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This is about science produced by the California Institute of Technology and originally broadcast by station KPCC Pasadena California. The programs are made available to this station by the national educational radio. This program is about airplanes meeting to discuss this subject. Dr. Albert Hibbs chief of space sciences at Cal TX Jet Propulsion Laboratory and Dr. Peter lissom an assistant professor of aeronautics. Here now is Dr. hit about 40 years ago Sir Walter Raleigh who was famous not only because he was a direct descendant of these are Walter Riley of so many years ago who discovered tobacco and founded Virginia but famous also because he made a few statements about airplanes and one of them was that the story of man's flight was a long story of legends and dreams theories and fancies all suddenly transformed into facts a tale of the hopes of Mad Men
suddenly recognized as reasonable ambitions. Peter why is it that the airplane has been such a late comer to means of transportation. Well you know the real reason is that the airplane is what we describe as an interface vehicle. It travels free from the earth but it depends upon the earth and its surrounding atmosphere to maintain its precarious equilibrium. You see in this respect it's different from the ship or the ground vehicle like the car because they just sit on the earth. They reach their lowest gravitational potential innocence and the space vehicle can completely escape gravity given enough push of course. So you have to have that part of it but the airplane continually defies gravity like the man on the flying trapeze. But the ships are in a sense to do this in the way they hold themselves up in the water the water supports them of course but at least they're there in some sort of an equilibrium of the medium they're in like an airplane. Oh yes well you see there we have help from our old friend Archimedes and he also helps the
blimps there. He's helped didn't seem to serve them very well because we don't see them around very much. The important thing about the aerial vehicle is that the way it stays up is by continually pushing the air down. And if one thinks about this one realizes that that's how a propeller works. I mean a propeller blows backwards but not down. Not done it's not quite so obvious in the case of a wing that want to wing really is that it deflects the air downwards and by pushing the air downwards you are able to achieve the thrust and the lift which manages to sustain you. How does this make it so complicated though that seems like a fairly simple idea. Well it is really and actually all these devices are essentially momentum generators. They have to grab a certain amount of air they have to capture it in some way and then they've got to work on it with their engines and push it down roads. But the real trouble is that there is light. We we've known that for years
Shakespeare called it the insubstantial. And you see we are heavy. Some of us are heavier than we would like to be even. And so if we want to lift our own true true solid flourish we've got to grab vast quantities of air and the way the airplane does that or the way any flying device does that is by utilizing some form of capture area like its wings or its roaches or a duct. And then it sort of rushes along forward picking up the say they're operating on it with its engines and blowing it downwards with the wing with something that Jerry is really the size of the wing that goes through the air and that's that area that counts in looking at it and that is really the main point. It's essentially the wingspan which which serves to show you how much air that you will be able to capture. And so you see the whole point then is this that the amount of air that you can capture depends on how wide you can
spread your arms to grab it and how fast you can run forward to grab as much as you can. So we see that if you're traveling fast we've got a large vehicle then you can capture a lot of it. Then you don't have to push it down very hard. But if you are going slowly or if you happen to have a small vehicle then you are capturing mascot's very very small and in that case you have to blow the air that you've got down rather rapidly. And so this means that you require a lot of power and there really tragic thing about this the thing that's worried me for years since Or since I was very small dory I thought how nice it would be to design a flying machine that one could fit in a suitcase or something like that and the fact is that if you try to make something smaller you are ultimately faced with these enormous power requirements and even worse if you want to make something go slowly. You're faced with these requirements because you just
can't get the air you have to get it to come to you. Time slow thing requires a very big wing or a lot of power. That's when I raised the point and I always love to think about this in terms of. The fact that for an ordinary fixed wing airplane you need actually an infinite amount of power to fly slowly. And I always think of the Red Queen's the lovely remarked Alice that at least in the aeronautical world it takes all the running one can do to stay in the same place. But I look up or does it. A helicopter does it because it is able by its rotors to induce and cajole the air to come in into its disc and then operate on but its par requirements are still still substantially more there requires more power to accomplish the same transportation than it actually. It requires more power to standstill than a headache than it does to go forwards once you start moving forward in a helicopter your power starts to reduce and there is a speed at which you have minimum.
That's one reason I suppose why helicopters are really rather short range aircraft. They just can't quite carry all of fuel or the engines or something to make up for that. Yes actually they're not as short range as they used to be. They fly helicopters across the Atlantic I believe they landed in Iceland and places like that. How fast is a good fast helicopter go. Well. The sort of magic number that people talk about which I suppose is just as magical as the four minute mile or the 34 inch bust is 200 nuts. And it's sort of widely suggested that you can't really make helicopters go faster than that I've no doubt that they will make it go faster but I can see the reasons that they said you can't. What you have to realize is that the blades are going round and round and the helicopter's itself is going forwards and so that when you think of a head up helicopter going at high speed
you see it as a great bundle of flapping blades going madly in all directions. The hole itself lumbering on afterwards and it reminds me irresistibly of the character in the romantic novel who mounted on his horse and rode off madly in all directions. I mean that's a high speed helicopter to me so. So this is it this is the picture on it which makes the air plane complicated the need for a. Either a great deal of power or a great deal of wing area or something to give them enough momentum to the air to balance the weight of you plus your airplane. Well yes that doesn't really it isn't that so much that makes it complicated. You can design almost anything to fly these days. But what makes it complicated is that you have to do that is elected. And as as and as smartly as you can to reduce weight everywhere and also you have to keep the plane stable. Airplane has six degrees of freedom of course when it's in the air can
go up down sideways and round in about. And this means that there are serious stability problems which become more severe when the airplane just tries to go slowly as anyone who's tried to ride a bicycle at extremely slow speeds will be aware of when you're going fast there's no real trouble. Well this is the reason that. Aircraft an aircraft traffic is going more first toward higher speed jet aircraft and longer haul airplanes. There there seems to be a certainly a tendency for aircraft travel to be dominant at the very long haul XLI thousand mile type range but there's not really very much aircraft travel on a commercial basis at least for something in the range of 50 to 500 miles in there that's still dominated by trains and busses and so on. Is this the problem that is forced just for economic and commercial purposes to go into the long range halls where aircraft.
Yes I think that is is one of the main reasons that one of the things is that it's very hard to design these special sort of airplanes that can have this requirement of landing in a very short distance and operating profitably over the short hauls of course for almost a century. We've realized that this was really the way to fly. There was if you want to travel long distance obviously flying is the way. But the way that aeronautics could really be used was on the short haul and. But even to George Caylee I love this gravitation in 1816. He was an English knight who played around with aeronautics and he made what I think is rather beautifully perceptive and nicely phrased remark that the reaches of the atmosphere constitute a navigable ocean that comes to the threshold of every man's door and ought not to be neglected as a source of human gratification and advantage. And you see he used to
come to the threshold of every man's door not to Los Angeles International Airport but that's a lot. That's one of the problems I know we are everyone who flies on airplanes knows we have these gigantic airports they're very big. They cost a lot of money. They're great sources of noise. And also the airplanes which land and take off there do so at rather high speed so that if anything goes wrong it's customarily fatal to the passengers. Is this a requirement or are we stuck with this now or can we go back to what Mr. Kaley suggested to our to our own threshold. Well fly shorter distances from our convenient airport. It's not forseeable. I think that it really is and I think that that we are going to see much more emphasis put on this business of designing airplanes for what is known as the short haul or stage length which is a length of less than 500 miles and something that will land you right in the middle of the city. For example in New York one envisages putting out very little
short little airfields on top of the pier. And when we think in the Los Angeles area of having half a dozen small airports in the various parks or. Baseball fields or something where an airplane which is capable of landing in a very short distance can land. But then we come back to something well like a helicopter which you mentioned a while ago has a terrible power problem is a very inefficient beast. Speed limited expensive to operate. How can we fit all these things together. Well I think that the way what we have to do it is that we have to just think a little bit more deeply about what it is that we're trying to do to the and to try to understand the air and analyze its emotions and problems. See this is the modern thing of course here anthropomorphism added next. Doctor engineer Well you know I'm I'm really a very poor engineer
and that that's why I like to identify myself with these things. But you know the problem is this that we are faced ultimately with the fact that a wing will only carry a certain amount of left at least conventional wings and then it stores. Right. And the whole thing is that if you fly slowly you are going to be in danger of stalling in an ordinary airplane. And if you fly low then and your stall then you are in danger of hitting the ground with disastrous consequences. And actually you know all this going back the helicopter is interesting because the man who really invented the helicopter a Spaniard named one of the last CFI. Seem to realize very vividly and this was about 40 years ago. They exactly these problems of store the problems of the danger associated with low and slow flight and any spike biography. There's a rather
amusing little anecdote there. He describes the palmy days before the First World War when he was present at some airfield in Spain and a senior Spanish army officer was about to take his first reluctant flight in an airplane. Now being both a general and a Spaniard this gentleman had a very clear concept of his own importance and he summoned the pilot before his flight. He asked the pilot if he had slept around and felt calm and collected. The pilot responded in the affirmative. He then asked the pilot if he was aware of his the general's importance to the army and to Spain. The pilot nodded vigorously. Very well confirmed the general. We will make the ascent. But before commencing I give you my orders to ensure maximum safety you are to fly very low and very slowly exactly the wrong
order in fact from what you are just talking about. Well I don't know whether the general survived his most injudicious orders but whatever happened it made a very vivid impression on jealousy ever and he replies that if you couldn't get the air to come to you you would have to go to it by swinging your writers. Well is that the answer Oh no I don't think it is. I think that's the answer to the helicopter. But I think it's got almost to the end of its development the way we see it now. I think that what we're going to have to do is we're going to have to troll here and we're going to have to. To realize the that this what the problem is stall is caused by and how by tailoring the air we can prevent the story. Now what has it been let's get right down to it what's a problem the stall caused by. Let me talk about that I hope but I don't get too technical but I'll try to stop you if you do please. You know when when one moves a surface through the air it's covered with a thin sheet of slow moving air.
This might be about a quarter of an inch thick on an ordinary wing which is called the boundary layer. And this sheet of air on the wing goes much more slowly sort of sticks to the wire absolutely sticks to the ring and. When one tries to increase the angle of attack this is a which sticks to the ring becomes more and more stupid sluggish and finally the air can't even make its way all the way back to the trailing edge of the ring and it separates off the surface so the Marley tip the wing up and up and up and I'll try to get more lift out of it. Now you suddenly run into this problem. Absolutely absolutely it's sort of like stripping a piece of scotch tape off a table and suddenly all the air strips off the upper surface and the air which had been going backwards and downwards and away in hot areas yeah absolutely producing momentum now go straight backwards and when it loses all the lift that you would have tane from that and then you know when it says that the wing is stored
it's essentially just no more wing it. Not knowing absolutely the lower surface still helps but the opposite office doesn't seem sort of like a physical law. It happens and that's the matter. Well it did seem like a physical law for many many years in aeronautics and many famous pilots were killed because of this. However in recent years we've been thinking more and more about trying to handle this problem and trying to handle it at source. By getting rid of the slow energy in the pantry they're getting rid of it getting rid of it so we say how do you get rid of it. Well the obvious way make little holes in the wing and suck this in or out or maybe even blow through these little holes. The funny thing you can do both methods and they both work in the one case. If you suck the air out you simply suck it through these tiny holes in the wing you suck away the sluggish air and in the other
case you blow high energy out along the top of the wing. And this is where revives really makes it makes a higher energy boundary layer and I suppose and this will not separate or will not go through this process at high angles. That's right and I've always been amused that they should. You should be able to achieve this object by either sucking or blowing and actually there's there's an old rather corny story that these two take Meek's are referred to occasionally as the with and as opposed to the Russian methods setting. The Western method you see when rehabilitates these delinquent particles This of course is blowing when Ree had debilitates the delinquent air particles by the addition of expensive high quality well-educated air and in the Russian method which is sucking the air in particles. I simply removed and disposed of
which works better. I well I'm sorry to say but the Russian approach is considerably more efficient so they have the secret of boundary layers. In actuality or due do we and the Russian engineers in actual apart from me from your your retreat into anthropomorphism again. How do how do the engineers really do it. Is there any favorite method among engineers between these two opposing ideas. Well I think I should put it like that like this. That there is no question that the suction technique is the most efficient run on the other hand. The blurring technique always works. You can always make too much of a good thing. And we actually use it quite extensively on a number of naval airplanes which of course have a very small airfield to land on and a rather weird ending if they don't and so they can get a high speed and then come in slowly. That's exactly it and they use the blowing
technique. It's true you know that this blowing method reply requires considerably more power but it's easier and it works. And I suppose any civilization which uses these complicated power mechanisms to raise and lower the car window for the open tin cans or polished shoes can't be said to take energy conservation very seriously. Well this would solve the problem of stalagmite so you could come into an airport at slow speed and land. How about taking off. Well a short runway. That's it. It's not a stalling and I know that isn't that essentially a power problem and a rather interesting thing is that we can actually go even further with this idea of high energy blowing air jets and this is to get a very high energy very large amount of air and blow it out backwards and downwards from the entire trailing edge of the wing not just in the boundary layer. No no no the trailing edge of the wing is open and one forms
a high energy sheet and this is a means of reducing the stall problem and also at the same time it provides one is quite a lot of thrust. Sort of a while jetting. Absolutely and in a flap like where and it's called rather than originally a jet flap. And when I speak about Jet flaps to people they only think that I'm talking about the flaps for a Boeing 707 or something I had those flaps on that jet are not jet fuel mechanical you said Jettison at all yet. So your own mechanical pieces of metal which force the air to do what they hope to do and don't do any sort of persuasion. But you know the jet flight is really a fascinating thing because it exhibits a phenomenon known as the thrust paradox. And it's called The Trust paradox because it seems like one of those rare but the like for locations when one gets something for nothing. Yes that is rare and the point of it is this that you get your lift by
blowing downwards. But at the same time you get thrust from the device and the way it works is something like this. When you blow the Cerro off the back of the ring it goes downwards to start and helps you with the left. However as it goes on downstream you can imagine this sheet trailing out of the back of the ring. It's gradually turned by the oncoming air until finally it ends up going horizontally. And now of course you see you're blowing it straight backwards. So now you've got thrust from the system. So you see with this device we obtain first lift from it and then most obligingly it turns and provides us with Thrust not seem very nice you could do away with a wing altogether and just replace it down completely with a source of pipe and a jet flap and. That would be nice and that is possible but we must remember that the whole point of the jet flap is that it's a type of leverage system and you get many times more lift than the lift you put actually into the jet
itself because when you have a wing with a large wing span it. The jet flap isn't able to induce it's able to persuade much more air for you to turn and to provide you with more momentum. I think the really fascinating thing about it is that when you have a jet flap you don't need any propellers or or ordinary jet engines gas turbans for thrust because here we have for the first time really fully integrated. You know that's a fashionable with these days. But this is a fully integrated lifting system like a bird. Absolutely our feathered friends have have used this for years. You see what one really means by an integrated lifting system it is this that old airplanes you had a lifting system which was the wing and then you had a thrust system between the engines which were screwed under the wing somewhere and so you had these two things going along. Possibly not particularly well matched or
related but the bird uses its wings both for thrust and for lift. And the jet flap would use its single wing in this jet flap for both thrust and left to stall. Doesn't come to the problem of how you get off on a short take up does it does a jet clap help you can shorten Ah yes actually it does and the reason it does that is because it gives you a appreciably higher lift than an ordinary wing would give you and it gives you these this very large additional increment in thrust. Of course you won't get any more thrust from the system than you had from your engine stock. Yes but it can be more efficiently used. Absolutely it was the most most large jet airplane to take off with quite a lot of flap on them a fair amount of flap settings. And this is said they can get off the airplane and get off the airport rather rapidly before they fall into the ocean or hit a freeway.
This means that the drag is rather high and so a fair proportion of your engine power is used in simply overcoming the drag of your lifting devices and people have always been very frightened about using so-called powered lifting devices to get off the ground. I mean pointing the engines straight now no more straight down no using the engines to operate some sort of boundary control in the wings to give more lift. Because they've always said I can do that but I'm going to lose so much thrust that it's not going to pay off. All I see in it but yet what they just slap you don't lose is that I think perhaps in the case of the jet black for the first time we have a system in which we can obtain all this extra lift and not pay any penalty and thrust and that's why it's such a fascinating idea. They have actually built an airplane a jet flap airplane in England which has made. Series of flights which I understand have been more or
less successful I think. Well is this going to land to come back to the short range aircraft or is this going to make it possible to not only solve a short range transportation problem here but perhaps open up transportation and other countries which don't now have railroads and roads and bus lines and waterways and so on as it is the shorter short flight aircraft going to solve this need so I don't have to put a railroad across the Amazon. Well I really think it is I think that's the most fantastic field for transport. We were talking a little while ago about the demand for travel in the statement of 500 miles and saying that in the United States for example there's something like 30 billion passenger miles traveled in the 500 mile stage then of which quite a lot of that is done by Bass or train or horse or relitigate but very
little by airplane. But you know if we were to think about the other areas of the world think about their transportation demands. We would we would find absolutely staggering figures for the demand for this sort of travel. You've only got to think of those great land masses. India Africa South America. It's continents that are work off to the industrial revolution. They don't have England waterways and they struggle with overcrowded rail and road systems to move the teeming peoples of the World Bank in various people talks about building railroads in these countries but it's too late in history to build railroads. So now it seems that perhaps we can answer their needs with aircraft if only we take the attitude that we're not going to use brute force to push the air where we want it but as you say coax it understand it. Cooperate with it and
About science
About airplanes
Producing Organization
California Institute of Technology
KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland (College Park, Maryland)
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This program focuses on the science of airplanes.
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Interview series on variety of science-related subjects, produced by the California Institute of Technology. Features three Cal Tech faculty members: Dr. Peter Lissaman, Dr. Albert R. Hibbs, and Dr. Robert Meghreblian.
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Guest: Munger, Edwin S., 1921-
Host: Hibbs, Albert R.
Producing Organization: California Institute of Technology
Producing Organization: KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland
Identifier: 66-40-1 (National Association of Educational Broadcasters)
Format: 1/4 inch audio tape
Duration: 00:29:08
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Chicago: “About science; About airplanes,” 1966-08-12, University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC, accessed October 21, 2021,
MLA: “About science; About airplanes.” 1966-08-12. University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Web. October 21, 2021. <>.
APA: About science; About airplanes. Boston, MA: University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Retrieved from