D-21 MACH 3 DRONE

VSKYLABS Physics-based D-21 Mach-3 launchable drone was implemented in v2.0.

Here is important information regarding its operation:

The VSKYLABS D-21 Mach-3 drone is defined as a *Weapon* in X-Plane 12:

  • To load or remove the D-21, simply use the X-Plane 12 weapon-loading screen.
  • The D-21 affects weight, balance and overall drag characteristics of the carrying aircraft, resulting in authentic aircraft handling and performance characteristics.

SR-71A vs M-21 weight and balance configuration:

  • Originally the D-21 was carried and launched from the M-21 which was a variant of the A-12 aircraft.
  • The M-21 configuration was lighter than the SR-71A configuration. A stripped-down A-12 aircraft which was modified to carry the 11,000 lbs D-21 drone on its back, in the aft section of the aircraft. The M-21 aircraft CG had to be modified to allow reasonable change in overall CG once the D-21 was launched.
  • The modification of the M-21 included changes in empty-weight, as it was crucial to allow completing the air-refuel phase for Mach-3 climb schedule (fully loaded with fuel), and also carrying the 11,000 lbs drone.This resulted in a lower empty-weight of the M-21 was reduced compared to the SR-71A.
  • The VSKYLABS SR-71-TB recognizes when the aircraft is loaded with the D-21 drone, or when it is removed (by launch or by manually removing the D-21 weapon by using X-Plane 12 weapons loading system) and sets the weight and CG accordingly, to allow a full air-refueling of the M-21, while carrying the D-21, yet remain in the maximum weight and CG envelope.
  • Once the D-21 is launched, or removed manually, aircraft configuration shifts back to SR-71A. The process runs in real-time and only mild change in CG is noticeable.
  • Loading/unloading the D-21 Drone: Can be done via X-Plane 12 Weight & Balance / Weapons menu, or with direct interaction using your mouse/touch controller. Interaction zones are located on the drone (to remove it) and on the upper surface of the aft fuselage (to install it). Removing/installing the drone is affecting the SR-71A / M-21 aircraft weight and balance configuration.

D-21 operation and launch:
  • The VSKYLABS SR-71-TB cockpit includes a modified replica of the authentic D-21 startup and launching panel, which was slightly modified to be integrated in the front cockpit (originally it was located in the back seat of the M-21, which was a modified variant of the A-12).
  • The modified panel in the VSKYLABS SR-71-TB is fully functional, allowing to power the drone, set the fuel pumps, ignite the ram-jet, which spools up to launch-thrust threshold (equipped with a PSIA gauge), going through its FCU tests, then having the 'GO' approval for launch.
  • The D-21 was a ram-jet driven vehicle. Launching the D-21 requires exceeding (or nearly exceeding) the Mach-3 envelope (above Mach 2.7), therefore completing a full climbing profile. Failing to do so will prevent the D-21 from starting up, and the 'NO-GO' light will illuminate.
  • The release sequence includes an initial pitch-up moment, for clearing the M-21. After the D-21 clears the M-21 vertical stabilizer area, its ram-jet engine spooled up and the initial pitch attitude translated to climb/cruise attitude. This is being simulated in the VSKYLABS D-21.

D-21 launch panel and checklist:

  • Complete a Mach-3 climb schedule (including air refueling).
  • Sufficient ram-jet thrust exceeds above Mach 2.7 - verify on-speed!
  • Power up the D-21.
  • Ejecting fairing - the nose/tail fairing are already ejected. In the real D-21 launches from the M-21, flying with the aerodynamic covers until launch was abandoned due to safety issues. In later test-flights, the D-21 was attached to the M-21 without the covers, from takeoff to launch.
  • Engine fuel pumps - activate.
  • Ignition - ignite the ram-jet engine.
  • Monitor launch thrust (PISA indicator + green light).
  • AFCS tests - all green.
  • Verify GO green light.
  • Launch!

The release sequence includes an initial pitch-up moment, for clearing the M-21. After the D-21 clears the M-21 vertical stabilizer area, its ram-jet engine spooled up and the initial pitch attitude translated to climb/cruise attitude. This is being simulated in the VSKYLABS D-21.

Reference images and videos: 


Reference video - Lockheed D-21 narrated by Kelly Johnson.
A fascinating video showing deeper information regarding the D-21, including the general mission outlines and the launch sequence, with the authentic back-seat panel (08:50 in the video):



Here's a short video showing several launches of the VSKYLABS D-21 during early development (additional information can be found in the video details section):