Taking a critical look at an airplane you’re thinking of building isn’t much different for you than it is for us. In fact, we at KITPLANES® consider many of the same things you do, or should, in terms of aircraft design and performance. We know you’re interested in how an airplane performs—does it meet stated performance goals and do so in a reasonable way? (I’ll explain that comment shortly.) But we’re also trying to view each airplane design as a whole, not just as a set of performance numbers and subjective handling qualities.
Some builders get caught up in the excitement of the project and put their sensibilities on hold. They are able to ignore the subtle cues that suggest—but don’t yet prove—that a company or an airplane might not be as presented. Homebuilt aircraft history is full to overflowing with sob stories of airplanes that didn’t meet claimed performance; companies able to cash deposit checks but unable to deliver kit parts; and pro-jects that, sadly, go unfinished.
When you visit the factory—and you definitely should—evidence of raw materials to build kits (above) and ongoing projects (below) should be visible.
The Front Door
Our intention is to provide valuable information on the airplane and the company, and that starts as soon as we arrive at the factory. A quick aside: Though we sometimes test-fly aircraft at major airshows, we generally prefer to visit the factory to conduct the evaluation. Why? Mainly because it allows us the freedom of time. If the weather’s marginal for a flight test, we can postpone until it looks better. We also don’t have to share time with the company personnel who are trying to actually sell kits. Their time at airshows is better spent moving the merchandise than hanging with the rogue scribbler.
Conducting the review at the factory also gives us a chance to see how the company operates, and it’s one opportunity you should not miss in your own research. Even better is attending an on-premises workshop; you get to see how the company operates, and at the same time gain valuable experience with the materials and processes involved in the actual building. What could give you better insight than spending time with the staff and the kit itself?
Unless you’re visiting on a Friday afternoon or Saturday morning, the kit company’s shop should be busy. (One exception is when the company runs early shifts, as many do in the hotter parts of the U.S. during the summer.) That’s not to say full to the rafters with parts and workers standing elbow-to-elbow. Today’s manufacturing technologies allow companies to do more with fewer people. But you also want to see how much of the final kit is produced in-house. Can the company form its own parts from sheet metal? Are the molds for composite parts there? (The exception is normally for companies that use fiberglass only in cowlings and fairings; it’s often more efficient to have an outside contractor supply the ‘glass.) Does the company making a tube-and-fabric utility airplane do its own welding? The goal of this “snooping around” isn’t to count inventory, but to get a sense of the company’s health.
Next on the list is to spend some time looking at the airplane itself. At KITPLANES® we have a blanket policy to wait until all of the Phase I flight-testing has been completed before we conduct a flight test. For starters, that’s the best legal angle because, technically, the airplane isn’t supposed to carry passengers until Phase I is complete. You are also not being compensated as a test pilot, so it pays to politely ask the status of the aircraft’s test flying and absolutely determine how many hours it has flown.
Before you fly, there are important questions worth asking: How does the demo aircraft differ from the final kit? What factors might influence the difference in performance between the demo plane and stated performance? Typically, kit companies derive their brochure numbers from the factory demo airplane, so the airplane you fly should be able to duplicate these performance figures. If it can’t, you need to know why. Either something has changed—it’s common for small companies to try different cowlings, landing-gear configurations, propellers and even whole engines on one airframe—or the numbers are suspect.
In addition, it’s critically important to have at least a basic plan. This could be as simple as taking off, climbing to altitude in the general direction of the local “practice area,” performing a few basic maneuvers, doing speed checks, and then descending back to the airport for landings. Indeed, this outline generally describes most of our review flights. (It explains our enthusiasm for actually getting to go places in test aircraft!) Remember, though, that the job here is not to learn what the airplane is like to live with but to verify a few performance points, make a top-line evaluation of handling qualities, and see if the airplane is comfortable to sit in and fly.
Tools of the Trade
Before electronic instruments were prevalent, we used to drag along a small gear kit to help ensure we were getting the best in-flight data possible. With the aid of a portable GPS and a device such as the Proptach (an optical, electronic portable tachometer), it’s possible to nail down key performance specs by reducing (but not eliminating) the variables. The GPS allows you to run a number of “speed trials” and get an accurate groundspeed. (I recall doing the same test before GPS, where a DME station was handy; before that, test pilots would use ground-reference points a known distance apart.)
In today’s aircraft, the electronic instrumentation is difficult (though not impossible) to skew and generally quite accurate. As such, we typically bring little in the way of investigative gear into the cockpit unless the demo plane is minimally equipped.
However, we rely on some technology to help us take notes. First is a digital voice recorder—the brand isn’t important—with an external-microphone input. We then put a small microphone into the headphone ear cup to capture cockpit chatter. It’s vitally important to record the flight somehow. In your demo flight—just as in ours—the workload is simply too high to see what you need to see and take physical notes at the same time.
Who Are You Talking To?
To make the system work, we typically call out the major indications during the flight and also make a point to call out the passage of altitude benchmarks during the initial climb phase. Digital recordings have a time stamp, so it’s easy to look back at the flight and calculate rate of climb and descent.
Lately, I’ve taken to the new GoPro Hero2 compact digital video camera. The second-generation version includes an external-microphone input where the first didn’t. I take an inexpensive lavalier microphone, drop it into one of the headset cups and connect it to the camera. In most aircraft, you can suction-cup-mount the Hero2 to the canopy so it’s within reach and has a clear, wide-angle view of the instrument panel and primary flight controls. It’s amazing what you don’t remember doing during a flight that you can plainly see in a replay of the video.
For purposes of having all of the data in one place, I’ll recite the aircraft, approximate loading, fuel state (how much and where it is among the various tanks) and local atmospheric conditions for the recording. Take a moment to get the local ATIS or AWOS information on the recording as well. That way, when you’re back at home listening to your recording of the flight, you can normalize some of the observed performance against known atmospheric conditions. Did you think the takeoff roll seemed longer than the specified value? You can check density altitude later and see that the airplane thought it was at 3000 feet MSL…ah, that makes sense.
The first takeoff is normally conducted as a standard departure. I’ll ask the demo pilot for recommended rotation and initial-climb airspeeds. I’ll then try to describe the takeoff for the recording, explaining how smoothly the power comes up, how well the airplane tracks the runway centerline, noting any tendency for it to dart for the runway lights and, especially, how it feels just coming off the ground. Some aircraft have their landing gear positioned so that as you bring the nose up (in a tricycle-gear design), no other pitch inputs are required to hold the desired climb attitude. Some tend to pitch nose-up after the weight has come off the gear; see if you can sense this tendency.
The reviews are typically with a company test or “demo” pilot, usually for reasons of safety and insurance coverage.
As the airplane leaves the ground, call out for the recording so that the climb clock can start. Then make a note of passing through the first 1000 feet and each 1000 feet of altitude thereafter. It’s easier to mark whole thousands rather than to refer to altitude as AGL (above ground level). During the initial climb to altitude, note the airspeed and indicated climb rate, and then look at the engine gauges to note things like manifold pressure, rpm, fuel flow, the highest EGT and CHT values (along with any unusual spreads, if the instrumentation shows all of the cylinders at once), as well as oil temperature and pressure.
Beyond the hard values, you’re looking to see how the airplane handles at relatively high power and low speed. It should be easy to put the nose at any point on the horizon and hold it there. You should not have high control pressures in any axis, though it’s not unusual to have comparatively high rudder pressure in aircraft without adjustable rudder trim. If you do have to really mash on a pedal, make a note of it for the recording and try to remember to observe how it is during level flight. Different aircraft will have different force gradients; a design you’re sure will never have the ball centered based on excessive climb-phase pressures might just surprise you.
Generally, we try to reduce the number of turns in the initial climb to get a better sense of the climb rate, but that’s not always possible for reasons of weather, navigation or terrain. Just make a note of the turns—or simply that you are turning—for the record.
Electronic instrumentation takes much of the guesswork out of flight testing. Still, you can’t just take every indication at face value. Is the true airspeed calculated by the Garmin G3X (left) accurate? Is the fuel flow shown by the TruTrak engine monitor correct? In-flight cross-checks will get you close, but be sure to apply common sense to performance claims.
Because our flight-review time is limited, we can’t take data points all over the performance map. Instead, we choose a few to spot-check, in part to see how the airplane performs on its own merits but also as a cross-check to the claimed figures. When it comes to conducting your own flight tests, you’ll be surprised to discover that collecting good cruise numbers—at various altitudes, weights and atmospheric conditions—takes an astounding amount of time and surgical care. I spent several days with my Sportsman trying different altitudes with various combinations of engine rpm, manifold pressure and fuel flow.
For a non-turbocharged airplane, best cruise speed will typically be the highest altitude at which the engine produces maximum-recommended cruise power. Some aircraft have a fairly sharp drop-off in performance with altitude; that is, as the airplane climbs, it becomes significantly slower. Others, usually those with long, thin wings, can hang on to near-peak cruise numbers to a higher altitude. This is a design point you obviously can’t do much about.
Determine ahead of time what the power settings will be for the cruise portion of the flight. It’s not important to verify that what the demo pilot says is, say, 75% right there and then, but make a note to check the figures later. Remember, too, that engine power is a combination of throttle opening (manifold pressure), engine speed (rpm), and fuel flow (gph). On aircraft with a constant-speed propeller, your best bet is to choose an altitude and power setting that permits wide-open throttle, which both maximizes power output and also eliminates any instrumentation variable.
A good portion of the flight review will focus on aircraft handling, but that’s not the only important variable.
The pitot-static system is prone to errors, both from the location or design of the pitot head and/or static source, but also from instrument errors. What’s more, you can’t expect a non-articulated pitot head to be accurate at cruise angles of attack and equally so at an AOA near stall. As a result, the stall speed is likely to read quite low—the indicator might say 40 knots, but the airplane is actually traveling considerably faster. That’s why professional flight testing, such as is done by the CAFE Foundation, employs an articulated pitot head that follows the path of relative wind independent of the aircraft’s AOA.
In cruise, we tend to use a two-way GPS run to validate performance. There are more detailed methods using three- and four-way runs, but we’ve found the upwind/downwind process to be reasonably accurate and quick enough to implement easily. Before the flight, check the winds aloft. Your job is to fly directly upwind at a given power setting and indicated airspeed (IAS) and, after the value has stabilized, record groundspeed. (Be sure you have converted from the report’s true north to magnetic north.) Turn 180° and repeat. And be sure the airplane’s IAS has stabilized after the turn. GPS-derived true airspeed (TAS) has the benefit of needing no information from the onboard instruments beyond altitude and outside-air temp. Generally, the altimeter is fairly accurate, and it’s possible to take the forecast temperature at altitude as a rough check of the outside air temperature system. Remember that a higher-than-actual OAT reading will skew TAS values upward. While you’re checking numbers and reading them aloud for the recording, see how the airplane handles in cruise. Are the control forces acceptable—not too heavy or light? How is the balance? A classically balanced aircraft has the lightest forces in roll, heavier in pitch and reasonably stiff in yaw. Designs that are very light in pitch and yet require a lot of effort in roll tend to be hard to fly smoothly and accurately—not always, but mostly.
Stalls and Spins
Our policy is to avoid spins and aggressive stalls in virtually all designs. The exceptions might be those aircraft designed for aerobatic flight, and only then do we break the rule if there’s a parachute available and the test pilot feels like egress would be possible without extensive ground training. We’re not beyond a simple aileron roll or steep turns with some G force sans parachute, but the risk/reward equation gets pretty lopsided much beyond that line.
We work up to stalls progressively, starting with power-off, straight ahead slow flight gently drawn toward the first indication of a stall. If the airplane shows good manners, we’ll try other configurations—full flaps if we started out clean, for example, but we’ll work through the intermediate steps as necessary—and even some stalls in coordinated turns. We’re looking for a strong announcement before the stall and a gentle break with little to no tendency to drop a wing. Be wary of the excuse that the demo plane has “a little rigging problem” as an explanation for a serious wing drop. Don’t you think the company would want its demonstration aircraft to be the best it can be? Shouldn’t it be better built than customer examples?
Returning for Landings
On the way back downhill, you can try a few simple maneuvers to check basic stability. With the power reduced, trim the airplane for a given speed, preferably near maneuvering speed. Pull on the stick to reduce the IAS by 10 knots and then release the stick. (You may have to “bracket” the stick to maintain wings level, but try not to impart any pitch force.) See what the airplane does next. A longitudinally stable aircraft will pitch back in the direction it came from, overshoot slightly, stabilize slightly more nose-low than before, and then move nose-up to recover. Most aircraft have this motion, called a phugoid, completely damp out in three or four cycles. An airplane whose nose stays where you left it when you let go of the stick has poor longitudinal stability and/or a lot of control-system friction.
We also look for the airplane to be self-correcting in yaw—the vast majority of them are—and we want to see how they respond when the controls are released in a coordinated turn. Some aircraft hold the set bank angle and some want to return to wings level, while others want to tighten up the turn. This is called neutral, positive and negative roll stability, respectively. All aircraft are a little different, so we’re looking for the outliers—designs that do something quickly, unexpectedly.
Back to the Barn
Landing an unfamiliar airplane is always a crapshoot. I’ve had so-called easy airplanes play rough, and I’ve flown some theoretically difficult designs that were forgiving enough that we could reuse the airplane after my flight. During your demo flight, you might not get the chance to commit the landing, but it’s worth watching a few things. First, how busy is the demo pilot? A lot of stick movement—assuming you have reasonably smooth atmospheric conditions for the flight—can indicate low-speed instability. Second, how fast is he flying it? A normal baseline approach speed is 1.3 times the landing-configuration stall speed. If your demo pilot is coming in with the tail on fire, there could be a reason beyond his desire to use the bathroom. A demo pilot who refuses to use full flaps should make you wonder why all that flap was put into the design in the first place.
After landing, before you move on to other matters, take a moment to double-check that your recorder worked and whip out your digital camera. Grab detail shots of the airplane, especially the panel and interior. You will have questions later—heck, we frequently do, as we are sitting down to write the review—that you didn’t even think to ask in the heat of the moment. You might get the answers from your photos, and, after listening to the recording of your flight, it’s certain you’ll be a much better-educated customer. That is the whole point, isn’t it?