An aerodynamics question (for experts only)
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Ozexpat,
Well, thinking about it, a certain ammount of knowledge has to be assumed. The assumption is that, in a properly structured course, the student has the knowledge required to be sitting in front of you for their briefing. After all, you can't start every briefing by "In the beginning, there was darkness...."
But, as you say, enough about intructional technique and back to the topic at hand, which I see as a deeper look at PofF for interest, not necessity.
So, for Gonewest and anyone else interested:
Lets look at Kermodes model.
His aircraft is in S&L.
Thurst is increased.
The Pilot does not select a lower nose attitude, so the aircraft commences a climb.
He makes the simplification, stated later, that "Assuming that the path actually travelled by the aeroplane is in the same direction as the thrust..."
On that basis, it is not possible to enter a climb without seeing an increase in Lift to initiate it.
Argument:
Kermodes thrust is acting along the flight path. Therefore, when in S&L, Thrust is horizontal (to the world).
a) If all other forces were in balance, and
b) The pilot maintains the same attitude (granted, this requires control inputs),
c) assumption: ignore prop effects (imagine its a jet)
then initially only one thing will happen: the aircraft will accelerate horizontally. Hence speed will increase.
As speed has increases, this will effect lift production.
Thus far:
Pitch attitude unchanged.
Flight path unchanged.
therefore AOA is constant, along with everything else in the lift formula apart from speed (which has increased).
Hence lift is increased.
[Incidentally, drag will have increase as well, exactly in proportion, so the Total Reaction has also increased if you are using a 3 force model, but that is not of direct interest. The key point is that an extra upwards force component is now present that will start the aircraft climbing.]
Therfore, to initiate a climb in this manner, Lift has increased.
Yet Kermode clearly shows how, once established in a steady climb, Lift is actually less than it used to be in S&L. No arguement from here!
How do we get to a from a stage where Lift is greater than weight to establish a climb to being less than weight to sustain one?
The answer lies in looking at the Angle Of Attack.
We've said the pilot is maintaining the same attitude, however the flight path is now sloping upwards. Hence AOA will be decreasing. The higher the climb rate, the more the AOA decreases until that effect on lift production overwhelms the effect of the increased speed. Eventually, lift will decrease (in line with Kermode) until the forces all balance out. At which point the flight path (along with AOA) remains constant.
Summary:
Conditions:
- Attitude constant.
- Thrust increased.
Results in:
- Speed increased.
- Lift increased.
- Climb Rate.
- AOA reduction leading to new equilibrium, as Kermode, with L<W
Alternatively, it is perfectly possible to climb, sustainably, without increasing thrust. (proviso - unless you are already at ceiling, or already on the back of the drag curve, in which case a stall will result). The key thing is the necessity to get to a regime of greater excess power. This is not the same as saying more power.
Select a higher nose attitude by using the elevators. This increases AOA. At that moment, speed is unchanged, but the AOA increase makes more lift. Aircraft has unbalanced upwards force, so accelerates upwards. Since there is currently no excess power, kinetic energy must initially be traded to gain gravitational potential energy, so aircraft slows down.
But the speed decrease has the effect of reducing power required, so we now have some excess power with which to sustain climb, albeit with a lower airspeed.
Meanwhile, the AOA decrease described earlier, plus the speed recuction, combine via the lift formula to end up with a net reduction in lift to eventually be less than weight, i.a.w. Kermode steady climb analysis.
Summary:
Conditions:
- Attitude increased.
- Thrust constant.
Results in.
- Lift increase.
- Climb rate (initially zoom).
- Speed reduction.
- Power required decreased.
- Sustainable climb.
- AOA (& speed) reduction leading to new equilibrium, as Kermode, with L<W.
So we can see two methods by which a climb can be initiated, either increase thrust or increase pitch. Both of them involve an initial increase in lift to establish the climb, followed by a decrease as the new equilibrium is established.
Q.E.D.
In reality, we tend to do both for sustained climbs, i.e. increase thrust and select a higher pitch attitude. For temporary climbs (or descents), say to correct our cruising altitude, we tend to make a small power increase (decrease) and let everything else come out in the wash. The mechanism is, however, as shown.
Footnotes:
(1) Of course, a steady climb isn't really an equilibrium. If you fly a constant air speed in a climb, then your TAS is steadily increasing, so you are not technically in a state of uniform motion i.a.w. Newton. It may not seem like a big deal, but it can make a big difference in certain circumstances.
(2) As mentioned earlier, S&L isn't really a uniform state of motion either (due earth curvature), but it doesn't make much difference unless you fly very fast. Feeling keen? Try doing some sums for Concorde or an SR-71.
(3) In spite of the argument above, it is possible to show how a a climb can be established without a transient lift increase. it just isn't the way average aircraft usually do it. Can anyone see the hole in Kermodes assumptions?
CPB
Well, thinking about it, a certain ammount of knowledge has to be assumed. The assumption is that, in a properly structured course, the student has the knowledge required to be sitting in front of you for their briefing. After all, you can't start every briefing by "In the beginning, there was darkness...."
But, as you say, enough about intructional technique and back to the topic at hand, which I see as a deeper look at PofF for interest, not necessity.
So, for Gonewest and anyone else interested:
Lets look at Kermodes model.
His aircraft is in S&L.
Thurst is increased.
The Pilot does not select a lower nose attitude, so the aircraft commences a climb.
He makes the simplification, stated later, that "Assuming that the path actually travelled by the aeroplane is in the same direction as the thrust..."
On that basis, it is not possible to enter a climb without seeing an increase in Lift to initiate it.
Argument:
Kermodes thrust is acting along the flight path. Therefore, when in S&L, Thrust is horizontal (to the world).
a) If all other forces were in balance, and
b) The pilot maintains the same attitude (granted, this requires control inputs),
c) assumption: ignore prop effects (imagine its a jet)
then initially only one thing will happen: the aircraft will accelerate horizontally. Hence speed will increase.
As speed has increases, this will effect lift production.
Thus far:
Pitch attitude unchanged.
Flight path unchanged.
therefore AOA is constant, along with everything else in the lift formula apart from speed (which has increased).
Hence lift is increased.
[Incidentally, drag will have increase as well, exactly in proportion, so the Total Reaction has also increased if you are using a 3 force model, but that is not of direct interest. The key point is that an extra upwards force component is now present that will start the aircraft climbing.]
Therfore, to initiate a climb in this manner, Lift has increased.
Yet Kermode clearly shows how, once established in a steady climb, Lift is actually less than it used to be in S&L. No arguement from here!
How do we get to a from a stage where Lift is greater than weight to establish a climb to being less than weight to sustain one?
The answer lies in looking at the Angle Of Attack.
We've said the pilot is maintaining the same attitude, however the flight path is now sloping upwards. Hence AOA will be decreasing. The higher the climb rate, the more the AOA decreases until that effect on lift production overwhelms the effect of the increased speed. Eventually, lift will decrease (in line with Kermode) until the forces all balance out. At which point the flight path (along with AOA) remains constant.
Summary:
Conditions:
- Attitude constant.
- Thrust increased.
Results in:
- Speed increased.
- Lift increased.
- Climb Rate.
- AOA reduction leading to new equilibrium, as Kermode, with L<W
Alternatively, it is perfectly possible to climb, sustainably, without increasing thrust. (proviso - unless you are already at ceiling, or already on the back of the drag curve, in which case a stall will result). The key thing is the necessity to get to a regime of greater excess power. This is not the same as saying more power.
Select a higher nose attitude by using the elevators. This increases AOA. At that moment, speed is unchanged, but the AOA increase makes more lift. Aircraft has unbalanced upwards force, so accelerates upwards. Since there is currently no excess power, kinetic energy must initially be traded to gain gravitational potential energy, so aircraft slows down.
But the speed decrease has the effect of reducing power required, so we now have some excess power with which to sustain climb, albeit with a lower airspeed.
Meanwhile, the AOA decrease described earlier, plus the speed recuction, combine via the lift formula to end up with a net reduction in lift to eventually be less than weight, i.a.w. Kermode steady climb analysis.
Summary:
Conditions:
- Attitude increased.
- Thrust constant.
Results in.
- Lift increase.
- Climb rate (initially zoom).
- Speed reduction.
- Power required decreased.
- Sustainable climb.
- AOA (& speed) reduction leading to new equilibrium, as Kermode, with L<W.
So we can see two methods by which a climb can be initiated, either increase thrust or increase pitch. Both of them involve an initial increase in lift to establish the climb, followed by a decrease as the new equilibrium is established.
Q.E.D.
In reality, we tend to do both for sustained climbs, i.e. increase thrust and select a higher pitch attitude. For temporary climbs (or descents), say to correct our cruising altitude, we tend to make a small power increase (decrease) and let everything else come out in the wash. The mechanism is, however, as shown.
Footnotes:
(1) Of course, a steady climb isn't really an equilibrium. If you fly a constant air speed in a climb, then your TAS is steadily increasing, so you are not technically in a state of uniform motion i.a.w. Newton. It may not seem like a big deal, but it can make a big difference in certain circumstances.
(2) As mentioned earlier, S&L isn't really a uniform state of motion either (due earth curvature), but it doesn't make much difference unless you fly very fast. Feeling keen? Try doing some sums for Concorde or an SR-71.
(3) In spite of the argument above, it is possible to show how a a climb can be established without a transient lift increase. it just isn't the way average aircraft usually do it. Can anyone see the hole in Kermodes assumptions?
CPB
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Looks behind, hoping that B2N2 isn't toooo close behind... 
CPB ... I don't dispute any of what you say, with the possible exeption of that last bit. I'm not so sure that it's a case of there being any holes in what Kermode says. Remember that he's not trying to teach anyone to fly, merely to understand what is happening. For this, he needs to break things down, to make the various aspects of each topic easier for people to read and grasp.
Surely it is the flying instructors' job to put all of that in the context of how it is applied to the type of aeroplane being used for the training?
Indeed, in your own explanation, you simplified some of it by referring to a jet, rather than a prop. A wholly reasonable simplification, I might add, but isn't this pretty much the same as what Kermode was trying to do?
B2N2 ... feel free to jump in whenever you like. I won't be able to keep posting for much longer anyway, as I'm heading off shortly and epect to be away for at least a month. I hope that won't mean that this most interesting thread dies in the meantime.
CPB ... I don't dispute any of what you say, with the possible exeption of that last bit. I'm not so sure that it's a case of there being any holes in what Kermode says. Remember that he's not trying to teach anyone to fly, merely to understand what is happening. For this, he needs to break things down, to make the various aspects of each topic easier for people to read and grasp.
Surely it is the flying instructors' job to put all of that in the context of how it is applied to the type of aeroplane being used for the training?
Indeed, in your own explanation, you simplified some of it by referring to a jet, rather than a prop. A wholly reasonable simplification, I might add, but isn't this pretty much the same as what Kermode was trying to do?
B2N2 ... feel free to jump in whenever you like. I won't be able to keep posting for much longer anyway, as I'm heading off shortly and epect to be away for at least a month. I hope that won't mean that this most interesting thread dies in the meantime.
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You need to understand an aeroplane operates in a force field so is not like a spacecraft. A spacecraft will accelerate if a net force is applied, otherwise it will continue in a straight line.
An aeroplane behaves similarly in the two dimensions parallel to the Earth's surface but not when altitude is concerned. Here the force field generated by gravity comes into play. As you climb, you move through this field. Although you gain no momentum at a steady rate of climb, you do gain potential energy by changing your position in the gravity field. This requires an input of work/energy. And that comes from a vertical vector greater than the weight of the aircraft.
Newton's 3rd Law only really brings anything to the party when you try to explain how propellors and turbines work. People don't normally explain lift this way because a wing is completely different to a thing which merely deflects air downwards.
An aeroplane behaves similarly in the two dimensions parallel to the Earth's surface but not when altitude is concerned. Here the force field generated by gravity comes into play. As you climb, you move through this field. Although you gain no momentum at a steady rate of climb, you do gain potential energy by changing your position in the gravity field. This requires an input of work/energy. And that comes from a vertical vector greater than the weight of the aircraft.
Newton's 3rd Law only really brings anything to the party when you try to explain how propellors and turbines work. People don't normally explain lift this way because a wing is completely different to a thing which merely deflects air downwards.
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I was on my way out to dinner earlier this evening, when a thought struck me. And, before you ask - yes, thanks, it WAS a painful experience!
Anyway, it occurred to me that we need to be a bit careful when talking about lift increasing in the initiation of a climb, from S+L flight. The sum of all lift is considered to act thru the Centre of Pressure, at a right angle to the relative airflow. This gets awkward to describe without the aid of diagrams but, if worst comes to worst, I'll make some and post them.
Anyway, the simple act of applying some or all of the reserve thrust, increases the magnitude of the thrust force. In a diagram, this is represented by lengthening the thrust vector by a representative amount. The additional thrust creates the change in AofA, and the increased angle creates a movement of the CofP and, in our blackboard/whyteboard diagram, we see that the lift vector line is inclined toward the tail of the aircraft, in relation to the horizon. This is because it is still acting at a right angle to the relative airflow.
The actual physical length of the lift vector line is still the same but its inclination, relative to the horizon has effectively reduced it's magnitude in comparison with the assumed weight vector line, which is still acting vertically downward thru the CofG. This is why we've said, for years, that lift is less than weight in a climb and it matters not at all whether it's at climb initiation, or in the ideally envisaged steady-state climb.
The "total reaction" is now of greater interest to us as this is what determines our climb. To find the location and magnitude of the vector for total reaction, we resort back to our imaginary diagram and draw a line from the top of the lift line, parallel to the thrust line. This line obviously moves forward. Stop drawing this line when a tangential line will meet the forward end of the thrust vector line. Connect this point to the CofP by a straight line and you've found the vector for total reaction.
This is the vector line that we compare to the weight vector line, to find a new equilibrium that allows the aeroplane to stabilise in the climb. Thus, it really isn't true to say that lift is either equal to weight or greater than weight. This cannot be true because we have upset those forces in initiating the climb.
There are other factors that come into consideration, such as :
1. the effect of prop torque, which I think the Americans call P-factor; and
2. how to sustain the climb.
I'm ignoring those because the basic topic is already complex enough.
Who wants to go next?
Anyway, it occurred to me that we need to be a bit careful when talking about lift increasing in the initiation of a climb, from S+L flight. The sum of all lift is considered to act thru the Centre of Pressure, at a right angle to the relative airflow. This gets awkward to describe without the aid of diagrams but, if worst comes to worst, I'll make some and post them.
Anyway, the simple act of applying some or all of the reserve thrust, increases the magnitude of the thrust force. In a diagram, this is represented by lengthening the thrust vector by a representative amount. The additional thrust creates the change in AofA, and the increased angle creates a movement of the CofP and, in our blackboard/whyteboard diagram, we see that the lift vector line is inclined toward the tail of the aircraft, in relation to the horizon. This is because it is still acting at a right angle to the relative airflow.
The actual physical length of the lift vector line is still the same but its inclination, relative to the horizon has effectively reduced it's magnitude in comparison with the assumed weight vector line, which is still acting vertically downward thru the CofG. This is why we've said, for years, that lift is less than weight in a climb and it matters not at all whether it's at climb initiation, or in the ideally envisaged steady-state climb.
The "total reaction" is now of greater interest to us as this is what determines our climb. To find the location and magnitude of the vector for total reaction, we resort back to our imaginary diagram and draw a line from the top of the lift line, parallel to the thrust line. This line obviously moves forward. Stop drawing this line when a tangential line will meet the forward end of the thrust vector line. Connect this point to the CofP by a straight line and you've found the vector for total reaction.
This is the vector line that we compare to the weight vector line, to find a new equilibrium that allows the aeroplane to stabilise in the climb. Thus, it really isn't true to say that lift is either equal to weight or greater than weight. This cannot be true because we have upset those forces in initiating the climb.
There are other factors that come into consideration, such as :
1. the effect of prop torque, which I think the Americans call P-factor; and
2. how to sustain the climb.
I'm ignoring those because the basic topic is already complex enough.
Who wants to go next?
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I hesitate to post again having made a pigs ear once, and still a long way away from my Kermode, however
In a climb, during initiation and also once stable, if forces are resolved vertically and horizontally with respect to earth rather than the aircraft this should isolate the vertical forces responsible for the vertical component of the climb.
Amongst these will be a vertical component of the now inclined thrust, and acting in the opposite direction ,that is in the same direction as the weight ( or mass) of the aircraft, will be a vertical component of the now inclined drag force.
This will hopefully explain why although aerodynamic lift may be reduced in a climb, the combination of the vertical component of this and the vertical component of the thrust have to be greater than the S/L vertical force required, in order to balance the weight and the added downward component of the drag forces.
In a climb, during initiation and also once stable, if forces are resolved vertically and horizontally with respect to earth rather than the aircraft this should isolate the vertical forces responsible for the vertical component of the climb.
Amongst these will be a vertical component of the now inclined thrust, and acting in the opposite direction ,that is in the same direction as the weight ( or mass) of the aircraft, will be a vertical component of the now inclined drag force.
This will hopefully explain why although aerodynamic lift may be reduced in a climb, the combination of the vertical component of this and the vertical component of the thrust have to be greater than the S/L vertical force required, in order to balance the weight and the added downward component of the drag forces.
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Hmm. Sorry Ozexpat, but you are way off base in several areas in your post.
Your Para 3:
[Whilst accepting that local AOA changes can be caused by thrust changes for prop aircraft, both of us have elected to ignore prop effects for the time being. Certainly a Jet discussion should suffice for considering climbing - the mechanics are not going to be fundementally different by powerplant.]
Changing thrust will not directly influence AOA. Granted, it may do indirectly by causing a pitching moment, but we are assuming a Piloted aircraft, i.e. the pilot controls that attitude of the aircraft.
The flight path has not yet changed, and the attitude is unchanged. Therefore the AOA is constant. there must be some other mechanism for commencing the climb. That mechanism is either a speed increase leading to more lift, or a pitch increase leading to more lift, in order to generate an upwards force to initiate the climb.
Your para 4:
No it isn't. We're talking steady state climb here, and both you, I , and Kermode agree that lift is less than weight at that point. The length of the line represents the magnitude of the force, so if it were the same, lift would be the same.
Look at the Kermode excerpt. He specifically states that he is resolving forces parallel and at right angles to the flight path. He is not talking about just the vertical component of lift, he is talking lift, all of it.
Your Para 5:
You are adding vectors here. No problems with that - vectors can always be added. But the Total Reaction is the addition of Lift and Drag. What you describe however is the addition of Lift and Thrust, and hence is not the 'Total Reaction'.
Incidentally, I think maybe you ment to make that an 'Excess' Thrust line, because then at least your diagram would have accounted for all the forces, even if the 'total reaction' was misidentifed.
What your diagram basically shows is that excess thrusy must be present in order for a climb to be maintained. Thats fine, correct, and I'm not arguing with it.
But it does not show how the aircraft gets into the climb!
To show that once an aircraft is climbing, a vertical component of thrust exists, is not an arguement to show how that condition came to be.
I reiterate: During the cruise, thrust and drag are horizontal, and lift and weight are vertical. If the aircraft is displaced vertically upwards in can only be because lift has increased, or weight has decreased. If something has not been dropped, fired, kicked or fallen off of the aircraft, then the only remaining possibility is that Lift has been increased. [note 1]
Let me show it another way. If you enter a climb, you feel G. Maybe not much, perhaps sub-threshold, but we all know it is there.
What is G? Answer = Load Factor (N)
What is Load Factor? Answer = Lift / Weight.
Therefore, if you are feeling G, Lift exceeds weight.
[G relative to aircraft Normal Axis. For progressively steeper climb angles, although you still feel your own weight, more and more of it will be on your back rather than the seat of your pants. In a sustained vertical climb, you'd have zero lift, and zero load factor, although you obviously would still feel your weight by virtue of the seat back pushing you up]
Note 1: Or our model is wrong. Which it is, in fact. Both Kermode and I have so far assumed that Thrust acts along the aircrafts flight path. This is not true, but rarely much of a real issue. But when you see highly agile aircraft performing high AOA manoeuvres with a large excess thrust, it becomes significant. Consider a slow fly past by a modern fighter. It will have a big AOA - maybe very big. Hence its thrust line would already be pointing up. If it then applies max burner you can easily see that a climb will result without lift necessaraly having been increased. But that isn't really the kind of thing we are talking about here. As I said earlier - mundane aircraft, routine manoeuvres.
Also, to reiterate, I agree totally that this is way deeper than most pilots need. Nevertheless, people have expressed an interest, and in mechanics terms it is not that deep - just a free body diagram and a few forces.
Cheers.
CPB
Your Para 3:
The additional thrust creates the change in AofA...
Changing thrust will not directly influence AOA. Granted, it may do indirectly by causing a pitching moment, but we are assuming a Piloted aircraft, i.e. the pilot controls that attitude of the aircraft.
The flight path has not yet changed, and the attitude is unchanged. Therefore the AOA is constant. there must be some other mechanism for commencing the climb. That mechanism is either a speed increase leading to more lift, or a pitch increase leading to more lift, in order to generate an upwards force to initiate the climb.
Your para 4:
The actual physical length of the lift vector line is still the same ...
Look at the Kermode excerpt. He specifically states that he is resolving forces parallel and at right angles to the flight path. He is not talking about just the vertical component of lift, he is talking lift, all of it.
Your Para 5:
You are adding vectors here. No problems with that - vectors can always be added. But the Total Reaction is the addition of Lift and Drag. What you describe however is the addition of Lift and Thrust, and hence is not the 'Total Reaction'.
Incidentally, I think maybe you ment to make that an 'Excess' Thrust line, because then at least your diagram would have accounted for all the forces, even if the 'total reaction' was misidentifed.
What your diagram basically shows is that excess thrusy must be present in order for a climb to be maintained. Thats fine, correct, and I'm not arguing with it.
But it does not show how the aircraft gets into the climb!
To show that once an aircraft is climbing, a vertical component of thrust exists, is not an arguement to show how that condition came to be.
I reiterate: During the cruise, thrust and drag are horizontal, and lift and weight are vertical. If the aircraft is displaced vertically upwards in can only be because lift has increased, or weight has decreased. If something has not been dropped, fired, kicked or fallen off of the aircraft, then the only remaining possibility is that Lift has been increased. [note 1]
Let me show it another way. If you enter a climb, you feel G. Maybe not much, perhaps sub-threshold, but we all know it is there.
What is G? Answer = Load Factor (N)
What is Load Factor? Answer = Lift / Weight.
Therefore, if you are feeling G, Lift exceeds weight.
[G relative to aircraft Normal Axis. For progressively steeper climb angles, although you still feel your own weight, more and more of it will be on your back rather than the seat of your pants. In a sustained vertical climb, you'd have zero lift, and zero load factor, although you obviously would still feel your weight by virtue of the seat back pushing you up]
Note 1: Or our model is wrong. Which it is, in fact. Both Kermode and I have so far assumed that Thrust acts along the aircrafts flight path. This is not true, but rarely much of a real issue. But when you see highly agile aircraft performing high AOA manoeuvres with a large excess thrust, it becomes significant. Consider a slow fly past by a modern fighter. It will have a big AOA - maybe very big. Hence its thrust line would already be pointing up. If it then applies max burner you can easily see that a climb will result without lift necessaraly having been increased. But that isn't really the kind of thing we are talking about here. As I said earlier - mundane aircraft, routine manoeuvres.
Also, to reiterate, I agree totally that this is way deeper than most pilots need. Nevertheless, people have expressed an interest, and in mechanics terms it is not that deep - just a free body diagram and a few forces.
Cheers.
CPB
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CPB ... I knew it was a mistake not to have a drawing, or series of them, to show how it all develops. But in any event, I suspect that we'll have to agree to differ on this subject, as I no longer have the time available to pursue it, due to an up-coming trip away.
However, just a thing to consider...
We started this idea with the premise, from Kermode, that if the pilot did nothing to the flight controls after increasing power (thrust), the aircraft would enter a climb. If it's a single engine, prop-driven aircraft, it'll yaw too tho we've agreed not to bother with that aspect for now.
Anyway, because the aeroplane has entered a climb, the flight path HAD changed.
Okay, maybe the more correct terminology is the "Vertical Component of Lift", but that's just a word game anyway because the Total Reaction is the result of the acceleration that has led to the climb being initiated by simply increasing thust. At this point I am, of course, staying away from the principles associated with maintaning a climb.
With respect, I thought that's precisely what I showed.
I suspect that some care is necessary with this statement. "G" is actually acceleration, which can be positive or negative. It can also be zero, of course. To illustrate the point, in S+L flight, the Load Factor is 1 and G is zero. I agree that Load Factor will increase in any of the normal manoeuvres (I'm trying to stay away from the forces in the pull-out from a steep dive, of course, or abrupt levelling after a very steep climb), but the increase isn't especially noticeable in normal manoeuvres with the possible exception of a turn with a moderate to steep bank angle.
G will increase as well, any time that any form of acceleration (by the straight physics definition of it) is applied. But the increase is really quite miniscule in the initiation and maintenance of a climb, unless you're talking about jet fighters, space rockets, etc. This would seem to be out of the range of the topic as it was originally started.
Anyway, I would be very cautious about even mentioning such a complication as "G" in a climb.
Makes me wonder how we managed to make it more complicated then, eh?
I'll come back to this thread whenever I can, but my rapidly aging copy of Kermode will be no closer to me than it is right now...
However, just a thing to consider...
Changing thrust will not directly influence AOA. Granted, it may do indirectly by causing a pitching moment, but we are assuming a Piloted aircraft, i.e. the pilot controls that attitude of the aircraft.
The flight path has not yet changed, and the attitude is unchanged.
The flight path has not yet changed, and the attitude is unchanged.
Anyway, because the aeroplane has entered a climb, the flight path HAD changed.
But the Total Reaction is the addition of Lift and Drag. What you describe however is the addition of Lift and Thrust, and hence is not the 'Total Reaction'.
But it does not show how the aircraft gets into the climb!
What is G? Answer = Load Factor (N)
G will increase as well, any time that any form of acceleration (by the straight physics definition of it) is applied. But the increase is really quite miniscule in the initiation and maintenance of a climb, unless you're talking about jet fighters, space rockets, etc. This would seem to be out of the range of the topic as it was originally started.
Anyway, I would be very cautious about even mentioning such a complication as "G" in a climb.
...in mechanics terms it is not that deep - just a free body diagram and a few forces.
I'll come back to this thread whenever I can, but my rapidly aging copy of Kermode will be no closer to me than it is right now...
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Ozexpat,
Well - certainly agree about a diagram - picture versus a thousand words and all that.
Well, actually, thats an inference about what Kermode says. What he actually says is that unless a lower pitch attitude is selected, the aircraft will climb. That is not the same thing as saying this is a stick free situation.
However, now that you've said that, I think I can see what you are thinking about. Unless I am mistaken, you seem to be saying:
Increasing power makes the aircraft pitch up, and thus causes a climb directly, with there being no need for an increase in lift to deflect the aircraft from its flight path.
My position is this - that for an aircraft to be deflected upwards there must be an unbalanced force, acting upwards. With the exception of high thrust high AOA situations as discussed towards the end of my last post, that force must be lift.
I have shown that if a pilot maintains attitude, a thrust increase will cause a speed increase. More Speed, Same AOA = More lift.
I approached the problem this way because it seemed simpler to choose a circumstance that removed the need to consider pitching moments.
Nevertheless, you want to consider Pitching moments as well. Fair enough - I accept that in many aircraft, particularly primary trainers, application of thrust causes a nose up pitching effect. Surely you can see therefore, that at as the nose pitches up, AOA is increasing. In fact you've said it yourself:-
If AOA has increased, lift has increased since nothing else has changed in the lift formula (speed decay has yet to occur).
So again, whether the aircraft pitches up as a result of pitching moments, or because the pilot intentionally pitches up to enter the climb, (or even holds the same attitude and accelerates), whichever way you cut it the mechanism that deflects the FLIGHT PATH is a lift increase, which was my original contention that you took issue with.
And I think this is the root of what is wrong with your view - you seem to be mixing up rotational effects with translational effects.
I know you feel that you have a good simple model that explains climbing, but I'm afraid that its wrong. I don't mean oversimplied, I mean 1+1=3 sort of wrong, because it misuses laws of mechanics.
Moving on:
Well, I'll admit that its been a while since I flew an aircraft with a G meter. But let me ask you a question - in a 60 Degree Banked turn how many G are you pulling? I reckon its 1 more than straight and level, i.e. 2. By your reckoning it would be 1.
But thats by the by.
I was just trying to provide another way for you to see that a lift increase is present.
Let me close by wishing you well on your trip. I'm off down route for a few days too.
CPB
Well - certainly agree about a diagram - picture versus a thousand words and all that.
We started this idea with the premise, from Kermode, that if the pilot did nothing to the flight controls after increasing power (thrust), the aircraft would enter a climb.
However, now that you've said that, I think I can see what you are thinking about. Unless I am mistaken, you seem to be saying:
Increasing power makes the aircraft pitch up, and thus causes a climb directly, with there being no need for an increase in lift to deflect the aircraft from its flight path.
My position is this - that for an aircraft to be deflected upwards there must be an unbalanced force, acting upwards. With the exception of high thrust high AOA situations as discussed towards the end of my last post, that force must be lift.
I have shown that if a pilot maintains attitude, a thrust increase will cause a speed increase. More Speed, Same AOA = More lift.
I approached the problem this way because it seemed simpler to choose a circumstance that removed the need to consider pitching moments.
Nevertheless, you want to consider Pitching moments as well. Fair enough - I accept that in many aircraft, particularly primary trainers, application of thrust causes a nose up pitching effect. Surely you can see therefore, that at as the nose pitches up, AOA is increasing. In fact you've said it yourself:-
The additional thrust creates the change in AofA, and the increased angle creates a movement of the CofP and, in our blackboard/whyteboard diagram, we see that the lift vector line is inclined toward the tail of the aircraft, in relation to the horizon. This is because it is still acting at a right angle to the relative airflow.
So again, whether the aircraft pitches up as a result of pitching moments, or because the pilot intentionally pitches up to enter the climb, (or even holds the same attitude and accelerates), whichever way you cut it the mechanism that deflects the FLIGHT PATH is a lift increase, which was my original contention that you took issue with.
And I think this is the root of what is wrong with your view - you seem to be mixing up rotational effects with translational effects.
I know you feel that you have a good simple model that explains climbing, but I'm afraid that its wrong. I don't mean oversimplied, I mean 1+1=3 sort of wrong, because it misuses laws of mechanics.
Moving on:
"G" is actually acceleration, which can be positive or negative. It can also be zero, of course. To illustrate the point, in S+L flight, the Load Factor is 1 and G is zero.
But thats by the by.
I was just trying to provide another way for you to see that a lift increase is present.
Let me close by wishing you well on your trip. I'm off down route for a few days too.
CPB
Last edited by Capt Pit Bull; 27th Jul 2002 at 01:00.
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Bluskis,
Yes, agreed.
Although conventionally, the climb analysis is carried out parallel and perpendicular to the flight path, that is just because it is convenient for resolving the forces.
There is no mechanics reason why you can not choose to use any set of axes that meets your purposes.
What you are saying is certainly true.
[edited for brain fade]
CPB
Yes, agreed.
Although conventionally, the climb analysis is carried out parallel and perpendicular to the flight path, that is just because it is convenient for resolving the forces.
There is no mechanics reason why you can not choose to use any set of axes that meets your purposes.
What you are saying is certainly true.
[edited for brain fade]
CPB
Last edited by Capt Pit Bull; 27th Jul 2002 at 09:13.
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CPB ... just a quick one before I blast off...
Okay, yes, fine, lift increases. But it does so - at least initially - because of the extra thrust. The wings don't start contributing to lift immediately. The difference is the thrust, which is why we teach the trainee to apply both a power increase and an AoA increase together. This means the aircraft enters the climb in a more smoothly controlled manner and then maintains the climb (yes, okay, up to a certain point).
But, clearly, as was also said earlier, in a vertical climb, the wings produce zero lift. So there's a point at which the wings cease to generate that force. The upward force ("lift" seems to be the wrong term in this context) is then based solely on thrust.
I believe its important for a trainee to understand where the lift comes from.
You've just lost me here. Any turn at all can hardly be defined as S+L flight. Or maybe I should've qualified that condition by using the full terminology :- "straight and level unaccelerated flight"?
Happy trails mate!
Okay, yes, fine, lift increases. But it does so - at least initially - because of the extra thrust. The wings don't start contributing to lift immediately. The difference is the thrust, which is why we teach the trainee to apply both a power increase and an AoA increase together. This means the aircraft enters the climb in a more smoothly controlled manner and then maintains the climb (yes, okay, up to a certain point).
But, clearly, as was also said earlier, in a vertical climb, the wings produce zero lift. So there's a point at which the wings cease to generate that force. The upward force ("lift" seems to be the wrong term in this context) is then based solely on thrust.
I believe its important for a trainee to understand where the lift comes from.
But let me ask you a question - in a 60 Degree Banked turn how many G are you pulling? I reckon its 1 more than straight and level, i.e. 2. By your reckoning it would be 1.
Happy trails mate!
