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How to start an argument... - 3/15/2003 12:52:40 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		Maybe I have too much time on my hands!!

Anyway, I was thinking of the names given to various manoeuvers. What is usually called a "Stall Turn" in Britain and Australia is often called a "Hammerhead" in the USA.

I prefer the US vertion, as, is this figure, the aircraft is never actually stalled.

Opinions?

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How to start an argument... - 3/15/2003 2:10:53 PM   
3D_CAP232



Posts: 306
Joined: 6/6/2002
From: Leicester,
Status: offline 		Hi,
Hmmm....i always thought it had stalled if done properly...next to zero forward speed and a little power to make the rudder effective and to go over....just watch a full size do it properly and you'll see what i mean.


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How to start an argument... - 3/15/2003 2:20:07 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		I've DONE it in full sized aircraft hundreds of times. In an aircraft with a constant speed propeller, it is usual to leave full power on (most full size aerobatic aircraft have a much lower power to weight ratio than most models).

You have, however, hit the main point of my discussion on the head. An aircraft is stalled when its wing exceeds its critical angle of attack, regardless of airspeed. In a Hammerhead, the wing is kept at an angle of attack that corresponds with zero lift (or else the lift the wing produced would pull the aircraft off the vertical line) so it never approaches the critical angle of attack.

An aircraft can stall at any speed in any attitude. Similarly, it can remain UNSTALLED at any speed in any attitude.

Awaiting comments!!

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       Post #: 3

Argument or Discussion ? - 3/15/2003 3:21:56 PM   
EXCAP232



Posts: 1318
Joined: 12/15/2001
From: Frederick, MD, USA
Status: offline 		Hammerhead or Stall Turn the wing is "stalled" which means it is not producing lift. The propeller is producing lift or the plane won't climb.

In competition power is reduced until the plane stops climbing and then the rudder is applied to rotate the plane within 1/2 wingspan or less. If you reduce the power completely it is really a chance maneuver.

In "3D" flying the plane is maneuvered "post stall" which means the wing is not flying. Thrust (lift) from the engine is vectored over the control surfaces. In this attitude the propeller becomes the wing and lift is produced by it (just as it is produced by a helicopter).

EXCAP232

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       Post #: 4

discusstion is fine!! - 3/15/2003 3:52:29 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		Hi Cap!!

A common misconception!!

A stalled wing still produces lift. It is, however, operating at a greater angle of attack (the angle of the chord-line to the relative air flow) than that which produces the maximum lift for a particular speed (known as max co-efficient of lift (CL max) or Critical angle of attack (alpha crit)) Therefore, while below the critical angle of attack, lift INCREASES with increased angle of attack, ABOVE alpha crit lift REDUCES with increased aoa, but the wing is still producing some lift.

In a "Stall Turn" the wing must be flown at an angle of attack that produces NO lift. This will be zero aoa for a symetrical wing, and LESS THAN ZERO for a lifting section. Therefore it is operating at much less than alpha crit, has laminer airflow (even at very low airspeed) and is NOT stalled.

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Re: discusstion is fine!! - 3/15/2003 4:02:34 PM   
P-51B



Posts: 6173
Joined: 10/11/2002
From: An Iceburg in, ANTARCTICA
Status: offline 		[QUOTE]Originally posted by Rossan
Hi Cap!!

A common misconception!!

A stalled wing still produces lift. It is, however, operating at a greater angle of attack (the angle of the chord-line to the relative air flow) than that which produces the maximum lift for a particular speed (known as max co-efficient of lift (CL max) or Critical angle of attack (alpha crit)) Therefore, while below the critical angle of attack, lift INCREASES with increased angle of attack, ABOVE alpha crit lift REDUCES with increased aoa, but the wing is still producing some lift.

In a "Stall Turn" the wing must be flown at an angle of attack that produces NO lift. This will be zero aoa for a symetrical wing, and LESS THAN ZERO for a lifting section. Therefore it is operating at much less than alpha crit, has laminer airflow (even at very low airspeed) and is NOT stalled. [/QUOTE]

Not wanting to get into this soon to be quagmire, this is a hit and run comment...


A stall is when the wing is not producing sufficient lift (as opposed to no lift) to keep the airplane aloft.
In the mentioned manouver, the wing is not producing lift sufficient to fly the plane (the propellar may be, but not the wing), and thus it is a stall. If it is flown sufficiently vertical so as to produce no lift, all the better, it is still a stall turn.

Although the term stall turn is a correct one, hammerhead does have more pizazz.

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A common misconception!! - 3/15/2003 4:23:02 PM   
EXCAP232



Posts: 1318
Joined: 12/15/2001
From: Frederick, MD, USA
Status: offline 		Say what? When the wing is vertical then it is not at any angle of attack. It is just being pulled vertical by the prop.

Exit discussion.

EXCAP232

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       Post #: 7

How to start an argument... - 3/15/2003 4:28:48 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		Angle of attack equals angle between chord line and relative airflow. If the aircraft is moving, the wing has an angle of attack.

And, if its just being "Pulled by the prop", how can you do an upline with a glider?

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       Post #: 8

How to start an argument... - 3/15/2003 4:44:23 PM   
P-51B



Posts: 6173
Joined: 10/11/2002
From: An Iceburg in, ANTARCTICA
Status: offline 		[QUOTE]Originally posted by Rossan


And, if its just being "Pulled by the prop", how can you do an upline with a glider? [/QUOTE]

Uhhh...conservation of energy...commonly called momentum.

Really, this time I'm done here.

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       Post #: 9

How to start an argument... - 3/15/2003 4:56:15 PM   
robert


 

Posts: 2448
Joined: 3/2/2002
From: private, IRELAND
Status: offline 		Heeeheeeheee, this, is a funny thread.....

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       Post #: 10

How to start an argument... - 3/15/2003 5:26:28 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		Hi P51,

Didn't see this when I first replied:-

[QUOTE]A stall is when the wing is not producing sufficient lift (as opposed to no lift) to keep the airplane aloft. [/QUOTE]

Sorry, not correct. If an aircraft is in a controlled descent, the wing is producing less lift than weight, but it is not stalled. Same when pushing into an outside loop.

A wing is stalled when it is at an angle of attack higher than CL max. As, at a particular weight and under one G this will corellate with a particular speed, we have the concept of "Stall Speed". If, however, the aircraft is under less than one G, it will stall at a lower speed. If it is under zero G (As in a "Stall Turn" , the wing is not being asked to produce any lift. is at a much lower angle of attack, and WILL NOT STALL.

Now back off guys, or I'll start quoting formula!!

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How to start an argument... - 3/15/2003 5:33:44 PM   
robert


 

Posts: 2448
Joined: 3/2/2002
From: private, IRELAND
Status: offline 		[QUOTE]Originally posted by Rossan
Now back off guys, or I'll start quoting formula!! [/QUOTE]

You wouldn't dare!

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       Post #: 12

How to start an argument... - 3/15/2003 5:56:19 PM   
Rossan


 

Posts: 87
Joined: 6/30/2002
From: Altrincham, UNITED KINGDOM
Status: offline 		Go ahead...Make my day!!

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How to start an argument... - 3/15/2003 6:19:22 PM   
CHassan



Posts: 1230
Joined: 8/26/2002
From: Beavercreek, OH, USA
Status: offline 		Stall = separation of airflow from the boundry layer. Thats good enough for me.

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       Post #: 14

How to start an argument... - 3/15/2003 7:29:54 PM   
JimTrainor


 

Posts: 1308
Joined: 10/25/2002
From: Ontario, ON, CANADA
Status: offline 		Silly me. I'm a novice, but I thought they were two different maneuvers.

I just thought a stall turn was when you "pin the tail" and give rudder input simply to get the plane to "fall" over in the plane (i.e. geometry) of the wing. You know you've done it right when you see a little pendulum like wiggle on the down line. I gathered that the near complete loss of airspeed just prior to the turn is why it's called "stall".

... and hammer head was more of a power on maneuver that looks more like that plane is driven through a U shape at the top of up line. The turn is wider than the stall turn.

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       Post #: 15

How to start an argument... - 3/15/2003 11:37:16 PM   
Doug Cronkhite


 

Posts: 2164
Joined: 12/20/2001
From: San Diego, CA, USA
Status: offline 		Sorry guys..

Stall turn is actually the incorrect name here since the wing never truly stalls. This maneuver has been called a hammerhead since the beginning of aerobatic competition some 70 years ago. Regardless, both names describe the same thing;

Pitch to vertical upline, pivot of 180 degrees as the aircraft stops, followed by a recovery to level flight.

Now to the technical aspects of it..

Any wiggle following the pivot at the top is NOT doing it right and is in fact a downgrade dependant upon the amount of wiggle. Flying over the top of the maneuver is also a downgrade depending on the difference between the upline and downline of the maneuver. The actual deduction varies depending on what type of competition you're flying (full scale, pattern, IMAC).

Doug Cronkhite

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       Post #: 16

How to start an argument... - 3/16/2003 12:00:33 AM   
JimTrainor


 

Posts: 1308
Joined: 10/25/2002
From: Ontario, ON, CANADA
Status: offline 		I didn't express myself clearly. I realize it would not be good form. I simply meant the wiggle indicates the plane didn't simply power through the turn and make a "U". It came to a stop before rotating through 180 degrees to the downline. The wiggle is the rotational energy dissipating if not damped out by the pilot. And if done well (i.e. a genuine rotation, no a "U" then there will be significant angular momentum to manage as it comes around. That's been my interpretation.

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