How much lift thrust would a 252 CFM 120mm fan provide?

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66 replies · 77K views
russ_watters said:
No. It comes from Bernoulli's equation and Bernoulli's equation is actually about kinetic energy. Note the similarity to the kinetic energy equation: 1/2 M V^2.

Thank you russ, this has explained it.

Also, thank you for confirming the 0.75N value. (I'm just glad laser and myself got there eventually)
 
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russ_watters said:
No. It comes from Bernoulli's equation and Bernoulli's equation is actually about kinetic energy. Note the similarity to the kinetic energy equation: 1/2 M V^2.

well that's good, it means there was no dependence on knowledge of some funky aspect of fans; it came down to properly using Bernoulli's equation.

i used to be afraid of being wrong, but the only way to improve and master things is by trying and learning from mistakes. thanks for the correction/information.
 
last night i was too lazy to look at the NASA page (general thrust equation) i had previously linked to see why it didn't including the 1/2. it does include but not in a "thrust for idiots" type way. yet i looked at their page on propeller thrust and that one is totally a (propeller) "thrust for idiots" page, which really helped me understand. i trusted russ_watters answer, but i wanted an extended version. i figure there is a few others who may find it useful too. here is the link:

http://wright.nasa.gov/airplane/propth.html

btw, it does say that you use the blade length to calculate the area, so the fan in this topic will have a higher thrust than calculated. looking at typical ducted fans, the thrust will be 25% greater when taking the revised area into consideration. minus the 5% losses, it'll be about 20% greater thrust than calculated, so 0.9N per fan.
 
Lazer57 said:
Keep it under 3 pounds if you want it to lift off the ground with two of those.

Yeah, I know. I can't imagine everything else in the aircraft weighing more than 3 pounds with those fans.
 
What power source are you going to use? Weight considerations from batteries etc?