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Salutti tutti,
Some interesting data from a design study of the LIV:
30.2 ft wing span.
98 sq ft wing area.
3,200 lbf gross weight.
0.012 zero lift drag coefficient
0.8 Oswald planform efficiency factor.
0.88 propellor efficiency.
350 hp sl brake horsepower.
0.45 lb/hp/hr brake specific fuel consumption
90 gal fuel capacity.
9.307 wing aspect ratio.
3.245 ft avg chord
32.653 lbf sq ft.
Vmax 335.54 mph.
Cl max 1.4. Cl max Flaps 2.2.
Cl (0 ft) V max 0.113.
V stall flaps 76.196 mph (66.17 knots) @3,200 lbs.
V stall clean 95.516 mph (82.9 knots) @3,200 lbs.
AoA Cl max 15.510 degrees.
AoA V max 1.257 degrees.
Drag induced 0 ft Vstall: 191.54 lbf. Drag parasite 0 ft V stall: 27.44
lbf. Drag total 0 ft V stall: 218.9 lbf. L/D 0 ft V stall: 14.614
Drag induced 0 ft V min drag: 72.48 lbf. Drag parasite 0 ft V min drag:
72.48 lbf. Drag total 0 ft V min drag: 144.96 lbf. L/D 0 ft V min drag:
22.075.
Drag induced 0 ft V max: 15.52 lbf. Drag parasite 0 ft V max: 338.5 lbf.
Drag total 0 ft V max: 354.09 lbf. L/D 9.039.
Cl min power: 0.918. Velocity min power 117.9 mph (102.38knots) Power
minimum 52.08 hp.
Power required 0 ft Vstall 55.15 hp. Power required 0 ft V max 312.9 hp.
There are pages of calculations, graphs etc but the above are of the most
interest. Of interest to the ongoing discussion are the V stall figures:
66.17 knots @3,200lbs with flaps. Also 82.9 knots @ 3,200 lbs clean.
Some years ago back in Australia homebuilt aircraft were built under what
was then the 101.8 category. One very important consideration was that
aeroplanes built in this category meet the 61 knots max stall speed for
single engine aircraft. In a discussion I had with the chief testing pilot
of the then CAA before the first Australian built Lancair IVs ever flew he
said "61 knots great, 62 knots we arm wrestle, 63 knots no way". After the
first of type LIV in Australia flew (VH-HOT) it was outfitted with
calibrated instrumentation and from memory the calibrated stall speed was
61.5 knots and I believe that was at 2,900 lbs gross. Whew! went all the
other LIV builders in Australia.
Coming back to the V stall figure of 66.17 knots @ 3,200 lbs, working back
to what the stall speed would be at 2,900lbs the figure is 62.99 knots and
allowing for that VH-HOT has winglets which decrease the stall speed by a
knot or so the figure comes back to 61.99 knots or thereabouts...a nice
correlation with the 61.5 knots CALIBRATED speed of VH-HOT. This gives me
confidence that the calibrated Vstall of the LIV @ 2,900 lbs is 61.5-62
knots, for the sake of the discussion I'll use 62. As those who have been in
the LIV world should know well the ASI is somewhat optimistic in the low
speed range by as much as 5-6 knots or more depending on the aircraft and a
wise person would do his airspeed calibration carefully to establish his
correct airspeeds.
Using 62 knots V stall (flaps) calibrated airpeed @ 2,900 lbs for an LIV
(with winglets) at 3,200 lbs the calibrated V stall comes up to 65.13 knots,
at 3,550 lbs it is 68.6 knots, at 4,000lbs it is 72.8 knots, at 5,000 lbs it
is 81.4 knots. Calibrated!! don't forget.
For an LIV without winglets add a knot or so to the above figures and you'll
be in the ball park.
Looking at the clean stalling speed of 82.9 knots @3,200 lbs (without
winglets) is interesting. Calculating to V stall at 2,900 lbs is 78.9 knots.
Going up to 3,550 lbs it goes up to 87.31 knots. 4,000 lbs Vstall is 92.7
knots. 5,000 lbs V stall is 103.62 knots.
Suppose in your LIV turbine lead sled at 4,000lbs your hydraulics fail and
are not able to lower flaps for landing or stooge around and burn off fuel
to lighten up your approach to land is now up around 120 knots (struth
mate!)
Suppose in your LIV turbine lead sled at 4,000lbs you've been out for a
short test flight and are returning to land still in clean configuration
(thinking tested to 8.7 g...the gear can take it) and approaching the
circuit at lets say for the arguement 130 knots a Cessna/Piper/something or
other isn't where he has said he is and suddenly pops up in your vision
filling the windscreen and you instintively roll hard and pull,lets say 60
degrees of roll and 2 gs...you're dead...the stall is 131 knots...your
aeroplane has rolled onto it's back...splat, another hole in the ground,
another statistic and great loss of credibility to those in the Lancair
world who operate within published limits.
Suppose on your test flight above you have found that your LIV wants to fly
a little bit right wing low...typical of many LIVs.Not really a problem you
say, I'll draw the fuel from the right wing first to balance the aeroplane.
But is your aeroplane really rigged correctly if you need a fuel imbalance
to fly wings level? On two fast build LIVs that I know (certainly there are
others) the shear box had been installed twisted by the factory such that
the left wing had 0.3 degrees more angle of attack than the stbd. And you
did check your incidences to be exact didn't you?? On other fast build wings
I've measured a difference of as much as 0.5 degrees difference of the tip
incidence with the root incidence set correctly. Have you checked yours?
Sure you can fly with a fuel imbalance to fly wings level but now one wing
has more angle of attack than the other.
Coming back to the now long drawn out test flight above you are returning to
land having taken fuel from the stbd wing to balance wings level at lets say
140 knots for a margin, still in clean config when you spot the
Cessn/Piper/something or other filling the windscreen and you roll left and
pull, 60 degrees and 2 gs and push up the power at the same time. In the
seconds that it takes to clear the oncoming aircraft the turbine spools up
and the power kicks in...lots of power and instinctively you roll the stick
to the right to counter the now 160 lbs or more of torque that the ailerons
must balance (at the ailerons), the left aileron goes down, the tip upwash
increases and the AoA goes beyond the stall helped along by the fact that
the left wing has that little bit extra angle of incidence....rolled
inverted again!! Splat. etc. And the JIM Franz AoA indicator didn't save
your bacon this time either ...with the sensing ports on the stbd wing.
I won't even look at what turblence might do. Suffice to mention Sod's Law:
If it can happen it will happen.
Build 'em light, be safe, and be carefull.
Ciao,
Roberto d'Italia.
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