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This new column will feature a brief description, photo or video, and/or reference that talks about a Flight Test Technique that students at USAF Test Pilot School are currently learning. It’s an alphabetical list of FTTs together with a chronological account of what future test pilots and flight test engineers are doing right now. It will complement the previous Friday’s FTT tweets as well.

taws_2What is an FTT? It is the fundamental maneuver building block used by flight test engineers and experimental test pilots.

If you are wondering “what is a systems FTT?” then start here.

Examples of systems flight test on civil aircraft include TAWS–terrain avoidance and warning system.

Terrain awareness and avoidance are one of the hottest areas of system flight test, research and development.

TAWS (terrain avoidance warning system)–a terrain database integrated with an aircraft navigation system and multi-function displays.

@NASADryden and @LockheedMartin have been been flight testing Automatic Collision Avoidance Technology integrated with the aircraft flight control system/autopilot on an F-16 flying test bed at Edwards AFB. Click here for the NASA website, photos, and videos about the project.

3 Videos
NASA’s Automatic Ground Collision Avoidance System from @AvWeekGuy:
1. Overview: Training and Flying NASA’s ACAT Flying Test Bed

2. F-16 low level from Lake Owens to Sierra Nevada Mountains

3. Synthetic Vision Systems (SVS) are also designed to increase terrain awareness:  @GulfstreamAero /Honeywell SVS Flight Test

Previous: Doublets and Singlets

 

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This post summarizes references and #FTT tweets from the previous Friday. What is #FTT Friday?

#FTT Friday
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?


For more information, you can read the post What is an FTT? or check out the alphabetical index or the FTT blog category for several examples, test cards, and videos of FTTs.

This new column will feature a brief description, photo or video, and/or reference that talks about a Flight Test Technique that students at USAF Test Pilot School are currently learning. It’s an alphabetical list of FTTs together with a chronological account of what future test pilots and flight test engineers are doing right now. It will complement the previous Friday’s FTT tweets as well.

What is a doublet?
1. An elementary open loop maneuever performed in a single axis of motion.

2. A flight control input used in flying qualities flight test to excite an aircraft mode of motion. Here is a video of a Bonanza doing a rudder doublet to excite the lateral directional modes of motion.

3. A symmetric input in both directions–for example, you could push the stick forward one inch then pull the stick back (past neutral) one inch and then return to center.

What is a singlet?
An asymmetric flight control input in one direction. For example, you could push the stick forward one inch then then return to center.

Here is a time history plot of the singlet – the flight control input (elevator) is the third line, and the other lines are the aircraft response.

NASA paper - singlet time history

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This post summarizes references and #FTT tweets from the previous Friday. What is #FTT Friday?

#FTT Friday
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?


For more information, you can read the post What is an FTT? or check out the alphabetical index or the FTT blog category for several examples, test cards, and videos of FTTs.

Previous

This almost weekly column will feature a brief description, photo/video, and or reference that talks about a Flight Test Technique that students at USAF Test Pilot School are currently learning. It’s an alphabetical list of FTTs together with a chronological account of what future test pilots and flight test engineers are doing right now. It will complement the previous Friday’s FTT tweets as well.

Envelope expansion FTT is the build-up approach applied to flying qualities flight test.

What is the “envelope” in Envelope Expansion FTT? (PDF)

Envelope Expansion starts at a nominal speed and altitude and gradually explores faster speeds & more extreme altitudes.

6 kinds of flight test equipment for Envelope Expansion testing

In this news article, @DiamondAircraft describes the Envelope Expansion flight test of their Diamond Jet.

Find videos, photos, and links on a Pinboard dedicated to FTTs here.

FTT index

Growing alphabetical index of FTTs — which one do you want to see added?

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On the last Friday of each month, 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.

#FTT Friday
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?


Previous

What is a phugoid?
There is an oscillatory mode of motion that a pilot will subconsciously dampen out. It is an exchange of altitude for airspeed. The aircraft pitches up and climbs while slowing down, and after it reaches its peak, it pitches down and accelerates. This mode is usually very lightly damped, which means it will continue for a long time before dissipating, as you can see in this video.

One of the most surprising characteristics of the phugoid mode is that the period is inversely proportional to L/D. Aircraft like gliders with a high L/D ratio have a very short period.

Visualize the phugoid in a simulator.

3 References on Phugoid Motion in Aerodynamics

1. Lecture on Phugoid Motion

2. Excel spreadsheet for reducing and visualizing phugoid data

3. Cornell lecture notes on dynamic stability

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This post summarizes references and #FTT tweets from the previous Friday. What is #FTT Friday?

#FTT Friday
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?


For more information, you can read the post What is an FTT? or check out the alphabetical index or the FTT blog category for several examples, test cards, and videos of FTTs.

This new column will feature a brief description, photo/video, and or reference that talks about a Flight Test Technique that students at USAF Test Pilot School are currently learning. It’s an alphabetical list of FTTs together with a chronological account of what future test pilots and flight test engineers are doing right now. It will complement the previous Friday’s FTT tweets as well.

What are some examples of systems FTTs?

1. The powerplant, or engine, is a system that interacts with many other systems on the aircraft. Here are examples of propulsion FTTs.

2. The F-35 has an electro optical targeting system (EOTS), as seen in this video.

3. The F-14D conducted flight test to evaluate its infrared search and track pod, as this video describes.

4. Here is the demonstration of the advanced target pod on the F-16 and F-15.

As you can see, sensors like these and radars are an area of intense focus in systems FTTs.

What questions do systems FTTs answer?

1. Does the sensor have the correct resolution?

2. Can it distinguish targets from x range and y altitude?

3. Does system function throughout the aircraft envelope (altitude, G, airspeed, temperature, etc.)?

4. Do the controls and human-machine interface meet their intended function appropriately without causing confusion or errors? These four videos illustrate human factors questions.

More information about Systems FTTs

For more information about systems FTTs, you can read this guide to radar systems flight test and data analysis: AGARD FTT Series – Vol 4, Anttenae Patterns and Radar Reflection. You can also find out what Test Pilot Schools teach about systems FTTs, and finally, this thought experiment with a simple ipod may illustrate some aspects of systems FTTs as well.

 

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This post summarizes references and #FTT tweets from the previous Friday. What is #FTT Friday?

#FTT Friday
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?


For more information, you can read the post What is an FTT? or check out the alphabetical index or the FTT blog category for several examples, test cards, and videos of FTTs.

National Test Pilot School logoNational Test Pilot school is the world’s leading civilian test pilot school, based at Mojave Airport in California. Their website explains the courses they offer, equipment available, and introduces the faculty and staff.

You can also find NTPS on facebook–where you’ll see more personal pictures of the day-in and day-out happenings there, or you can find more test pilot schools on Pinterest.

There is an excellent three part video series that describes the people and planes of NTPS.

Part 1

Part 2

Part 3

 

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Check out @FlightTestFact on Twitter or Pinterest for more flight test safety references, videos, and information daily.

DSCN3734As a baby learns how to walk, he or she concentrates intensely on maintaining balance.  As we get older, we can walk and run without thinking much about our balance. However, if you put on a pair of roller skates or jump on a skateboard, you quickly remember Newton’s laws and the effect of our center of gravity on balance.

In this picture of Jake, he has plenty of static stability while seated. If he were to stand, he would not be able to balance as well, especially at this early age.

The center of gravity, or CG, is a theoretical point in the “middle” of an airplane, or a human body, upon which we could balance the entire thing on the tip of a pencil (or any other pointy thing that could support its weight).

Here are two experiments you can try to explore static stability.

1. Standing straight up

Stand up. Your CG is directly over your feet. Have someone gently push your shoulders (not so hard that you have to move your feet). You will likely sway back a little bit and then return to your initial stance.

2. Leaning forward

Now lean forward just a little bit–perhaps you can enlist some help and get someone to take a picture of you from the side. That way, you can see how far forward you are leaning.  You should lean far enough forward that you cannot lean forward anymore without falling over or losing your balance–in other words, if you lean any farther forward, you will have to move your feet to keep from teetering over. Notice how your weight shifts–before it was evenly distributed on your whole foot, but now, your weight is on the balls of your feet.

What would happen if someone nudged you, gently pushed you in the back? You would fall over. This is an example of negative static stability.

Static stability is the initial tendency to return to the original state, and the illustration below shows the stability of a ball on a smooth surface.
Static Stability

In the first case, the ball is at rest in the bottom of the bowl. If you nudge the ball, it rolls back towards the bottom of the bowl and will eventually come to a stop–this is an example of positive static stability. In the second case, the ball is on a flat table. If you move it, it will not move back to its original spot. The third case corresponds with when you were leaning forward. If you nudge the ball, it will roll off the top of the bowl, just as you would have fallen over if someone nudged you.

The Porch Swing

One last thought experiment for you to understand the effect of center of gravity. Find a porch swing that you can sit on all by yourself.  Sit on the far left or right of the swing (not the middle) and push yourself really good. You will notice that the swing oscillates, especially when it gets to the top of its swing arc. Now redo the experiment but sit in the middle. The oscillation is gone. When you don’t sit in the middle of the swing, the CG is not in the center of the swing, and this is what causes the slight oscillation at the top of the swing arc.

All of these phenomena occur in airplanes as well, but there are more degrees of freedom, more axes of motion, which adds layers of complexity. Read more about longitudinal static stability on wikipedia, though a google image search might prove more helpful.

For More Exploration

Additional ways to explore stability and CG include scooters, skateboards, bicycles, etc. Be sure to do everything with caution and the proper safety equipment though.

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Don’t just imagine your dreams–explore them, because we need you. The aerospace industry needs innovators. The flight test community is looking for the next Neil Armstrong, and that’s what this column is about, helping you take that next small step.

Thanks for reading Launch Your Flight Test Career #17. Send a message to @FlightTestFact on Twitter to ask questions about launching your flight test career.

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