CERTIFICATION BASIS
14 CFR part 27 CAR 06 Rqmts 27-Amdt. 21 Original Original Original IGE
CONTROL Ref.
27.25
27.143
27.1587 AC 27-1B, Sections
27.45 &
27.143 Test Conditions
1. MGW Sea Level
2. Max. IGE wt. Lesser of:
a. Max. alt.
cap.
b. 7000' Hd
3. Critical CG
4. Critical Rotor RPM
5. Wind of not less than 17 kts.
1. MGW Sea Level
2. Wt.
selected by applicant to max. t.o. and ldg. alt.
3. Critical CG
4. Critical Rotor RPM
5. Critical wt.
6. Wind of not less than 20 mph
1. MGW Sea Level
2. Max.
approved wt.
for t.o./ldg at alt above sea level.
3. Critical CG
4. Critical Rotor RPM
5. Wind not less than 20 mph.
1. No specific requirement.
RFM
6. Max. safe wind is perf.
info.
7. Max. safe wind is perf.
info.
6. Max. safe wind is perf.
info.
Remarks
7. If 17 kts.
wind demo'd to alt. less than 7000', a corresponding WAT limit must be established.
FIGURE AC 27.45-2 IGE CONTROLLABILITY REQUIREMENTS
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AC 27-1B, Chg 4 3/31/2014 600 CORRECTED SHAFT HORSEPOWER 500 - ENG SIN 12345 400 300 MIN CERTIFIED
SPECIFICATION ENGINE 200 100 1000 1100 1200 1300 1400 1500 CORRECTED TOT °F FIGURE AC 27.45-3 _ SHAFT HORSEPOWER VS TURBINE OUTLET
TEMPERATURE - SEA LEVEL STANDARD DAY Page B - 22
20 -20° - 30° to -50° 50° 16 PRESSURE ALTITUDE - FEET (X 1000) 200 400 500
SHAFT HORSEPOWER AVAILABLE FIGURE AC 27.45-4 UNINSTALLED TAKEOFF POWER AVAILABLE Page B - 23
AC 27-1B, Chg 4 3/31/2014 20 10 o 14 TRANSMISSION LIMIT PRESSURE ALTITUDE - FEET (X 1000) 200 300 400
SHAFT HORSEPOWER AVAILABLE FIGURE AC 27.45-5 INSTALLED TAKEOFF POWER AVAILABLE, ANTI-ICE OFF, 400 RPM Page B - 24
1000 FT BOGO FT FT 4000 FT 2000 FT SEA LEVEL
- 120
PERCENT TORQUE EXAMPLE: OAT = 17.5°C TOT = 760° C Hp = 4000 FT REQUIRED TORQUE = 70% CONDITIONS: ZERO AIRSPEED RPM 100% ANTI-ICE OFF GENERATOR LOAD 100 AMPS OUTSIDE AIR TEMPERATURE - °C FIGURE AC 27.45-6 POWER ASSURANCE CHECK CHART Page B - 24.1
AC 27-1B, Chg 4 9/17/2009 AC 27.49. § 27.49 (Former § 27.73) (Amendment 27- 44) Performance at Minimum Operating Speed.
(For § 27.73 prior to Amendment 27-44, see AC 27.73)
a. Explanation. Amendment 27-44 adds a requirement to determine out-of-groundeffect (OGE) hover performance. Once reserved for special missions, OGE operations are now a common practice.
(1) The word "hover" applies to a helicopter that is airborne at a given altitude over a fixed geographical point regardless of wind. Pure hover is accomplished only in still air. For the purpose of this manual, the word "hover" will mean pure hover.
(2) The regulatory requirement for hover performance, § 27.49, refers to hover in–ground-effect (IGE) and OGE. Hover OGE is the absence of measurable ground effect. Hover OGE is established when the power required to hover is the same at different heights above the ground.
(3) The objective of hover performance tests is to determine the power required to hover at different gross weights, ambient temperatures, and pressure altitudes.
Using non-dimensional power coefficients (Cp) and thrust coefficients (Ct) for normalizing and presenting test results minimizes the amount of data required to cover the helicopter's operating envelope.
(4) Hover performance tests must be conducted over a sufficient range of pressure altitudes and weights to cover the approved ranges of those variables for takeoff and landing. Additional data should be acquired during cold ambient temperatures, especially at high altitudes, to account for possible Mach effects.
(5) The IGE hover ceiling for which data should be obtained and subsequently presented in the flight manual should be the same height consistent with the minimum hover height demonstrated during the takeoff tests. Refer to AC 27.51 for the procedure to determine this hover height.
b. Procedures.
(1) Two methods of acquiring hover performance data are the tethered and the free flight techniques. The tethered technique is accomplished by tethering the rotorcraft to the ground using a cable and load cell. The load cell and cable are attached to the ground tie-down and to the rotorcraft cargo hook. The load cell is used to measure the rotorcraft's pull on the cable. Hover heights are based on skid or w heel height above the ground. During tethered hover tests, the rotorcraft should be at light gross weight. The rotorcraft will be stabilized at a fixed power setting and rotor speed at the appropriate skid or wheel height. Once the required data are obtained, power should be varied from the minimum to the maximum allowed at various rotor RPM. This technique will produce a large Ct/Cp spread. The load cell reading is recorded for each Page B - 24 2
stabilized point. The total thrust the rotor produces is equal to t he rotorcraft's gross weight plus the weight of the cables and load cell plus cable tension. Care must be taken that the cable tension does not exceed the cargo hook limit or load capacity of the tie-down. For some rotorcraft, it may be necessary to ballast the rotorcraft to a heavy weight in order to record high power hover data. IGE hover performance may be affected by the composition and slope of the surface beneath the rotorcraft. Therefore, the tests should be conducted over a smooth, level, hard surface.
(2) The pilot maintains the rotorcraft in position so that the cables and load cell are perpendicular to the ground. To ensure the cable is vertical, two outside observers, one forward of the rotorcraft and one to one side, can be used. Either hand signals or radio can be used to direct the pilot. The observers should be provided with protective equipment. Positioning can also be accomplished by attaching two accelerometers to the load cell, which sense angle or movement along the longitudinal and lateral axes.
Any displacement of the load cell will be reflected on instrumentation in the cockpit, and by reference to this instrumentation, the rotorcraft can be maintained in the correct position. Increased caution should be utilized as tethered hover heights are decreased because the rotorcraft may become more difficult to control precisely. The tethered hover technique is especially useful for OGE hover performance data because the rotorcraft's internal weight is low and the cable and load cell can be jettisoned in the event of an engine failure or other emergency.
(3) To obtain consistent data, the wind velocity should be less than 3 knots as there are no accurate methods of correcting hover data for wind effects. To minimize inaccuracies due to hysteresis, collective movement should be made in only one direction. Rotorcraft with high downwash velocities may tolerate higher wind velocities.
The parameters usually recorded at each stabilized condition are:
(i) Engine and transmission torque.
(ii) Rotor speed.
(iii) Ambient and engine temperatures, such as Measured Gas Temperature (MGT).
(iv) Pressure altitude.
(v) Fuel used (or remaining).
(vi) Load cell reading.
(vii) Generator(s) load.
(viii) Wind speed and direction.
(ix) Hover height.
Page B – 24.3
AC 27-1B, Chg 4 9/17/2009 As a technique, it is recommended the rotorcraft be loaded to a center of gravity (CG) near the hook to minimize fuselage angle changes with varying powers. All tethered hover data should be verified by a limited spot-check using the free flight technique.
The free flight technique in AC 27.49.b.(4) will determine if any problems, such as load cell malfunctions, have occurred. The free flight hover data must fall within the allowable scatter of the tethered data.
(4) If there are no provisions or equipment to conduct tethered hover tests, the free flight technique is also a valid method. The disadvantage of this technique, as the primary source of data acquisition, is that it is very time consuming. In addition, a certain element of safety is lost OGE in the event of an emergency. The rotorcraft must be re-ballasted to different weights to allow the maximum Ct/Cp spread. When using the free flight technique, either as a primary data source or to substantiate the tethered technique, the same considerations for wind, recorded parameters, etc., as used in the tethered technique, apply. Free flight hover tests should be conducted at CG extremes to verify any CG effects. Applicants must account for any rotorcraft stability augmentation system that may influence hover performance.
(5) Comprehensive hover performance tests are typically conducted at low, intermediate (~7000 feet Hd), and high altitude test sites, with prepared landing surfaces, in conjunction with takeoff, landing, controllability, and maneuverability testing. Alternatively, a predicted hover performance model developed for high altitude may be used if verified by limited flight-testing. The extrapolation guidelines in AC
27.45.b.(2) are still applicable. These higher altitude hover tests could typically be conducted in conjunction with the limited controllability tests. If the applicant is able to demonstrate to the FAA/AUTHORITY a method to provide a reliable hover reference, it is acceptable to conduct OGE tests without ground reference. Hover performance can usually be extrapolated up to a maximum of 4,000 feet above the highest test site altitude.
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AC 27.51. § 27.51 TAKEOFF.
a. Explanation. Section 27.51 details the conditions under which takeoff data must be obtained. The flight manual must contain the technique(s) to be used to obtain the published flight manual takeoff procedures. Technique should not be confused with exceptional pilot skill and/or alertness as mentioned in § 27.51. Because rotorcraft differ, different pilot techniques are sometimes required to achieve the safest and most optimum takeoff performance. The recommended technique that is published in the flight manual must be determined to be one that the operational pilot can duplicate using the minimum amount of type design cockpit instrumentation and the minimum crew. Only rotorcraft takeoff techniques will be covered in this section.
b. Background.
(1) Certain special takeoff techniques are necessary when a rotorcraft is unable to take off vertically because of altitude, weight, power effects, or operational limitations.
The recommended technique used to take off under such conditions is to accelerate the rotorcraft in-ground-effect (IGE) to a predetermined airspeed prior to climbout. Takeoff tests are performed to determine the best repeatable technique(s) for a particular rotorcraft over the range of weight and altitude for which certification is requested.
(2) Utilizing the total power available to execute a takeoff may not be operationally feasible due to such items as HV or aircraft attitude constraints. In such situations, hover power required plus some power increment may be the maximum recommended for use.
(3) Wheel or skid height should be not less than that demonstrated satisfactorily for the high speed, low altitude portion of the HV curve, or that height below which ground contact may occur when accomplishing takeoff procedures.
(4) For rotorcraft fitted with wheels, a running takeoff procedure may be accepted.
c. Procedures.
(1) There are different takeoff profiles which may be used to complete a maximum performance takeoff in a rotorcraft. The manufacturer will normally determine which method is best for a particular rotorcraft. The most commonly accepted method is the hover and level acceleration technique. In this technique, the rotorcraft is stabilized in a hover at the reference height. From the stabilized hover, the rotorcraft is accelerated to the climbout airspeed using the predetermined takeoff power. When the desired climbout airspeed is achieved, the rotorcraft is rotated and the climbout is accomplished at the scheduled airspeed(s) and constant rotor RPM. Power adjustments may be accomplished to maintain the targeted power except where procedure requires high workload outside the cockpit (i.e., that portion of takeoff where Page B -25
AC 27-1B, Chg 4 9/17/2009 horizontal acceleration close to the ground has pilot scan outside the cockpit and adjustment of engine torque or temperature would require an undue increase in workload). The recommended takeoff procedure must be demonstrated to remain clear of the HV “avoid” areas without requiring exceptional piloting skill or exceptionally favorable conditions.
(2) The hover reference height is established as the minimum skid or wheel height above the takeoff surface from which a takeoff can consistently be accomplished in zero wind without contacting the runway surface. The takeoff must be accomplished with power fixed at the power required to hover at the hover reference height and must not require exceptional piloting skill to avoid runway surface contact.
AC 27.51A. § 27.51 (Amendment 27-44) Takeoff.
a. Explanation. Amendment 27-44 revised the requirement to perform the test at the most critical center-of-gravity (CG) location as opposed to the most forward CG. While it is not always the case, the forward CG is particularly critical for most rotorcraft.
Additionally, the change clarifies that the test must be performed at the maximum weight requested for takeoff for altitudes above sea level. The previous requirement stated that the test be performed at a weight selected by the applicant for altitudes above sea level. That weight was traditionally interpreted to mean the maximum requested takeoff weight for that altitude and it is now stated that way in the rule.
b. Procedures. The policy material pertaining to the procedures outlined in this section remain in effect.
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AC 27-1B, Chg 4 3/31/2014 AC 27.65. § 27.65 (Amendment 27-14) CLIMB: ALL ENGINES OPERATING.
a. Explanation.
(1) Rotorcraft other than helicopters.
(i) Section 27.65 requires that the steady rate of climb be determined for each rotorcraft other than helicopter with maximum continuous power on each engine for the range of weights, altitudes, and temperatures for which certification is requested.
Equivalent levels of safety have been found wherein the applicant was allowed to select a climb airspeed that was not the actual VY. The selected airspeed must be consistent with the speed used to show compliance with such items as cooling, stability, etc. The rate of climb resulting from the selected climb airspeed versus that from the actual VY shall not differ to an extent that a pilot will be encouraged, by appreciable increases in climb performance, to fly a climb airspeed different from that published in the flight manual.
(ii)For rotorcraft other than helicopters, the climb performance data obtained above must be used to show that a minimum climb gradient can be achieved for each weight, altitude, and temperature within the range for which certification is required.
This gradient must be at least 1:10 if testing is done to determine the required takeoff distance over a 50-foot obstacle. If this option is selected, an explanation of the takeoff distance determination requirements and procedures may be found in paragraph AC 29.63 of AC 29-2C.
(iii) If takeoff distance is not determined, the minimum climb gradient must be 1:6 for standard sea level conditions.
(2) For helicopters, VY must be determined for standard sea level conditions at maximum weight using maximum continuous power on each engine. Although not required, the steady rate of climb may be determined using the procedure in paragraph AC 27.65c of this section (Procedure to Determine All-Engine-Operating Climb Performance).
[Section AC 27.65 continued on next page.] Page B – 26.2