Ground Testing of an Operational Fighter Aircraft for P-Static Discharge Effects

Abstract

Static electrification o f an aircraft in flight cau­ ses electrical discharge's from the aircraft structure. These discharges are typically accompanied by radio fre­ quency noise in the electromagnetic spectrum utilized by aircraft communication and radio navigation systems.Such interference frequently disrupts or totally disables co­ mmunications,and has been demonstrated to cause signifi­ cant navigation errors. It therefore becomes essential to isolate the sources of these electrical discharges and design appropriate fixes for these problems. In the paper,a case of p-static noise on an operatio-r nal RF-4C aircraft is discussed.A method for the isola­ tion of p-static noise sources is described,along with proposed solutions for the identified problems. INTRODUCTION ELECTROSTSTIC DISCHARGE MECHANISMS AND EFFECTS One of the most persistant problems in operation of airborne communications and radio navigation systems is precipitation static or p-static.A direct outcome of pstatic is the coupling of EMI into the on-board comm-nav systems in the HF and VHF bands.However,p-static interf­ erence frequently extends, into the UHFbands as well. There are three stages of the aircraft electrificati­ on process, namely-p-ststic charging of the aircraft or parts of it,charge distribution between sections of the structure,and discharge from the airframe. Most approaches for reduction of p-static interferen­ ce aim at the elimination of charge ditribution effects .focusing on control of discharges from the airframe^) essentially because it is these discharges that gener­ ate the harmful effects. The charging process increases the electrostatic pot­ ential of the aircraft in respect to the environment, until a breakdown phenomenon occurs causing discharges, which induce interference into avionic systems.These di­ scharges can include any or all of the three effects (Figure 1 ) : ^ Corona discharges .mainly at aircraft extremCH2294-7/86/000-0288 $01 .OC(C)l986 IEEE 288 eties,where potential gradients ate higher (Figure 2a). -Streamer discharges from dielectric surfaces (such as radomes , windshields) to surrounding metal frames (Figure 2b). -Sparks between inadvertantly unbonded metal sections in close proximity (figure 2c). METHODS FOR REDUCTION OF P-STATIC EFFECTS Simple methods exist for p-static control: -Sparks can be avoided by adequatly bonding and the maintaining of continous conductivity of the struc­ ture I M W O W fvuo ( M K o w w e tB STMAMtftS Ott PACT**/*/> *•** iMJVtArtMfr