Ptkay
3rd May 2010, 13:17
When discussing one of the recent accidents,
the question has been put up, what happens to the a/c when it
hits an inversion layer on approach.
Assuming the high drag landing configuration, will the sudden
increase in air density (lower air temperature) increase the drag
faster than lift, hence causing sudden loss of speed and altitude.
Suggestions form a Russian forum.
The configuration of the aircraft on landing glide path, Cx (drag coefficient) and Cy (lift coefficient) is extremely large. On the glide path, the aircraft is included in the inversion layer, in which the temperature drops, and its density increases. In contrast to a slight increase in lift, drag force increases substantially (the mechanization of the wing contributes to this). As a result, there is an unbalanced moment on the dive. If, moreover, there was still a small forward pitch moment and the crew did not prepare in advance to the entrance of this layer, they begun to drop under the glide path.
This situation is well described by VV Ershov in his memoirs.
"... ... ... Seconds was enough to make a huge drag force on the release at 45 degrees flaps vigorously reduced speed. The plane began to drop the nose and went under the glide path. The captain gave the command to add the power and began to pull the column. But here a cruel joke played by the front CoG: the plane was loaded so that the nose was noticeably heavy. If this happened in the good old IL-18, then all the vertical manoeuvres and landing would require only the more energetic pull on the column. In IL-18 I did it hundreds of times - and had no problems. But this plane did not obey the steering. (Meaning the Tu-154.). Column was pulled all the way, the elevator had been pulled up to a maximum angle, and its force managed to lower the tail and raise the nose of the plane. However, the plane went lower and lower under the glide path. There was only one thing to do: go to GA take-off mode and expect the power to become effective. It eventually became effective and the rate of climb was growing at increased power. The machine began to lift the nose, the trajectory of decline twisted up ... and then cleared the ground ... .... "
VV Ershov "Writings of a sled dog "
Google Tłumacz (http://translate.google.pl/translate?js=y&prev=_t&hl=pl&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Fforum.smolensk.ws%2Fviewtopic.php%3Ff%3D2%26t %3D48375%26start%3D11460&sl=ru&tl=en%2Fforum.smolensk.ws%2Fviewtopic.php%3Ff%3D2%26t%3D4837 5%26start%3D11460)
the question has been put up, what happens to the a/c when it
hits an inversion layer on approach.
Assuming the high drag landing configuration, will the sudden
increase in air density (lower air temperature) increase the drag
faster than lift, hence causing sudden loss of speed and altitude.
Suggestions form a Russian forum.
The configuration of the aircraft on landing glide path, Cx (drag coefficient) and Cy (lift coefficient) is extremely large. On the glide path, the aircraft is included in the inversion layer, in which the temperature drops, and its density increases. In contrast to a slight increase in lift, drag force increases substantially (the mechanization of the wing contributes to this). As a result, there is an unbalanced moment on the dive. If, moreover, there was still a small forward pitch moment and the crew did not prepare in advance to the entrance of this layer, they begun to drop under the glide path.
This situation is well described by VV Ershov in his memoirs.
"... ... ... Seconds was enough to make a huge drag force on the release at 45 degrees flaps vigorously reduced speed. The plane began to drop the nose and went under the glide path. The captain gave the command to add the power and began to pull the column. But here a cruel joke played by the front CoG: the plane was loaded so that the nose was noticeably heavy. If this happened in the good old IL-18, then all the vertical manoeuvres and landing would require only the more energetic pull on the column. In IL-18 I did it hundreds of times - and had no problems. But this plane did not obey the steering. (Meaning the Tu-154.). Column was pulled all the way, the elevator had been pulled up to a maximum angle, and its force managed to lower the tail and raise the nose of the plane. However, the plane went lower and lower under the glide path. There was only one thing to do: go to GA take-off mode and expect the power to become effective. It eventually became effective and the rate of climb was growing at increased power. The machine began to lift the nose, the trajectory of decline twisted up ... and then cleared the ground ... .... "
VV Ershov "Writings of a sled dog "
Google Tłumacz (http://translate.google.pl/translate?js=y&prev=_t&hl=pl&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Fforum.smolensk.ws%2Fviewtopic.php%3Ff%3D2%26t %3D48375%26start%3D11460&sl=ru&tl=en%2Fforum.smolensk.ws%2Fviewtopic.php%3Ff%3D2%26t%3D4837 5%26start%3D11460)