When we have tail wind during approach , with respect of Aerodynamic forces that effect on airplane , the whole part of fuselage move forward due to tailwind, also we have about 70kts IAS (in general aviation) . In this situation we unable to make normal descend as the same as no wind condition . Now my question is : what is the actual force causes this issue according to IAS that shows normal descend speed?
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asked Jul 21, 2020 at 17:19
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2$\begingroup$ It's not a force. It's a velocity that causes the differences. Assuming you are defining "normal descent" as given glide path relative to the ground, rather than a given descent rate. $\endgroup$– quiet flyerCommented Jul 21, 2020 at 17:28
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$\begingroup$ If you are just going for a given descent rate and you don't care about the glide path w/ respect to the ground, then the basic premise of the question is flawed; there is no issue at all; the required combinations of angle-of-attack (or pitch attitude) and power setting are identical in the cases with and without the tailwind. The question could use more clarification as to whether your goal is a given vertical speed, or a given glide path with respect to the ground; and if the former, then the question needs improvement because it is based on a flawed premise. $\endgroup$– quiet flyerCommented Jul 21, 2020 at 21:54
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$\begingroup$ Related, but probably contains too much detail until the more basic priniciples are thoroughly understood -- aviation.stackexchange.com/a/56259/3468 $\endgroup$– quiet flyerCommented Jul 21, 2020 at 22:11
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$\begingroup$ Anyway, will wait till the question is a bit clearer before attempting to convert some of these comments into an actual answer. $\endgroup$– quiet flyerCommented Jul 21, 2020 at 22:29
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$\begingroup$ Are you asking why you need less power when trying to descend on a given glide slope (with respect to ground) w/ a tailwind, than in no wind, using the same airspeed in both cases? And in more detail what is the force that causes this difference, or if it's not a force, then what is causing the difference? Critical to specify what you are holding constant (I'm guessing glide path respect to ground, and airspeed) and what you are allowing to vary (I'm guessing power, and vertical speed, and naturally groundspeed too.) But it's not clear from the question as it stands at present. $\endgroup$– quiet flyerCommented Jul 21, 2020 at 22:33
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1 Answer
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The 3 degree glidslope remains fixed relative to the earth, so a higher rate of descent will always be required to stay on the slope if you increase speed. Conversely, less rate of descent is needed at slower speeds.
It just makes sense if you think about it, but if you need a practical demonstration try this: Draw a diagonal sloping line from corner to corner on a piece of paper. Square it up in front of you, and place your finger at the corner furthest from you. Now pull the paper left or right, and move your finger toward you to trace the line. If you move the paper very slowly sideways you can move your finger slowly. If you move the paper quickly you will need to move your finger quickly.
This is the effect of wind, it changes your groundspeed. With a tailwind you are moving more quickly over the ground, so you have to come down faster or you will go above glidepath.
Does this help?
answered Jul 23, 2020 at 1:51
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$\begingroup$ So its depend on groundspeed and not a exterior force , when the groundspeed becomes higher, rate of descend must be increases to maintain 3.00 degrees of glide path . Its done . thanks for your explanation🌹 $\endgroup$ Commented Jul 23, 2020 at 19:51