lml@lancaironline.net Mailing List Archive

Grayhawk,

Yes... 208/195 is only about 1.067 ratio.

However, changes in speed with changes in prop efficiency is not linear.

What you are missing is that speed (absent the details of the drag polars) up in this range generally goes as about the cube root of power, or in this case, thrust HP ( Thp = Bhp X nProp) where nProp is the efficiency of the prop at the given airspeed, RPM and Hp loading.

Actually, one ought to use the TAS numbers, but short of that:

So (208/195)^3 about = to 1.21 - - thus, my comment that the numbers reported suggest about a 20% improvement in prop efficiency.

Regards, George

PS. Has anybody developed a set of drag polars for a Lancair IV P ?

-----Original Message-----

-----Original Message-----
From: Sky2high@aol.com [mailto:Sky2high@aol.com]
Sent: Sunday, December 29, 2002 8:43 AM
To: Lancair Mailing List
Subject: [LML] Re: Scimitar Prop vs. Original Hartzell Prop - Comparison

In a message dated 12/28/2002 7:47:19 PM Central Standard Time, marv@lancaironline.net writes:

The increase from 195 to 208 suggests an improvement in prop efficiency on
the order of 20% or so.

If the old prop was a miserable 85% (it should be in the 87 to 91 range)
then the new prop would be up around 102% or so in efficiency.

(208-195)/195=.103 or about a 10% improvement

I've been told that props are usually 80% efficient - a 10% improvement would bring that to 88% efficient.

Grayhawk