Speedometer insensitive to icy conditions and heavy rainfall

A speed measurement system measuring the relative velocity V of a mobile body relative to an ambient air mass independent of weather conditions, the mobile body being adapted to move at least at subsonic and transonic speeds, said speed measurement system comprising:

• an elongated fin disposed in the ambient air mass, having a profile defined by a spanwise axis ZZ′ and a set of points having the coordinates X and Y forming the fin profile for each point of spanwise axis ZZ′, one axis OX of X values defined sensibly pursuant to the longitudinal axis of the fin profile and an axis OY of Y values being perpendicular to the axis OX of X values comprising:
• a portion A and a portion B, said portion A having a thickness increasing in the direction of B and forming the leading edge of the fin, said portion B having a decreasing thickness and being located at the rear of portion A relative to the fin moving direction in the mass of air and forming the back of the fin,
• at least one heating means,
• at least one dynamic pressure tap PB located in the portion B, comprising at least one orifice having its opening facing in the opposite direction of the displacement direction of the fin in the mass of air,
• an angle BETA defined between the axis OX and the intrados or the extrados of the portion A of the fin,
• at least one static pressure tap PS placed on a fuselage or on a base of the fin,
• at least one means for measuring and/or calculating the angle of attack ALPHA of the fin,
• at least a calculating means configured to determine the speed V of the mobile body relative to the mass of ambient air from at least the values of static pressure and dynamic pressure,
• wherein,
• the fin is relatively thin and has a wedge shape at least in its portion A, the leading edge of the wedge is a sharp angle of radius less than or equal to 2 mm;
• the fin has at least partially a tapered and truncated shape comprising at least one sharp edge of radius less than at least 2 mm between the portion A and the portion B so that in transonic speed the wave shock created at the said sharp angle is stabilized and/or the path of field lines is modified at the aft of the fin;
• the portion B, forming the aft part of the fin, comprises at least a zone having a circular shape convex or concave B1 and/or B2 to filter particles so that the particles of greater density than the density of the air, trapped in the fluid flow to the aft of the fin, are ejected and/or spread out under the effect of centrifugal forces to the area near a pressure tap PB said B1 and/or B2 zone allowing to channel and/or to stabilize the path of the airflow to the aft of the fin, said fluid flow having a roll-shaped and/or a vortex axis substantially parallel to the axis ZZ′;
• the fin comprises at least one rib disposed substantially perpendicular to the span axis ZZ′ of the fin and extending at least in the portion B of the fin, said rib being adapted to the channel airflow in a region close to the dynamic pressure tap PB located at the aft of the fin;
• the function F (V)=(PS−PB)/PS enabling to deduct the relative speed V of a mobile structure with respect to a mass of ambient air independent of weather conditions, is a univocal function in the direction of (PS−PB)/PS to V, strictly increasing as a function of the speed V, this in the entire subsonic and transonic domain for each value of the angle of attack ALPHA and/or a sideslip angle GAMMA.