Tailstrike warning system

Abstract

An aircraft tailstrike warning method includes identifying a first value representing an aircraft angle of attack, identifying a second value representing a maximum aircraft angle of attack, identifying a difference between the first value and the second value, and providing a tailstrike warning when the difference between the first value and the second value is less than a threshold amount.

Claims

1. An aircraft tailstrike warning method comprising: identifying an aircraft angle of attack, identifying a maximum aircraft angle of attack, determining a dynamic limit of aircraft proximity to tailstrike based on the aircraft angle of attack and the maximum aircraft angle of attack, and displaying the dynamic limit as a distance from a reference point multiplied by a scale factor, the scale factor selected such that the dynamic limit is not displayed when the aircraft is at a predetermined angle of attack for takeoff or approach at a first reference airspeed.

2. The method of claim 1, wherein the scale factor is selected such that the dynamic limit is not displayed when the aircraft is at the predetermined angle of attack for takeoff.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts an example of an aircraft's angle of attack, flight path angle, and pitch angle, in accordance with an embodiment.

(2) FIG. 2 depicts a flight sequence for an aircraft in a landing sequence, in accordance with an embodiment.

(3) FIG. 3 depicts a method of providing a tailstrike warning for an aircraft, in accordance with an embodiment.

(4) FIG. 4 depicts a tailstrike warning system, in accordance with an embodiment.

(5) FIG. 5A depicts a visual tailstrike proximity warning system, in accordance with an embodiment.

(6) FIG. 5B depicts a visual tailstrike proximity warning system, in accordance with an embodiment.

DETAILED DESCRIPTION

(7) In the following description of embodiments, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific embodiments in which the claimed subject matter may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the claimed subject matter.

(8) In some embodiments, a tailstrike warning for an aircraft is determined by analyzing an angle of attack of the aircraft. Advantageously, the systems and methods may provide pilots with warnings that are more readily understood and more useful in taking corrective actions.

(9) FIG. 1 depicts an example of an aircraft 100 and its angle of attack α, flight path angle θ, and pitch angle γ, in accordance with an embodiment. As used herein, an aircraft's angle of attack can be understood to include the angle between a reference line of the aircraft (for example, the chord line, identified as 102 in FIG. 1) and a flight-path (a vector representing the relative motion of the aircraft through the surrounding air, identified as 104 in FIG. 1). As used herein, an aircraft's flight path angle can be understood to include the angle between the flight path vector and the horizontal (identified as 106 in FIG. 1). As used herein, an aircraft's pitch angle can be understood to include the angle between the reference line of the aircraft and the horizontal. Both pitch and flight path angle are both measured from the horizontal 106 and the counterclockwise direction is assumed to be positive.

(10) FIG. 1 illustrates this relationship during a positive pitch descent. In this case the flight path angle is negative since the aircraft is descending. As can be seen in FIG. 1, the angles are related by Equation 1:
α=θ−γ  (Equation 1)

(11) When an aircraft is on the ground, the angle between the flight path vector and the horizontal—the flight path angle—is zero. When the flight path angle goes to zero, the relationship in Equation 1 becomes Equation 2:
α=θ+0  (Equation 2)
or, equivalently,
α=θ  (Equation 3)

(12) FIG. 2 depicts a flight sequence 200 for an aircraft during landing, in accordance with an embodiment. FIG. 2 illustrates the relationship between angle of attack α, flight path angle θ, and pitch angle γ of an aircraft during the landing sequence.

(13) The first stage 202 of the sequence of FIG. 2 illustrate the aircraft in approach. As can be seen in the first stage 202, there is an angle (i.e., the flight path angle) between the flight path vector 210 and the horizontal (i.e., the ground 212) during approach.

(14) When the aircraft touches down, the aircraft begins to move parallel to the horizontal. This can be seen in the second 204 and third stage 206 of the landing sequence (touchdown and roll, respectively). Thus, the flight path vector and the horizontal are aligned beginning at the second stage 204 (touchdown) and so the flight path angle goes to zero. The angle of attack (between the flight path vector 210 and the chord line 208) may be non-zero during the second stage 204 (touchdown), but goes to zero during the third stage 206 (ground roll).

(15) Tailstrikes occur when an aircraft is on the ground and an aircraft's pitch exceeds a critical angle, referred to herein as the tailstrike pitch angle θ.sub.ts. As shown in Equation 3, the angle of attack equals the pitch angle when the aircraft is on the ground, and so the tailstrike angle of attack (α.sub.ts) is equal to the tailstrike pitch angle (θ.sub.ts) when a tailstrike occurs. Accordingly, as an aircraft's pitch angle approaches a tailstrike pitch, the aircraft's angle of attack also approaches a tailstrike angle of attack.

(16) Utilizing this relationship between tailstrike angle of attack and tailstrike pitch, some embodiments herein provide a tailstrike warning by analyzing an aircraft's angle of attack rather than the aircraft's pitch. Advantageously, this may beneficially allow pilots to receive warnings using more familiar flight parameters. In addition, during landing and takeoff (when tailstrikes occur), pilots are keenly attuned to angle of attack information. By maintaining their focus on angle of attack—rather than diverting it to pitch angle—pilots more easily avoid a tailstrike while also performing other flight maneuvers.

(17) In some embodiments, an aircraft's proximity to a tailstrike (α.sub.d) may be determined as a function of the angle of attack. In some further embodiments, an aircraft's proximity to a tailstrike may be determined as the difference between a maximum allowable angle of attack (α.sub.max) and a function of the current angle of attack (f(α)).
α.sub.d=α.sub.max−f(α)  (Equation 4)

(18) In some embodiments, the function f(α) includes adjusting the angle of attack for its time rate of change to give a rate adjusted angle of attack (α.sub.r). Including the rate adjusted angle of attack may provide for better advanced warning of a tailstrike. For example, an angle of attack that is only a few degrees from a tailstrike angle of attack may not be considered problematic if the angle of attack is maintained. However, an aircraft with an angle of attack that is relatively far from a tailstrike angle of attack may be in a more precarious position if that aircraft also has a high rate of change of angle of attack.

(19) In some embodiments, α.sub.r is determined by
α+k.sub.αα′  (Equation 5)
where α′ is the time rate of change of a and k.sub.α is a “gain factor” to control sensitivity of α.sub.r to the rate of change of the angle of attack. As one of skill in the art will readily recognize, Equation 5 is one example of a function of a rate adjusted angle of attack, and other functions may be used without deviating from the scope of the claimed subject matter.

(20) In some embodiments, k.sub.α can be varied to adjust the sensitivity of α.sub.r to the rate of change of the angle of attack. Consequently, the sensitivity of the tailstrike proximity (α.sub.d) can be varied by adjusting k.sub.α. k.sub.α may be adjusted for different flight conditions, different aircraft, different cargos, and different crews, for example.

(21) Returning to Equation 4, the tailstrike proximity (α.sub.d) can also be varied by adjusting α.sub.max. In some embodiments, α.sub.max may simply be the tailstrike angle of attack α.sub.ts. It may be advantageous, however, to provide a safety margin from the tailstrike angle of attack, to account for pilot error, sloped runways, etc. In some embodiments, a safety margin may be a degree difference from the tailstrike angle of attack. In some embodiments, the degree difference is 2 degrees. In some embodiments, the safety margin may be a percentage difference from the tailstrike angle of attack. In some embodiments, the safety margin may be variable. For example, different safety margins may be used for take-off versus landing, for different cargo weights, for different experience levels of pilots, for different runways, different flight conditions, etc.

(22) In some embodiments, the tailstrike proximity (α.sub.d) is utilized to provide audible and/or visual alarms. In some embodiments, a sequence of escalating alarms are instigated as the tail strike proximity decreases (that is, as f(α) approaches α.sub.max).

(23) FIG. 3 depicts a method of providing a tailstrike warning for an aircraft 300, in accordance with an embodiment. Method 300 begins with receiving an angle of attack of the aircraft 302. The angle of attack is analyzed to determine a tailstrike proximity 304. Once the tailstrike proximity it determined, the proximity is compared to a predetermined threshold 306. When the tailstrike proximity meets the predetermined threshold, method 300 provides a tailstrike warning 308.

(24) Determining the tailstrike proximity may include analyzing a rate of change of the angle of attack of the aircraft. Analyzing a rate of change of the angle of attack of the aircraft may include any of the algorithms and relations described in this document and may include other algorithms and relations. For example, the angle of attack may be adjusted by the rate of change multiplied by a constant, such as in Equation 5.

(25) Determining the tailstrike proximity may include determining the difference between a maximum allowable angle of attack and an adjusted angle of attack. An example of such a determination includes Equation 4 above, but other algorithms and relations could be used. The adjusted angle of attack may include the angle of attack and a time rate of change of the angle attack multiplied by a constant. The maximum allowable angle of attack may be determined by adjusting a tailstrike angle of attack by a safety margin, such as the examples described in this document. The safety margin may include a number of degrees from the tailstrike angle of attack.

(26) The tailstrike warning may be an audible warning and/or a visual warning, such as modifying a flight director. Modifying a flight director may include adding a tailstrike proximity ceiling on the flight director. A position of the tailstrike proximity ceiling on the flight director may be determined by the tailstrike proximity, such as those described below with respect to FIGS. 5A and 5B.

(27) FIG. 4 depicts a tailstrike warning system 400, in accordance with an embodiment. Tailstrike warning system 400 includes a tailstrike proximity warning control system 402, which receives inputs from an angle of attack sensor 404 and provides an output to a tailstrike warning module 406.

(28) After receiving an angle of attack of an aircraft, tailstrike proximity warning control system 402 determines a tailstrike proximity of the aircraft by analyzing the angle of attack of the aircraft, and then compares the tailstrike proximity of the aircraft to a predetermined threshold. When the tailstrike proximity warning control system 402 determines the threshold has been met, the control system sends a signal to the tailstrike warning module 406. A processor or other circuitry may be included in the tailstrike proximity control system 402 to process all data received.

(29) Angle of attack sensor 404 may determine the aircraft's orientation to oncoming airflow. The angle of attack may be determined using AoA Sensors such as Safe Flight Instrument Corporation's Swept Vane AoA Sensor, Paddle Vane AoA Sensor, Integrated AoA Sensor or Lift Transducer. AoA Sensors are also produced by UTC, ASI, Thales, and others. Angle of attack may also be determined by any other mechanism for measuring angle of attack, such as differential pressure.

(30) In some embodiments, tailstrike warning module 406 may include an audible, visual, tactile, or any other alarm. Such alarms may include flashing lights, horns or other audible alarms, or a voice announcing the tailstrike proximity warning. This may aid pilots who are not focused on the flight director to direct their attention there for a visual indication of tailstrike proximity.

(31) In some embodiments, the frequency of the alarm increases as the safety margin for a tailstrike decreases. The frequency of the alarm may be a linear function of the tailstrike proximity. In some embodiments, the frequency of the alarm may change as the tailstrike proximity meets a sequence of predetermined thresholds.

(32) FIG. 5A depicts a visual tailstrike proximity warning system, in accordance with an embodiment. Flight director 500 includes a fixed aircraft symbol 502, horizon line 504, runway 506, pitch indices 508, and a tailstrike ceiling 510.

(33) Tailstrike ceiling 510 provides the pilot with a visual indication of the proximity of the aircraft to a tailstrike. In some embodiments, the position of tailstrike ceiling 510 on flight director 500 is determined by analyzing an aircraft's angle of attack.

(34) In some further embodiments, the position of tailstrike ceiling 510 is based on the proximity to a tailstrike (α.sub.d) described above. In one example, the position of tailstrike ceiling 510 on the flight director may be a linear function of α.sub.d. The linear function may include multiplying α.sub.d by a constant scale factor (k.sub.d).

(35) In some further embodiments, k.sub.d may be chosen so that the ceiling is not visible on the flight director when the aircraft is at the nominal angle of attack α.sub.ref for either takeoff or approach at the normal reference airspeed v.sub.ref. For example, the deviation (α.sub.d, ref) between the maximum allowable angle of attack and the nominal angle of attack may be calculated by
α.sub.d, ref=α.sub.max−α.sub.ref  (Equation 6)

(36) From this equation, the scale factor k.sub.d can be determined. Returning again to FIG. 5, the distance from the aircraft symbol to the top of the flight director is known. Since both α.sub.d, ref and the distance from the fixed aircraft symbol to the top of the flight director are known, the scale factor k.sub.d can be calculated.

(37) In some other embodiments, the distance indicated on the flight director may be a non-linear function of α.sub.d.

(38) Flight director 500 depicts an aircraft on approach to landing, but one of ordinary skill in the art will readily appreciate that a similar display could be used to depict a take-off situation.

(39) A flight director may include additional information not shown in FIG. 5A, as is known in the art. Further, one of skill in the art will readily recognize that other visualizations may be used for the depicting the proximity to a tailstrike and/or providing a tailstrike warning, and that flight director 500 is only one example.

(40) FIG. 5B depicts a visual tailstrike proximity warning system, in accordance with an embodiment. Flight director 550 includes a fixed aircraft symbol 552, horizon line 554, pitch indices 556, and a tailstrike ceiling 558. Tailstrike ceiling 558 differs from tailstrike ceiling 510 in that it allows a pilot to see the area of the flight director above the tailstrike ceiling.

(41) One skilled in the relevant art will recognize that many possible modifications and combinations of the disclosed embodiments can be used, while still employing the same basic underlying mechanisms and methodologies. The foregoing description, for purposes of explanation, has been written with references to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations can be possible in view of the above teachings. The embodiments were chosen and described to explain the principles of the disclosure and their practical applications, and to enable others skilled in the art to best utilize the disclosure and various embodiments with various modifications as suited to the particular use contemplated.

(42) Further, while this specification contains many specifics, these should not be construed as limitations on the scope of what is being claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.