Standalone trailing probe for aero metrical measurements

This article describes a design of a probe intended for aero metrical instrument testing which is being hanged under an airplane. The probe collects data in an undisturbed airfield and compares them with data provided by dashboard instruments. The differences reveal quality of an airplane prototype design during maiden flights. The most important flight instruments are an altimeter and an air speed indicator. These instruments can be tested by comparison with data from a trailing probe. While commonly used probes fed pressure from the probe entry points up to the airplane cabin by pipes, the prototype described in this paper uses wireless data link to transfer data to a data acquisition unit. Beside the altitude and speed the probe also measures its angle of attack and angle of sideslip which are used onboard to compensate for errors caused by probe alignment within the airfield. The designed system consists of two parts: the probe itself and a winch mechanism. Because the probe sensors are standalone the measured data reflects exactly the situation at the probe entry points. It means the probe measurements have to be corrected with regards to the length of the wire released from the winch and also for the speed of flight that influences the angle between the horizontal axe of an airplane and the wire connecting the airplane and the probe. Because the winch mechanism introduces problems with mounting and data correction the probe is designed to allow direct mounting on the airplane wing after removing its tail stabilization part. This design feature prepares the probe to be used also as an entry point for the new system for position angles measurement. Precision of the probe, pros and cons of both methods are discussed in the article.