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


Sanjay Dhall <sdhall@...>
 

The following links show results of tests performed on LS0417mod and
GU25(11)8:

http://airfoiltools.com/airfoil/details?airfoil=ls417mod-il

http://airfoiltools.com/airfoil/details?airfoil=gu255118-il

One way to compare 'efficiency' of airfoils is to look at Cl/Cd ratios in
our speed ranges.

At this site you can see and compare plots of each airfoil's performance, Cl
and Cd vs angle of attack at various Reynold numbers (a measure of
turbulence). So as an example, doing a comparison at the lowest Reynolds
number of 50k (least turbulent), Cl and Cd would appear to marginally favor
the LS0417mod for angle of about 5 to 10 degrees.

At the time of original design using GU and later redesign using LS
airfoils, the original designers would have looked for comparable
performance, without the downside (flow separation) of GU airfoil.

However, with the GU you add vortex generators. I am not sure how these
detract from efficiency during normal flight.

Similarly, with the LS, you add sparrow strainers. The sparrow strainers
surely add some drag given that they are about 1/4 -1/3 sq. ft. frontal
area.

But I would imagine that, rather than reinventing this wheel, such
comparison must be present somewhere in the newsletters and archives, or
published by QAC from their own research and airfoil choice in the past.

Sanjay





From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Mike Perry
Sent: Tuesday, October 30, 2012 2:32 PM
To: Q-LIST@...
Subject: [Q-LIST] GU vs LS-1 (was Re: Q-talk 155 . . . .)





Hello all:

I have wondered for a long time, has anyone documented the performance
difference between the GU and the LS-1? and the difference between the
GU with Vortex Generators and without? wind tunnel data? anything?

I think if I was building a single seat Quickie I would use the GU
canard but not otherwise. I suspect either airfoil is better than most
other airfoils. But I have no data to compare them, and no data to
compare the the GU with VGs to the LS-1. I think wind tunnel data
exists, but it doesn't include the VGs. I think you are crazy to fly
behind the GU without VGs (Murphy will get you!).

Anyone got some numbers?

Mike Perry
ps: I agree with Sam re the Q2 but not sure about the Tri-Q.

On 10/29/2012 6:01 PM, Trevor Fernihough wrote:

Hi folks,
Two question for the group of folk who have built and are flying /
have flown their Q's.

I have cut the foam previously (years go in fact) to build the Canard
as a Q2. Subsequently I decided to go in the direction of the Tri-Q
and bought the kit including the new templates for the LS wing, carbon
fibre spars and undercarriage. The undercarriage is now fitted to the
fuselage. When looking to recut the foam for the canard, it is evident
that the new profile just goes outside of the already cut foam,
leaving me to have to get new foam blocks (no simple matter here in
Australia).

First question: Listening in on your chit chat, leads me to believe
that the GU is a more efficient wing than the LS canard, and that by
installing vortex generators on the GU, I would have the more
efficient canard without the contamination deterioration issue.

Have I interpreted the facts correctly in that regard ?

If so, then the second question is: To use the previously cut GU foam,
is it simply a matter of squaring off the inside ends of the innermost
cores and laminating the wing just exactly as though it were for the
Q2 with the shear web etc just as per plan. This was obviously built
to take landing loads and begs the question that if now not doing so,
it could be / should be laid up with less cloth saving unnecessary
weight ?

Any thoughts and advice greatly appreciated

Regards

Trevor

__.


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