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 An Arc en Ciel air race is
typically made of 500 to 3,500 nautical miles legs. At the end of each leg, a 24 to 72
hours stopover allows some well deserved rest to the crews, and let them do routine
maintenance or fine-tuning on their airplanes. A very wide range of aircraft are allowed
to enter the competition, and a handicapping formula gives equal chances to anyone.
A reference speed is defined for every airplane.
Where piston engines aircraft are concerned, this reference speed is the 75% power setting
airspeed published in the aircraft flight manual, at the most efficient altitude. For
turboprops airplanes, it is the maximum cruise power airspeed published by
the manufacturer. Those speeds are quite representative of the way the aircraft are
actually operated during the race.
Now, let's say that the reference
airspeed of a given airplane is 200 knots. Assuming that its crew flew a 1,000 nautical
miles sector in 5 hours, the actual ground speed would be 200 knots. Therefore, the
actual speed to reference speed ratio is 100%. An actual flight time of 6 hours
would mean a speed of 167 knots, and a ratio of only 83%. The winner is the one
with the highest ratio : each crew is actually battling against its own machine,
and everyone has a fair chance regardless of the airplane flown.
OK, that is the theory. Things get
more complicated in the field, as most--if not all--airplanes do not have the range to fly
the longer legs non-stop. They must make one or more calls along the way to refuel. It is
up to the crew to choose these intermediate stops. The stopwatch keeps on ticking,
so this risky and uncertain choice is central to strategy they must develop to have a hope
of wining. The time it takes to refuel and get through the inevitable customs formalities
depends on the efficiency, preparation and luck of each crew. Some will spend only a few
minutes on the ground, while others may be considerably delayed if their fueling point is
not picked wisely enough. Amazingly low 10 minute stopovers have been recorded
on several races. Yes, that is 10 minutes to flow 100 gallons of gasoline into 6 different
tanks, clear immigration and customs, then settle the bill and clear a flight plan--good
job. On the other hand, crews have sometimes had to take a cab ride downtown to change
money, as the fuel company on the airport would not accept their currencies. Needless to
say such a sector is lost. That is the difference between success and failure, it
takes more than being a good jock at the controls to win the race. Strategy and
planning are paramount.
One thing is certain : the
atmosphere during those refueling is very tense, even feverish, set as they are against
unfamiliar air strips in the desert, the brush or the jungle.
Almost all propeller aircraft are
accepted in the races, the minimum requirements usually being a speed of at least 145
knots and a range of 1,200 nautical miles. Extra fuel tanks may be carried on some races.
Pilots in command should be instrument rated and have 800 hours minimum of flight
experience, including 150 hours of instrument flight. Copilots should have at least 200
hours.
Two different kinds of
airplanes are represented in the races : those equipped with piston engines,
and those fitted with turbine engines, also called turboprops.
Some of the piston engine
airplanes are not turbocharged, and reach their optimum speed at an altitude of
approximately 2,500 meters (8,000 feet). Others are fitted with turbocharged engines which
reach their best performances are 7,000 meters or above (21,000 feet). While at first
glance an airplane engine may seem to be the same as that of a powerful automobile, in
fact their manufacturers must deal with several problems involving the enormous difference
in atmospheric pressure between the ground and the usual flight levels.
One has to keep in mind that, when
overflying the Andes for instance, a plane has already more than half of the Earth's
atmosphere oxygen below it. Turbocharged airplane, unless they have pressurized cabins,
must carry along oxygen cylinders and masks which make the plane heavier and constrain the
crew. In addition wind speed increases with altitude. This is all-important for the
pilot's strategy. When the wind is behind him, he should climb as high as possible--this
is to the turbocharged engines advantage. When flying into the wind, he should descend to
reduce the adverse effect, and there the non-turbocharged airplane shine because of their
lower fuel consumption that translates into greater range and less pit stops.
The second group of airplanes, the turboprops, have performance levels equal or better
than those of the fastest turbocharged piston airplanes. They are also better equipped and
more comfortable, reducing crew fatigue. But their fuel consumption is high, and even
disastrous at low altitude.
It is not an easy thing to decide
in advance which aircraft will be most appropriate. Some are not deiced and, when flying
trough clouds, a fine layer of ice can deposit on the wing, slowing the aircraft down. But
deiced aircraft carry at all times heavy and unaerodynamic wing boots they might actually
never use. Some carry extra fuel tanks for greater range, but the added fuel weight
restricts the speed and altitude of the flight. Others take-off with a lighter load,
hoping that the extra speed will make up for the time lost on the ground during the
necessary fuel stop. Sometimes it works, sometimes it doesn't...
The race therefore depends
on the pilots' judgment and the selection of routes, because the winds also
change direction and strength. Resistance to fatigue is also important. Spending twenty
hours in a four-seater designed for flight of three or four hours, crammed with extra
fuel, oxygen, a life raft and various other bits and pieces is not exactly comfortable...
Crew positions are computed at
the end of each sector, both for the past leg and overall, from the departure of the race.
Here is how it looks like, in relation to the reference speed based handicapping formula :
--------------------------------------------------------------------------
13 crews sector overall
13 placed 1689 Nm 15171 Nm
--------------------------------------------------------------------------
Team 1 ABC:21/05/94 22:40 9:58 flT 79:02 flT
XYZ:21/05/94 8:38 169.46 kts 191.96 kts
(Cessna 210N N731MT) 92 % 103.8 %
Vref 185 kts Gr.2 position 4 2
--------------------------------------------------------------------------
Team 2 ABC:20/05/94 23:15 5:30 flT 47:10 flT
XYZ:21/05/94 4:45 307.09 kts 321.65 kts
(Cessna Conquest N1210U) 98.7 % 103.4 %
Vref 311 kts Gr.3 position 2 3
--------------------------------------------------------------------------
The first column of numbers
shows the take-off and landing times from airports ABC to XYZ. The positions are displayed
on the next two columns, for the past leg first (i.e. from ABC to XYZ), then overall, i.e.
from the starting point of the race to XYZ. The first line shows the flight times, and the
second line the actual airspeed achieved by the aircraft.
That actual speed is then compared
to the reference speed defined before the race for that particular airplane. For instance,
in the column sector pertaining to the last leg, aircraft Team 1 had
a ground speed of 169.46 kts, which translates into 92% of its reference speed
of 185 kts, labeled Vref. Team 2 achieved 98.7% and therefore
takes the lead. Both aircraft were actually fourth and second on that leg, as shown on the
position lines.
The last column pertains to the
overall results, since departure. And there Team 1 faired better, with a 103.8%
ratio versus 103.4% for Team 2.
You may notice that Team 1
is noticeably slower than Team 2. It doesn't matter, because the reference speed
principle filters the differences between aircraft. This results sample clearly indicates
that Team 2 did a good job on that sector, but that Team 1 was better on
the previous ones, and sails ahead on the overall results.
These are the results as they are
distributed to the competing pilots, usually in the feverish atmosphere of an hotel lobby
in the middle of the night following the arrivals.
For outside release, to sponsors
or journalists, we use a different presentation which has the advantage of being less
technical and very down to earth, highlighting the competition between closely placed
competitors :
--------------------------------------------------------------------------
sector overall
13 crews ABC=>XYZ DEF=>XYZ
13 placed 1944 mi 17458 mi
--------------------------------------------------------------------------
Team 1 position 4 2
Cessna 210N time behind best 0:24:29 1:28:12
--------------------------------------------------------------------------
Team 2 position 2 3
Cessna Conquest time behind best 0:00:59 1:43:54
--------------------------------------------------------------------------
The data used is exactly the
same, but the differences in percentages have been translated into time behind,
to be consistent with other motor-sports like car racing. Here Team 2, which came
second on that leg, is only 59 seconds behind the lead aircraft (and remember, that was a
5:30 hour long flight !), announcing a fierce battle for the next sector. Overall, Team
2 is in fourth position, being 1 hour and 43 minutes behind the leader. Team 1
is only 1 hour 28 minutes behind the leader overall, after 17,458 miles of racing.
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