Why do some airplanes break sharply at the stall, while some are gentle?

Q:
What makes different types of aircraft "snap" over faster during stall practice?

RyanbATC


A:
coordinated flight. The more out of coordination the airplane is, the more likely it is to "snap" or drop a wing.... If you want the indepth..........


So, your flying along, uncoordinated, essentially slipping as you fly thru the air. This means one wing is moving a bit faster than the other. When your doing stalls uncoordinated, usually the left wing is moving faster than the right, thus the right wing stalls before the left causing the right wing to drop. Do Power on stalls with your feet on the floor, it will fall to the right (assuming the airplane is your typical US style where the prop turns clockwise (as viewed from cockpit). Now, if you over correct with rudder, then it will fall on the left wing.

If the airplane is coordinated and still likes to snap (few training style aircraft fall into this, in fact, few certified airplanes today display this trait), then it's do to all of the other wonderful thinks inherent in flight, Gyroscopic precession, P Factor, etc.

Aarinu

Q:
Thanks for the explanation but I was actually looking for the types...

Yes, for instance, the Piper Warrior III's I flew in didn't really "stall." Well they did, but with me in them and my CFI (we totaled around 270lbs thats it), it was a mush, barely a large nose drop haha.

The Piper Arrows the other students used will drop significantly. I'm wondering why....

Is it some aerodynamic forces etc...weight? something to do with the camber of the wing? diherderal (sp?)?

RyanbATC


A:
I'd guess a combination of a lot of things. The varying and particular center of gravity that day (fuel, pilots, etc). As well, the wash-out of the wings, the position, distance, and incidence of the horizontal stab/elevator.

Probably more things too, but just some variables.

Kyle



It helps to understand that a stall is basically an increase in the separation of the smooth airflow over the wing into a detached, turbulent flow far enough forward that lift is insufficient to maintain flight. As the angle of attack increases, the separation point moves forward, until the point is far enough forward that there is an abrupt increase in separation that no longer supports all the weight of the aircraft (oversimplifying, of course).

So the specific wing design (airfoil, span, chord, taper, etc.) is one major factor. Different airfoils will have different stall characteristics. But many other factors intrude, also, such as how much twist is in the wing (and where), what the airflow does as it approaches the leading edge of the wing (some need little stall strips to make a stall a bit more even, for example), what sticks out (exhaust pipes, antennas, etc.) in the path of the wing's airflow, and how carefully the aircraft's actual design was translated into a piece of hardware. So a Cherokee has a very mild stall, an Ercoupe won't really stall at all, a Cessna is not as mild as a Cherokee, but still reasonably gentle, and a Bonanza can, under some circumstances, be pretty wicked.

On a specific aircraft, how the aircraft is rigged, how it is loaded, any damage, and installed external devices can all affect the stall behavior (and ice -- wow!).

Then there is pilot execution: keeping the aircraft coordinated, how much aileron input, flap setting, abruptness, power setting and more.

And the above is far from a complete list, but should give you the general idea.

Larry N.



The most significant effect is the wing design.

On an aircraft with gentle stalling characteristics you'll find that the wing root stalls before the tips. The loss of lift is gentle because the wing tips aren't stalled and so continue to lift, the loss of lift is inboard and therefore any asymmetry has a lesser effect on rolling moment. Also, because the tips aren't stalled aileron control is retained.

This effect is obtained by a combination of changes in wing section from root to tip and also introducing twist along the wing so that the tips have a lower incidence than the root. Wing planform is also important. Highly tapered wings can to stall viciously at the tip.

Light aircraft are generally deigned to have gentle stalling characteristics because of the nature of pilots expected to fly them. I learned to fly in a C150 in the UK when spinning was one of the exercises. Standard C150 wouldn't spin reliably enough for training purposes because of its gentle stall, and we switched to the Aerobat version for that.

mgh



Power can make a stall "appear" worse than it really is. A high powered airplane requires a much higher climb angle to stall at full power than a similarly lower powered airplane. Take a 172R and 172S up back to back and do power on stalls. The 172S's angle will be between 5 and 10 degree's higher than the R model.

Aarinu

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