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 Aircraft (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 takeoff and landing 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 Takeoff and Landing (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 runway at One of the early "definitions" of STOL was Washington National, Friendship, "500 feet over a 50 foot obstacle." It was and LaGuardia airports 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. airport. 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- Drag 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-wing 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 flap- habitually associated with them. ped wings. 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 stall. 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.