The German Aerospace Center's (DLR) DG 300-17 measures the speed polar of other gliders. The results of these measurements make it possible to increase the cruise speed of non-powered aircraft.
DLR (CC-BY 3.0).
The single-seat DG 300-17, made of glass-reinforced plastic (GRP), may look like an ordinary glider, but it is in fact quite extraordinary. The performance of the DG 300 has been accurately measured and it is used as a reference to assess the performance of other gliders. In cooperation with the Technische Universität (TU) Braunschweig, it has been specially equipped with the instruments needed for this task. It thus acts as a measuring device for other gliders - in a way, it is the calibration standard for determining their speed polars. The speed polar shows the rate of descent of an aircraft versus its horizontal airspeed.
An important condition for an accurate evaluation of other gliders is that the performance differential between both aircrafts should not be significant. In order to find a good compromise to match the broad performance spectrum of all types of gliders, the DG 300-17 has a wingspan of 17 metres, two metres more than the standard version - hence the type designator "17". The DG 300 was designed by Wilhelm Dirks and manufactured on behalf of DG Flugzeugbau GmbH by the Slovenian company Elan. In the past, the relative motion between both gliders was determined from photos in a quite complex manual procedure. However, today, DGPS data (Differential Global Positioning System) are used for accurate positioning.
The following modifications differentiate the DG 300-17 from the standard DG 300 Elan:
Missions - research focus
The DG 300-17 high-performance glider is deployed for the following research experiments:
The DG 300-17 measures the speed polar of other gliders. The results of these measurements make it possible to increase the cruise speed of non-powered aircraft. Determining the speed polar is a complex procedure: all absolute measurements will lead to distorted results as they will always be influenced by the movement of the air mass in which the aircraft flies. This can be solved by using a comparison flight procedure. This technique measures the relative motion of a glider in relation to the calibration glider, rather than its absolute motion in relation to the ground. In this way, distortions caused by large-scale movement of air masses are eliminated: both the calibration glider and the glider that is being measured fly in the same air mass. However, even this procedure requires calm weather conditions and free of turbulence if one wants to obtain sufficient accurate results.
In order to qualify the DG 300-17 as a calibration aircraft, it is not only equipped with the necessary instrumentation system but it is also serviced with special care by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). Even small scratches on the coating could alter its performance and eventually make the aircraft useless as a calibration standard. For this reason, the DG 300-17 is used in calibration flights only and its performance is checked in continuously repeated control surveys.
Last modified:13/12/2018 10:47:53