Stall speed DECREASES with bank angle

[Ed_Wischmeyer]

Since I've got digital flight data recording in the RV-9A, from time to time I use that system to record performance data. The current project is measuring stall speed vs bank angle.

The first two measurements were taken on today's flight, right after each other, in level flight. Flight parameters were flaps up, 11" manifold pressure, 3700 MSL, pretty close to standard day. The last measurement was taken a few months ago under pretty much the same conditions.

Here's what I recorded for stall speed vs bank angle. Yes, it's a little embarrassing that I didn't have my bank angles more precise, but here's what I recorded for stall speeds:
7? bank 64 KIAS
24? bank 60 KIAS
80? bank 55 KIAS

Obviously, I'm messing with y'all, but it shouldn't be too hard to figure out what I did. First prize is a used oil filter, second prize is two used oil filters...

The point of this exercise is, of course, to refute the misunderstanding that bank angle and stall speed are directly related to each other. There's a few key details that need to be included to make that statement valid...

[gmcjetpilot]

Originally Posted by Ed_Wischmeyer

Since I've got digital flight data recording in the RV-9A, from time to time I use that system to record performance data. The current project is measuring stall speed vs bank angle.

The first two measurements were taken on today's flight, right after each other, in level flight. Flight parameters were flaps up, 11" manifold pressure, 3700 MSL, pretty close to standard day. The last measurement was taken a few months ago under pretty much the same conditions.

Here's what I recorded for stall speed vs bank angle. Yes, it's a little embarrassing that I didn't have my bank angles more precise, but here's what I recorded for stall speeds:
7° bank 64 KIAS
24° bank 60 KIAS
80° bank 55 KIAS

Obviously, I'm messing with y'all, but it shouldn't be too hard to figure out what I did. First prize is a used oil filter, second prize is two used oil filters...

The point of this exercise is, of course, to refute the misunderstanding that bank angle and stall speed are directly related to each other. There's a few key details that need to be included to make that statement valid...

Only one way to stall is increase angle of attack beyond critical... Stall speed increases with bank angle and load factor... but since your stall speed was going down at higher angles, I assume at 7° bank you were above 1G (pulling back on stick) and 80° bank at 1G (approx). I guarantee you were not in STEADY STATE FLIGHT.... it was transient. Only one way to stall is increase angle of attack beyond critical...

Any licensed GA Pvt Pilot should know the relationship to bank angle, load factor and stall speed.... and the old saying you can stall in any ATTITUDE.

[BobTurner]

I?ll take Ed at his word when he said level flight. As he increased the bank, he had to pull the nose up. This resulted in the pitot tube no longer being parallel to the direction of flight, leading to indicated speed being lower than calibrated airspeed.

[sailvi767]

It takes 5.76 G?s to maintain level flight at 80 degrees AOB.

[Ed_Wischmeyer]

After looking again at the recorded flight data, the 7? bank angle came about from not pulling the stick straight back. My (lame) excuse is that I've not flown any aerobatics for a half dozen years since my second spinal surgery...

[scsmith]

Well, if I needed any used oil filters, I might rise to this.

[Ed_Wischmeyer]

So here?s the rest of the story?

7? bank; 64 KIAS; 1.24 g
24? bank; 60 KIAS; 1.12 g
80? bank; 55 KIAS; 0.91 g

The first stall occurred in level flight (wings level, constant altitude) at 65 knots. All I did was quickly pull back on the stick, as might happen if you were avoiding a bird or (hopefully not) another airplane in the traffic pattern. ( https://www.youtube.com/watch?v=Q716BDswa-g) This was a wings-level accelerated stall, not a 1 g stall. (The 7? bank angle was because I didn?t pull straight back on the stick, something you learn not to do when you start aerobatics. Sigh.)

The key point is that this was not a 1 g stall, which would have occurred at a lower airspeed. But it was stabilized, level flight going into the stall. By the way, the recorded g readings are pretty noisy so take them with a grain of salt. (g readings on airliner Digital Flight Data Recorders are comparably noisy.) The fooler is that this was not the minimum stall speed in level flight, it was just *a* stall speed in level flight.

The second stall was done by the book, establish the bank angle and slow down till it stalls. One second before the stall, the bank angle was 28.5?, so the data point attributed to the stall may have been just a little late.

The last stall was not done holding altitude in a turn. It was done at less than one g, hence the low speed. Interestingly enough, when I stalled it in that extreme bank, there was no nose drop, just buffeting. I recovered promptly. Also, that stall occurred before the variable beep rate stall warning could give more than one beep.

As demonstrated by these three stalls, bank angle by itself has nothing to do with stall speed. G loading is what drives stall speed.

The key point most often missed is that ONLY when the airplane is holding constant altitude in a turn, only then does bank angle influence stall speed ? and it?s not the bank angle per se, it?s the g required to hold altitude in the turn. If you don?t care about holding altitude, you can do all kinds of crazy things, like stalling in an 80? bank at less than the 1 g stall speed. Most pilots understand this, but a significant few do not.

Don?t try these kinds of maneuvers yourself if you haven?t paid the right dues, like aerobatics and unusual attitudes ? especially unusual attitudes. And make sure you have lots of altitude, a good horizon, and no traffic.

[BobTurner]

Originally Posted by Ed_Wischmeyer

The last stall was not done holding altitude in a turn.

c.

I claim foul. In post #1 you said it was all done in level flight!

[Ed_Wischmeyer]

Originally Posted by BobTurner

I claim foul. In post #1 you said it was all done in level flight!

No, I was a scumbag and said "under pretty much the same conditions." I never actually said level flight for the third stall, I just made it easy to infer that.

You will be assessed one time out and have lost your first challenge. And when the next play starts, it will be too late to appeal.

[skylor]

Originally Posted by Ed_Wischmeyer

The key point most often missed is that ONLY when the airplane is holding constant altitude in a turn, only then does bank angle influence stall speed – and it’s not the bank angle per se, it’s the g required to hold altitude in the turn. If you don’t care about holding altitude, you can do all kinds of crazy things, like stalling in an 80° bank at less than the 1 g stall speed. Most pilots understand this, but a significant few do not.

Actually, many pilots misunderstand this. While it’s definitely true that stall speed is a function of wing loading, a descending turn at constant speed and descent rate does not significantly reduce wing loading as many think. In other words, to fly a 60 degree bank descending turn at less than 2 g’s* means that your pitch angle will not be constant, the nose will drop and the descent rate will increase.

Skylor

* There is a very slight reduction in g-loading from the descent angle (the cosine of the descent angle) but within normal bank angles and descent rates (even up to 60 degrees bank) this effect is virtually negligible.