TEST-FLIGHT PLANS
By Jim Hiller | jetmodeler@earthlink.net
TEST FLIGHTS on complex airplanes, such as jets and warbirds, tend to be quite an undertaking. Proper preparation takes some thought and effort to ensure success. My experience with test flights of complex airplanes, including some prototypes, tends to be with approximately 15 to 20 models per year. This has been quite a project throughout the years; however, it can be an enjoyable challenge with proper preparation. I have developed my own test-flight plan that works well for me.
The primary objective is a successful test flight with no damage to the airplane. The second objective is to learn as much as required to prepare the airplane for the new owner to successfully transition to flying it. This secondary objective can often be met in only one flight, but that’s not always the case if problems are encountered and need to be addressed before the second flight. A test pilot can only check so much; building, setting up the flight controls, and balancing the airplane are extremely important to a successful test flight.
The setup of the model prior to the first flight is of utmost priority. My first question is whether the center of gravity (CG) is correct according to the manufacturer’s recommendation or whether it has been calculated using a known method. The standard method for calculating a good CG to start with is located on many websites. If you are in doubt, do a search, because many model airplane websites carry such programs of varying complexity up to, and including, canard and flying wing versions.
One tip: When calculating the CG, always extend the wing dimensions to the centerline of the fuselage. This is particularly important for swept-wing designs. Moving on to the control setup, use the manufacturer’s recommendations when they are available, unless they are known to be questionable, such as those with excessive throws that were developed for 3D pilots or if you do not perform 3D maneuvers and prefer normal pattern-type control responses.
At least one jet manufacturer recommends such types of throws, along with an extremely nose-heavy CG. The excess elevator throw in this setup is required to overcome the nose-heavy condition to complete a successful landing. Without it, the pilot cannot raise the nose on landing and can wipe out the landing gear because of a lack of control authority, so be careful when deviating from a manufacturer’s recommendations.
I tend to spend quite a bit of time checking the programming of the control movements, the dual-rate options, flap setups, and the flight-mode trim setup. These features are available on most modern transmitters. A standard setup for the pilot should provide options if the setup is off. Of course, a test pilot who is experienced with a particular airplane can hit the setup pretty darn close before the first flight.
A great feature to use when you are in doubt about control throws is dual rates. My technique is to put elevator dual rate on the left front-face switch and set it up so that middle rate is what I expect to be correct. Low rate is 10% to 15% less and high rate is 25% more travel. High rate provides an option if things go wrong; that extra control throw has bailed me out of some strange happenings on test flights.
The ailerons are set up in a similar fashion, only using a separate switch, which is typically the right front-face switch. This standard setup allows my natural reactions to change control rates without a lot of the thought that is required to find the correct switch. Having separate switches for the elevator and ailerons on the test flight provides the ability to individually determine the best throws for each surface and perform the first landing with the best setup possible. The switch setup can be changed to your personal preference after the test flights.
On to the flight-mode trims, which are not always fully understood by all. This feature is wonderful for trimming the airplane’s multiple flight conditions. Flap-equipped airplanes can use three flight modes. Assign them to the flap switch.
Flaps up is “normal flight,” flaps in takeoff position is “takeoff,” and flaps full-down is “landing.” Each flight mode now has its own trim settings so that the airplane can be trimmed for each flap position, allowing it to land with full flaps in a properly trimmed condition on the test-flight.
Airplanes tend to either climb or dive with flap deflection based on the airplane’s design, so trimming the airplane in each flap position is included in my test-flight card. The advantage is that the first landing is with a properly trimmed airplane.
Finally, set your trim settings to flight-mode trims. This is also a good time to set the throttle to a two-position for turbines. The shutoff only takes a single push of the throttle trim. The elevator and aileron trims are set to flight modes.
That’s a good, basic setup. By standardizing my setup for a test flight, I know what to do instinctively, which is important when difficult situations occur.
On to the test flight and how to effectively work through an involved flight plan. The first takeoff is normally made with the flaps
up, unless prior experience with a similar aircraft has proven no unusual pitch-trim issues with flap deployment. I clean up the airplane quickly, with the landing gear and flaps up, as I gain altitude to start checking out the aircraft’s performance. The first check is level trim in pitch, roll, and yaw—that is, elevator, aileron, and rudder. The goal is to release the controls and have the airplane continue in a straight line, which is simple, basic stuff.
Now let’s move on to the control throws. The aileron rate is checked in all three rates then my preferred rate is selected. The owner is kept informed on all three rate checks so that they can decide their preference. The elevator rate is then checked. This is a bit more involved because I like a tight turn to check the maximum travel at each rate. I prefer the airplane at full up-travel to just barely break into a stall, which allows the pilot to pull full control in an exciting situation, without experiencing a violent, deep stall.
The big stuff—slow flight with the landing gear down and the flaps deployed in takeoff and landing positions—happens now. The trim for level flight is repeated in each flap position and flight mode, followed by slowing to a full-elevator pull, again checking for the model’s stall characteristics. After the landing flap position has been completed, both the airplane and I should be ready for landing because I have experienced how it handles during slow flight while at a safe altitude—not 5 feet off the ground during the landing flare.
I hope this gives you some ideas on how to test-fly your new jet, and that it helps keep you out of trouble. Most pilots have variations based on their personal preferences, but good test-pilot skills are developed with a good plan and the execution of that plan.
SOURCES:
Jet Pilots Organization (JPO)
www.jetpilots.org
Elite Aerosports
(954) 444-8809
www.eliteaerosports.com
AeroPanda
https://aeropanda.com
Boomerang RC Jets
(765) 548-3757
www.boomerangrcjets.com
