Originally posted by boomer135
reply to post by ProudBird
I got ya. On another question, when we dump fuel, what do you think the safe altitude to do this is? Meaning that at what altitude will the fuel evaporate?
If an aircraft is dumping fuel in IFR conditions, assign an altitude at least 2,000 feet above the highest obstacle within 5 miles of the route or pattern being flown.
The ecological aspects of fuel jettison have been most closely studied by the United States Air Force (USAF). These studies have shown that, in general, fuel jettisoned above 5,000 to 6,000 feet will completely vaporize before reaching the ground. Therefore, Boeing’s general recommendation is to jettison fuel above 5,000 to 6,000 feet whenever possible, although there is no restriction on jettisoning at lower altitudes if considered necessary by the flight crew.
Fuel jettison studies have indicated that the most significant variables related to fuel vaporization are fuel type and outside air temperature. Some studies found that temperature can have a very significant effect on the altitude needed to completely vaporize fuel. For example, one USAF study found that a 36-degree Fahrenheit (20-degree Celsius) reduction in temperature can change the amount of liquid fuel reaching the ground by as much as a factor of 10. Other factors such as fuel jettison nozzle dispersion characteristics, airplane wake, and other atmospheric conditions can affect the amount of fuel that reaches the ground.
Even though fuel is vaporized, it is still suspended in the atmosphere. The odor can be pronounced, and the fuel will eventually reach the ground. Boeing is not aware of any ecological interest promoting a prohibition on fuel jettisoning. Because of the relatively small amount of fuel that is jettisoned, the infrequency of use, and the safety issues that may require a fuel jettison, such regulations are not likely to be promulgated.
Air traffic controllers assign the aircraft concerned an airspace in which the fuel can be dumped, if possible above an unpopulated area. The minimum altitude is set at 1,500m above ground, but most dumps are in fact carried out at an altitude of four to eight kilometres. The aircraft is not permitted to fly in closed circles and must be flying at a minimum speed of 500 km/h.
The wake turbulence behind the aircraft makes most of the fuel released through the nozzles vaporise into a fine mist, which remains in the atmosphere until being broken down by the sun's energy into carbon dioxide and water. Only a minimal amount of the dumped kerosene actually reaches the ground. If a fuel dump is made at the minimum altitude of 1,500 m, given a ground temperature of 15°C and assuming that the air is still, then it is calculated that 8% of the total fuel dumped will reach the ground. Assuming the aircraft was flying at the minimum speed of 500 km/h, this results in the ground being affected by 0.02g per square meter, which is the equivalent of a spirit glassful of kerosene spread over an area of 1,000 m2.
The above assumes total stillness of the air, which is in fact highly unlikely. Even the slightest air movements, which automatically stir the air up, make fuel evaporate almost entirely before it can reach the ground. This explains why even the most sensitive monitoring equipment has not yet succeeded in discovering kerosene-related impurities in plant and soil samples taken after a fuel dump.
Originally posted by ProudBird
Then, determine WHAT the possible payload sizes can be. Divide that into the volume of air that you calculated, above. This gives you the density of whatever "material" has been "sprayed".
Originally posted by ProudBird
reply to post by boomer135
I understand for in-flight re-fueling ops that speed is primary.....once the "thirsty" jet hooks up, you want to deliver as quickly as possible....and often others are waiting their turn. Plus, flying formation is a bit taxing.
edit on Sun 26 February 2012 by ProudBird because: (no reason given)