Question on forces acting on an aircraft in climb
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Question on forces acting on an aircraft in climb
Hi Guys,
I was reading through Gary Bristow's book,Ace the Pilot Technical Interview and in the first chapter,there is a question asking about the forces acting on the airplane in flight and the answer is as follows:
"Drag,thrust,lift and weight.When thrust and drag are in equilibrium, an aircraft will maintain a steady speed.For an aircraft to accelerate,thrust must exceed the value of drag.When lift and weight are in equilibrium,an aircraft will maintain a steady,level attitude.For an aircraft to climb,lift must exceed weight of the aricraft. In a banked turn,weight is a constant,but lift is lost due to the effective reduction in wingspan.Therefore,to maintain altitude in a banked turn,the lift value needs to be restored by increasing speed and/or the angle of attack."
What I find peculiar is the part when he mentioned about the aircraft climbing.He states that lift must exceed the weight of the aircraft.But I supposed he failed to mentioned that thrust also plays a part when an aircraft climbs cause without thrust,your airspeed will decay and lift won't be enough to sustain the climb.That's what I feel.
However,I would like the opinion of fellow PPRUNERS on this topic as I feel that you guys are in a better position to answer.Thank you.
I was reading through Gary Bristow's book,Ace the Pilot Technical Interview and in the first chapter,there is a question asking about the forces acting on the airplane in flight and the answer is as follows:
"Drag,thrust,lift and weight.When thrust and drag are in equilibrium, an aircraft will maintain a steady speed.For an aircraft to accelerate,thrust must exceed the value of drag.When lift and weight are in equilibrium,an aircraft will maintain a steady,level attitude.For an aircraft to climb,lift must exceed weight of the aricraft. In a banked turn,weight is a constant,but lift is lost due to the effective reduction in wingspan.Therefore,to maintain altitude in a banked turn,the lift value needs to be restored by increasing speed and/or the angle of attack."
What I find peculiar is the part when he mentioned about the aircraft climbing.He states that lift must exceed the weight of the aircraft.But I supposed he failed to mentioned that thrust also plays a part when an aircraft climbs cause without thrust,your airspeed will decay and lift won't be enough to sustain the climb.That's what I feel.
However,I would like the opinion of fellow PPRUNERS on this topic as I feel that you guys are in a better position to answer.Thank you.
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If I recall correctly from PPL lesson 2, in a climb, lift is less than weight and thrust is greater than drag. I remember this because it was somewhat bizarre as you'd expect lift to be greater than weight because you're going up. But not so. What gets you up is excess thrust.
If I recall correctly from PPL lesson 2, in a climb, lift is less than weight and thrust is greater than drag. I remember this because it was somewhat bizarre as you'd expect lift to be greater than weight because you're going up. But not so. What gets you up is excess thrust.
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Vibes,
The text you quote is so full of mistaeks and ambiguity that it's not worth commenting on.
There is a long thread on this subject elsewhere in 'Tech Log'... not sure I can still find it.
What JulieFlyGal says is correct. It was also the conclusion of the other thread.
CJ
The text you quote is so full of mistaeks and ambiguity that it's not worth commenting on.
There is a long thread on this subject elsewhere in 'Tech Log'... not sure I can still find it.
What JulieFlyGal says is correct. It was also the conclusion of the other thread.
CJ
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Hi All,
First and foremost,thank you very much for answering to my queries especially JulieFlyGal,I really appreciate the comment given and I tend to agree with you.
As for CJ,I don't see why I am not able to make any clarifications on this great forum when the fundamental purpose of this forum is for us to come and share our ideas and thoughts.If you feel that my queries are not worth your time to answer,then I feel that you shouldn't be here in the first place.
And CJ,why don't you look up the book itself before accusing what I've quoted as "so full of mistaeks and ambiguity that it's not worth commenting on".And if making a mistake is wrong,why don't you start correcting yourself first by learning how to spell?
First and foremost,thank you very much for answering to my queries especially JulieFlyGal,I really appreciate the comment given and I tend to agree with you.
As for CJ,I don't see why I am not able to make any clarifications on this great forum when the fundamental purpose of this forum is for us to come and share our ideas and thoughts.If you feel that my queries are not worth your time to answer,then I feel that you shouldn't be here in the first place.
And CJ,why don't you look up the book itself before accusing what I've quoted as "so full of mistaeks and ambiguity that it's not worth commenting on".And if making a mistake is wrong,why don't you start correcting yourself first by learning how to spell?
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Vibes
CJ said the text you quoted was full of ambiguities.
I have to say, I agree. There is almost nothing in that paragraph that is correct.
"Drag,thrust,lift and weight.When thrust and drag are in equilibrium, an aircraft will maintain a steady speed.For an aircraft to accelerate,thrust must exceed the value of drag.When lift and weight are in equilibrium,an aircraft will maintain a steady,level attitude.For an aircraft to climb,lift must exceed weight of the aricraft. In a banked turn,weight is a constant,but lift is lost due to the effective reduction in wingspan.Therefore,to maintain altitude in a banked turn,the lift value needs to be restored by increasing speed and/or the angle of attack."
The stuff in red is wrong, or only true in particular circumstances (that are not specified). The stuff in green is correct.
IF its quoted correctly, then the book seems (to me) to be of very dubious quality.
Now, you can take that opinion or leave it; neither I (nor CJ) are obligated to go out and buy it to conduct a full review for your benefit. Likewise, I am not required to provide you with a complete lesson covering these topics; (although I am available for consultancy for a very reasonable rate!).
pb
CJ said the text you quoted was full of ambiguities.
I have to say, I agree. There is almost nothing in that paragraph that is correct.
"Drag,thrust,lift and weight.When thrust and drag are in equilibrium, an aircraft will maintain a steady speed.For an aircraft to accelerate,thrust must exceed the value of drag.When lift and weight are in equilibrium,an aircraft will maintain a steady,level attitude.For an aircraft to climb,lift must exceed weight of the aricraft. In a banked turn,weight is a constant,but lift is lost due to the effective reduction in wingspan.Therefore,to maintain altitude in a banked turn,the lift value needs to be restored by increasing speed and/or the angle of attack."
The stuff in red is wrong, or only true in particular circumstances (that are not specified). The stuff in green is correct.
IF its quoted correctly, then the book seems (to me) to be of very dubious quality.
Now, you can take that opinion or leave it; neither I (nor CJ) are obligated to go out and buy it to conduct a full review for your benefit. Likewise, I am not required to provide you with a complete lesson covering these topics; (although I am available for consultancy for a very reasonable rate!).
pb
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Originally Posted by Vibes
As for CJ, I don't see why I am not able to make any clarifications on this great forum when the fundamental purpose of this forum is for us to come and share our ideas and thoughts.If you feel that my queries are not worth your time to answer,then I feel that you shouldn't be here in the first place.
It was simply the text you quoted that got my hackles up, because it contained so much rubbish (as Capt Pit Bull also points out), that I really saw no point in refuting every single ambiguity.
But I agree I didn't reply correctly to your final question, and as you say, that's what PPRuNe is about.
See below.
And CJ,why don't you look up the book itself before accusing what I've quoted as "so full of mistaeks and ambiguity that it's not worth commenting on". And if making a mistake is wrong,why don't you start correcting yourself first by learning how to spell?
And apologies if you didn't get the deliberate "speling mistaek".
What I find peculiar is the part when he mentioned about the aircraft climbing.He states that lift must exceed the weight of the aircraft.But I supposed he failed to mentioned that thrust also plays a part when an aircraft climbs cause without thrust,your airspeed will decay and lift won't be enough to sustain the climb.That's what I feel.
Much of the confusion seems to come from the differences between what I would call 'flight dynamics' and steady-state flight.
You're exactly right. If you start climbing by pulling back on the stick, momentarily the lift is greater than the weight, but if then you don't increase the thrust, the airspeed will decay.
Another thing that seemed to cause confusion is the coordinate system....
Lift, thrust and drag are all defined relative to the flightpath, while weight/gravity always acts along the vertical.
In a steady-state climb, lift, thrust and drag on the one hand, and gravity on the otherhand, are no longer at right angles. Hence, lift is less than in horizontal flight. Thrust is no longer equal to drag, but more, because it now has to compensate for the component of the weight no longer 'supported' by the lift.
The extreme case, quoted in the other thread, is of course a steady-state vertical climb, where the lift (force at right angles to the flightpath) is now zero, and thrust minus drag is equal to the weight.
When the question was first asked in the other thread, most of us had some trouble fully getting our head around it.
So my compliments to you for getting it right first time!
Cheers,
Christian
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Bristow Book
Guys, having read the bristow book at length some 2 years ago, not having interviewed in over 12 years prior, I was very disappointed to say the least! It is simply full of holes! There is some good stuff but you would have to really know your stuff to sort the wheat from the chaff here....
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I totally disagree with captainsmiffy....
I find the information contained in this thread to be quite enlightening. In my almost 40 years of flying, I never knew some of these things...and
I take Bristow as 'gospel'.
NOT!!!!!!!!!
(Only joking with you, captainsmiffy!!!!)
Fly safe,
PantLoad
By the way, the U.S. Navy has great pubs explaining how an airplane flies.
I take Bristow as 'gospel'.
NOT!!!!!!!!!
(Only joking with you, captainsmiffy!!!!)
Fly safe,
PantLoad
By the way, the U.S. Navy has great pubs explaining how an airplane flies.
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The U.S. Navy book is: "Aerodynamics for Naval Aviators".
I haven't read it yet, but everybody here has been unequivocally recommending it, so I'll be ordering it too.
Just Google the title. It can be had for about $10, and even less second-hand.
CJ
I haven't read it yet, but everybody here has been unequivocally recommending it, so I'll be ordering it too.
Just Google the title. It can be had for about $10, and even less second-hand.
CJ
Warning Toxic!
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Nobody please ever spend any money on ACE the Pilot Technical Interview! IMO, I think it is complete and utter confusing erroneous garbage. If you walk past a bookshop table with it remaindered out very cheap (or free), stillwalk on by! This rubbish does not merit discussion here.
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Hi Guys,
First and foremost,thank you for all the responses you've made to this thread.I really do appreciate it especially the clarification made by CJ.My apologies to CJ for the misunderstanding in the earlier posts.With regards to the book by Bristow,as far as I understand,I have heard about it containing misleading info.Hence,I decided,on my own accord,that the best way to learn is by taking his questions and clarifying whatever answers that were given by him.Though its a long method of learning,I feel that it is good as I get the opinions of many professionals in this field.Hence,its been great to be in the company of you guys as IMO the experience you guys have in this forum beats any books that's been written.And aviation,with a huge range of subjects from meteorlogy to aerodynamics,could be quite misleading in a sense that you have so many books and so many different authors,each expressing their own opinion.Thus,that's why I've asked time and again,many silly questions with regards to aviation cause books can only tell you so much.And I supposed in aviation,experience is the best lesson.And this forum has lotsa of them
First and foremost,thank you for all the responses you've made to this thread.I really do appreciate it especially the clarification made by CJ.My apologies to CJ for the misunderstanding in the earlier posts.With regards to the book by Bristow,as far as I understand,I have heard about it containing misleading info.Hence,I decided,on my own accord,that the best way to learn is by taking his questions and clarifying whatever answers that were given by him.Though its a long method of learning,I feel that it is good as I get the opinions of many professionals in this field.Hence,its been great to be in the company of you guys as IMO the experience you guys have in this forum beats any books that's been written.And aviation,with a huge range of subjects from meteorlogy to aerodynamics,could be quite misleading in a sense that you have so many books and so many different authors,each expressing their own opinion.Thus,that's why I've asked time and again,many silly questions with regards to aviation cause books can only tell you so much.And I supposed in aviation,experience is the best lesson.And this forum has lotsa of them
Warning Toxic!
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I was so concerned at the inconsistencies I found in this book, I started folding over the corner of the pages I wanted to check out and study further. Letīs say it quickly became apparent that something was amiss with the book! It looks to me like an author overreached themselves, and proof readers were used who didnīt know a whole lot about aviation, and if the spelling seemed OK, that was just dandy by them!
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Originally Posted by Rainboe
... proof readers were used who didnīt know a whole lot about aviation, and if the spelling seemed OK, that was just dandy by them!
In this case it sounds as if the book could have done with a couple of expert copy editors,before being handed to the proof readers.
Originally Posted by Vives
...I've asked time and again,many silly questions with regards to aviation...
The problem is usually with the answers: how much does the person asking the question already know, and how much needs explaining?
CJ
In a banked turn,weight is a constant,
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It would probably be of great asistance to the instigator of this post if someone could find and post a series of simple explanatory vector diagrams. I seem to remember that such diagrams were used to great effect during "theory of flight " briefings when I was learning to fly.
Such a diagram would show, for example, how the resultant of the lift vector
(lift and thrust) would be balanced by the resultant of the weight vector (weight and drag) in a constant climb, etc., etc.
I am unable to recall where I have seen the diagrams published, but it could have been "Flight Briefing for Pilots" by Allan Bramson.
Does anyone know what I am talking about?
Such a diagram would show, for example, how the resultant of the lift vector
(lift and thrust) would be balanced by the resultant of the weight vector (weight and drag) in a constant climb, etc., etc.
I am unable to recall where I have seen the diagrams published, but it could have been "Flight Briefing for Pilots" by Allan Bramson.
Does anyone know what I am talking about?
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pineridge, Vibes,
Here's my earlier scribble (call it a vector diagram if you like) I did for the thread I mentioned earlier.
This one is strictly for the force balance in a steady-state climb, drawn for the horizontal and the vertical balance.
Re the sin(ac) and cos(ac) ... the "ac" is "angle of climb", happened to be the term used in the other thread for the flight path angle or climb angle.
Turns is another story.
Wizofoz, I've seen so many badly worded explanations I won't start on that one yet...
CJ
Here's my earlier scribble (call it a vector diagram if you like) I did for the thread I mentioned earlier.
This one is strictly for the force balance in a steady-state climb, drawn for the horizontal and the vertical balance.
Re the sin(ac) and cos(ac) ... the "ac" is "angle of climb", happened to be the term used in the other thread for the flight path angle or climb angle.
Turns is another story.
Wizofoz, I've seen so many badly worded explanations I won't start on that one yet...
CJ
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In a banked turn,weight is a constant,