How HIGH CAN PLANES fly? What is the COFFIN CORNER? Explained by CAPTAIN JOE

dear friends and followers welcome back to my channel where today we'll be talking about how high can your plane fly what determines the cruising altitude what are optimum max and recommended altitude what are the dangers of flying too high and what does all of this have to do with the shock wave of a sonic boom we've got a long way to climb so let's get started let's go number 435 write shortened right alpha short of november today's video is brought to you by the captain joe online shop click the link in the description box below to get your captain joe 747-8 today to start off we have to define the difference between the service ceiling and the absolute ceiling now the service ceiling also called the maximum operating altitude is the density altitude where the aircraft produces a climb of 500 feet per minute this is with all engines running at maximum continuous power and flying at the best rate of climb speed in clean configuration now for the 747-8 this altitude is 43 100 feet at an empty weight but comment below if you know what the maximum operating altitude is for the 747 400 freighter you'll be surprised now this altitude is the limit for an aircraft to fly at legally with passengers on board and is usually only used for testing purposes by the manufacturer in most cases operationally the aircraft would reach its service ceiling below this altitude sometimes by many thousand feet this is because the heavier the aircraft is the more lift it is required to climb now since the wings can only produce so much lift the weight determines that altitude where the climb rate will hit 500 feet per minute or in other words the service ceiling now as for the absolute ceiling this one is exactly what it sounds like this is the point where the aircraft can no longer climb and will stall if an abrupt climb is attempted this altitude is never used by commercial aircraft and we'll just leave it at that but please comment below if you know the absolute ceiling of the boeing 747-8 i couldn't find any official number but one plane that won't fly as high but can easily land on your desk is the brand new captain joe 747-8 by herper in scale 1 to 250 click the link in the description box below and it will take off towards your home today so now that we know the terms let's talk about what determines where an aircraft cruises now we know that the weight is what determines the aircraft's ceiling but why do some aircraft fly below this altitude now surely the higher the aircraft can get the more efficient it will be now this is true to some extent however many other factors can determine a lower altitude for crews for example air traffic control may not allow us to climb higher because other traffic in the area is blocking that level or there may be strong tailwinds at lower levels which would be more efficient than climbing above it it's also worth noting that as our weight decreases during flight due to the burnt fuel we can climb higher what is called a step climb such step climbs are often listed in your operational flight plan and are often caused by better tailwinds at higher levels colder temperatures jet streams etc which benefit your fuel economy now some airlines even get live updates and recommendations by dispatch to climb or descend to save fuel so often a passenger jet will start its cruise at lower flight levels let's say at 34 to 36 000 feet and slowly climb its way up to 40 000 feet after which it sooner or later will reach the top of descent if atc allows it pilots can also request a slow continuous climb over a longer period of the cruise part resulting in a half an hour climb for example it's great for plane performance and passenger comfort in 12 years i only experienced or requested such a continuous climb once we requested to climb from flight level 320 to 360 and chose a hundred feet per minute climb rate to reach our desired cruising level now comment below if you can figure out how long it took us to complete that climb now let's quickly look at what this v-nav cruise page has to show us on the cdu of the boeing 747 you'll see three different types of altitudes optimum max and recommended altitude now let's quickly talk about all three of them so the optimum altitude is based on the weight of the plane meaning with decreasing weight due to fuel burn the optimum altitude will rise then the cost index resulting in speed and predetermined fuel burn so currently we're flying in econ mode which determines the speed by the cruise cost index it also gives you adequate stall and over speed margins and lastly the pressure altitude but entered flight plan winds do not alter the optimum altitude also it is the cruise altitude for minimum fuel burn when the long range cruise mode is activated with this button right here then we have the maximum altitude now first to know the optimum or the recommended altitude can never be higher than the maximum altitude so the maximum altitude is determined by the current weight of the plane the outside air temperature so the colder the higher it will be the thrust limit because every engine has an altitude limit and the selected speed but more about that in a minute most importantly though the max altitude shall never be surpassed and the recommended altitude displays the most economical altitude to fly for the next 250 to 500 nautical miles based on the weight selected speed pressure altitude and especially the entered flight plan forecasted winds and temperatures now coming back to the selected speed near the maximum altitude now some of you may have heard the term coffin corner now this term refers to a dangerous situation when aircraft climbs too high and reaches an altitude and speed combination that prevents further climb due to stall but also prevents descent due to over speed now pilots flying near the coffin corner can quickly find themselves at risk of breaking an aircraft limitation or losing control of the aircraft now this is because a descent would cause acceleration which could break the maximum speed limit of the aircraft called mac max operating or mmo this scenario is best prevented by proper flight planning stopping the aircraft from climbing too high and being at risk of stall or over speed of course all aircrafts are designed to tolerate speeds a little higher than the stated mmo but this doesn't mean pilots can or should operate near or above this number it is called coffin corner for a reason as stall and over speed are coming from top and bottom of your speed tape now i mentioned at the start of the video that the coffin corner had a relationship to sonic booms this is because as air passes over the top of the wing it accelerates if the aircraft flies too fast a shockwave can form above the wing as the airflow accelerates to or even above the speed of sound when this happens lift is greatly reduced and the drag increases as it detaches and becomes very turbulent which can cause a phenomenon known as mac tuck so mack tuck causes the nose of the aircraft to drop or sort of to tuck under increasing the rate of descent and therefore increasing the aircraft's air speed which makes the problem even worse this can then also lead to control blanketing where the airflow is so disturbed and separated acting like a blanket over the control surfaces making them ineffective or unusable in other words it could be impossible to recover from a mac dive and that's why pilots are careful to never approach the coffin corner in the first place it looks great on pictures but it's no good for jet airliners if you are interested in learning more about the aerodynamics of high-speed flight let me know in the comments and it may become a future video that's it for today thank you very much for your time here's your checklist for today subscribe to my channel check activate notification bell check follow my instagram account check and perform a touch and go at my website check and don't forget a good pilot is always learning wishing you all the best your captain joe [Music] you

Channel: Captain Joe

Views: 316,210

Keywords: How high can planes fly, plane climbing too high, plane into space, captain Joe, captain Joe flying, high altitude, flight level, stall, overspeed, coffin corner, service ceiling, absolute ceiling, Boeing 747, altitude limits, dangerous, crash, shockwave, fuel burn, fuel consumption, fighter jet, air travel, air safety, aviation, facts, stall recovery, mach number, mach crit, fear of flying, zfnhva, tech, flying too fast, warning, flight control loss, concorde, a380, Airbus, Boeing

Id: 6vN1ammihDs

Length: 10min 38sec (638 seconds)

Published: Thu Feb 11 2021