Taifun Polar Graphs

Abstract: I am trying to compare the Taifun as a "sailplane" however I can´t still find the polar graphs, does anyone have them?

Subject: Taifun Polar Graphs
From:"lchapa77" <lchapa@
Date: 10/24/06 5:17 PM
To: Taifun17E@yahoogroups.com

Hello everyone, I am trying to compare the Taifun as a "sailplane" however I can´t still find the polar graphs, does anyone have them? if not, I can have a very good idea of the performance for cross country soaring by knowing the following - What would be the speed at a 500 fpm constant sink rate? that is MPH or Knots @ 500 fpm constant sink? I know the minimum sink is aroung 0.95m/sec @ 52.8 MPH, but what will be that number at 2.0 or 2.5 m/sec ?
Thanks,

Leobardo

Subject:Re: Taifun Polar Graphs
From:"Finbar Sheehy" <finbarsheehy@>
Date:10/25/06 8:41 PM
To:Taifun17E@yahoogroups.com

I have not been successful in finding anyone with actual measured performance data for the Taifun (yet), but in the meantime here's something that may help you a bit.

If you know the best L/D and the speed for best L/D you can approximate the sink rate of a glider (except close to or below stall speed) as follows:

Sink rate = S
Speed = V
(note, both in the same units, i.e., knots, kph, etc.)

Then S = A x V^3 + B/V

where

A and B are defined as follows:
A = 1/(2 x VL^2 x L/Dmax)
B = VL^4 x A

where
L/Dmax is the maximum value of L/D
VL = Speed for best L/D

According to the Taifun manual (which I don't really trust - see below), L/Dmax = 28.6 at VL= 59kt
so
A = 5 x 10^-6
B = 60.86

and Sink(kt) = 0.000005 x V(kt)^3 + 60.86/V(kt)

Again, this would be approximately true, away from the stall, and it doesn't take different flap settings into account.

Sample points: (Speed(kt)/Sink(kt)/LD) (50/1.84/27) (55/1.94/28)
(60/2.09/28.6) (70/2.58/27) (80/3.32/24) (90/4.32/21) (100/5.61/17.8)

This formula would suggest minimum sink is about 1.8 kt (185 fpm) at a speed of 45 kt. However, this is a speed barely above the stall, so the formula is probably invalid, and both the minimum sink speed and minimum sink rate will be higher than this.

Note that the manual also specifies a minimum sink rate of 2.3kt at 51kt airspeed. If the glider truly gets 28.6:1 at 59 kt then its sink rate at 59kt would be only 2.09kt, which is less than the stated minimum sink of 2.3kt, so I don't have tremendous faith in the numbers in the manual - but as I said I haven't yet found anyone who has actual data.

Subject: Re: Taifun Polar Graphs
From: "taildragger_uk" <drpiercy
Date:10/26/06 12:57 AM
To:Taifun17E@yahoogroups.com

It would be interesting if anyone can set up a side-by-side glide with a glider of known performance - say a ASK13. I'll try and do something similar myself, but it may take some time to set up. Also, it will only be a short test - I can't afford to pay for a high tow for the glider!

Can I put in a request for members to post the empty weights of their Taifuns? The poorest part of my Taifun 17E I is the 360lbs load. I'd like to know if this is typical or exceptional. My plane has the EB2400 engine with the Muhlbauer propeller. Serial Number is 1017.

Thanks

Dave

Subject: Re: Taifun Polar Graphs
From: "Finbar Sheehy" <finbarsheehy@
Date: 10/26/06 3:58 AM
To: Taifun17E@yahoogroups.com

Haim,

Thanks for the data! That result would be consistent with a sink rate of 2.25 kt, and your airspeed was close to the minimum sink speed. That would lend some support to the book figure for minimum sink, and would suggest a much lower L/Dmax, around 23:1 or 24:1.

For the L/Dmax to be truly 28.5:1, then in your experiment there would have to be a headwind of about 12kt (22 km/h) or a sinking airmass of about 0.45 kt (0.23m/s), or some combination of the two (e.g., a 6kt headwind and 0.225kt of sink - not so easy to detect).

Did you note what groundspeed your GPS was showing? Did you time the descent?

This is a notoriously difficult measurement because the atmosphere is never really still - I've used GPS to measure my 40:1 sailplane (granted, not in totally still air, but late in the day) and on long (10+nm) glides that I thought would average out any short-term variations I've nevertheless returned measurements from the high 20s to the mid 60s.

Probably the best method is a comparison with a known aircraft. A Ximango may be a good comparison, as there is some (limited) data for the Ximango - Johnson tested one.

Subject: Re: Taifun Polar Graphs
From: "hzaklad" <zaklad@
Date: 10/26/06 4:31 AM
To: Taifun17E@yahoogroups.com

Unfortunately I did not record the ground speed which is essential for this study. I suppose that each one of us can perform this test with a carefully monitored GPS. I will try again on a calm day.

Subject: Re: [Taifun17E] Re: Taifun Polar Graphs
From: Haim <zaklad@
Date: 10/25/06 11:14 PM
To: Taifun17E@yahoogroups.com

Hello Finbar

Recently, In a course of descend from altitude I performed the following test which may serve as an indicator of accuracy of the claimed L/D=28.5.

Conditions:

Morning glide from 7000 ft to 5000ft

Absolutely calmed air

Outside temp estimated at 12-15C

one person on board

1/2 tank fuel

Flaps-"0"

I used a GPS programmed to continuously display L/D

Results: