Help me with a brain teaser - guaranteed to drive aerody gurus insane!?!
Icebreaker,
No confusion on my part at all, an aircraft with an efficient wing like a 738 with winglets would be at a lower angle of attack when straight or on a steady turn than something like a Concorde.
I would also suggest a 738 with winglets would be at a slightly lower angle of attack than a 734 at the same mass as it has a more efficient wing, and could have a slightly higher mass for the same angle of attack as a 734 of a lower mass.
As you would be aware lift is not a sole function of angle of attack or thrust, and my contention is that design engineers will have similar optimized angles of attack in cruise for sub sonic aircraft, they optimize the wing design with the wing section, area, geometry, and high lift devices, and lift dumping devices.
The pilot can modify the airspeed, angle of attack, wing section, area, geometry, high lift devices, and lift dumping devices whilst in flight for the phase of flight they are in.
So I guess I will have to agree to disagree that “Only difference is the heavier aircraft will require more AOA” or ““the only diffence [difference] would be attiude [attitude] (AOA) & thrust” for straight and level or in a steady turn.
No confusion on my part at all, an aircraft with an efficient wing like a 738 with winglets would be at a lower angle of attack when straight or on a steady turn than something like a Concorde.
I would also suggest a 738 with winglets would be at a slightly lower angle of attack than a 734 at the same mass as it has a more efficient wing, and could have a slightly higher mass for the same angle of attack as a 734 of a lower mass.
As you would be aware lift is not a sole function of angle of attack or thrust, and my contention is that design engineers will have similar optimized angles of attack in cruise for sub sonic aircraft, they optimize the wing design with the wing section, area, geometry, and high lift devices, and lift dumping devices.
The pilot can modify the airspeed, angle of attack, wing section, area, geometry, high lift devices, and lift dumping devices whilst in flight for the phase of flight they are in.
So I guess I will have to agree to disagree that “Only difference is the heavier aircraft will require more AOA” or ““the only diffence [difference] would be attiude [attitude] (AOA) & thrust” for straight and level or in a steady turn.
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Providing that aircraft x and aircraft y are the same type, then for the same airspeed and same c of g the heavier aircraft will require a higher AOA. If your talking different types with different wings and specifications then you cant relate the AOA in that way, it is too broad a statement.
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I do not even know what algebra is but I figured it out the other way.
The size of an airplane notwithstanding, the same laws of gravity apply to everyone. And all planes fly in the same air.
Soi, the same bank angle and the same speed should produce similar results.
But I reckon that at first sight I figured the bigger AC had a bigger turn radius.
The size of an airplane notwithstanding, the same laws of gravity apply to everyone. And all planes fly in the same air.
Soi, the same bank angle and the same speed should produce similar results.
But I reckon that at first sight I figured the bigger AC had a bigger turn radius.
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swh,
with regard to the AOA, of course we are talking about identical aircraft (as ifleeaircraft says) and not only that, but referring to that same particular aircraft, as even the same models have manufacturing differences, which would lead to slight variations.
with regard to the AOA, of course we are talking about identical aircraft (as ifleeaircraft says) and not only that, but referring to that same particular aircraft, as even the same models have manufacturing differences, which would lead to slight variations.
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The wheel has turned full-circle!
Piltdown man,
that's exactly the point of my opening thread! I know that "C" is the answer (been there, done that) but I wanted it demonstrated aerodynamically and/or mathematically by those who can. I don't think anyone has actually suggested it was anything but C, but there have been a few differing opinions on the physical aspects of why this is so.
Ultimately, when asked the question, I can't really say the answer is "C - because, well, because it just is alright!!!". Hence my request for the maths behind it.
Thanks for all the feedback guys, very interesting input - and sorry about opening a mini can of worms there. I knew it would cause some angst amongst the aerody gurus.
Righto, next question: "How does an autofocus camera work?"
that's exactly the point of my opening thread! I know that "C" is the answer (been there, done that) but I wanted it demonstrated aerodynamically and/or mathematically by those who can. I don't think anyone has actually suggested it was anything but C, but there have been a few differing opinions on the physical aspects of why this is so.
Ultimately, when asked the question, I can't really say the answer is "C - because, well, because it just is alright!!!". Hence my request for the maths behind it.
Thanks for all the feedback guys, very interesting input - and sorry about opening a mini can of worms there. I knew it would cause some angst amongst the aerody gurus.
Righto, next question: "How does an autofocus camera work?"
humblest apologies, being an engineer it must be my English comprehension skills which has let me down
SWH, the point others where making was that
all else being equal i.e same aircraft type, same configuration, that an aircraft being operated at a heavier weight requires a larger AOA maintain altitude.
all else being equal i.e same aircraft type, same configuration, that an aircraft being operated at a heavier weight requires a larger AOA maintain altitude.
I would agree with you if you included the CG position being the same.
Putting fuel in an aft trim tank can reduce the angle of attack, do you remember the effect of CG position on stall speed ?
swh,
Had to think about this for a couple of days, is this how it goes?
A conventionaly configured (e.g. forward wing, rear stabiliser) aircraft requires a down force from it's tail in order to fly level, and this force must be counteracted by lift from the wing.
A rearward c.g, therefore, reduces this trim force, and therefore will increase the total lift force for a given A of A. Thus an aircraft with a rearward c of g will produce less induced drag and stall at a lower speed.
I would imagine the opposite would be true for a canard or three-lifting-surface configuration.
HOWEVER a particuar wing stalls at a particual A of A regardless of weight or c of g.
Am I close?
Had to think about this for a couple of days, is this how it goes?
A conventionaly configured (e.g. forward wing, rear stabiliser) aircraft requires a down force from it's tail in order to fly level, and this force must be counteracted by lift from the wing.
A rearward c.g, therefore, reduces this trim force, and therefore will increase the total lift force for a given A of A. Thus an aircraft with a rearward c of g will produce less induced drag and stall at a lower speed.
I would imagine the opposite would be true for a canard or three-lifting-surface configuration.
HOWEVER a particuar wing stalls at a particual A of A regardless of weight or c of g.
Am I close?
Okay Maccherscmitt, you figgered the right question thru the turning nomogram/ line astern refuel caper.
The correct answer to your other question is the same: point and shoot!
The correct answer to your other question is the same: point and shoot!
HOWEVER a particuar [particular] wing stalls at a particual [particular] A of A regardless of weight or c of g.
{will just talk conventional geometry for simplicity all else being equal i.e same aircraft type, same configuration, same mass}
Aircraft A
With a forward CG you will reach that AoA at a higher speed due to the higher down force (lift component perpendicular to the relative air flow in the same direction as gravity) needed to be generated by the tail plane to counter the lift - weight (mass x g) couple .
This is an aerodynamic moment about the CG which effectively increases the weight of the aircraft by the amount of down force generated.
Aircraft B
Another method to generate the same couple with an aircraft of the same mass is to redistribute the mass so part of the fuel load fuel is carried in the tailplane. The additional weight (mass of fuel x g) in the tailplane can be sufficient to counter part or all of the lift weight couple (for this example I will take the extreme, and have zero down force by the tail).
In straight and level flight, the lift needed to be generated by
Aircraft A = mass x g + amount of down force by the tail
Aircraft B = mass x g
So aircraft B will have a lower AoA, as the total lift needed to be generated in just mass x g, this will apply in all phases of flight.
Another way to look at it is that an aircraft with an unfavorable CofG location (read forward limit) can have a higher AoA than that of a aircraft with a higher mass with a favorable CofG position, in any phase of flight.
Going back to what you said before “all else being equal i.e same aircraft type, same configuration, that an aircraft being operated at a heavier weight requires a larger AOA maintain altitude”, so another consideration is CofG location.
Long range aircraft about these days use the optimisation of CofG in flight to reduce the induced drag, this compounds as less fuel is needed not only for the reduction of induced drag, also the reduced fuel load.
