Stalls in turbulence

[David Pavlich]

I'm a non-pilot, but basic aerodynamics tell you that a spin is a stall that has one wing stalled more than the other which creates the environment for autogyration. Being a non-pilot, I've been following this thread with more than a little passing interest. It seems to me that if these veteran pilots have given you proper answers, it rests with you whether or not you choose to fly in anything but calm weather. It seems to me, however, that you will spend the majority of your time on the ground or flying within 20 miles of your home airport since weather changes from minute to minute. Good luck!

David

[Steve Jeff]

I'm a non-pilot, but basic aerodynamics tell you that a spin is a stall that has one wing stalled more than the other which creates the environment for autogyration.

My examples are related exactly to this aspect.

It seems to me that if these veteran pilots have given you proper answers, it rests with you whether or not you choose to fly in anything but calm weather. It seems to me, however, that you will spend the majority of your time on the ground or flying within 20 miles of your home airport since weather changes from minute to minute. Good luck!

David

I really appreciate all the help here, but all I want is to understand why are things so, that's why I asked for help. I have no intention to argue or to contradict. Also, I flew in bad weather, it is true that not very often, but that's because I generally prefer good weather, not necessarily those reasons. What I want to know is more theoretical understanding of issues relating to flight in bad weather. Thanks!

[WLIU]

I will offer once last piece of analysis.

Looking at the Cessna 150 manual, you typically fly down final at 65mph at full flaps. Some folks teach to fly 70mph. The 1G stall speed in that condition at gross weight is 48mph and the 2G stall speed is 67mpg. So you are not close to having a problem with turbulence until at least 1.5G of acceleration. Not an issue unless you choose to fly when there are airmets out for wind shear and severe turbulence.

An hour of aerobatic instruction will answer the question about how stalls and spins work.

Fly safe,

Wes
N78PS

[pacerpilot]

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?

Steve, it seems to me you're overthinking this and have a bit of misunderstanding about wind/turbulence. By reading your post I think what you're concerned with is the "feeling" of "updrafts/downdrafts" and a theoretical 180 degree change in wind direction. Many people visualize these conditions in their minds as "columns" and "sheets" of air moving independently. It really doesn't happen/look that way at all. Normal turbulence as we know is just regular old bumpy/wavy air caused by the usual conditions. It's uncomfortable sure, but it won't make your airplane fall out of the sky. Wes and Marty did excellent jobs of explaining those issues and should have dispelled any worry about that. What I have seen personally is pilots trying to constantly compensate for turbulence and they work themselves, and the airplane, like they're pulling giant aluminum taffy! I guess you could overcompensate and force yourself into an accelerated stall. It makes sense since that's basically how we practice them so if you "felt" a descent and honked back on the stick at a low airspeed you could make a dent in the ground. Doing so in a turn obviously makes it worse. The "up/downdraft" condition is most commonly horizontal gusts which result in momentary slight increases or decreases in airspeed with associated vertical movement of the airplane. This is what I understand as "shear". We're not flying through vertical columns like that of a thunderstorm (at least I hope not!) but small changes in speed which cause the up and down movement. It ain't much but it feels that way sometimes. We also encounter lumpy air close to the ground due to surface friction, but it usually doesn't do as much as gusts.
I was trained not to "chase" the airplane through these conditions. I've been flying one of the types with lighter wing loading and I have to be careful not to work too hard in turbulence. She bounces and goes vertical but I remember the basics-attitude, airspeed, etc. As Marty and Wes illustrated the wind shear thing really is a "heavy" airplane problem. Anyhow, just a non-technical response to your question. Hope it helped a bit.

[pacerpilot]

Steve, I just got an email from the FAA informing me of a Webinar on "How to Avoid Losing Control". Sounds like a good one, you should check it out. There free and usually very well presented.

[steveinindy]

Usually 5 or max 10 kts above normal app speed. I would say that is small difference for updrafts, downdrafts.

Plus figure in that the approach speed (at least as specified in most design manuals; whether people actually pay attention to it is arguable) is Vso x 1.3 or something along those lines. You shouldn't be bumping along just above stall unless you're crossing the fence.

Don't know, there are lots of crashes due to stall/spin in traffic pattern. But I hope all of them are due to maneuvering, inadequate speed maintained by pilot etc.

That probably has more to do with the pilot coming in slow and then trying to whip around base to final, overshooting, winding up cross-controlled and exiting both controlled flight and their range of experience almost simultaneously.

Most of the "he stalled due to encountering an up- or downdraft" stories that get circulated become rather clear cut attempts at protecting the reputation of a friend and colleague than something based on reality. If you're flying cautiously and conscientiously, you probably have effectively zero chance of a stall event due to turbulence. The only scenarios (outside of wake turbulence as Frank pointed out) I can think of that would yield a crash would be someone being already too slow or if you encountered something more along the lines of a microburst level downdraft. The latter is only a problem if you're stupid enough to try to land or take off in anything (airliner all the way down to an ultralight) with convective weather that close in. You're not, as WLIU brought up, going to see 2 g or higher in the pattern in VMC unless you're flying well beyond the techniques taught to private pilots (that is, trying to do a mini-airshow tight and steep turn on base to final, etc)

I am not a master of the subject and have far fewer flying hours than most who have contributed thus far but this is my conclusion based on what I know about aircraft and weather. If I am wrong, someone please teach me where I fall short.

[Flyfalcons]

Stalls in turbulence just isn't a concern in the real world.

[Steve Jeff]

During flare, after using the crab method to compensate for a crosswind, when you de-crab you are cross-controlling close to stall speed, why there's no wing drop or even an incipient spin behaviour? I figure out it may be a slip here, but you are wings levek, not banked as in a slip and being so close to stall, why opposite aileron doesn't increase the angle of attack of the opposite wing?

[pacerpilot]

The wing isn't stalled and, you're in ground effect. A crab is a wings level condition so AOA isn't going to change. If you pull back on the yoke/stick you'll get an AOA change. The ailerons don't affect AOI or AOA, the elevator does. Remember, we "stick" the tail to the runway in taildraggers to prevent bouncing and floating once the tailwheel touches or is about to touch. Once in the landing configuration, even slightly above stall full back stick cannot cause the plane to climb once the tailwheel is on the ground. In a nose dragger, you can balloon because the tail can be lowered further by this action. But if you're slow enough you should stall/land perfectly. But still, ailerons won't change AOA/AOI.

[Steve Jeff]

The ailerons don't affect AOI or AOA,

Why on some airplanes opposite aileron induces a spin or at least further wingdrop if you try to pickup the wing at stall using ailerons?