Mailing List flyrotary@lancaironline.net Message #50202
From: Al Gietzen <ALVentures@cox.net>
Subject: RE: [FlyRotary] Re: single rotor
Date: Wed, 3 Mar 2010 11:06:02 -0800
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>

Looking at the two sizes of the engine, it takes 1.6 times as much horsepower to develop 1.18 times as much static thrust!  Somehow this does not compute for me….I always doubt the performance figures in a sales presentation and when they don’t make sense to me…..???

 

Bill B (hoping this generates an educational experience for me  :>) 

 

We’re talking about the amount of force exerted by the prop with the plane (motor) standing still.

So, it seems to make sense to me that the power needed to accelerate the air to generate the thrust would go as the cube root; and the cube root of 1.6 is very close 1.18.

 

To move the amount of air it takes to generate the thrust certainly does take horsepower.  Very much the same as the power it takes to drive the pump (or generator) on a dyno.  So I don’t know how Tracy was interpreting the question.

 

Al

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