current AH2 corner speeds

[FLS]

So... I'm a bit confused.  Please correct me where I'm wrong, but I'm just trying to understand the concepts.

Stall speed is a function of the speed of the air moving over the wing, right?

Indicated airspeed is basically the speed of that air moving over the wing, but it's tied to the amount of air molecules that is actually moving over the wing, right?  That's why as you go higher, you move faster through the thinner air, but the indicated being the same means it's moving through the same amount of molecules of thinner air, doesn't it?

Shouldn't the IAS remain consistent for stall speed regardless of altitude?  I tend not to think in terms of numbers while playing the game, so I've never particularly noticed.

Wiley.

It's because thrust and drag change differently with altitude. The power on stall would be affected not the power off stall. For turning at corner speed it's the same, the thrust and drag are not affected equally by altitude.

[Wiley]

It's because thrust and drag change differently with altitude. The power on stall would be affected not the power off stall. For turning at corner speed it's the same, the thrust and drag are not affected equally by altitude.

Ah!  Because the prop's doing the same thing regardless of alt, it's affected by air density.  Thanks!

Wiley.

[FLS]

The prop is like the wing at altitude, it's the engine power that's decreasing thrust with altitude until the high blower or whatever you have kicks in to mitigate it giving you a jump in performance. You can see that in the climb rate charts.

I'm not saying there's no change in prop efficiency but I think engine power is a bigger factor.

[Traveler]

So... I'm a bit confused.  Please correct me where I'm wrong, but I'm just trying to understand the concepts.

Stall speed is a function of the speed of the air moving over the wing, right?

WRONG , a Stalled wing has nothing to do with with Speed.  It's all about AOA.

Indicated airspeed is basically the speed of that air moving over the wing, but it's tied to the amount of air molecules that is actually moving over the wing, right?

Wrong, Airspeed indicators work by measuring the difference between static pressure, captured through one or more static ports; and stagnation pressure due to "ram air", captured through a pitot tube.

That's why as you go higher, you move faster through the thinner air, but the indicated being the same means it's moving through the same amount of molecules of thinner air, doesn't it?

Not entirely correct.  At increased altitude (more accurately, density altitude), for the same given indicated airspeed (IAS) the aircraft's true airspeed (TAS) will be higher.

Shouldn't the IAS remain consistent for stall speed regardless of altitude?
 

 Most aircraft exhibit a small difference between the airspeed actually shown on the instrument (indicated airspeed, or IAS) and the speed the instrument should theoretically show (calibrated airspeed or CAS). This difference, called position error, is mainly due to inaccurate sensing of static pressure. It is usually not possible to find a position for the static ports which, at all angles of attack, accurately senses the atmospheric pressure at the altitude at which the aircraft is flying.

Again, one more time, a stall has nothing to do with airspeed.  AOA is what causes the wing to stall.

[FLS]

Wiley stall speed is the slowest speed you can maintain level flight because the AOA is at the critical AOA. Going slower reduces lift and you descend. Increasing AOA also reduces lift and you descend.

In other words the stall occurs at the critical angle of attack and stall speed refers to the speed where that AOA produces level flight.

[Traveler]

Wiley stall speed is the slowest speed you can maintain level flight because the AOA is at the critical AOA. Going slower reduces lift and you descend. Increasing AOA also reduces lift and you descend.

In other words the stall occurs at the critical angle of attack and stall speed refers to the speed where that AOA produces level flight.

This is true: "the stall occurs at the critical angle of attack"   

This is not ture: "Stall speed refers to the speed where that AOA produces level flight"  if the aircraft is in level flight, the wing is not stalled because the critical AOA has not been exceeded.

[FLS]

This is true: "the stall occurs at the critical angle of attack"   

This is not ture: "Stall speed refers to the speed where that AOA produces level flight"  if the aircraft is in level flight, the wing is not stalled because the critical AOA has not been exceeded.

It is true by definition. If you are at the critical angle of attack and flying level you are at stall speed. If you are slower you are descending, if you are faster you are climbing, and if you increase AOA you are no longer flying level.

[PJ_Godzilla]

It is true by definition. If you are at the critical angle of attack and flying level you are at stall speed. If you are slower you are descending, if you are faster you are climbing, and if you increase AOA you are no longer flying level.

Or, of you tend to think graphically, its a point of zero slope and maximum on the cl versus alpha curve... increase or decrease  alpha from here and cl decreases.

If at stall speed and clmax flying level, weight equals lift. decrease speed and weight will exceed lift, increase and vice versa.

The part I'm wondering about though, is with/without flap. THe impact of flap on clmax is well known - I'll cite fig 13 in the URL for some examples: http://adg.stanford.edu/aa241/highlift/clmaxest.html

If we go back to the 2.45*stall speed rule of thumb, the trick to understanding flap impact on stall speed is to know, apriori, the incremental CLMax per increment of flap on your a/c. If I knew that, I could, since lift is linear with CL, expect to be able to lower the root of stall speed by an offsetting proportion - but none of this is clean or easy in the moment. However, it'd be pretty helpful if anybody (like maybe FLS) has clmax versus flap deflection for some of our in-game stuff, like especially 109s.

[Traveler]

It is true by definition. If you are at the critical angle of attack and flying level you are at stall speed. If you are slower you are descending, if you are faster you are climbing, and if you increase AOA you are no longer flying level.

Please where is that definition?  Read the definition for a Stall condition.  It's not level flight.

[FLS]

Please where is that definition?  Read the definition for a Stall condition.  It's not level flight.

You keep saying stall instead of stall speed. I'm using the FAA definition of stall speed.

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf

[Oldman731]

You keep saying stall instead of stall speed. I'm using the FAA definition of stall speed.

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf

"The minimum speed below which further controlled flight is impossible is called the stalling speed."

That has nothing to do with level flight.  Just sayin'.

- oldman

[Traveler]

You keep saying stall instead of stall speed. I'm using the FAA definition of stall speed.

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf

there is no speed at which a stall can not happen.

Please look at page .4-3 of your stated source.

Source: FAA-H-8083-3A, Airplane Flying Handbook page 4-3.
STALLS A stall occurs when the smooth airflow over the airplane’s wing is disrupted, and the lift degenerates rapidly. This is caused when the wing exceeds its critical angle of attack. This can occur at any airspeed, in any attitude, with any power setting.

[PJ_Godzilla]

I'm pretty sure FLS is banging his head against the wall right now.

Maybe not in FAA terms, but in strict engineering terms,

V(stall) = (2W/(rho*S*CL(max)))^.5

So, I don't see why you guys keep talking stall when he clearly says "stall speed".

He stipulated: CLMax (alpha crit) and level flight (neither descending nor ascending, thus in equilibrium, L=mg).

If that condition obtains, any decrease in speed (lift = 5 rho v^2 cl S, mg = constant for our purpose here, albeit time-dependent in reality) will result in a lift decrease and you will descend, any increase and you will ascend.

Okay, so he might be mis-quoting the book - but his statement is entirely logical and correct.

Traveler is also correct in stating "there is no speed at which a stall can't happen", but that is a fundamentally different statement than that made by the equation I cite (eg, accelerated stall is entirely possible above the stall speed).  Oldman's statement is also correct - but misses the point of the definition, though, I'll note, the equation in no way cares that you be in level flight but rather only cares that you are in vertical force equilibrium.


You guys need a referee and a translator.

[Traveler]

I'm pretty sure FLS is banging his head against the wall right now.

Maybe not in FAA terms, but in strict engineering terms,

V(stall) = (2W/(rho*S*CL(max)))^.5

So, I don't see why you guys keep talking stall when he clearly says "stall speed".

He stipulated: CLMax (alpha crit) and level flight (neither descending nor ascending, thus in equilibrium, L=mg).

If that condition obtains, any decrease in speed (lift = 5 rho v^2 cl S, mg = constant for our purpose here, albeit time-dependent in reality) will result in a lift decrease and you will descend, any increase and you will ascend.

Okay, so he might be mis-quoting the book - but his statement is entirely logical and correct.

Traveler is also correct in stating "there is no speed at which a stall can't happen", but that is a fundamentally different statement than that made by the equation I cite (eg, accelerated stall is entirely possible above the stall speed).  Oldman's statement is also correct - but misses the point of the definition, though, I'll note, the equation in no way cares that you be in level flight but rather only cares that you are in vertical force equilibrium.


You guys need a referee and a translator.

The problem for me is the two different definitions provided for Vs by the FAA : "VS Stalling speed or minimum steady flight speed at which the aircraft is controllable”
which is it?

Vs =  A stall occurs when the smooth airflow over the airplane’s wing is disrupted, and the lift degenerates rapidly. This is caused when the wing exceeds its critical angle of attack. This can occur at any airspeed, in any attitude, with any power setting.
   OR
Vs = minimum steady flight speed at which the aircraft is controllable.

 We flight instructors have spent thousands of hours having students fly at Vs +5 to demonstrate positive control in the realm of slow flight in preparation for landing drills.  If the AOA reaches the critical angle of attack, the wing stalls, there is no aircraft control until the AOA is reduced.  So how can Vs  represent  two different flight realms, one controlled and one out of control?

[PJ_Godzilla]

This is worthy of some thought.

The second Vs you cite is the one, on review, cited in the equation to which I refer. It is the minimum speed at which you can generate enough lift to offset weight. Anything below that, and, since CL is at max, you simply don't have enough dynamic pressure to cancel weight.

The first one, imj, is almost meaningless because and as you note, at any speed you can cause separation and even flow reversal on the upper surface of the wing. You're into accelerated ("speed higher than") the defined Vs. Further, you've got sufficient energy, in that state, to recover a lot of dynamic pressure, given control authority. 

But that's just my interpretation. You're in the Flight instruction business. I am merely an aging aero guy who crossed over to the dark side of management long ago. It's a worthy topic.