Aircraft banking angle indicator

An aircraft banking angle indicator which includes a banking angle sensing arrangement for generating an actual banking angle signal, a maximum banking angle input device for manually entering a selected maximum banking angle, a signal processing arrangement having respective inputs connected to the banking angle sensing arrangement and to the maximum banking angle input devices for generating an excessive banking output signal indicative of a banking angle exceeding the maximum banking angle, and an indicating arrangement having a signal input connected to the banking angle output signal for indicating the excessive banking angle.

The invention relates to aircraft control devices, and more particularly to 
an aircraft banking angle indicator, and means coupled to the banking 
angle indicator for visually indicating excessive manually entered banking 
angles and automatic means for automatically restoring the aircraft to a 
safe banking angle. 
BACKGROUND AND PRIOR ART 
In piloting an aircraft it can happen to a pilot finding him or herself in 
difficult weather conditions that visual contact is lost, and as a result 
the pilot may inadvertently bring the aircraft into an unsafe attitude. 
Such unsafe attitudes, known to pilots as spins or stalls, are often 
caused by the aircraft getting into an excessive banking angle. Under such 
conditions a less experienced pilot will subconsciously tend to pull back 
on the control wheel or stick, which will aggravate the unsafe attitude 
and lead to pilot vertigo, in which case the pilot loses spatial 
orientation and possibly crashes the aircraft. 
This condition is especially prevalent in smaller aircraft not normally 
equipped with instruments that automatically inform the pilot of any 
dangerous attitude of the aircraft. 
It can be shown and is well known that in case a pilot enters a dangerous 
attitude such as a spin, the safest corrective action includes a leveling 
of the wings with the horizon, but if he cannot see the horizon he may be 
unable to perform the leveling maneuver. 
It is known in the prior art to provide an aircraft gyro-horizon indicator 
with signal lamps as positional attitude indicator means, as disclosed in 
U.S. Pat. No. 3,852,710. The known attitude indicators, however, have the 
drawback that they require constant attention of the pilot who has many 
other indicators that require his attention. It is therefore an object of 
the instant invention to provide an unsafe attitude indicator that 
constantly monitors the banking angle and only makes an indication in case 
the aircraft banking angle exceeds a given value as selected by the pilot. 
It is a further object to provide such an indicator that cooperates with 
the aircraft control elements to automatically restore the aircraft to a 
safe banking angle in case it should inadvertently be exceeded. 
SUMMARY OF THE INVENTION 
In accordance with the stated object there is provided an aircraft banking 
angle indicator which includes a banking angle sensing arrangement for 
generating an actual banking angle signal, a maximum banking angle input 
device for manually entering a selected maximum banking angle, a signal 
processing arrangement having respective inputs connected to the banking 
angle sensing arrangement and to the maximum banking angle input devices 
for generating an excessive banking output signal indicative of a banking 
angle exceeding the entered maximum banking angle, and an indicating 
arrangement having a signal input connected to the banking angle output 
signal for indicating the excessive banking angle. 
In accordance with a further feature there is provided a banking angle 
indicator which includes an aircraft attitude control arrangement in the 
aircraft, having an input connected to the banking angle output signal for 
automatically restoring the aircraft banking angle to a value no greater 
than the entered maximum banking angle. 
In accordance with still another feature, there is provided a banking angle 
indicator including a gyro with an axis disposed substantially in a plane 
perpendicular to the axis of the aircraft in the banking angle sensing 
arrangement, and an electronic reading arrangement coupled to the gyro for 
reading the banking angle from said gyro. 
According to a still further feature, there is provided a banking angle 
indicator wherein the gyro is a part of an aircraft turn coordinator, or a 
part of an aircraft flight director system, or an artificial horizon 
indicator. 
According to an additional feature, the banking angle indicator according 
to the invention has an analog signal which is analogous to the sensed 
banking angle including an analog-to-digital converter in the signal 
processing arrangement for converting the actual banking angle signal to a 
digital signal indicative of the actual banking angle, and it may further 
include an analog-to-digital converter in the banking angle input 
arrangement for converting the selected maximum banking angle to a digital 
signal indicative of the selected banking angle. 
The banking angle indicator according to the invention may further include 
a microprocessor in the signal processing arrangement, inputs to the 
microprocessor for respectively reading the digital signal indicative of 
the actual banking angle and the digital signal indicative of the selected 
banking angle; a comparator arrangement in the microprocessor for 
comparing the digital signal indicative of the actual banking angle and 
the digital signal indicative of the selected banking angle and generating 
a comparator output signal indicative of an actual excessive banking 
angle, i.e. banking angle greater than the selected banking angle, wherein 
the output signal indicative of the excessive banking angle is connected 
to the visual signal input for visually indicating the excessive banking 
angle. 
In the banking angle indicator according to the invention, the comparator 
output signal may further have a directional signal indicative of the 
direction of the excessive banking angle, wherein the visual indicating 
arrangement includes an input connected to the directional signal, and 
visual indicators for indicating direction of the corrective action 
required to restore the aircraft to a safe banking angle. 
The banking angle indicator may further have servo actuators with inputs 
coupled to the excessive banking angle output signal, and outputs 
connected to the attitude control means, and furthermore aileron controls 
coupled to the excessive banking angle output signal, and additionally an 
audible signal generator coupled to the signal processing arrangement for 
audibly indicating presence of a banking angle exceeding the excessive 
banking angle. 
Further objects and advantages of this invention will be apparent form the 
following detailed description of the presently preferred embodiments 
which are illustrated schematically in the accompanying drawings.

Before explaining the disclosed embodiments of the present invention in 
detail it is to be understood that the invention is not limited in its 
application to the details of the particular arrangements shown since the 
invention is capable of other embodiments. Also, the terminology used 
herein is for the purpose of description and not of limitation. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 an aircraft gyro 11, with its axis in a plane substantially 
perpendicular to the axis of the aircraft, is mounted with its gyro axis 
12 in a gimbal 13 balanced about an axis 14 substantially parallel with 
the axis, shown by arrow A, of the aircraft in which it is mounted. The 
gyro may be dedicated to the banking angle indicator according to the 
invention, but it may as well be a part of some other aircraft instrument 
such as an artificial horizon, a flight director or a bank and turn 
coordinator, an automatic pilot or any other flight instrument having a 
suitable gyro. The gyro has, as in most flight instruments an electronic 
readout that transmits its functions to other parts of an integrated 
avionics system. The electronic readout can have many different forms and 
is illustrated as an example as a scale 16 attached to the gimbal 13 with 
optical gradings, that is interrogated by a light beam 17 from a light 
source 18, directed at a photo sensor 19. Any movement of the aircraft 
about its longitudinal axis, including banking, is indicated as 
information embedded in the light beam 17 as received by the photosensor 
19. 
Depending upon the type of gradings on the scale 16, the banking angle can 
be read out by a banking angle reader circuit 21 either in the form of an 
analog output on lead 22 or in the form of a digital output in some 
suitable digital format. If required, the signal on lead 22 is converted 
to a binary-digital format in an analog-digital converter 23 (A/D 
converter) which on lead 24 generates an absolute digital binary value 
representing the degree of angle of banking, and on output 26 a signal 
indicating left or right banking in the form of a high or low logic level 
on lead 26. In conventional binary logic, lead 26 carries the "sign" bit 
of the binary digital output, while the lead 24 carries the remaining 
bits. A banking angle selector 27 has a dial 28 for manually entering the 
desired maximum angle of banking on e.g. a potentiometer 29 which 
generates on lead 31 an analog potential representing the desired maximum 
angle of banking which is entered by the pilot as the maximum banking 
angle he wishes to stay within. 
Another A/D converter 32 converts entered maximum banking angle also to 
binary digital information. A digital comparator 34 receives the absolute 
banking angle values from the two A/D converters 23,32, and generates an 
output which may be logic high e.g. if the value on lead 24 is greater 
than the value on lead 33, i.e. lead 36 goes from logic low to logic high 
if the actual banking angle sensed by the gyro 11 is greater than the 
selected maximum banking angle entered on the banking angle selector 27. 
A logic circuit having two AND-gates 37/38, each with inputs a and b, 
evaluates the signals on the three leads 24,26 and 36 to determine if the 
actual banking angle is excessive, i.e. greater than the selected banking 
angle, and if it is to left or right. An inverter 39 presents an inverted 
logic value of the signal on lead 26 to input a of AND-gate 38, while 
input a of AND-gate 37 receives the un-inverted signal from lead 26. 
Assuming that a right banking angle is indicated by a logic high on lead 
26, and an excessive banking angle is indicated by a logic high on lead 
36, both inputs a and b of AND-gate 37 will be high, and its outputs will 
be high, and an indicator light 41 labeled "R" will light up, indicating 
to the pilot an excessive right banking angle. Conversely, indicator light 
labeled "L" will light up, indicating if an excessive left banking angle 
is indicated. 
The two indicator lights 41,42 may be located in an 
instrument-panel-mounted display which may advantageously include the 
components of the banking angle selector 27, as shown in FIG. 6, wherein 
each of the two light indicators 41,42 is shaped as an arrow indicating to 
the pilot the required corrective direction he is to undertake in order to 
regain stable flight attitude. 
An audible indicator 44 may be provided which includes a loudspeaker 46 
driven either by a voice synthesizer 47 which verbally directs the pilot 
or simply issues an alert signal as known from conventional aircraft 
indicators, such as stall-alarms and the like. 
An automatic banking angle restoring arrangement, acting on the aircraft 
ailerons and/or rudder is shown in the form of an hydraulic system 
including an hydraulic cylinder 51 with a piston 52 coupled through 
linkage 53 to the aircraft ailerons (not shown). The hydraulic cylinder 51 
is connected to a hydraulic valve with a valve spool 54 operated by two 
opposite solenoids 56,57, respectively connected via amplifiers 58,59 to 
the outputs of respective AND-gates 37,38. A hydraulic pump 61 supplies 
hydraulic pressure to an inlet port a of the hydraulic valve 54, which has 
its other inlet port b connected to a hydraulic fluid tank 62, as is 
conventional in hydraulic control systems. In case AND-gate 37 becomes 
active, indicating excessive right banking angle, the valve spool 54 is 
activated by solenoid 56, causing pressure to be applied to the top end of 
the hydraulic cylinder 51, causing its piston 52 to go down, or conversely 
to go up if AND-gate 38 is activated. 
FIG. 2 shows the banking angle indicator integrated with the light 
indicators 41,42, according to the invention, into a conventional electric 
turn coordinator. The directional arrows are shown separately as arrows 
41a and 42a at the top of the instrument face panel 64, which also 
includes the selected angle of bank dial 28 (A/B) and other elements and 
displays as required for the operation of the turn coordinator, such as 
gyro power (GYP), test (TEST), an aircraft banking angle symbol 27 and so 
forth, which are incidental to the instant invention. A sound outlet for 
the speaker 46 may also be provided on the instrument face. A green light 
indicator 63 showing normal banking angles is driven by an inverter 66 
from output 36 in FIG. 1. 
FIG. 3 is an elevational view of the turn coordinator of FIG. 2, showing a 
gyro 11, printed circuit boards 66,67 for mounting the electronic 
components, and a cable connector 68 for attaching connecting cables to 
other aircraft instruments. 
FIG. 4 is a block diagram showing the interconnections of the major 
function blocks of the invention, including the gyro on/off switch 69 
(GYP), the gyro 11, a power supply 71, the gyro cable connector 68, the 
angle of banking control panel 64, a volume control 77 for the 
speaker/buzzer 46, a silhouette bar 72, i.e. the aircraft symbol on FIG. 
2, a clinometer 73, also seen on FIG. 2, a test switch 74 with a lamp, the 
analog-to-digital converters 23,32, an electronic control 76 including the 
electronic circuits of FIG. 1, and/or a microcontroller performing the 
same control functions, but using a stored program in memory, a correction 
display with display lights 41a,42a, a color-coded display 63, an 
alpha-numeric display 64 for indicating various aircraft indications, the 
voice synthesizer and the speaker/buzzer 46. 
The flow chart of FIG. 5 shows the major steps of the operation of the 
banking angle indicator of the invention. After Start 100, i.e. setting 
power on, initiating the instruments and so forth, the actual banking 
angle is measured in step 101 and converted to digital binary format in 
step 102. The maximum banking angle is selected in step 103 and also 
converted to digital binary format in step 104. The actual and selected 
banking angles are compared in step 106, which determines if the actual 
banking angle is not greater than the selected banking angle in step 107. 
If the actual banking angle in step 107 is no greater than the selected 
banking angle, the measuring process continues in step 102, but if the 
actual banking angle is greater than the selected angle a determination is 
made in step 108 to determine if the banking angle is left or right. If 
the actual banking angle is found to be left, an indication of excessive 
left banking angle is made in step 109, and the left servo is activated in 
step 111 to correct the banking angle to the right. Conversely, if in step 
108 a right banking angle is determined, the next step 112 indicates 
excessive right banking angle to the servo, which makes correction to the 
left.