DSpace Repository

Welcome to the NLR Reports Repository

Royal NLR conducts research, which is published in reports. Only a minor part of these reports is made public. This repository holds these public, so called Technical Publications (TP), mainly produced from 1996 up till now.

Technical publications published before 1996 may be obtained using the request-form. Other types of NLR-reports are Contract Reports (CR) and Technical Reports (TR), which in general are not public. You may however request a copy by using the request-form. In some cases permission may be granted, depending on specific properties and contractor of the report. Reports will be supplied as pdf-file.

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Recent Submissions

Scaled flight testing supporting the development of radical new aircraft
(SFTE, 2023) Jentink, H.W.; Bremmers, F.
Scaled flight testing can contribute to valuable reduction of risk and cost in the development of a radical new aircraft. The role of scaled flight testing in the aircraft development process is described, where it is essential that the relationships between the small-scale and full-scale results are properly defined. The validity of results of scaled flight testing for predicting the full-scale aircraft properties is addressed next. A 1:8.5 scaled version of a typical large passenger aircraft was built, tested in the wind tunnel and flight tested. During the flight tests an accurate flight test instrumentation system measured the scaled aircraft flight parameters. Results of the scaled flight testing have been compared with full-scale test results which validates the value of the scaled flight testing methodology. In a next step the scaled flight testing methodology is applied to investigate and demonstrated the benefits of distributed electric propulsion. The scaled aircraft has been re-built in the same shape but the jet propulsion is replaced by propulsion with six propellers. The development, manufacturing, wind tunnel test and taxi tests are described, flight tests still have to be performed. Finally the role of the flight test engineer in the scaled flight test campaigns has been compared with the role of a flight test engineer in a typical full-scale flight test campaign. The roles were chosen very similar and that worked out very well in these scaled flight test campaigns.
Reduced Flight Inspection runs for ILS using RPAS
(SFTE, 2023) Heijstek, J.J.; Wilmes, I.J.M.P.; Verpoorte, J.; Stuip, M.; Tervoort, A.A.; Bosch, J.
This paper summarizes the Reduced Flight Inspection approach applied in The Netherlands, which is periodic flight inspection with some measurements moved from the aircraft to the ground. The paper contains the justification of the ground measurements being performed using a measurement car with an extensible antenna mast, and outlines the development in The Netherlands of the alternative ground measurement approach based on Drone Flight Inspection.
Distributed electric propulsion tested on scale in aircraft
(SFTE, 2025) Jentink, H.W.; Deck, K.T.; Heer, P. de
A scaled aircraft with distributed electric propulsion was built and tested in flight. The approach for the tests, the test campaign and the results are presented. Demonstrating the benefits of distributed propulsion and identifying the risks of the development with scaled flight testing are the objectives of the tests. The scaled aircraft was first installed in a large wind tunnel to acquire aerodynamic data and to test the aircraft and the aircraft systems. The electric propulsion system with propellers was also operated in the wind tunnel to acquire thrust effects. After the wind tunnel campaign, the batteries were installed and the aircraft was tested on the ground. Regretfully, a thermal runaway of the batteries caused an incident destroying the aircraft. The aircraft was built again with modified batteries and modifications in the power distribution system. Iron bird tests preceded the ground testing of the aircraft with batteries. Lessons learned from the incident and improvements in the design of the aircraft are addressed. After stationary ground tests, the aircraft was subjected to taxi tests on Deelen Air Base in the Netherlands and eventual flight tests were on the airport in Grottaglie, Italy. The aircraft was operated from a ground control station in which pilots and test engineers controlled the aircraft Beyond Visual Line Of Sight (BVLOS). The test flights were initially attributed to qualify the aircraft for the flight envelope foreseen for the test objectives and in a second phase dynamic manoeuvres were executed by a dedicated autopilot. Accurate instrumentation was installed in the aircraft that measures, amongst others, air data, inertial data, angular position of surfaces and engine parameters. Furthermore, the electrical power system is closely monitored to reveal the condition of batteries and systems. Manoeuvres were performed with symmetric thrust on left and right propellers and with asymmetric thrust. Controllers were developed by partners ONERA and CIRA to control and steer the aircraft with differential thrust, also with the remote human pilot in the loop. The control during one-engine-inoperative conditions was also subject of the campaign. Results demonstrate the DEP technology with respect to flight dynamics and control.
On the effect of infrared camera positioning for in-flight boundary layer transition measurements
(SFTE, 2026) Mertens, C.; Rius-Vidales, A.F.; Kotsonis, M.; Jentink, H.W.
Infrared thermography is an optical measurement technique that is attractive for in-flight measurements of the boundary layer transition location on aircraft wings because it requires minimal instrumentation of the test object. A known drawback of this technique is however that the position of the infrared camera with respect to the analysed surface can influence the measurement accuracy. The positioning of the infrared camera on the test aircraft for in-flight measurements is a complex design trade-off that is influenced by many different factors. In this paper, measurement results from a wind tunnel experiment where adverse infrared camera positions were emulated are presented. Relatively simple corrections for the perspective distortion and the directional emissivity effects were subsequently applied to the image data. The results show that the boundary layer transition location can be extracted accurately and reliably under relatively steep viewing angles, with up until 75 degrees between the principal viewing axis and the surface normal direction. These results are useful for the design of in-flight experiments, where the demonstrated feasible range limit for the orientation between the infrared camera and the test surface can be used as a design constraint.
Delivery from the sky : investigating visual cues to communicate robot intentions in simulated public spaces
(Nature, 2026) Lingam, S.N.; Petermeijer, S.M.; Obaid, M.; Martens, M.H.
As robots such as drones begin delivering packages from the sky in public spaces, humans will interact as recipients. Clear communication of a drone’s vertical motion and delivery intentions is essential to reduce feelings of uncertainty and build trust among the public. This study investigates how visual cues, including delivery methods and interfaces, communicate a drone’s drop-off and take-off intentions and affect recipients’ uncertainty in a simulated public environment. Through a video-based online questionnaire, 150 participants viewed scenarios where a drone delivered a package either by landing or via a cable-drop mechanism, each presented with or without visual interfaces such as onboard lights, a display, or ground projection. Participants rated the scenarios for uncertainty, understandability, predictability, trust, and convincingness, and provided qualitative feedback. Results show that visual interfaces improved participants’ ability to predict drone actions, increased certainty in approaching the drop-off spot, and improved trust. While lights posed challenges with visual clarity, both display and projection interfaces conveyed vertical motion and delivery intentions effectively. Projection was particularly recommended, as it marked the drop-off spot on the ground and a safety boundary. We discuss the implications of our findings beyond delivery scenarios, considering broader public space interactions with robots operating in vertical planes, and highlight the need for validation through real-world experiments.