|
BlastOHotAir -> Indoor Sports Arena Blimp Operations (11/14/2007 3:58:02 AM)
|
I just thought some of you might be interested in hearing about an opportunity I have had to turn my R/C hobby into "employment". I have been flying an R/C blimp during pre-game and halftime activities associated with Houston Rockets basketball games in the Toyota Center in downtown Houston, Texas. Although I have been flying a variety of aerobatic, pattern, scale, and combat airplanes for years, learning to fly this blimp was quite a challenge.
The blimp itself is about the size of a Hummer H1. It is huge. It has two thrusters to provide lift and directional thrust, and a tail rotor for yaw control. The blimp has a bag large enough to provide about 15-17 total pounds of lift capacity. The blimp is set up for flight operations by filling the bag with helium, and after installing the gondola, batteries and tail rotor, ballasting the blimp so that it has a very slight negative buoyancy, roughly about one pound. In a calm arena, with no air currents, the blimp is flown by applying just enough thrust to lift the blimp slowly, about 1.5 pounds of thrust, and once you have obtained a desired flight altitude, reducing the thrust so that the thrust matches the negative buoyancy. It should be noted that if the blimp is moving upward, removing the thrust does not stop the blimp from rising. It has intertia, as the total assembly has a mass of about 45 pounds, and we are moving it around with only one or two pounds of thrust. If the pilot reduces the thrust too much, the blimp will slowly stop its rise, and then stop falling. So, it takes a light touch and a lot of patience to fly the blimp with precision.
Once the pilot has obtained a stable altitude, the thrusters can be rotated forward or backward, vectoring the thrust so that the blimp will move in the desired direction. Steering isjust like altitude control in that using the thruster starts the tail moving in one direction, but reverse thrust must be applied before obtaining the desired direction of movement, because the blimp also has rotational inertia, and it takes time to stop any rotational movement.
The blimp has very poor aerodynamics, so lateral velocity needs to be limited to no more than 2 -3 mph, or the pilot will lose directional control. Also, as the thrusters are vectored to provide directional thrust, lifting thrust is decreases as a function of the sin of the angle of the thrusters from vertical. If the thrust angle is kept within 15 degrees of vertical, the impact on lift thrust is less than 2%, and the pilot does not have to change the throttle to maintain altitude stability.
The hardest part of flying the blimp is not flying the blimp, but flying the air currents in the arena. The currents in the arena can apply more "thrust" to the blimp than the thrusters are capable. At full throttle, the two 12" propellers can provide about 14 pounds of thrust. There are downcurrents in the arena that will push the blimp down toward the crowd, and all 14 pounds of thrust is not enough to overcome the downward air current, so the pilot has to know where these columns of air are, and just make sure that he flies through them quickly.
There are also side currents in the arena that can drag the blimp into the stands or up into the return air registers. When the blimp is caught in one of these currents, the pilot will have to rotate the thrusters into a "flying" position, basically full forward, and apply lots of thrust to pull the blimp out. This causes several problems. First, the thrusters are no longer providing lift, and the blimp will start dropping toward the floor if the thrusters are left in the flying position for too long. Second, the thrusters are no longer pushing toward the center of gravity of the blimp, and now create a torsional moment arm, and the blimp will start to pitch up or down, depending if the thrust is forward or backward. And third, the pilot must notice the instant the blimp frees itself from the air current and immediately cuts the power setting to keep the blimp from accelerating or getting into a wild, uncontrollable rocking chair motion.
And finally, there is the fun of distributing gift coupons to the crowd from a dispenser located on the bottom of the gondola. Here, the pilot has the opportunity to move around the crowd, come down to a low altitude, and "tease" the crowd. It is amazing what people will do to try to win a coupon that will give them rights to a three dollar toy. And the pilot must make sure that he never gets in reach of an energetic spectator, because if they DO get in range, they tend to treat the thing like a beach ball, and once someone bounces it, there is a time that it will fly in a ballistic trajectory until it slows down, and the pilot has absolutely NO control of where it is going!
All in all, this is a fun, paying sideline to my R/C hobby. Keep your eyes ane ears open on Monster.com. These opportunities can be found, and for those in the Houston area, the Rockets are looking for a few good additional pilots who love basketball and have a few evenings free.
|
|
|
|
