TP 13579 PROCEEDINGS of the 2nd International Meeting ... - UQAC

IMAPCR ’99
Contamrunway Snow Tests
78. Marijn Giesberts, Research Engineer, National Aerospace Laboratory (NLR), The
Netherlands, stated that the current JAR AMJ 25X1591 is only advisory. It does not provide
correct answers for water precipitation drag for smaller types of aircraft. The models are
based on the theory of EWD for snow.
79. The objectives of the European Project were to improve the AMJ models concerning:
• precipitation drag of smaller aircraft when operating from runways covered with water,
slush, or dry natural snow;
• evaluation of hydroplaning speed and associated effects.
80. Mr. Giesberts stated that because of the physical differences between snow and water, AMJ’s
theory of EWD is basically wrong. Snow is permeable and porous. It can take on a variety of
forms and densities and is thermodynamically unstable.
81. Snow/slush tests were conducted on three aircraft under the following conditions:
• SAAB 2000 at the Malmen Airport (Sweden) with 100 mm of fresh snow
(SD [snow density] = 0.1) and 30 mm slush (SD = 0.56);
• NLR CITATION II at the Skavata Airport (Sweden) with 40 mm of fresh snow
(SD = 0.125);
• Dassault Falcon 2000 at the Ivalo Airport (Finland) with 100 mm snow (SD = 0.11).
82. The tests show that:
• precipitation drag in natural dry snow at low speeds is substantial because of
compression drag;
• no hydroplaning occurs on dry snow;
• the snow drag increases with speed, but is less than what AMJ predicts;
• for SD > 0.5 (slush), precipitation behaves like a fluid;
• dry snow has no impingement on wings or fuselage.
83. Based on the test results, a new theoretical model was developed for predicting spray
patterns and impingement drag by the National Aerospace Laboratory (NLR). A new
method was also developed for predicting drag due to dry snow. The Engineering Sciences
Data Unit (ESDU) spray patterns method (item 83042) was updated and the ESDU model
of drag calculation due to impingement (item 98001) was improved.
84. The overall conclusions were:
• the current AMJ 25X1591 underestimates the drag due to water/slush for smaller
aircraft;
• the drag by dry snow as predicted by AMJ 25X1591 is incorrect;
• the new NLR model for dry snow drag looks promising;
• the NLR theoretical model for spray prediction and precipitation drag looks promising.
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