Given the right information, it is possible to predict certain aspects of helicopter performance. For example, given the gross weight of the helicopter, the pressure altitude, the height of the skids above the ground, and the outside air temperature, it is possible to predict the percentage of torque you’ll require to hover. Given all that and an airspeed, it is possible to predict the fuel flow rate in gallons per hour.
The Army requires that all pilots make certain of these computations before taking off on any given mission, so that they can (i.e.) ensure that they take enough fuel to complete the mission with a safety margin before landing, but not so much that they’re too heavy for the necessary maneuvers on the mission. This makes sense.
What doesn’t make sense, to me at least, is the way they teach us to make the computations. They could just give us the 10 or 20 relevant equations and just tell us to solve them as necessary. That’d be fast and accurate, but it would require some knowledge of algebra. This would violate the army’s policy of putting all information in terms that an eighth grader could understand. As a result, a large section of the flight manual they give us is charts: pages and pages of charts. Complex charts–none of the equations in question take fewer than three variables. 30 pages of a single chart, because it’s trying to represent in two dimensions a five-variable equation. Solving for the solutions the Army wants could be as simple as constructing a spreadsheet and plugging in the relevant numbers; it’s instead a tedious exercise in plotting, reading, and correlating various charts using only graphical methods. I wouldn’t mind the charts; they’re useful instructional tools to help people visualize the data. It seems absurd to me that they don’t even mention the possibility of solving these problems algebraically, though.
When my father was young, the Vietnam war was going on. He tells a story about one of his friends who entered the army–I can’t remember if he joined voluntarily or was drafted, but for the purposes of the story it doesn’t matter. He ended up in artillery school, where the army used giant tables to calculate the necessary angles for firing. His instructors were astonished when, using only a high-school knowledge of ballistics and a newfangled hand held electronic calculator, he could compute his angles significantly faster than by referencing the tables.
Tonight I emailed Bell Helicopters asking for any equations they have which are relevant to performance planning for the TH-67. Let’s see whether or not they get back to me with them.
I might be able to get ‘em if you can’t. Let me know.
That would be awesome! If I haven’t heard back from them in a week, I’ll email you.