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Effect of Weight - maintaining altitude

  • brentonrule
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brentonrule created the topic: Effect of Weight - maintaining altitude

Hi Bob, I am on page 7.11 of your study text and Question 10 says for an a/c at a particular GW to maintain level flight at a particular height and IAS, a particular power setting is required - (all good so far). The goes on to ask if GW is increased what happens?

4 choices.

a) larger angle of attack and more power
b) larger angle no power change
c) same angle more power
d) smaller angle more power

My answer would be (c) but your answer is (a)

Page 7.5 talks about the best L/D ratio angle of attack as being the same for all a/c no matter what weight. The only change is speed/thrust/power.

Please clarify this for me.

Thanks, Brenton
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bobtait replied the topic: Re: Effect of Weight - maintaining altitude

It is true that if you want to fly at the best lift/drag ratio [i.e. maximum range], you must fly at a particular angle of attack. Therefore if weight is increased, you must fly faster to get the extra lift at the same angle of attack.

However this question is not talking about flying for maximum range. It says you intend to fly at the same speed and the same height. Therefore if weight is increased, you must generate more lift. To generate more lift at the same speed you must have a bigger angle of attack [no longer the best lift/drag ratio]. The bigger angle of attack will provide the extra lift required, but it will also increase the drag. If you want to fly at the same speed [as the questions requires], you must increase the power to over come the extra drag and prevent the aircraft from slowing down.
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