Plane cannot be stalled

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Frank Uckër
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Re: Plane cannot be stalled

Post by Frank Uckër »

Again, at the risk of personal attack:
As for stalling an airplane on, absolutely you can do it
Yes, with a hard, unpleasant landing.
Three point a taildragger and you've stalled it on
No. It is easy to three point a tailwheel aircraft and land it without the stall warning horn/light going off. And even if it does, all that means is that you are approaching the stall - not that you actually exceeded the stalling AOA.
in three point attitude many taildraggers wings are beyond the stalling angle of attack.
No. Go out and measure it. It's nowhere near that much. You can prove this by taking off in the three point attitude without stalling. The stall warning horn/light won't even go off.

Again, at the risk of personal attack ... the only way you get a high AOA is with a high rate of descent. Draw a picture and look at the relative airflow. If you flare to land, that vastly decreases the AOA. Anyone that flares an aircraft to land - and doesn't just smash it on, carrier style - is NOT performing a "full stall landing".

This thread is depressing. Massive disinformation and personal attacks. What a great combination.
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Re: Re:

Post by Beefitarian »

Bede wrote:
Sorry Beef, but you are completely incorrect. Once you have set the wheels down you are not stalled. Remember that adage about you can stall at any airspeed...as long as the critical angle of attack is exceeded. What is the AOA when you are going down the runway at 40KIAS? Once you figure that out, look at a lift drag curve for the airfoil and see if the wing is stalled. The wing is still producing a significant amount of lift, just not enough to sustain the aircraft in flight.
So if you are going too slow to maintain level flight and your wheels are touching the ground you're in a non vertical decent then?
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Re: Plane cannot be stalled

Post by iflyforpie »

Frank Uckër wrote: No. Go out and measure it. It's nowhere near that much. You can prove this by taking off in the three point attitude without stalling. The stall warning horn/light won't even go off.

Piper J3 Cub. 16 degrees AOA in three point. USA35B airfoil. Max Cl 15 degrees. :D
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Post by Beefitarian »

I get what you guys are trying to say.

It's not an officially licensed stall product until you have the air flowing from below with cute little line drawings depicting the direction of airflow at an angle beyond CL but I'm just going to call the condition of not producing enough lift to support the plane a stall until at someone coins another name for it other than high speed taxi.
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Re: Plane cannot be stalled

Post by Beefitarian »

iflyforpie wrote: When you slow down to a high taxi speed in a nose dragger, the wings are still producing lift. Maybe not enough to lift the aircraft, but they are still producing lift. If you raise the nose gear off the ground (like soft field) they will produce more lift, reducing the weight on the tires.
This will happen until a certain speed that is too low. What's it call when that happens?
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Re: Plane cannot be stalled

Post by photofly »

but I'm just going to call the condition of not producing enough lift to support the plane a stall until at someone coins another name for it
With the greatest of respect, you can call it whatever you like - but "not producing enough lift to support the plane" is emphatically not the definition of - or even the tiny weeniest bit related to - a stall. Stall is related to angle of attack - only.

A wing produces lift throughout the stall, and, for as long as you're descending at a constant rate, it produces exactly enough lift to support the aircraft, otherwise the aircraft would be accelerating downwards. If you have enough power you can even fly level, in a full stall. (You do need vast amounts of power though, more than you have in a piston single).

To answer the obvious next question, before someone asks:

Why then, if the wing generates enough lift, does an aircraft like a 172 descend in a stall? Answer: Because in a stall, the drag becomes enormous. In order to maintain the airpseed at which the wing continues to support the weight (the entire weight) of the aircraft height is traded in for energy to overcome the drag.
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Bede
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Re:

Post by Bede »

Beefitarian wrote: I'm just going to call the condition of not producing enough lift to support the plane a stall until at someone coins another name for it other than high speed taxi.
What photofly says below is correct.

Not producing enough lift is just that, not producing enough lift- it has nothing to do with a stall. In the condition, the aircraft would be be accelerating downwards, (think outside loop, negative G's).
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Re: Plane cannot be stalled

Post by photofly »

To do a basic (and obvious) calculation: let's say you have a 172 with a weight of 1000kg, that yoke full back in a stall descends at a constant vertical speed 300 metres / min (I think that works out at about 2200lbs, and 1000fpm.)

The energy liberated by the descent is 5m/s . 9.81 m/s/s . 1000 kg = 49 000 kg.m.m/s/s or 49kW

49kW converts to 66hp. If you can get 66hp more out of the whirly thing on the front, you don't need to trade in the height, and will no longer descend.

Startling fact: beef the engine of the 172 up by 80-90hp (to allow for prop inefficiency) and you could fly straight and level with the yoke full back.

Of course, then someone will complain that the elevator is misrigged, and adjust it so that the stable angle of attack increases even further, and the drag goes up even further, and the aircraft starts to descend again...
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Last edited by photofly on Mon Oct 03, 2011 11:08 am, edited 1 time in total.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
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Post by Beefitarian »

So the stall is not the wing being unable to support the plane that is a condition with no name.

A stall is when the wing changes it's direction in the relative airflow.
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Re: Plane cannot be stalled

Post by photofly »

A stall is when the wing changes it's direction in the relative airflow.
No. A wing is stalled when its angle of attack exceeds the critical angle of attack, which is the angle of attack for which the coefficient of lift is at a maximum.

That's all there is to it.

EDIT: to clear up some terminology: stalling is not an event, like landing. Being stalled is a condition, like being pregnant. You don't "pregnant" - you become pregnant.
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Last edited by photofly on Mon Oct 03, 2011 11:13 am, edited 1 time in total.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
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Re: Re:

Post by Doc »

Bede wrote:
Beefitarian wrote: I'm just going to call the condition of not producing enough lift to support the plane a stall until at someone coins another name for it other than high speed taxi.
What photofly says below is correct.

Not producing enough lift is just that, not producing enough lift- it has nothing to do with a stall. In the condition, the aircraft would be be accelerating downwards, (think outside loop, negative G's).
So, lets say the roof of a Buick creates lift. It must, right? Now, at what angle of attack will the airflow over the roof of the Buick actually "stall"? Assuming we buy the fact that the airflow over the wing is responsible for lift, and not the deflection of the air by the wing, then at a certain speed, the Buick must become airborne. Yes? No?
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Re: Plane cannot be stalled

Post by photofly »

So, lets say the roof of a Buick creates lift. It must, right? Now, at what angle of attack will the airflow over the roof of the Buick actually "stall"? Assuming we buy the fact that the airflow over the wing is responsible for lift, and not the deflection of the air by the wing, then at a certain speed, the Buick must become airborne. Yes? No?
It's the sharp trailing edge of the wing that's important. (CF. Kutta-Joukowski condition.) Buicks don't have sharp trailing edges, by design, otherwise they'd be wing shaped, and generate a lot of lift. This is considered to be a bad thing in a car.

However, if you were to put a buick in a wind tunnel and vary its angle of attack, then I expect you'd find it would generate some lift. As you increase this angle the coefficient of lift would likely increase, until some maximum value. Beyond that it would decrease. For angles of attack beyond that maximum value the buick would be stalled.

By the way, you can't assume it's not the deflection of the air by the wing that's responsible for the lift. Whichever way round you decide is cause and effect, the upward momentum called "lift" must give an equal and opposite momentum to the air, by deflecting it, downwards. Whether this "causes" the lift or is an inevitable side-effect of lift is just interpretation.
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Post by Beefitarian »

You're just personally attacking me but that can be a real issue in NASCAR that resulted in changes to their car body designs. Carry on.
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Re:

Post by photofly »

Beefitarian wrote:You're just personally attacking me but that can be a real issue in NASCAR that resulted in changes to their car body designs. Carry on.
I wouldn't dream of attacking you. The truth is I love you to bits. I really do. However I don't love you enough to agree with you when what you say is wrong. (In this case, the idea that it's just the roof of a Buick that would generate lift, rather than considering the shape of the whole vehicle.) EDIT: Oh! So sorry ... that was Doc! If it's any consolation I love him too, almost as much.

I'm sure the NASCAR designers are well aware of how their car bodies generate lift, and whether and how to shape the trailing (and other) edges of their vehicles to maximise downforce (negative lift) or whatever other features of airflow they find desirable.

I'm also sure that if you ask their chief aerodynamicist to cast his eye over what I've written, he'd agree with me.
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Post by Beefitarian »

Part of their issue was smooth belly pans reducing the drag from the formerly bumpy stuff under them like steering components. They had some flaps that opened if the car was going backwards as they were designing the lift to be negative in a forward direction so it would help traction via a down force. In some cases if the car spun out as it was going backwards the lift became positive and the car took flight in a very uncontrolled manner.
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Re: Plane cannot be stalled

Post by Frank Uckër »

Piper J3 Cub. 16 degrees AOA in three point
No. I just went out to the flightline and measured the AOA of a tailwheel aircraft tied down.

Using a 4 foot level (with the bubble between the lines) I got a 6.75 inch rise on the flat-bottom wing.

Now, tangent of theta is opposite over adjacent, which is 6.75/48 = 0.140625

And the arctangent of 0.140625 is 8 degrees - a long, long way from Clmax.

I used something called "high school trigonometry" to calculate this.
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Re: Re:

Post by Doc »

photofly wrote:
Beefitarian wrote:You're just personally attacking me but that can be a real issue in NASCAR that resulted in changes to their car body designs. Carry on.
I wouldn't dream of attacking you. The truth is I love you to bits. I really do. However I don't love you enough to agree with you when what you say is wrong. (In this case, the idea that it's just the roof of a Buick that would generate lift, rather than considering the shape of the whole vehicle.) EDIT: Oh! So sorry ... that was Doc! If it's any consolation I love him too, almost as much.

I'm sure the NASCAR designers are well aware of how their car bodies generate lift, and whether and how to shape the trailing (and other) edges of their vehicles to maximise downforce (negative lift) or whatever other features of airflow they find desirable.

I'm also sure that if you ask their chief aerodynamicist to cast his eye over what I've written, he'd agree with me.
I'm not sure if it was Bentley or Audi a few years back at Le Mans, but two of their three cars became airborne. Very flat bellies and just the wrong angle of attack I guess. The third was immediately pulled from the race.
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Re: Re:

Post by Doc »

Doc wrote:
photofly wrote:
Beefitarian wrote:You're just personally attacking me but that can be a real issue in NASCAR that resulted in changes to their car body designs. Carry on.
I wouldn't dream of attacking you. The truth is I love you to bits. I really do. However I don't love you enough to agree with you when what you say is wrong. (In this case, the idea that it's just the roof of a Buick that would generate lift, rather than considering the shape of the whole vehicle.) EDIT: Oh! So sorry ... that was Doc! If it's any consolation I love him too, almost as much.

I'm sure the NASCAR designers are well aware of how their car bodies generate lift, and whether and how to shape the trailing (and other) edges of their vehicles to maximise downforce (negative lift) or whatever other features of airflow they find desirable.

I'm also sure that if you ask their chief aerodynamicist to cast his eye over what I've written, he'd agree with me.
I'm not sure if it was Bentley or Audi a few years back at Le Mans, but two of their three cars became airborne. Very flat bellies and just the wrong angle of attack I guess. The third was immediately pulled from the race.
http://www.popsci.com/cars/article/2008 ... cecars-fly
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Post by Beefitarian »

Frank Uckër wrote:
Piper J3 Cub. 16 degrees AOA in three point
No. I just went out to the flightline and measured the AOA of a tailwheel aircraft tied down.

Using a 4 foot level (with the bubble between the lines) I got a 6.75 inch rise on the flat-bottom wing.

Now, tangent of theta is opposite over adjacent, which is 6.75/48 = 0.140625

And the arctangent of 0.140625 is 8 degrees - a long, long way from Clmax.

I used something called "high school trigonometry" to calculate this.
Attack!
Isn't the angle of attack measured from some cord thingy not the "flat-bottom wing"?
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Re: Plane cannot be stalled

Post by Frank Uckër »

I am now in search of hemlock and razor blades.
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Post by Beefitarian »

Excellent. I hope my use of the wrong spelling for the theoretical line through a wing making it into a rope helped.
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Re: Plane cannot be stalled

Post by iflyforpie »

Frank Uckër wrote:
Piper J3 Cub. 16 degrees AOA in three point
No. I just went out to the flightline and measured the AOA of a tailwheel aircraft tied down.
What kind? How level was the ground? How inflated were the tires? Did it have a Scott or Maule tailwheel?
Using a 4 foot level (with the bubble between the lines) I got a 6.75 inch rise on the flat-bottom wing.

Now, tangent of theta is opposite over adjacent, which is 6.75/48 = 0.140625

And the arctangent of 0.140625 is 8 degrees - a long, long way from Clmax.
You aren't qualifying these claims with any data like aircraft type and airfoil. The bottom of the wing is not necessarily the chord line.

It also seems to me that you are absolutely sure that every single taildragger is below the angle for Cl max regardless of type or configuration. All you have really proved is what I already said, that not all taildraggers are stalled in the three point configuration (I believe I mentioned the Citabria).
I used something called "high school trigonometry" to calculate this.
That's great. I graduated high school years ago.
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Re: Plane cannot be stalled

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Whatever :roll:
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Re: Plane cannot be stalled

Post by trampbike »

This thread is depressing. As Eric, Bede and a couple of others have written: you are not stalled when on rolling on the ground or parked in the hangar! Heck you are not even stalled while flying a 0 airspeed if you are at 0g... A lot of people here seem to be confused between beeing stalled and having less lift than weight. BTW, the elevator is nothing else but an angle of attack control. Of course is you reduce the travel of it up to a certain point, you can have an airplane that can't be stalled.
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Re: Plane cannot be stalled

Post by burhead1 »

Plane cannot be stalled to a Buick.

Ladles and Jellyspoons, I come before you to stand behind you and tell you something that I know nothing about.

:smt040

Carry on if nothing else its a good read!
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