Engineering topics
Publications and source records attributed to Christiansen, R. S..
This paper discusses the development of handbook techniques for the preliminary assessment of V/STOL aircraft performance while hovering in the proximity of the ground. In particular, the suckdown forces due to entrainment are described for configurations using a single jet. Corrections to current methods are suggested from an analysis of recent large-scale test data.
A large-scale ground-effects test of a single jet in hover was conducted as a first-case study for future tests to provide the V/STOL community with an improved data base. The objectives for this single-jet hover test were to (1) document the jet characteristics and then (2) gather the associated force data. These data are then compared with results obtained from existing prediction methods. A conically convergent nozzle was mounted to a turbojet engine, and an 8-ft-diam suckdown-plate model measured the lift-loss forces in ground effect. Jet-exit characteristics (pressure profile, temperature, turbulence, etc.) are documented for several nozzle pressure ratios. Characteristics that may give rise to scale effects are discussed. Results from this first study indicate that small-scale tests, and current prediction methods, will lead to significant errors in the lift-loss estimation of a single-jet configured aircraft, hovering in ground effect.
Future V/STOL aircraft will require efficient techniques for changing the thrust vector from the vertical direction for VTOL operation to the horizontal direction for conventional flight. Most V/STOL concepts utilize thrust vectoring nozzles to provide this variation in the thrust vector direction. An experimental test program was initiated to demonstrate the capabilities of a large scale 'D' vented thrust deflecting system coupled with a high bypass ratio turbofan engine. Data were obtained for a 'D' vented nozzle mounted behind a YTF-34-F5 turbofan engine. Preliminary data are presented for a variety of test conditions. Attention is given to aspects of 'D' vented nozzle design, the test apparatus, engine-nozzle compatibility, exit area variation, longitudinal vectoring performance, nozzle temperature distribution, and large scale - small scale comparisons.
The development needed for the evolution of selected V/STOL research vehicles into optimized antisubmarine warfare (ASW) aircraft configurations, using numerical procedures and traditional analytical methods, has been examined. Three propulsion systems, which represent state-of-the-art development aimed at solving the thrust-vectoring and attitude-control problems of V/STOL aircraft, are analyzed. The use of NASA computer programs for aircraft synthesis (ACSYNT), and for optimizing configurations (COMMIN), coupled with contractor-supplied propulsion system data provides for accurate performance prediction of the selected ASW configurations. Particular emphasis on the transition phase between the research vehicle and the optimized configuration demonstrates the strengths and weaknesses of using generic research aircraft instead of building prototypes to demonstrate new technology