Test pilots aren't born with this knowledge, they learn it. I have no desire to be a test pilot, but I'd love to learn what they know - and apply that knowledge to my flying, so I can aviate as precisely and efficiently as they do. Until recently, there were two places to get a test pilot education.
The U.S. military wants a nine-year commitment from its pilots, and there's no guarantee it will select you for its Air Force or Navy test pilot schools. Civilians can attend the National Test Pilot School in Mojave, California, but the tuition is pricey.
More important, to succeed in these courses students really need a degree in aeronautical engineering and the ability to read, write, speak, and understand complex mathematical formulas filled with Greek letters. Then I learned about a new course offered by the Experimental Aircraft Association - Flight Testing Techniques for Homebuilders.
The three- or four-day course is held periodically (the next one starts October 11) at the EAA Aviation Center in Oshkosh, Wisconsin. The fourth day is an advanced session for EAA Flight Advisors (who help homebuilders prepare for their first flights) and those who've completed the basic course. Neither course involves flying. The tuition for the basic course is $400 and includes all materials, three nights' lodging, and meals. The advanced session is an extra $100.
More important, the course is taught in English, not Greek. It's designed to familiarize homebuilders with flight test techniques, but I reasoned (correctly, it turned out) that a test pilot's education is the same regardless of the aircraft he (or she) flies. Of the 12 students, I was the only one not building an airplane. Our teacher, and course developer, was Ed Kolano, a former U.S. Marine Corps aviator who graduated from and taught at the U. S. Naval Test Pilot School.
Kolano began with an introduction to tables and graphs, which turn flight test data into useable performance information. Pilots want and need to know numbers, he said - how fast, how high, how far, how slow, etc., and gathering the data that create these numbers is the goal of flight testing. We began with aircraft performance issues, which are engine-related and aerodynamic.
Before addressing practical test techniques, we reviewed the forces that act on an aircraft and determine its performance. Four forces act on an aircraft in flight - lift, weight, thrust, and drag. In straight and level flight lift equals weight. Lift does not equal weight when the aircraft is in accelerated flight, such as a turn.
There are two types of drag - parasite and induced. Parasite drag is not caused by the production of lift but by skin friction and things, such as landing gear, that stick out in the breeze. Induced drag is a byproduct of lift. Parasite drag increases with speed (or when you lower the gear), and induced drag increases when you fly at a slower speed and higher angle of attack, which increases lift.
An engine produces some amount of brake horsepower, but not all of it converts to thrust horsepower. Engine accessories, such as generators and fuel pumps, steal some of it. The propeller, which is not 100 percent efficient, takes more. A fixed-pitch prop is most efficient at just one power setting. Every other setting is a trade off. Props pitched to give good cruise performance also give poor climb performance, and the opposite is true for climb props. A constant speed prop is a partial solution to these inefficiencies.
Most pilots learn these facts as students, so they shouldn't be revelations. But they seemed to be because Kolano taught us how they combine to create performance, and how a change in one affects all the rest. In three days the basic facts of flight became more than rote recitations students learn to pass a test. They became magic keys that opened the door to efficient flight.
Take aircraft range and endurance, for example. Both are determined by fuel quantity and, more important - consumption. To achieve maximum range the pilot must fly at the airspeed that gives the highest ratio of speed to fuel flow. This occurs at L/D max - maximum lift over drag. To achieve maximum endurance - the minimum fuel flow possible - pilots must fly at the minimum power setting required for level flight.
Most pilots know that flying at speeds and power settings different from those that result in the most efficient performance cause range or endurance to suffer. But test pilots have to know why they suffer because they must derive the most efficient "numbers" during their tests.
Simply put, to maintain a constant altitude lift must equal weight, and to maintain a constant speed, thrust must equal drag. Lift/weight and thrust/drag are not independent factors. They work together and create the aircraft's performance. Level slow flight, for example, generates the necessary lift, but with it comes a lot of drag, which means the engine must produce more thrust - and consume more gas.
To determine optimum flight, the pilot flies a series of tests at a constant altitude, recording the power required to maintain level flight over the range of airspeeds from stall warning to maximum level speed. Leaning the mixture properly is essential, and the pilot should fly the tests at different altitudes to determine the optimum performance for a range of altitudes - just like pilots find in a pilot operating handbook. He should fly all of these tests at two different aircraft weights - minimum and maximum.
Kolano made it clear that flight testing is not a quick process. It's many short flights flown to tight - but not impossible - tolerances. Any pilot is capable of flying the tests he taught. For example, from a stabilized level flight condition near the maximum level flight speed, reduce the throttle slightly. Maintain a rock-steady altitude as the airplane decelerates until the airspeed change decreases to less than two knots in one minute. The pilot records his data, and repeats the test at progressively lower throttle settings until the aircraft can no longer maintain level flight. When he's finished, the pilot has mapped the front side of the power curve. (He uses another technique to map the back side of the power curve.)
The test data include pressure altitude (set the altimeter to 29.92), observed airspeed (look at the airspeed indicator), manifold pressure/rpm (as appropriate), fuel flow, fuel weight, outside air temperature, and remarks. Remarks should include things that affect the data such as turbulence or an airspeed needle that didn't settle down.
After describing a number of different tests it became obvious that a fuel flow indicator and an exhaust gas temperature gauge are important flight test instruments. The latter enables precise, consistent mixture settings. The former makes the test flights go more quickly. Without a fuel flow indicator to measure fuel consumption, the process takes more time and more flights, but the results should be the same.
After the tests the pilot converts his data into performance graphs and tables. He calculates the density altitude from the pressure altitude and outside air temperature, and uses the density altitude and observed airspeed (and calibrated airspeed corrections) to calculate the aircraft's true airspeed. Then he applies the corresponding fuel flow data. The result is a plot from which the pilot can determine his maximum range and endurance airspeeds, fuel flow required for any airspeed, and the range/endurance/fuel penalties for flying non-optimum airspeeds.
Naturally, this is a simplification of a more detailed process, but the example is the essence of performance flight test techniques. The course taught the specifics for this test and all the others that measure an aircraft's performance.
Kolano also taught us about non-performance subjects such as control systems, stability, flying qualities, the pilot-airplane interface, and developing a flight test program. Although these subjects are technical, Kolano taught from the pilot's in-cockpit perspective.
One of the most enlightening bits of knowledge was Kolano's comment on "bad" data points, those that don't fit the trend of the others. "You can throw it out," he said, "but don't discard it if you don't know why it's bad." This is where that "Remarks" section of the data card can come in handy.
For me, this the course was a "light bulb" experience. It shed light on the reality that flying isn't a matter of doing A and B to achieve C, it's understanding why A affects B and results in C, and how all of them work as a whole to create the magic that is flight.
I'll probably never flight test an airplane - and a three-day course does not a test pilot make. But what I learned changed how I look at flying - and the aircraft I fly. Now, when I rent an airplane I'll be able to make a good guess at how close it'll be to its book performance by looking at it. If it's a flying bug morgue with a scarred, but properly dressed prop and an engine close to overhaul, I'll add a serious fudge factor to my fuel reserve.
This airplane will have extra parasite drag and won't produce its normal amount of thrust horsepower. To achieve a book speed will require more than the book power setting, which means it'll burn more gas than the book says. I won't know how much without a few tests, but I know how to do those now, too.
In aviation, knowledge - understanding why, not just how - is the power of safety. And there's no reason all pilots can't put a test pilot's knowledge to work for themselves.
For more information on the Homebuilt Flight Test Techniques course, contact the EAA Education Office at 888/322-3229, 920/426-6890, or e-mail [email protected].
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