Takeoff And Landing Mode

The switchblade wing version of the FDL-7C (that is, the FDL-7MC) was the preferred version for the 1964 studies. A switchblade wing version of the McDonnell Douglas Model 176 configuration, without a windshield, is presented in Figure 3.22. This was part of the McDonnell Douglas TAV (Trans-Atmospheric Vehicle) effort; that vehicle was powered by either an Aerojet, Sacramento, Air Turboramjet or an airbreathing rocket propulsion system. The inward-turning, variable capture area inlet [DuPont, 1999] provides the correct engine airflow from landing speeds to Mach 5 plus. The propellant tanks were cylindrical segment, multi-lobe structures with bulkheads and stringers to support the flat metal radiative thermal protection shingles (similar to those planned for the now defunct X-33). The nose was transpiration-cooled with a low-rate water-porous spherical nose. The sharp leading edges (the same leading edge radius was used for the nose tip) were cooled with liquid metal heat pipes. This approach was tested successfully during the 1964 to 1968 time frame, and found to be equal in weight and far more durable than a comparable ceramic tile/carbon-carbon system. Whenever the landing weights were heavier than normal, the switchblade wing provided the necessary margin for these operations.

For an aircraft the takeoff mode is not an issue: it is a runway takeoff and runway landing. However for a space launcher the issue is not so clear-cut. With

inward tuning inlet (after A.J. DuPont)

Figure 3.22. USAF FDL-7C/Model 176 equipped with a switchblade wing and retractable inward-turning inlet for airbreathing rocket applications.

inward tuning inlet (after A.J. DuPont)

Figure 3.22. USAF FDL-7C/Model 176 equipped with a switchblade wing and retractable inward-turning inlet for airbreathing rocket applications.

mass ratios for launchers much greater than for aircraft (4 to 8, compared to less than 2 for aircraft) runway speed may be impractical for some launchers with high mass ratios. So the principal option is vertical takeoff (VTO), with horizontal landing (HL) remaining viable. However, in some launcher studies, the study directives mandate horizontal takeoff whatever the mass ratio. Many launcher studies have been thwarted by this a priori dictate of horizontal takeoff. In reality, horizontal or vertical takeoff, like the configuration concept, is less a choice than a result of the propulsion concept selected. Horizontal takeoff requires that the wing loading be compatible with the lift coefficient the configuration can generate and the maximum takeoff speed limit. For high sweep delta planforms, such as that of the Model 176, the only high-lift device available is the switchblade wing and a retractable canard near the nose of the vehicle.

The basic FDL-7C/Model 176 was not designed for horizontal takeoffs. As presented in Figure 3.23, the takeoff speed, as a function of the SSTO launcher mass ratio to orbital speed, is very high for the basic delta lifting body, even for low mass ratio propulsion systems (squares). With the lowest mass ratio, the takeoff speed is still 250 knots (129 m/s) and that is challenging for routine runway takeoffs. Landing and takeoff speeds are for minimum-sized vehicles, that is, values of tau in the range of 0.18 to 0.20, where the gross weight is a minimum. Adding the switchblade wing provides a reasonable takeoff speed for all mass ratios (triangles). This takeoff speed with the switchblade wing deployed is approximately also the landing speed with the wing stowed. All of the launcher vehicles have very similar empty plus payload weight (operational weight empty); the landing speeds are essentially constant for all configurations and propulsion systems, corresponding to the lower

0 0

Post a comment