Re: GU vs LS-1 (was Re: Q-talk 155 . . . .)


Mike Perry
 

Thanks Sanjay, that's what I was looking for.

Also worth remembering: VGs produce some drag; probably greater than 8
lbs. for a typ Q2 install. TANSTAAFL. (See Wainfan's article in the
Sept. '12 Kitplanes for VGs and drag)

Mike Perry

On 10/31/2012 6:44 PM, Sanjay Dhall wrote:

Curiosity has got the better of me. Looking through archives to find a
numerical answer to the GU vs LS airfoil debate, I was not able to locate
any definitive info that confirmed which of the two airfoils was more
efficient. It is well understood that the GU has a separation problem when
there is contamination (rain and bugs) and resolved using VG's. But
from an
efficiency standpoint, I decided to dig in and perform an airfoil
analysis.
I analyzed the LS0417mod and the GU25 airfoils, using an airfoil analysis
software called Javafoil. Below are the results computed at ~150mph. The
analysis is 2D, assumes laminar flow, and that no air has separated
from the
airfoil surface.
I have posted the detailed inputs and analysis results to the files
section
of Qlist group section. A summary of numerical results is below.
Analyzed both airfoils at various angles of attack from 0 to 15 degrees (0
to 10 degrees shown below). At each angle, gathered Lift and drag
coefficients. Calculated L/D ratio. These numbers are shown below. Notice
that the numbers become quite close at angles of 4 to 8 degrees. But GU
shows higher lift coefficients. This appears consistent with the common
notion that the GU is more efficient. The analyzed data shows that to
produce equal lift as the GU, the LS needs to have about 1degree higher
attack angle. For the entire canard surface that leads to about 8lbs
additional drag on the LS. So the entire comparison of the 2 airfoils used
on the canard comes down to a difference of 8 pounds of drag on a Quickie.
To put it in context, compare 8 lbs of drag to engine thrust of about
300-350lbs from an O-200.
If you see a fly in the ointment, please point it out. But then, this
dilemma was actually resolved about 30 years ago, wasn't it?
_____________________________
Attack Lift/Draft (coeff's)
Angle LS GU ratio
0 24.49 48.47 1.98
1 29.35 39.54 1.35
2 33.84 43.48 1.29
3 35.23 46.21 1.31
4 38.33 47.20 1.23
5 41.06 49.29 1.20
6 42.01 49.38 1.18
7 42.09 49.53 1.18
8 40.94 48.91 1.19
9 38.71 48.50 1.25
10 35.64 46.91 1.32
_____________________________
Thanks
Sanjay

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