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6 Answers

Stall in turbulence

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General Aviation

I have some doubts which I don't master regarding the possibility of having a stall in turbulence. Considering I do most of my flights in good weather, I don't have much practical experience reagrding these issues.

1. Let's say I took off, climbing at 65kts and there is a 15 kts headwind. If at 100ft, SUDDENLY the wind direction changes and becomes a 15 kts tailwind, my airspeed will suddenly drop to 65-30=35 kts, right? I guess it will end up in a spin and being too low to recover...

2. On final, I encounter an updraft, I noticed that updrafts are +Gs, so is this scenario at risk for an accelerated stall?

3. How aircraft manufacturers make that all certified aircrafts are able to sustand the same amount of gusts? I mean all are certified to sustand 50 ft/s up gust (I think I remebered it correctly), but considering the fact a light sport aircraft will be more loaded due to low mass (inertia) than a heavier aicraft for the same gust?

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6 Answers

  1. lo_fly on Jan 24, 2013

    1. Stalls occur when the critical angle of attack is exceeded, a gust of wind parallel to the relative wind (such as a tailwind gust) will affect only the INTENSITY of the relative wind around your wings, not the ANGLE, thus you are not risking any stall.
    The only effect will be a decrease in climbing performances because of the decreased lift produced by the wings.

    2. An updraft, conversely, will change the angle of attack of your wing because the different direction of the relative wind, so your aircraft can stall in case of a strong gust.

    3. I didn’t get the last question.

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  2. Wes Beard on Jan 24, 2013

    Hello Steve,

    1. In this situation you are talking about a windshear. Please read up in the AIM (7-1-26) about windshear. A proper windshear recovery is to add full power and pitch up to Vx (if you had an angle of attack indicator) it would be right below the critical angle of attack. What you are trying to accomplish is the greatest lift possible to keep yourself from being pushed into the ground. It is a very real and serious condition. The good news is that most commercial airports have a windshear detection system and the tower will advise if windshear is possible. The greatest chances of windshear are in the presence of summertime thunderstorms.

    2. If you encounter an updraft that is steady over a period of several seconds (not likely) the airplane have a momentary increase in angle of attack will calm down and start climbing.. When you lower the nose to stay on your glidepath, the AofA will decrease. You are talking more about the quick updraft that dissipates just as quickly. We typically call this turbulence. It is possible to exceed the critical angle of attack and stall the airplane but due to how quick it happens… recovery happens just as quick. The most you may notice is the stall horn sounding as it occurs very quickly. There have been cases where the pilots either didn’t recover by pushing down on the nose quick enough or reacted incorrectly and stalled / spun the aircraft into the ground but this is unusual.

    3. The velocity-gravity diagram (V-G) has a upward line that indicated 50 ft/s gusts. It stops at the load limit of the airplane and at that speed where the two lines meet… we call VA. The normal category aircraft have a upper limit of +3G. The importance of VA cannot be over stressed, any gusts while the airplane is below VA will cause the airplane to momentarily stall and recover as in answer two. Any gusts with the airplane above VA could very well cause structural damage and depending on how hard the turbulence is, can cause aircraft to come apart. Aircraft should only ever exceed their designed ultimate load factor in the middle of a thunderstorm cloud. If you are there, slow to below VA and try to ride it out. Best to stay as far away as possible.

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  3. SteveJeff on Jan 27, 2013

    What about the airspeed answer at question 1?

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  4. Wes Beard on Jan 28, 2013

    Your airspeed is going to fluctuate for question one. But don’t assume that a 30kt airspeed means you are in a stalled condition. Only exceeding the critical angle of attack means you are stalled. The important thing on a windshear is to try and maintain altitude but you must lose altitude to lower the angle of attack because you don’t want to stall.

    There are some windshear encounters that even high powered jets cannot escape let alone small under powered piston aircraft. Best recommendation is to not takeoff or land in the vicinity of convective activity.

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  5. SteveJeff on Jan 28, 2013

    How that you are not stalled at 30 kts? I figure when you lose the speed, your aoa will change and the airplane will drop the nose abruptly like in a whip stall.

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  6. Daniel ENRIQUEZ EGUIGUREN on Nov 23, 2014

    It´s complicate to explain, but I‘ll try to do my best.
    1. Yes, you will be stalled. The airfoil needs air to attack, so if you encounter a windshear your airspeed will drop below stall speed. L=Cl.p.V^2/2 this is the lift formula, in a wind shear situation Cl remains the same, density remains the same, but airspeed decreases since L∝V^2 At 35 kts you will have nearly as 1/4 of lift as flying at 65 kts; so you will be stalled, but don‘t worry cause you will not enter a spin, a spin is caused by differential wing stall this depends upon angle of attack. Small GA aircraft have less mass therefore less inertia, thus responds quickly to changes in wind variations and power inputs, I have flown in a wind shear situation, the airspeed varies a lot but as I stated small aircraft reacts quickly. To recover from a wind shear apply full power and maintain Vx to get the maximum lift. Please read http://www.skybrary.aero/index.php/Low_Level_Wind_Shear for additional information about wind shear.

    2. Yes you can enter on an accelerated stall, thats what we want when fly in turbulence you must maintain Va or less because. If you encounter a really strong updraft you can pull +4gs or more, this can damage aircraft structure, so engineers invented Va. Va is the speed at which the aircraft stalls before reaching the critical load factor. The stall is less than a few seconds, so no spin here either.

    3. A gust create a load factor. Large airliners can sustain +2gs load factor, they don´t need more because of the weight. Small planes to sustain the same gust needs a heavier structure so they can sustain +3.8gs these is because F=m.a

    I hope it helped if you don‘t understand something you can email me

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