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byoungplumbing(at)gmail.c
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 Posted: Mon Feb 20, 2012 9:09 am Post subject: stall?????? |
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| Quote: | I did do stall tests at altitude. 28mph pilot only. Landing straight and level,not diving, just letting that last 3 or 4 ft.
diminish it stalls at 35mph single, 40....2 up. Unless I drop the tail.... then 28mph stall.
The only thing that makes sense is ground effect.
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vic sorry this got longer than I had planned.. but read to the end. maybe it will make sense. and remember the angles and speeds mentioned are only examples, and not accurate numbers.
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I have to jump on this one,,,, what do you mean by "the above" are you saying when 3 or 4 ft above the runway, and while slowing down when you hit 35mph single, 40....2 up. is when it starts to drop in? and if you drop the tail it wont drop till 28? if I have a clear picture in my minds eye.. then it is not stalling at 35 to 40... when you get to those speeds the amount of lift is decreasing.
the faster the wing goes the more lift it can produce at any given angle of attack.
examples.
at 8 deg angle of attack at 50 a wing may create 1000 pounds of lift, at 60 same wing, same angle of attack it may produce 1100 pounds of lift and at 70 1200 pounds of lift.
at 40 maybe 900 pounds of lift. at 30 maybe 800 pounds of lift.
so lets say we have a 1000 pound airplane,,, flying at 8 deg angle of attack... at 50 mph it will fly straight and level at any faster speed it will be in a climb . and slower it will be descending because it is no longer producing enough lift to carry the weight.
so how do you fly this airplane at 70 mph... you have to fly at 6 deg angle of attack. if at 6 deg angle of attack and 70 mph, the wing produces 1000 pounds of lift it will fly straight and level.
lets go the other way. if we fly at 40, in order to get 1000 pounds of lift you may need 11 deg of angle of attack. produces straight and level. no stall. but the tail has to be down more. than at 50 mph.
at 30 mph you need 13 deg angle of attack to produce 1000 pounds of lift. straight and level.. no stall
at 28 the wing hits the critical angle of attack, (and for example purposes I will say this is 13.5 deg. ) the air over the wing separates and the wing stalls. when this happens the lift drops from 1000 to just above 0. basically you get the parachute value of the wing surface. this is the definition of a stall...
so during a landing, you are flying at 50 mph at 8 deg angle of attack, and you start to slow. you will have to keep adding more angle of attack to keep the same lift and you can do this till you reach 28 and 13.5 deg angle of attack.. and at that exact moment, when the angle of attack reaches 13.5, the wing starts to fall through the air and the angle of attack will jump because the plane is no longer going level it is dropping at a 30 deg angle toward the ground,,, added to the 13.5 deg in the wing, the angle of attack is 43.5 deg. and these numbers are progressing as the stall deepens. as you slow further you may be dropping at a 45 deg angle, added to the 13.5 is a 58.5 deg angle of attack. or even more.
to get out of a stall, you have to push the nose down, if you are dropping at 45 deg, you have to push over to nearing 45 deg angle, this will do 2 things, (1) the air will reattach to the wing, and (2) you will regain speed. if you pull out gently you have recovered from a stall. if you pull out too hard, you may go into an accelerated stall at an increased g level.
so what does all this have to do with stalling at 28 vs 35.. if you are slowing down past 40 to 35 and you do not increase the angle of attack sufficient to maintain the lift to a degree to carry the weight of the plane. the amount of lift goes down, and the plane drops to the ground... it has not stalled. it is controlled descending flight till the wheels bounce on the ground.
back to the example if we are at 40 mph and 11 deg angle of attack, 5 feet off the ground,,, and we slow to 35 without increasing angle of attack.. you will start to drop... and if the angle of drop is 5 deg. remember we were at 11 deg angle of attack add to that 5 more degrees due to the drop angle. the wing is now at 16 deg angle of attack... the wing will only go to 13.5. so yes you have stalled the wing at 35. and this would fall under the category of an accelerated stall. and something is going to get bent... if you do it 2 inches off the ground, no problems. and if you are straight and level at 2 inches from the ground and keep pulling on the stick, you can slow to 28 before the angle of attack goes beyond 13.5 and you stall.
boyd young
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Vic Peters
Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine
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| Posted: Mon Feb 20, 2012 9:26 am Post subject: stall?????? |
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Yes 3 or 4ft above runway.
Makes sense now. A rapid descent not a stall.
[quote] ---
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Vic
912ul Xtra
Maine
Too old to cut the mustard but not the cheese. |
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