Introduction to Flying Qualities Testing for Homebuilders Offered at NTPS

Chuck Firth

Originally published January 1998

(Chapter 1000 member Chuck Firth submitted the following article to Sport Aviation for publication back in December 1996. Since they apparently did not recognize this quality article when they had a chance, deciding instead probably to print yet another article about an overly rich business owner and his Lancair 4P, we publish it here so that it can finally get out to the masses--ed)

What You Don't Know....

"I never realized how much more there was to know," was one of the comments during the outbrief following the first Flying Qualities class for homebuilders at NTPS. And as a participant in the second class, I have to agree. Four long, hard days of classroom instruction, preflight test planning, flying, data reduction, and analysis made me a believer.

The National Test Pilots School offers this class and another for evaluating homebuilt aircraft performance at their facility in Mojave, California. The classes are designed specifically for the amateur builder with little or no flight test experience. If you consider how much time goes into building an aircraft, and how little comparatively goes into planning and executing a test plan, then the reason you might want to enroll is clear.

"The classes are about safety," answered Al Lawless, one of the staff flight test engineers at NTPS and the course designer, when asked why NTPS created the curriculum. "We're not going to make you a test pilot or even a test engineer; but what we hope to do is instill a healthy respect for flight dynamics. We want the homebuilder to understand in a fundamental way that goes beyond flight training what forces are at work and how the builder can affect them."

National Civilian Flight Test and Research Center at Mojave

NTPS is the civilian equivalent of the military schools at Edwards Air Force Base and Patuxent River. Founded in 1981 by the legendary Sean Roberts at the request of McDonnell Douglas and Lockheed, the school offers a broad range of courses in test piloting and flight test engineering. An impressive staff of flight instructors, flight test engineers, and project directors not only teach but also conduct flight research for a variety of government and commercial enterprises, including the U.S. Air Force, U.S. Navy, and NASA. It's even possible to earn a Master's degree in Flight Test and Evaluation. Facilities include full service maintenance hangars, laboratories, simulators, and classrooms for 90 students. The fleet is comprised of 44 fixed and rotary wing aircraft ranging from supersonic Saab Draken TF-35 fighters to Cessna 150's. If that's not enough, Burt Rutan's Scaled Composites is a stone throw away and more than willing to put together anything theoretically flyable.

Introduction to Flying Qualities

My class consisted of five students with a variety of flying and homebuilding experience. Mike Hynes is the director of aviation research at Oklahoma State University and Bert Postma manages the Stanford University flying club at Palo Alto, California. Keith Beveridge was also a student and you may know him from his articles in KitPlanes magazines and as the managing editor. The class roster was complete with David White, a medical doctor from Minnesota and RV-4 builder, and myself, a project manager for Northrop Grumman Corporation with a Stinson Voyager under restoration.

The Flying Qualities class started each day just after sun up and didn't end until early evening. Day One included an introduction to the terminology, conventions, and mathematics of flight test, followed by a walking lecture in the four NTPS hangars on basic airworthiness and mechanical flight controls. (The hangars and the flight line got to be familiar places because of the wide variety of aircraft and the hands on approach taken by the staff.) Basic static stability came next, then longitudinal static(pitch) stability theory for both conventional-tailed aircraft and canards. We concluded with maneuvering stability theory and then briefed for the first test flight the next morning. That's a lot for one day and it didn't let up.

Classroom instruction is in the hands of group of highly qualified instructors. In addition to Al Lawless, the course designer and a former U.S. Air Force captain and flight test engineer, the instructor staff included Greg Lewis, Deputy Director NTPS, MIT grad and former USAF test pilot, Steve Cherry, USAF test pilot and flight instructor, and Nadia Roberts, a test engineer and former Canadian Air Force captain who also happens to be married to school founder Sean Roberts.

Out of the Classroom and into the Wild Blue

The Mojave desert area is a pristine flight test environment with a storied history. If you can name a U.S. military aircraft, it's probably been tested here, and a fair number of foreign and domestic aircraft too. The Mojave airport where NTPS is located is a former Marine Corp Air Station nestled between Edwards Air Force Base to the south and the Navy's China Lake test facilities to the north As you might expect, there's no lack of MOA controlled or restricted airspace to fly. Go a little further and you're into the Nevada test ranges. NTPS routinely flies the same airspace as the military schools and has long standing agreements regarding access and use.

Starting with Day Two, test flights were scheduled for each morning. On all but one of these flights (four in my class), an NTPS staff flight test pilot flew the mission, which in our case took place in at Beech B-76 Duchess, fully instrumented to measure the forces, angles, and control surface deflections, while each student recorded data at each test point. On a typical flight, we climbed out from Mojave's runway 22 with a clearance from the Edwards TRACON to operate below 10,000 feet in the MOA north of the field. Basic data regarding airspeed and altitude, manifold pressure, fuel quantities, and outside air temperature were recorded first. This was followed by a trim maneuver, or trim shot, to establish the stable flight measurements for baseline, then graduated departures from trim during which test data were recorded. All of us acquired a healthy respect for the job of a flight test engineer in a maneuvering aircraft trying to get accurate reads while his ears are spinning and his head is down.

In what was a surprise to all of us, the remaining test flight is in the hands of the student. It also is probably the most important flight for homebuilders as well because it provides a one-on-one experience with one of the staff pilots in a Cessna 150 during which the student executes all the test maneuvers. (NTPS quite likely has the only Cessna 150's in the world that can actually be trimmed for stable flight.) It gave each of us a chance to practice useful skills for homebuilt aircraft evaluation and, at least for me, pointed out the skills our staff pilots had acquired through many years of practice. Nothing like a personal 2g pushover after breakfast.

The test flights are carefully structured to put the classroom discussion of flight theory in a practical context for the homebuilder. NTPS staff pilots Mark Hussey and Wen Painter, along with Greg Lewis who doubled out of the classroom, would demonstrate the test technique and then explain the various ways each test point could be measured. Of course potentiometers, transducers, and accelerometers are the stock-in-trade of flight test, but there are many techniques that are relatively simple and inexpensive. I came away with an understanding of just how much can be accomplished with speed tape, markers, a stop watch, a clipboard, some graph paper, a ruler, and a few yards of yarn. Throw in a video camera, a calculator, and your own ability to sense force changes and you've got the basics.

Back to Base

Following the morning flight, we again were in the classroom to debrief. Data reduction, analysis, and all the questions we could ask were the order of the day. As you can imagine, NTPS has the usual large selection of model airplanes to hand fly the test points again if necessary and there was no shortage of chalk talk at the marker board to illustrate critical relationships. And fortunately for those of us with a few years since our last mathematics class, data reduction and graphical plots can be done on PC's using software written by NTPS. Of course, if you really need to feel the pain, you can do the reduction by hand and get the full measure of the calculus derivatives that support this.

After debrief we would launch into the day's lecture topics. For Day Two lateral-directional (roll, yaw) stability and aircraft dynamics were the topics. On Day Three we changed speed a little and took up the subject of fixes for deficiencies found in flight test and an extended discussion of stalls performance and characteristics. And finally on our last day, the discussion was focused on expanding the flight envelope and closed-loop (i.e., pilot in the loop) handling qualities for homebuilts. These last topics tied together the previous four days effort and served as a way relate what is without a doubt a highly technical discipline to the shop craft and recreation of sport aviation in experimental aircraft.

Who Should Go to School

This all might sound a little intimidating. It's a tough class, there's no way around that, but it's within the reach of most every pilot. The staff at NTPS understands that the average homebuilder is not going to keep up with the a full blown flight test course, and frankly, doesn't need one. You won't be expected to solve complex mathematical equations, but it does help to know basic algebra. And if you've completed a private pilot's ground school, you know enough about basic flight laws to handle the daily discussion.

So when should you take the class? Just before you get ready for first flight is one option. There's another way to look at this though. As you build, the way you rig and align flight lift and control surfaces will affect the flying qualities of your aircraft. Small changes or variations from the design specifications can make a big difference. So another option is to take it before you complete major sections of your aircraft. Now consider this: The design of your aircraft has undergone some amount of flight test, right? Don't know or you're not sure what the test data you've read means? Perhaps taking the class before selecting a design is a good idea. This argument can go on and on through such variations as modifying an already flown aircraft or trying out a design of your own. The point is, if you're interested, it's the right time.

Coursework, Class Size, Dollars and Cents, Communications

The Flying Qualities class is broken down into 15 topic areas. About half are lecture topics taken straight from the flight test engineer's class offered by NTPS. The other half are specially designed for homebuilders and include such things as airworthiness and certification (as defined by the FAA) and first flight considerations. The Performance class will be approximately the same number of topics and will also split the material between standard course lecture materials and homebuilt aircraft requirements. Each student receives a complete manual for the class and supplementary test cards for daily flight test. And, although five was a good class size for us, you can expect a class of about twelve. There is no shortage of instructors, airplanes, or airspace, so twelve should be a comfortable group to work with.

NTPS offers both the Flying Qualities and Performance Evaluation classes in two formats. One is an in-week five day class and the other a four day long weekend. Cost varies with the length of the class, primarily due to the number of test flights. The four day class costs $900 and the five day is offered for $1,100. All classes are currently based at the Mojave facility but may be taught a remote locations in the future. For more information, contact Al Lawless at NTPS, 805-824-2977. You can also write to NTPS at 1030 Flightline, P.O. Box 658, Mojave, CA. 93501, or fax at 805-824-2943. You can also go to their web site at http://www.ntps.com.


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Revised -- 26 August 1998