possible that will affect the structural integrity down of the various field length performilnce of the basic airplane. targets advocated throughout the years, with a little information on each: Short Field (1) 1952: 500 feet; this was the point of "Short-field Aircraft" is a catchall term departure for many discussions under which can be lumped all aircraft which among commercial manufacturers, use advanced technology to achieve shorter the Army, and the Office of Naval than ordinary and distances. Research. In 1953, the Cessrla The term embraces short takeoff (STOL), Aircraft Company actually pro- reduced takeoff (RTOL). and vertical-or-short duced an airplane capable of tak- takeoff (V/STOL) types of machines. ing off and landing over a 50-foot RTOL and STOL obstacle in 450 feet. The airplane There have been two definitions associ- was a heavily-modified L-19A. The ated with each of the names Reduced Takeoff "improvement" over CTOL was ap- and Landing (RTOL) and Short Takeoff and proximately 25 percent. Landing (STOL), and much confusion has ex- (2) 1959: 1,200-2,000 feet, developed in isted because this fact was not appreciated. part by technical studies growing The confusion existed because, while Conven- from ONRtArmy-sponsored tional (CTOL) airplane research performed at the Univer- technology and its associated performance sity of Wichita. The aircraft associ- were represented by existing types of airplanes, ated with these field lengths were as was VerticalIShort Takeoff and Landing transports in the 30,000 - 60.000 (V/STOL) by the performance of the helicopter, pound class At this same time, no hardware and no steady performance Lockheed Aircraft started develop- targets existed for STOL. During the early years ment of a "BLC-130" with com- in the development of STOL technology, the parable performance. typical argument was over what single fixed takeoff and landing distances should be striven (3) 1968: 1.000 feet. The FAA marked for through the application of the technology. off 1,000-foot sections of at One of the early "definitions" of STOL was Washington National, Friendship, "500 feet over a 50 foot obstacle." It was and LaGuardia and desig- surprisingly long in coming out that there were nated these as "STOL" strips. An actually two entities to define separately. airline using Dornier "Sky Servant" heavy twins (7,700 pounds) used The first was STOL technology, the ag- these strips. Though this airline gregation of technical developments that would operated only for a while, it pro- enable the design of an airplane with field vided information on tbe feasibility length requirements substantially less than of introducing STOL airplanes into those of a CTOL airplane, of the same payload, the mix of traffic at a heavily-used range, and speed. . The second was STOL airplane, and to its definition no fixed field performance require- (4) 1970: 2,000 feet. This was a relaxa- ment could be attached except arbitrarily. 5 ne tion of the 1,000-foot "requirement" field performance of successful airplanes above. Surveys of the larger com- designed to a given state of the art is size de- muter operators at that time indi- pendent as shown in Figure 1-3. A STOL cated that they would have been airplane, then, is an airplane which utilized content with about 3,500-foot field STOL technology effectively to produce some performance. percentage improvement in performance, no (5) 1975: 3,000-4,000 feet. This length matter how short or long its field requirement is. is associated with medium weight Potential users, however, insist on thinking transport category airplanes in dimensional terms so here is a sample run- (146.000-206.000 pounds) in a NASA-funded set of short-haul * Stalter. J L . and Wanson. Robert K . Jr . "Experimental In- systems studies by Douglas, vestlgatlon of a Means of Obtaln~ngIndependent Control of Lift and Lockheed, Boeing, and others. Ad- In Land~ngApproach." Unlverslty of Wlchlta Englneerlng Re- port UWER-3155. Contract DA 44-177-TC-356. U.S Army Transpor- vanced ni-lift technology and tatlon Research Command. April. 1959 materials were necessary at these CIVIL AIRPLANES UP TO 34,000 POUNDS CTOL STOL, RTOL

+ Landing Landing

I I I 8 I. 1 1 5 10 15 20 25 30 X 100=TAKEOFF AND LANDING DISTANCES IN FEFT

SO-FOOT OBSTACLE TAKEOFF AND LANDING DISTANCES FIGURE 13 weights. Environmental considera- tions from short fields or aircraft carriers, tions were invoked. thought in terms of better field performance thancould be displayed even by the propeller From these cases it can be seen that the airplanes of the period. They were diverted from field length requirements, and the aircraft mis- the helicopter by its slowness and fearsome sions and sizes of principal interest at the mo- maintenance costs, and thought instead of ment, wers all mixed up together, which tre- short-field fixed- airplanes which, while quently happens when most of the application somewhat heavier and more complicated than effort over a considerable period is devoted to conventional airplanes, would offer acceptable studies rather than to the production and logistics and some of the desired performance marketing of actual equipment. gains. To try to make sqme sense of the above, a discussion of STOL aircraft is presented using Conventional high-lift technology seemed a historicalltechnical approach. The initial to have reached a plateau, so attention was question, of course, is "what is 'short'?" or directed towards "powered lift." The means "short with respect to what?" As has been were to be propellers which bathed most of the seen, there is no way to answer using field wing in their slipstreams and could be used in lengths; thus, a defimrion based rather on the conjunction with very sophisticated wing flaps state of the technical art must be adopted. This and drooped airlerons which deflected the definition requires that a technology associated slipstreams downward to obtain additional lift. with "conventional" is adopted first, and that Further, an old concept called "boundary layer "short" (plus recently "reduced") be related to control" (BLC) or "circulation control" was in- it through inspection of the techiological levels voked to increase the maximum lift of the - habitually associated with them. ped . The application of BLC delays the breakaway of the airstream over a wing by Conventional Technology. Perhaps the removing (suctiun) or re-energizing (blowing) &st period to use to describe "conventional" the slow-moving layer of air-the bolir ~dary is the period between 1946 and 1950. By 1946 layer--close to the wing surface, the decay of the biplane and the wooden airplane no longer which causes the wing to . represented the highest level of technology. The technical product of the war years which Under Army, Navy, and Air Force sponsor- appeared first on the civil market was charac- ship, exploratory programs on prototype ver- :erized by conventional-airfoil straight wings, sions of liaison airplanes, fighters and single or double-slotted part-span flaps, and transports using BLC with or without propellers propeller engines. The turbajet engine tech- went on throughout the 1950's. In France, the nology of wartime was working its way through Breguet company developed a deflected the military inventory, and would appear on tCle slipstream, four-propellered airplane with flap civil market in the 1956-59 period ir. the forms of and control-surface refinements, the Model 940 the Boeing 707, the tlouglas DC-8, and the transport. In 1967 its successor. the Model 941, Convair 880. These three airplanes were was demonstrated in a series of simulated "CTOL's" ;II the sense that, though they scheduled airline trips, but nothing resulted. employed complicated flaps and leading edge devices, the effectiveness of their wings in pro- The state of the STOL art by 1960, then, ducing high lift was no better than that of the was portrayed by: (1) extremely complex wing propeller airplanes hat preceded them. Their flaps and slats with or without BLC; (2) large field length requiremenis were very long, propellers, with or without interconnects to pre- 9,000-10,000 faet, so from elther the perfor- vent rolling and yawing in event of engine mance or the technology standpoint they would failure on multi-engined airplanes; (3) roll con- have to be considered simply as defining a jet- trol refinements (spoilers or drooping ailerons); airplane CTOL developmental level. and (4) large tail surfaces, perhaps with BLC applied. STOL Technology. The initial impet~~sfor the development of a STOL technology was Airplanes with lifting jet engines or lift fans provided by the military. Civil propeller were studied for their STOL-mode charac- airplanes of the 1946-1950 era had no great teristics, but were really overloaded V/STOL trouble operating from the airports of the day. airplanes. The military, however, concerned over opera- Civil jet airplane manufacturers meanwhile had been working. Though there was one test * Sawn. Raymond C elel. "Summary of Short-haul Systems of a large jet airplane with BLC in the Studies." NASA TM X-3010. January. 1975 mld-1960's, the most notable achievement was the Boeing 727, not usually thought of as a imum gross weight is completely unacceptable, STOL machine. Through careful tailoring of the even though it may be suffered only part of the wing shape and flap and slat configuration, time. Bodng engineers produced a high-speed, swept wing whose high-lift performance was The fate of the propeller STOL's was simi- almost the equal of the powered-lift straight lar except for the Twin Otter DHC-6. The Twin wings of the experimental STOL airplanes. Otter is in regular service as a commuter Using this wing and the higher thrusthrveight airliner, but its success is due in part to its ratios available from turbofan engines, they simplicity and ruggedness; few of the nation's achieved a 7,250-foot requirement of the airports from which it operates tax its 707-120. Almost at the same time Douglas capability. The Twin Otter is on the upper end achieved similar performance gains using of the present general aviation size spectrum, early-generation "supercritical" (not Whit- so it is probable that unless needs for serving comb) wings with long double-slotted flaps, progressively shorter fields appear, STOL tech- and fan engines. The second gencration jet nology of greater sophistication than the Twin airliners could thus be called true STOL Otter's (double-slotted flaps and droopy, dou- machines, in terms both c' %sir high-lift tech- ble-slotted ailerons) will be unnecessary at nology and of the percentas:: improvement in 12.500 pound gross weights and below. field length achieved. In the large commercial airplane area, The technological improvements over the which commuter airlines can now enter, the first generation jets were low-speed engine situation is somewhat different. Increases in thrusthrveight ratios up about 33 percent and design gross weight are accompanied by in- maximum lift capability up about 60 percent. creases in wing loading, from which follow the Later (1965-1975) efforts have been con- increases in field IengtP. 3quirement shown in centrated in the following areas: (1) "exter- Figure 1-3. Therefore, "to fit" into a given field, nally-blown flaps" (EBF), an adaptation of the progressively heavier airplanes require old deflected slipstream concept to the fan progressively more sophisticated high-lift engine; and, (2) "Augmentor wings," the addi- devices to increase the supporting capacity of tion of auxiliary surfaces using a jet-pump prin- their heavily loaded wings. Conceivably, this ciple to augment the effect of blowing-type requiremant would be encountered occa- BLC. An augmentor-wing prototype airplane sionally by a commuter serving relatively high- exists. volume traffic, but since the relationship be- tween demand and available runway length is The present situation illustrates a rather generally direct rather than inverse, the occa- curious fact: developments in the powered-lift sions calling for large STOL airplanes will pro- area did enable wing lift capacity to be raised, bably be exceptional. There exists at this time, but close behind came developments in non- however, a large commercial STOL airplane, powered lift-carefully tailbred wings, flaps the DeHavilland DHC-7, which is entering ex- and leading-edge devices--which nullified the perimental service on a Canadian two-sector gains from powered lift. It alsc appeared that route, the airports on which are "close-in" the weight gained by powered lift airplanes of STOL strips. The airplane is at the top of the any sort was not tolerable commercially. The size range for commuters operat- little 319A of 1953 grossed 10 percent ing under present CAB regulations, but this more weight than the s!andard L-19A. The limitation is not necessarily permanent. weight penalty dir~lin~sheswith increasing airpiane size until for an airplane the size of the Recently there has been the appearance of Boeing 367-80 (prototype 707) which was flown the idea of the "Reduced Takeoff and Landing" with BLC, it is only about two percent. When airplane, a concept sitting somewhere between one considers, however, that two percent of the present CTOL's and the non-existent design gross weight is about four percent of "powered-lift" STOL category. useful load and perhaps eight percent of payload, the reason for the unattractiveness of The technical features of RTOL are very powered lift becomes apparent: with average low wing loading and/or "a little" powered lift. load factors of 40-60 percent and breakeven As explained previously, field-length require- load factors in the 40-percent-or-so range, an ment must be associated with aircraft size as eight percent penalty in seats available at max- well as with technology. The study by Savin, et a/., was built around a range of sizes for 40 to 300 passevlgers, narrowed finally to 150 pas- '" Ibid. sengers. lo Gross weights of 146,000 to 206,000 pounds are developed, depending on the field length requirement at all. There are other con- length requirement and the technology used. It straints, however; here are some: is shown in the study that field lengths of 3,500 and 4.000 feet, at standard sea level conditions, (1) A short-field airport must accom- can be realized by airplanes of this size using modate aircra't on ramps and taxi- mechanical flaps or upper-surface-blown flaps, ways and terminal facilities, as well with wing loadings from 72 to 100 pounds per as the runway itself. Even if ter- square foot. The increase in direct operating minal facilities (except runways) cost of such airplanes over CTOL airplanes of were suppressed, the ramp area re- like capacity would be pn the order of two per- quired to accommodate any cent or so. Interpreted as a fare increase (fixed reasonble number of aircraft is IOCIDOC ratio) this is probably tolerable in the surprisingly large. It could con- very special locations for which the aircraft ceivably be large enough so that, were devised. with parking areas laid end to end, it would be longer than the runway Technologies discussed by Savin, el a:., required. This would have the effect applied to airplanes of general aviation size, of relieving the short-field require- would produce far shorter field length ment itself! capabilities. For example, the well known DHC-6 Twin Otter can in fact be considered (2) Short-field aircraft are typically technically an RTOL rather than an STOL considered as applied to sectors airplane; its advertised minimum field length is with at least one end in or near a just under 2,000 feet. The nearest counterpart Central Business District. Unless CTOL, the Swearingen Metro, requires 3,550 tie presence of special features of feet at the same gross weight. the arecrivers or lakes, for ins- Ideally, aircraft should at maximum tance--renders land acquisition weighthhrust or weight/ power speeds. Prilc- cost negligible and noise and tically, CTOL airplanes cruise at or near obstruction problems tolerable, the minimum trip-cost speeds, which can usually city-center "STOLport" is of ques- be shown to be higher than are maximum tionable feasibility from the finan- weighthhrust speeds. The idea that CTOL cial and public acceptance view- aircraft might be reoptimized for cruise using points. STOL technology is attractive from this view- (3) Short-field aircraft consume more point. Using an example from long ago, the fuel per mile than CTOL aircraft, Cessna 319A STOL airplane would have had and have greater hardware weights the same field length requirement as its parent, and greater complexity. They are the L-19A, at a gross weight exceeding 3,300 therefore wasteful of energy com- pounds, or about 50 percent more than that of pared to their CTOL counterparts. the L-19A. Reoptimizing for high speed cruise In the past it has been acceptable instead of short-field performance would have simply to assign marginal costs and dropped wing area an approximately corres- to ask whether the resulting fare in- ponding amount, and while the gross weight of creases would be acceptable (the the airplane would end up little less than the answer has usually been "yes" but 319A's 2,300 pound weight, the airplane would nobody really knows). The rising be more nearly in match-that is, the minimum- importance of enersy conservation cost cruise would be closer to its maximum now suggests that short-field ap- weighthhrust speed. No present day small plications should be inspected on airplanes are so matched, for various reasons an ener~y-levelbasis, using a con- (the 61 knot stalling speed, for one), but some cept which includes the entire sup- studies have indicated that energy conserva- porting system along with the tion may be possible. The above oxample is aircraft, and compares it with alter- vastly oversimplified (optimization analyses for native sys;ems. jet airplanes, for example, must include wing- fuel volume requirements and their load-reliev- V/STOL Technology ing effects on structure weight) but the concept The Airship. The oldest V/STOL aircraft is worthy of attdntion. was of course the balloon. Unsatisfactory as a From the standpoint of technical feasibility transportation device for use other than sport, alone, one can design an airplane to any field the balloon quickly gave place to the airship. Three classes of airship existed by the end of mally valve helium, but maintains its altitude by World War I: making the trade3 between displacement and aerodynamic lift that are necessary the day (1) Rigid (envelope fully framed, gas as carried in internal ballonets) progresses and the envelope warms up, ex- panding the helium gas within (the envelope (2) Semi-rigid (envelope possessed a shape and size in non-rigid airships are main- "keel" structure running its entire tined by slipstream-air-filled internal balloneid). length and part way up the sides) The larger airships could store ballast in flight (3) Non-rigid (unframed envelope, the by using engine exhaust conaensation to nickname "blimp" coming from the replace ths old sand bag ballast. sound an early non-rigid pade The top speed of the existing non-rigids is wheq its envelop was whacked about 35 mph, and their usual operating sharply with a finger). altitudes are very low. A typica: Goodyear non- Rigid airships were constructed in Ger- rigid has a six-plssenger (about 1,020 pounds) many before and during World War I. The payload, and requires a flight crew of one and a United States had one such machine completed sn;all ground crew of perhaps six. Ground sup- for the Navy as a contribution toward war port equipment in the field consists of one large reparations ("Los Angeles," German number equipment van, a portable mast, and crew LZ 126), and built three ("8,~?ndoah" ZR-1; transportation. "Akron." ZRS-4; and, "Mac~. ZRS-5) all of ifl the racent material on airships, two ma- which were lost. The British bul . a series, the jor techr13logicaldevelopment possibilities ap- "R" airships, the last two of which, R-100 and pear. R-101, were constructed concurrently. R-101 The first is due to the release from the was lost The "Hindenburg" had a gas capacity limitations of the properties of meterials used in of about 7 million cubic feet. a typical payload of about 30,000 pounds, an all-up weight of the past for hull framing, envelope, and ballonets. The airships of the early 1930's were abcut 260,000 pounds, a 159,000 pound useful framed with what amounted to 17ST aluminum load and a maximun speed of 88 mph. By the alloy. An all-metal airship, the Navy's ZMC-2, end of the rigid airship era a total of 160 rigids helped stimulate the development of 4lclad, had been built. l1 which is aluminum-alloy coated with pure Italy produced an early series of semirigid aluminum. Since then, nigher strength airships, and in the mid-1920's bdilt two large aluminum alloys have become available, and ones, "Norge" and "Italia." "Italia" was lost on synthetic fabrics have replaced the fabrics used a polar exploration flight. in the old airshi~s. In the years from 1931 to 1972 the The second is an evolutionary develop- Goody . ,. .,orporation built 334 non-rigids, all ment in hull shaping. This development has but 10 of them for the Navy. This represented gone in several directions at once, helped by about 75 percent of the nation's total produc- various advocates, but essentially the technical tion. The surviving non-rigids are all used by basis is the following: The cigar-shaped hull of Goodyear for advertising. The company the conventional airship IS not an efficient pro- rebuilds these airships periodically using subs- ducer of aerodynamic lift. The lift force is very tantially the technology of the time of their weak, and is accompanied by a penalty known design, thus keeping their Airworthiness Cer- as induced drag (induced by lift, that is). Also tificates active and current, and avoiding the this hull is unstable and tends to nose in the need to type-certificate an advanced airship. direction of the lit: force beina develo~ed.so it The airship's total lift is secured by a com- must be fin-stabilized lise a r;;issle o; bomb. It bination of displacement lift and aerodynamic has thus been clear that while the cigar shape lift. The displacement lift is of course due to the was desirable from the standpoint of minimiz- difference in weight between equal volumes of ing drag from hoad-on winds, it was addressed helium or hydrogen and air: the aerodynamic to only a small part of the total aerodynamic lift comes from the force oi the passing air on problem, sinca an airship is se!dom exposed to the envelope; this is increased or decreased by direct head-on wilds. increasing or decreasing the angle of attack, as On the other hand, the airplane deals with on an airplane wlng. An airship does not nor- "induced" drag and stability problems relatively successfully There should, then, ~s " VWek Joseph A Jr . (ed ) "Proceedlngsof the Interagen- cy Workshop on Llghter Than Air Vehicles." MIT Fllght Transporta- some benefit to be gained from shap~ngan air- tlon 1-aboratory Report R75-2 January, 1975 ship hull somewhat like an airolane, enabling it

The "Harrier" is a singleengine monoplane, its pilot; in the present state of require- turbofan engine incorporating four exhaust ments for hirman tralning and cer- stacks which can swivel downward over 90 tification the vehicle is not the degrees for hover. answer to every householder's dream; and Exotic Aircraft (5) for airworthiness certificaticn pur- There is a small group of arrcraft which fits poses it is an airplane. w~ththe into no single category such as those used costs that this implies. above. Their performance and technology is Considerable engineering genius m~xed,and they are included in this section as nevertheless has been brought to bear on the indications of the variety of concepts that have concept, and one type is flying today. though been conc'dered in attempts to solve aviation's not in commercial quantity product~on. problems or to increase its versatility. Everyman's Helicopter Flyins Jeep The Idea here is that of tne absolute The Flying Jeep was a military develop- minimum one-man machine. consisting of a ment intended to provide one to four sola~ers seat. a rudinlentary undercarnage. a small with airborne battlefield transportation of the engine. a rotor, and a handle by which to steer same nature as was provided on the ground by Such machines surface occasionally. and enjoy the quarter-ton truck. A V/STOL alrcraft was ex- brief notoriety before unaccountably disap- ecuted: it had No shrouded propellers in pearing. tandem (or In otie version four free propellers) with axes vertical, between which sat the pilot This history of appearaflces and vanlsh- and his passengers. No version of the ma~hlne lngs seems to be the outgrowth of the fact that proved tractable In the alr or maneuverable on each such machine is a true helicopter. with the the ground, and the concept was shelved. teething troubles and unstable behavior in the air that are characteristic of such craft. By the Airp!anelCar t~methese are Ironed out. the devlce has g;own In one form or another the hybrid to perhaps 400-500 pol~ndsempty weight. no a1rplane:car has been around for a long time. longer a plaything but a rea! aircraft, which for an obv~ousreason -again it offers the hope must thereupon be certificated. maintained as of traveling In elther of two transportation an alrcraft, and so forth. systems using only one veh~cle.A small car has added to it a power-takeoff drlve and extra com- Flying Saucers ponents of its control system. To the car are at- The terrn "ftylng saucer" IS not technically tached, when desired, a tail conta~ningan ex- def~nable As a name for "something" the tension shaft for the propeller and mountlng tall saucer seems to be on its way into the nat~onal surfaces. and the wing. The a~rplanepart of the folklore As a device or class of devlces. the asssmblage car: be towed home to the garage saucer possesses an attraction based partly on in ofie concept. or left at the alrport In another. the inherent difficulty of making it fly at all: ~t The difficulties wlth thls attractive idea presents a challenge. seem to be the following: Considered as an a~rcraft. the saucer- (1) as an automob~lethe vehlcle 1s shaped vehicle can be v~ewedas alrplane and cramped (more at least than the as hoverinq device "family car") and laden with extra As an a~rplane.the saucer-shaped vehlcle machinery; 1s slmply a round-w~ngedvarient of the f~xed- (2) as an a~rplanei: suffers from having wing aircraft The round wlng IS under a con- to drag the car around, dlmlnishing s~derableaerodynamic d~sadvantage (that of its effic~encyas a fly~ngmachine: excessive Induced drag) compared w~ththe slender wlngs with which ail vlable subsonic (3) it has an interface problem Either it alrplane types are equ~pped Round-winged must be hauled through the streets. airplanes have. however, been built and flown. vulr~orable to minor tidff~c, accl- most notably one concelvad during World War dents any of which can render it im- II for the Navy as :he min~mal"container" for med~atelyuseless as ar' plrplane. or two of the heav~estp~ston englflcs. A reduced- the airplane part must be left at the scale prototype was flown. but the full-scale alrport to accrue the usual t~e-down mach~newas rendered obsolete by the ad;rent fees or hangar rent; of the jet englne The round-winged fighter's (4) In flight ~t must be operated by a entire wlng was bathed In the sl~pstreamsfrom its large propellers, and though not a V/STOL. seaplanes, helicopters, airships. or balloons. the fighter did signal the resurgence of the idea More than 50 years ago it was recom- of the wing-deflected slipstream and its ap- mended that "flight stops" be piaced along the plication to VETOL. highway. Such stops would be nothing more To hover, a vertical flow of air must be than a landing and take-off strip adjacent to a established to provide the sustaining force on gasoline service station. This would combine the aircraft. To hover efficiently-that is, with- motor car and airplane service to assure max- out the expenditure of much energy-the imum and dependable service. Flight stops diameter of the vertical airstream must be as were to be a part of the national highway large as practicable and its velocity very ;ow. system. l3 A recommendation was made that This the helicopter provides admirably with its No arterial motor highway large diameter rotor. Attempts to produce a should be built in the future without sustaining force equal to that of a helicopter, including adjacent flight stops every but using a device that accelerates a smaller 30 to 50 mlles for the personal flyer. diameter airstream faster, use more energy Flight stops will mean a landing area than the helicopter uses. for practically every town and hamlet It follows that unless space limitations are located on such superhighways. critical. the helicopter '9 the way to go. If rotor thus providing those sma!l com- diameter is limited (the slipstream small and munities with an additional means of fast) a ring-shaped shroud can be put around transportation. " the rotor and will help some (this is the This scheme, started in the late 1920's by "shrouded propeller" of the flying jeep). The the Richfield Oil Corporation, failed largely due ring can even be configured to look like a to the fact that personal aircraft were still too "saucer" but there is no aerodynamic advan- expensive In both initial and maintenance tage in doing so, though some needed stiffness costs. The depression of the 19303 also played of the shroud may be gain&. ~tspart in pre!enting the commercial success There are classes of V/STOL aircraft con- of the venture. cepts which use shrouded propellers because This section will discuss varioas types of of diameter limitations, but they do not resem- landing facilities with particular emphasis on ble saucers because of the inefficiency of the general aviation airports. The discussion will round wlng in forward flight. include airport classification. airport design As matters stand, none of the exotic aircraft and layout, airport administration and opera- In this group has found a commercial applica- tion, and general aviation support facilities on tion. Although there is always room to say "but the airport. they might in tne future" and always danger in saying "they never will." there is no present Airport Classification reason for thinking that the compromises and Classification by Aircrafl Type Inefficiencies that have characterized them in The ground-air interface in the Unlted the past will be overcome to an extent that will States consists of a national network of landing glve them a place. relative to the successful facilities which can be categorized by the types types of aircraft, more important than they now of vehlcles served as follows: Is occupy. Airports serving AIR SUPPORT FACILITIES land airplanes 11.160 Introduction Seaplane bases serving seaplanes 472 The interface between ground and air is a landing facility which links the air and the sur- Heliports 1.430 face transportation systems. This facility is Total 13,067 commonly identified as an "airport" since most of the landing facilities fall into the category of Airports are designed around one or more serving primarily land airplanes as opposed to landlng areas called runways which may range - from 50 feet wide and 1,500 feet long to 500 feet '' Froasch Charles and Prokosch Walter A~rporfPlannrng. wide and 14.572 feet long. l6 Seaplane bases 1st ed . (John W~leyqnd Sons 1946). p 165 are primarily docking facilities adjacent to " lbrd. p 74 natural lakes. rivers. and ocean or bay areas '' Federal Avtat~on Adm~n~strat~on.January 1. 1975. Srat~stlcsreleased In news release 75-83,May 27. 1975 which support seaplanes (land airplanes with '@JohnF Kennedy lnternat~onalAirport. New York pontoons) and flying boats (airplanes des~gned