Patent GB-743529-A (GB)
Title: Instrument for indicating the distance an aircraft can fly on the fuel available in the fuel tanks of the aircraft
IPC: G01F9/00
Filed: 1952-10-06
Abstract: 743,529. Electric analogue calculating systems. SVENSKA AEROPLAN AKTIEBOLAGET. Oct. 6, 1952 [Aug. 26, 1952], No. 25015/52. Class 37. [Also in Group XXXVIII] Apparatus for determining the distance for which an aircraft can fly on the fuel available in its tanks comprises a potentiometer energized from a voltage source and regulated by a fuel flow meter to supply a voltage representing the remaining fuel supply and a variable resistance in series with the potentiometer output which is adjustable in response to the altitude of flight to a value calibrated to represent the rate of fuel consumption at such altitudes, whereby a current is produced proportional to the quotient of remaining fuel quantity and rate of fuel consumption which is measured by a pointer indicator calibrated to show the remaining available flight range. In Fig. 1 the aircraft fuel flow meter impulses contacts 1 at a rate proportional to fuel consumption to operate relay 2 stepping the slider 3 of a potentiometer energized from a constant alternating voltage source 5 to develop a signal F (Qr) proportional to the remaining fuel in the aircraft tanks; the slider being restored to the live end of the potentiometer on refuelling by switch 41 reversed on opening the filling cover to energize relay 42 and indicator lamp 40 over contact 43, which relay instantaneously opens contact 43 and closes contact 44 so that the relay contacts oscillate at a frequency determined by shunting condenser 45, and contact 44 steps relay 2 until cam 46 opens a contact in series with relay 42 when the potentiometer slider is restored. The slider signal is coupled through cathode follower 6 to energize stepped variable resistance 8 calibrated as a function of the economical rate of fuel consumption F(QH) at different altitudes which is in series with the primary of transformer 10, whose secondary develops a signal proportional to F(Qr)/F(QH) which after correction for tail or head windage by tapped potentiometer 24 is amplified in tube 11 and applied to the grid of triode 12 over normally closed contact 32 of relay 47. The grid of triode 14 receives a signal from the slider of potentiometer 16 energized from the alternating voltage source, and the anodes of the two triodes are coupled subtractively through transformer 17 to rectifier voltmeter C having two scales (Fig. 2, not shown) calibrated respectively in distance and altitude, the potentiometer 16 being calibrated to develop a distance loss signal given by in which Q 1  = fuel consumed during an altitude change, #H.fH 1  = economical rate of fuel consumption at the greater altitude, k 1  = cotan angle of climb, and #Sc is shown to be the loss of available flying distance due to the altitude change. Linear tapped potentiometer 22 the slider of which is driven by the same shaft 23 as resistance 8 is energized by the alternating voltage source, and in operation a control knob 25 is pushed in to free ratchet 31 and is turned to adjust shaft 23. Contact arm 48 engages its upper contact to energize relay 47 over normally closed contact 28 and the input of triode 14 is earthed over contact 33 while the slider of potentiometer 22 is connected over contact 32 to the grid of triode 12. The altitude for which the economical flight range is desired is read off on the dial of the voltmeter as the knob 25 is rotated to adjust resistance 8 and potentiometer 22 together, and after adjustment the latter is released, so that contact arm 48 engages its lower contact, and the voltmeter indicates the difference between the inputs to the grids of triodes 12, 14, i.e. the computed remaining flight range compensated for loss due to altitude changes. When a change of altitude is undertaken, pressel switch 26 is closed and the required new altitude set in by knob 25. Relay 37 is energized to operate clutch 38 coupling cam 36 (shaped to give the required calibration law to potentiometer 16) to shaft 23 whereby the slider thereof is adjusted in accordance with the altitude setting, and simultaneously relay 52 operates over contacts 57, 51; condenser 53 being charged and lamp 29 lit. Withdrawal of knob 25 removes a shortcircuit from thermal relay 39 which opens contacts 51, 57 after a predetermined time allowing attainment of the new altitude, relays 37, 52 are released, then lamp 29 is de-energized, and clutch 38 disengaged. The slider of potentiometer 16 is restored by a spring to its zero position, and no longer influences the reading of the range indicating instrument after the climb is completed, so that the available range is then determined by the new altitude. Reversal of switch 28 indicated by associated lamp 30 enables the instrument C to indicate available flight range during altitude setting, and subsequently the altitude of flight for a required maximum range. Altitude may be set in directly from the aircraft altimeter.