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Old 01-14-2014, 02:20 PM   #1 (permalink)
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Pulling G's in the Vertical

Hey guys,

First post here. I'm a CFI and a WWII combat sim enthusiast. Sometimes, the love for one overlaps with the other, hence this post.

I'm teaching one of my acquaintances about the basics of flight, when the subject of lift came up. They asked about how WWII fighter pilots could pull up vertical in a propeller aircraft, since the max listed AoA was exceeded (for example, if max AoA is 30*, how can a WWII bird pull straight vertical?).

Touching on regular turn aerodynamics - in a normal turn, drag is increased and lift is reduced unless nose-up is added to compensate for both. This has the net effect of decreasing airspeed.

Similarly, to turn tighter, the pilot must increase the bank angle, therefore decreasing available lift even more, requiring either more power input or a trade of altitude for airspeed to maintain the turn.


Let's say that you pull the nose straight up in a WWII-era fighter, after building up a few hundred knots of airspeed, say 400kt. Straight vertical. This is in a prop plane with a thrust-to-weight ratio of less than 1.0.

Please correct me if I'm wrong here, but I have three separate questions (and answers, if I worked through these correctly).
  1. Once you get past the transition from flying straight and level to a nose-high attitude that is excessively high (i.e. higher than what a slower airspeed would allow due to AoA limitations), any lift your wings are producing is now from lift being generated by relative wind created from the aircraft's momentum moving forward. In other words, it's not sustainable, but lift will be produced while the aircraft has enough momentum to keep moving forward at or above to V-stall. This would be true from when the aircraft is between straight-and-level flight to just below 90* vertical attitude. Is this correct?
  2. Once the aircraft reaches vertical, lift does not matter (or rather, has no effect and therefore does not matter). The only need for relative wind is control surface deflection, correct? The aircraft remaining in the vertical depends on the remaining momentum (what we would usually refer to as thrust), being greater than both weight and drag.
  3. Does an aircraft bleed airspeed faster pulling a high-G turn in the vertical, compared to the same aircraft pulling a lesser-G turn in the vertical? Both aircraft pitch nose-up, from 0* (straight and level) to 90*. Provided that both aircraft are below maneuvering speed and both airframe designs allow them to pull (for sake of argument) 10G's max load before stalling, will the aircraft that pulls 8Gs bleed airspeed faster than one that pulls 4Gs? Since we are no longer relying on the wings for 100% lift, and we're not losing any lift in the turns, my work thus far says it shouldn't matter.

I've spent hours reading and cannot find any true technical l discussions of it, as most of the materials I've come across are either GA or aerobatic in nature and don't cover this in enough detail.

I'd appreciate your help and input.

Thank you.

Last edited by Skyyr; 01-14-2014 at 04:03 PM.
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Old 01-15-2014, 11:14 AM   #2 (permalink)
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Typing from my phone, hence a short answer.
AoA isn't really determined by the attitude your airplane is flying. In ideal vertical flight your AoA is equal to the angle of incidence of your wings and remains unchanged as far as you have forward(vertical) speed. Thus your wing never stalls. To negate the lift generated by the wings the elevator is used to generate opposite lift(forward pressure needed to sustain vertical flight decreases, as the climb slows down, Reaching zero at the top of ascent).

Question number two.
Higher G means higher AoA, thus the drag is higher when pulling higher G. Still to answer your question I would need a clarification
Are you asking about a sustained G loop, or a transition to vertical Flight, during which maximum load reached(and maintenance until attaining to vertical flight) is 8/10G?
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Old 01-16-2014, 06:11 AM   #3 (permalink)
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Short answer: zoom effect
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