Theory on lift
Nope the model is correct note the acceleration of the flow in the 'torus' model
The relative wind [flow] is accelerated at the top---which 'pulls' the bottom flow into greater density hence higher pressure--- one wants a pressure increase on the bottom and decrease at the top the FAA publications are all very good
airplane flying handbook,glider flying handbook, aircraft W&B handbook instrument flying handbook, helicopter flying handbook, pilot's handbook/encyclopedia of aeronautical knowledge, seaplanes, ski planes and float and ski equipped helipcopter flying hand book...and although this is biased to FAA rules the instrument procedures handbook and they are very cheap too... those are what I use for ground school with my flock...very accurate!!!
there is some some blatant plagiarizing from Hurt and Davies' but that's ok the government can steal...look at Taxes...
The relative wind [flow] is accelerated at the top---which 'pulls' the bottom flow into greater density hence higher pressure--- one wants a pressure increase on the bottom and decrease at the top the FAA publications are all very good
airplane flying handbook,glider flying handbook, aircraft W&B handbook instrument flying handbook, helicopter flying handbook, pilot's handbook/encyclopedia of aeronautical knowledge, seaplanes, ski planes and float and ski equipped helipcopter flying hand book...and although this is biased to FAA rules the instrument procedures handbook and they are very cheap too... those are what I use for ground school with my flock...very accurate!!!
there is some some blatant plagiarizing from Hurt and Davies' but that's ok the government can steal...look at Taxes...
Last edited by Pugilistic Animus; 31st Aug 2012 at 01:00.
two things I meant Rotorcraft flying handbook they cover gyroplanes too
and I realize I'm not being 100% perfect in my explanation like 98%...trust me the real story is quite involed no need for that here... I'm trying to relax too...
Edit Chris Weston that's coolway to see it...
and I realize I'm not being 100% perfect in my explanation like 98%...trust me the real story is quite involed no need for that here... I'm trying to relax too...
Edit Chris Weston that's coolway to see it...
Last edited by Pugilistic Animus; 30th Aug 2012 at 22:11.
I just needed one more post...cuz I'm a little bit superstitious...
this hotty has the theory all worked out...
boy would I love to do rolling circles and humptybumps with her...
Another lovely lady who I love
this hotty has the theory all worked out...
Another lovely lady who I love
Last edited by Pugilistic Animus; 30th Aug 2012 at 22:48.
I'd just like too add a few more cheaps books to the ones I listed above
FAA aviation weather..for folks flying in the US ---Aviation weather services
Buck's Weather Flying... Taylor's Instrument Flying..Langwiesche's Stick and Rudder...Webb's Fly the Wing...Mike Goulian's and Geza Sourvizoy's basic and advanced aerobatics... Mallinson and Wollard's Handbook of Glider Aerobatics...good stuff for airplane pilots too
For those who aren't engineers but are interested in aerodynamics H.H Hurt's Aerodynamics for Naval Aviators
For those going to jets of course DP Davies Handling the Big Jets listed earlier
in addition to the book I
if you bought them all they's probably set you back about 300$ or so
I wouldn't recomnend pilots read any of my engineering aerodynamics books though...
...seriously!!!
FAA aviation weather..for folks flying in the US ---Aviation weather services
Buck's Weather Flying... Taylor's Instrument Flying..Langwiesche's Stick and Rudder...Webb's Fly the Wing...Mike Goulian's and Geza Sourvizoy's basic and advanced aerobatics... Mallinson and Wollard's Handbook of Glider Aerobatics...good stuff for airplane pilots too
For those who aren't engineers but are interested in aerodynamics H.H Hurt's Aerodynamics for Naval Aviators
For those going to jets of course DP Davies Handling the Big Jets listed earlier
in addition to the book I
if you bought them all they's probably set you back about 300$ or so
I wouldn't recomnend pilots read any of my engineering aerodynamics books though...
...seriously!!!
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Sites and books
Hi John Tullamarine, Pugillistic Animus, Bubbers44, other books lovers,
Perhaps could PPRuNe's "Theory on lift "thread have a list of useful web links (like AF447 list, John !
) and useful good books ?
Perhaps could PPRuNe's "Theory on lift "thread have a list of useful web links (like AF447 list, John !
) and useful good books ?
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the J58 was not a turboramjet (TR)
Hi Italia,
Don't know if you are still receptive to getting to grips with the J58 as it's been a while since your June post. I don't believe anyone followed up on your points.
Incidentally, Ryman had already correctly killed the TR.
Some of the information in the sources you are referencing is wrong, including classifying the J58 as a TR, unfortunately. One source will reference another source and misunderstandings/errors get perpetuated despite their dedicated authors.
TR was probably coined by someone because it sounded more exotic than bypass bleed engine (which is what P&W called it). They had to fit Mach3's worth of impressive ram into the name somehow.
What follows only needs to look at the engine airflow, not the very significant airflow which goes around the engine and causes so much interest in the intake and exhaust thrust contributions.
First we'll see how similar the airflow is to that in a familiar Mach2-type military turbofan or bypass engine. Then we'll see the reason why it could never have been a TR.
Going one step at a time thro each engine, an F100 at Mach2 say, and the J58 at M3.
F100: all the air destined for the engine goes thro its first compressor, also called the fan.
J58: all the air destined for the engine goes thro the 1st 4 stages of its only compressor
F100: some of the fan exit air goes down the engine bypass duct, the rest goes thro its 2nd compressor ( and combustor and turbines)
J58: some of the 4th stage exit air goes down the 6 external engine bypass or bleed tubes, the rest goes thro the remaining 5 compressor stages (and combustor and turbine)
F100: the engine bypass air mixes with the turbine exit air upstream of the afterburner fuel manifolds
J58: the engine bypass air mixes with the turbine exit air U/S of the A/B fuel manifolds
These air paths are for all intents and purposes identical. If you wanted to classify the two engines you could even put them in the same drawer but it wouldn't have TR on the label. After the above you may wonder what was so special about the J58. Apart from the huge challenges overcome with materials, etc. it was different to an F100 type at lower speeds though because the bleeds were closed. So it had a bypass ratio varying from zero at low speeds to some higher value at cruise. This variable bleed made it unique. An F100 BPR just varies a bit about some nominal value.
The TR could have been, on paper at least, but it wasn't as the following shows (ref 'The Engines of Pratt&Whitney' by Jack Connors).
Early versions of the J58 were a plain afterburning turbojet (shown on many web photos).P & W converted it for M3 cruise by adding 6 bypass bleed ducts from the middle of the compressor to the turbine exit (shown on many web photos).
Alternatively, it could have been modified with blocker doors to close off the compressor inlet and a big annular passage around the engine for the ram air which would discharge into a common afterburner. So here, finally, is your TR, but it never happened because it would have been more mechanically complex and heavier. The bleed tubes were a much more elegant solution by virtue of their simplicity. They did the job.
The crucial insight here is you can't turn a turbojet into a TR just by adding a few bypass tubes.
Not wishing to belabor a point, an authoritative source on ramjet configurations (avail on the web) is 'A century of Ramjet Propulsion Technology Evolution' by Ronald S. Fry.
And for the jet engine an equal mine of essentially first-hand, and therefore accurate, information (avail on the web) is 'Gas Turbine Technology Evolution' by Bernard L. Koff.
I hope you have found the above of some value.
Don't know if you are still receptive to getting to grips with the J58 as it's been a while since your June post. I don't believe anyone followed up on your points.
Incidentally, Ryman had already correctly killed the TR.
Some of the information in the sources you are referencing is wrong, including classifying the J58 as a TR, unfortunately. One source will reference another source and misunderstandings/errors get perpetuated despite their dedicated authors.
TR was probably coined by someone because it sounded more exotic than bypass bleed engine (which is what P&W called it). They had to fit Mach3's worth of impressive ram into the name somehow.
What follows only needs to look at the engine airflow, not the very significant airflow which goes around the engine and causes so much interest in the intake and exhaust thrust contributions.
First we'll see how similar the airflow is to that in a familiar Mach2-type military turbofan or bypass engine. Then we'll see the reason why it could never have been a TR.
Going one step at a time thro each engine, an F100 at Mach2 say, and the J58 at M3.
F100: all the air destined for the engine goes thro its first compressor, also called the fan.
J58: all the air destined for the engine goes thro the 1st 4 stages of its only compressor
F100: some of the fan exit air goes down the engine bypass duct, the rest goes thro its 2nd compressor ( and combustor and turbines)
J58: some of the 4th stage exit air goes down the 6 external engine bypass or bleed tubes, the rest goes thro the remaining 5 compressor stages (and combustor and turbine)
F100: the engine bypass air mixes with the turbine exit air upstream of the afterburner fuel manifolds
J58: the engine bypass air mixes with the turbine exit air U/S of the A/B fuel manifolds
These air paths are for all intents and purposes identical. If you wanted to classify the two engines you could even put them in the same drawer but it wouldn't have TR on the label. After the above you may wonder what was so special about the J58. Apart from the huge challenges overcome with materials, etc. it was different to an F100 type at lower speeds though because the bleeds were closed. So it had a bypass ratio varying from zero at low speeds to some higher value at cruise. This variable bleed made it unique. An F100 BPR just varies a bit about some nominal value.
The TR could have been, on paper at least, but it wasn't as the following shows (ref 'The Engines of Pratt&Whitney' by Jack Connors).
Early versions of the J58 were a plain afterburning turbojet (shown on many web photos).P & W converted it for M3 cruise by adding 6 bypass bleed ducts from the middle of the compressor to the turbine exit (shown on many web photos).
Alternatively, it could have been modified with blocker doors to close off the compressor inlet and a big annular passage around the engine for the ram air which would discharge into a common afterburner. So here, finally, is your TR, but it never happened because it would have been more mechanically complex and heavier. The bleed tubes were a much more elegant solution by virtue of their simplicity. They did the job.
The crucial insight here is you can't turn a turbojet into a TR just by adding a few bypass tubes.
Not wishing to belabor a point, an authoritative source on ramjet configurations (avail on the web) is 'A century of Ramjet Propulsion Technology Evolution' by Ronald S. Fry.
And for the jet engine an equal mine of essentially first-hand, and therefore accurate, information (avail on the web) is 'Gas Turbine Technology Evolution' by Bernard L. Koff.
I hope you have found the above of some value.
Last edited by Jetdriver; 16th Oct 2012 at 18:06.
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Thanks, Peter! That was a nice clarification.
In Figure 5 there are 3 large diameter tubes running along the mid-portion of the engine - those are the bypass tubes, correct?
In Figure 5 there are 3 large diameter tubes running along the mid-portion of the engine - those are the bypass tubes, correct?
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A symmetrical airfoil in level flight has a positive (greater than zero) angle of attack. is: The airfoil may be symmetrical, but it coes not encounter the airflow symmetrically. The airflow patterns around a symmetrical airfoil with a positive angle of attack are very similar to a cambered airfoil, with a greater amount of air flowing over the "top" of the air foil, at a higher velocity than the air flowing underneath.
A symmetrical airfoil at a zero angle of attack will produce no lift, but that ain't the same as level flight.
Haven't been reading the right books then. Off the top of my head, I think that "Aerodynamics for Naval Aviators" gives a clear explanation of this, although I don't have a copy in front of me at the moment. Many other books on aerodynamics also explain this, including diagrams and photos from wind tunnels using smoke streamers to show airflow.
There's nothing mysterious about this at all.
A symmetrical airfoil at a zero angle of attack will produce no lift, but that ain't the same as level flight.
Could never get a good answer for this one out of the books!
There's nothing mysterious about this at all.
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Even an asymmetrical profile does nothing without AOA. At zero AoA its lifting force is downward.... The upper surface has negative AoA due its fatter presentation vice lower, flatter plate.
It is a trick, parlayed into fame by the Swiss plumber.....
See, by the time the flow separates evenly, the aft portion of the flat plate on the bottom has gone Newton.....
It is a trick, parlayed into fame by the Swiss plumber.....
See, by the time the flow separates evenly, the aft portion of the flat plate on the bottom has gone Newton.....
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Even an asymmetrical profile does nothing without AOA. At zero AoA its lifting force is downward.... The upper surface has negative AoA due its fatter presentation vice lower, flatter plate.
It is a trick, parlayed into fame by the Swiss plumber.....
See, by the time the flow separates evenly, the aft portion of the flat plate on the bottom has gone Newton.....
It is a trick, parlayed into fame by the Swiss plumber.....
See, by the time the flow separates evenly, the aft portion of the flat plate on the bottom has gone Newton.....
Absolutely, 100 percent, purely wrong. Sorry to be blunt, but this is completely untrue. A typical cambered airfoil does produce considerable lift at zero angle of attack.
Here is a wikipedia article about angle of attack It includes a graph of coefficient of lift for a typical airfoil. You will see that the coefficient of lift at zero AoA is non-zero and positive.
If you're not inclined to believe Wikipedia, here's a page from NASA on the wright flyer, which includes another graph of lift coefficient vs AoA. It also shows non-zero, positive coefficient of lift at zero AoA. Additionally it contains a table of lift force, and a graph of same. Both show lift force at zero AoA to be non-zero and positive.
Here's another page showing a a graph of, among other things, the lift coefficient data for the airfoil on a Cessna 172. Coefficient of lift at zero AoA??? non-zero and positive.
Here's a page from the website of the US centennial of flight.
Care to make any bets as to what's on that page?
If you guessed that it contains a graph of coefficient of lift vs AoA, showing Coefficient of lift to be non-zero and positive at zero AoA, you'd be correct.
Obviously, if your understanding of the facts is this flawed, any conclusions you have drawn from the is inevitably equally flawed.
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Howdy.
The wing is not connected at leading edges, nor at the trailing edges.
It is hollow, and typically cambered, fat section forward. In the wind tunnel, air starts to flow over the wing, at zero angle of attack. The upper surface wants to move, which portion of the upper surface leaves first, trailing edge, or leading edge?
IOW, where is the center of lift on the upper surface, chordwise? Behind the equidistant point LE/TE? And how does this orient the chordwise axis to the longitudinal centerline? Negative?
You have no tail surface, only wing. How will you fly? Worse still, how will you increase the decreasing AoA?
The wing is not connected at leading edges, nor at the trailing edges.
It is hollow, and typically cambered, fat section forward. In the wind tunnel, air starts to flow over the wing, at zero angle of attack. The upper surface wants to move, which portion of the upper surface leaves first, trailing edge, or leading edge?
IOW, where is the center of lift on the upper surface, chordwise? Behind the equidistant point LE/TE? And how does this orient the chordwise axis to the longitudinal centerline? Negative?
You have no tail surface, only wing. How will you fly? Worse still, how will you increase the decreasing AoA?
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I have to agree with A Squared. Lyman, you're talking about a phenomenon that is separate and more involved than what was being discussed. The simple, and correct, answer to what was being discussed is that an asymmetric wing will produce positive lift at zero AoA. How the wing is held at zero AoA is not relevant.
Just to be clear - the discussion so far seems to be discussing the geometric AoA, which is in reference to the chord line. The zero lift AoA is the geometric AoA required for a lift coefficient of zero. Absolute AoA is the geometric AoA minus the zero lift AoA - any airfoil, symmetrical or not, will produce zero lift at zero absolute AoA.
The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero.
Angle of Attack Awareness and Angle of Attack Management [Ch. 2 of See How It Flies]
http://faculty.washington.edu/lum/aa.../lecture27.pdf
Just to be clear - the discussion so far seems to be discussing the geometric AoA, which is in reference to the chord line. The zero lift AoA is the geometric AoA required for a lift coefficient of zero. Absolute AoA is the geometric AoA minus the zero lift AoA - any airfoil, symmetrical or not, will produce zero lift at zero absolute AoA.
The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero.
Angle of Attack Awareness and Angle of Attack Management [Ch. 2 of See How It Flies]
http://faculty.washington.edu/lum/aa.../lecture27.pdf
Last edited by italia458; 14th Oct 2012 at 04:48.
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The lift does nothing useful, it requires long methodical experimentation, and months and years of frustration, snd many dead airmen.
Ahhh....."wiki". So many sharp as a tack partisans, so much smarter than the average bear...
Those arrows, are they on your airplane? There are arrows, right? I must look sometime...
Italia: "The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero."
Que paso?
Ahhh....."wiki". So many sharp as a tack partisans, so much smarter than the average bear...
Those arrows, are they on your airplane? There are arrows, right? I must look sometime...
Italia: "The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero."
Que paso?
Last edited by Lyman; 14th Oct 2012 at 16:09.
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Hi peter kent
I rebel against illogic, and squishy nomenclature. The potential for mistaking a value of lift should not be dependent on a formula that is merely an arbitrary definition.
At the point where an airfoil begins to develop lift becomes my datum. Zero means zero, or should. Just a quirk of mine, but not just me. It is an accepted datum in the industry,
There should not be confusion, and associating "Zero" angle of attack with actual work does just that. I prefer to let the design drive the nomenclature, not the reverse.
No problemo, peter
I rebel against illogic, and squishy nomenclature. The potential for mistaking a value of lift should not be dependent on a formula that is merely an arbitrary definition.
At the point where an airfoil begins to develop lift becomes my datum. Zero means zero, or should. Just a quirk of mine, but not just me. It is an accepted datum in the industry,
There should not be confusion, and associating "Zero" angle of attack with actual work does just that. I prefer to let the design drive the nomenclature, not the reverse.
No problemo, peter
Last edited by Lyman; 14th Oct 2012 at 15:54.
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Hi Lyman,
I apologise for being sloppy in my post. I was answering Italia on the J58 question he had addressed to me. I know nothing worth contributing on lift unfortunately.
I apologise for being sloppy in my post. I was answering Italia on the J58 question he had addressed to me. I know nothing worth contributing on lift unfortunately.
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A different slant on Bernoulli, I think
Perhaps someone can help with this one.
My brain generally reels reading the lift posts but I do have a question on what the authors are saying below.
The relevant bit is
"The BE is a statement of the conservation of energy. For it to be applied the system must be in equilibrium and no energy added to the system.... A great deal of energy is added to the air.... A 250 ton plane is doing a lot of work to stay in the air."
and the crucial statement:
"We have shown that the pressure and velocity of the air over a real wing in flight are not related by BE."
http://home.comcast.net/~clipper-108/Lift_AAPT.pdf
This seems at odds with people who use Bernoulli to trade off static pressure with velocity when designing real aircraft. These professional plane makers mention no qualifiers as regards work transfer.
Just one example
'Ch 10. The relation between supervelocity and pressure coefficient'
in a book bursting at the seams with Cp plots and much, much more for all airliners from DC-8 on and written by a Fokker man.
Aerodynamic Design of Transport Aircraft
So shouldn't the college aerodynamics professor author at the top of the post be preparing students to go into industry?
My brain generally reels reading the lift posts but I do have a question on what the authors are saying below.
The relevant bit is
"The BE is a statement of the conservation of energy. For it to be applied the system must be in equilibrium and no energy added to the system.... A great deal of energy is added to the air.... A 250 ton plane is doing a lot of work to stay in the air."
and the crucial statement:
"We have shown that the pressure and velocity of the air over a real wing in flight are not related by BE."
http://home.comcast.net/~clipper-108/Lift_AAPT.pdf
This seems at odds with people who use Bernoulli to trade off static pressure with velocity when designing real aircraft. These professional plane makers mention no qualifiers as regards work transfer.
Just one example
'Ch 10. The relation between supervelocity and pressure coefficient'
in a book bursting at the seams with Cp plots and much, much more for all airliners from DC-8 on and written by a Fokker man.
Aerodynamic Design of Transport Aircraft
So shouldn't the college aerodynamics professor author at the top of the post be preparing students to go into industry?
Last edited by peter kent; 14th Oct 2012 at 22:44. Reason: clarification