Re: Re: 1.4 g F1D performance

From: Jake Palmer <82.jake_at_gmail.com>
Date: Mon, 14 Apr 2014 10:23:08 -0700

I'm looking at the rubber spreadsheet to figure out some numbers. I know
the spreadsheet isn't 100% accurate, but it offers some ideas on
performance.

Using a 9" loop at 585mg net weight, 105% of max turns (several people seem
to achieve these numbers), 5% remaining turns, and an average RPM of 42, I
arrive at a 37 minute flight time. The peak torque is around .55, and I
see what I consider cruise torque (under .13) beginning at around 400 turns
used.

Using a 6" loop at 385mg net weight, 105% of max turns, 5% remaining turns,
and an average RPM of 42, I arrive at a flight time of 25 minutes. The
peak torque is around .54, and the cruise torque starts at around 270 turns
used.

The much shorter torque burst leads me to question whether VP props are
viable for the Kibbie Dome. I also question whether 30 minutes really is
possible anywhere but Lakehurst.


On Mon, Apr 14, 2014 at 10:03 AM, <ykleetx_at_gmail.com> wrote:

>
>
>
> Josh,
>
> You can't use the Hunt program to predict flight performance when the
> overall weight is the same and the only difference is the rubber.
>
> The program's prediction of time is directly proportional to the inverse
> of the sink rate and an empirically derived factor that assumes that the
> rubber weight is roughly 1.4X that of the airframe weight. And if the
> rubber weight is not 1.4X, there is a "penalty" factor. This penalty
> factor does not correctly account for the difference between 0.6 g and 0.4
> g of rubber.
>
> Whatever the maximum performance of 0.6g would be -- say 45 minutes, the
> new rules will be slighly more than 2/3 of that, or 30 minutes. Why
> slightly more? I am assuming that the added weight could eventually allow
> us to stiffen up the airframe and *possibly* improve performance.
>
> -Kang
>
>
>
Received on Mon Apr 14 2014 - 10:23:09 CEST