PPRuNe Forums - View Single Post - Question on forces acting on an aircraft in climb
Old 2nd May 2009, 19:54
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ChristiaanJ
 
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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.
Sorry if you misunderstood me.
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?
If your quote is anything to go by, I certainly see no reason to look up the book itself.... as an aeronautical engineer I do have better literature on my bookshelves....
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.
What I find interesting that your "feel" was right from the start - in the other thread I mentioned it took a fair amount of kicking the idea around, and drawing diagrams, before everybody agreed.

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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