wrote: > 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 doe= s > not compute for me=85.I always doubt the performance figures in a sales > presentation and when they don=92t make sense to me=85..??? > > > > Bill B (hoping this generates an educational experience for me :>) > > > > We=92re talking about the amount of force exerted by the prop with the pl= ane > (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 o= f > 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=92t know how Tracy was interpret= ing > the question. > > > > Al > --000feaf190a04cfe3e0480ea88d1 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable

Al is correct about it taking HP to make static thrust with a prop but= the assumption about the relationship between HP and static thrust is subj= ect to a lot of variables.=A0 There is no fixed relationship between static= thrust and HP.=A0=A0 If there were, you could not account for the ability = of most helicopters to=A0hover.=A0=A0

=A0

=A0You could easily increase static thrust by 1.18 by increasing the d= iameter of the prop=A0and the=A0reduction ratio of the redrive=A0with=A0NO = increase in HP.=A0

=A0

But my real point was that static thrust is not a very useful measurem= ent to us.

=A0

Tracy

On Wed, Mar 3, 2010 at 11:06 AM, Al Gietzen <ALVentures@cox.net<= /a>> wrote:

Looking at the two siz= es of the engine, it takes 1.6 times as much horsepower to develop 1.18 tim= es as much static thrust!=A0 Somehow this does not compute for me=85.I alwa= ys doubt the performance figures in a sales presentation and when they don= =92t make sense to me=85..???

=A0
<= /div>

Bill B (hoping this ge= nerates an educational experience for me=A0 :>)=A0

=A0<= /font>

We=92re tal= king about the amount of force exerted by the prop with the plane (motor) s= tanding still.

So, it seem= s to make sense to me that the power needed to accelerate the air to genera= te the thrust would go as the cube root; and the cube root of 1.6 is very c= lose 1.18.

=A0<= /font>

To move the= amount of air it takes to generate the thrust certainly does take horsepow= er.=A0 Very much the same as the power i= t takes to drive the pump (or generator) on a dyno. =A0So I don=92t know ho= w Tracy was interpreting the question.

=A0<= /font>

Al

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