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#21
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spins from coordinated flight
Dudley Henriques wrote: Todd W. Deckard wrote: I return to the original question: if the ball is in the middle will it spin? If you introduce a climbing turn stall with the ball centered, you might get a temporary wing drop at the break but unless you introduce a yaw rate as the stall breaks; no yaw rate...no spin! There is a possibility that a flip to the outside can occur in a low speed but large bank climbing turn, since the angle of attack of the outboard wing is greater than that of the inboard wing. Thus, in a left climbing turn of 30 degrees or maore bank, the right wing experiences a higher angle of attack, and will stall first if the airspeed drops low enough, and especially if an accelerated stall is induced. I have had this demonstrated tome in a C150. The result is dramatic. The craft flips to the right, as in a half snap roll, ends up upside down, and one is obliged to recover by certain mens. My instructor then practiced much back stick to get back to right side up, managing the zoom safely. It's a bit more of a thrill and happens quicker than a conventional spin. It can be done in both directions, plenty of altitude, please.... NOTE: If you analyze angles of attacks in urns, level, descending, climbing, using a spiral helical surface as reference, you will see that in turning descent, the inner wing experiences a greater angle of attack and will fall safely to the inside of the turn, but when climbing the oppsite wing stalls first. Te flip to upside down is a total surprise. Hence in climbing steeply out of a takeoff, the speed, turn rate and bank must all be carefully managed. Usually, the less the turn rate, the better, the ball must alwys be kept centered and the airspeed must be kept always at least 1.2 Vso or more. A further hint is that in a cross-wind condition, especially when higher level winds are of a changing direction (usually rotates to the right on ascent in the northern hemisphere), it is best to make the first turn into the wind; If you take off of RY270 and the surface wind is from 300, the wind at 200 feet AGL will be from 310 and that at 400 feet AGL will be at 320 degrees, and likely of a higher wind speed. A gradual right turn (10 degrees bank) will present you with increasing airspeed and a more rapid rate of climb; wery safe and very efficient. On descent to landing, opposite things happen. As you descend, the head wind speed diminshes, and in the northern heispere it shifts a bit to the left. Here in Ohio, if there is any significant surface wind, I usually keep about 10 knots extra on early final (if Vso is 60 kts, I carry 70 or 80 kts. When about a half mile from touchdown, I often see a 5 to 10 konot drop in airspeed with no action on my part. Crosswind components accordingly dimiish in speed and shift a bit to the left. A crab angle serves on the first part of final descent. If any significant crosswind remains below 200 feet, a shift into a side slip, where fuselage is aligned with the runway while the upwing wing is down is best for touchdown, often on one wheel for a moment. Angelo Campanella |
#22
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spins from coordinated flight
The answer to the ball question is no. It won't spin. A ball centered airplane in a climbing turn is compensated by rudder and is considered coordinated (in the classic sense).
Ok, now I'm confused again. If "stall plus yaw" is all that's necessary, and all (normal) turns involve yaw, then why won't it spin? Do I have the wrong definition of "yaw"? Jose -- You can choose whom to befriend, but you cannot choose whom to love. for Email, make the obvious change in the address. |
#23
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spins from coordinated flight
Todd W. Deckard wrote:
But the links that Dan_Thomas sent me indicated that the airplane would not stall "straight ahead" if you were in a climbing turn. The outside wing has a higher AoA which diverges even further as it initially drops. Dan isn't wrong. Climbing turn stalls are a bit complicated to nail down to a strict behavioral pattern as each airplane and indeed each stall entered in a specific airplane will probably be exhibiting slightly different stall behavior due to varying control inputs by the pilot. The result of this is that climbing turn stalls can produce different results depending on what the pilot is doing with the airplane up to and at the instant of the stall break. Basically, if you are (as we say) coordinated, the top wing will stall first and the airplane will roll off in that direction. The reason for this is that as the stall is approached both wings start losing lift causing the airplane to mush into a slip. The highest wing gets interference from the fuselage and usually quits first. If you watch the ball as this happens, as you get near to stall, you'll probably notice that if you can't hold it centered, and a slip develops, that high wing will usually be the one to go first. This doesn't always happen however :-)) and if you skid the airplane, the bottom wing can break first. The bottom line is that in most climbing turn stalls, you will get a roll off as the stall breaks, but remember, this is a ROLL OFF, not a yaw rate!! Just reduce the angle of attack and use aileron to raise the lowering wing and no pro spin forces are present. -- Dudley Henriques |
#24
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spins from coordinated flight
Stefan,
I am currently chanting the "ball centered = no spin" mantra. However I am very sympathetic to your explaination that its a difference in AoA. In the end, that may be the purest way to explain the spin. If this thread sustains I'll listen in and see what I can sift out. Todd "Stefan" wrote in message news:4bb62$4773ba89 While I agree that this is a correct and simple recipe and therefore quite useful in practice, I don't agree that it helps to *understand* the situation, because *reason* for the spin is not the yaw rate. The reason for the spin is an asymmetric angle of attack, i.e. one wing is more stalled than the other. Of course this situation can only occur if there is some yaw, which leads us to the recipe given above. Recipe: As there is always some yaw in a coordinated turn (otherwise it wouldn't be coordinated), you can perfectly enter a spin from a coordinated turn. Aerodynamic reason: The inner wing has a higher angle of attack than the outer, so it stalls first or, if both wings stall, it is more stalled. Asymmetric stall condition - spin. |
#25
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spins from coordinated flight
Todd W. Deckard wrote:
In your knife edge demonstration you could measure this if you rotated the ball inclinometer 90 degrees. I *believe* it would show you were in coordinated flight. Didn't even have a ball indication in that airplane. You don't use them in aerobatics. Even for primary instruction, it's best to get the student's head outside the cockpit and away from the ball as soon as possible and concentrated on nose attitude where it belongs. Personally, I feel the ball is the least necessary instrument on the entire panel :-) -- Dudley Henriques |
#26
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spins from coordinated flight
Your right, a string taped to the canopy is much better. Hah!
Todd "Dudley Henriques" wrote in message I feel the ball is the least necessary instrument on the entire panel :-) -- Dudley Henriques |
#27
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spins from coordinated flight
Jose wrote:
The answer to the ball question is no. It won't spin. A ball centered airplane in a climbing turn is compensated by rudder and is considered coordinated (in the classic sense). Ok, now I'm confused again. If "stall plus yaw" is all that's necessary, and all (normal) turns involve yaw, then why won't it spin? Do I have the wrong definition of "yaw"? Jose A "normal" turn is accomplished by splitting the lift vector, NOT by holding in yaw. Yaw should only be present in the turn dynamic during the entry into the turn and exit from the turn. Once stabilized in the turn, there should be no yaw present. There could be however if the turn was a slipping turn or a skidding turn. -- Dudley Henriques |
#28
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spins from coordinated flight
On Dec 27, 5:42*am, "Todd W. Deckard" wrote:
Can you depart and spin from coordinated flight? *Specifically a coordinated climbing turn? You have to have yawing motion. However, its very common for students to not be able to maintain coordination during a climbing stall to the right; which is why its a common way to introduce unexpected spins (I don't do that though). -Robert, CFII |
#29
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spins from coordinated flight
Todd W. Deckard wrote:
Your right, a string taped to the canopy is much better. Hah! Todd "Dudley Henriques" wrote in message I feel the ball is the least necessary instrument on the entire panel :-) -- Dudley Henriques Actually, the horizon line is the best yaw indicator on the planet. In lieu of that, a wingtip in a vertical climb, or the sight picture directly over the nose in a vertical dive. -- Dudley Henriques |
#30
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spins from coordinated flight
In my experience, a stall break while straight and level or in a 60 degree
bank if perfectly coordinated will drop the nose straight down. The kicker is that 98% of the pilots have lazy feet and don't really keep the aircraft coordinated. If power is ON, the aircraft will need more rudder to control yaw and that amount of rudder will increase as speed is decreased approaching the stall. Some airplanes may not have enough rudder to stay coordinated to the stall, most pilots will not use the rudder that is available. Some airplanes will not spin, even wit yaw supplied by maximum rudder input at the stall in a pro-spin direction. The Beech Skipper [BE77] requires that the stall be entered, just before the stall, full pro-spin rudder is applied to induce a roll. At a 90 degree bank angle, sudden and full aileron in the opposite direction as the rudder is necessary to stall the wing crisply at the outer half. That will cause the airplane to roll rapidly and enter a spin. If not timed or done correctly, the aircraft will enter a spiral. In the accidental spin, the pilot is likely to do exactly the same thing, just not with thought and skill. The plane is stalled while yawing [uncoordinated] and when the break happens, the poorly trained and non-current pilot's reaction will often be to try to pick-up the wing that is falling and the nose with aileron and up elevator. The natural reaction, which training and experience correct, is to "fight" the falling nose, the falling wing, with normal control input. IF the aircraft is coordinated perfectly, the difference in lift vector is due slightly to the radial airspeed difference between the L&R wings, but more my the dihedral built in the airplane. The problem is that flight is very dynamic, control forces are changing, humans have reaction times, and the control authority created by the aerodynamic surfaces rapidly falls with a small decrease in airspeed [lift equation] and the other forces, such as P-factor and engine torque involve inertia and mass. "Todd W. Deckard" wrote in message ... | | "Dudley Henriques" wrote in message | ... | There is only one thing you have to know about spins. To enter one you | need 2 things to be present; stall and a yaw rate. | | So to corner your answer to my question: you cannot? spin from coordinated | flight. | The airplane must be yawed during the stall break (thus the inclinometer | ball slips or skids | to one side). | | My question is not to seek out practical advice in spins, or recoveries. It | is to explore two | academic debates: Can a certificated airplane depart if the ball is | precisely in the middle | and is there something telling in the emphasis from the foreign sources | cited that exposes a | gap in our US training practices and material. | | Thank you for your response. | | I'll be making a new years resolution to try it out in the neighboorhood | Decathalon (with an appropriate | chaperone) but as it is cold and snowy I thought I would put it to the | uunet. | | Best regards, | Todd | | |
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