Single Prop Engine Turning and Stalling

[Ken]

Peter, Ryan covered the adverse yaw point quite well. The spin recovery I shared is the "standard" and, although I don't know what year that was adopted by NACA/NASA, I'll guess that the Fokker's design predates it. A Cub will behave the same way, actually ... pro and anti-spin aileron is part of a learning demo I've done in it. Newer aircraft were designed not to behave this way.

With regard to the left break tendency with either engine installation - I'll be honest, I can't say for sure, maybe another poster knows. My educated guess is that there is some twist, offset, or cant built into that airplane that results in the left break by overshadowing the prop disc influence. It idle, it probably isn't that influential. I've heard tales that some military airplanes were built to intentionally break in one direction to provide predictability for pilots, but that may just be a tale. Neat topic!

[Fogg]

Thanks Ryan and Ken.

I'm glad to hear that Netherlands East Indies Captain Van Lent's recovery technique makes some sense.
The D.21's rudder was enlarged during testing, so I think the rudder was also used.

I'll be honest, I can't say for sure, maybe another poster knows. My educated guess is that there is some twist, offset, or cant built into that airplane that results in the left break by overshadowing the prop disc influence.

Thanks for that. It's a good working assumption for me. Of course other people's inputs are welcome.

[JDK]

OK, I'm going to go way out on a limb here, so let's see how much dubious theory I can string together! I'm no pilot, and no aerodynamic theorist - I have people for that - so this is just some other random historically based thinking aloud

A few aircraft of the period had an offset engine mount (and one type of engine) such as the Bloch MB 152 (a pusher is the offset engine and nacelle in the Supermarine Walrus) you could expect a a break to spin having a very strong tendency to one direction. AFAIK, the Fokker didn't and most types of the period didn't.

It's probably fair to call the Fokker D XXI a conservative and relatively simple design, albeit of a advanced popular conventional layout of the period. It's therefore reasonable to assume it did not have any (then) advanced features relating to stall characteristics - better data pending, of course.

Here we move from asymmetric aircrew derived airflow, to asymmetric structure (normally assumed to be related to stall / spin mitigation - but possibly for other purposes with an incidental staff effect) and asymmetric weight / loading.

Other aircraft had aerodynamic vertical tail surfaces to give a lifting force to the port or starboard (later model 109F onward) or an offset fin leading edge (Hawker Hurricane) but I don't think they would have much influence in spin entry past stall - comment?

Earlier still, in W.W.I there were some Italian types that had longer wings on one side than the other.

It's possible that the Fokker had a significantly greater weight or mass on one side or other that meant that was more of a factor in stalling to one direction, although not an intentional effect, and possibly not recognised as such. My guess would be that would need to be a relatively large mass, relatively far from the centreline. Sounds unlikely.

As it evident in this thread, the spin (and stall) are not always properly understood today. However it was during W.W.I that pragmatic combat experience meant that some pilots figured out how to get out of a spin, though it does not seem that spin recovery was taught in the period - I can't find a reference to it in the Gosport System. However it was certainly soon after W.W.I that the now standard spin recovery technique was taught.

http://www.crossandcockade.com/forum/fo ... asp?TID=75

http://en.wikipedia.org/wiki/Spin_%28flight%29#History

http://www.gosport.info/History/Flying_ ... story.html

Pre W.W.I

Flying at slow speeds resulted in constant danger of a stall and a spin. The result was often fatal because no one had yet discovered how to recover from a spin. Such was the situation presented to Wilfred Parke in August of 1912. He fell into a left-hand spin during a military test. After pulling hard on the stick and pushing the rudder to the left with no result, he eased off the rudder and pushed it to the right, into the spin. The plane immediately righted itself with about 50 feet to spare.

Parke was a detail-oriented test pilot and immediately analyzed and wrote down his experience. Now that someone had entered a spin and lived to tell how to correct it, the mystery of the spin was finally solved. It would take years for the word to spread however, because Parke died shortly thereafter. Eventually the spin would become part of the aerobatic bag of tricks.

http://www.flightsimbooks.com/jfs2/chapter1.php

1930s

... In the curriculum they advanced to flipper turns, spirals, and spin recovery. First flights in the open cockpit planes were made with an instructor, with communication through a device called a “Gosport,” ...

http://www.navalaviationmuseum.org/Exhi ... ary-9.aspx

Just some thoughts!

[RyanShort1]

Thanks Ryan and Ken.

I'm glad to hear that Netherlands East Indies Captain Van Lent's recovery technique makes some sense.
The D.21's rudder was enlarged during testing, so I think the rudder was also used.

Trust me, aileron alone is likely NOT going to save you from a spin, but it can affect the rate of turn, and sometimes other things, too.

Ryan

[Ken]

As an aside, during USAF pilot training, we spun the T-37 ad naseum (no pun). Heavyweight, lightweight, left, right ... seems like there may have been other parameters as well. All these logged dutifully in the gradebook to show our spectrum of experience. Established in the spin, we would note the nose position, rotation rate, etc, etc. It was not simply an "enter and recover" process. Although I don't remember the exact effect, the gyroscopic force of those two little engines kept the nose higher in one direction than the other. IIRC, inverted spins were IP-only maneuvers. Cool stuff. That reminds me also of the flight characteristics demos we accomplished in the T-38: deep stalls, high AOA rudder rolls and talking about how those quirks were similar to the Space Shuttle. All in all, some pretty good training offered up by Uncle Sam.

[Fogg]

Trust me, aileron alone is likely NOT going to save you from a spin, but it can affect the rate of turn, and sometimes other things, too.

OK, so the ailerons could be used to play with the rotation speed, but not stop the rotation, so to say.