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Aug 10, 2019, 10:06 PM
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DIY to measure the friction force of air on moving object in your garage

When airplane rests in still air, the weight of drop tank is the only force upon drop tank. In flight, the force of air on drop tank will become important, which is the friction between air and moving drop tank. The combined force will exceed the gravity force.

How much force on the drop tank in flight? I propose a simple test, use leaf blower to blow on the drop tank.

Most leaf blower works at around 150 mph, and diameter of nozzle is pretty close to the diameter of drop tank in most 90mm EDFs. So if the blower blows the air to the front end of drop tank at close distance, we can assume the air speed on the drop tank is somewhat smaller but close to 150 mph. Those has pitot tube can actually very easily measure the air speed from blower to the drop tank. The farther away nozzle from drop tank, the lower speed of airflow.
  • Secure a bamboo stick or 3mm piano wire on upright position. Secure the drop tank horizontally on the tip of bamboo stick/piano wire. This may actually be challenging to achieve but I will just leave it like that for future whoever interested to explore in experiment.
  • Turn on blower and point the airflow toward the drop tank in a headon manner (simulate the airflow toward drop tank in flight), keeping the drop tank in the center of airflow. If drop tank has stabilizer, it is easier to maintain drop tank at the center of airflow. The drop tank will be blown away from the upright position, causing the piano wire to bend. Measure the average angle the piano wire is bent. In theory, the 150mph is the velocity of air at the nozzle. So the nozzle should be placed as close as possible to the tip of drop tank
  • Next place the hook of fish scale on the location in bamboo stick or piano wire where the drop tank was placed, pull the hand holder of fish scale horizontally in the same direction as leaf blower airflow, UNTIL the angle of bamboo/piano wire bent by the fish scale equals the angle by the leaf blower airflow. Record the force at this bent position. This force should be a close estimate of the force when the airflow acts on the drop tank, which gives us idea how much force air acts on drop tank in flight. One can actually explore the relationship between the distance between nozzle to drop tank versus the force. A very good aerodynamic experiment for aerospace engineering? lol

One can actually explore the relationship between the distance between nozzle to drop tank versus the force. A very good aerodynamic experiment for aerospace engineering? lol
Last edited by edwen303; Aug 11, 2019 at 01:55 AM.
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