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Soapbox: Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. Stall airspeed varies wit

Soapbox: Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. Stall airspeed varies with a number of factors; this includes the mods described in the article, and weight change from burning fuel, passengers, payload etc. AOA is more invariant to that as a metric for choosing stall speed, speed down final etc.

sumofproducts 3y ago
I was very skeptical of this until I had the chance to fly one of those brand-new C172 models that come equipped with 'em. They're so convenient! Sure, ye olde haptic feedback + inner ear + stall horn/shaker combo has always worked for me—but if you are a new or overwhelmed or complacent or unlucky pilot, having a big angry indicator sitting atop the glare shield furiously (visually & audibly) informing you of the approaching cross-control stall that is about to bury you in your base-to-final grave makes danger IMPOSSIBLE to miss. The LEDs were bright enough to be clearly visible even under direct sun, but the Geiger-esque clicking and chattering increasing in urgency as I approached critical AoA made it for me. No need to put your head down or even alter your scan to include it: you can hear trouble coming!
- speedbird 3y ago
  This +++. Most important parameter is AoA and we only have poor proxy for it in most GA. Nuts
ultrarunner 3y ago
Soapbox next to your soapbox: GA planes are old specifically because of the FAA and their overly restrictive regulations. The cost involved to create an AoA sensor & readout is minimal and at least one company has done it with an IMU only. The cost to certify, sell, and install an AoA sensor (in terms of both money and time waiting to get on the schedule of an FAA-blessed installer) is more than most people find it to be worth. Food for thought: this also applies to shoulder harnesses in many cases. Aviation could be cheaper, safer, and better in general if the FAA was not stuck in the 60s.
- sokoloff 3y ago
  AoA indicators are able to be installed in certified aircraft as minor modifications, per the FAA policy from 2014. There are FAA regulations that are overly conservative IMO, but I think the FAA has a sensible stance on AoA indicators.
  - almostnormal 3y ago
    CS-SC251c in the EU.
- jrockway 3y ago
  I don't think that's completely true. There is a combination of market size and regulatory burden; not a lot of people are buying GA aircraft (compared to say, the number of people buying iPhones), so there isn't an enormous financial incentive to get people out of their C172 or Bonanza. I also think that these old airplanes are really ships of theseus. Maybe there are some original stickers and seats, but that's about it. Safety and avionics upgrades on these old airframes are definitely in the financial reach of many readers of this forum, and I'm sure many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups. Day to day they probably feel a lot like airline pilots.
  - vdqtp3 3y ago
    > many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups Yes and no. They're out there, but they aren't as common as you'd think or hope. AoA in particular is rare. There's an awful lot of planes that are still running GNS430 or GNS530s (probably more than any other single setup), and more than a few with the original nav/comm equipment like the KX170B. A real glass panel (something like the G1000 or G3X) is really rare in an old plane. Maybe 5-10%?
- KennyBlanken 3y ago
  The FAA is stuck in the 60's because there is a massive industry supporting the ancient technologies in general aviation. Modern stuff, like you point out, is far more reliable, cheaper, lower power consumption, and more functional. That better reliability means less need for aircraft mechanics and avionics shops. Nobody would want their discreet component transponder overhauled if it could be replaced with a cheaper unit that uses modern wizardry like logic chips or even (gasp) a microcontroller. Ditto for leaded fuel air cooled piston engines with manual mixture controls that require teardowns all the time. That bullshit is only still around because Continental and Lycoming want it to.
andoando 3y ago
But we got a nice tea kettle whistle to tell us were about to die.
- buildsjets 3y ago
  I've always thought it sounded like a kazoo. Or sometimes a harmonica. But I like the imagery of a a little tea kettle on a hob under the panel.
gameshot911 3y ago
Gentle reminder that it's good practice to define your acronyms at least once, particularly for audiences they may not be SMES.
- stordoff 3y ago
  SMES = Subject Matter Experts? (searching SMES/SME mostly brings up small and medium-sized enterprises)
  - mango7283 3y ago
    Yes, subject matter expert is what it means in that context. Now I need an SME in linguistics to tell me if the usage as an acronym on that sentence is irony or not.
lovecg 3y ago
I’ve been thinking that now that we have glass cockpits the airspeed indicator could automatically reflect the current stall speed under all conditions. I.e. green arc could shrink in a steep turn, etc.
- the__alchemist 3y ago
  I concur that this would be an equivalently-useful mechanism to displaying AOA directly.
teeray 3y ago
My favorite anecdote I heard of from a flight instructor is that of a cargo plane taking off that had some heavy vehicle tied down in its hold. It broke free of its straps during takeoff and rolled to the back of the aircraft, which shifted the CG such that the plane entered an unrecoverable stall and crashed.
- aaronharnly 3y ago
  I’m not sure if this is the one your instructor was referencing, but there was a fairly notorious such event in Afghanistan about a decade ago. https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://www.faa.gov/lessons_learned/transport_airplane/accidents/N949CA https://www.faa.gov/lessons_learned/transport_airplane/accid...
  - wkat4242 3y ago
    Also the excellent (as usual) write up from Admiral Cloudberg https://admiralcloudberg.medium.com/strength-in-numbers-the-crash-of-national-airlines-flight-102-4d693bf58eeb https://admiralcloudberg.medium.com/strength-in-numbers-the-...
- wlonkly 3y ago
  There is a video which makes its way around the Internet regularly of this crash[1] which was attributed to exactly that, killing all seven on board. (Which makes it pretty heavy for an anecdote, admittedly.) [1] https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://en.wikipedia.org/wiki/National_Airlines_Flight_102
analog31 3y ago
I'm not a pilot, but now I'm curious. What do you actually do if the plane stalls, or is about to do so? Other than die?
- Toutouxc 3y ago
  You decrease the angle of attack, i.e. you let the nose drop a bit. When the stall has fully developed into a spin, you perform the spin recovery procedure for your aircraft. Hopefully you still have some altitude left.
- Zak 3y ago
  To add to what Toutouxc said, stalls are a fairly routine training/familiarization maneuver in most light aircraft. The typical recovery is just to push forward on the stick/yoke. A manual[0] I found with a web search claims a Cessna 185 on floats may require up to 200 feet to recover. Stalling one wing but not the other usually results in a spin, for which recovery requires both breaking the stall and stopping the rotation. The ailerons, located near the wingtips are not effective (or even counterproductive) during a spin because air is not flowing smoothly over the stalled wing; the rudder, located on the tail is used to stop the rotation. This usually requires more altitude for recovery. If you stall one wing but not the other at an altitude of 15 meters (49 feet), it's very likely you're going to contact the surface in a manner you did not intend. Inappropriate control inputs, such as trying to correct the resulting bank using the ailerons guarantee it. It's still a good idea to attempt to recover rather than sit still and pray because a more controlled impact is usually more survivable. [0] https://aerocet.com/uploads/A-10010.pdf https://aerocet.com/uploads/A-10010.pdf
ExoticPearTree 3y ago
> Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. All aircraft equipped with a six pack, you have an artificial horizon indicator which can tell you what is your angle of attack. And Cessna's have them in all planes, even 50-60 years old ones.
- jnsaff2 3y ago
  The angle of attack is the angle between the chord line of the wing and the oncoming air (or relative wind). This is distinct from what the artificial horizon measures. The artificial horizon is concerned with the aircraft's orientation relative to the gravitational pull of the Earth, indicating whether the nose of the aircraft is above or below the horizon and how much the wings are tilted relative to the horizon. Artificial horizon is not a reliable indicator of angle of attack.
  - ExoticPearTree 3y ago
    > Artificial horizon is not a reliable indicator of angle of attack. Keyword being "reliable", but it is pretty close to it. That's how you get to fly safely through clouds using only an artificial horizon indicator.

sumofproducts 3y ago

I was very skeptical of this until I had the chance to fly one of those brand-new C172 models that come equipped with 'em. They're so convenient! Sure, ye olde haptic feedback + inner ear + stall horn/shaker combo has always worked for me—but if you are a new or overwhelmed or complacent or unlucky pilot, having a big angry indicator sitting atop the glare shield furiously (visually & audibly) informing you of the approaching cross-control stall that is about to bury you in your base-to-final grave makes danger IMPOSSIBLE to miss. The LEDs were bright enough to be clearly visible even under direct sun, but the Geiger-esque clicking and chattering increasing in urgency as I approached critical AoA made it for me. No need to put your head down or even alter your scan to include it: you can hear trouble coming!

speedbird 3y ago
This +++. Most important parameter is AoA and we only have poor proxy for it in most GA. Nuts

ultrarunner 3y ago

Soapbox next to your soapbox: GA planes are old specifically because of the FAA and their overly restrictive regulations. The cost involved to create an AoA sensor & readout is minimal and at least one company has done it with an IMU only. The cost to certify, sell, and install an AoA sensor (in terms of both money and time waiting to get on the schedule of an FAA-blessed installer) is more than most people find it to be worth. Food for thought: this also applies to shoulder harnesses in many cases. Aviation could be cheaper, safer, and better in general if the FAA was not stuck in the 60s.

sokoloff 3y ago
AoA indicators are able to be installed in certified aircraft as minor modifications, per the FAA policy from 2014. There are FAA regulations that are overly conservative IMO, but I think the FAA has a sensible stance on AoA indicators.
- almostnormal 3y ago
  CS-SC251c in the EU.
jrockway 3y ago
I don't think that's completely true. There is a combination of market size and regulatory burden; not a lot of people are buying GA aircraft (compared to say, the number of people buying iPhones), so there isn't an enormous financial incentive to get people out of their C172 or Bonanza. I also think that these old airplanes are really ships of theseus. Maybe there are some original stickers and seats, but that's about it. Safety and avionics upgrades on these old airframes are definitely in the financial reach of many readers of this forum, and I'm sure many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups. Day to day they probably feel a lot like airline pilots.
- vdqtp3 3y ago
  > many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups Yes and no. They're out there, but they aren't as common as you'd think or hope. AoA in particular is rare. There's an awful lot of planes that are still running GNS430 or GNS530s (probably more than any other single setup), and more than a few with the original nav/comm equipment like the KX170B. A real glass panel (something like the G1000 or G3X) is really rare in an old plane. Maybe 5-10%?
KennyBlanken 3y ago
The FAA is stuck in the 60's because there is a massive industry supporting the ancient technologies in general aviation. Modern stuff, like you point out, is far more reliable, cheaper, lower power consumption, and more functional. That better reliability means less need for aircraft mechanics and avionics shops. Nobody would want their discreet component transponder overhauled if it could be replaced with a cheaper unit that uses modern wizardry like logic chips or even (gasp) a microcontroller. Ditto for leaded fuel air cooled piston engines with manual mixture controls that require teardowns all the time. That bullshit is only still around because Continental and Lycoming want it to.

andoando 3y ago

But we got a nice tea kettle whistle to tell us were about to die.

buildsjets 3y ago
I've always thought it sounded like a kazoo. Or sometimes a harmonica. But I like the imagery of a a little tea kettle on a hob under the panel.

gameshot911 3y ago

Gentle reminder that it's good practice to define your acronyms at least once, particularly for audiences they may not be SMES.

stordoff 3y ago
SMES = Subject Matter Experts? (searching SMES/SME mostly brings up small and medium-sized enterprises)
- mango7283 3y ago
  Yes, subject matter expert is what it means in that context. Now I need an SME in linguistics to tell me if the usage as an acronym on that sentence is irony or not.

lovecg 3y ago

I’ve been thinking that now that we have glass cockpits the airspeed indicator could automatically reflect the current stall speed under all conditions. I.e. green arc could shrink in a steep turn, etc.

the__alchemist 3y ago
I concur that this would be an equivalently-useful mechanism to displaying AOA directly.

teeray 3y ago

My favorite anecdote I heard of from a flight instructor is that of a cargo plane taking off that had some heavy vehicle tied down in its hold. It broke free of its straps during takeoff and rolled to the back of the aircraft, which shifted the CG such that the plane entered an unrecoverable stall and crashed.

aaronharnly 3y ago
I’m not sure if this is the one your instructor was referencing, but there was a fairly notorious such event in Afghanistan about a decade ago. https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://www.faa.gov/lessons_learned/transport_airplane/accidents/N949CA https://www.faa.gov/lessons_learned/transport_airplane/accid...
- wkat4242 3y ago
  Also the excellent (as usual) write up from Admiral Cloudberg https://admiralcloudberg.medium.com/strength-in-numbers-the-crash-of-national-airlines-flight-102-4d693bf58eeb https://admiralcloudberg.medium.com/strength-in-numbers-the-...
wlonkly 3y ago
There is a video which makes its way around the Internet regularly of this crash[1] which was attributed to exactly that, killing all seven on board. (Which makes it pretty heavy for an anecdote, admittedly.) [1] https://en.wikipedia.org/wiki/National_Airlines_Flight_102 https://en.wikipedia.org/wiki/National_Airlines_Flight_102

analog31 3y ago

I'm not a pilot, but now I'm curious. What do you actually do if the plane stalls, or is about to do so? Other than die?

Toutouxc 3y ago
You decrease the angle of attack, i.e. you let the nose drop a bit. When the stall has fully developed into a spin, you perform the spin recovery procedure for your aircraft. Hopefully you still have some altitude left.
Zak 3y ago
To add to what Toutouxc said, stalls are a fairly routine training/familiarization maneuver in most light aircraft. The typical recovery is just to push forward on the stick/yoke. A manual[0] I found with a web search claims a Cessna 185 on floats may require up to 200 feet to recover. Stalling one wing but not the other usually results in a spin, for which recovery requires both breaking the stall and stopping the rotation. The ailerons, located near the wingtips are not effective (or even counterproductive) during a spin because air is not flowing smoothly over the stalled wing; the rudder, located on the tail is used to stop the rotation. This usually requires more altitude for recovery. If you stall one wing but not the other at an altitude of 15 meters (49 feet), it's very likely you're going to contact the surface in a manner you did not intend. Inappropriate control inputs, such as trying to correct the resulting bank using the ailerons guarantee it. It's still a good idea to attempt to recover rather than sit still and pray because a more controlled impact is usually more survivable. [0] https://aerocet.com/uploads/A-10010.pdf https://aerocet.com/uploads/A-10010.pdf

ExoticPearTree 3y ago

> Stall speed is an approximation. It's baffling that GA aircraft don't have one of the most safety-critical measurements: AOA. All aircraft equipped with a six pack, you have an artificial horizon indicator which can tell you what is your angle of attack. And Cessna's have them in all planes, even 50-60 years old ones.

jnsaff2 3y ago
The angle of attack is the angle between the chord line of the wing and the oncoming air (or relative wind). This is distinct from what the artificial horizon measures. The artificial horizon is concerned with the aircraft's orientation relative to the gravitational pull of the Earth, indicating whether the nose of the aircraft is above or below the horizon and how much the wings are tilted relative to the horizon. Artificial horizon is not a reliable indicator of angle of attack.
- ExoticPearTree 3y ago
  > Artificial horizon is not a reliable indicator of angle of attack. Keyword being "reliable", but it is pretty close to it. That's how you get to fly safely through clouds using only an artificial horizon indicator.