EFFECTIVITY
CONFIG 1 AIRPLANES WITH DELCO INS
798 Page 16
34-41-00
Apr 25/86
I
IN SINGLE DME UPDATING, THE INS USES SLANT RANGE INPUTS FROM A SINGLE DME STATION TO UPDATE THE PRESENT POSITION OF THE AIRPLANE. THE DME UPDATING PROCESS IS ACCOMPLISHED BY A CONTINUOUS INTEGRATION OF THE ALONG-RANGE AND CROSS-RANGE ERRORS DETERMINED BY THE INS. FOR SIMPLICITY, THE ABOVE ILLUSTRATION SHOWS ONLY TWO STEPS OF THIS PROCESS.
AT TIME T1, POINT A1 REPRESENTS THE ACTUAL PRESENT POSITION OF THE AIRPLANE AND POINT I REPRESENTS THE PRESENT POSITION AS CONTAINED IN THE INS SYSTEM. THE FIRST UPDATED POSITION (POINT 1) IS DETERMINED BASED ON MEASURED SLANT RANGE (THE DISTANCE FROM A1 TO THE DME STATION) AND THE CALCULATED SLANT RANGE (THE DISTANCE FROM POINT I TO THE DME STATION).
AT TIME T2, THE ACTUAL POSITION OF THE AIRPLANE IS AT POINT A2 WHEREAS THE COMPUTED POSITION (BASED ON UPDATE POSITION 1) IS AT POINT C2. THE INS NOW HAS ENOUGH DATA TO ESTIMATE BOTH CROSS-RANGE AND ALONG-RANGE ERROR COMPONENTS AND, BASED ON THESE, THE AIRPLANE POSITION IS UPDATED TO POSITION 2.
THE CROSS-RANGE AND ALONG-RANGE CORRECTIONS ARE CONTINUOUSLY MADE AS THE UPDATED POSITION IS GRADUALLY WALKED TOWARD THE ACTUAL POSITION OF THE AIRPLANE.
...XA
INS/DME Updating - See [1], 34-41-00 Page 1
Figure 8 (Sheet 2)
EFFECTIVITY
AIRPLANES WITH DELCO INS
CONFIG 1798 Page 17
34-41-00
Apr 25/86
(g) tests for and isolates INS malfunctions
3. INS/DME Updating Feature (AF 116-150, 152-199; LH 011-030, 051-070, 082-099;
________________________ XA AZ 221-299; MD 501-599; GN 601-699; AT 701-750; VM 751-799; less airplanes XA with PMS, see *[1] 34-41-00 page 1.
A. The Carousel IV-A INS system can be operated as a self-contained inertial system or can be automatically updated by radio navigation (DME) signals when such signals are available. If no radio navigation signals are available, the INS can improve its accuracy by comparing inertial position data contained in each navigation unit and generating an optimum inertial position.
B. The DME systems (Ref. 34-55-00) determine the slant range distance from the airplane to selected DME ground stations by measuring the time it takes a pulse from the DME on board the airplane to leave the airplane, reach the DME ground station and return to the airplane. This time is directly proportional to the distance between the airplane and the ground station.
C. The DME system provides a pair of pulses to the INS: the first pulse corresponding to the transmit pulse and the second pulse corresponding to the reply pulse. The time difference between these two pulses is converted by the INS computer into slant range data.
D. The INS/DME interface is shown in Fig. 2. DME No. 1 receiver is tied to INS 1 inertial navigation unit, and DME No. 2 receiver is tied to INS 2 inertial navigation unit. To affect a dual DME solution (Fig. 8), DME range information is interchanged between all three navigation units via the intersystem data transfer channels. Each navigation unit receiving valid DME data transmits to the other two navigation units the value of slant range being received along with the latitude, longitude, and altitude of the interrogated DME station. INS 3 is not tied to a DME receiver but receives DME data from the other two systems via the intersystem data transfer channels.
E. Optimum DME updating occurs when slant range data from two separate DME stations is available. But in many areas, only single DME reception is available. The INS can make updating calculations with either single or dual DME inputs. A simplified explanation of both dual and single DME updating techniques is presented in Fig. 8.
F. In addition to the DME update capability, the INS has a three system mixing feature that is employed during aided-inertial operation when DME data is not available. Inertial latitude and longitude data from each INS is compared and all three INS systems select the mid values of each to use as a best estimate of present position. The transition from DME update to the three system mix, and reverse, is smoothed to prevent steering transients.
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