You know I've read about operation ceilings for years, not until this video did I understand what actually causes them. Would be interesting to see that graph for different planes: airliners, early prop planes, SR-71, modern jets, concorde etc
High-speed buffet is something that is only really a barrier for modern jet powered subsonic aircraft. The phenomenom is better known to the public as the "sound barrier". This means that prop planes simply can't fly fast enough to achieve high-speed buffet under normal circumstances (although in World War 2, some of the fastest planes had problems with it during dives), and supersonic aircraft have wing design that allows them to tolerate it, thus allowing them to, well, fly faster than the speed of sound. There's still a reasonable concept for "coffin corner" for any aircraft, but for supersonic aircraft, as well as "slow" aircraft, it's more just the point where your stall speed catches up with your maximum airspeed.
@@Keldor314 "A prop plane simply can't fly fast enough" Eh. Something like a Tu-95 might be able to push its critical mach. The things have comparable top speed to jet airliners.
@@petersmythe6462 This was first encountered with the P-38 during dives, it was the only plane that could both fly fast and high enough for this to happen.
The SR-71 is a Unique beast. It leaked like a siv on the ground but at operating altitude, it was just fine. Rumors are the successor to the SR-71 (which is still classified) uses an alternative power plant and propulsion system. That's about it. The name and it's very unique, and just mere rumors.
I read that while piloting the U2 at very high altitude, 90,000 feet more or less, the pilot has to maintain air speed to within 5 knots. Go above or below and the U2 plane will stall and fall out of the sky. This video helps explain why.
@@triggas80 They drop like rocks when stalled, and controls do nothing until they regain sufficient speed. A heavy fast plane can drop thousands of feet before regaining control, and passengers fall back into their seats.
I kept seeing this channel recommended to me in my feed, this video specifically, and I thought to myself, "I'm an avid student of aerodynamics and flight, I know what coffin corner is. Surely, I don't need to re-learn it." Turns out, it doesn't matter. Between the beautiful explanations, and an always-captivating Australian accent (seriously, how do Aussies always have beautiful speaking voices?), I found myself enjoying an explanation in 5 minutes that I had spent 30 minutes suffering through in Uni.
Just found this channel recently. The videos I have thus far seen look great. I am no pilot, nor am I likely to become one. However I find the different aspects of how planes fly to be a fascinating topic and as such, videos like what you guys and gals are making are great for someone like myself who has some understanding of planes and how they work, but also have garnered all of that understanding on their own. Keep up the good work.
Crisp clean audio, simple yet effective graphs, and visual aids that are straight forward and not overly complicated for the specific subject matter. A+!
Great video. So concise and clear! I have been working on a russian aircraft, the MDB M55 Geofisika, holding the world record for highest tangential altitude, higher than the U2. I remember the pilot told me at that altitude the buffet margin was 15 kn only. .
@@flightclubonline De nada! I love your short videos. A suggestion for a future featured video: why high altitude aircrafts, like the U2 and the M-55, look like gliders.
@@pagheca That is, more or less, answered by this exact video. By designing them like gliders, you significantly reduce the mMin, this increasing the total height of the triangle
0:30 altitude is just one of several factors that dictates stall speed. It isn't just altitude. Load factor, total weight, temperature (air density)... location of center of gravity, power, power location (nose, wing, tail), and power type...
They aren't trying to explain what determines the stall speed of any one aircraft, they're trying to explain what causes the coffin corner. In that regard, an aircraft's stall speed increases with altitude. If this was a video about what factors dictate how aircraft are designed in regards to stall speed and pre- and post- stall characteristics, they would mention those factors. But it's not, so they aren't going to make an hour long segment on irrelevant pedantry.
FO Bonin was blamed for not understanding this very dangerous situation which developed in a storm on AF447.Too much of criticism on Bonin. Buffets due to a stall or an overspeed or that created by the storm were difficult to ascertain given the time and position in which he were in. His AOA reached 50 degrees and the computers stopped telling him that the plane was stalling, while the plane was in straight and level flight.If the sidesticks moved together and the AoA indications were shown to Bonin .....AF447 might not have occured. Nice vid as always!!!
"Too much criticism on Bonin". Bullshit. He was a plain dumbass. No excuse for him. He fucking kept the plane stalling till the ocean. He had 35000 feet and 4 minutes to understand what was happening. A 10 year old kid playing FS2000 would have done a better job.
Read this chronology to see how stupid the crew was: it.wikipedia.org/wiki/Cronologia_del_Volo_Air_France_447. Original accident report: www.bea.aero/docspa/2009/f-cp090601e3/pdf/f-cp090601e3.pdf
@@itellyouforfree7238 well, there were several severe things that contributed to the crash, as always. But I'm on your side, i think the CoPilot should have been aware of the situation, or if not he should have at least given the controls to the more experienced FO next to him. He just pulled back on the stick, not having any clue what's really happening. However, in Flightsim this is way easier to understand i think, given the circumstances of night, stormy... terrible accident nonetheless.
Excellent description. Of note, on modern airplanes the limits are visually displayed as shown at 0:26. I spent a lot of time on the MD-11 and it was common to see these limits depicted by the airspeed indicator at high altitude. As expected, the limits were reduced when in a turn and after an extended period of cruise (hours) they would decrease and in many cases disappear altogether. While they were designed to allow a margin of error, in all cases they were respected.
I think you mean "elevators". If the plane was stalled, the nose was pitched up at a steep angle the turbulent flow from the wings did indeed cross the elevators and the usual procedure to un-stall the aircraft didn't work. It was called a "deep stall".
Raising the elevators on the 727 aided in reducing both high speed and low speed buffet, but in extreme conditions it would still be affected. I believe the F-101 was one of the first to use this concept, followed by commercial examples like the DC-9 and B-727. The F-4 used elevators (actually stabilizer) on the centerline that actually drooped to avoid the problem (negative dihedral).
It doesn't sound like a good idea. Those warnings are there for a very good reason and a lot of AC crashes have come from pilots either ignoring them or disabling them all together.
Enjoyed it! However, if an airplane somehow got into that coffin corner, would neccesarily accepting a stall and then recover be the only way to solve this?
Thank you for the good question. The answer is complex but accepting a stall is probably not a good solution. This document is a good resource. Have a look at the "High Altitude Aerodynamics - Principles" section: www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/ap_upsetrecovery_book.pdf
A structurally tough fighter plane like an F-15 could probably stall in the coffin corner and fall and still be able to recover at a lower altitude. A *very* tough plane like the X-1A research plane were built to withstand insane amount of G-forces and it actually did recover from extreme high altitude/high speed stalls. However, most passenger airliners and other civilians planes will probably break apart midair. Entering the coffin corner is NOT recommended in most airplanes.
There is no good way out, hence "Coffin Corner". Any increase in speed will cause loss of vertical control. Any decrease in speed will cause a stall. You can't climb, decent will add speed leading to loss of vertical control, attempting to slow down will lead to a stall, and trying to increase speed will lead to loss of vertical control. A stall recovery will lead to adding speed to recover from the stall. Generally any way out of the coffin corner either ends with inflight breakup or lithobraking... If you could manage it, a protracted stall might allow one to reach denser air and regain control, but the problem is you have almost no control authority to enter or stabilize such a stall, and if you had enough control authority your Vman would be higher so you would just be having the same problem at higher altitude and speed...
A easier way to explain it is to use smaller planes as it is easier to visualize. You plane can only go so fast before the wings rip off. Aka airspeed limit. You also have a fixed wing area. As you climb the air thins but you can still only go so fast. Lets say your in a Cessna 172 your limit speed is 125 knots. at 0 ft it takes only maybe 60 knots to make enough lift to lift the entire plane. HOWEVER at higher altitudes such as 10k ft you must be going around 100 knots to support the same weight. Eventually those 2 numbers cross and that point is your service ceiling. For smaller planes which don't have to worry about mach effects you can have the throttle all the way in going full power and you will just stay at the same height. (around 12k ft for a small plane). Its like as you go up your wing gets smaller and smaller.
Due to lower density of air and Lower pressure, the Mach number for buffeting decreases with height as the instability of airflow over the tail wing is usually higher due to a lower density so air compresses more quickly. Think of it as squishing water and dough, the dough is hard to squish, like high density, low altitude air, and the water is easy to squish, like low density high altitude air. The more squish, the more compressive the fluid and the easier it can buffet. Compressibility is a pain but reading from Wikipedia online should suffice if you want more reading.
2:28 "the mach number for the high speed buffet decreases with increasing altitude", does not mach(mcrit) stay constant for high speed buffet? It should have been TAS I think???
Well explained. Numerous aircrew and passenger lives were lost as a result of not observing this. IIRC Aeroflot's Tu-154 stalled and crashed at Uchkuduk in 1985 after a "coffin corner" high altitude excursion.
Wait… isn’t Mcrit and therefore MMax roughly constant with altitude for an aircraft? Max (buffet) values for TAS, IAS, CAS and EAS all decrease with altitude, but not the max Mach no. So, shouldn’t the chart showing Min and Max airspeeds show an effectively vertical line for Max value if it’s being expressed as Mach Number and a sloping line if represented by any other airspeed?
Very informative, guys. I wonder where I should look (other than a high performance instructor) for more information on how CAS/TAS/Mach are all related and how to understand the relationship intuitively?
A good rule of thumb is TAS increases 2% per 1,000'. If you're indicating 300KCAS at 25,000' your TAS is 50% higher (450TAS). Back in my 727 days some of the old heads flew pretty fast if we were late. The 727 had very high limits for a transport- Vne 400kts, Mmo .9M. Once in a while we'd get Mach buffet at .88 or so. An inexperienced F/O would instinctively pull back (we're flying too fast) which only made it worse since the increased AoA increased the speed of air over the upper wing surface where the shockwave was forming. The correct response was an immediate thrust reduction. Finally, many transports don't have the thrust to reach the coffin corner so it's not an operating concern.
Thank you for the video. There are however many wrong things said. To name a few: - at a given weight, Stall speed increases with altitude : at a given CAS, Mach Number increases with altitude, and increasing Mach Number decreases both stall AoA and the lift versus AOA Curve. In other Words, your stall speed maybe 150kt CAS at SL, but can be 180kt at FL380 - high mach buffeting is a function of Mach and incidence, primarily (it may vary a bit with altitude due to reynolds effect on shockwaves). When you fly at Sea Level, your VMO (lets say 330kt , which is Mach 0.5 at SL) prevents you from flying at a Mach number where Buffeting may occur. When flying at higher altitudes, you fly at a given mach number (CAS is way lower), and at this mach number, if your incidence is too high (e.g too heavy or maneuvering at high load factors), you may encouter buffeting. That is why regulations require that the operating enveloppe (at a given weight) is being limited by a minimum maneuvering capability. To put in a nutshell, when altitude increases : your lower boundary increases due to the increase in stall speed, and your upper boundary decreases (due to margins to buffeting, or simply due to MMO itself), up to a point at which the margin may be as low as a few knots (check U-2 spyplane info).
I was looking for news on the Ukraine War, and this channel pops up. As an airline pilot, of course, I was curious about its contents, and I loved it. I immediately subscribed. Good job and two thumbs way up.
You didn't really explain why the coffin corner is so deadly. The problem is you can't speed up because it will result in shock waves disrupting airflow over the elevator resulting in a loss of pitch control, which in most aircraft will result in a pitch down which will result in even more speed. This cycle generally only ends with lithobraking (slowing down by flying though rock). You also can't slow down because that result in an aerodynamic stall, and recovery from stall requires adding airspeed which puts us right back into the overspeed regime. Similarly attempting a controlled descent will also result in over speed with the same result. Attempting to climb will just lead to a stall. The only thing that might save you is flying into colder denser air, but you can't even turn to get to that air because the turn will cause you to stall as well. Basically as long as everything keeps working perfectly and you don't run out of fuel you can fly indefinitely in the coffin corner but as soon as anything changes you're going down and there won't be any way to regain control in most cases. There are two ways of accidentally ending up in the coffin corner. The first is flying into a sudden increase in headwind. The other is to have been flying with a strong tailwind that suddenly stops.
‘Coffin Corner’ in US football is the sideline and goal line meeting where it’s valuable to land a punt. At least it used to be. I wonder which use of that term came first.
Re stall angle and extreme altitude/speed. Are you implying that Mach effects add to the very high altitude incipient stall, in other words the high angle of attack flow path can induce a local shock? This part of the video caught my attention. Nice video, thanks.
But shouldn't the air resistance decrease when you go to the higher altitudes and therefore the maximum speed you can go should increase rather than decrease before you hit the turbulent eddies and stall? What am I missing here?
Wait a second. Why is the high-altitude stall AoA different from the low-altitude stall AoA? I’m an aerospace engineer and I don’t think I’ve heard that before. It’s that a Reynolds Number effect?
Intersting, didnt know that. Also didnt know how much smaller the actual operational range is with maneuvering margins in place. always wondered why planes didnt fly as high as possible
1:09 it’s incorrect. IAS stall speed does increase with altitude due to compressibility effects (IAS over-reads) and lower AOA stall. Otherwise the stall speed would not be increasing on the speed tape with increasing altitude. I ❤️ your channel btw. =)
*Fair warning about BUFFET* : The most common flight civilian trainer (US at least) is the Cessna 172. I have not always experienced Buffet. Neither, apparently, did AF447. Designed in? Yes. Foolproof? No.
(and I should add) ...that's the trouble with fly by wire. Induced Buffet can be filtered out or Stick Shaker added, by software. MCAS is a perfect example of software between the control surfaces and the Pilot that betrayed all on-board.
Another fly-by-wire example is in 2013 when a Russian Test Pilot's resourcefulness saved himself and an Su-35S from a Flight Control Failure starting from gear-up until the Pilot's _incredible_ landing 50 minutes later.
1:40 That's incorrect. Altitude has nothing to do with critical angle of attack. In other words, buffeting or flow separation and stall ALWAYS happen at the same angle of attack for any given airfoil, ie wing.
Thank for leaving a comment but I believe that this is video correct as aerodynamics at high level behave differently. You may be interested in this article about the 2009 Air France Flight 447 accident: www.ainonline.com/aviation-news/2012-05-14/understanding-high-altitude-aerodynamics-critical
Angle of attack only matters because of the pressure effects it has behind the wing. Altitude, of course, affects the pressure. Thus, both factors must be considered when understanding flow separation
![Coffin Corner Explained - [How YOU can spot the coffin corner by looking at the Airspeed Indicator]](http://i.ytimg.com/vi/KPJxz39Ieao/mqdefault.jpg)
This channel is a hidden goldmine
I tend to agree. I’ve watched some excellent explanations of very complex issues.
You are a hidden goldmine
1)First rule about flight-club, don't talk about flight-club
@@Poop-nu1so damn you did it before I could
the FF you
You know I've read about operation ceilings for years, not until this video did I understand what actually causes them. Would be interesting to see that graph for different planes: airliners, early prop planes, SR-71, modern jets, concorde etc
High-speed buffet is something that is only really a barrier for modern jet powered subsonic aircraft. The phenomenom is better known to the public as the "sound barrier".
This means that prop planes simply can't fly fast enough to achieve high-speed buffet under normal circumstances (although in World War 2, some of the fastest planes had problems with it during dives), and supersonic aircraft have wing design that allows them to tolerate it, thus allowing them to, well, fly faster than the speed of sound.
There's still a reasonable concept for "coffin corner" for any aircraft, but for supersonic aircraft, as well as "slow" aircraft, it's more just the point where your stall speed catches up with your maximum airspeed.
@@Keldor314 "A prop plane simply can't fly fast enough"
Eh. Something like a Tu-95 might be able to push its critical mach. The things have comparable top speed to jet airliners.
@@petersmythe6462 This was first encountered with the P-38 during dives, it was the only plane that could both fly fast and high enough for this to happen.
@@petersmythe6462 Maybe, but the prop tips could go supersonic first resulting in some serious damage to the blades.
The SR-71 is a Unique beast. It leaked like a siv on the ground but at operating altitude, it was just fine. Rumors are the successor to the SR-71 (which is still classified) uses an alternative power plant and propulsion system. That's about it. The name and it's very unique, and just mere rumors.
I read that while piloting the U2 at very high altitude, 90,000 feet more or less, the pilot has to maintain air speed to within 5 knots. Go above or below and the U2 plane will stall and fall out of the sky.
This video helps explain why.
😯👍
Was going to say something about it living in the cusp of that corner, but I got here a bit late.
Now imagine some SAM locking unto you and launching a missile
You cant really maneuver, you are a sitting duck essentially
Planes are meant to glide tho they don't just drop ?
@@triggas80 They drop like rocks when stalled, and controls do nothing until they regain sufficient speed. A heavy fast plane can drop thousands of feet before regaining control, and passengers fall back into their seats.
I kept seeing this channel recommended to me in my feed, this video specifically, and I thought to myself, "I'm an avid student of aerodynamics and flight, I know what coffin corner is. Surely, I don't need to re-learn it."
Turns out, it doesn't matter. Between the beautiful explanations, and an always-captivating Australian accent (seriously, how do Aussies always have beautiful speaking voices?), I found myself enjoying an explanation in 5 minutes that I had spent 30 minutes suffering through in Uni.
Oh wow, that's so kind of you. Thank you very much for your feedback.
Now I understand a lot better the difficulty of flying the U2.
Just found this channel recently. The videos I have thus far seen look great. I am no pilot, nor am I likely to become one. However I find the different aspects of how planes fly to be a fascinating topic and as such, videos like what you guys and gals are making are great for someone like myself who has some understanding of planes and how they work, but also have garnered all of that understanding on their own.
Keep up the good work.
Welcome aboard!
Your videos never disappoint! Loving these ATPL videos ❤️ hoping for more to come.
Yay! Thank you!
What accent is it? Is it kiwi or aussie ?
Crisp clean audio, simple yet effective graphs, and visual aids that are straight forward and not overly complicated for the specific subject matter. A+!
Great video. So concise and clear!
I have been working on a russian aircraft, the MDB M55 Geofisika, holding the world record for highest tangential altitude, higher than the U2. I remember the pilot told me at that altitude the buffet margin was 15 kn only. .
That's insane! Thank you so much for sharing.
@@flightclubonline De nada! I love your short videos.
A suggestion for a future featured video: why high altitude aircrafts, like the U2 and the M-55, look like gliders.
@@pagheca de nada? Kkk
@@pagheca That is, more or less, answered by this exact video. By designing them like gliders, you significantly reduce the mMin, this increasing the total height of the triangle
Very much the same with U-2 and TR-1 family...
excellent material, dear Flight Club team! these videos can also be useful for those struggling with ATPL theory
Thank you so much for not playing music! Great video. Subscribed.
Thanks for the sub!
Loved the Aussie accent on that Sheila.
Though my knowledge on this is next to 0, I feel like this video explained it really well because I actually understood it.
Wow, that's good news to me. Thank you!
Coffin corner was an expression used by the Merchant Marine for the tail end of convoys, where tankers or munitions ships were located.
This channel got me through CPL Systems and Aero
Loves the visuals. What software do you guys use?
Thank you! Adobe after effects.
This explanation could not possibly be any better
0:30 altitude is just one of several factors that dictates stall speed. It isn't just altitude. Load factor, total weight, temperature (air density)... location of center of gravity, power, power location (nose, wing, tail), and power type...
They aren't trying to explain what determines the stall speed of any one aircraft, they're trying to explain what causes the coffin corner. In that regard, an aircraft's stall speed increases with altitude.
If this was a video about what factors dictate how aircraft are designed in regards to stall speed and pre- and post- stall characteristics, they would mention those factors. But it's not, so they aren't going to make an hour long segment on irrelevant pedantry.
Brilliant presentation, you are gifted communicators.
Great animations. Easy to understand.
FO Bonin was blamed for not understanding this very dangerous situation which developed in a storm on AF447.Too much of criticism on Bonin. Buffets due to a stall or an overspeed or that created by the storm were difficult to ascertain given the time and position in which he were in.
His AOA reached 50 degrees and the computers stopped telling him that the plane was stalling, while the plane was in straight and level flight.If the sidesticks moved together and the AoA indications were shown to Bonin .....AF447 might not have occured.
Nice vid as always!!!
"Too much criticism on Bonin". Bullshit. He was a plain dumbass. No excuse for him. He fucking kept the plane stalling till the ocean. He had 35000 feet and 4 minutes to understand what was happening. A 10 year old kid playing FS2000 would have done a better job.
Read this chronology to see how stupid the crew was: it.wikipedia.org/wiki/Cronologia_del_Volo_Air_France_447. Original accident report: www.bea.aero/docspa/2009/f-cp090601e3/pdf/f-cp090601e3.pdf
@@itellyouforfree7238 well, there were several severe things that contributed to the crash, as always. But I'm on your side, i think the CoPilot should have been aware of the situation, or if not he should have at least given the controls to the more experienced FO next to him. He just pulled back on the stick, not having any clue what's really happening. However, in Flightsim this is way easier to understand i think, given the circumstances of night, stormy... terrible accident nonetheless.
Excellent description. Of note, on modern airplanes the limits are visually displayed as shown at 0:26. I spent a lot of time on the MD-11 and it was common to see these limits depicted by the airspeed indicator at high altitude. As expected, the limits were reduced when in a turn and after an extended period of cruise (hours) they would decrease and in many cases disappear altogether. While they were designed to allow a margin of error, in all cases they were respected.
How did disrupted airflow from the main wings affect airplanes with ailerons high on the tail like the 727? Thanks in advance!
I think you mean "elevators". If the plane was stalled, the nose was pitched up at a steep angle the turbulent flow from the wings did indeed cross the elevators and the usual procedure to un-stall the aircraft didn't work. It was called a "deep stall".
Raising the elevators on the 727 aided in reducing both high speed and low speed buffet, but in extreme conditions it would still be affected. I believe the F-101 was one of the first to use this concept, followed by commercial examples like the DC-9 and B-727. The F-4 used elevators (actually stabilizer) on the centerline that actually drooped to avoid the problem (negative dihedral).
I have no idea why I was recommended this but I guess today I'm going to enjoy being nerded at about pilotry going through these videos. Sweet
Welcome aboard!
Rule #1 of flight-club: you do not talk about flight-club
Im not even into the aviatics science but I find this as an incredible piece of knowledge. Thanks for the very well made video! :)
Glad you enjoyed it!
Some small jets have a "go fast" switch that disables warning about getting outside of the maneuvering envelope. These are an extremely bad idea.
It doesn't sound like a good idea. Those warnings are there for a very good reason and a lot of AC crashes have come from pilots either ignoring them or disabling them all together.
Sounds like BS.
Obviously not meant to be used outside of emergencies.
Enjoyed it! However, if an airplane somehow got into that coffin corner, would neccesarily accepting a stall and then recover be the only way to solve this?
Thank you for the good question. The answer is complex but accepting a stall is probably not a good solution. This document is a good resource. Have a look at the "High Altitude Aerodynamics - Principles" section: www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/ap_upsetrecovery_book.pdf
@@flightclubonline Thank you! I appreciate it
A structurally tough fighter plane like an F-15 could probably stall in the coffin corner and fall and still be able to recover at a lower altitude. A *very* tough plane like the X-1A research plane were built to withstand insane amount of G-forces and it actually did recover from extreme high altitude/high speed stalls. However, most passenger airliners and other civilians planes will probably break apart midair. Entering the coffin corner is NOT recommended in most airplanes.
There is no good way out, hence "Coffin Corner". Any increase in speed will cause loss of vertical control. Any decrease in speed will cause a stall.
You can't climb, decent will add speed leading to loss of vertical control, attempting to slow down will lead to a stall, and trying to increase speed will lead to loss of vertical control. A stall recovery will lead to adding speed to recover from the stall. Generally any way out of the coffin corner either ends with inflight breakup or lithobraking... If you could manage it, a protracted stall might allow one to reach denser air and regain control, but the problem is you have almost no control authority to enter or stabilize such a stall, and if you had enough control authority your Vman would be higher so you would just be having the same problem at higher altitude and speed...
@@jdrissel descent doesn’t add speed. You can descend at constant speed.
Thanks for the video, it’s very good and educational. Also easy to understand because of that beautiful voice
Thank you! 😃
A easier way to explain it is to use smaller planes as it is easier to visualize. You plane can only go so fast before the wings rip off. Aka airspeed limit. You also have a fixed wing area. As you climb the air thins but you can still only go so fast. Lets say your in a Cessna 172 your limit speed is 125 knots. at 0 ft it takes only maybe 60 knots to make enough lift to lift the entire plane. HOWEVER at higher altitudes such as 10k ft you must be going around 100 knots to support the same weight. Eventually those 2 numbers cross and that point is your service ceiling. For smaller planes which don't have to worry about mach effects you can have the throttle all the way in going full power and you will just stay at the same height. (around 12k ft for a small plane). Its like as you go up your wing gets smaller and smaller.
From 2:27 you said "" The Mach number for high speed buffet decrease with increase in altitude "" how this happens can anybody help me with this
Due to lower density of air and Lower pressure, the Mach number for buffeting decreases with height as the instability of airflow over the tail wing is usually higher due to a lower density so air compresses more quickly.
Think of it as squishing water and dough, the dough is hard to squish, like high density, low altitude air, and the water is easy to squish, like low density high altitude air. The more squish, the more compressive the fluid and the easier it can buffet.
Compressibility is a pain but reading from Wikipedia online should suffice if you want more reading.
So where are service ceilings rated? Below or at the maneuver ceiling?
2:28 "the mach number for the high speed buffet decreases with increasing altitude", does not mach(mcrit) stay constant for high speed buffet? It should have been TAS I think???
Nice explanation!
Well explained. Numerous aircrew and passenger lives were lost as a result of not observing this. IIRC Aeroflot's Tu-154 stalled and crashed at Uchkuduk in 1985 after a "coffin corner" high altitude excursion.
There was also a coffin corner in Meadowlands stadium in New Jersey, rumored to contain the grave of Jimmy Hoffa.
Wait… isn’t Mcrit and therefore MMax roughly constant with altitude for an aircraft? Max (buffet) values for TAS, IAS, CAS and EAS all decrease with altitude, but not the max Mach no. So, shouldn’t the chart showing Min and Max airspeeds show an effectively vertical line for Max value if it’s being expressed as Mach Number and a sloping line if represented by any other airspeed?
Is that correct - that the low speed buffet occurs at a lower angle of attack at higher altitudes?
As usual great video. Can you make another about INS and IRS?
Absolutely! It's on the list. Thank you.
Very informative, guys. I wonder where I should look (other than a high performance instructor) for more information on how CAS/TAS/Mach are all related and how to understand the relationship intuitively?
A good rule of thumb is TAS increases 2% per 1,000'. If you're indicating 300KCAS at 25,000' your TAS is 50% higher (450TAS). Back in my 727 days some of the old heads flew pretty fast if we were late. The 727 had very high limits for a transport- Vne 400kts, Mmo .9M. Once in a while we'd get Mach buffet at .88 or so. An inexperienced F/O would instinctively pull back (we're flying too fast) which only made it worse since the increased AoA increased the speed of air over the upper wing surface where the shockwave was forming. The correct response was an immediate thrust reduction. Finally, many transports don't have the thrust to reach the coffin corner so it's not an operating concern.
@@gerardmoran9560 Isnt there also a warning that pops up reminding the pilot?
Thank you for the video. There are however many wrong things said. To name a few:
- at a given weight, Stall speed increases with altitude : at a given CAS, Mach Number increases with altitude, and increasing Mach Number decreases both stall AoA and the lift versus AOA Curve. In other Words, your stall speed maybe 150kt CAS at SL, but can be 180kt at FL380
- high mach buffeting is a function of Mach and incidence, primarily (it may vary a bit with altitude due to reynolds effect on shockwaves). When you fly at Sea Level, your VMO (lets say 330kt , which is Mach 0.5 at SL) prevents you from flying at a Mach number where Buffeting may occur. When flying at higher altitudes, you fly at a given mach number (CAS is way lower), and at this mach number, if your incidence is too high (e.g too heavy or maneuvering at high load factors), you may encouter buffeting. That is why regulations require that the operating enveloppe (at a given weight) is being limited by a minimum maneuvering capability.
To put in a nutshell, when altitude increases : your lower boundary increases due to the increase in stall speed, and your upper boundary decreases (due to margins to buffeting, or simply due to MMO itself), up to a point at which the margin may be as low as a few knots (check U-2 spyplane info).
Concise and accurate. Excellent video. ✈
Thank you kindly!
I was looking for news on the Ukraine War, and this channel pops up.
As an airline pilot, of course, I was curious about its contents, and I loved it.
I immediately subscribed.
Good job and two thumbs way up.
Daaaamn. Did not know that. Nice vid.
What's cool is the U-2 flies almost exclusively right there 1 or 2 knots away from stall AND overspeed at altitude.
All the comments saying "I am a aviation student" or "I work with planes"
Well I don't work with planes, and I do not know why I am here.
You didn't really explain why the coffin corner is so deadly. The problem is you can't speed up because it will result in shock waves disrupting airflow over the elevator resulting in a loss of pitch control, which in most aircraft will result in a pitch down which will result in even more speed. This cycle generally only ends with lithobraking (slowing down by flying though rock). You also can't slow down because that result in an aerodynamic stall, and recovery from stall requires adding airspeed which puts us right back into the overspeed regime. Similarly attempting a controlled descent will also result in over speed with the same result. Attempting to climb will just lead to a stall. The only thing that might save you is flying into colder denser air, but you can't even turn to get to that air because the turn will cause you to stall as well. Basically as long as everything keeps working perfectly and you don't run out of fuel you can fly indefinitely in the coffin corner but as soon as anything changes you're going down and there won't be any way to regain control in most cases.
There are two ways of accidentally ending up in the coffin corner. The first is flying into a sudden increase in headwind. The other is to have been flying with a strong tailwind that suddenly stops.
You can descend without increasing speed. This is the way out.
‘Coffin Corner’ in US football is the sideline and goal line meeting where it’s valuable to land a punt. At least it used to be. I wonder which use of that term came first.
U-2 is difficult to fly, because it operates near the coffin corner.
Re stall angle and extreme altitude/speed. Are you implying that Mach effects add to the very high altitude incipient stall, in other words the high angle of attack flow path can induce a local shock? This part of the video caught my attention. Nice video, thanks.
That was really interesting! thank you.
But shouldn't the air resistance decrease when you go to the higher altitudes and therefore the maximum speed you can go should increase rather than decrease before you hit the turbulent eddies and stall? What am I missing here?
Sound's speed decrease with air density, so you have the formation of shockwaves at lower speeds
Does this apply to supersonic aircraft as well?
Yes. They just have a much higher maximum Mach.
Cool info!
Thanks!
The part of the court you don't want to inbound the ball to?
Wait a second. Why is the high-altitude stall AoA different from the low-altitude stall AoA? I’m an aerospace engineer and I don’t think I’ve heard that before. It’s that a Reynolds Number effect?
Mainly compressibility I think.
Why Mach max decrease with altitude increase ?
Good morning to all from SE Louisiana 3 Mar 22.
My god, a TH-cam channel based on airplane topics and they call it “flight-club” genius.
Intersting, didnt know that.
Also didnt know how much smaller the actual operational range is with maneuvering margins in place.
always wondered why planes didnt fly as high as possible
Damn I thought this was going to about some special section of the cargo hold
Awesome
Does this apply to jet fighters?
Yes, but they have a much higher Mach limit.
Ohh ok this explains why flying the U2 spy plane back in the day was so difficult. It was flying close to its coffin corner
??Does this NZ narrator ALSO do the "Chickens in my backyard" videos.???
To be fair though, if you are up that high and do stall, at least you have (in theory) a fair bit of altitude to play with and correct the stall...
This isn't a problem if your aircraft is supersonic and/or has a stupidly high TWR with post-stall maneuverability..
I'll take your word for it.
Is it MOCK or MACK?
Mach
thanks
You're welcome!
1:09 it’s incorrect. IAS stall speed does increase with altitude due to compressibility effects (IAS over-reads) and lower AOA stall. Otherwise the stall speed would not be increasing on the speed tape with increasing altitude.
I ❤️ your channel btw. =)
This is what the internet was SUPPOSED to be for!
Ah yes, the buffet. My favorite buffet is Jimmy.
TH-cam Recommendations at it again... I have no idea how i even ended up here.
Interestingly, "Coffin Corner" is a term in American Football and I was very confused about what punting had to do with airplanes.
Very interesting
*Fair warning about BUFFET* : The most common flight civilian trainer (US at least) is the Cessna 172. I have not always experienced Buffet. Neither, apparently, did AF447. Designed in? Yes. Foolproof? No.
(and I should add) ...that's the trouble with fly by wire. Induced Buffet can be filtered out or Stick Shaker added, by software. MCAS is a perfect example of software between the control surfaces and the Pilot that betrayed all on-board.
Another fly-by-wire example is in 2013 when a Russian Test Pilot's resourcefulness saved himself and an Su-35S from a Flight Control Failure starting from gear-up until the Pilot's _incredible_ landing 50 minutes later.
@@arcanondrum6543 buffet in FBW types such as a330/350 isn’t filtered or induced by the system. It’s a natural aerodynamic buffet.
I might have a low speed buffet for brunch.
I thought this was about a secret corner in the plane for shipping coffins by plane 😂
Well really it's when the punter drops it in the corner around the 5 yard line.....
So a supersonic jet is designed not to have shockwaves that stall out the elevator?
Yes.
So how do fighter jets fly so fast
Different planes have Different aerodynamits, Speed and Flight altitude.
different elevator placement, ussualy underor in front of wings to avoid shock waves
By having a maximum speed that’s much higher. They still have a coffin corner.
The U-2 spy plane routinely flies in its coffin corner. At operating altitude, it has to stay within a 5 knot speed range.
Nice video but where is km/h for speed and "m" for altitude. ;)
Google it.
They’re not generally used in aviation.
It is also the Pina Colada zone.
Now class, with this information, who can tell me the operational ceiling of an unladen swallow?
My theory on the Chinese crash
a 4.5min video could be that much efficient. Thanks.
Thank you.
1:40 That's incorrect. Altitude has nothing to do with critical angle of attack. In other words, buffeting or flow separation and stall ALWAYS happen at the same angle of attack for any given airfoil, ie wing.
Thank for leaving a comment but I believe that this is video correct as aerodynamics at high level behave differently. You may be interested in this article about the 2009 Air France Flight 447 accident: www.ainonline.com/aviation-news/2012-05-14/understanding-high-altitude-aerodynamics-critical
@@flightclubonline I appreciated the work you've done so far. Thank you for this article too, I have been trying to understand that for a long time.
Angle of attack only matters because of the pressure effects it has behind the wing. Altitude, of course, affects the pressure. Thus, both factors must be considered when understanding flow separation
Jimmy Buffet likes this
I always thought a coffin corner was a kick/punt in American Football.
plane was flying at "mack" .23 xD
No.. it’s a football punt coverage ?
well coffin corner is the pin end of a start line. wait wrong aerofoil orientation.
Airplane fall down go boom
Help Mr. Wizard!!! I don't want to be a pilot anymore!!!
I got tricked ! I thought this was Fight Club
🙏🙏
Thank you!
1 “correction”, it’s not just “jet” aircraft…….
If you thought the planes that flew into the twin towers were flying 550mph…