Learning about lift generation - a waste of time.

[Garfly]

I agree OME, you don't need a science degree, on the other hand, from my reading about stall/spin prangs, the problem is not due to pilots not getting that a nose up attitude (or rather a stick back situation) can lead to stalls. (As you point out, a child can learn that by throwing a balsa wood model).

What is surprising about LOC accident statistics is just how many very experienced flyers end their days that way.

They knew about attitude and AoA perfectly well.

We don't need to learn to think like scientists, we need to learn to feel like birds.   

Edited January 4, 2021 by Garfly

[facthunter]

Angle of attack has very little to do with the actual attitude of the planes reference to the horizon. DOWN is not so easy to determine if your eyes are closed or you are in mist or cloud. You cannot ride a motorbike in thick fog where you cannot see the ground at all.  You HAVE to let your feet stay in contact with it to even be able to move slowly. An inclinometer is only valid if you are stationary or moving very steadily in a straight line and you are upright. If you use a plumbob on a merry go round it won't point straight down nor will it be much help on a pushbike in motion during turns braking or accelerating.

      Measuring the angle of attack of the wing (which does practically all the supporting  of the plane in flight) does enable you to tell if you are operating in a SAFE range of permissible angles and where there would be more lift if you increased the AoA. It could be called a measure of lift in reserve but I think it's a clumsy term.  You can represent the same information on a "fast" - "slow" scale relating the the optimum L/D AoA for that particular airfoil .   If you are indicating FAST you are safe for the situation you are in. Since it adjusts for flaps, loads and dynamic loadings it's a very valid instant safety check. Nev

[APenNameAndThatA]

39 minutes ago, old man emu said:

I have now struck through the obviously offensive words in my original post in the hope that the discussion can now be centred on the theme of the thread, a discussion of whether or not knowing the mathematical description of lift generation is of greater value to the average pilot than learning by experience the simple fact that as the nose of an aircraft goes up beyond a certain angle, the wing is unable to produce sufficient to "Lift" cause the aircraft to be supported at a constant altitude?

 

And can we keep the discussion within the usual envelope of the majority of pilots who don't have teh need to cross the boundaries of the envelope of enjoying a flight?

 

Wrong *again*. There is no angle above which the nose goes which results in a stall. There is an angle of attack above which a stall will occur, but that is a different angle. 
 

And *again*. A wing does not have to be stalled to no longer be able to keep the aircraft at a constant altitude.  
 

And *again*. Your original post was about physics and now you are talking about maths. You can understand the basics of the physics without doing the maths. 
 

And *again*. When you make a post that is about two subjects, it is about two subjects. It’s not like you get to say silly things and then get to have them ignored. When you go around saying that a spirit level can do the same thing as an angle of attack meter, someone might believe you.
 

My guess is that it might have sunk in that you can’t use a spirit level on a stationary airplane to measure the optimum angle of attack, and that it might be sinking in that you can’t use a spirit level to measure angle of attack. So I suppose that’s a plus. 
 

But, hey, I can pick holes in other things. Technically, the *subject* of a thread is what the thread is about. The *theme* of a thread is what the thread ends up saying about the subject. For example, one subject of this thread is: discussion of whether or not... One of the themes of this thread is: nope,... 

[Gerryc]

Angle of attack is to do with the angle of the airfoil to the relative wind.Until people understand where the relative wind is they will have trouble.

I have just been reading Fly Better by Noel Kruse. What I got out of it is if you have your stick hard against your balls you are either stalled or about to.

[spacesailor]

" Angle of attack is to do with the angle of the airfoil to the relative wind.Until people understand where the relative wind is they will have trouble.  "

I tried to put into words the fact that " the AoA " is irrelevant, in that an airliner dropped vertically into the sea while still at a level attitude.

super powered aircraft can lift Vertical from the ground with zero forward motion and NO airflow over the wings. ( can't think of that name off hand). " jump jet"

The Komit rocket plane flies vertically quite a long way to it's target, ( yes it has airflow over it's wing ) 

were is the Maths in that deadly airliner disaster.

spacesailor

 

[Garfly]

Ya mean this accident?  

 

Air France Flight 447

From Wikipedia, the free encyclopedia

 

Excerpt:  

 

 

"Roughly 20 seconds later, at 02:12 UTC, Bonin decreased the aircraft's pitch slightly, airspeed indications became valid, and the stall warning sounded again; it then sounded intermittently for the remaining duration of the flight, but stopped when the pilot increased the aircraft's nose-up pitch. From there until the end of the flight, the angle of attack never dropped below 35 degrees. ..... However, the aircraft was now too low to recover from the stall. Shortly thereafter, the ground proximity warning system sounded an alarm, warning the crew about the aircraft's now imminent crash with the ocean. In response, Bonin (without informing his colleagues) pulled his side stick all the way back again,^[31][2] and said, "[Expletive] We're going to crash! This can't be true. But what's happening?"^{[74][31][2][75][28]} The last recording on the CVR was captain Dubois saying: "(ten) degrees pitch attitude."

The flight data recordings stopped at 02:14:28 UTC, or three hours 45 minutes after takeoff. At that point, the aircraft's ground speed was 107 knots (198 km/h; 123 mph), and it was descending at 10,912 feet per minute (55.43 m/s) (108 knots (200 km/h; 124 mph) of vertical speed). Its pitch was 16.2 degrees (nose up) ..... The aircraft struck the ocean belly-first at a speed of 152 knots (282 km/h; 175 mph), comprising vertical and horizontal components of 108 knots (200 km/h; 124 mph) and 107 knots (198 km/h; 123 mph) respectively. All 228 passengers and crew on board died on impact from extreme trauma and the aircraft was destroyed.^[77][2][75]

[spacesailor]

Thats the one I read about,

BUT

why did it happen ?.

spacesailor

[Garfly]

The report's conclusion is long and detailed; frozen pitots are involved as is CRM.

 

Two things we can learn though: a). "Don't pull back" and b). Pitch angle and "AoA" ain't the same.

[Jerry_Atrick]

I have a slightly different theory on AF447.. If you are an ATPL pilot and you have not learned not to pull back and the difference between the AoA and pitch angle, somethig is woefully wrong. As I recall, it was a releiving officer - I think a second officer - that had the right hand seast while the captain took a break. He pulled the yoke back which caused the stall.. The first officer, who was in the left hand seat had tried nose down and various other things. The captain came, but all too late, immediately put the aircraft nose down, but it apparently wasn;t responding. It was later concluded that all the while, the second officer inthe right hand seat had held the control column firmly back all the way down. Now, I can understand that in the later period when all is looking lost, but at altitude?

 

Unfortunatley, we are unable to inquire into the minds of anyone, but I would not rule out suicidal intentions on the second officer. We all know from the earliest training that pitch angle and AoA are different and that we need to pitch the nose down (in most situations).. We don't always practice it... but.. in this case, the frozen pilot, could possibly have been frozen for more depressing reasons.

 

I will try and dig it up, but I think there was a in an LSA or glider where the deceased pilot and passenger were found to be naked in the aircraft and not in a position where the pilot would be able to attend the controls at the time of the accident. The AAIB ruled the accident was effectively due to them mucking about; the aircraft losing control and crashing. Er, in a plane without autopilot, I think most pilots would know simply trimming an aircraft is not enough to ensure control is maintaied, even in stable aircraft. Again I wouldn't rule out suicide...

[old man emu]

16 hours ago, Yenn said:

OMEs bubble and his A of A meter would not agree with each other.

It is very clear that nobody has bothered to read and comprehend my description of how a spirit level could be calibrated to be used as an AoA gauge. 

 

To turn it into an AoA indicator, the aircraft would be lifted by the tail until the chord line of the wing was aligned to the longitudinal plane (usually about 4 degrees nose down-tail up). Once that alignment was made, the slip indicator can be fitted to the aircraft so that the bubble is centralised.

 

The aircraft is then returned so that the longitudinal axis is aligned with the horizontal plane. At this point the bubble should be off-centre by the same angle as the chord line is to the longitudinal axis of the aircraft. The position of the bubble can be marked on window of the indicator. This shows the position of the chord line at its best angle to the airflow to produce Lift, as concluded by the aircraft designer. (Clarification:  If the longitudinal axis of the fuselage is "level", the chord of the wing will be at the AoA set by the designer - usually about 4 degrees.) 

 

The aircraft can then have the nose raised until the chord line of the wing is at 15-16 degrees above longitudinal plane. The location of the bubble is marked. That mark shows the position of the longitudinal axis of the aircraft when the wing will begin to stall. The distance between the two marks is 12 degrees, in theory. 

 

 

 

 

 

[Thruster88]

You cannot use a spirit level in an aircraft because of acceleration.  

[Garfly]

 

Also because the wind (relative or otherwise) can't get at the bubble.

 

(Like it can with this little guy:)

 

 

[facthunter]

That's all you need in principle. A strand of wool would suffice . Also effective in front of you a a SKID indicator in a glider  (or a twin). Push it about with the rudder and keep your flight balanced.. Your turn needle (uses a gyro) lift it with aileron, as long as you aren't stalled. Nev

[old man emu]

52 minutes ago, Garfly said:

Also because the wind (relative or otherwise) can't get at the bubble.

Why would it have to? I would like to see your reasoning for that statement.

 

1 hour ago, Thruster88 said:

You cannot use a spirit level in an aircraft because of acceleration.

That's a statement that cries out for an explanation

[Yenn]

OME the bubble is relating itself to down as it appears to the aircraft, and down could well be up. At the top of a loop it is. but it still has no relationship to the relative wind.

[onetrack]

Quote

You cannot use a spirit level in an aircraft because of acceleration

Quote

That's a statement that cries out for an explanation

 

 

OME - When a spirit level is used on the ground, gravity is pulling the liquid in the bubble in one direction - directly downwards.

This ensures the bubble stays centred between the lines when the spirit level is level.

But in an aircraft, acceleration may be getting applied to the liquid in the level (G-forces), in directions other than directly downwards.

This will make the bubble travel to a different position, relative to the markings, than where it would be normally, when on the ground.

Edited January 5, 2021 by onetrack

[old man emu]

I see that I should have set the parameters for this discussion.

1. Flight in the airspeed range of zero to 250 kts - what the majority of private pilots use.

2. Flight below 10,000 ft on QNH - where the majority of private pilots fly.

3. Flight in the "NORMAL" category - no aerobatics beyond stalls and incipient spins, no descents at angles greater than, say, 45 degrees.

[Garfly]

Hi OME,

I think I've tried to set out my reasoning in some earlier posts in this thread..

It may be too simple an explanation but I reckon that AoA is ONLY about airflow whilst a spirit level is ONLY about gravity (where the earth is at any given moment.) Your bubble, oriented fore and aft would indicate a true pitch angle but that wouldn't help us even fly straight and level because, after all, we can descend/climb at a zero pitch deck angle just as we can fly straight and level at a range of pitch angles. 

Could you explain your resistance to the idea that pitch angle and angle of attack are 2 different things?

Anyone who's done skidpan training knows that the way your wheels are pointing does not equate to your direction of travel.

We're not on rails when we fly. You might say we're always in a 3D skidpan, no?

Why do you imagine that all AoA indicator vanes (from RC to Airliners) are stuck out in the airflow (or are clever software emulations of the same thing)?

Anyway, it's always a good thread that provokes us into nutting out the basics.  😉

[old man emu]

7 minutes ago, onetrack said:

This will make the bubble travel to a different position, relative to the markings, than where it would be normally, when on the ground.

Then how come we rely on slip indicators to advise us of rotation around the vertical plane (yawing)

 

9 minutes ago, onetrack said:

But in an aircraft, acceleration may be getting applied to the liquid in the level (G-forces), in directions other than directly downwards.

I think that this statement indicates a lack of understanding of Vector Analysis of Forces. 

 

Also the device is attached to the aircraft. Therefore, it is subject to the same vectors of Force as the aircraft.

[old man emu]

17 minutes ago, Garfly said:

Could you explain your resistance to the idea that pitch angle and angle of attack are 2 different things?

Where, Oh where, did I ever say that? We both know that the AoA is the angle between the wing (wing chord to be precise) and the direction of travel (undisturbed airflow). The angle of pitch is the angle between the main body axis and the horizon. The angle of the chord in relation to the longitudinal axis of the aircraft is set by the designer and set by the rigger. The designer normally fixes that angle so that, in straight and level flight, the angle between the longitudinal axis of the aircraft and the chord line of the wing is the same as the angle between the undisturbed airflow and the chord line of the wing. This angle is expected to result in the creation of the most Lift the aerofoil can create. 

 

The angle of pitch is controlled by the pilot, mainly by the use of the elevator/s, or control of thrust. The angle of pitch can vary from zero to 360 degrees (or 180 up and over and 180 down and around). Using the device in the way I have described provides the pilot with a source of reference for the upwards pitch angle of the aircraft. The device has been calibrated to give an indication of the angle of attack. It is never supposed to give a true, accurate reading of the AoA at any instant, but simply to give an indication of the range of AoA's in which it is possible for the aerofoil to produce sufficient Lift from the combination of aerofoil design and Thrust to counter the force of gravity and remain at a predetermined height above a reference point (the ground)

 

Have you even read my description of calibrating a level indicating device in order to show pitch angle. If you have, but don't understand what is being done, please ask me to expand on the method.

[Thruster88]

1 hour ago, old man emu said:

Then how come we rely on slip indicators to advise us of rotation around the vertical plane (yawing)

 

I think that this statement indicates a lack of understanding of Vector Analysis of Forces. 

 

Also the device is attached to the aircraft. Therefore, it is subject to the same vectors of Force as the aircraft.

Slip indicators work because they are only showing if the ACCELERATION force is parallel with the vertical axis (no slip or skid) or not. Slip indicators do not show YAW. The words used in this sentence may not be technically correct but you should get my drift. 

Edited January 5, 2021 by Thruster88

[Garfly]

Okay, OME such a device might do service as a pitch angle indicator and be useful in your standard straight ahead stall training exercise but no more than an artificial horizon would ... or, at last resort, THE horizon.

 

But by calling it a (quasi) Angle of Attack device you risk giving the impression that you don't accept the usual distinction between AoA and deck angle.

 

But getting back to the thread title, in my opinion, learning about lift generation is NOT a waste of time if that learning means an intuitive grasp of the fact that stalling can happen at any pitch attitude.  After all, hardly anyone gets into trouble in a light aircraft from a standard straight ahead stall.  In VMC, at least, the crazy pitch angle will surely get your attention well before you fall out of the sky.  

 

This Aviation Safety article puts it well:

 

 

" ... though many of the pilots I fly with understand intellectually that an airplane can stall/spin at any airspeed and in any attitude, their only practical stall experience consists of performing a contrived, wings-level stall to a Practical Test Standard.

Such limited stall experience imparts little practical experience vis–vis real-world stall/spin accident scenarios. As a result, many pilots never realize just how close they may be to stalling the airplane when performing a so-called dumb stunt, or how close they may be to a stall/spin departure when skidding a turn in the traffic pattern."

 

https://www.aviationsafetymagazine.com/features/recovery-room/

Edited January 5, 2021 by Garfly

[spacesailor]

" bubble spirit level "

In the beginning All air Navigators Had to use the " bubble sextant ". 

To do the " fix " when above the clouds.

spacesailor

[old man emu]

Too much of this discussion has been taken up with AoA -v- pitch angle and what tools could a pilot have to gauge how close to that magic number the chord line is. 

 

Once again, I posed a simple question, only to have fired back situations that the average private pilot, flying sensibly and with an eye to safe operation, would be unlikely to encounter. 

 

My simple question was: 

So why should the myths, falsehoods and the Newton/Bernoulli debate about lift generation of a body with one curved surface and one relatively flat surface, continued to be pounded into pilots when they do not advance the the skill level of pilots in operating an aircraft?

 

Why is it critical to the practical application of piloting skills that the pilot knows that 

 

Do you know the CL of the aerofoil used by your regular aircraft? Do you know the density of the parcel of air you are currently in? Can you do the mental calculation to convert knots to metres per second? What is the wing area of your aircraft. Oh, and what is the weight of your aircraft at the instant for which you want to know the lift the wing is producing?

 

One can only agree wholeheartedly with the sentiment expressed here:

 

" ... though many of the pilots I fly with understand intellectually that an airplane can stall/spin at any airspeed and in any attitude, their only practical stall experience consists of performing a contrived, wings-level stall to a Practical Test Standard. Such limited stall experience imparts little practical experience vis–vis real-world stall/spin accident scenarios. As a result, many pilots never realize just how close they may be to stalling the airplane when performing a so-called dumb stunt, or how close they may be to a stall/spin departure when skidding a turn in the traffic pattern."

 

It's like being able to recite the Karma Sutra by rote, but still being a virgin.

[Garfly]

Ha, ha ... I was calling for a return to old Bernoulli many posts back but you seemed keen to carry on with the angle of the dangle!

I was kind of sorry that you looked out your kitchen window that day and got side-tracked.  (See original post 😉 

Anyway, at least we can all agree that practical flying knowledge trumps maths and physics.

And it seems that we both agree with the practical chap in the quote: "many pilots never realize just how close they may be to stalling the airplane when performing a so-called dumb stunt, or how close they may be to a stall/spin departure when skidding a turn in the traffic pattern."

But to enquire about why it's so, is not to think like a scientist, necessarily. Every bird* and ag-pilot** knows and feels intuitively that one can stall a wing at any speed and at any angle of pitch but at only one angle of attack.   

Oops, we're back there again.

 

*Okay, not chooks.

** Okay, not our Student Pilot, he's still learning.  LOL

Edited January 5, 2021 by Garfly