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author | Thomas Gubler <thomasgubler@gmail.com> | 2013-02-24 16:01:08 +0100 |
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committer | Thomas Gubler <thomasgubler@gmail.com> | 2013-02-24 16:01:08 +0100 |
commit | 2707d2c1dde65dfb9ba48258994badb4b57f9627 (patch) | |
tree | bb7c4b742511ad4443f8a4b7c937a180b0208e1a /apps/systemlib/airspeed.c | |
parent | 2c2c65d446f991b273ee1f275fd2bc8440f74844 (diff) | |
download | px4-firmware-2707d2c1dde65dfb9ba48258994badb4b57f9627.tar.gz px4-firmware-2707d2c1dde65dfb9ba48258994badb4b57f9627.tar.bz2 px4-firmware-2707d2c1dde65dfb9ba48258994badb4b57f9627.zip |
more fixes for the airspeed readout
Diffstat (limited to 'apps/systemlib/airspeed.c')
-rw-r--r-- | apps/systemlib/airspeed.c | 40 |
1 files changed, 28 insertions, 12 deletions
diff --git a/apps/systemlib/airspeed.c b/apps/systemlib/airspeed.c index 5c68f8ea5..32943b2f5 100644 --- a/apps/systemlib/airspeed.c +++ b/apps/systemlib/airspeed.c @@ -40,14 +40,25 @@ * */ -#include "math.h" +#include <stdio.h> +#include <math.h> #include "conversions.h" #include "airspeed.h" -float calc_indicated_airspeed(float pressure_front, float pressure_ambient, float temperature) +/** + * Calculate indicated airspeed. + * + * Note that the indicated airspeed is not the true airspeed because it + * lacks the air density compensation. Use the calc_true_airspeed functions to get + * the true airspeed. + * + * @param differential_pressure total_ pressure - static pressure + * @return indicated airspeed in m/s + */ +float calc_indicated_airspeed(float differential_pressure) { - return sqrtf((2.0f*(pressure_front - pressure_ambient)) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C); + return sqrtf((2.0f*differential_pressure) / CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C); } /** @@ -55,14 +66,14 @@ float calc_indicated_airspeed(float pressure_front, float pressure_ambient, floa * * Note that the true airspeed is NOT the groundspeed, because of the effects of wind * - * @param speed current indicated airspeed + * @param speed_indicated current indicated airspeed * @param pressure_ambient pressure at the side of the tube/airplane - * @param temperature air temperature in degrees celcius + * @param temperature_celsius air temperature in degrees celcius * @return true airspeed in m/s */ -float calc_true_airspeed_from_indicated(float speed, float pressure_ambient, float temperature) +float calc_true_airspeed_from_indicated(float speed_indicated, float pressure_ambient, float temperature_celsius) { - return speed * sqrtf(CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C / get_air_density(pressure_ambient, temperature)); + return speed_indicated * sqrtf(CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C / get_air_density(pressure_ambient, temperature_celsius)); } /** @@ -70,12 +81,17 @@ float calc_true_airspeed_from_indicated(float speed, float pressure_ambient, flo * * Note that the true airspeed is NOT the groundspeed, because of the effects of wind * - * @param pressure_front pressure inside the pitot/prandl tube - * @param pressure_ambient pressure at the side of the tube/airplane - * @param temperature air temperature in degrees celcius + * @param total_pressure pressure inside the pitot/prandl tube + * @param static_pressure pressure at the side of the tube/airplane + * @param temperature_celsius air temperature in degrees celcius * @return true airspeed in m/s */ -float calc_true_airspeed(float pressure_front, float pressure_ambient, float temperature) +float calc_true_airspeed(float total_pressure, float static_pressure, float temperature_celsius) { - return sqrtf((2.0f*(pressure_front - pressure_ambient)) / get_air_density(pressure_ambient, temperature)); + float density = get_air_density(static_pressure, temperature_celsius); + if (density < 0.0001f || isnan(density)) { + density = CONSTANTS_AIR_DENSITY_SEA_LEVEL_15C; + printf("Invalid air density, using density at sea level\n"); + } + return sqrtf((2.0f*(total_pressure - static_pressure)) / density); } |