Appendix 5 A5-5 Figure 3. Sample Tasks for Evaluating Airplane Handling Qualities (continued)
C. Closed-Loop Precision Regulation of Flight Path Generally, these are tightly-bounded, pilot closed-loop tasks expected to be performed in routine commercial flight. These controlling tasks are almost exclusively within the Normal Flight Envelope, or not far outside the NFE boundary.
-- ILS and precision touchdown, various atmospheric disturbance and initial offset.
-- Formation flying (as simulator for maneuver tracking).
SPD/ALT/HDG tracking, in various atmospheric disturbance and cockpit display status, for:
-- Takeoff -- Climb -- Cruise -- Descent -- Hold -- Configuration changes/power or thrust changes -- Transition between aforementioned
d. Figure 4 provides guidance for determining the probability of occurrence associated with being in a particular portion of the flight envelope (Xe), in a particular atmospheric disturbance level (Xa), and with a particular flight control failure state (Xc). It also describes how the flight envelope probability (Xe) should be modified for interrelationships with the atmospheric condition.
Figure 4. Probability of Occurrence Guidelines
A. Flight Envelope (Xe) Probability of occurrence (at flight envelope boundary) Normal Flight Envelope Generally associated with routine operational and/or prescribed conditions, either all engines operating or one engine inoperative.
100 Operational Flight Envelope Generally associated with warning onset; outside the normal flight envelope.
10-3 Limit Flight Envelope Generally associated with airplane design limits or EFCS protection limits.
10-5 Refer to this Figure and Figures 5 and 6 for more detail on determining which flight envelope is applicable.
It may be necessary to consider several of the pertinent flight parameters together to determine which flight envelope a given flight condition is in. For the more influential flight parameters, such as angle-of-attack (AOA), speed, and load factor normal to the flight path (Nz), the choice of which flight envelope a condition is in may be determined by as few as one of the parameter values. Since the flight envelopes cover ranges of parameters (e.g., for Flaps UP, Nz in the LFE can be from 1.6 to 2.5), the above target probabilities for OFE and LFE might vary slightly depending on the expected airplane behavior and the assigned task.
Figure 4. Probability of Occurrence Guidelines (continued)
Appendix 5 A5-6
B. Atmospheric Disturbance Level Probability of occurrence (at flight envelope boundary) Light: Turbulence that momentarily causes 100 slight, erratic changes in altitude and/ or attitude (pitch, roll, yaw). Crosswinds up to10 kts.
100 Moderate: Turbulence that is similar to light turbulence, 10-3 but of greater intensity. Changes in altitude and/or attitude occur. Usually causes variations in indicated airspeed. Crosswinds up to 25 kts.
10-3 Severe: Turbulence that causes large, abrupt 10-5 deviations in altitude and/or attitude. Usually causes large variations in indicated airspeeds.
Crosswinds substantially in excess of the minimum required crosswind to be demonstrated safe for takeoff and landing.
10-5
C. Flight Control System Failure State
Probability of occurrence (at flight envelope boundary)
Normal Operation: 100
Probable Failures: 100 - 10-5
Improbable Failures: 10-5 - 10-9
D. Modifying The Flight Envelope Probability for Interrelationships With Atmospheric Conditions
The above probability of occurrence values apply when considered separately. When obvious interrelationships exist due to the design or the intended or expected operation of the airplane, the way to address this within HQRM is to modify the flight envelope probability value. For example, a severe windshear event may result in a flight envelope probability of 100, not 10-3 or 10-5 as shown above for the OFE or LFE, since the operational procedure for escape would be to pull toward the AOA limit in windshear. Similarly, an airplane may experience overspeed, from VMO cruise, into the OFE due to a gust, in which case the modified flight envelope probability would be 100, not 10-3. This probability adjustment concept would also apply to EFCS failure cases where, for example, loss of warnings or exposure to reduced airplane stability might contribute to excursions outside the normal flight envelope (NFE) or OFE, in which case the flight envelope probability should be appropriately increased.
Appendix 5 A5-7
e. Three different flight envelopes (or portions of the airplane’s flight envelope), called the normal, operational, and limit flight envelopes have been defined as a function of various flight parameters. These flight envelopes are shown for flaps up and flaps down configurations in figures 5 and 6, respectively.
Figure 5. Flaps UP Flight Envelopes
Normal Flight Envelope Operational Flight Envelope Limit Flight Envelope NFE LFE OFE V
DET
* or or -150
* *
0.8
0.0
- 1.0 or IB V ENG INOP
or
or
1.6
1.3 LIM LIM
LIM DYN
LIM
LIM DYN
2.5 LIM
LIM
or
V
MMO
ALTITUDE AOA ROLL BETA BUFFET V PITCH V PITCH VMO MFC VFC sw CLMAX
CLMAX LIM STDY LIM STDY VSW j or ±670 ±500 ±400 VFTO ±400 V
1.3VS LOWEST SELECT NFE NFE OFE LFE +300 MD VD NZ NZ LIM or *Rudder appropriate to task/operation/ or rudder lock evaluation
Appendix 5 A5-8
Appendix 5 A5-9 Figure 6. Flaps DOWN Flight Envelopes
V
DET
or or -150
*
*
0.8
0.5
0.0
or IB
ENG INOP
or
or
1.6
1.3
LIM DYN
LIM
LIM DYN
2.0 LIM LIM
or
V
ALTITUDE AOA ROLL BETA BUFFET V PITCH V PITCH VFE VFE + V sw CLMAX
CLMAX LIM STDY LIM STDY VSW j or ±670 ±500 ±400 V2+X X ±400 LAND NFE NFE OFE LFE +300 NZ NZ Normal Flight Envelope Operational Flight Envelope Limit Flight Envelope NFE LFE OFE LIM VFE + V TO & L +3000 TO & L +3000 ±300
TAKEOFF VRFE * * V *Rudder appropriate to task/operation/ or rudder lock evaluation
Appendix 5 A5-10
f. Figure 7 presents the method for combining the various flight condition parameter probabilities to determine the minimum acceptable handling qualities rating for each combination of these parameters. This method is shown graphically in Figure 8.
Figure 7. Combining Values
A. Analyze Failures/Determine Flight Control System Failure Probability (Xc)
-- Predicted failure rates/check failure co-dependence -- Equipment Inoperative Dispatch under MEL -- Service Difficulty Records (continuing airworthiness)
B. Determine Flight Envelope Probabilities (Xe) and Atmospheric Probabilities (Xa) for the flight condition
C. Modify the flight envelope probability if inter-related with the atmospheric condition (See Figure 4, Section D.)
D. Repeat process to identify all cases where Xc * Xa * Xe 10 -9
E. Determine: “Flight Condition” (Xc * Xe)
-- PROBABLE FLIGHT CONDITION: 10-5 (Xc * Xe) < 0 -- IMPROBABLE FLIGHT CONDITION: 10-9 (Xc * Xe) < 10-5
Appendix 5 A5-11 Figure 8. Probability Guidelines to Determine HQ Requirements
0 -1 -2 -3 -4 -5 -6 -7 -8 -9
PROBABLE FAIL IMPROBABLE FAIL EFCS FAILURE RATE -10Xc Xc= -9 -8 -7 -6 -5 -4 -3 -2 -1 0 EFCS *Based on (Xe+Xc) Xe Xc Xa IMPROB FLT CONDPROB FLT COND* PROBABILITY -10x
FLIGHT ENVELOPE &
ATMOSPHERIC DISTURBANCE **Gust intensity variations may be expected with altitude and between u, v, w axes
OFE LFENFE
MOD SEVERELIGHT 3 5 8 14 20GUST** fps SHEAR XWIND 10 18 25 33 45 kts
SMALL RAMP INCR & JFK DEN MSY DFW (TO&L) ug FLIGHT
ENVELOPE
ATMOSPHERIC
DISTURBANCE
Appendix 5 A5-12
g. Figure 9 shows the minimum acceptable FAA handling qualities rating for a given flight condition, defined as a combination of the flight envelope conditions and the level of atmospheric disturbance, relative to the probability of the failure condition being evaluated.
Figure 9 is not meant to imply that every atmospheric disturbance level and every flight envelope combination must be tested. It simply shows the minimum acceptable handling qualities rating for a handling qualities task conducted in a specific environmental state (i.e., atmospheric disturbance level), in a specific segment of the flight envelope, and in a specific system failure state.
Figure 9. Minimum HQ Requirements
ATMOSPHERIC DISTURBANCE (Xa)
FLIGHT LIGHT MODERATE SEVERE CONDITION FLIGHT ENVELOPE (Xe) (Xc*Xe) NFE OFE LFE NFE OFE LFE NFE OFE LFE
PROBABLE
CONDITION S S A A C C C C C
IMPROBABLE
CONDITION A A C C C C
S=SATISFACTORY A=ADEQUATE C=CONTROLLABLE
NFE – Normal Flight Envelope
OFE – Operational Flight Envelope
LFE – Limit Flight Envelope
Appendix 6 A6-1
Appendix 6
Correction Of Air Minimum Control Speed To Standard Conditions
The following analysis presents three methods of correcting a flight test derived value of air minimum control speed to standard conditions. These methods are applicable only to rudder deflection limited VMCA, for either jet or propeller driven airplanes. The effect of banking into the operating engine is accounted for, and the method will work with either fixed pitch or constant speed propellers, including the effects of windmilling drag. For rudder pedal force limited VMCA, see Appendix 7.
Theoretical Basis
Given the static lateral/directional equations of motion for straight line, unaccelerated flight:
Fy Cy a yaC Cy rr = CL · sin
Mx Cl Cl aa Cl rr
Mz Cn Cn aa Cn rr Cna
where:
CL = 295 2 W V Se Cna = 295 2 F l V S b na e e
W = weight - lbs
Ve = equivalent airspeed - kts
S = wing area - ft2
Fna = asymmetric net thrust - lbs
Fna = (Fn + Dw) for engine inoperative
Fna = (Fn + Fi) for engine at idle
Fn = net thrust of the operating engine - lbs
Fi = idle engine net thrust - lbs
Dw = windmill drag - lbs
Appendix 6 le = distance from aircraft center line to engine thrust line - ft b = wingspan - ft Constant Cn Method For the case where full rudder deflection is achieved, r is a constant, and the system of equations can be resolved to an identity which shows that Cna is a linear function of CLsin .
Cna = A·CL sin + B (4) If it is assumed that test and standard day VMCA occur at the same angle-of-attack and bank angle, the asymmetric yawing moment coefficient will be constant, and VMCA can be corrected to standard conditions by the relationship:
= · for Turbojets = · for Propeller driven where:
THPs = Maximum AFM scheduled Brake/Shaft horsepower multiplied by standard day propeller efficiency.
THPt = Test day brake/shaft horsepower where VMCA was achieved multiplied by test day propeller efficiency.
= Atmospheric density ratio at standard conditions.
= Atmospheric density ratio at test conditions.
Windmilling shaft horsepower is not considered, because the current part 25 takeoff requirements for propeller driven airplanes result in such large performance penalties with a windmilling propeller that all part 25 turboprops to date have had autofeather installed.
Since both net thrust and shaft horsepower vary with speed, use of these equations will require an iterative solution. Because this constant Cn method does not consider the effect on VMCA due to variations in bank angle, weight, sideslip angle, or adverse yaw, its use is limited to corrections of 5 percent or less in asymmetric net thrust or power.
A6-2
Appendix 6 A6-3 For corrections beyond 5 percent, the relationship shown in equation (4) should be used, and enough flight test data should be obtained to define the correlation between Cna and CLsin.
Graphical Method
In theory these data could be obtained by varying any combination of asymmetric power or thrust, airspeed, weight, and bank angle that would provide a representative variable set.
However, since VMCA and stall speed are nearly coincident for most airplanes, there are some severe constraints on most of the variables. Typically, any reduction in maximum asymmetric power or thrust will cause VMCA to decrease below stall speed, and any increase in weight will cause stall speed to increase above VMCA; therefore, the only parameter that can reasonably be varied is bank angle.
To maximize the spread between stall and minimum control speed, VMCA tests are normally done at the lightest possible weight, at the maximum allowable asymmetric power or thrust (even with a short duration overboost, if the engine manufacturer will agree). At typical test altitudes (2000-3000 feet) and prototype gross weights, it will usually still not be possible to define VMCA with the full 5° bank, because of stall buffet.
To obtain the data necessary for extrapolation to the 5° bank limit, and to maximum asymmetric power or thrust, testing at three bank angles is required for the definition of the Cna vs CL sin relationship. These data should be obtained by shutting down the critical engine (normally the left), setting maximum allowable power or thrust on the operative engine, and slowing down while maintaining constant heading until full rudder deflection is achieved. The first point, a wings level condition, is easy to set up, and results in a speed well above stall buffet. A second point, at zero sideslip, will be achieved at approximately 2° - 3° bank (flown with a yaw string, or instrumented sideslip vane) and will provide an intermediate speed, still above buffet. The third data point is flown with as much bank angle that can be used without excessive buffeting (no more than would be accepted as the minimum level of stall warning). If necessary, an additional point can be obtained by banking 2° - 3° into the inoperative engine.
To use this method, instrumentation is necessary for the determination of net thrust/shaft horsepower, and an accurate calibrated airspeed system is required, as well as engine/propeller charts for windmill drag, charts for propeller efficiency, and the ability to measure bank angle to at least a tenth of a degree.
Appendix 6 A6-4 Data obtained using this method with a typical business jet and a large jet transport are shown in the following two graphs:
These plots represent the capability of the airframe to produce yawing moment by a combination of rudder deflection (full, in this case), and the sideslip which results from the bank angle. In order to determine the limiting condition for VMCA, it is necessary to know what the applied yawing moment is (due to the engine-out moments), and to plot the applied moments on the same plot, in a similar form. It is possible to do this by choosing a gross weight to be used to calculate CL, and since standard bank angle will be 5°, the only remaining variable in CLsin is Ve. By choosing the appropriate values of Fn available versus Ve, a plot of Cna versus CLsin can be made which represents the applied yawing moments. If the weight chosen represents some standard minimum weight, and the available net power or thrust values represent the maximum