 So, welcome to lecture number 13, which is the first lecture of capsule number 7 after the mid-sim. Today we are looking at three components of a flight, gliding, climbing and ceiling. So, again this presentation has been prepared by this student called Odet Vohara. We are already familiar with him because if you recall, he was the one who made the presentation on the atmosphere also. This is the second presentation that he prepared for me while he was here as an intern during this summer. Okay. So, the layout is very straight forward, we are going to look at some birds, we are going to look at how they glide, then how they climb and what are the limits to their altitude of employment or the operative ceiling, that is all the three things today. Okay. So, let us see the gliding flight, this is how aircraft glide, okay, right, okay. So what exactly is gliding flight? Not hitting somebody with a thermocall plane, that is not a gliding flight. Gliding flight is basically the art of silent flight or flight without any thrust. In the history of aviation, I have spoken a lot about Otto Lillianthal and so many other people. They were the ones who perfected the aerodynamics of flight by learning how to glide and it is only later on that sustained flights were possible because of the provision of power plant on the aircraft. But if you really want to enjoy flight and if you want to test your skill or airmanship as we say, then gliding flight is the most challenging and exciting thing, okay. So even though glide is a very silent flight, still we have forces acting on the aircraft in the glide and this is a dramatical representation. So we do not glide like this, okay, this is a very large angle but just to increase the visibility, we have an aircraft which is operating at an angle with the horizontal. It is mass acts downwards towards the center of the earth and from the flight path perpendicular would be the lift force. The drag force would be along the flight path opposing the flight and the angle between the path at which it operates or glides in this case with the horizontal is the flight path angle or in this case the sink angle or the gliding angle theta. Not sink angle, that is the wrong thing, it is the gliding angle theta, okay. So if you resolve the forces on an aircraft during glide, we can see that there is the lift component will be cos theta and the drag w sin theta t will be 0. So straight away we get tan of theta would be 1 by L by D, okay. I have not said D by L because we are interested in L by D as a parameter. You could always say tan theta is equal to D by L where theta is the gliding angle. So obviously if you want to have a low tan theta which means if you want to have a lower glide path angle you would like to have higher L by D. So L by D is directly controlling the angle during the glide. So hence aircraft with higher L by D will be in general gliding at a lower angle theta compared to aircraft with the lower L by D, okay. So when you glide you actually cover some horizontal distance in glide from the point where you start to the point where you hit the ground. The horizontal distance on the ground is called as the range in a glide and the range is going to increase when either the theta reduces or when the L by D max increases. In other words if you are gliding at a condition such that L by D is L by D max you will get the least angle of theta and longest range during glide, okay. So that is now how do you know at what angle I should fly, at what angle of attack I should fly so that L by D is L by D max for a pilot it is very difficult to know. So the pilot determines this only by speed and also by flight experience or flying experience. Another important point is after your glide starts how much time can you stay in the air that is called as the sink rate or the rate at which you lose the altitude D h by D t sink rate. So it is very obvious that if your sink rate is low you may travel distance less or more we do not care but you will be in the air for maximum time after your glide starts. So it is not necessary that the distance traveled will be the largest when you are operating at the minimum sink rate. The distance traveled is a function of only L by D and the angle glide angle theta but the sink rate during glide is a function of D h by D t. So we will see we will derive the expression. So from the previous figure you know where we had L equal to half rho V square SCL okay and W cos theta not equal to W but W cos theta it is equal to W when you have theta equal to 0 or when you are in level flight and we also know that tan theta is equal to 1 by L by D so that means sin theta upon cos theta is equal to 1 by L by D so cos theta will be you can replace it. Now D h by D t as you can see from the previous figure is actually the sink rate V sin theta. So I take sin theta as cos theta into 1 by L by D put it inside now you can push this cos theta inside it will become cos square theta cos cube theta rather and there is L and D so L contains CL you can replace L by D by CL by CD so you will get CL cube also inside but suppose for example a situation where theta is very small which is normally the case in the case of gliding okay. So now we want to find the condition at which what should be the CL and hence what should be the V because V and CL are connected to each other what should be the CL at which I get the maximum sink rate and I am assuming that cos theta is almost equal to 1 so therefore this expression will now become minus root of 2W CL rho s into CD by CL outside so CD square comes in CD square and CL square so there will be a cube there okay so D h by D t will become minus 2W by rho s CD by CL power 3 by 2 this is a familiar ratio we had this ratio also for the minimum power required in flight so hence it is interesting that you can get the condition at which the sink rate will be minimum so the range in the glide is maximum when you fly at CL by CD maximum the endurance or the sink endurance is maximum or the sink rate is minimum when you fly at a condition at which CL 3 by 2 by CD is maximum because that maximum will give you the lowest D h by D t so the conditions are not the same as I mentioned a few minutes ago okay and you can derive this expression by going further into it you can get this expression so the L by D for maximum endurance will be approximately 0.866 times L by D max okay so you do not fly at max L by D but you fly at around 86% of the max of L by D okay now just to get some idea about sink rate and how it changes I have taken one of the most successful gliders in the world called as the Schweizer SGS 126 it is a old version there is a new version called as 1-36 this aircraft went out of production many years ago there is a better version available but this is one of the world's most famous and popular gliders so let us see how does the sink rate of this glider change for various conditions so the same glider I have shown under 4 conditions or what are these conditions basically these conditions are the speeds at which you fly remember for the pilot there is nothing like what is CL by CD maximum what is CL 3 by 2 by CD maximum these ratios are only for us those who do analysis or performance calculations or those who do design for the pilot everything is speed so the pilot relates speed to L by D so the pilot is told that if you want to glide maximum distance glide at this particular speed if you want to be in there for maximum time glide at this particular speed then your sink rate will be the minimum so you can see the sink rate can be between 1.8 knots to 3.2 knots now knots is a standard speed unit for aviation those of you do not understand knots or do not appreciate knots just multiplied by almost 1.853 or let us say by 2 to get kilometers per hour so you will get an idea about almost 1 meter per second so it will give you an idea just multiply by almost 2 to get in meter per second that is what probably you are more familiar with so the airspeed you can see the 4 colors shown there also correspond to how much distance is covered in the glide so when the aircraft is gliding it can cover around 6000 feet all of them began from the same altitude but they hit the ground at different distances depending on the speed at which they are travelling right so while we are at this particular point I wanted to just share some excitement with you about gliding and soaring so can someone tell me the difference between these two terms as far as the aviation is concerned what is meant by gliding and what is meant by soaring what do you think anyone the mics are all around here so I will give you an example the birds are soaring and the aircraft are gliding in general ok aircraft normally do not soar they only glide but birds are the ones that are champions in soaring so now do you get yes what is your what is your view yes yeah ok that is very much close and it is correct actually essentially anybody wants to add to this soaring and gliding so pretty much pretty much true what he said but one can elaborate it a little bit more so in gliding you are only sinking down continuously you can minimize the sink rate or you can maximize the range ok but you are always coming down it is a continuous downward spiral but soaring is something where you can even go up or you can maintain the altitude for a very long time so that you cannot do unless you have a power plant but power plants cannot be there in gliders so then we use ambient wind so if you are able to maintain your altitude in air in a power off situation for a very long time mainly using the thermals as you said or upward drafts of air then you are soaring ok but you should do this without any power neither flapping the birds when they soar the eagles which they soar they do not flap their wings they are not using the propulsive power to keep up they are basically looking at the currents so sometimes they glide and then they soar and then they glide and then they soar ok so we try to emulate them in the gliders but we also have a category of aircraft called as sail planes we have gliders and we have sail planes so what do you think is the difference between a glider and a sail plane what is a glider and what is a sail plane a sail plane is a very advanced glider a very efficient glider is called as a sail plane because sail planes are designed essentially for soaring and gliders are designed basically for gliding ok but each can do the other thing also subject to the flying skill now since there is no power plant available or since there is no means of thrust then there are 3 ways of launching or 3 ways of operating a glider or a sail plane the first way is called as winch launch this is the most common one and let us have a look at what is meant by winch launch hey this is Bruno I am excited to share with you what we have been working on over the last year we have spent literally hundreds of man hours refurbishing this old glider winch and now we are winching out of Nephi Utah so these guys have made a new winch and if you are from Europe or the UK you are probably going to make a deal you see this all the time if you are from the US check this out this is going to be your winch now some of you who are not very much you will see very beautiful view views here and some people winch is at the end of the runway I was not exaggerating when I said how stinking and amazing this is here the glider is climbing faster than an airliner taking off we have about 8000 feet of rope on the drum right now we can do as much as 11000 feet and with that we can get many thousands of feet in the air above the airport with just a single launch at this point of the launch we are now getting towards the top and so the glider starts to roll forward to get ready to release the rope now the glider is almost vertical you can see you can actually hear it almost it clicks off so here is the release right here that was the back release there it goes and now we are free so we just push the nose down so that way we can maintain air speed and I am going to raise the main gear which you can see underneath us and now we are free to soar with the birds and fly for many hours with thousands of feet above the airport we have plenty of altitude to go find a thermal and enjoy the day hey thanks for joining us and hope you enjoy this video so now just a simple question there is a winch which is pulling the aircraft when the winch when the rope becomes almost vertical the rope is released and now the glider is free to fly how much time do you think it can keep flying there is no power plant what do you think so is there a limit to how long can you stay in the air what is that limit come on you can guess so let me ask you it is a different way what is required so that you do not come down upward draft of air is there a limit to how much upward draft of air is available in nature there is no limit it all depends upon weather condition location and where you are so what do you think is the world record for maximum glide after a launch how many hours do you think it has been possible for a person to stay in the air after launching take a guess is it like 2 hours or is it 4 hours 8 hours can you stay for 8 hours yes you can there is no limit it could be actually even 20 hours it all depends on where you are flying what is the condition if you keep getting thermal you can keep up in the air so the question for you on model is what is the world record for soaring after a launch let us see how many hours people have been able to stay up in the air after a single launch right winch is not shown winch is basically a drum winch is a drum on which you wind a rope or a cable and then that at the end of the runway you put that and using an electrical motor you wind it at high speed so it pulls the aircraft as it pulls the aircraft the aircraft gains altitude so the cable is still connected and then when it reaches some height you release it there is a hook in the aircraft the pilot releases it so the rope falls and the aircraft is already up so it can glide so winch basically is a thing that pulls a drum cable mounted on a drum that pulls the aircraft that is a winch and that is put at the end of the runway okay the other way in which you can launch a glider is called as aero tow this is a expensive way but here is a flying school which tries to sell itself by showing you how you can do okay so this is called as aero tow how would you describe soaring in which an aircraft schedule a flight and find your definition and then the rope is released this is expensive but it is very common in areas where there are many winch failures there are complaints that winches get stuck so this is also one very common way of doing it can you think of a third way what would be the third manner in which you can provide the force for a glider yes one can start from a high ground go down why so one can use mgh the altitude let us say there is a mountain you go to the top that is what we do in hang gliders we go to the top of a mountain and then we jump down but we are going to start from the level ground here so what can you do anything else can be done yes catapult catapult launch is also possible but catapult is like a winch only it is a type of a winch but catapult normally is slightly different because but yes I mean you can use it for launching but I would call it like a winch type only any other way you can think we can do it so we can do it by cheating by putting a small engine on the glider and saying that oh this is a very small engine it just provides minimum amount of thrust when do we need it just to take off and whenever there is a problem the engine on otherwise engine is off and the aircraft is gliding such a launching is called as a motor gliding or a motor glider it is a small aircraft actually so here is again one of the best motor gliders available today is this one it is kilometers LBD is 36 in the glide this is a sales video which says that you can do so many things so many choices so this is the engine 115 horsepower so this makes you independent of either an arrow toe or the winch so these are the three ways in which you can launch a glider now let us say you are an aircraft which has got an engine or multiple engines and it fails if you have two engines both of them fail if you have one engine that engine fails okay so what you expect is there is going to be a crash is going to come down but that does not happen so let us see what else can happen an aircraft can also glide because an aircraft without engines is a glider so this happened in a very famous incident this is a very interesting video and also when you come to the end you will know the reason why it happened and I am sure you will have a big laugh okay so this happened to a flight brand new aircraft Boeing 767 purchased by Air Canada okay let us see what happened so I think this video is only a recreation we do not have the original video obviously so it is called as a gym league glider let us see we can get quickly what happens it is a glider flight 143 it is a routine flight one they flown many times before but this time no one on board knows they have only enough fuel to reach halfway so Boeing 767 recently purchased it is on the flight everything is fine Captain Bob Pearson and first officer Maurice Quintel believe they have 22,000 kilograms of fuel in reality they have only 22,000 pounds a miscalculation with the fuel while converting volume into weight has gone unnoticed compounded by other service fuel gauges catastrophic failure so they think they have 22,000 kilograms of fuel but actually they have 22,000 pounds of fuel and a pound is basically 2.204 pounds is 1 kilogram so they are carrying 2.2 times less fuel which means they are nearly half so they planned a mission they filled a fuel and they only carried half the fuel needed so obviously now everybody grouped up not just the pilot the person who fills it the person who reports it everybody grouped up the left engine dies first so the world engine so one engine failure is not a big problem many aircraft as an altitude of 41,000 feet and only one engine they decide to make straight for Winnipeg so this is important so the altitude is 41,000 feet and one engine is not working now it has just no fuel so it has become it has shut down so what they decide is they decide that they will go to Winnipeg straight normally an aircraft is flown along a particular route so that is not a straight line that follows the air routes they will ask the ATC give us a direct routing to Winnipeg as a safety measure so that we can reach there as quickly as possible because one engine is not working finally dies the second engine also gone Winnipeg, Air Canada 143 Air Canada 143 go ahead we have just lost both engines holy cow their brand new twin engine jet has suddenly become a glider but this glider unlike any other weighs 95 tons and has 69 soles on board the plane is now descending 1000 feet for every 3 miles it moves through the air knowing its distance from the nearest 1000 feet is a loss for every 3 miles in the air so you can work out the sink rate now this is a question you can do in a tutorial you are going to sink now so at 41,000 feet they have started their glide and they are losing 1000 feet for every 3 miles so how much can they go if it is continuous 20 miles that's the airport is therefore essential with no engine power the aircraft has only basic instruments working and these won't give them the information they need because there are no engines there are no instruments now only the mechanical instrument that I taught you that's the indicator how far are we from the field now you are 35 correct make that 39 miles from Winnipeg 39 miles away is Winnipeg but with an altitude of only 8,000 feet the news from now they have come to 8,000 feet from 41,000 feet they have come to 8,000 feet Winnipeg is 39 miles away they were losing 1000 feet for every 3 miles so they can go 20 miles max you are ahead of times the co-pilot is not good but RAM is available but what will RAM give you not RAM but RAT what will it give you it can't give you power to fly RAT only gives you power for lowering the landing gear flight control systems that was there otherwise they would have not really worked because even to glide properly you need to control the angle so yes they had RAT it came down it worked but it gave power for landing gear removal etc let's see it comes in the end Bob we can last maybe another 20 miles right so now the pilot calculate that we can travel if we fly in the optimum condition travel 20 miles Winnipeg is from 30 odd miles away 43 miles away so we can't make it to Winnipeg so then they ask where do we go we are not going to make Winnipeg the only chance now is to land at Gimli Gimli is a decommissioned air force base with no control tower but it is only 12 miles away so 12 miles away there is a disused air force runway called as Gimli now because it is disused there is no air traffic control there is no safety equipment nothing in fact to their horror they realize that they don't know it but when they go there they realize Gimli is now becoming a drag race hub and there were people below running cars on the runway and there were 2 cyclists on the runway when they came into land they saw the funnel the problem now is not reaching the runway but overshooting it they are too high and they are coming in too fast so now they are beyond the range normally a pilot can slow down his airplane by operating flaps but without full hydraulics they don't have any they perform now what is called a gravity drop so understand the problem now earlier Winnipeg was far away so you cannot reach now Gimli is nearby but now you will overshoot because you are gliding and you will travel 20 miles it is only 12 miles so you have to now how do you change the sink rate by control surfaces they are not available because flaps are not working so they will do a gravity maneuver increase the drag the nose gear was 50% jammed it didn't go fully down side slipping while stepping hard on the right rudder pedal this is called crossing the controls it turns the plane slightly sideways against the direction of travel offering greater air resistance and slowing the plane down however alarming this may have seen to all on board he knows it is their only hope of getting down in one piece there is one more surprise for flight 143 they have an order the airfield is not empty as they hoped but is being used as a drag racing strip there are people on the ground there are cars on the ground so they have side slipped gone this way and then gone this way captain Pearson has never been so focused he holds on for dear life waiting for that sickening crunch as his plane skids down the runway captain Pearson realizes he still has work to do he pushes hard on his differential brakes in an effort to steer the plane away from two boys straight in front of him they were cycling at last he wrestles the metal giant to a halt with no fuel no flaps damaged landing gear and no emergency equipment it was only the decisive actions and the superb skill of the flight crew of Air Canada 143 that turned a potential tragedy into a triumph thankfully everyone was able to walk away from Air Canada Flight 143 and many things have happened to them since then but they can be sure that they will never forget the day they flew the Gimli glider so now interesting thing is what happened after this so you might think that it is a very heroic act by the pilots but both the pilots were suspended why were they suspended? because they did a stupid thing of making mistake in units they loaded fuel they are from Canada but the aircraft is now working so they think it is in kilograms but actually it is in pound the aircraft came from USA in USA they still work in FPS system so the indications are all in FPS for the fuel indicator so when it says 22,000 they think it is kilograms actually it is pound but shouldn't they know they are supposed to read the manuals they are supposed to be prepared now the people who fuel the aircraft so everybody goofed up and the emergency happened so both were suspended the licenses were cancelled and then there was an enquiry after sometime they were reinstated and then they went on one of the pilots actually only passed away in 2015