The F-117 used faceted designs on the fuselage and wings.[5]The F-117 had cross-axis coupling and destabilizing engine nozzles.[1] This caused the weapons bay, engines, exhaust nozzles, fuel tanks and avionics to be located further to the rear than would typically occur on a similar aircraft.[1] This caused an aft CG location which was good for reducing trim drag which also reduced radar cross-section as the radar signature is minimized when the control surfaces are not deflected.[1] The cross-axis instabilities are caused by wing vortices that come from a junction at the leading edge of the wing and the engine inlet.[1] The vortices loose coherence at high angles of attack, which causes a decrease in elevon effectiveness and a pitch axis instability.[1] It is always possible to depart from controlled flight if the airspeed was allowed to fall to zero during a steep climb.[1] If an engine fails on takeoff, the pilot should take their feet off of the floor, retract the landing gear (to engage the auto-trim) and concentrate on attitude and bank angle to accelerate to single-engine climb speed.[1] The F-117 did not have a speed brake.[2] The wing aspect ratio was 1.65.[6] A pair of all-moving V-tail control surfaces were not used for pitch control.[3] Each vertical tail was a fixed stub and an all-flying rudder.[3] The wings were swept to 67.5 degrees.[3] A landing parachute is deployed when the nosewheel touches down during landing.[3] It had a wingspan of 43′ 4″, a length of 65′ 11″, a height of 12’5″, and a wing area of 1140 ft^2.[3] Its maximum speed at sea level was 700 mph (M0.92), but the normal maximum operating speed was 648 mph (M0.87) at sea level.[3] The empty weight was 30,000 lbs and the MTOW was 52,500 lbs.[3] The aircraft is unstable in pitch and yaw for most of the flight envelope.[4] It exhibits a large dihedral effect and a nose up pitching moment with sideslip angles and high AOA.[4] The faceted design causes surface pressure spikes that are vulnerable to acoustic vibration that may crack the skin panels.[5]
The low aspect ratio, propulsion losses by inlet recovery and nozzle thrust coefficient account for significant performance reduction.[6] Most of the wing lift comes from a leading-edge vortex.[6] The low aspect ratio makes proper airfoil contouring less important.[6]
[[F-117 Longitudinal Instabilities]]
[[F-117 Lateral instabilities]]
[[F-117 Directional Instabilities]]
[[F-117 Model Tests]] – clarified the post-departure behavior of the aircraft
[[F-117 Directional Control]] – increases sideslip feedback gain to minimize destabilizing pitching moment
[[F-35 Auto Recovery Mode]] – F-35 would also depart flight if airspeed was allowed to bleed of in a sustained high-pitch climb
F-117 PAARS – shows a recovery from a vertical attitude
Sources
- [1] R. Loschke, “Development of the F-117 Flight Control System,” in AIAA Guidance, Navigation, and Control Conference and Exhibit, Austin, Texas: American Institute of Aeronautics and Astronautics, Aug. 2003. doi: 10.2514/6.2003-5762.
- [2] J. Abercrombie, F-15 Eagle The Early Years.
- [3] “THE HAVEBLUE/F-117 STORY.” Accessed: Jun. 28, 2024. [Online]. Available: https://roadrunnersinternationale.com/haveblue.html
- [4] R. Colgren, D. Enns, R. Colgren, and D. Enns, “Dynamic inversion applied to the F-117A,” in Modeling and Simulation Technologies Conference, New Orleans,LA,U.S.A.: American Institute of Aeronautics and Astronautics, Aug. 1997. doi: 10.2514/6.1997-3786.
- [5] “Structural developments of recent aircraft – F-117.” Accessed: Jul. 08, 2024. [Online]. Available: https://arc.aiaa.org/doi/epdf/10.2514/6.1995-1470
- [6] “The Effect of Signature Constraints on the F-117 Configuration Development.” Accessed: Jul. 14, 2024. [Online]. Available: https://arc.aiaa.org/doi/epdf/10.2514/6.2003-5761
Backlinks
[[Center of Mass]]
[[Dihedral Effect]]
[[Disadvantage of Elevons]]
[[F-14 Wing]]
[[F-117 Low-Observable Design]]
[[F-117 Nighthawk]]
[[Inlet Critical Pressure Recovery]]
[[V-Tail]]
[[Vortex Lift]]
[[Wing Aspect Ratio]]