steep turns at slow airspeeds

[Horizon]

As a student, it seems you're warned quite extensively about the danger of making a steep turn at slow airspeeds. The typical claim is that "the stall speed increases with bank-angle".

Of course, this is true. However, isn't that only true if you're pulling back and deliberately maintaining altitude?

Lets say you're flying a small airplane at say maybe 70KIAS. Pretty slow, right? Now, enter a 60-degree bank. Isn't it true that you could successfully complete this turn so long as you don't try maintaining altitude...and that the AC would never be in danger of stalling?

Granted, the sink-rate might be quite high, but let’s say that at this altitude, it's not an issue.

 

[TOOL CRIB]

As a student, it seems you're warned quite extensively about the danger of making a steep turn at slow airspeeds. The typical claim is that "the stall speed increases with bank-angle".

Of course, this is true. However, isn't that only true if you're pulling back and deliberately maintaining altitude?

Lets say you're flying a small airplane at say maybe 70KIAS. Pretty slow, right? Now, enter a 60-degree bank. Isn't it true that you could successfully complete this turn so long as you don't try maintaining altitude...and that the AC would never be in danger of stalling?

Granted, the sink-rate might be quite high, but let’s say that at this altitude, it's not an issue.

correct.

 

[avbug]

A stall isn't a function of angle of bank, nor of airspeed, but only angle of attack. It isn't a function of pitch attitude or power, but of angle of attack.

Don't exceed the stalling angle of attack for your wing, you don't stall.

Pilots new to turbojet operations are often quite surprised to learn that the recovery from a steep unusual attitude isn't rolling wings level and pushing the nose over, but unloading the wings by rolling steeply and letting the nose fall through the horizon. Does this stall the airplane? No; one rolls into a steep bank to dump the vertical component of lift, allowing the aircraft to fall through to a level attitude where the wings are leveled. Pushing the nose over, expecially during a high rate of climb, could damage the airplane, starve the engine for oil, or any other number of things. Rolling into he bank doesn't cause a stall, but rather provides a safe return to normal flight.

Likewise, the steep turn in your airplane isn't what causes the stall; it's the increase in angle of attack required to maintain level light with an increase in bank. If you're not interested in maintaining level flight, and therefore have no need to increase your angle of attack as you increase your angle of bank, then you're no closer to stall. Put another way, if you were to have available in the cockpit an AoA (angle of attack) Indicator, you could note your AoA in level flight, and without changing your power or trim, merely roll into a steep bank. IF AoA remains the same as bank angle increases, you'll see a descent in proportion to the bank angle. If instead you hold altitude, and make no other changes, you'll need to increase AoA to do so, and as you do, you move closer to a stall.

Remember that a stall can occur going straight up or straight down, and at airspeeds at the top hairy edge of your aircraft limitaions just as easily as toward the bottom. A stall isn't a function of all the things that we commonly associate with a stall...except angle of attack, because for all of the ways that we think about it, a conventionl stall is still nothing more than an increase beyond the wing's critical angle of attack at any given point along the span of the wing.

 

[Horizon]

Great information, thanks.

 

[FL420]

Remember that a stall can occur going straight up or straight down............

True, and an important point to remember as the ground gets bigger with the nose pointed straight down. Be smooth and don't panic!

and at airspeeds at the top hairy edge of your aircraft limitaions just as easily as toward the bottom.

Somewhat true with the reminder that well before Vne or Vd you will have enough G available to pull the wings off before you stall. Again. Be smooth and don't panic!

Another point worth remembering. If you can maintain zero G, no lift is required, so you will not stall. The trick is maintaining enough airspeed to maintain enough elevator authority to maintain zero G until gravity is working its magic on bringing the nose down. Once again. Be smooth and don't panic!