I'll add some screenshots later from the film of the conversation in which a claimed cfii shows huge ignorance to basic physics and understanding of how a plane flies.
I'll chime in here. I'm the guy that he's referring to.
What sparked this was IcePac's comment that "
NO plane can climb [sustained] while knife-edge." I spoke up and said that any plane with a thrust/weight ratio of 1.0 or greater can climb, regardless of lift vector or orientation.
Icepac, instead of realizing that he made a mistake by stating no aircraft could climb knife-edge (F-16's, F-22's, Su-37's, etc. all have T/W ratios of 1.0 or more and can climb at any angle, sustained), decided to try to dig himself deeper by stating that ONLY the wing can produce lift.
Lift comes from three primary areas:
1) from the portion of the thrust vector that directly opposes weight,
2) from the ram-air/impact effect of the relative wind defecting into a vector that opposes weight
3) from the lifting airfoils/wing(s)
Instead of simply acknowledging that, he decided to devolve the conversation further where we got onto the subject of stabilizers. I stated that stabilizers produce lift as part of number three (above) (they do - all airfoils, by design,
must produce lift). What he didn't seem to understand was that it produces lift in downward direction, but it is still a lifting force and it is
still called a lifting force, and he proceeded to argue that the tail doesn't produce lift, which is why it's so much smaller than the primary airfoil (wing). He didn't seem to understand the difference between lift (as a force) vs lift vectors. His argument was akin to stating that a car driving in reverse isn't really "driving", because it's not moving forward (I actually presented that example to him to point out the flaw in reasoning) - just because lift is in a downward direction doesn't change the fact that it's lift.
I then pointed out that rolling an aircraft inverted changes the lift vectors of the airfoils relative to gravity (in other words, roll inverted [
without changing the overall AoA, other than inverting it] and your stabilizer, left uncorrected, will naturally create lift directly upwards, against the aircraft weight). Keep in mind we're talking traditional/GA aircraft here for simplicity (not military/aerobatic aircraft with neutral or otherwise different cambers). He then asked a series of completed unrelated questions, showing a lack of understanding about leverage forces and how the tail is smaller because it has a further arm/fulcrum from the CG.
Anyone who is familiar with aerodynamics, please feel free to examine and critique the above, if you find it incorrect (which it's not).
To address his question, you can dive and pick up enough airspeed, then roll 90* and use the rudder to deflect the airflow enough to maintain level flight... with enough airspeed. In fact, you can do it for several seconds at a time in the right aircraft (it must have good rudder authority). The wind deflection against the fuselage and the rudder is enough to keep it airborne. However, both of these surfaces will create an usually large amount of form drag and, eventually, will slow the plane down to the point that it's no longer sustainable.
However, given enough altitude, you can fly a series of "waves" (descend for speed, hard rudder for climb, descend for speed), to stay in flight for a good while. This is probably what he saw, as I've experienced the same thing myself. It takes a smart pilot, but at 20k, you can probably get a good two minutes of flight time out of something like a Yak-3.
Given enough speed, ANY surface will produce lift.
See here for a close-enough related real-life event:
https://www.youtube.com/watch?v=AJ76BSassms