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1. 07:10 PM - Vortex Generators ()
2. 10:23 PM - Vortex generators update (aerosiam)
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Subject: | Vortex Generators |
Paul:
I read your May 26, 2008 Matronics Allegro-List post on the above subject
with great interest. I also have an Allegro 2000 and am contemplating adding
vortex generators. I assume from your post that you used the Stolspeed
Feathers VGs. Did you follow their instructions concerning installing the
VGs? The Allegro 2000 has a main wing chord of 42 inches. 7% of this is 2.94
inches. Did you place the tips of the VGs 2.94 inches back from the leading
edge? From the end of the flaps to the wing tip the wing chord varies, but I
notice that the instructions from Stolspeed state that for a wing with a
swept-back leading edge (varying chord) they still call for a line 7% of
chord back from the leading edge and parallel to the leading edge. I don't
understand this. Is this still 7% of the main wing chord of 42 inches? If
the chord is varying, why are the tips of the VGs at the same constant
distance back from the leading edge? Further comments from you and others on
this subject would be appreciated.
Hugh McKay in North Carolina, USA
Hugh McKay
Allegro 2000
Rotax 912UL
N661WW
Message 2
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Subject: | Vortex generators update |
To answer Hugh's question in his post titled 'Vortex Generators' Stolspeed say
the VGs can be placed at 8-12% of the chord. I wanted to place them quite far
forward (7%)for the following reasons
The Allegro has a fairly sharp leading egde
Air velocity is probably highest around 7% chord at the stall
The tapered sections are quite narrow (and the most vulnerable to a stall) and
the vortices need time to propagate.
I discussed this with the VG designer and he agreed.
Fitting is simple and the Stolsped instructions are very good. The tapered section
takes a little head-scratching but is actually easy.
You only need to mark 3 points on the wing.
On the constant chord section mark 2 points 2.14 inches back from the leading edge.
The first point (A) is at the wing root, the second (B) exactly where the
chord changes from constant to tapered. Ping a chalk line.
Place the front tips of the VGs touching the chalk line. This puts the tallest
part of the 'fin' at 7%
Now measure the chord at the wingtip fairing join (ignore the fairing itself) and
mark point C at 7% minus 0.8 in (the distance from the front tip to the fin
of the VG.)
Ping a chalk line from point B to C (start of tapered section to the wingtip -
ignoring the fiberglass fairing)
The back of the template must be 90 degrees to the airflow. Mark a series of lines
parallel to the main spar. It's probably easier in removable felt pen rather
than chalk to avoid the dust for adhesion. Use the lines as a reference for
the back of the template.
A couple of notes...
Suggest you try only the tapered section first then full span if you want.
If you are going to do stall tests with and without VGs, are you current and familiar
with stall recovery? I flew with a chief instructor which was a comfortable
feeling! Did you get your stall warning working?
Talked to the Italian dealer who said the Allegro will recover from a spin normally
and immediately with full opposite rudder. After 3 turns autorotation speed
increases.
See http://www.mcp.com.au/allegro/flight-test/flight-test.html about sharp stall and wing drop power on
See http://www.aero-siam.com/page143.html for VG flight report and pictures of VGs
Suggest you fit the horiz stab VGs and test fly before fitting the wing VGs
Aircraft will take off sooner and land and float a little later. Touchdown 31 kts
CAS in ground effect.
Easier to bump the tail (and take off too soon) because the nose angle is higher
for a given stick input.
I have a dynon pitot set several degrees below incidence. The factory pitot does
not seem to suffer position error.
I will check measurements when I am next at the field.
Regards
Paul
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=189510#189510
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