Optimizing Air Pressure for Building a Hovercraft: Tips and Tricks

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SUMMARY

This discussion focuses on optimizing air pressure for building a hovercraft using a plastic garbage bag and an old computer fan. The key to achieving lift is maintaining high airspeed and pressure within the bag, which is influenced by the size and number of holes created for air release. The formula for lift, F = ρv²A, emphasizes the importance of air density (ρ), velocity (v), and the area of the holes (A). Experimentation is recommended to find the optimal balance between hole size and quantity to maximize lift without risking bag rupture.

PREREQUISITES
  • Understanding of basic physics principles, particularly fluid dynamics
  • Familiarity with the lift equation F = ρv²A
  • Knowledge of air pressure and its effects on lift generation
  • Experience with hands-on experimentation and prototyping
NEXT STEPS
  • Research the effects of hole size on airflow and lift in hovercraft design
  • Learn about fluid dynamics principles relevant to hovercraft operation
  • Experiment with different configurations of hole sizes and quantities to optimize lift
  • Explore materials and designs for hovercraft construction to reduce friction
USEFUL FOR

This discussion is beneficial for hobbyists, engineers, and students interested in hovercraft design, fluid dynamics, and practical applications of physics in engineering projects.

Aki
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I'm building a hovercraft, and I am using an old computer fan to blow air into a plastic garbage bag and fill it up. I need to poke a few holes on the bottom of the garbage bag to let the air out, and I want to have a less friction as possible. What size should the holes be? And how many?
 
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Aki said:
I'm building a hovercraft, and I am using an old computer fan to blow air into a plastic garbage bag and fill it up. I need to poke a few holes on the bottom of the garbage bag to let the air out, and I want to have a less friction as possible. What size should the holes be? And how many?
You need to start by figuring out the physics of a hovercraft's lift.

The hovercraft lifts off the ground when the downward force of the air is equal to the weight of the hovercraft.

Since
F = dp/dt = vdm/dt = v\rho dV/dt = vA\rho ds/dt = \rho v^2A

where \rho is the density of the air, v is the air speed and A is the total area of the holes, if you know the speed of the air leaving the bag and the total area of the holes, you can work out the lift. What you want to do is keep the speed of the air high since it contributes lift as v^2.

Since v^2 is proportional to the pressure, you want to keep the pressure in the bag high and let out a lot of fast jets of air through a lot of very tiny holes. If you don't make enough holes, the bag will burst. If you make too many, you won't get enough lift (pressure will be too low). I think the easiest thing to do is experiment with it.

AM
 
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