I’ve devised an activity that I’d really like you to try to explain pilot gains–please let me know what you think!
Pilot “gain” or “gains” is easy to define but difficult to understand. The easiest way to explain it is to imagine that you are driving down the highway, tuning your radio, and you look up to see you are headed to the edge of the road. You jerk the wheel to keep from going off the road.
You don’t always jerk the wheel when you drive–the way you input “steering commands” is known as “gains.” (Gain is actually a coefficient in formula that describes a closed loop system’s dynamics.)
When you “jerk” the stick or wheel of an airplane, often things don’t happen as you would expect.
It is very difficult to simulate the “fear” or aggressiveness that one uses when you jerk the steering wheel in panic. The study of this kind of input to the aircraft control system in flight test is known as Handling Qualities.
Activity #1 — Practicing the Maneuver
1. Without touching the boundary lines or squares, slowly draw a line from the dot to the X.
2. Repeat it at a faster pace.
3. Do it as fast as possible. (Hint: you will probably touch the lines if you go fast enough.)
4. Estimate how fast you can do it without going outside the lines–now do it at that rate.
If you were a test pilot, you would fly a maneuver in the simulator or in your mind for practice. That’s what we just did. Now, let’s see if you have the right stuff.
Activity #2 — Flight Test Maneuver
1. Perform the same exercise as before, but do it as fast as possible ON YOUR FIRST TRY. No warmups allowed.
Did you touch the lines? If you tried really hard, you probably did. What if touching the lines was equivalent to an aircraft malfunction or even a crash?
The lines were closer together which changed the nature or difficulty of the task. How would you describe this phenomenon, using scientific terms, measurements, etc.? You could time yourself for each drawn line. You could measure how many times your drawn line crosses a printed line. How could you compare one run to another? How would you compare performance on squares of different size? Now you can see that characterizing this phenomenon is not easy, and exploring it in an airplane is even more difficult.
There is a video of an FTT performed to evaluate this at USAF TPS here.
On the last Friday of each month (this month is an exception), the column What is an FTT describes some of the fundamental maneuver building blocks performed by test pilots to gather data during flight test missions. An FTT is in some sense a description of an experiment. It is a key element of the scientific method applied to aerospace sciences, engineering, and aviation.
You can access all of these posts by clicking on the FTT category hyperlink below the post title.
Each Friday, @FlightTestFact will deliver examples, definitions, and explanations of flight test techniques for the entire day. You can view these tweets by searching for #FTT and #flighttest as depicted below. You can also click on the picture below to be taken to the twitter search results. What FTT would you like to know more about?