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1. 08:30 PM - Re: KIS TR-1 Airfoil (Flyinisfun@aol.com)
2. 11:46 PM - Re: KIS TR-1 Airfoil (Propellerjan)
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Subject: | Re: KIS TR-1 Airfoil |
Jan,
I used a Lyc. 0-320 and in order to compensate for forward weight Rich
suggested I move the tail (as I built) rear 1 1/2" to the rear of the fusel
age
shell. I put the 1 1/2" extension to the elevator as suggested and
enlarged the wing fillet. As you've probably seen on this blog the proble
ms I've
expressed landing etc. By moving the tail surfaces rearward, would this
have changed the dianamics of the air foil, lift? As you probably noticed
,
I installed VG's on the top of the wing and under the horizontal stab and
it changed the lift situation, lowering the touch-down speed and has even
given me some float down the runway. By taping the hinge line, are you
suggesting this would do what the VG's are doing? Any comment?
TR-1 owner and builer,
Jesse Wright
In a message dated 1/12/2013 1:43:47 P.M. Mountain Standard Time,
propellerdesign@tele2.se writes:
--> KIS-List message posted by: "Propellerjan" <propellerdesign@tele2.se>
KIS TR-1 Airfoil
In the search for information to calculate an optimum propeller for the
KIS I0-240 I found a lot of information and thoughts about its handling
especially during landing.
When picking an airfoil for a airplane project that is about the last
thing to do before the design is set in stone. The wing area is determined
in
respect of stall speed with flap arrangement.
When having MTOW, wing aspect ratio and wing area, we can calculate speed
and lift coefficient, CL
The speed we use for this will be where we spend most of the time, not
stall speed and not top speed, but climb and normal cruise speed. So in th
is
range the airfoil should have the lowest drag, if it was an airliner that
spend most of its time climbing and cruising at high altitude at low
indicated speed it will be at similar CL most of the time (but Mach Nr wil
l play
its roll)
All aircrafts that see any production see an increase in installed power
and weight. If this was in the design of the KIS from start I don=C3=A2
=82=AC=84=A2t know,
but the prototype had a Limbach from start if understand it correctly, and
several hundred lbs less weight.
Most seem to have the I0-240B engine installed now and a MTOW of 1450 lb
or so. And it is cruising at around 140 kts. This give an lift coefficient
,
of around CL 0.3 at cruise, it mean that an airfoil with higher camber
would have been better then the current N-63A215, where the 3:d last digit
tell
the designed CL So it have an airfoil designed for higher speeds, but no
meaning to have that, no one cruise at WOT at SL, but most cruise at 65-75
%
power from 2000=C3=82=C2=B4 to 8000 or 12000=C3=82=C2=B4
The NACA 6x- series isn=C3=A2=82=AC=84=A2t the best with today standa
rd, rumour says
that the NACA screwed up when publishing these new airfoils with a faulty
design that they could not take back.
An Harry Riblett GA-37A315 would be a better choice, it have gentler
stall, and will show less drag at both cruise and climb, The difference be
tween
Riblett and NACA is that the nose radii is placed correctly on the Riblett
.
The Riblett will have about 7-8% higher CLmax.
I draw up both airfoils for evaluation and when aligning the portion where
main and after spar will be, it is a different of 1 degree at the chord
line. (From nose radii to trailing edge)
The NACA is in Green
>From the main spar and back there is very little difference in shape,
meaning the lift at same angle will be about the same with this difference
in
angle
The chord line is just a reference line that is convenient to draw and
measure, but aerodynamically it is almost a fictive line, the important li
ne
or angle of an airfoil is the zero lift angle, from this line the lift is
generated if it is given an angle to the relative wind, think of an symmet
ric
airfoil where the zero lift line and chord line is the same, and at alpha
zero it will not produce any lift.
An airfoil with camber will produce lift even if the chord line is at
alpha zero, or slightly negative, because the zero lift line will have a
positive alpha to the wind.
To make a cambered airfoil to produce zero lift, the nose have to be
lowered until the zero lift line is parallel to the wind, so an cambered a
irfoil
is said to have a zero lift angle of minus some degree depending of the
camber, it can be -1 to -6 degree on common airfoils and camber.
The NACA 63A-215 have a zero lift angle of -1.64 degree, and the Riblett
GA-37A315 -2.14 degree.
A difference of 0.50 degree.
The lift slope Cl alpha=C3=82=C2=B4 is depending on the wing aspect ratio,
for a AR
of 6, the slope of the lift curve is CL=C3=82=C2=B5 = 2Phi / 1+2/A2 =
2Phi / 1 + 2 /
6 = 4.71239 per radian
Or 4.71239 / 57.3 = 0.08224 per degree
The original wing is 3 degree up from chord line to fuselage reference
line, so if we fly it with the reference line horizontal the wing CL is
3 -
-1.64 = 4.64 degree a 0,08224 = 0,38 CL.
The GA-37A315 will be 1 degree less measured at the chord line, so 2 -
-2.14 = 4.14. so CL with fuselage level will be 0.34
It means that at higher speeds the nose down angle will be 0.5 degree less
.
Lets say we cruse at 165 MPH TAS @ 8000=C3=82=C2=B4 and 1450 Lb the CL wil
l be 0.30
plus the fact that the wing have to carry the down force from tail plane.
Both airfoils have a negative pitch moment of 0.05, the Riblett just a
little more then the NACA due to more camber.
The load at the tail is its moment times the wing chord and area, times
dynamic pressure.
Divided with tail length.
It will be about 84-85 lb down force at cruise if CG is at 25% chord
So the wing then will carry 1535 lb or CL 0.32
A CG further back will reduce negative lift and then reduce induced drag.
(And reversed.)
1450 lb at after limit will reduce down force at the tail with 10 lb
at forward limit it will ad 35 lb to a total lift the wing have to do of
1570 lb or CL 0.33
A CG to forward and the elevator will not be able to hold the nose up with
flaps, to far back and it will be sensitive on the stick. Then we come
into:
Nose drop at landing, sounds like ground effect, when closer to ground the
down wash from wing is flattened out, meaning the tail will have less down
force.
With a horizontal stab area of just a bit over 17% of the wing area, seems
small, even if the tail arm is long.
One reason for the elevator not be up to the job can also be the tail
incidence, 0.5 - 0.75 degree down might help. (but hard to fix that now)
Seems like, longer elevators chords is a good thing, 1,75=C3=A2=82=AC
=C2=9D longer chord
move the hinge line to 60% chord/40% elevator. (about =C3=A2=82=AC=C5
=93normal=C3=A2=82=AC=C2=9D)
And VG's, seems to help, it means something is wrong from start, to small
elevator or wrong incidence. Or to small H.- tail area or all three.
The Wing =C3=A2=82=AC=9C Fuselage fairing should be expanding and
10% of the chord at
the trailing edge, according to Raymer, It mean in my eyes it should be
10% of the local chord, so mid chord it is 5% of the total chord length.
I don=C3=A2=82=AC=84=A2t see anyone on Matronics talks about if they
sealed the control
surface hinge gaps with tape. That will make a big difference. Tape them
with Tesa fabric tape on the bottom side of the Hinge line, inside the
elevator, inside the rudder, inside the aileron, and bottom of the flap hi
nge
line.
Having them unsealed is like driving with the parking brake on.
On a Kitfox it is the difference of being able to make a 3-point or not
with or without sealing the elevator gap.
Jan Carlsson
JC Propeller Design
Ps. Sorry to say, I have never been onboard a KIS.
--------
www.jcpropellerdesign.com
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Message 2
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Subject: | Re: KIS TR-1 Airfoil |
If the VG's help, it suggest something is wrong from start, it is also reported
a difference when using flaps with and without VG's.
So I say the airfoil is wrong or no good, if VG's fix that it is good, but it is
no longer a laminar airfoil, so a NACA 23015 (or -13,5 as on RV's) would have
been just as good, it have a higher max CL and a lot less Cm ( - moment) If
making a new wing, or still building, the GA-37A315 will be great, with lower
drag, higher Max CL, same Cm as the N-63A215
There is soft VG's made and sold in Australia.
http://www.stolspeed.com/
It seems that it is not just one plane or pilot that have problem, so it is plane
related not pilot.
At the rear end we talk about tail volume, so longer arm and more area give a more
stable airplane, by moving the H-stab 1,5 inch you increase tail volume by
1,11%
But increasing the chord by 1,5" it increase with 6%
One thought i got was to (when building) to split and move the elevators out 2"
each way, glass in a new part in the middle before cutting the clearance for
rudder. then fill the gap between counter balance and stab.
Because the VG's under the stab helps, it suggest that larger up elevator will
not help, the underside of the elevator is probably stalled, It is common to have
the H-stab incidence -0,5 - -0,75 degree (nose down) to help with flare in
ground effect.
Taping the hinge gap air tight will help, having an mm or two of airstream blowing
straight up here will not help anything, but it need to be sealed, the glider
plane style convex mylar seal just reduce drag from the gap itself air will
still leak under the TE of that seal, air will get in at the ends of the control
surface and at the gap opposite of the hinge line.
Drag wise it will not be so noticeable as on a glider with a L/D of 40-50, but
many small creaks will end up in a big river.
Jan Carlsson
www.jcpropellerdesign.com
--------
www.jcpropellerdesign.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=392153#392153
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