AOA vs Airspeed

That was a very interesting video. Thanks for posting it.
 
That's why I recommend everybody take some upset training. Good stuff there!
 
MD11Pilot said:
Video of simulator upset training. Denzel wasn't that far off. I have done this exact scenario and I prefer the 1/2 g 45 degree bank to the nearest horizon and then recover.

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Denzel wasn't. Alaska261 was flying upside down for a while.
1620:25 CAM-1 are we flyin?... we're flyin... we're flyin... tell 'em what we're doin.
1620:33 CAM-2 oh yea let me get *
1620:35 CAM-1 *
1620:38 CAM-1 gotta get it over again... at least upside down we're flyin.
1620:40.6 PA [sound similar to CVR startup tone]
 
luvflyin said:
Denzel wasn't. Alaska261 was flying upside down for a while.
1620:25 CAM-1 are we flyin?... we're flyin... we're flyin... tell 'em what we're doin.
1620:33 CAM-2 oh yea let me get *
1620:35 CAM-1 *
1620:38 CAM-1 gotta get it over again... at least upside down we're flyin.
1620:40.6 PA [sound similar to CVR startup tone]
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Weren't they able to keep it flying upside down till the jack screw finally snapped?
 
ARFlyer said:
Weren't they able to keep it flying upside down till the jack screw finally snapped?
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As I recall the jack screw was already broken and the elevator was jammed up against a stop, which finally broke. The resulting angle on the elevator was then unflyable and unrecoverable. It went to a crazy big angle.

The saddest part of that one is listening to the ATC recordings of the airplanes around them telling the controller they're in serious trouble and inverted. Not a thing they could do, but watch. And one of them marked the coordinates when they were abeam the downed aircraft on the ocean.
 
Unloading, which can very a unintuitive thing for lower time pilots, often fixes a lot of issues. Unload and roll, unload to go around in the flare.........that was my life for a while.
 
pikespeakmtnman said:
The Top Gun (and Top Gun 2) discussion is in another thread
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mv8i3H.gif
 
Something I didn't hear in the video is not only does unloading make the ailerons more effective and lower stall speed, it makes the engines more effective too. At 1/2 G you have cut the weight of the airplane in half, dramatically improving the thrust to weight ratio which makes recovery form the stall much quicker.
 
INTJ said:
Something I didn't hear in the video is not only does unloading make the ailerons more effective and lower stall speed, it makes the engines more effective too. At 1/2 G you have cut the weight of the airplane in half, dramatically improving the thrust to weight ratio which makes recovery form the stall much quicker.
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You recover from the stall by lowering the AOA. Thrust is not a factor. You could recover the from the resulting loss of altitude with better thrust to weight, though I'm dubious that accelerating the plane downward to keep less than 1 g is going result in a better altitude gain.
 
INTJ said:
Something I didn't hear in the video is not only does unloading make the ailerons more effective and lower stall speed, it makes the engines more effective too. At 1/2 G you have cut the weight of the airplane in half, dramatically improving the thrust to weight ratio which makes recovery form the stall much quicker.
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Um, not exactly. You've reduced the induced drag by 50% but the mass remains the same. Power to mass (more correct physics term) hasn't changed.
 
flyingron said:
You recover from the stall by lowering the AOA. Thrust is not a factor. You could recover the from the resulting loss of altitude with better thrust to weight, though I'm dubious that accelerating the plane downward to keep less than 1 g is going result in a better altitude gain.
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Yeah. Hard to point the plane at the ground. Every "survival instinct" in your DNA says Noooo!! But in some situations that's the only way to survive. That's what a lot of training is about. Overriding survival instincts.
 
jsstevens said:
Um, not exactly. You've reduced the induced drag by 50% but the mass remains the same. Power to mass (more correct physics term) hasn't changed.
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Though I wasn't thinking in terms of mass, I get it that mass hasn't changed. However, I also know an aircraft accelerates the fastest at zero g, and you don't have to be pointed at the ground to see this work. Are you the saying that the increased acceleration at zero g is due to reducing induced drag? I never looked at the AoA gauge when unloading to accelerate.

I also have experienced something similar at the top of a loop. If you unload, you will increase your altitude gain. Is this too due to reducing induced drag?
 
INTJ said:
Something I didn't hear in the video is not only does unloading make the ailerons more effective and lower stall speed, it makes the engines more effective too. At 1/2 G you have cut the weight of the airplane in half, dramatically improving the thrust to weight ratio which makes recovery form the stall much quicker.
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This doesn't make sense to be. By unloading the Gs, you reduce weight, but not mass.
 
Really good video, thanks for sharing.
 
INTJ said:
Though I wasn't thinking in terms of mass, I get it that mass hasn't changed. However, I also know an aircraft accelerates the fastest at zero g, and you don't have to be pointed at the ground to see this work. Are you the saying that the increased acceleration at zero g is due to reducing induced drag? I never looked at the AoA gauge when unloading to accelerate.

I also have experienced something similar at the top of a loop. If you unload, you will increase your altitude gain. Is this too due to reducing induced drag?
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F=MA. Lowering g doesn't change that. However, accelerating away from earth, the total F is thrust - gravity, and accelerating toward earth total F is thrust + gravity. I think.
 
Lindberg said:
F=MA. Lowering g doesn't change that. However, accelerating away from earth, the total F is thrust - gravity, and accelerating toward earth total F is thrust + gravity. I think.
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I'll bet monemtum has something to do with all this as well. Oh well, I was taught "pilot aerodynamics" by the USAF and they admitted their course would make aeronautical engineers go nuts.

The end of all this is I know unloading can fix a lot of issues, often in flight envelopes where it's not so intuitive.......
 
INTJ said:
Though I wasn't thinking in terms of mass, I get it that mass hasn't changed. However, I also know an aircraft accelerates the fastest at zero g, and you don't have to be pointed at the ground to see this work. Are you the saying that the increased acceleration at zero g is due to reducing induced drag? I never looked at the AoA gauge when unloading to accelerate.

I also have experienced something similar at the top of a loop. If you unload, you will increase your altitude gain. Is this too due to reducing induced drag?
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Yes. The drag caused by the wing generating lift. I got bits and pieces of the combat air manuvering course as taught on the F-5, which by today's standards is very underpowered. They'd turn at 6+ Gs for 180 degrees or so then unload the airframe by pushing to 0 G (often in a nearly vertical bank) to accelerate and gain energy then repeat.
 
jsstevens said:
Yes. The drag caused by the wing generating lift. I got bits and pieces of the combat air manuvering course as taught on the F-5, which by today's standards is very underpowered. They'd turn at 6+ Gs for 180 degrees or so then unload the airframe by pushing to 0 G (often in a nearly vertical bank) to accelerate and gain energy then repeat.
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A friend went through the test pilot course at Pax River and he said they had to unload the T-38 to go supersonic.
 
Velocity173 said:
A friend went through the test pilot course at Pax River and he said they had to unload the T-38 to go supersonic.
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T-38As and Bs could easily hit the number without any kind of descent to accelerate, it just took a lot more time and fuel than if you do an unloaded descent to start the party. The Cs and PMP-Cs can still go super, but have a tougher time due to the increased weight of the avionics and drag of the fat lip of the intakes, and consequently have do a dive to get there.
 
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jsstevens said:
Yes. The drag caused by the wing generating lift. I got bits and pieces of the combat air manuvering course as taught on the F-5, which by today's standards is very underpowered. They'd turn at 6+ Gs for 180 degrees or so then unload the airframe by pushing to 0 G (often in a nearly vertical bank) to accelerate and gain energy then repeat.
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This in itself isn't evidence to support either argument (AOA vs G).

In BFM you have to use the tools available to achieve the desired outcome, and those tools differ from aircraft to aircraft; in the Eagle, we used an indicated AOA as the conditions for the best possible acceleration (8 AOA, which was sometimes a slightly positive G), and in the T-38 we used G as the conditions for best accel (about 0.5G).

Of course these jets have two very different wings and very different P-sub-S charts, but the question is, is the difference in indication used to achieve the best acceleration a result of those design differences, or a result of what indicator happens to be most effective in showing the pilot the conditions necessary for best acceleration?
 
Hacker said:
T-38As and Bs could easily hit the number without any kind of descent to accelerate, it just took a lot more time and fuel than if you do an unloaded descent to start the party. The Cs and PMP-Cs can still go super, but have a tougher time due to the increased weight of the avionics and drag of the fat lip of the intakes, and consequently have do a dive to get there.
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Yeah I guess they unload to go thru the number quicker. He said on climb out they were about to go supersonic but hadn't reached their operating W area, so his IP up front told him to come out of AB for a bit. Once in their area, a quick parabola and boom!
 
Velocity173 said:
Yeah I guess they unload to go thru the number quicker. He said on climb out they were about to go supersonic but hadn't reached their operating W area, so his IP up front told him to come out of AB for a bit. Once in their area, a quick parabola and boom!
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I did several boom rides as a T-38 IP in As. We'd climb to 390 and once in the area would go to AB and descend to go supersonic. We didn't unload for that demo. Where we would unload was when trying to gain energy. We'd do a straight ahead wifferdill, pulling the nose up and climbing then unloading. In the T-1 and C-130 we'd just add power to gain energy and maybe slightly unload.
 
Hacker said:
Did you not reference the "green donut" when doing acro in the T-38?
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Probably, but airframe buffet was a better indicator. Light symmetrical buffet happened at .6 AOA (green donut) and that was a comfortable range for maneuvering. Max practical lift was around .8 AOA (red) and the buffet was moderate and symmetrical. Stall was around 1.0 AOA and the buffet was heavy and asymmetric. I tended to maneuver the airplane as needed and used buffet for my indicator until the pattern, where the AOA gauge was a bigger part of the crossheck. I still remember unloading and using the G meter to gauge the amount of unloading.
 
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BTW, I did not mean to take this thread from the best way to recover a large plane from a severe unusual attitude to the best way to gain energy in a military jet. However, it IS good to knock the cobwebs out. My last logged flight was Dec of 2004 in a T-1 and a couple months ago I got a special issuance Class III, and the first step for me is to correctly remember all the aviation rules and theory. Interestingly, the three times I have driven aircraft since my USAF fini flight I found the hand eye skills were fine, but I was rusty in the rules......
 
Do I understand AOA right?

'The biggest limitation on using the ASI as an indicator of stall is that it does not accommodate for bank angle etc. (the old adage, "you can stall at any airspeed").
The AOA will not lie, however.
You can be at 200kts and crank in enough bank to stall. ASI will look ok but the AOA will tell the true story.
 
Let'sgoflying! said:
Do I understand AOA right?

'The biggest limitation on using the ASI as an indicator of stall is that it does not accommodate for bank angle etc. (the old adage, "you can stall at any airspeed").
The AOA will not lie, however.
You can be at 200kts and crank in enough bank to stall. ASI will look ok but the AOA will tell the true story.
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It isn't that airspeed "lies", it is that airspeed is simply an approximation of the AOA at which a stall will occur in straight and level flight.

AOA is the true and correct measure of wing performance.
 
Again, airspeed isn't lying. It is that AIRSPEED DOES NOT DETERMINE STALLING.

Stall occurs when the angle of attack increases the critical angle, the part where further increase in AOA does not net an increase in lift.
The only way out of a stall is to decrease the angle below that point.

The so-called "stall speed" is the speed when in an attempt to maintain unaccelerated flight at that speed, you are putting to the critical angle. It's not just bank angle that messes up using the ASI. Any accelerated flight can do it. If you haul back on the yoke either to zoom or to try to stop a dive you can exceed the critical angle above the "stall speed" as well.
 
Well you are preaching to the choir on that, but until the FAA stops using the term stall speed, until every flight manual is changed, and until every instructor stops saying stall speed, every airplane stops using asi markings as such and has an AOA installed I think we are doing new pilots a disservice to say the asi is not lying when it comes to stall indications.
 
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