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Old Oct 06, 2012, 10:32 AM
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Texas Buzzard
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Joined Mar 2004
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Ducted Fan & Velocity of the air in tailpipe.

I used to watch F-84s takeoff carrying two 500 lb boms + 6 HVAR rockets fully fueled. They were able to takeoff. ( in the 1950s)

Having some experience in free flight and controline I marveled at how that jet engine could produce the needed thrust to make all that mass accelerate. I envisioned all the gasses escaping from the tailpipe and wondered what mass was being driven throught that tailepipe.

I knew some basic physics, i.e., Newtons 3rd Law, and it seemed that the very low density of the escaping gases would have to have a great velocity in order to produce the significant thrust needed.

If we were to compare the Momentum of the exhaust gases to the momentum of the airplane at first it seems that they would be equivalent to one another..... friction aside.

I have an electric ducted fan rated at 1.8 pounds of thrust by the manufactuer.
I know the density of air is 1.29 grams per liter.

What would the exaust velocity of the air have to be to produce 1.8 pounds of thrust?

You might want to rewrite this question......... ??? Please do not tell me to buy an anemometer.....ha, ha.
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