GB2469994A

GB2469994A - A wing flex measuring system

Info

Publication number: GB2469994A
Application number: GB0907392A
Authority: GB
Inventors: Stephen Geary
Original assignee: Dublin Institute of Technology
Current assignee: Dublin Institute of Technology
Priority date: 2009-04-30
Filing date: 2009-04-30
Publication date: 2010-11-10
Also published as: GB0907392D0

Abstract

The present application describes a method and system suitable for measuring the lift generated by an aircraft wing by determining the degree of flex experienced by a wing in flight. The measured lift may be used in a variety of manners including as an input to a stall warning system or the measured flexing of the wing may be integrated over time to determine the life time cyclic load on the wing. This may give an indication of its operating life or warn of failure. The system comprises a cable attached to the tip of the wing, inside the wing, and it is attached to a biasing member near the fuselage. The motion of the cable is measured to determine the amount of flex in the wing and, therefore, the lifting force.

Description

A Wing Lift Measurement System

Field of the Application

The present application relates to the field of aiiianes and in particular to measuring the lift generated by a wing.

Background of the Applic atioi

It s well known and understood that lift is generated by the creation of a diffcreiitial velocity between air passing above and below a wing. fo achieve this, the upper surface is more curved which causes an ii crease in velocity on that surface. As yekcity is inversely proportional to pressure a differential pressure is generated with higher pressure present on the lower surthce. Fr is believed that one. third of lift is created by this upward pushing force and two thirds is caused by the lower pressure on the upper surface creating a suction force Under any circumstances in aviation it is important to have a method of approximating lift in an aircraft, since its absence results in a stall with potentially lethal results. Typically, this is achieved using instruments which employ AOA (angle of attack) sensors, pitot and static probes which are located on the forward section of the fuselage. These give readings in the cockpit of oncoming airspeed on the wing against the angle of attack. The data from these instruments is also combined to give engineered data of lift being generated. They are also used to ensure that an aircraft is flown in a safely within limits.

However, these instruments do not measure lift precisely or the exact point of stall on a wing, instead they measure other factors and compare these with theoretical or experimental data for the aircraft.

It would be advantageous if a method could be provided to measure the amount of lift being generated on a wing.

Snrnrna rv The principle behind the present application is that wings flex relative to the amount of lifi being generated on their surfaces.

The. present application seeks to measure the degree of wing flex, a measured. This measure may then be employed as a indication of lift. This has the advantage that the amount ()f lift is being measured rather than estimated by combining measures such as AOA sensors and airspeed.

Description of Drawings

Figure 1 is a representation of the front profile of half an aircraft known in the art illustrating the transverse axis,

I

Figure 2 is an exemplary embodiment of the sensing arrangement for a wing flex measuring system according to the present application, Figure 3 is a block diagram of a wing flex measuring system employing the sensing arrangement of Figure 2, Figure 4 is a stall warning system employing the sensing arrangement of Figure 2, Figure 5 is a component age measuring system employing the sensing arrangement of Figure 2, Figure 6 is an aircraft stabilisation system employing the sensing arrangement of Figure 2, and Figure 7 is a system monitoring differences between wing lift on opposing wings of an aircraft.

Detailed description of Drawings

For the purpose of this application we will define the primary axis as the axis drawn through the fuselage 3 of the aircraft 1 from tail to nose. The transverse or lateral axis y-y' runs substantially transverse to the primary axis and substantially parallel to the wings in a reference state, for example their rest position on the ground, as shown in Figure 1.

The system of the present application measures the extent of movement of the wing or part thereof from the transverse axis, i.e. relative to its reference state. The system measures the movement of the non-active surfaces, i.e. the main wing structure and not active surfaces such as ailerons and flaps, which of course move independently with respect to the main wing structure.

A simple and effective method for measuring this flex, as shown in Figure 2, employs a longitudinal member 10 extending along a section of the wing 4 to the wing tip 6. The member is restrained within a housing 14. The housing suitably comprises a protective tube with a clearance diameter sufficient to allow comfortable movement of the longitudinal member but at the same time restricting the longitudinal member to linear movement along the transverse axis.

As the wing flexes, the longitudinal member is caused to be stretched. This stretch or stress may be measured using for example a stress sensor. Alternatively, if the member is fixed at one end and resiliently attached at the opposite end, its movement may be employed as a measure of wing flex.

An exemplary arrangement, as shown in Figure 1, employs a steel or similar cable as the longitudinal member with a corresponding housing, i.e. effectively a Bowden cable. The cable is suitably fixed close to or at the wing tip 6 and extends to a point proximate to the fuselage 3. At this point, the cable is resiliently attached, e.g. by means of sprung drum 12 or similar arrangement which feeds out or draws in the cable as the wing flexes.

A sensor (not shown) may be employed to measure the position of a reference point on the cable, thus giving an indication of the flex in the wing. Suitable sensors would include LVDT (Linear variable differential transducer) or a linear potentiometer.

Similarly, a sensor may be provided on the drum measuring the degree of rotation and hence the amount of cable paid out.

In either case, as shown in Figure 3, the sensed signal may be conditioned by a signal conditioner 22, for example to remove noise. Depending on the arrangement of the sensor and cable, conditioning may be employed to linearize the sensed signal with respect to wing flex and\or lift. It will be appreciated by those skilled in the art that a variety of techniques may be employed, including for example the use of look-up tables in the digital domain. The signal 24 representing a measure of wing flex and\or lift may be used in a variety of different ways as will be discussed below.

The cable may be positioned along the front or rear spar in a position so as not to interfere with any flight controls. Similarly, those skilled in the art would appreciate that careful design may be required with fuel tanks and other similar areas. The housing is suitably fixed 16 at intervals to prevent movement of the housing.

It will be appreciated that whilst the cable may be positioned along any section of the wing and limited in length to that section, greater sensitivity is obtained by extending the full length of the wing. However, as wings are designed to flex more at their extremities, a cable which does not extend to the fuselage may be perfectly acceptable.

In one implementation, the wing flex signal may be used as an input for a stall warning system as shown in Figure 4. In the stall warning system, the signal from the wing flex sensor is passed through signal conditioning 23 as appropriate to a comparator 28 where it is compared a predetermined alarm level. Whilst, this may be advantageous in any aircraft, it may be particularly useful in light aircraft used for aerobatics. Typically, these aircrafts are pushed to the absolute limits and at times the pilot is guessing the point of stall to pull off a dangerous manoeuvre.

However, as pilots push the envelope, accidents occur as a result of wing stall. The wing flex signal would suitably be fed to a stall alarm system, in which the wing flex signal is continuously monitored and compared to the alarm level, if this minimum alarm level is reached, the comparator of the stall alarm system would cause a suitable alarm to be triggered. This alarm may be audible (buzzer), visual (flashing light) or other, e.g. a stick shaker which shakes the joystick when the aircraft is close to the point of stall. A combination of these different types of alarms may be employed.

The wing flex signal may also be used to counteract for turbulence, as shown in Figure 6. Turbulence is a factor in aviation which causes violent shaking of aircraft wings. This is a hindrance as it causes passenger uneasiness and also wear on aircraft parts. The wing flex signal may be employed as an input to a turbulence reducing system (active stability). As before the signal may be appropriately signal conditioned beforehand. In this configuration, the turbulence reducing system monitors the wing flex signal for wing flutter. Upon detecting wing flutter, the turbulence reducing system 40 would generate an actuating signal for the ailerons or other active wing surface to counteract the flutter, e.g. using slight flickering movements equal but opposite to that of the turbulent fluttering of the wing. Suitably, the turbulence reducing system may be incorporated into the autopilot function of the aircraft. It will be appreciated that an appropriate control loop function may be employed to ensure that the system remained stable.

Another use for the device, shown in Figure 5, may be to determine accurately the effective age of certain components on the wing, including the wings themselves. Currently flying hours are used to age the service life of the components. Whilst flying hours are measurable, they only reflect the average stress and strain on components. As a result at times, components may be replaced earlier than necessitated or worse later than necessitated. It would be desirable, if a better method of aging components was available. The wing flex signal provided above provides a useful input which may be employed in a component aging system, i.e. a system that calculates the actual stress and strain that the components along the wing are enduring. Such a system could prove safer, both also could save money if service life of the component could be extended if it is enduring less stress then manufacturer have intended. It will be appreciated that the degree of stress and strain may not be linearly related to the wing flex signal. Accordingly, an appropriate function may be employed 38 to convert measured wing flex signal into a stress\strain signal. This function may be polynomial in nature.

This stress\strain signal may then be integrated 33 to produce an indication of the component wear over time. As components may incur different stress/strain based on its location and function in the wing, different functions may be employed for different components. In each case, the measured age may be compared with its theoretical age limit (including a safety margin as appropriate) and a warning signal generated indicating that replacement of the part was required. Similarly, as components may be replaced at different times, individual measures may be provided for each component so that appropriate replacement occurs at the appropriate time.

Another use for the wing flex signal would be to provide an alarm for sudden weight loss on an aircraft wing. In this arrangement, signals of wing flex 20a, 20b from each wing are compared and an alarm triggered in the event that they deviate by a significant amount. Suitably the comparison includes suitable hysteresis to ensure that momentary non-significant changes are ignored. Such a signal may be employed to both commercial and military aircraft. In the case of a militaiy aircraft, the difference could be used to indicate wing damage and the extent of it as a result of being hit in combat. In commercial aircraft, it could be employed to indicate the loss of an engine from the wing.

Although, the present application has been described with reference to the use of a cable-housing assembly as a sensor, other techniques may be employed including the use of reference transponders on the wing tips and on the fuselage and measuring differences there between. The transducers may be optical (e.g. laser based) or radio frequency based.

Claims

Claims 1. A wing flex measuring system for a fixed wing aircraft having a primary axis defined by the fuselage of the aircraft and a transverse axis represented by the normal position of the wings at rest, the system comprising a sensor for measuring the relative movement of at least one non-active section of the wing with respect to the transverse axis.
2. A wing flex system according to claim 1, wherein the sensor comprises a longitudinal member restrained within a housing extending along the at least one non-active section of the wing and fixed at a first end.
3. A wing flex system according to claim 2, wherein the sensor further comprises a stress sensor measuring stress in the longitudinal member.
4. A wing flex system according to claim 2, wherein the sensor further comprises a biasing member restricting movement of the longitudinal member at its second end.
5. A wing flex system according to anyone of claims 2 to 4, wherein the longitudinal member comprises a cable.
6. A wing flex system according to any preceding claim, wherein the longitudinal member runs substantially from the fuselage to the wing tip.
7. A wing flex system according to any preceding claim wherein the housing is positioned within the wing in a manner to prevent interference with other elements within the wing.
8. A wing flex system according to any preceding claim wherein the housing runs along the rear or front spar.
9. A wing flex system according to any preceding claim, wherein the housing comprises a protective tube with a clearance diameter sufficient to allow comfortable movement of the longitudinal member but at the same time restricting the longitudinal member to linear movement along the transverse axis.
10. A stall sensing system comprising a wing flex system of any preceding claim.
11. A stall sensing system according to claim 10 wherein an alarm is set when the measured degree of flex falls below a predetermined set point.
12. An operating life measuring system for measuring fatigue in the wings of an aircraft, the system comprising a wing flex system of anyone of claims 1 to 9, further comprising an integrator for integrating a function of wing flex over time.