GB2188455A

GB2188455A - Navigational aid for microlights

Info

Publication number: GB2188455A
Application number: GB08607450A
Authority: GB
Inventors: Charles Richard Stubbs; David Owen Lewis; David Woodsworth Linney
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-03-26
Filing date: 1986-03-26
Publication date: 1987-09-30
Also published as: GB8607450D0

Abstract

A navigational aid for microlights has a keypad 16 and a display 18 mounted on a body 10. The body 10 is secured to a strap 12, which can be used to attach the device to a pilot's thigh. Marks 41 and 42 and a rule 44 printed on the body 10 facilitate the drawing of guide lines for estimating drift and the measuring of distances on an aeronautical chart. The device enables a user to enter latitude and longitude for locations at the start and end of a number of straight legs of a planned flight. The user also enters the planned true air speed, the rate of fuel consumption at this speed, the local magnetic variation, and the strength and direction of the prevailing wind. The device calculates and displays on request the total estimated fuel consumption, and the magnetic heading and resultant groundspeed for each straight leg. <IMAGE>

Description

SPECIFICATION Navigational aid for microlights This invention relates to a navigational aid for use in microlights and light aircraft.

Before flying a microlight, the pilot must carefully plan the intended route. A typical route consists of several straight legs, which are drawn with erasible crayon onto the pilot's aeronautical chart. By measuring the length of each straight line, the pilot can calculate the distance along each leg of the route from the map's scale. By using a protractor lined up with the nearest meridian of longitude to the halfway point, the pilot can also determine the direction, or bearing, of the planned route along each straight leg. The planned route over the ground is called the intended track of the aircraft.

Aircraft flight is affected by wind. Shortly before take off, the pilot obtains a local forecast of the wind strength and direction. For each leg of the route, the pilot must now calculate the direction in which the aircraft must be pointed, in order to traverse the intended track. The direction in which the aircraft must be pointed is called the aircraft's heading. The speed of the aircraft through the air is called the true air speed. The actual route traversed by the aircraft over the ground is called the track made good. The speed at which the aircraft traverses its actual route over the ground is called its groundspeed.

The calculated required heading of the aircraft must be adjusted for magnetic variation in the locality of the planned leg of the flight.

The resultant magnetic heading may need further adjustment to correct errors inherent in the aircraft's compass, these being normally less than two degrees in magnitude. Once these adjustments have been made, the pilot may then use the aircraft's compass reading to control the heading of the aircraft.

The airspeed registered on the aircraft's airspeed indicator is the indicated air speed. This will be different from the aircraft's true air speed. There are errors inherent in the instrument itself. The indicated air speed corrected for these errors is called the rectified air speed. There is also a density error caused by air pressure differences at the altitude at which the aircraft is flying. Rectified air speed can be converted to true air speed using a commonly known mathematical formula. For nearly all practical purposes, indicated air speed, rectified air speed and true air speed can be considered equal for microlights.

The pilot will plan to fly the aircraft at a certain true air speed. This speed must be fixed in advance so that heading and groundspeed calculations can be performed. At the planned true air speed the aircraft will consume a known quantity of fuel per hour. From the distance and groundspeed values previously calculated, the pilot is able to estimate the time of flight for each leg and the total amount of fuel that will be consumed during the flight.

Once airborne, it often happens that the track made good differs from the intended track by a few degrees of direction. This is usually because the wind actually experienced during the flight differs either in strength or direction from the values assumed in the route planning calculations. The amount by which the track made good differs from the intended track is called the aircraft's drift. The pilot must make a change to the aircraft's heading in an attempt either to regain the intended track or to fly directly to the planned end of the current leg.

In order to estimate the magnitude of the drift, many microlight pilots draw straight lines on their aeronautical charts before take off at angles of either five or ten degrees to the right and left of each intended track. These lines then act as a guide for visually estimating the magnitude of drift. A pilot is able to determine his current position from visible landmarks that are shown on the aeronautical chart.

It is customary for microlight pilots to keep a note of actual time elapsed while traversing each leg of the route. The actual flight time is then compared with the time of flight calculated at the pre-flight planning stage. If the two times are significantly different, this warns the pilot that his calculation of estimated fuel consumption is probably no longer reliable.

The manual methods for route planning are time consuming and error prone. Heading and groundspeed are determined for each leg either by a triangle of vectors drawn to scale, or by using a so-called 'Navigational Computer', which is really a form of circular sliderule and protractor combined.

There are electronic navigational aids available, but these are expensive and too unwieldy to be used in microlights. They are intended for use in light aircraft and small commercial aircraft.

According to the present invention there is provided a navigational aid for microlights comprising a body in the form of a small rectangular box, means for attaching the body to an adjustable strap, the body being surmounted on its upper face by an electronic keypad and an electronic display, the whole being a device for calculating the required magnetic heading and resultant groundspeed of an aircraft given the latitude and longitude of the locations at the start and end of a straight leg of a planned route, the prevailing wind strength and direction, the aircraft's planned true air speed and the local magnetic variation, these values being entered into the device by depressing keys on the electronic keypad and the results of the calculation being shown on the electronic display, the device having the capability of storing electronically within itself like information for a number of straight legs and of calculating estimated fuel consumption for the whole route given the rate of fuel consumption for the aircraft at the planned true air speed, this value being entered into the device by depressing keys on the electronic keypad and the result of the calculation being shown on the electronic display.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows in perspective the body of the device attached to a section of the adjustable strap; Figure 2 illustrates the attachment of the adjustable strap to the base of the body; Figure 3 shows a block diagram of the electronic components that are housed within the box.

Referring to the drawing the navigational aid for microlights comprises a body 10 in the form of a small rectangular box and an adjustable strap 12 secured to the base of the body 10 by, for example, rivets 14 or similar means. The adjustable strap 12 can be used to attach the device to a microlight pilot's thigh.

Mounted on the upper face of the body 10 are an electronic keypad 16 and a microprocessor controlled electronic display 18. Within the body 10 are a number of electronic components, including a microprocessor 20, a static random access memory (RAM) 21, a programmable read only memory (PROM) 22, a programmable input/output port (PlO) 23 and a a clock source 24. The PlO 23 is connected to the keypad 16 via one port 30 and to the electronic display 18 via the other port 31.

The PlO 23 is connected to the microprocessor 20, the static RAM 21 and the PROM 22 via a data bus 32 and an address bus 33.

At one end of the body 10 are marks 41 and 42. A straight line drawn from corner 40 to mark 41 makes an angle of five degrees to a line drawn parallel to edge 43 of the body 10. A straight line drawn from corner 40 to mark 42 makes an angle of ten degrees to a line drawn parallel to edge 43 of the body 10.

A microlight pilot can use marks 41 and 42 to draw five and ten degree guide lines on an aeronautical chart for estimating the magnitude of drift experienced during a flight.

Along edge 43 is printed a measuring rule 44 calibrated in units of distance to a certain scale A microlight pilot can use this rule 44 to measure distances between locations shown on an aeronautical chart.

A program stored within the static RAM 21 enables the functions described below to be performed. Values are entered into the device by depressing keys on the keypad 16.

A user of the navigational aid is able to enter into the device a planned true air speed for an aircraft, the estimated rate of fuel consumption at this speed and the local magnetic variation. The latitude and longitude values of up to a hundred sequenced locations can also be entered into and stored within the device, these being the start and end locations of straight legs of a planned aircraft flight.

Once the user has entered values for the strength and direction of the prevailing local wind, the device is able to calculate the magnetic heading required to be flown and and the resultant groundspeed for each straight leg. The user can cause these results to be calculated for a selected leg of the flight and displayed on the electronic display 18 by depressing keys on the keypad 16. The device will also calculate and display on request the estimated total fuel consumption for the whole flight.

For any leg of the flight, the user is able to enter the time taken to traverse a fraction of the leg, the value of this fraction as a number of tenths, and the amount of drift to the left or right experienced by the aircraft while traversing this part of the leg. The device will then automatically calculate and display on request the strength and direction of the wind as actually experienced by the aircraft. It will also calculate and display on request the magnetic heading now required to be followed by the aircraft in order to reach the location at the end of the planned leg, and the resultant groundspeed of the aircraft.

Claims

1. A navigational aid for microlights comprising a body in the form of a small rectangular box, means for attaching the body to an adjustable strap, the body being surmounted on its upper face by an electronic keypad and an electronic display, the whole being a device for calculating the required magnetic heading and resultant groundspeed of an aircraft given the latitude and longitude of the locations at the start and end of a straight leg of a planned route, the prevailing wind strength and direction, the aircraft's planned true air speed and the local magnetic variation, these values being entered into the device by depressing keys on the electronic keypad and the results of the calculation being shown on the electronic display, the device having the capability of storing electronically within itself like information for a number of straight legs and of calculating estimated fuel consumption for the whole route given the rate of fuel consumption for the aircraft at the planned true air speed, this value being entered into the device by depressing keys on the electronic keypad and the result of the calculation being shown on the electronic display.

2. A navigational aid for microlights as claimed in Claim 1 wherein means is provided for releasably securing the adjustable strap to the base of the body.

3. A navigational aid for microlights as claimed in Claim 1 or Claim 2, wherein a measuring rule is provided along one or both of the longer sides of the body, the or each rule being calibrated in units of distance to a certain scale.

4. A navigational aid for microlights as claimed in any preceding claim, wherein visible marks are provided on one of the shorter sides of the body in such positions that a straight line drawn from one of the corners at the far end of the base of the body to one of the marks will make an angle of five degrees with a line drawn parallel to a longer side of the base of the body, and a straight line drawn from one of the corners at the far end of the base of the body to another or the other mark will make an angle of ten degrees with a straight line drawn parallel to a longer side,of the base of the body.

5. A navigational aid for microlights as claimed in any preceding claim, wherein a function is provided that calculates the strength and direction of the wind as actually experienced by the aircraft during a flight along a straight leg, the magnetic bearing now required to be followed by the aircraft in order to reach the location at the end of the planned leg, and the expected resultant groundspeed of the aircraft, given the time taken so far to traverse part of the leg and the current position of the aircraft, the latter being expressed as a fraction of the total distance along the leg together with the magnitude and direction, whether to the right or to the left, of the drift experienced by the aircraft away from the planned route, these values being entered into the device by depressing keys on the electronic keypad and the results of the calculation being shown on the electronic display.

6. A navigational aid for microlights substantially as described herein with reference to Figs. 1-3 of the accompanying drawing.