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capacity, the initial cost of STOL aircraft may be one-third that of the helicopter. STOL aircraft, moreover, may be operated at seat mile costs from one-half to one-fourth those of current rotary-wing operations, as the bar chart on page 32 points out.

Block-to-block speeds of STOL aircraft will produce total transportation times (door to door) between the inner city and points 25 to 75 mi. distant one-third of present surface-transportation modes and will produce time savings of the order of one-half to 1 hr or more per journey.

Stol Aircraft Designs  Available for Interim Operation in Metropolitan Areas. At present no separate regulatory classification exists for STOL aircraft. Certificated aircraft having STOL characteristics, are therefore, required to furnish performance data designed for traditional fixed-wing application. Some of this data might not be based upon procedures which take full advantage of STOL aircraft capability. Furthermore, no specific provision is made in data that must be published, according to the aircraft certification regulations, for such devices as the high-drag turbopropeller configuration or reverse thrust. It may well be that special regulatory provision should be considered for the future to permit the most effective exploitation of STOL aircraft characteristics. 

In many respects, therefore, the following information may be overly conservative. Furthermore, since much of the data available to the FAA is propeitary, we have not identified particular aircraft types. Instead, we have used available performance information to develop composite aircraft characteristics. It should be noted that composite aircraft data will indicate the state of the art as manifested by aircraft currently in operation. It is a measure, therefore, of what the aircraft industry is able to produce now. Further development of such techniques as the jet flap as boundary-layer control (Ed.—See page 40) will doubtless result in further performance improvements. It would appear, however, that much of the performance gain can be expected to be translated into additional payload as soon as the extent of the ultimate market for STOL aircraft becomes clear.

Landing Distance. The single-engine composite will have a ground run in the landing configuration of 240 ft and a total landing distance of 605 ft from a height of 50 ft, as shown by the diagram at top right. The twin-engine composite will have a ground run of 330 ft with a total landing distance of 747 ft from a 50-ft height, as shown by the second illustration at the right.

These data assume landing in zero wind and standard atmosphere. Inasmuch as the landing distances represent absolute performance with all engines operating and, with the exception of the 50-ft obstacle clearance, do not contain performance margins to cater to operational variables, it would appear that an additional margin is required. Air-carrier operating regulations require that landing distances of aircraft not exceed 60% of the effective runway length: Under certain circumstances the landing distance for turbopropeller aircraft must not exceed 70% of the effective runway length. Considering the fact the STOL-aircraft approach speeds will be approximately one-third that of their larger fixed-wing relatives, smaller margins would appear to be in order. Furthermore, since touchdown speeds would rarely exceed 40-50 mph, none of the serious problems of hydroplaning on wet surfaces (Ed.—See Schmidt review, page 56) need be anticipated. Accordingly, a landing distance from 50 ft that does not exceed 80% of the effective runway length would appear quite conservative.

Takeoff. The single-engine composite has a takeoff ground run of 375 ft; and the total takeoff distance including climb to 50 ft is 680 ft, as

COMPOSITE STOL LANDING PROFILES
For single-engine STOL aircraft.
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For multi-engine STOL aircraft.
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COMPOSITE STOL TAKEOFF PROFILES
For single-engine STOL aircraft.
[[image]][[/image]]

For multi-engine STOL aircraft.
[[image]][[/image]]

February 1966                                                           35