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Date: Mon, 19 Dec 2005 17:17:39 -0700
From: Bob White <rlwhite@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Props
Message-Id: <20051219171739.c25bcfbe.rlwhite@comcast.net>
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Hi Buly,

That formula will give speed in fps.

3.14*64*(5500/2.17) = 509346

508346/720 = 707 fps

88 fps = 60 mph so 707 fps = 482 mph which is well below the speed of
sound.

Bob W.

On Mon, 19 Dec 2005 18:44:03 -0500
Bulent Aliev <atlasyts@bellsouth.net> wrote:

> Thanks Dave. it makes me feel better now that I know I was wrong. My  
> problem now is: I can spin my "monster prop" (static) up-to 4000RPM  
> and 50" MP I don't think I can get much more in motion and may not  
> get enough rpm for flight. I'll see first how much difference it will  
> make on fast taxi. John Slade also will bring his Performance prop  
> one day, so we can compare them.
> BTW the prop tip speed formula given to me was:
> Prop D" x 3.1416 x RPM divided by 720
> Buly
> 
> On Dec 19, 2005, at 6:06 PM, David Leonard wrote:
> 
> > Oh, BTW Bully.  You will also note that at 6000 RPM the prop is  
> > doing 2750 which a lot of certified props will turn, even if 74"long.
> >
> > Also, short prop are not necessarily less efficient, its just that  
> > the speed of peak efficiency is shifted to a higher airspeed, and  
> > probably that peak is a little more narrow.
> >
> > Dave Leonard
> >
> >
> > On 12/19/05, Buly <atlasyts@bellsouth.net> wrote:
> > Yesterday somebody gave me the formulas to calculate the prop tip
> > speed. I did some calculations and looks like us with the 2.17
> > redrives are kind of painted in the corner. Hope I'm wrong, but if I
> > want to keep the tips from going supersonic, I have to cut down the
> > prop to 64" or keep the engine below 5500 RPM. The choice is either
> > inefficient prop and adequate power, or efficient long prop and not
> > getting all the power from the engine? Am I wrong?
> > Buly
> > atlasyts@bellsouth.net
> >
> >
> >
> >
> > --
> > Homepage:  http://www.flyrotary.com/
> > Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/
> >
> >
> >
> > -- 
> > Dave Leonard
> > Turbo Rotary RV-6 N4VY
> > http://members.aol.com/_ht_a/rotaryroster/index.html
> > http://members.aol.com/_ht_a/vp4skydoc/index.html
> 
> Bulent Aliev
> atlasyts@bellsouth.net
> http://home.bellsouth.net/p/s/community.dll? 
> ep=16&ext=1&groupid=164323&ck=
> 
> 
> 


-- 
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