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#1
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Yesterday's IFR flight with questions
"Peter R." wrote No. I can visualize how flaps will disturb airflow over the horizontal stabilizer of high wing aircraft, but I am having difficulty visualizing how airflow over the horizontal stabilizer of a low wing is disturbed by the lowering of flaps. It isn't about disturbing the airflow over the stabilizer. The tail provides "downward lift" to offset the fact that the center of lift of the wing is behind the cg. When you lower the flaps you move the center of lift of the wing even further aft, and this means the tail must work even harder. If the tail is near stall due to icing, lowering the flaps may cause a full tail stall which will result in the nose pitching down quite severely. You probably won't be able to recover because the technique is totally different compared to recovering from a normal wing stall and the altitude loss can be dramatic even when proper technique is used. The NASA video is highly recommended viewing. |
#2
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Yesterday's IFR flight with questions
" wrote: A Lieberman wrote: I'm going to answer these before I read the other replies, to avoid prejudicing my own answers. Apologies for any duplication. Question 1 on Sleet. In my case, it was 43 on the ground, and on my climb to my altitude, the temperature remained well above 32 while I was in IMC. I climbed to 6000 which was my designated altitude. I broke out at 5,500. How far up can sleet be created and not melt before hitting the ground? There was a layer of clouds above me. Seems that from the ground to 6000 feet, I came across some hardy sleet pellets to survive that long in above freezing temperatures? I fly some IMC in winter here in central Canada and the NE US in my Warrior, and do occasionally encounter ice at altitude. Still, I would not take off if I saw sleet or ice pellets, period. I probably wouldn't even try it in a twin with boots, due to the risk of severe clear. Question 2 on icing. Had I not climbed up like I did, I would have never seen the ice on the wings or stabilator. I now know to look on that temperature probe for first signs of icing as I did today, but will it readily show up in IMC without reflections of the sun? Clear icing will show up easily on the probe, even at night, because it changes the shape of the tip. Rime icing, maybe less so. Figuring on 500 feet per minute descent, for me, 1500 feet is rather thick for 3 minutes. You might not want to descend that slowly through an icing layer. I don't think there's any reliable measure for how slowly or fast you can ice up -- I haven't had this happen to me, but I know people who've had the windscreen ice over almost instantly, as if someone threw a bucket of paint on it. You have to be prepared to land in a slip, looking out the storm window, if your defrost cannot clear it. If you're going to have to descend through a possible icing layer, set up everything in your favour beforehand: carb heat on, pitot heat on, defroster on, a big post-it note on your flap switch or handle saying "DON'T TOUCH" (flaps can cause a tail stall if you've encountered ice), and a fairly steep approach slope. Try to keep the throttle as far open as you can and don't slow down too much. Oh, did I mention? Don't touch the flaps. All the best, David I wonder, if you had enough altitude after breaking out below, would it be advisable to perform a gentle power-off stall to find out what your new stall speed is with the ice? Or would the new stall characteristics be so unpredictable as to make the aircraft unstable? -Nick |
#3
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Yesterday's IFR flight with questions
Nick Kliewer wrote:
I wonder, if you had enough altitude after breaking out below, would it be advisable to perform a gentle power-off stall to find out what your new stall speed is with the ice? Or would the new stall characteristics be so unpredictable as to make the aircraft unstable? There's no way in hell I'd do that. Take a lesson from the last time I flew in such heavy rain that the airspeed indicator became grossly inaccurate: slow down to your usual speed paying particular attention as it decelerates. If it starts feeling sloppy, you need more power. If you don't have enough power, you were going to crash anyway. Think of the last time you did slow flight... you remember how it just slopped along? That's bad. Tight controls; that's good. Feel for the ground after arriving with normally tight controls... perfect. -- Mortimer Schnerd, RN VE |
#4
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Yesterday's IFR flight with questions
I wonder, if you had enough altitude after breaking out below, would it be
advisable to perform a gentle power-off stall to find out what your new stall speed is with the ice? Or would the new stall characteristics be so unpredictable as to make the aircraft unstable? The new stall charactaristics may be asymmetric, and recovering from such a stall iced up may be a problem. If there's precip, even after you break out you may continue to ice up, so the new stalling charactaristics will be transitory, replaced by even worse ones. I'd stay the hell away from stalling while iced up. Jos -- He who laughs, lasts. for Email, make the obvious change in the address. |
#5
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Yesterday's IFR flight with questions
Jose wrote:
I wonder, if you had enough altitude after breaking out below, would it be advisable to perform a gentle power-off stall to find out what your new stall speed is with the ice? Or would the new stall characteristics be so unpredictable as to make the aircraft unstable? The new stall charactaristics may be asymmetric, and recovering from such a stall iced up may be a problem. If there's precip, even after you break out you may continue to ice up, so the new stalling charactaristics will be transitory, replaced by even worse ones. I'd stay the hell away from stalling while iced up. Well, I'd at least stay away from stalling until I was less than 6" above the runway! Matt |
#6
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Yesterday's IFR flight with questions
Nick Kliewer wrote:
I wonder, if you had enough altitude after breaking out below, would it be advisable to perform a gentle power-off stall to find out what your new stall speed is with the ice? Or would the new stall characteristics be so unpredictable as to make the aircraft unstable? The latter. If your tail ices up, all bets are off. The recovery from a tail stall is the opposite of the recovery from a wing stall (you pull back instead of pushing forward), but good luck figuring that out in a few seconds under high stress. All the best, David |
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