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michapma
08-03-2004, 07:32 AM
Back in March there was a great discussion (http://forums.ubi.com/eve/forums?q=Y&a=tpc&s=400102&f=23110283&m=506105692&p=1) on stalls and spins in FB. (I would have bumped it, but I didn't want people to feel obliged to read 5 pages of posts to get to my question.) In that thread several things were explained by those in the know. The main topic of the thread was stalls and spins -- how they are in reality and how FB's modeling corresponds. Here are a few ideas that I think noone would dispute, mixed together with some of the fairly concrete points from the thread. I am having a problem understanding something, and these points provide a background for my question. More background is available here (http://www.av8n.com/how/htm/spins.html), which is also a direct source for some of the following points.

<UL TYPE=SQUARE><LI>The stalled condition of an airfoil (such as a wing) is the result of the loss of smooth airflow over the top surface of the wing. The airflow detaches itself from the wing, meaning there is turbulent air flow. A significant loss of lift results. The severity of the condition (and loss of lift) varies with angle of attack, which leads to the next point.
<LI>The stall of an airfoil is a function of its angle of attack (AoA). The angle of attack beyond which a further increase in AoA does not correspond to an increase in (coefficient of) lift is called the critical angle of attack. There are several implications from this. One important one is that stalls are not a function of airspeed. For each aircraft there is an airspeed, which is dependent on various factors, at which the AoA required to maintain level flight corresponds to the AoA at which stalling occurs. This is called the stall speed. However, aircraft can stall at any airspeed, as long as the AoA becomes sufficiently high.
<LI>A stalled wing still produces some lift, i.e., supports the weight of the aircraft to some exent. "Nothing magical happens at the critical angle of attack." How much lift is lost depends on the angle of attack and the design of the wing.
<LI>It is possible and normal in a stall for some sections of an airfoil to be stalled and other sections of the same airfoil to not be stalled. One reason for this is that different sections of the wing may have different angles of attack, both as a funciton of wing design and the attitude at which the aircraft is flying. Many wings are designed to stall on the inside of the wing first.
<LI>When an aircraft is in coordinated flight, the result of loss of lift due to the stalled condition leads to an imbalance with the forces opposing lift. These opposing forces can be the weight of the aircraft, the centrifugal force on the aircraft in a turn, or both. In each case, as long as the aircraft is in coordinated flight (no yawing) the result of the imbalance of lift and its opposing forces is for the nose to "drop." When the aircraft is flying upright, this is due to the forward center of mass of the aircraft, which corresponds to the center of gravity (CoG). In turns, the nose does not necessarily "drop" in a downward direction, but opposite to the direction of lift. The reason for this is, analogous to the case of upright flight, the forward center of mass. The situations are analogous, because in a turn the acceleration is also radial, coming from the path of the curve and not only from gravity. In a horizontal turn with a 90-degree bank angle, the acceleration opposing the acceleration due to lift is entirely due to the radial acceleration and not due to the acceleration of gravity. (Recall that force is mass times acceleration.)
<LI>If both wings are providing equal amounts of lift during a stall, no rolling motion will result. The result is a "straight-on" stall, meaning the nose drops without one of the wings dropping. However, if one wing is stalled differently from the other, different amounts of lift will be produced, and possibly at different locations on the wings. The resulting asymmetry of lift will tend to cause a rolling motion. (This point is not necessarily stated correctly, so please correct it if you see a problem.)
<LI>Near the critical angle of attack, roll damping begins to go away. This means that wings at or beyond the critical AoA that are rolling will want to keep rolling all by themselves. At even higher AoA, the roll will not just continue but accelerate, all by itself. "This is an example of the 'departure' that constitutes the beginning of a snap roll or spin."
<LI>In order for a spin to develop, two things are required: at least one wings to be in a stalled condition, and a yawing motion of the aircraft. This simply means that the aircraft must be stalled, and the aircraft must yaw in order to enter a spin.[/list]

Here are is an important criticism of FB in regard to these points. The "classic" nose drop as a result of the wings stalling is almostly completely absent in FB. That is, when an aircraft is in coordinated flight and the wings stall, the nose should drop. This essentially does not happen in FB. Instead, what usually happens is a wing will drop. Although the aircraft in FB do not necessarily enter into a fully developed spin, they do not exhibit the expected nose drop. During accelerated stalls, in which the aircraft is turning and subject to an acceleration greater than gravity, the reaction of the aircraft seems to be

Please note that in the points listed above, I've tended to use the term stall to refer to the condition of the wings not producing increasing lift with increasing angle of attack. I am trying to differentiate this from the resulting motions of the aircraft due to the stalled condition of the wings. The reason for this is to help avoid confusion. If the stall is understood as being the nose drop that results from the stalled condition of the wings, then it can be justly claimed that it is not possible to stall in FB. I have no problem with this fact, it is essentially correct. However, to simply state that you cannot stall in FB is misleading. For example, it might be inferred that FB is unable to calculate the condition (AoA) under which a wing enters the stalled condition. I reject referring to the nose drop as the stall for this reason. It is more accurate and less confusing to say that the nose drop resulting from stalled wings is absent in FB.

Here is one more relevant fact that I will mention before going on: "In a spin, at least one wing is stalled, and the two wings are operating at very different angles of attack." This is so stated by Denker to combat the thought that in a spin one wing is stalled and the other is not. This may be the case, but is "not a defining property."


Now to my question! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif


I understand well enough what a stall is. I understand well enough what the later stages of a spin. What I do not understand is the transition of the aircraft from a stalled condition to a spin mode. I accept that it is necessary for the aircraft to yaw in order for a spin to occur. However, what does the yaw accomplish? I just can't (at the moment) picture what is happening to the aircraft as it transitions. This is the so-called incipient spin, which is the beginning stage of the spin. This lasts approximately through the first full turn of the spin. If the aircraft continues to spin through this stage, the spin will stabilize into a fully developed spin. A common example is a flat spin. The wing on the inside of the spin is more deeply stalled than the outside wing, and the centrifugal force balances rolling moment of the wings. This is a very stable flight condition. Denker justly compares it to the flight of a samara (maple seed, or whirlybird): a single wing by itself loves to spin. To exit the spin, it is necessary to stop the spinning motion and unstall the wings, which usually involves opposing the spin with rudder and pushing the nose to a lower attitude with the elevator.

So my question is: what happens to an aircraft between the stalled condition of the wings in the presence of yaw and a fully developed spin? In other words, what forces and motions are involved in bringing the aircraft into a spin, and from bringing from the incipient spin into the fully developed spin?

I'm also a bit confused about the term autorotation. This is not the use of the term as in the context of helicopters. Denker defines quite precisely: "At a sufficiently high initial angle of attack (somewhat greater than the critical angle of attack), the roll will not just continue but accelerate, all by itself. This is an example of the 'departure' that constitutes the beginning of a snap roll or spin. The resulting undamped rolling motion is called autorotation." This seems to stand in contrast to its use in which it describes the motion of the fully developed spin. That is, autorotation appears to be used synonomously with the fully developed spin, as in the following sites:
http://naca.larc.nasa.gov/reports/1928/naca-report-273/
http://www.sunrise-aviation.com/Spin.html

So which is autorotation?

Yes, it took me long time to write this post! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-tongue.gif

Thanks for any and all responses... http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Mike

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)
But we are all that way: when we know a thing we have only scorn for other people who don't happen to know it. - Mark Twain, Personal Recollections of Joan of Arc

michapma
08-03-2004, 07:32 AM
Back in March there was a great discussion (http://forums.ubi.com/eve/forums?q=Y&a=tpc&s=400102&f=23110283&m=506105692&p=1) on stalls and spins in FB. (I would have bumped it, but I didn't want people to feel obliged to read 5 pages of posts to get to my question.) In that thread several things were explained by those in the know. The main topic of the thread was stalls and spins -- how they are in reality and how FB's modeling corresponds. Here are a few ideas that I think noone would dispute, mixed together with some of the fairly concrete points from the thread. I am having a problem understanding something, and these points provide a background for my question. More background is available here (http://www.av8n.com/how/htm/spins.html), which is also a direct source for some of the following points.

<UL TYPE=SQUARE><LI>The stalled condition of an airfoil (such as a wing) is the result of the loss of smooth airflow over the top surface of the wing. The airflow detaches itself from the wing, meaning there is turbulent air flow. A significant loss of lift results. The severity of the condition (and loss of lift) varies with angle of attack, which leads to the next point.
<LI>The stall of an airfoil is a function of its angle of attack (AoA). The angle of attack beyond which a further increase in AoA does not correspond to an increase in (coefficient of) lift is called the critical angle of attack. There are several implications from this. One important one is that stalls are not a function of airspeed. For each aircraft there is an airspeed, which is dependent on various factors, at which the AoA required to maintain level flight corresponds to the AoA at which stalling occurs. This is called the stall speed. However, aircraft can stall at any airspeed, as long as the AoA becomes sufficiently high.
<LI>A stalled wing still produces some lift, i.e., supports the weight of the aircraft to some exent. "Nothing magical happens at the critical angle of attack." How much lift is lost depends on the angle of attack and the design of the wing.
<LI>It is possible and normal in a stall for some sections of an airfoil to be stalled and other sections of the same airfoil to not be stalled. One reason for this is that different sections of the wing may have different angles of attack, both as a funciton of wing design and the attitude at which the aircraft is flying. Many wings are designed to stall on the inside of the wing first.
<LI>When an aircraft is in coordinated flight, the result of loss of lift due to the stalled condition leads to an imbalance with the forces opposing lift. These opposing forces can be the weight of the aircraft, the centrifugal force on the aircraft in a turn, or both. In each case, as long as the aircraft is in coordinated flight (no yawing) the result of the imbalance of lift and its opposing forces is for the nose to "drop." When the aircraft is flying upright, this is due to the forward center of mass of the aircraft, which corresponds to the center of gravity (CoG). In turns, the nose does not necessarily "drop" in a downward direction, but opposite to the direction of lift. The reason for this is, analogous to the case of upright flight, the forward center of mass. The situations are analogous, because in a turn the acceleration is also radial, coming from the path of the curve and not only from gravity. In a horizontal turn with a 90-degree bank angle, the acceleration opposing the acceleration due to lift is entirely due to the radial acceleration and not due to the acceleration of gravity. (Recall that force is mass times acceleration.)
<LI>If both wings are providing equal amounts of lift during a stall, no rolling motion will result. The result is a "straight-on" stall, meaning the nose drops without one of the wings dropping. However, if one wing is stalled differently from the other, different amounts of lift will be produced, and possibly at different locations on the wings. The resulting asymmetry of lift will tend to cause a rolling motion. (This point is not necessarily stated correctly, so please correct it if you see a problem.)
<LI>Near the critical angle of attack, roll damping begins to go away. This means that wings at or beyond the critical AoA that are rolling will want to keep rolling all by themselves. At even higher AoA, the roll will not just continue but accelerate, all by itself. "This is an example of the 'departure' that constitutes the beginning of a snap roll or spin."
<LI>In order for a spin to develop, two things are required: at least one wings to be in a stalled condition, and a yawing motion of the aircraft. This simply means that the aircraft must be stalled, and the aircraft must yaw in order to enter a spin.[/list]

Here are is an important criticism of FB in regard to these points. The "classic" nose drop as a result of the wings stalling is almostly completely absent in FB. That is, when an aircraft is in coordinated flight and the wings stall, the nose should drop. This essentially does not happen in FB. Instead, what usually happens is a wing will drop. Although the aircraft in FB do not necessarily enter into a fully developed spin, they do not exhibit the expected nose drop. During accelerated stalls, in which the aircraft is turning and subject to an acceleration greater than gravity, the reaction of the aircraft seems to be

Please note that in the points listed above, I've tended to use the term stall to refer to the condition of the wings not producing increasing lift with increasing angle of attack. I am trying to differentiate this from the resulting motions of the aircraft due to the stalled condition of the wings. The reason for this is to help avoid confusion. If the stall is understood as being the nose drop that results from the stalled condition of the wings, then it can be justly claimed that it is not possible to stall in FB. I have no problem with this fact, it is essentially correct. However, to simply state that you cannot stall in FB is misleading. For example, it might be inferred that FB is unable to calculate the condition (AoA) under which a wing enters the stalled condition. I reject referring to the nose drop as the stall for this reason. It is more accurate and less confusing to say that the nose drop resulting from stalled wings is absent in FB.

Here is one more relevant fact that I will mention before going on: "In a spin, at least one wing is stalled, and the two wings are operating at very different angles of attack." This is so stated by Denker to combat the thought that in a spin one wing is stalled and the other is not. This may be the case, but is "not a defining property."


Now to my question! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif


I understand well enough what a stall is. I understand well enough what the later stages of a spin. What I do not understand is the transition of the aircraft from a stalled condition to a spin mode. I accept that it is necessary for the aircraft to yaw in order for a spin to occur. However, what does the yaw accomplish? I just can't (at the moment) picture what is happening to the aircraft as it transitions. This is the so-called incipient spin, which is the beginning stage of the spin. This lasts approximately through the first full turn of the spin. If the aircraft continues to spin through this stage, the spin will stabilize into a fully developed spin. A common example is a flat spin. The wing on the inside of the spin is more deeply stalled than the outside wing, and the centrifugal force balances rolling moment of the wings. This is a very stable flight condition. Denker justly compares it to the flight of a samara (maple seed, or whirlybird): a single wing by itself loves to spin. To exit the spin, it is necessary to stop the spinning motion and unstall the wings, which usually involves opposing the spin with rudder and pushing the nose to a lower attitude with the elevator.

So my question is: what happens to an aircraft between the stalled condition of the wings in the presence of yaw and a fully developed spin? In other words, what forces and motions are involved in bringing the aircraft into a spin, and from bringing from the incipient spin into the fully developed spin?

I'm also a bit confused about the term autorotation. This is not the use of the term as in the context of helicopters. Denker defines quite precisely: "At a sufficiently high initial angle of attack (somewhat greater than the critical angle of attack), the roll will not just continue but accelerate, all by itself. This is an example of the 'departure' that constitutes the beginning of a snap roll or spin. The resulting undamped rolling motion is called autorotation." This seems to stand in contrast to its use in which it describes the motion of the fully developed spin. That is, autorotation appears to be used synonomously with the fully developed spin, as in the following sites:
http://naca.larc.nasa.gov/reports/1928/naca-report-273/
http://www.sunrise-aviation.com/Spin.html

So which is autorotation?

Yes, it took me long time to write this post! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-tongue.gif

Thanks for any and all responses... http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Mike

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)
But we are all that way: when we know a thing we have only scorn for other people who don't happen to know it. - Mark Twain, Personal Recollections of Joan of Arc

Zayets
08-03-2004, 07:39 AM
To be honest I never thought so deep regarding this.But when you think is pretty obvious that you will have to yaw opposite of your spin to stop this movement.Then,gravity will "push" your crate towards the earth from where you can recover , assuming you are nosed down.Which shouldn't be too hard to achieve.

Zayets out

http://server5.uploadit.org/files/Zayets-sigIAR.jpg

michapma
08-03-2004, 08:41 AM
Yep. Recovery was not my question, but did you know that not all aircraft have the same recovery procedure? The P-39 for example has a procedure that starts with control inputs completely opposite to the normal procedure. This doesn't seem to work in FB, but amazingly enough it did in IL-2! Here's the procedure directly from a Q-1 manual:

14. SPINS.
Deliberate spinning is not recommended. However, if a spin occurs, rapid recovery can be made as follows:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>a. PRERECOVERY.
(1) Throttle must be off.
(2) Propeller control must be in the low rpm position.
(3) Stick full back.

b. RECOVERY.
(1) Apply full opposite rudder when spin is at its slowest.
(2) Wait until rudder effect is noticeable, then apply full forward stick and ailerons agains the spin regardless of ammunition load in the wings.

c. The spin is usually oscillatory in rate, and it is mandatory that the opposite rudder be applied when the spin is at its slowest.

d. If the procedure above is followed, the airplane will recover in one-half turn. If the procedure is not followed closely, the airplane may not recover.<HR></BLOCKQUOTE>

That's right, stick in the full back position at first! I've also read a similar procedure, in which rudder is applied with the spin until the slow part of the spin oscillation, then reversed.

Spins are complicated!

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)
But we are all that way: when we know a thing we have only scorn for other people who don't happen to know it. - Mark Twain, Personal Recollections of Joan of Arc

x6BL_Brando
08-03-2004, 10:02 AM
Hi,

A very learned piece of collation, thk you Mich - very thought provoking. I can't answer your questions, but I'd like to comment on a couple of points.
I have experienced the straight stall more than once in FB. For example, I was in a 3M Sturmo the other day, in a coop, and zoomed up to try and get a shot at an enemy fighter. I did get him, but at the same time I realised that my airspeed had fallen to about 120kph (as shown by the speed bar) and the plane was nearly vertical. I hurriedly pushed the nose down, but the plane was like a brick, and no real measure of control was regained until I was pointing downwards and had picked up enough speed to try using either rudder or ailerons (around 150&lt;170 kph. I could tell for sure that it would have dropped into a spin if I'd used them, esp. the rudder. So my point/question is: wasn't my loss of feel and surface response definitely the precursor to, if not the actual stall? Another 5 or 10 Kph slower, the plane would have become totally brick-like and dropped vertically - with only the hope that the weight of the engine would pull the nose down and made the chance of a recovery possible.

Regarding the very specialised instruction for stall & spin recovery provided for the P39, it should be said that each plane generally had it's quirks in these circumstances. I have a book about Spitfires and their developement which recounts the technique used by the early test pilots in the event of a spin.
A small drogue chute was kept in a box attached within hand's reach of the pilot. Its cable was shackled to a pylon behind him and, in the event of a spin the chute was to be thrown out of the cockpit; which side of the central axis it went depending on the direction of the spin. The main danger was getting caught across the throat by the cable if anything went wrong, but fortunately the Spit was a sweet handler and the drogue was never deployed.

Taylortony
08-03-2004, 10:25 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by michapma:
Yep. Recovery was not my question, but did you know that not all aircraft have the same recovery procedure? The P-39 for example has a procedure that starts with control inputs completely opposite to the normal procedure. This doesn't seem to work in FB, but amazingly enough it did in IL-2! Here's the procedure directly from a Q-1 manual:

14. SPINS.
Deliberate spinning is not recommended. However, if a spin occurs, rapid recovery can be made as follows:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>a. PRERECOVERY.
(1) Throttle must be off.
(2) Propeller control must be in the low rpm position.
(3) Stick full back.

b. RECOVERY.
(1) Apply full opposite rudder when spin is at its slowest.
(2) Wait until rudder effect is noticeable, then apply full forward stick and ailerons agains the spin regardless of ammunition load in the wings.

c. The spin is usually oscillatory in rate, and it is mandatory that the opposite rudder be applied when the spin is at its slowest.

d. If the procedure above is followed, the airplane will recover in one-half turn. If the procedure is not followed closely, the airplane may not recover.<HR></BLOCKQUOTE>

That's right, stick in the full back position at first! I've also read a similar procedure, in which rudder is applied _with_ the spin until the slow part of the spin oscillation, then reversed.

Spins are complicated!

http://giap.webhop.info

_http://people.ee.ethz.ch/~chapman/il2guide/_ | http://www.forgottenskies.com/
But we are all that way: when we know a thing we have only scorn for other people who don't happen to know it. _- Mark Twain, Personal Recollections of Joan of Arc_<HR></BLOCKQUOTE>


I'm also a bit confused about the term autorotation. This is not the use of the term as in the context of helicopters. Denker defines quite precisely: "At a sufficiently high initial angle of attack (somewhat greater than the critical angle of attack), the roll will not just continue but accelerate, all by itself. This is an example of the 'departure' that constitutes the beginning of a snap roll or spin. The resulting undamped rolling motion is called autorotation." This seems to stand in contrast to its use in which it describes the motion of the fully developed spin. That is, autorotation appears to be used synonomously with the fully developed spin, as in the following sites:
http://naca.larc.nasa.gov/reports/1928/naca-report-273/
http://www.sunrise-aviation.com/Spin.html

So which is autorotation?

Yes, it took me long time to write this post!

Thanks for any and all responses...

Mike

Ok I will try to help you on this one and put it in a easy to understand format, A helicopter rotor is in all essense a spinning wing or even look at it as a sort of propeller

The Engine on an airplane is used to overcome drag and provide an airflow over its wing this is what produces lift on the Aircraft. On a Helicopter the engine is used to power the rotating wings to overcome the drag of the blades and turn the rotors which are producing lift as well as thrust due to is fwd slant. when the engine stops the rotors disengaged from the engine and by managing the collective lever, Which alters the angle of attack of the blades) the pilot uses the Airflow to spin the rotors up giving up altitude in return for airflow through the rotors which maintains control..

(Rather like one of those childs toys, the stick with the little propeller on, as you swing it through the air the propeller spins on it, that is what the rotor does and this is autorotation.)

As the Helicopter descends the rotors get faster and potential energy of the airflow through them is converted into kinetic energy which is stored in the rotors. As the helicopter reaches the ground it is traveling downward at quite a speed, at this point the pilot lifts the collective, which raises the angle off attack on the rotor blades converting the stored energy into lift slowing the rotors and decelerating the descent of the helicopter. An ideal situation is vertical desent is stopped at touchdown.

(Again think of the childs toy as you swing it then stop mving it the propeller continues to turn for some time, this is the built up energy in the propeller on it, just like the rotors.)

[This message was edited by Taylortony on Tue August 03 2004 at 09:35 AM.]

tsisqua
08-03-2004, 10:32 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>So my question is: what happens to an aircraft between the stalled condition of the wings in the presence of yaw and a fully developed spin?<HR></BLOCKQUOTE>

The plane becomes filled with pilot poo . . .

I been there, and when the spin is unintentional (it was just supposed to be spin "entry") on the part of an "experienced" CFI who keeps saying "Uh, Oh!" it doesn't help matters any. That was the day on which I later had my first solo.

When the plane is yawed while in an already stalled condition, the airflow is interrupted only upon one wing; one wing maintain at the very least the critical AoA, while the other, lower wing is robbed of airflow. The resulting force takes the plane around . . . and around . . . and around. Oh, yes, did I mention down? The rudder can effectively return the plane to a normal stalled condition by taking up the slack for the stalled wing . . . the rudder doesn't stall in that attitude , and in that attitude, opposite rudder can stop the spin . . . let's all pray for plenty of altitude to get this all done. At the point that the spin is converted to a normal stall, normal stall recovery can be applied.

Now, the important things to remember:
1. Make sure that you are higher than the 3,000 ft. that I was at when a moron said "Let's spin this PA-28, it will be good for you . . . "

2. Begin recovery efforts immediately, upon spin entry, not waiting for a full blown spin.

3. Never, never, never, EVER spin a 140hp Piper Cherokee PA-28. It wasn't supposed to do that http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

Tsisqua

http://server6.uploadit.org/files/tsisqua-bird1.JPG

[This message was edited by tsisqua on Tue August 03 2004 at 09:40 AM.]

[This message was edited by tsisqua on Tue August 03 2004 at 09:42 AM.]

El Turo
08-03-2004, 10:39 AM
A spin and a stall are more or less two different descriptions of the same event, just at two separate points in a timeline. Perhaps this is where your confusion is coming into play in trying to separate the two at a finite point, unless I'm misreading you. A spin is really not much more than a stall left uncorrected and is STILL a condition of "stall", but as a "spin", is merely a descriptor of an advanced timeline state of the stall.

Much like in a car, if no correction or change is made in control input when we begin to slide/spin going around a gravel curve (like, letting off the gas or reversing steering wheel), it will continue to slide/spin until another force acts upon it (like smacking into the guardrail.. or in an aircraft.. mother Earth).

As for spin recovery in FB, I've noticed that dropping full flaps usually results in an immediate spin/stall recovery when paired with opposite rudder.. which is a bit suspect.

As for auto-rotation, I believe TT nailed it nicely.

Best,

~T.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

NegativeGee
08-03-2004, 11:01 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by michapma:
I'm also a bit confused about the term autorotation. This is not the use of the term as in the context of helicopters. Denker defines quite precisely: "At a sufficiently high initial angle of attack (somewhat greater than the critical angle of attack), the roll will not just continue but accelerate, all by itself. This is an example of the 'departure' that constitutes the beginning of a snap roll or spin. The resulting undamped rolling motion is called _autorotation._" This seems to stand in contrast to its use in which it describes the motion of the fully developed spin. That is, autorotation appears to be used synonomously with the fully developed spin, as in the following sites:
http://naca.larc.nasa.gov/reports/1928/naca-report-273/
http://www.sunrise-aviation.com/Spin.html

So which is autorotation?
<HR></BLOCKQUOTE>

This bulletin defines the term as meaning:

"This will promote the wingtips to stall before the inboard sections and produce autorotation, that is, uncontrolled rolling into an incipient spin, usually at great surprise to the pilot!"

Civil Aviation Authority AAC 1-75 (http://www.casa.gov.au/avreg/aircraft/AAC/PART-1/1-075.HTM)

This is what the NASA paper appears to be studying, the other link seems to use the term in a rather ambiguous context, but it is still refering to the same phenonemon.

Anyway, thanks for the good read http://ubbxforums.ubi.com/infopop/emoticons/icon_cool.gif

"As weaponry, both were good, but in far different ways from each other. In a nutshell, I describe it this way: if the FW 190 was a sabre, the 109 was a florett, or foil, like that used in the precision art of fencing." - G√ľnther Rall

http://www.invoman.com/images/tali_with_hands.jpg

Look Noobie, we already told you, we don't have the Patch!

NegativeGee
08-03-2004, 11:17 AM
Also, read the 11th post in this thread over at SimHQ (by Spitfrnd). They discuss a bit about autorotation too:

http://www.simhq.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=82;t=002820;p=

"As weaponry, both were good, but in far different ways from each other. In a nutshell, I describe it this way: if the FW 190 was a sabre, the 109 was a florett, or foil, like that used in the precision art of fencing." - G√ľnther Rall

http://www.invoman.com/images/tali_with_hands.jpg

Look Noobie, we already told you, we don't have the Patch!

TX-EcoDragon
08-11-2004, 04:38 AM
oh man. . I just wrote up a good 3 pages. . . and at 3:30 am. . . when I made a quick reply in another thread it used my reply window that was open. . . and as such I lost what I had written for you. Now I am in a sour mood and am going to bed. Tomorrow I will try to redo it.

S!
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Vengeanze
08-11-2004, 05:14 AM
Hmmm, I always thought that a stall was the effect of having two of these jumping asyncronic on both wings
http://www.telusplanet.net/public/lorejj20/ToyRoom/AMsmurf.gif http://www.telusplanet.net/public/lorejj20/ToyRoom/AMsmurf.gif

...while a spin was when one of em fell off leaving just one of these jumping on the inner wing
http://www.telusplanet.net/public/lorejj20/ToyRoom/AMsmurf.gif

/Ven
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"Maybe for someone more easy to write something than to make something?"
- Oleg Maddox

triggerhappyfin
08-13-2004, 05:21 AM
Hi, michapma!

Great thread!!
You got me read "how it flies" - great reading and source of knowledge http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif.


<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Here are is an important criticism of FB in regard to these points. The "classic" nose drop as a result of the wings stalling is almostly completely absent in FB. That is, when an aircraft is in coordinated flight and the wings stall, the nose should drop.
<HR></BLOCKQUOTE>

Last night I did some testing on different planes in FB. I found the prescence of nosedrop while stalling the planes being there but in some different levels. Some dipping more,some less. Although holding back on stick made som planes just fall like a brick maintaining level position - Would this behaviour be correct?

Some planes beeing easier to maintain level in stall and some of them beeing more prone to dip one of the wingtips.

more or less rudder needed to maintain level flight - adding aileron was only developing spin.

So far it seem to be somewhat right according to stalling as it is described in the "See how it flies"

By the way the tests I made was done in low speed - testing in what speed stall occured.

All planes were easy to recover in this kind of testing - providing altitude beeing enough.
Just not add ailerons as these help developing
spin - just as the theory says.

Also too hasty throttle management also developed spin - as it should due to propwash.

The FW-190 was the most nervous handeled ones http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif.

Should the planes drop nose in highspeed stalls too? The margins beeing very small in high speed should result in a violent enter into spinning - in my opinion.

By the way great reading this "see how it flies".

http://img78.photobucket.com/albums/v257/Triggerhappyfin/ace1_copy.bmp
Heads-on firing was not a safe practice after all ?
Jussi Huotari: It was not specially recommended‚.....
And later, as the Russians were armed with 20mm cannons, it was unwise to meet them heads-on