stall speed

Stall speed is the airspeed at which a given aircraft stops producing lift and stops responding to aerodynamic control inputs. The stall speed varies inversely with angle of attack in most cases, and is clearly defined for wings with the same airfoil profile from root to wingtip. For aircraft with non-constant airfoil wings, or flexible wings, such as hang gliders, stall speed is more difficult to define.

A hang glider wing stalls first at the root, since that part of the wing has a higher angle of attack than the wingtips. As the glider goes slower and slower, or the nose is raised higher and higher, the stall progresses from the root out to the tips. This is what makes a hang glider stable, or self-correcting in pitch (see hang glider). As more and more of the wing stalls the glider becomes harder to turn, and responds more slowly. This is known as "mush" mode. There is a point at which the aircraft will not respond to any roll (turn) input, and this speed is generally accepted as the stall speed. The range from flying to mush to full stall is 2-4 mph for most hang gliders.

The size of the speed range of "mush" mode determines a very important characteristic of a hang glider or other similar aircarft: the stall break. A narrow mush range equals a sharp stall break.

For a typical hang glider, stall speed is 18-20 mph, minimum sink is about 21-22, trim speed is set to about 22-24, and best glide is somewhere in the 25-30 mph range. On specification tables, stall speed is often symbolized by "Vs", with "V" standing for velocity.

I know Captain Wings writeup is based on hang gliders, but the inclusion of the word aircraft came to my attention, and I would like to make a correction. Airplanes are a category of aircraft, so I will relate to them. Airplanes do not lose ALL response to aerodynamic control inputs. While the wing of an aircraft will lose lift during a stall, aerodynamic control inputs do not completely cease to respond. The ailerons will not be functional, as they rely on airflow over the wing, however, the elevator and rudder still work. Operation of the elevator is critical to the recovery of a stall. It is needed in order to decrease the angle of attack and resume smooth airflow over the wings, and as a result, the restoration of lift.

Rudder control is needed in case the stall develops into a spin, first the spin needs to be stopped by applying opposite rudder, then the stall can be broken by decreasing the angle of attack with forward control wheel pressure.

The staff of the flight school/rental/refueling company attached to the airport in my town was always changing, and between this high turnover, varying schedules, and the imperative of more profitable charter flights, I'd be shuttled from instructor to instructor quite frequently. There was the guy with the most stereotypical leather jacket-and-aviator glasses combo you'd ever see. There was the German guy, an honest-to-god Luftwaffe veteran. There was the guy with the Argentinian accent so thick and slurred I might as well have been talking to a bottle of Jack Daniels. There was the guy who would just take me along on charter flights. (I can't complain, I got to do stuff like take a 172 to Philadelphia.) There was the one woman. It's been too long to remember them all.

Anyway, part of the problem with not having an unbroken relationship with a single instructor was that oftentimes, the new instructors would have no idea what I knew, or what to teach me next. So it was one day, the fifth flight I'd ever made, that I went up with some fresh face, and he told me that we'd be doing stalls today. I don't remember exactly what I had done on my previous flights, but my logbook notes things like "fundamentals", "climbs and descents", and "turns to heading". The sorts of things you would teach someone who had just started learning to fly. So I pointed out to him that I wasn't sure that I was ready to do something like that, and I was uncomfortable, and last week's instructor had told me that we'd be doing takeoffs and landings today. But he breezily dismissed my concerns, telling me it would be "fun".

It might be worth keeping in mind that at the time, I was ten. I have no idea why I wanted to learn to fly before I left elementary school, but apparently it seemed like a good idea at the time. When I started, I had to sit on a telephone book to see out the canopy. By halfway through my thirteenth year, I was maybe two flights and some ground instruction short of soloing, but, the FAA requires that you be 16 before you solo (and 17 to get a license). I had hoped to get some sort of waiver, but after 7-year old pilot and media darling Jessica Dubroff died attempting to fly across the country, I believe they were somewhat guarded on the issue of underage flying. In any case, I never got around to polishing off my training. Maybe I still will, someday.

But I digress.

So, we got up to height and he told me what to do. I put in full power, dove to gain speed, and then pulled the power and the carburetor heat, and then pulled back on the column, driving the nose up until we fell below stall speed and the nose fell. (To be technical, stalling is actually a matter of lift and angle of attack and aerodynamics, and speed is more of a symptom, but we won't get into that.) The problem is, I never reached stall speed. I'd pull back with all my might (which, given my preadolescent status, might not have been too impressive), but nothing happened. We were losing altitude, all right, but apparently we stayed above stall speed, and the nose never fell. I put the power back in, gained speed, climbed again, and tried once more. Same thing. Once more. Same thing. At this point, I was feeling particularly lucky - no stalls, today, after all. I could practice something nice, like say traffic patterns, and then call it a day.

"Here, let me try."

I gave it to him. He checked the airspace, dove, cut the power, and pulled the nose up... up... up.. up, up, up, upupupup break. We finally hit stall speed. The nose fell. The nose is supposed to fall. Then you stomp the rudder opposite the direction that the nose breaks towards, add power, and point the nose down to pick up speed. This is how you recover from a stall. Simple. The nose pointed straight down. As you can imagine, the nose is not supposed to point straight down. The ground below us spun. The ground is really not supposed to spin. One of the major goals of teaching stalls is to educate how not to make this happen.

So, here I was, with precisely 3.5 hours worth of in-air experience, sitting in a tiny plane with doors that didn't even close right, while my instructor attempted to pull out of the tailspin he'd put us into. The engine whined and then cut off (later I learned that you are supposed to stop the propeller in a spin, but at the time it seemed fairly ominous). I experienced something that I had been introduced to (under happier circumstances) on earlier flights – freefall. A preflight checklist floated up from my lap and headed for the tail. In a brief moment of anthropomorphization, I sympathized. And after what must've been one of the most ironically serene twenty seconds of my life, he finally managed to correct his error and pulled us out, a few thousand feet or so down.

Breathe in.

Breathe out.

"So, you want to take her back up and try it again?"

So we did something else, I can't remember what. I don't think I was in a paying attention mood, and at that point I was probably questioning the wisdom of even trying to emulate his approach to flying. After a mercifully short time, we landed, and he signed my logbook in a perfunctory but irritatingly chipper way. He skipped the debriefing I was supposed to get, but I didn't hold it against him.

"Quite an adventure we had today!"

And I refused to ever fly with him again. It wasn't the last time I was given the wrong lesson, but most of the other errors tended to be in the opposite direction – two years in, I'd get taken up to practice slow flight, which is about as boring and basic as it sounds, and every now and then someone new would take it upon themselves to teach me something like "proper use of flaps", which I usually dealt with by reciting the lesson before they got it out, but I took these things in stride.

So, after all this text, what's the message here? Simple. If you run into a pilot named John R. Daly somewhere, fucking hit him for me.