39 loosing altitude so it is necessary to climb back up to 5,000 feet AGL to continue further flight testing.
Do not get so involved that the overall objective of the first flight is lost -- which is getting the pilot and aircraft safely back on the ground.
(10) The FLIGHT TEST PLAN for the first flight should call for a maximum of 1 hour of actual flight time. This is to reduce pilot fatigue and the possibility of an engine failure or airframe malfunction occurring due to vibration or construction errors.
NOTE: The pilot may elect to make several practice approaches to landing at altitude or low approaches to the active runway to get a solid understanding of the lower airspeeds, aircraft attitude, and overall feel of the aircraft in the landing configuration. Before each low approach at the airport, the tower/ UNICOM/chase plane should be advised of the pilot’s intentions. Avoid other traffic in the pattern, and use the landing checklist.
(11) When the pilot has completed all the tests called for by the FLIGHT TEST PLAN, notify the tower/UNICOM/chase plane of the intent to land.
Complete the landing checklist before entering downwind. Keep all turns less than 20 degrees of bank, but do not cross-control by using the rudder to move the nose. This will increase the bank angle, which most pilots will correct by using opposite aileron. If allowed to continue, and with back pressure on the stick, this will result in a cross-control stall and a roll to a near vertical bank attitude at the beginning of a spin with no altitude left for recovery.
(12) On final approach, the aircraft speed should be no less than 1.3 but no more than 1.4 times the recorded ‘‘first flight’’ pre-stall speed.
Homebuilt biplanes (high drag) should use an approach speed of 1.5 x stall speed on landings.
(13) Landings, especially the first one in an amateur-built or kit plane, are always exciting. Proceed slowly and do not over control. If the landing conditions are not ideal, be prepared to go around.
(14) The actual touchdown should take place within the first 1,000 feet with braking action being applied before the red (abort) flag marker on the runway.
(15) After taxiing in, secure the aircraft, debrief the flight with members of the team, then together perform a careful post-flight inspection of the aircraft.
NOTE: Remember to allow enough time to absorb what has been learned about the aircraft’s performance and the pilot’s and ground crew’s responses to it.
40 5/24/95AC 90-89A
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41 CHAPTER 4. THE FIRST 10 HOURS ‘‘One can get a proper insight into the practice of flying only by actual flying experiments.’’ Otto Lilienthal (1896) SECTION 1. THE SECOND FLIGHT
1. OBJECTIVE. To re-affirm the first flight findings.
a. Before the second flight, the pilot should ensure that all discrepancies noted on the first flight are corrected. It is probable that more ground runups, rigging adjustments, or taxi tests will be required. Under no circumstances should a pilot takeoff in an aircraft with known airworthiness problems.
The Law of Aerodynamics does not often forgive these types of mistakes.
b. The pre-flight inspection should be the same as performed for the first flight, including draining the oil and inspecting the oil and fuel screens for contamination.
c. The second flight, again lasting approximately an hour, should be a carbon copy of the first one, with the exception that all first flight discrepancies are corrected. If problems are not corrected, all further flight testing should be canceled until solutions are found.
SECTION 2. THE THIRD FLIGHT ‘‘Plan the flight, fly the Plan.’’ Sign on the wall at the Naval Test Pilot School, Patuxent River, MD
1. OBJECTIVE. To validate the engine reliability.
2. GENERAL. The third flight should concentrate on engine performance. Do not forget to record the engine’s response to any application of carb heart, leaning of the fuel mixture, changes to airspeed, and its response to switching fuel tanks.
a. Engine oil pressure, oil temperature, fuel pressure, and cylinder head temperatures should be monitored and recorded from 55 percent through 75 percent rpm. At the higher rpm, be sure not to exceed 80 percent of the maximum cruise speed. This is to avoid the possibility of encountering a flutter condition. Do not forget to record the engine responses to any applications of carb heat, leaning the fuel mixture, changes to the power settings (RPM and Manifold pressure), changes to airspeed, and its response to switching fuel tanks.
b. Resist the temptation to explore the more exciting dimensions of flight. Stick to the FLIGHT TEST PLAN and perform a conscientious evaluation of the engine. After landing, review the data with the crew members. Make adjustments as needed, perform another post-flight inspection of the aircraft, and record oil and fuel consumption.
c. After three hours of flight testing, the pilot should be able to make the initial determination that the aircraft is stable and engine is reliable in cruise configuration.
SECTION 3. HOURS 4 THROUGH 10 ‘‘Keep your brain a couple steps ahead of the airplane.’’ Neil Armstrong
1. OBJECTIVE. To build on the data established by the first three hours and start expanding on the flight test envelope in a thorough and cautious manner. This operational data will be added to the aircraft’s flight manual.
2. GENERAL. These next seven 1-hour test segments should confirm the results of the first 3 hours and explore the following areas:
a. Gear retraction (if applicable)
42 5/24/95AC 90-89A
b. Climbs and descents to preselected altitudes.
(monitor engine performance)
c. Airspeed indicator in-flight accuracy check NOTE: After each test flight, ALL DISCREPANCIES must be cleared before the next flight. The aircraft also must be THOROUGHLY INSPECTED prior to the next flight.
NOTE: It is recommended that all flight test maneuvers be preceded with two 90 degree clearing turns to ensure that the flight test area is free of other aircraft.
3. GEAR RETRACTION.
a. Before the gear is retracted in flight for the first time, it is advisable to put the aircraft up on jacks and perform several gear retraction tests, including the emergency gear extension test. These tests will determine if, in the last three hours of flight testing, any structural deformation or systems malfunctions have occurred. In addition to the gear retraction test, the pilot/chase pilot/ground crew should use this time to review the aircraft’s kit/ designer instructions and emergency checklist procedures for malfunctioning gear and plan accordingly.
If at any time the aircraft has suffered a hard landing or side loading on the gear during flight testing, the aircraft and its gear should be tested for operation and condition on the ground.
b. The first gear retraction test should be conducted with the aircraft flying straight and level at or above 5,000 feet AGL, over an airport or emergency field. The airspeed must be well under the maximum landing gear retraction airspeed. When the gear is being retracted, note if there is any tendency for the aircraft to yaw, pitch, or roll. Record what changes to the aircraft’s trim are required to maintain straight and level flight. If there are no adverse flight reactions or system malfunctions, cycle the gear several times. When satisfied with the straight and level gear retraction test, try an emergency gear extension but only if this is practical.
c. With the gear extended, slow the aircraft to 1.3 times the pre-determined stall speed, stabilize, lower the flaps to the take-off position, trim, and maintain straight and level flight.
d. Simulate a normal takeoff by increasing rpm to full power. Raise the nose 3 degrees, trim, and then retract the gear. Observe the following: aircraft reaction, such as pitch or roll; length of time for gear to retract; trim requirements;, and the time necessary to establish a 1,000-foot climb before leveling off.
e. Practice a simulated takeoff several times to ensure that the aircraft’s response is predictable and the gear retraction system is mechanically reliable.
4. CLIMBS AND DESCENTS. The purpose of these tests is to monitor engine performance and reliability. The pilot should start the test only after the aircraft has been flying straight and level for a minimum of 10 minutes to stabilize engine oil pressure and temperatures.
a. Engine oil pressure and temperatures must be kept within the manufacturer’s limits at all times during these tests. High summer temperatures may place restrictions on the flight test program because both oil and cylinder head temperatures will increase 1 degree for each 1 degree increase in outside temperature.
(1) Climbs. Start the first climb at a 15 degree climb angle, full power, at a predetermined designated altitude (e.g., 1,000 feet). Maintain the climb angle for 1 minute. Record the engine temperatures and pressures. Reduce power, stabilize the engine temperature, and repeat the test. For the second climb test, the Flight Test Plan should call for increasing the climb time -- record the results. When satisfied that an engine cooling problem does not exist at this climb angle, repeat the tests using steeper climb angles until the pilot has reached 15 degrees or encountered an engine manufacturer’s limit or a 5-minute climb period at full throttle has been reached.
(2) Descents. Should begin above 5,000 feet AGL with both the engine temperatures and pressures stabilized.
(i) The test pilot should use carb heat and clear the airspace below him before starting the descent. The first descent should be at a shallow angle, at low rpm and last for 30 seconds, not exceeding 1.5 times the estimated stall speed of the aircraft. During long, low power descents, the pilot must be on the alert for too rapid cooling of the engine usually identified by a signifi-
43 cant drop in oil and CHT temperature. If a noticeable drop occurs, increase the engine rpm and reduce the angle of descent. If not corrected, the repeated rapid cooling of the engine may cause thermal shock to the engine cylinders and eventually cause cylinder head cracking or seizure.
(ii) Conduct each test as before, but increase the time by 30 seconds until limited by the engine manufacturer’s restrictions or 5-minute descents are reached. Record temperatures, pressures, altitudes, and airspeeds data for climbs and descents for addition into the aircraft’s flight manual.
5. AIRSPEED IN-FLIGHT ACCURACY CHECK. The following procedure for airspeed calibration is offered for evaluation:
a. A measured course should be chosen with readily identifiable landmarks at each end. The landmarks should be a known distance apart, and the length of course should be at least 1 to 2 miles long.
b. The pilot must fly a precision course maintaining a constant altitude (e.g., 1,000 feet), constant airspeed, constant magnetic heading, and constant engine rpm. The pilot must record the temperature, altitude, indicated airspeed and the time over each landmark for both directions. The average of these speeds is the ground speed of the aircraft. An E6B computer will convert the temperature, altitude, and ground speed into True Indicated Airspeed for the tests.
NOTE: The difference between the E6B computer readings and the aircraft’s ground speed readings is the error in the instrument and the error caused by the installation of the system in the aircraft.
c. The airspeed calibrations runs should be made several times in opposite headings for each of the selected airspeeds the pilot wants to check.
Such accuracy test runs should start at the lowest safe airspeed and work up to cruise speed using 10 mph/knot increments.
d. Most errors will be found at the low end of the speed range due to the angle of the pitot mast to the relative wind and/or the location of the static ports. Recently, amateur-builders have been using Global Positioning Satellite (GPS) hand held receivers to check airspeed accuracy.
NOTE: Flight testing of all amateur-built aircraft is restricted to a flight test area. If a pilot must run additional tests on the aircraft that require more airspace, he should notify the FAA District Office that issued the aircraft’s operating limitations and request a change to those limitations. If a pilot is found to be operating an EXPERI- MENTAL AIRCRAFT in violation of the aircraft’s Operating Limitations, the FAA may take certificate action.
e. If the aircraft has retractable gear or flaps, test the accuracy of the airspeed indicator with the gear/flaps up and down.
f. Record all the data in order to prepare an airspeed calibration table for the flight manual.
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45 CHAPTER 5. EXPANDING THE ENVELOPE ‘‘Checklist! Checklist!! Checklist!!!’’ Jim Byers, Flight Instructor/Examiner SECTION 1. GENERAL
1. OBJECTIVE. To move from a known flight environment to an unknown flight environment using a series of planned and carefully executed steps.
a. Before beginning the next series of test flights, it is highly recommended that the aircraft undergo a ‘‘Condition Annual’’ inspection as identified in the FAA Operation Limitation the amateurbuilder received with the special airworthiness certificate. It is strongly recommended that the builder and/or pilot TAKE THE TIME to inspect the aircraft because within the previous 10 hours, the aircraft has been subjected to what can be referred to as a ‘‘shakedown cruise.’’
b. During the inspection, check the TORQUE (paint marks) on the engine mounts, propeller bolts, and landing gear. Double check the flight control hinges and rod end bearings for attachment and play.
Check all cable installations, cable tension, and control travel in addition to completing all the standard inspection and maintenance items. This inspection also should include checking the oil and fuel filters for metal or other forms of contamination.
c. Even if there have been no indications of CO contamination, perform another carbon monoxide (CO) test using the floodlight procedure (see chapter 1, section 7) or an industrial CO test meter.
There is a strong possibility that operational vibration and landing stresses may have opened new paths for CO to enter the cockpit.
SECTION 2. HOURS 11 THROUGH 20 ‘‘Fly Scared!’’ Admiral Jack Ready, U.S.N.
1. OBJECTIVE. To focus the next 10 hours of flight testing on the following: stall speed, best rate of climb speed, best angle of climb speed, and slow flight. It is recommended that stall speed tests be conducted with the aircraft’s fuel tanks full. (CG).
a. As with any unknown, approach slowly, incrementally, and follow the FLIGHT TEST PLAN.
To improve safety and reduce the possibility of spins, the aircraft should be tested with a forward CG loading. Start the stall tests at 6,000 AGL. Make clearing turns and stabilize the airspeed and altitude. The first full stall should be conducted with power off, no flaps, and gear-up if applicable. After clearing the area, reduce the airspeed to 1.3 times the predicted stall speed and trim. (NOTE: Do not trim within 10 knots of stall.)
NOTE: Some clean, high performance aircraft may not have any noticeable pre-stall buffet. The actual stall may be abrupt and violent with a large amount of wing or nose drop.
b. The preferred pre-stall and stall behavior is an unmistakable warning buffet starting lightly about 5 to 10 mph/knots above the eventual stall speed, growing in intensity as the aircraft slows down.
c. The desired stall characteristics should be a straight forward nose drop with no tendency for roll or pitch-up. This docile and forgiving behavior implies a stall that has started at the wing root and progressed smoothly outboard. This gives an early warning to the pilot in the form of the buffet from separated airflow over the wings and or tail. The ailerons will continue to operate in the attached air flow until the aircraft’s stall speed is reached and the wing stalls.
d. Begin by using the same procedures employed on the first flight. Secure cockpit items and put on carburetor heat. Decelerate slowly at 1⁄2 MPH/knot a second. Make small control inputs, keep the ball centered, and note the aircraft’s reaction.
46 5/24/95AC 90-89A
e. Let the aircraft stall and recover immediately, with stick forward and increasing power.
Note the stall speed.
f. Practice the same stall sequence several times at 1⁄2 mph/knot speed deceleration rate to determine the power-off, one g stall speed. Practice the same stall series with flaps, starting with the lowest setting first and working slowly to the full flap configuration. Record the findings.
g. After exploring the stall and recovery behavior in a slow deceleration with the ball in the middle, try a series of stalls with flaps up and then flaps down with a faster rate of deceleration. Do not exceed the deceleration rate expected in normal operations.
2. STALLS.
a. Power on Stalls. As before, use the same procedures moving from the known to the unknown.
Increase power incrementally and run a stall test at each new power setting until full power is reached.
It is not advisable to jump straight from idle to full power with the resultant large changes in pitch attitude, torque reaction, and slip stream effect on the wing and tail.
b. Conducting Power on Stalls. It is recommended that the aircraft be stabilized in level flight at low cruise power. The power-on stall is reached by slowly increasing the power to the desired power setting. The pilot then steadily increases the pitch attitude until the aircraft experiences the stall buffet. Remember to keep the ball in the center until the onset of the stall buffet.
(1) The power on stall may be more likely to cause a wing drop than one at idle. This is due to torque reaction and because the propeller slipstream tends to keep the flow of higher velocity air over the inboard (root) section of the wing despite the higher angle of attack. This allows the root portion of the wing to continue flying after the wing tip stalls, dropping a wing.
(2) Tip stalls usually do not give advance warning and will almost invariably result in some severe wing drop. These stalls are more likely to result in a spin, even if the controls are not mishandled. If the spin does not develop, considerably more height will be lost in the recovery than if the stall had been straight-ahead nose down.
(3) If the pilot yields to instinct and tries to correct the wing drop with aileron, it could result in a spin. Since a sharp wing drop could be regarded as the onset of spin auto-rotation, the recommended corrective action is to reduce power, exercise prompt application of full opposite rudder combined with lowering the nose to the horizon or below. Take care to avoid this situation until the aircraft’s spin behavior has been tested.
(4) Perform the same sequence of events for power on stalls as power-off stalls, unless limited by the designer’s instructions. Record all findings for the aircraft’s flight manual.
NOTE: Aircraft with retractable gear will have to go through a separate series of slow flight and stall checks with gear extended, with and without flaps. Record the different stall speeds for each configuration in the aircraft’s flight manual.
47 FIGURE 6. Climb Airspeed and Altitude Graph
c. Best Rate of Climb Speed Tests. To determine the best rate of climb for the aircraft, the following procedures are suggested:
(1) Perform the tests in smooth air, free from thermal activity. Select an altitude (e.g., 1,000 feet AGL) as a BASE attitude. Use a heading 90 degrees to the wind and for the best results, reverse the heading 180 degrees after each climb test.
(2) Begin a full throttle climb well below the predetermined BASE altitude and stabilize at a preselected airspeed approximately 15 mph/knots above the predicted best rate of climb speed. As the aircraft passes through the BASE altitude, begin a one minute time check. At the end of 1 minute, record the altitude gained. Descend down below the BASE altitude. Decrease the airspeed by 5 mph/ knots and run the test again. After each succeeding test, the pilot should decrease the airspeed by 5 mph/ knots until reaching an airspeed that is 10 mph/knots higher than the stall speed of the aircraft. Record the airspeed and altitude gained for each climb on a graph similar to figure 6.
(3) The airspeed that shows the greatest gain in altitude is the aircraft’s best rate of climb speed (Vy).
48 5/24/95AC 90-89A FIGURE 7. Best Rate of Climb Speed Graph
d. Best Angle of Climb Speed Tests.
(1) Best angle of climb speed can be found by using the same chart developed for the best rate of climb tests. Draw a line (tangent) from the zero rate of climb feet per minute (see figure 4) outward to a point, on the rate of climb airspeed curve. Where both lines touch, draw a line straight down to the airspeed leg of the chart.
(2) The airspeed that the line intersects is the best angle of climb airspeed.
e. Slow Flight Test.
(1) For added safety, the slow flight tests should be performed at 6,000 AGL or higher to allow room for spin recovery. THE PRIMARY PURPOSE
OF THESE TESTS IS FOR THE PILOT TO BECOME FAMILIAR WITH THE AIRCRAFT’S
HANDLING QUALITIES AT THE MINIMUM
GEAR UP/DOWN AIRSPEEDS AND POWER SETTINGS.
(2) The tests should be done with and without flaps. Start the tests at an airspeed of 1.3 times (X) the stall speed of the aircraft. Once the aircraft is stabilized and maintaining its altitude, reduce the airspeed by 5 mph/knots. Maintain the altitude. Keep reducing the airspeed until approaching a stall.
(3) Maintain 5 mph/knots above the previously determined stall speed. This figure is the initial slow flight airspeed. Practice with each flap setting, noting its affect on the aircraft’s performance.
If the aircraft has retractable gear, test in all gear and flap combinations. These tests will have to be run later in the flight test program but with the AIR- CRAFT AT GROSS WEIGHT to determine the actual slow flight airspeed and stall speeds.
(4) Remember, to help reduce the possibility of unplanned stalls in slow flight configurations, avoid bank angles of more than 5 degrees. When all the test data has been evaluated, and if the aircraft is equipped with a stall warning horn or indicator, set the stall warning at 5 mph/knots above the aircraft’s highest stall speed.
49 SECTION 3. HOURS 21 THROUGH 35: STABILITY AND CONTROL CHECKS ‘‘A superior pilot uses his superior judgement to avoid those situations which require the use of superior skill.’’ Old Aviation Proverb
1. OBJECTIVE. To determine the aircraft’s stability limits and range of control.
2. GENERAL. Before attempting to satisfy the requirements of Federal Aviation Regulations § 91.319 Aircraft Having Experimental Certificates:
Operating Limitations and declaring that the aircraft is controllable throughout the normal range of speeds, two things must be done.
a. Perform another complete inspection of the aircraft, including oil changes and fuel system filter checks.
b. Carry out a close examination of the stability and control characteristics of the aircraft. Stability and control checks will be centered around the three axes of the aircraft: longitudinal or roll axis (ailerons), the lateral or pitching axis (elevators), and the vertical or yaw axis (rudder).
c. All tests need a starting point. The starting point for stability and control checks is called the state of equilibrium. An aircraft is said to be in a state of equilibrium when it experiences no acceleration and remains in a steady trimmed condition until the force or moment balance is disturbed by an atmospheric irregularity or by pilot input.
FIGURE 8. Static Stability
3. DEFINITIONS.
a. Static Stability: (positive) is when an aircraft tends to return to the state of initial equilibrium position following a disturbance.
b. Static Stability: (neutral) is when an aircraft remains in equilibrium in a ‘‘new’’ position, following a disturbance from an initial equilibrium position.
c. Static Stability: (negative) is when an aircraft tends to move further in the same direction as the disturbance that moved it from the initial equilibrium position (figure 8).
50 5/24/95AC 90-89A FIGURE 9. Time
d. Dynamic Stability: is the time history of the movement of the aircraft in response to its static stability tendencies following an initial disturbance from equilibrium (figure 9).
e. Test for Static Longitudinal Stability.
(1) This test should be done first. All tests should be conducted with the aircraft in the forward of center CG. Climb to at least 6,000 feet AGL and trim the aircraft for zero stick force in straight and level flight at low cruising speed. (Note: Do not retrim the aircraft once the test has begun.) Apply a light ‘‘pull’’ force and stabilize at an airspeed about 10 percent less than the trimmed cruise speed. At this reduced airspeed it should require a ‘‘pull’’ force to maintain the slower speed.
(i) If it requires a ‘‘pull’’ force, pull a little further back on the stick and stabilize the airspeed at approximately 20 percent below the initial cruise trim speed.
(ii) If it requires a still greater ‘‘pull’’ force to maintain this lower airspeed, the aircraft has
POSITIVE STATIC LONGITUDINAL STABIL- ITY.
(iii) If at either test points, no ‘‘pull’’ force is required to maintain the reduced airspeeds, the aircraft has NEUTRAL STATIC LONGITUDINAL STABILITY.
(iv) If either of these test points require a ‘‘push’’ force to maintain the reduced airspeed then the aircraft has NEGATIVE STATIC LONGITUDINAL STABILITY.
(2) Repeat another series of static longitudinal stability tests using a ‘‘push’’ force on the control stick. At an airspeed 10 percent above the trim cruise speed the control stick should require a ‘‘push’’ force to maintain the airspeed. If a ‘‘pull’’ force is required, the aircraft has NEGATIVE STATIC LONGITUDINAL STABILITY.
WARNING: If the aircraft exhibits negative static longitudinal stability, seek professional advice on correcting the problem before further flight.
(3) After confirming the aircraft has positive STATIC longitudinal stability, the pilot can check for positive DYNAMIC longitudinal stability (short period). First, trim the aircraft to fly straight and level at normal trim cruise speed. With a smooth, but fairly rapid motion, push the nose down a few degrees.