How do you know 'when' an aircraft has stalled?

[turboplanner]

Hopefully it's still flying.

 

 

[dazza 38]

General Question... What happens to the tail when a conventional aircraft stalls?

Iggy and Metalman are on to something.

 

 

[djpacro]

I thought it might be a good idea to know what a stall is .....

[Powerin]

An aeroplane is the sum of it's components, if the wing exceeds the critical AoA what is happening the the rest of the airframe?

The thing that makes the wing exceed critical AoA is the elevator (apart from gusts of wind, updrafts etc that change the direction of airflow). So I reckon the elevator/HS is still doing something up to and beyond the stall. Isn't it? Otherwise if the elevator has lost effectiveness how do you recover?

If you are in that most stable of stalls, a spin, the rudder also still has authority to be able to recover (assuming the aircraft is spin recoverable).

 

So, if an aircraft is able to recover from stalls and spins, doesn't that mean that empennage control surfaces are still working in a stall?

 

 

[dazza 38]

I have read Fly Better.If that helps .Also FB:augie:

 

 

[Powerin]

Been treating this as a brain teaser, so I haven't researched anything yet...unlike Iggy

 

But it's equally possible that

 

 

[Powerin]

DJP is some sort of modern day Archimedes (Oh and.... Iggy doesn't do research )

Yes...coming to realise that DJP is some sort of demi-god who has come down to make our lives difficult by keeping us safe and alive.

 

 

[facthunter]

The tailfeathers should remain unstalled. One way this is done is to make the aspect ratio of them low. Small span/chord ratio. This is a recommended design feature for all homebuilt/simple aircraft.( FAR 23?). If your Cof G is way out, you can negate this effect and have the tailplane stall first. Put simply, this is NOT a good idea. Nev

 

 

[Guest davidh10]

With respect to my earlier post (#36), I thought it would be interesting (for myself as well) to work out the instantaneous change in effective AOA caused by flying into a rising or falling column of air, such as in and around thermals.

 

Change-of-AOA = ATAN( Vertical-relaive-speed / Horizontal-speed )

 

For horizontal speed of 60kn = 6076'/min:-

 

• Vertical-speed = 1100'/min ==> 10 degrees.
   
   
  
• Vertical-speed = 800'/min ==> 7.5 degrees.
   
   
  
• Vertical-speed = 500'/min ==> 5 degrees.
   
   
  
• Vertical-speed = 300'/min ==> 3 degrees.
   
   
  

 

 

As can be seen from the (rounded) values given above, for a cruise of 60 knots, the instantaneous change in AOA in degrees approximates the relative vertical speed in hundreds of feet per minute. While the calculation makes some invalid assumptions with respect to fluid mechanics, it provides a rough mental guide.

 

Did anyone imagine the magnitude of the change in AOA? Think about what this means if you are flying slowly, and thus with a high AOA, in thermals or turbulence.

 

 

[turboplanner]

.....which would be why we want the secret DJ.

 

 

[Sloper]

When gravity takes over and you find yourself inside a ready made coffin.

 

regards Bruce

 

 

[kaz3g]

I still recall the images of some Cessna 150s that have "candled" mustering.

One of my best friends died when his C150A went in mustering... too hot, too low, too slow!

 

kaz

 

 

[naremman]

[

 

I have developed a diabolical air exercise for them where they have their eyes closed and I fly the aeroplane quite comfortably to where we are in a vertical dive at low airspeed but stalled. I hand over, they open their eyes and notice the obvious - we are in a vertical dive so need to pull out. The situation invariably and suddenly gets much worse because they have not identified that the aeroplane was stalled. Few, if any, of the symptoms of an approaching stall existed.

 

I think I know where you are going on this one DJP. The key element here is the angle between the relative airflow and the chord line of the wing, irrespective of airspeed or where the nose is pointing.

 

Those of us with aerobatics experience probably have gained an insight to this on the occcasions when in the latter parts of a loop or stall turn, the windscreen is full of green and we have then overcooked the back pressure, followed by some form of protestation from the airframe.

 

Most of my aeros have been done in Airtourers and the buffet over the tailplane is usually the initial indicator that the limits are being approached. Chucking a roll of toilet paper out, with a good amount of height under you, and going streamer cutting is a great way to establishing the limits of both the pilot and aeroplane.

 

 

[turboplanner]

How do you know.......when an aircraft........has stalled?

 

 

[djpacro]

Seems that there must be text remaining after I delete stuff.

 

 

[Guernsey]

The tailfeathers should remain unstalled. One way this is done is to make the aspect ratio of them low. Small span/chord ratio. This is a recommended design feature for all homebuilt/simple aircraft.( FAR 23?). If your Cof G is way out, you can negate this effect and have the tailplane stall first. Put simply, this is NOT a good idea. Nev

How can a tailplane stall if it is flat on both upper and lower surfaces and does not have an aerofoil section. Just asking.

 

Alan.

 

 

[pudestcon]

How can a tailplane stall if it is flat on both upper and lower surfaces and does not have an aerofoil section. Just asking.Alan.

It still has an AOA to the airflow

Pud

 

 

[turboplanner]

Its no secret, turbo. I'm sure that everyone here (well, perhaps almost everyone) who was in a stalled aeroplane would know for sure that it was stalled.Discard all the previous text related to the symptoms of an approaching stall - consider what is left, does that satisfy you?

I thought it was going to be something I could learn from.

 

 

[Guest davidh10]

How can a tailplane stall if it is flat on both upper and lower surfaces and does not have an aerofoil section. Just asking.Alan.

That belief stems from taking the popular Bernoulli explanation of wing lift , which is fallacious. Just think about it. If that were the whole explanation, paper darts wouldn't work and aerobatic aircraft would fall out of the sky when upside down, since all the lift would be earthwards. The idea that a an aerofoil is half a venturi or that the air molecules passing over the top and bottom of the wing separate at the leading edge and arrive at the trailing edge at the same time (thus causing the reduced pressure due to increased velocity over a longer surface) are fallacies.

Look up the Neutonian explanation, which is much better and explains why aircraft can fly upside down or with wings that don't have an aerofoil section. It also explains ground effect, which the popular Bernoulli explanations cannot.

 

Put in very simplistic terms, the Neutonian explanation describes a rotating transverse vortex around the wing which throws air downwards at the rear of the wing. The mass of the air displaced downward produces the lift which is an equal and opposite reaction.

 

In fact there are invalid explanations using both theories and both men's theories can be used, if done correctly to explain lift. The difficulty is that in many cases, simplifying the explanation results in an invalid description.

 

For the benefit of students, RAA subscribes to the "Bernoulli lower pressure above the wing" fallacy, so for the sake of getting the question right in tests, just remember that, but also for your own benefit look at it a bit deeper. You may find the references below helpful.

 

http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html

 

http://www.allstar.fiu.edu/aero/airflylvl3.htm

 

 

[ahlocks]

There was once was this aeroplane that was put on a conveyer belt.....

 

 

[pudestcon]

There was once was this aeroplane that was put on a conveyer belt.....

Go bury yourself somewhere locks:no:

 

 

[turboplanner]

There was once was this aeroplane that was put on a conveyer belt.....

Yes, good waste of our time.

 

 

[Guernsey]

That belief stems from taking the popular Bernoulli explanation of wing lift , which is fallacious. Just think about it. If that were the whole explanation, paper darts wouldn't work and aerobatic aircraft would fall out of the sky when upside down, since all the lift would be earthwards. The idea that a an aerofoil is half a venturi or that the air molecules passing over the top and bottom of the wing separate at the leading edge and arrive at the trailing edge at the same time (thus causing the reduced pressure due to increased velocity over a longer surface) are fallacies.Look up the Neutonian explanation, which is much better and explains why aircraft can fly upside down or with wings that don't have an aerofoil section. It also explains ground effect, which the popular Bernoulli explanations cannot.

 

Put in very simplistic terms, the Neutonian explanation describes a rotating transverse vortex around the wing which throws air downwards at the rear of the wing. The mass of the air displaced downward produces the lift which is an equal and opposite reaction.

 

In fact there are invalid explanations using both theories and both men's theories can be used, if done correctly to explain lift. The difficulty is that in many cases, simplifying the explanation results in an invalid description.

 

For the benefit of students, RAA subscribes to the "Bernoulli lower pressure above the wing" fallacy, so for the sake of getting the question right in tests, just remember that, but also for your own benefit look at it a bit deeper. You may find the references below helpful.

 

http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html

 

http://www.allstar.fiu.edu/aero/airflylvl3.htm

Very, very, fascinating and useful information David and thanks for your reply. I have always understood that the centre of lift on a wing was nearer the centre of the chord rather than the rear. Very interesting reading especially my conceived idea that ground effect was caused by a compressed cushion of air under the aircraft.

 

Thanks,

 

Alan.

 

 

[turboplanner]

That belief stems from taking the popular Bernoulli explanation of wing lift , which is fallacious.

It's not fallacious, but any credible training data indicates that it only provides part of the lift.

 

It is very predictable and engineers used it to decide the aerofoil shape, big lifters having a lot of top curvature.

 

If it wasn't for Benoulli's principle we would still be riding in horses and carts because the carburettor uses the drop in pressure in the curved throat to create the vacuum which sucks the fuel from the jets into a more usable spray.

 

If anyone's interested in this they should search for the original thread which was HUGE but which eventually got to a good explanation of the combination of forces in an aerofoil.

 

All things were covered including how aerobatic aircraft with even cambers fly upside down.

 

 

[Yenn]

I have had a quick look at this thread and wonder what is going on. The question was how do you know when a plane has stalled. To me that is easy, it has stopped generating lift, so it must be going down, unless it is in a terrific rising air mass. As far as Bernoully's theory goes, I wonder why when the air pressure above the wing is supposed to be les than below it, why does the fabric section of my wing look as if it is sucked down into the wing. Maybe I should have a look at it when I am stalled. As far as knowing you are stalled when you exceed a certain angle of attack, I ask how do you know your angle of attack.