return airspeed energy error matching APM internals
    This is positive when we are going too slow

def airspeed_energy_error(NAV_CONTROLLER_OUTPUT, VFR_HUD):
    '''return airspeed energy error matching APM internals
    This is positive when we are going too slow
    '''
    aspeed_cm = VFR_HUD.airspeed*100
    target_airspeed = NAV_CONTROLLER_OUTPUT.aspd_error + aspeed_cm
    airspeed_energy_error = ((target_airspeed*target_airspeed) - (aspeed_cm*aspeed_cm))*0.00005
    return airspeed_energy_error