Aerodynamics of the Base to Final stall

[coloradobluesky]

Slips are more stable than skids. It is a skid that can lead to a quick stall with a wingdrop. The reason for this is that when the plane stalls in a slip, the high wing has to fall down. In a skid the low wing is already down so you enter the stall/wing drop quicker. Same with pushing on low rudder in a steep turn makes a skid.

The precaution about base to final turn is the pilot shouldnt be using the rudder to complete the turn and line the airplane up with the runway. He should use the primarily the ailerons and keep the ball centered with the rudder. Pilots don't want to do that because it means banking the airplane so close to the ground. But its the proper way to do it. Glance at the ball on the turn to final. Keep an eye on the airspeed too of course.

 

[JOhnH]

You are wrong.

Wouldn't it have been appropriate to explain why?

 

[MauleSkinner]

That's a nice theory. But at pattern altitude, you don't have the altitude necessary to recover if you get into a spin, even if you are expecting the spin to occur. Add in the surprise factor when someone inadvertently enters the spin, and there is no chance of recovery.

I disagree...many airplanes are recoverable in 500 feet or less. If the pilot has a proper conditioned response to the airplanes stall the spin probably won't develop, so it'll take less altitude to recover.

The problem is developing the conditioned response. Most pilots don't seem to want to do that.

 

[brcase]

While the AOA indicator is a tool that provides information, I don't think it will help with accidental stalls while turning. The people who do this would probably not look at the AOA indicator at that moment even if it was there.

I agree, the issue is that in small single engine airplane there are very few situations where the AOA indicator doesn't just mirror what the Airspeed indicator says. If you maintain your airspeed you won't have a problem. In analyzing stall spin accidents I believe most are caused by either the illusion of speed or simply the pilot not realizing they are going slow enough to stall. This is usually either caused by flying close to the ground (which makes you feel like you are going fast), flying downwind (which makes you look like you are going fast), and/or some other distraction.

Brian
CFIIG/ASEL

 

[PPC1052]

I disagree...many airplanes are recoverable in 500 feet or less. If the pilot has a proper conditioned response to the airplanes stall the spin probably won't develop, so it'll take less altitude to recover.

The problem is developing the conditioned response. Most pilots don't seem to want to do that.

If they had a "proper conditioned response," they probably wouldn't get into the spin in the first place. The base to final spin happens by accident, which pretty much guarantees that the pilot won't expect it.

Even if recovery is possible within 500 feet (which I doubt under these surprise circumstances), that's not much room for error. Add to this the consequences of failure, and I think it's unrealistic to expect successful recovery. Generally the base to final turn will be at less than 1000 agl.

 

[exncsurfer]

While the AOA indicator is a tool that provides information, I don't think it will help with accidental stalls while turning. The people who do this would probably not look at the AOA indicator at that moment even if it was there.

They might respond to the nice lady saying 'too slow, too slow, too slow' unless they're deaf too.

 

[Everskyward]

They might respond to the nice lady saying 'too slow, too slow, too slow' unless they're deaf too.

Or maybe not, the AF pilots didn't respond to "stall, stall, stall" and the Colgan pilot overrode both the shaker and the pusher. If you're distracted and panicked you may not be listening to these cues and/or not responding appropriately.

 

[455 Bravo Uniform]

If they had a "proper conditioned response," they probably wouldn't get into the spin in the first place. The base to final spin happens by accident, which pretty much guarantees that the pilot won't expect it.

Even if recovery is possible within 500 feet (which I doubt under these surprise circumstances), that's not much room for error. Generally the base to final turn will be at less than 1000 agl.

And hence my earlier question - can the AOA indicator even give enough warning time to react to impending stall and spin so as to avoid it altogether? If so, why can't a stall horn be set up to warn at the same incipient stage?

 

[MauleSkinner]

If they had a "proper conditioned response," they probably wouldn't get into the spin in the first place. The base to final spin happens by accident, which pretty much guarantees that the pilot won't expect it.

True. Of course, this whole conversation is useless if we don't define a spin. How many turns before it actually becomes a spin?

Even if recovery is possible within 500 feet (which I doubt under these surprise circumstances), that's not much room for error. Add to this the consequences of failure, and I think it's unrealistic to expect successful recovery. Generally the base to final turn will be at less than 1000 agl.

Also true...you might actually read the post I was responding to, though. He stated that there isn't enough altitude even without the surprise factor.

 

[exncsurfer]

And hence my earlier question - can the AOA indicator even give enough warning time to react to impending stall and spin so as to avoid it altogether? If so, why can't a stall horn be set up to warn at the same incipient stage?

Did you watch the video, the actual demos were near the end if you didn't make it that far. They seem to go 'red' before you ever hear the audible stall horn in the vid. Its kinda hard to tell though there are 3 planes and i don't know which one we're listening to.

skip to the 15 minute mark, here is a screen shot, all three are showing some sort of warning and the stall horn hasn't sounded yet:

 

[PPC1052]

And hence my earlier question - can the AOA indicator even give enough warning time to react to impending stall and spin so as to avoid it altogether? If so, why can't a stall horn be set up to warn at the same incipient stage?

I think the idea with the AOA is that is the instrument that you are watching, not the air speed indicator, as you fly the pattern. Thus, it's not that this is giving you a warning to pay attention to something you may not notice. What you do is train yourself to watch this the whole time (well, as much as is consistent with eyes outside in the pattern), and you always know how close you are to a stall.

With the stall warning indicator on the other hand, you think you are fine, you're not paying attention, then out of no where the stall warning goes off, and things hit the fan before you know what happens.

 

[PPC1052]

Also true...you might actually read the post I was responding to, though. He stated that there isn't enough altitude even without the surprise factor.

Okay. Now I'm confused. I thought you said:

I disagree...many airplanes are recoverable in 500 feet or less.

Have I lost the pace here?

 

[MauleSkinner]

Have I lost the pace here?

Apparently

 

[PPC1052]

Apparently

Then help me out. What did I miss?

 

[MauleSkinner]

Then help me out. What did I miss?

Whether or not the surprise factor was a factor in the statement.

 

[PPC1052]

Whether or not the surprise factor was a factor in the statement.

Which statement? Wait. Never mind. I don't think we disagree and I don't care enough to sort it out.

 

[denverpilot]

Did you watch the video, the actual demos were near the end if you didn't make it that far. They seem to go 'red' before you ever hear the audible stall horn in the vid. Its kinda hard to tell though there are 3 planes and i don't know which one we're listening to.

skip to the 15 minute mark, here is a screen shot, all three are showing some sort of warning and the stall horn hasn't sounded yet:
View attachment 50794

 

[455 Bravo Uniform]

Did you watch the video, the actual demos were near the end if you didn't make it that far. They seem to go 'red' before you ever hear the audible stall horn in the vid. Its kinda hard to tell though there are 3 planes and i don't know which one we're listening to.

skip to the 15 minute mark, here is a screen shot, all three are showing some sort of warning and the stall horn hasn't sounded yet:
View attachment 50794

Yes, but things seemed to progress pretty slowly to me. Maybe because it's such an early warning system?

I'd love to see a vid where someone actually spins the plane and see how much lead time there was between the "too slow" and the loss of altitude/stall/spin.

 

[denverpilot]

Yes, but things seemed to progress pretty slowly to me. Maybe because it's such an early warning system?

I'd love to see a vid where someone actually spins the plane and see how much lead time there was between the "too slow" and the loss of altitude/stall/spin.

Put those things in something that'll actually snap roll and see if they give you enough time.

 

[Velocity173]

If you just buy a canard, you won't have to worry about the base to final stall. Won't have to desecrate your perfect wing with an AoA contraption either.

 

[Ryan F.]

Will there be a cap on the AOA threads? Just wondering.

 

[Stewartb]

I think Tom needs an AOA so he can fly slower and land shorter.
https://www.instagram.com/p/BHYqpXUhBry/?taken-by=stolquest

 

[Velocity173]

I think Tom needs an AOA so he can fly slower and land shorter.
https://www.instagram.com/p/BHYqpXUhBry/?taken-by=stolquest

But he could have flown backwards if he had an AoA indicator.

 

[mscard88]

Will there be a cap on the AOA threads? Just wondering.

There's other threads about CAP if you want more.

 

[bobmrg]

Or maybe not, the AF pilots didn't respond to "stall, stall, stall" and the Colgan pilot overrode both the shaker and the pusher. If you're distracted and panicked you may not be listening to these cues and/or not responding appropriately.

Right. People do not understand how panic leads to tunnel vision.

Bob

 

[Salty]

Does an AOA indicator completely prevent stalls, or just lower the stall speed a lot?

 

[Dan Thomas]

Dan, I have to admit I have never heard your explanation. I searched some textbooks and online and do not find a reference. I am very intrigued with your premise and if you have some reference material to direct me to, that would be great.

http://www.langleyflyingschool.com/Pages/CPGS+4+Aerodynamics+and+Theory+of+Flight+Part+1.html#Stalls

Excerpt: "During a climbing turn, the inner wing has a smaller angle of attack than the outer wing; the outer wing will therefore stall first. The reverse is the case for descending turn, where the inner wing has a larger angle of attack and will therefore stall first. "

 

[SoCal RV Flyer]

That's a nice theory. But at pattern altitude, you don't have the altitude necessary to recover if you get into a spin, even if you are expecting the spin to occur. Add in the surprise factor when someone inadvertently enters the spin, and there is no chance of recovery.

Perhaps, but at least it's a plan of action. Better than just wishing that darn spin would go away.

We all agree that the best course of action is to not put ourselves in that situation in the first place.

 

[dmspilot]

http://www.langleyflyingschool.com/Pages/CPGS+4+Aerodynamics+and+Theory+of+Flight+Part+1.html#Stalls

Excerpt: "During a climbing turn, the inner wing has a smaller angle of attack than the outer wing; the outer wing will therefore stall first. The reverse is the case for descending turn, where the inner wing has a larger angle of attack and will therefore stall first. "

It seems like the left wing is more likely to stall first because of torque, p-factor, and propeller slipstream.

The helical effect is interesting but not sure I buy it. The author's grasp of physics is lacking. For example, centrifugal force is not a real force and the wing does not need to generate more lift "to offset the increased load factor." Load factor is a term given to the result of the increase in lift.

 

[Maui Cirrus CFII]

How do you factor in wind to get max range over the ground?

And does your AOA system provide an aural warning of the impending stall during the base to final turn?

Great question. I teach to use the single yellow bar with half donut or the hollow donut yellow bar for gusts.
Yes the system provides a "too slow!" audio alert see attached.

 

[Maui Cirrus CFII]

I'm pretty sure wing configuration changes things. Alpha Systems acknowledges this. It's fairly negligible for some airplanes, but for others their system does compensate for flap settings.

That the "practical approach" is to install it on the wing opposite the stall horn, and that it be "biased on the left side" implies that there is a difference in its indications. I would sure like to see the numbers on this. Something like when skidding to the left/right, stall will occur 1/2 of a "bar" earlier/later

In fact I talked with the inventor at Alpha today about this, and he said that yes in a perfect world you would want two, one on each wing. On a jet or twin on the nose. But the difference for example is that if its on the left wing, you will get precise info prior to a stall spin. If you are in a right wing stall/spin scenario the system will still be blaring at you but will be the chevron below the red arrow. Either way they are way beyond the blue donut. And that is where you don't want to be, unless you are 10 feet above the runway...

 

[Maui Cirrus CFII]

And hence my earlier question - can the AOA indicator even give enough warning time to react to impending stall and spin so as to avoid it altogether? If so, why can't a stall horn be set up to warn at the same incipient stage?

Because of the design. It whistles because of negative pressure. And by that time its too late. You are way way up the Cl curve.

 

[Maui Cirrus CFII]

I think the idea with the AOA is that is the instrument that you are watching, not the air speed indicator, as you fly the pattern. Thus, it's not that this is giving you a warning to pay attention to something you may not notice. What you do is train yourself to watch this the whole time (well, as much as is consistent with eyes outside in the pattern), and you always know how close you are to a stall.

With the stall warning indicator on the other hand, you think you are fine, you're not paying attention, then out of no where the stall warning goes off, and things hit the fan before you know what happens.

BINGO....

 

[Maui Cirrus CFII]

View attachment 50796

That was so good I had to share it in the COPA forum... Thanks for the laugh. I feel like Rocky Balboa in the 10th round...

 

[denverpilot]

Will there be a cap on the AOA threads? Just wondering.

The powers that be banned politics. What else will we entertain ourselves with? Hahaha.

 

[455 Bravo Uniform]

Good discussion though.

 

[Dan Thomas]

Because of the design. It whistles because of negative pressure. And by that time its too late. You are way way up the Cl curve.

Nonsense. The stall warning, according to the service manuals, is to be adjusted so that it sounds five to ten knots above the stall. That's a pretty good margin. We often find those things misadjusted, possibly by the folks that rebuild airplanes, or by folks that don't like it sounding all the time in slow flight, or by the mechanics who don't refer to the manuals. That last factor is very common.

The slot-suction type is adjustable, as is the vane type. Moving it up increases the margin, down decreases it.

The big problem with any stall warning or AoA indicator is that it won't stop a guy from doing the stupid stuff that kills people: the low pass with a sharp pullup is a classic example. Accelerated stall. Too many think a fat airspeed margin will keep them safe in all maneuvers, not understanding stall speed vs. load factor. The warning will sound, but only a few milliseconds before the airplane flips and crashes.

 

[citizen5000]

One way to stay out of trouble is to always be descending on base to final.

 

[SoCal RV Flyer]

One way to stay out of trouble is to always be descending on base to final.

Good tip. I almost always find myself a little high at this point anyway. I'd rather "chop & drop" and point the nose down than drag it in any day.

 

[Jimmy cooper]

I agree with 331. I've never used an aoa. I learned in an aeronca champ, flew it for 200 hours, then went to a 180 Cessna, lots of them around then, then to a super twenty one Mooney, which had a stall warning but usually only chirped on final.same with the 201, It went full horn just about at touch down . If you KNOW the airplane your flying, like take it to altitude and stall it a lot, etc. you'll find the aoa is in the seat of your pants. I find it amazing that many are getting an instrument ticket with only say, 200 hours total. They don't know much about how to fly, much less tackle a for real instrument approach! I never got an instrument ticket as I believed I would kill myself and maybe others by not spending enough time staying current flying IFR. Many people I knew had no instrument ticket yet flew all over the United States for years! Several pilots I knew that did have one died for the reason I stated. I should add here that I was taught NEVER to " drag it in" which meant you didn't know how to land correctly and you were asking for trouble!