b. If a chase plane is used , the following suggestions are offered:
(1) A single chase plane should be used on the first two flights and the first time the amateurbuilt aircraft’s landing gear is retracted. The chase plane pilot should be experienced in formation flying and thoroughly briefed prior to each flight.
(2) There should be at least two pilots on board the chase plane. One pilot’s sole duty is to fly the aircraft and maintain a safe distance from the amateur-built aircraft. The other pilot serves as an observer whose duties include checking for other traffic, the condition of the test aircraft, and communicating with the pilot on the frequency assigned by air traffic control (ATC) (e.g., 122.75 megahertz [MHz]).
(3) A good chase plane position is about 100/200 feet off the right side and slightly behind and below the test aircraft. Avoid flying directly behind the test aircraft. It is not uncommon that on first flights, fuel and oil leaks develop and small hardware and fasteners could vibrate off the aircraft.
NOTE: Pilots of Both Aircraft Must Keep Each Other Informed of Their Intended Action or Maneuver Prior to Execution.
c. In an emergency situation:
(1) If the test aircraft’s radio fails, the chase plane should serve as an airborne communication relay with the tower/ATC facility for the test aircraft.
(2) For other emergency situations, the chase plane should provide the test pilot with information or assistance as required. If necessary, the chase plane can guide the test pilot to a safe landing at the airport or an emergency field. If the test aircraft goes down off the airport, the chase plane can serve as an overhead spotter that can direct emergency personnel to the test aircraft location.
SECTION 3. EMERGENCY PROCEDURES ‘‘At the worst possible time, the worst possible thing will happen.’’ Murphy’s Law
1. OBJECTIVE. To develop a complete set of in-flight emergency procedures for the aircraft that are designed to make unmanageable situations manageable.
2. GENERAL. The FLIGHT TEST PLAN should have a special section on emergency procedures. The responses to each emergency should have been developed based on the aircraft’s predicted flight characteristics, airport location, surrounding terrain, and nearby emergency fields.
a. The following is a partial list of possible emergencies that may arise during the flight test phase and includes suggested responses:
(1) PROBLEM: Engine failure on takeoff.
RESPONSE: Fly the aircraft! Establish best glide speed. If time permits, try to restart engine. If altitude is below 800 feet and the engine will not start, land straight ahead or 20 degrees on either side of the runway centerline. This is suggested because in most cases the aircraft will run out of altitude or airspeed as the pilot attempts a 180 degree turn back to the airport. Declare an emergency and shut off the master switch, fuel, and magnetos to reduce the possibility of fire on landing. Above 800 feet, the chances of making a 180 degree turn to land downwind on the runway or another emergency field nearby are directly proportional to the wind velocity and the numbers of practice emergency landings the pilots has made in similar make and model aircraft.
(2) PROBLEM: Engine vibration increases with rpm.
RESPONSE: Fly the aircraft!
Reduce power or increase power to minimize the effect of vibration, but maintain safe airspeed and altitude. Run through the emergency checklist and land as soon as possible.
(3) PROBLEM: Smoke in the cockpit.
RESPONSE 1: Fly the aircraft! If the smoke smells like burnt plastic wire installation, shut off the master switch. Put on smoke goggles,
36 5/24/95AC 90-89A open the fresh air vents to clear the cockpit, and land as soon as possible.
RESPONSE 2: Fly the aircraft! If the smoke is bluish/grey and has an acrid odor like burning oil, shut off the fresh air/hot air vents and put on the smoke goggles. Monitor oil pressure and temperature. Be prepared to shut the engine down and land as soon as possible.
(4) PROBLEM: Engine fire.
RESPONSE: Fly the aircraft! Shut off the fuel selector, mixture master switch, and magnetos. Land as soon as possible.
(5) PROBLEM: Out of rig condition.
RESPONSE: Fly the aircraft! Try to use the appropriate trim to offset adverse control pressures. Keep the airspeed high enough to maintain altitude. Make small control inputs, reduce power slowly to avoid controllability problems, and land as soon as practical.
(6) PROBLEM: Cabin door opening in flight.
RESPONSE: Fly the aircraft! A partially open door usually affects the airflow over the tail causing reduced control response and vibration.
Reduce speed, maintain level flight, and yaw/slip the aircraft left or right to reduce vibration. Open the side vent window to reduce air pressure resistance in the cabin and attempt to shut the door. Sometimes putting the aircraft in a skid will assist in closing a partially open door.
b. Other possible emergencies to plan for include:
(1) Canopy opening unexpectedly
(2) Loss of communications
(3) Throttle stuck in one position
(4) Oil on the windshield
(5) Propeller throws a blade
(6) Fire in the cockpit SECTION 4. FIRST FLIGHT ‘‘Always leave yourself a way out.’’ Chuck Yeager
1. OBJECTIVES. The two objectives of the first flight are to determine engine reliability and flight control characteristics.
a. After completing the pre-flight inspection, the test pilot should ensure that the seat/shoulder harness is properly fitted and allows easy access to all the cockpit controls (verified by a crew member).
Following the FLIGHT TEST PLAN and using the starting checklist, warm up the engine until the engine instruments indicate normal operating temperatures and pressures.
b. A complete check of each aircraft system should be performed (e.g., carb heat, magnetos, static rpm, and brakes).
c. If the airport does not have a tower/unicom available, the pilot should transmit over 122.9 MHz the following message: ‘‘This is experimental aircraft N/emlowln/emlowln/emlowln/wdspc on the first test flight, departing runway /emlowln/emlowln/emlowln/wdspc at /emlowln/emlowln/emlowln/wdspc airport, and will remain in the local area for the next hour.’’ Transmit the aircraft N number, location, and intentions every ten minutes.
d. If the airport is equipped with a tower, notify them that an experimental aircraft is on its first test flight and requests take-off instructions.
e. After being given clearance to take-off, clear the area, line up on the runway centerline, release the brakes, and slowly add power to provide ‘‘Thinking Time.’’ When the throttle is fully advanced, glance at the an oil pressure gauge and tachometer to confirm they are in the green and indicating take-off rpm. A type certificated engine of a 100 horsepower will produce between 2100 to 2300 rpm on the take-off roll, depending on the type of propeller installed. If either oil pressure or tachometer is reading low, abort the takeoff!
f. If there is any unusual vibration, rpm exceeding the red line, or engine hesitation, abort the takeoff!
g. If in a tail wheel aircraft, keep the tail on the runway until the rudder is effective. This usually happens at approximately 35 mph on most aircraft.
h. As the aircraft accelerates and approaches the predicted/manufacturer’s lift off speed/point (green flag), gently ease back on the stick. The first take-off should be a gentle and well-controlled maneuver with the aircraft doing all the work.
i. If the aircraft does not want to rotate or unusual stick forces are experienced, abort the takeoff!
j. If the aircraft has retractable gear, do not raise the gear on the first two to three flights until the aircraft’s stability/control responses have been explored a little further.
k. It is recommended that after establishing a safe climb angle. the pilot DOES NOT throttle back, switch tanks, or make large inputs into the flight controls for the first 1,000 feet. At the preselected altitude, reduce power slowly to avoid a pitch up or pitch down that might be associated with rapid power reductions.
NOTE: Check if there is any additional stick or rudder input pressure during the climb.
Try reducing any abnormal stick pressures with trim. Each control input should be small and slow.
l. If any unusual engine vibrations, rapid oil pressure fluctuation, oil and cylinder head temperatures approaching red line, or decreasing fuel pressure is experienced, refer to the emergency check list and land as soon as possible.
SECTION 5. FIRST FLIGHT PROCEDURES ‘‘In my opinion, about 90 percent of your risk in a total program comes with a first flight. There is no nice in-between milestone. You have to bite it off in one chunk.’’ Deke Slayton
1. OBJECTIVE. To perform a series of tests to develop data that will ensure a safe landing.
a. The First Test Flight.
(1) After take-off, climb to 3,000 feet above ground level (AGL) and level off. Reduce power slowly. Complete the cruise checklist items.
Following the FLIGHT TEST PLAN, circle the airport or emergency field as the engine performance is being monitored.
(2) Limit the cruise speed to no more than
1.5 the predicted stall speed of the aircraft. This will reduce the chances of flutter. If the engine appears to be operating smoothly, try testing the flight controls.
(3) With the airspeed being monitored, each control input should be gentle and small. Start with the rudder first. Yaw the nose of the aircraft 5 degrees left and right. Note the response. Raise the aircraft’s nose 3 degrees up, note the response.
After the aircraft is stabilized, level off and try three degrees nose down, trim, and note the response. Try a gentle bank of no more than 5 degrees to the left, then one to the right. If the aircraft is stable and is operating smoothly, try a few 90 degree clearing turns, followed by two 360 degree turns: one to the left and one to the right at a bank angle of 10 degrees.
(4) If the aircraft is responding to the prescribed specifications, increase the bank angle in succeeding turns to 20 degrees. If no problems are encountered, climb to 5,000 feet AGL (using the climb checklist and monitoring engine gauges), level off, fly an imaginary landing pattern, and test the flaps. Do not forget to announce every 5 to 10 minutes the aircraft’s location, altitude, and intentions.
Practice approach to landing by descending to 4,000 feet AGL first, then to 3,000 feet. Remember, use the descent checklist.
(5) During these maneuvers, control pressures should increase in proportion to control deflection. If control pressure remains the same as control deflection increases or if stick forces become lighter as control deflection increases, the aircraft may have a stability problem. Avoid large control movements and land as soon as possible.
(6) Remember to keep informing the tower/UNICOM/chase plane of what is happening.
For 10 minutes of anticipated flight time, plan a brief rest period for the pilot. Fly straight and level, monitor the gauges, and enjoy the experience.
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(7) At low cruise power setting, straight and level, observe how the aircraft trims out. Do the ‘‘fixed’’ trim tabs on the rudder and aileron need adjustment? Are the adjustable aileron and elevator trim control effective? Is the control stick/yoke slightly forward of the mid-position in straight and level flight?
(8) Climb slowly back up to 5,000 feet.
Two questions must be answered before landing:
(i) Is the aircraft controllable at low speeds?
(ii) What is the approximate stall speed?
(9) These questions can be answered with an approach to a stall maneuver. Do NOT perform a FULL STALL check at this time!
(10) The necessity for an approach to a stall check is because it will help establish a preliminary stall speed (Vsi) in mph/knots so the approach speed for landing can be calculated. Also, the pilot will have knowledge of the aircraft’s handling characteristics at low speed.
b. Suggested Procedure.
(1) Level off at altitude; make two clearing turns; stabilize airspeed, heading, and altitude; apply carb heat; set the flaps in the landing configuration and reduce power slowly to 900 rpm. TRIM. If, as is not uncommon on first flights, the aircraft cannot be trimmed properly, the pilot can still proceed with the check as long as the stick forces are not unusually heavy.
(2) With the aircraft airspeed approximately 1.4 mph/knots times (X) the predicted stall speed, raise the nose slowly. It is desirable for the aircraft to start decelerating slowly, about 1⁄2 mph/ knot a second. A 30 mph/knot deceleration at 1⁄2 mph/knot per second will take only a minute.
(3) As the aircraft slows down, note all the things that happen as the speed bleeds off. Observe the changing nose attitude and how the stick force changes. Keep the turn coordinator or turn and bank ‘‘ball’’ in the middle.
(4) Note how much rudder it takes to keep the ball centered. Every few seconds make very small control inputs to check that the aircraft is operating in the prescribed manner. If the aircraft does not respond to small control inputs -- and it should not be expected to respond as quickly as it did at higher speeds -- make the inputs a little bit larger. Increase the amount of input progressively.
Do not simultaneously put in all three control inputs.
Give particular attention to the response to nosedown elevator inputs, which is necessary for recovery.
(5) Notice any changes in flight characteristics and the speeds at which they take place. Be especially alert for the onset of pre-stall buffet. Is the buffet felt through the stick? Through the airframe? Though the seat of the pants? Does the nose of the airplane want to rise or drop on its own? How strong is the buffet? Is it continuous? Would it get the pilot’s attention if they were concentrating on something else?
NOTE: On some high performance aircraft and aircraft with unusual wing designs, a pre-stall buffet may not exist and the stall may be abrupt and violent with a large degree of wing drop.
(6) Keep making small control inputs at intervals to check the aircraft’s responses. At approximately 5 mph/knots before the predicted stall speed, or at the first sign of a pre-stall buffet, note the airspeed and stop the test. Recover and write down the pre-stall indicated airspeed. This airspeed should be the reference stall speed for the first landing.
(7) The pre-stall recovery response should be a smooth and quick forward stick movement. This response should be enough to reduce the angle of attack to the point where the airplane is flying normally again.
(8) A wing drop would be unexpected so early in the approach to a stall, but if it becomes necessary to raise a low wing do it with rudder, NOT OPPOSITE AILERON. Use of ailerons at lower speed would increase the chances for a stall or a sudden departure from controlled flight.
(9) There is no need to gain more airspeed than the extra few mph/knots to fly out of a prestall condition. After returning to straight and level flight and using the information learned, the pilot can practice a few more recoveries from a pre-stall condition. Remember the aircraft will constantly be
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.
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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.