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spins from coordinated flight



 
 
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  #21  
Old December 27th 07, 06:04 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Angelo Campanella
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Posts: 30
Default 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  
Old December 27th 07, 06:07 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Jose
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Default 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
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  #23  
Old December 27th 07, 06:07 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Dudley Henriques[_2_]
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Posts: 2,546
Default 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  
Old December 27th 07, 06:10 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Todd W. Deckard
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Posts: 65
Default 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  
Old December 27th 07, 06:10 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Dudley Henriques[_2_]
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Posts: 2,546
Default 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  
Old December 27th 07, 06:14 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Todd W. Deckard
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Posts: 65
Default 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  
Old December 27th 07, 06:20 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Dudley Henriques[_2_]
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Posts: 2,546
Default 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  
Old December 27th 07, 06:23 PM posted to rec.aviation.piloting, rec.aviation.aerobatics
Robert M. Gary
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Posts: 2,767
Default 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  
Old December 27th 07, 06:25 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Dudley Henriques[_2_]
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Posts: 2,546
Default 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  
Old December 27th 07, 06:28 PM posted to rec.aviation.piloting,rec.aviation.aerobatics
Jim Macklin
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Posts: 2,070
Default 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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