Episode: 2714
Title: HPR2714: Airplane stalls and Angle of Attack
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr2714/hpr2714.mp3
Transcribed: 2025-10-19 08:01:59

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This is HPR episode 2,714 entitled Airplane Toil and Undle of Attack.
It is hosted by Brian in Ohio and in about 17 minutes long and Karina Cleanflag.
The summary is a primer on why Airplane is quit flying.
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Hey Hello Hacker Public Radio, Brian and Ohio here crawling out from under his rock
and doing an episode on subject matter that's been in the news a few times recently and that
was it has to do with the aircraft accident in Indonesia, the line error 737 that crashed
somewhere in the climb out. And there's been some misreporting about some stuff and I wanted
to clear that up but this is just helping out journalists out there who are willing to do the
hard work by even opening up a Wikipedia page. So what I want to talk about was why airplane stall
and what an angle of attack gauges. So to begin to start out let's talk about why
planes how they fly, how they produce lift and so things like balloons and
dirigables they produce lift by having gas inside of a bag that's lighter than the air around them
so they float. They so it could be just hot air balloon or something like helium or hydrogen inside
of a bag that all works. Those vehicles don't suffer from any kind of aerodynamics stall
because they produce most of their lift via this gaseous air so we won't be talking about that.
And things like hairier jets for you people in Europe who definitely know those we used them
here in the Marine Corps or even quadcopters, wrongly named drones as people call them, use a principle
called thrust vectoring which is producing lift by directing a bunch of propulsion
you know against gravity and they causes the thing to rise while things like the hairier jet
use that for could hover and take off that way. That again is not doesn't have anything to do
with the weight airplane produces lift or has anything to do with stalling. And then
helicopters do produce lift the way airplanes do they have a rotating wing and they do
suffer stall effects but I won't discuss those either because I really don't know anything about
helicopters. What I do know about is airplanes have been flying airplanes for many decades now
and I do know about airliner type aircraft I've never flown a 737 but I've flown planes that are
similar to it and I've flown planes with angle of attack gauges where you can actually see them
and I fly airplanes right now that have angle of attack sensors that feed information into the
flight control computers to help control the aircraft. So anyway airplanes produce lift in two ways
the first way this isn't an order but only in the way we're going to discuss them. The first
way is just general deflection of air off the body or the wing the bottom of the wing
that air hits it it deflects and you produce an equal and opposite reaction that creates some
lift. This is how kites fly, flat kites like a typical little diamond kite that you might have
flown as a child or maybe you still fly them now. Those fly because they deflect air downward
you get an equal and opposite reaction producing a vector up that can if it's strong enough if you
have enough wind can produce lift enough to lift something up. The second way which is the
really the the meat of it all is that airplanes produce lift by the thing called the Bernoulli
effect where gas that's accelerated drops in pressure and so an aircraft wing generally are
curved on the top and flatter on the bottom this is none of these things are 100% true there are
there are symmetrical wings that fly but not going to go down that rabbit trail this is for general
aircraft including airliners they they have curved up proportion of the wing the bottom wing is
flat or slightly curved or maybe convex for real slow flying aircraft and so the air going
across the wing on the top gets accelerated and as it as the wing goes through the air and it
drops in pressure and then so you have high pressure at the bottom and low pressure at the top
and that pushes the aircraft into the air so if you go fast enough you have a big enough wing
you produce enough lift to lift the aircraft off the ground and that's how airplanes produce lift.
So now stalling of a wing is a term that you hear sometimes of people misunderstand this
so an airplane wing stalling has nothing to do with its engine gliders have no engines and they fly
and they can they stall just like any other aircraft everything aircraft they just use gravity
for their energy source and so so it has nothing to do with an engine or anything like that it's
an aircraft wing is considered to be stalled when that air flowing over top of the top of the wing
becomes so disturbed that it no longer it doesn't have the low that low pressure
and their aircraft would fly and that can happen for a number of different reasons it can happen
because if I saw your wing it can happen that that brown that top player can be disturbed because
of dirt on the wing and so it's so definitely shape of the wing matters and disturbing the shape
can cause it to quit producing lift now the most
most most stalls of the wing that that that separation of that uproar air on the wing
most stalls happen when you exceed a thing called the angle the critical angle of attack
so the angle of attack of an aircraft is the relationship of the long axis of the wing
which is generally in in line with the fuselage with the body of the aircraft and the error it's
moving through is nothing to do with its general attitude towards the ground or or anything like
that when we fly aircraft on instruments we we do that using instruments that give us our
relationship to the earth and that's what you see in those those automatic or see the artificial
horizons but that is nothing to do with the angle of attack of the aircraft you can have
the angle of attack of the aircraft is just the relative deflection of the cord line that's what
that's what the the long axis of the wing is called but the should say long axis so that's the
axis from the front of the wing to the back of the wing not from the wing tip to wing tip from
the front of the wing to the back of the wing so the cord line the the relationship of the
cord line to the error going over it is called angle of attack and when you exceed the angle of
attack of whatever and it's varies for different airfoils you the wing is stalled and won't produce any
lift and this can happen at any speed and at any attitude you can stall the plane going straight up
you can stall the plane going straight down you can stall the plane upside down and when you go to
an air show and see an aerobatic pilot doing their routine a lot of those maneuvers in those in
those planes are a function of a wing not flying being stalled having exceeded the angle of
attack and controlling that so the plane is still controllable even though it has exceeded the
angle of attack it's just not flying anymore it's not falling falling with style so
when so you have to divorce the idea of attitude and relationship to the earth with angle of attack
also you have to divorce speed aircrafts we talk a lot even in the aviation circles about
stall speeds but stall speeds are always taking with a grain of salt because they vary with the
aircraft's weight the angle of bank and how quickly you move the controls those things all
will affect what you see on your airspeed indicator when the aircraft stalls now so so generally
you might say a plane has a stall speed of let's say a smaller plane maybe 50 knots that's a
level flight that would be just pulling the controls back and letting the nose and let the plane
slow down and then it'll stall and the nose will drop and go to your recovery but in
and in a turn now the plane is carrying more weight because of a centrifugal force and you get
gravity the aircraft is actually weighs more the wing needs to produce more lift and so it will
stall at a higher indicated speed that's that's the difference and it's the same angle of attack
it's at a different speed and so those two things have to be divorced when you talk AOA and
wind aircraft actually stalls well now when a plane stalls most aircraft are designed to to recover
if you look if you just let go of the controls they'll recover into back to safe flight if you
have enough altitude if some planes though especially swap doing aircraft can enter sort of stabilized
high angles of attack where without pilot input there's not going to be any recovering of the
aircraft the plane will just literally fall very stably out of the sky and you can look into the
Air France Airbus 330 accident out of Brazil a few years ago and read up and there's a vanity fair
article that has a long discussion about that very very good article so that so now it's a little bit
let's talk about let's talk about angle of attack gauges so an angle of attack gauge is a gauge
that some aircraft have that you can actually see and it will show you what the current angle of
attack is let's show you what the current relationship between the cord line of the wing and the
air flow over the wing and you can use that to fly the wing at very as efficiently as possible
and it's a very useful gauge if you've I'm only flown one aircraft that had an AOA gauge and
it's extremely useful it allows you to fly the correct speeds and the traffic pattern without
looking at an airspeed indicator and it just works like a champ great great gauges not a lot of
aircraft that have gauges AOA gauges up it's despite AOA gauges not being very common in aircraft
almost almost all I'd say all you know modern airliners have AOA sensors so these things
sense the angle of attack and with that and other inputs are able to provide information for
displays on the you know on your instrument panel so you don't actually see an AOA gauge but
that that information along with other inputs are mixed to produce all the information you need
to fly the aircraft what so then some of those systems are then integrated into sort of
automatic safety features and it's yeah there's no the investigation is not complete but it seems
maybe that's what happened with that 737 a bad AOA gauge led to the aircraft thinking it was
an installed condition and then pushing the nose over which is the correct solution for that
problem but and then the pilot's not being able to take control that the control that the
automatic input was more than they could overcome to fly the aircraft out even though it wasn't
stolen so the investigation starts so who knows that's it's a theory but I didn't really want to
address that what I wanted to address was just the poor reporting and people saying AOA gauge
measuring the angle of the nose how high it is it's just it has nothing to do with nose angle
in relationship to the earth it has everything to do with the air going over the wing and
the reasons aircraft the reason reasons aircraft would fly and fall is simple in the sense that
it's just has to do with exceeding the critical angle of attack but it's very it's it's such a
dynamics you know the aircraft is moving three dimensionally in space and it it you can exceed
the critical angle of attack in any attitude and at any airspeed so it's it's something that's
that's probably not taught a lot and it's not really thought about a lot but it's an important
concept to understand and and I thought of help you the Hacker Poet Radio community to to
be able to understand that and and have a better grasp what's going on and it just realized that
the journalists they don't really do a lot of hard work that's why I'm helping out
that's why I'm helping out to fill in some of those gaps anyway enough rambling thanks for listening
uh do you have any questions or feel free to email me or post a comment or make a show
and I'm just trying to know how crawling back under is rock good bye
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