine thrust at low altitude to increase airspeed to a safe level. The Test Cobra does not have high engine thrust available due to the altitude, so being nose down in the final phase means gravity increases speed to a safe level.

Could a test configured (limiters toggled off) F-35 do an Airshow Cobra? Absolutely. The pitch authority is there, both nose up and nose down, but what the latest demo practice showed us in the low speed pass is that the Energy Recovery phase could still be done at ~30-40 AoA in Mil power with a climb. So the pilot of said test configured F-35 could toggle off the limiter, pull the throttle to idle and the control stick full aft, wait for the nose to go past 90, toggle the limiter back on, keep holding full aft stick, engage afterburner, and power out in a climb.
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Unread post21 Jan 2019, 16:11

The post stall stuff will be what sells this plane to the American public. Right or wrong, that's what the 2019 demo team will be highlighting in an effort to dispel years of anti-F-35 bias.

Now you and I know that's the LAST thing it'll be doing in combat, but it's John Q. Public the USAF needs to impress, not us. It's just a damn shame there's not a way to illustrate how game changing its stealth, SA, sensors etc. are. So we're left with airshow demo's.

If the specs really were rate like a Viper and radius like a Hornet, they more than met those IMO. Truly, a fantastic piece of engineering and will likely go down as America's most deadly air to everything machine..
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