Aerospace Engineer Answers Airplane Questions From Twitter | Tech Support | WIRED

I'm Bill Crossley professor of aerospace engineering and I'm here to answer your questions from the internet this is airplane [Music] support Yeah Boy Nath asks why do commercial planes fly at 35,000 ft so at about 35,000 ft the air has less density which means less drag so you need less thrust to push the airplane through the air however the higher you get the less density there is the less thrust the engine can produce so we try to balance the thrust the engine can produce with the drag on the airplane and try to find the best

cruise altitude it's around 30 5,000 ft onion time e says as a plist I have to know how to explain the difference between models for example a 747 is 10 more plane than a 737 that's it that's PLS it's kind of a humorous comment so Boeing started with the 707 did the 727 then the 737 747 767 777 and then 787 some people think the number of the model means a bigger airplane that's not actually true it's just the order in which they came to Market lock strs asked how does GeForce work and what causes

a pilot to pass out so when you're flying in an airplane and the pilot pulls back on the stick to make the airplane go up the people and the pilot sitting inside the airplane want to keep going in the same direction but the plane pushes up on them so while the plane is pushing up all the blood is going to rush down and that's what the G forces are how much that force is number of G's is relative to gravity so I'm sitting here in my chair it's 1G the pilot pulls back a little bit

maybe it's 2 G's Max you'd ever see in a commercial airplane fighter pilots sometimes pull four five even six G's that's what caus them to black out is when that blood is running out from their brain into their feet and their legs so how do we keep them from passing out there's gits that actually squeeze their legs to help keep the blood up in their head and some Pilots even learn tricks to Grimace and scrunch themselves up to keep from passing out when they do hyg Maneuvers next up sentient stist says don't try telling me

that statistically airplanes are safer than cars well statistically they are safer than cars the chances of you having a fatal accident in an airplane is something one in 120 million trips Which is far safer than traveling by car or any other means of Transport Aviation has gotten safer and safer every single year we've gone from having a couple of fatal accidents a year to recently having one every couple of years there's been a huge Improvement in safety one of the reasons that they're safer is because the aviation industry we've got two trained pilots they've gone

through lots of training on board the aircraft have to be certified and our redundant systems multiple things so if one system fails other ones back them up and the whole air traffic management and a transport system is set up so that we know where the airplane is at all times and it's staying away from other airplanes so from a non-statistical point of view all that extra stuff we do for Aviation makes airplane flying safer than driving your car oof doof oof oof asks what happens when there's a bird strike depends on how big the airplane

is and how big the bird is and the relative mass of the two objects bird strikes have caused aircraft or helicopter Windows to break they sometimes get ingested into engines we actually design the engines to handle a bird ingestion one of the bird strikes is probably most famous is the Miracle on the Hudson where the Airbus ingested lots of geese into the engine so both engines went out and Captain Sullivan landed it on the Hudson River safely it was a question from Noah Zs landed at SFO I still don't believe that airplanes can fly I

understand the science of it but how can the wings generate that much lift the simple answer is the shape of the wing the speed of the airplane and the angle of tackle of the wing change the momentum of the air going past the airplane it pushes down on the air and the airplane pushes up kraton RSS asks can a plane fly within one engine yes it can actually the way aircraft are designed if you have more than one engine to be certified they all have to be able to operate with one engine out there's an

interesting thing you've probably noticed in commercial Aviation most of the airplanes operating today commercial aircraft only have two engines even the ones flying across the ocean 747 had four engines that was because if one engine went out you needed the three engines to get all the way to your destination or to come back to somewhere safe as engin have gotten more reliable and more efficient and bigger we're able to make aircraft with just two engines that can operate with one engine if one goes out to make it to a safe destination if one of the

engines goes out Tangerine maximum 2976 asks why is commercial Aviation not improved in the last 50 years it has improved quite a bit I think one of the things that if you're looking at the airplanes the airplanes don't look a whole lot different but they have been improved a huge amount they're much safer the engines they use are much more reliable we've moved from having multiple engines for Trans Oceanic flights to having two engines for Trans Oceanic flights electronics on the airplanes are much much smaller and much more reliable and so that makes the airplanes

lighter our impact on the environment because the airplanes are lighter and the engines are more efficient has gone down a huge amount in the last 50 years airplanes are much quieter when the airplane flies Over You on approach to the airport you hear it but it's not the roar you used to hear from the older turbo jet engines that look like skinny cigarettes underneath the wings now we got the big fat turbo fans which are much quieter so commercial aviation's improved a huge amount in the last 50 years the part about the air passengers experience

that's not the aerospace engineer that's up to the airlines that might not have improved much in the last 50 years next up RGB says what if airplanes were made of the same material black boxes are since black boxes generally survive plane crashes the plane might be intact too the black boxes are made of really strong material but the really strong material is really heavy and as aerospace engineers we have to figure out what's the right material to be strong enough to do everything needed to do and be reliable enough to make many many flights over

its lifetime but also be light enough for us to pick it up off the ground aircraft designers have settled on aluminum and composite fiber reinforced plastic are the two main things that aircraft are made of these days HSN 407 asks can I ask a flight attendant to change to an empty seat you always can ask the flight attendant there's all kinds of reasons why you might not be allowed to Airlines often use the different seats to generate Revenue so you might not be able to move to a seat you didn't pay for on some airplanes

if there's not a whole lot of passengers on them if you move to a different seat you change how the weight is Distributing that airplane and the pilots want you to be in a certain spot so the aircraft is easy to fly and stay safe Viper Says hey Aviation Twitter I have a question for you if both the pilots of a commercial airplane are compromised can't air traffic control take remote control of the aircraft answer today is no they can't because they don't have the equipment on board but actually aerospace engineers have been working for

quite a while to fly airplanes that have a lot of autonomous operations are remotely piloted the military regularly flies the predator and Global Hawk without a pilot on board the pilot or operator sits well off and they can do that to put this into commercial airlines would require a huge amount of upgrade to the equipment and it'd be just an expensive Endeavor at this point not to mention the certification issues some new entrance in Urban Air Mobility are pushing really hard at having more autonomous or perhaps even autonomous flights around a city where you don't

have a pilot on board that pilot would be remote so this is coming now minox ask is severe turbulence really safe at least from an airframe point of view from the aircraft point of view most of the turbulance will be rapid up and down acceler ations and so the airplane may drop and may climb during the turbulence but it's usually you're so high in altitude it's not going to throw you into the ground from a cruising altitude there is a concern about something called wind shear and if you encounter that as you're coming close to

an airport that can actually push the airplane down and there was a really well-known accident at Dallas Fort Worth when an airplane hit this wind shear and it actually crashed short of the runway we as an industry have put in sensors and better meteorological devices to make sure we're measuring so that if that's going on around the airport we don't fly into that next up exedran asks do planes have an MPG gauge which I think it means miles per gallon they sort of do especially modern aircraft today fuel is such an expensive part of flying

airplanes a flight from Indianapolis to New York will require several thousand pounds of fuel for that flight Airlines or anybody who operates an aircraft wants to use as little fuel as necessary and so the computers on board can track how much fuel is being burned what's the relative speed to the ground and can suggest what's the speed the pilot should fly at to be flying at the best range possible and that gives them the highest quote miles per gallon for the airplane at the trade in chick says I'm not the best at science but one

of my nerds let me know would it be possible to make an electric airplane if so what would be the pros and cons it is possible to make an electric airplane and actually there are a handful of electric airplanes actually out there already there's some small trainer airplanes two seats for people learning how to fly some of the pros are electric airplane cost a lot less to fly electricity is a lot cheaper than using jet fuel to fly an airplane or using aviation gas for a smaller airplane another Advantage is electric motors have a lot

fewer moving parts so the maintenance requirements much lower the reliability is much higher the biggest con batteries are heavy we've gotten to the point where batteries are pretty good and we can use them for airplanes for short flights but for long flights the physics just doesn't work we can't store enough energy in the battery in an airplane that's using jet a jet fuel which is petroleum based not only is there a lot of energy in that you burn it during the flight so the airplane gets lighter as it flies so if you're flying across the

ocean the airplane's a lot lighter than when it lands than when it takes off and because it's burning that fuel it means it's using less energy as you go along the distance Clyde and limbo asks how do plane wings not stap or break more often well that's because we do a good job designing them when we design an airplane we know about how many G's how strong maneuver that airplane is ever going to be able to perform and then we make sure that the wings are almost twice as strong as that maximum load that the

airplane can put in just the aerodynamics the airplane limits how many G's you can pull and then we design the wings to handle a load that's higher than that and that's why they don't snap or break next one is from cat's i1 can a science person please tell me how the drive driver of a plane can survive a noise vibration like a sonic boom it literally scared the crap out of me the pilot of the airplane won't actually feel the sonic boom when an airplane starts to go at the speed of sound the air starts

to behave differently I'm talking here in the studio my voice my vocal cords are making a pressure disturbance that's getting picked up by their microphones that's traveling at the speed of sound the airplane has enough thrust it tries to go faster than that and essentially the molecules of air can't get out of the way so instead they packed together and the properties of those molecules as a call change almost instantly so right across the sonic boom you have a change in pressure and temperature and density now what happens is that gets pushed out in front

of the airplane so if I take this airplane which is a supersonic trainer a mock cone will form in front of the airplane so the airplane won't actually be in the sonic boom but that Sonic Boom will radiate down toward the ground and that's probably what this person heard and it does sound a lot like thunder John gunderman asks can we bring back supersonic commercial flight pretty please and the answer is yes if you're willing to pay for it it's very expensive to fly fast in the speed of sound it's going to require a lot

of extra thrust to push you that far extra thrust extra Fuel and bigger engines more expensive airplane current commercial aircraft fly about 80% of the speed of sound or 85% of the speed of sound while supersonic airplanes like the Concord went almost two times as speed of sound so you can see there's a huge difference in that speed you're not allowed to fly faster than speed of sound over land currently in the US or in Europe if we can make that Sonic Boom a lot lower we can actually fly supersonic over land and it would

make it much more profitable for the operator nervous driver 334 asks I'm not an expert and then asks but why can't airports have a ramp at the end of the runway like some aircraft carriers do well the simple answer is aircraft carriers people operating on those are navy pilots and if their airplane doesn't make it off the end of the runway they know they're going into the drink we can't do that with commercial Aviation we need the airplane to have enough Runway that if the Pilot's trying to take off and something goes wrong he or

she can step on the brakes turn the engines off put on the thrust reversers and stop in time the other reason is if an airplane's coming in to land and something goes wrong in the landing you need a lot of extra margin to allow everything possible to stop that airplane in time Ralphie O8 asks why don't planes have parachutes I've always been curious well some airplanes do this is a picture of a cirrus SR20 the Cirrus is a small single engine airplane that was certified with a ballistic recovery system if something goes wrong on the

airplane the pilot or somebody else with the pilot can actually pull a handle it'll have a very small rocket that launches a parachute out and that lets the airplane sink to the ground at a controlled rate and people can get out of the accident so small airplanes can have parachutes the problem is the parachute needs to grow in size with the size of the airplane so airplan is much bigger than something like that single engine airplane the parachute would be too big it would take up too much room and be too heavy so the a

couldn't carry passengers or other Goods Primal poly says 50 years ago the X15 flew at Max 6.7 no aircraft since then has ever gone as fast but why so first off Mach 6.7 means that's 6.7 times the speed of sound we would think of that as Hypersonic flight much much faster than the speed of sound this is an X15 the X15 was a research aircraft and at the time we flew this we needed a pilot on board to make sure it could do all of its operations we used it to learn about what it takes

to fly that fast and what happens to the aircraft and the flow around it going that quickly since then we've actually flown aircraft or Hypersonic vehicles that don't have pilots on board the flight control system is good enough to do all those things and we don't put a pilot in any Jeopardy flying that fast SMI 744 99326 says it's true those jet engines produce a lot of thrust and you will get sucked into them with no real problem unfortunately it is true there's been a few incidents where that's happened also cargo containers have also been

sucked into engines when they're turned on on the ground when you're at the airport there's an area marked out usually where the airplanes parked at the gate and there's usually a spot is telling people on the ground stay out of this area Joey TV show season 2 asks generally speaking how much does it cost to build a plane I don't actually know how much it costs to build a plane because the manufacturers usually keep that as a company secret but I do know what the book price or listed price of an airplane is the 787

costs about $300 million if you look on Boeing's website caveat to that is when Boeing sells their airplanes to customers the airline might buy lots of airplanes and might work out a deal so maybe like when you go to buy a car and you end up paying less than the sticker price Airlines often pay a lot less than the sticker price but needless to say commercial airliners cost hundreds of millions of dollars godwood meter asks how many hours of Maintenance does his aircraft need for every flight hour actually the number of maintenance hours per flight

hour is an important metric for people who operate airplanes like airline pilots or even if you own your own airplane how long you can you fly it before you need to go do some maintenance commercial airplanes go through all kinds of levels of Maintenance depending on how many hours they've been flown there's some simple checks where they just look through major systems and make sure there's nothing they see in a visual inspection all the up to major overhaul where they almost take the airplane completely apart look for any kind of problems and put it back

together to make sure that that airplane can last for 30 or 40 years if you're waiting on a Tarmac or you're waiting to board the airplane you hear there's a maintenance issue that's usually unscheduled maintenance those are in most cases very minor something like a light in the fasten seat Bel signs is out they're not allowed to fly without that light working at trying to do right says I wonder why we have an air traffic controller shortage do you have any theories the airline industry continues to grow after the pandemic where it flight levels that

were way above what we saw before the pandemic in 2020 there's just a need for Aviation and there aren't quite enough people to fill those positions another thing is a lot of people have been attracted recently to other jobs Aerospace is really cool and so I'm looking forward to teaching lots of students in my classes to get them in the Aerospace industry SSB manin asks do planes need co-pilots or is it purely a safety mechanism if something should happen to the first pilot in modern aircraft that's true it really is a backup it's being redundant

we still have pilots on the aircraft to make decisions about flying airplane but for most of the airplane flights these days the pilots get to their Cruise altitude and they allow the airplane to fly itself and the pilots are on board to react to something that's unexpected or take control of air traffic control ask them to go to a different altitude Etc at fly Lakeland ask what's your favorite airplane my favorite airplane is the locked constellation it's a World War II era aircraft that was designed by locked it became the first airplane that could successfully

and reliability make it across the Atlantic Ocean not only I think it's a cool looking airplane I think it's a really neat airplane because it made the world smaller and one of the reasons I like being an aerospace engineer it's flying around the world makes the world smaller and I think making the world smaller makes the world a better place thick Cactus 85 asked how do jet engines work we like to have a sort of a joke statement here in aerospace engineering the jet engines suck squeeze bang and blow so this is a picture of

a jet engine with the cowling or the Nell taken off of it the front end has a compressor well at first it has an inlet the inlet is the suck that entrains the air into the engine then the compressor increases the pressure of the air that adds more energy to it then we add fuel to that air and we combust it in a combuster that adds a lot of heat so we've added a lot of energy to the flow it passes past the turbine which takes a little bit of the energy out to run the

compressor and then the shape of the nozzle at the back end of the jet engine makes sure we get the most push out of that exhaust so we're basically increasing the momentum of the flow from what's in the front of the engine to what's out that back and that difference in momentum is what gives us the thrust what I explained describes a turbojet engine this picture is actually a turbo fan engine and this big part at the front is a fan so in an engine like this the turbine part of the engine some of the

energy goes to the compressor some of it goes to turn this big fan this big fan accelerates a lot of air that doesn't go through the combuster that's more efficient than sending all the air through the combuster you just can't fly as fast propellers are at the extreme end of that propellers can't go very fast but they're even more efficient that's it that's are all the questions I have I hope you learn something until next time [Music]