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

Sanjay Dhall <sdhall@...>

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

From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Sent: Wednesday, October 31, 2012 4:01 PM
To: Q-LIST@...
Subject: [Q-LIST] Re: Q-talk 155 - Stay Safe. . . .

I say it's more efficient. From what I have read the only reason it was
changed for the Ls1 is because of the contamination issues which can mainly
be solved with VG's anyway. I agree that the LS1 is stronger (because of the
carbon spar), but that's not an issue with a Tri Q.

--- In Q-LIST@..., "SammyQ2" <sam.hoskins@...> wrote:

Hold on there cowboys. Who says the GU is "more efficient"? What does that
mean? Where does that evidence come from?

Just some anecdotal evidence:

Look at the planes flying into the fly-ins. Most of them have the GU

All of the mid-span canard breaks I have seen were GU canards. These were
from hard landings. Even saw it happen at oshkosh. Check the old
newsletters. Over the last 25+ years, I have proven to myself the LS canard
holds up well to hard landings.

The LS doesn't need the hard-to-clean dragon's teeth.

I win races with my LS canard.

For what it's worth, if I was to build a new plane, I wouldn't even
consider a GU canard. If I was building a new plane and someone GAVE ME a GU
canard, I would politely thank them, donate it to the local A&P school, then
build an LS canard.

Sam Hoskins
(Married to a hurricane named Sandy)

--- In Q-LIST@..., "johnogr300" <johnogr@> wrote:

Hi Trevor.
I also are about to start cutting foam for my Q2 wing and canard.
I`m interested to see the replies, as I am about to use the LS1 profile
with out the carbon-fibre spar I have been told that the GU is more
efficient, but I don`t want to put vortex generators on the canard, starts
looking like an unprofessional and ugly surface. I would like to know how
much more efficient the GL profile is compared to the LS1.
I`m looking to use the blue foam rather than the old orange.

--- In Q-LIST@..., Trevor Fernihough <spilligans@> 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



Join to automatically receive all group messages.