MTK 446 electronic timer: altimeter

You can measure the altitude from -9.6 m to 280 m twice during the flight. Just program the times when you want the altitude to be measured.

Altitude information can be downloaded to the CASIO or the Palm Pilot after the flight. The timer stores altitudes from the last 60 flights until they are read out from the timer and cleared. The timer uses the altitudes and time between measurements to calculate the average vertical speed.

During the first 10 seconds in WAITING mode the timer re-calibrates the altimeter for the ground level pressure. When this is complete it gives a long beep and you can fly. During this recalibration the fuselage hatch cover should be closed to exclude wind gusts. You should be quiet and avoid tapping the model during this process. If you are in a hurry you can fly before recalibration is complete, but in this case the altimeter readings will be incorrect. In-flight altitude measurements are made as pressure readings relative to the reading made during calibration and converted to height in metres by assuming that the calibration altitude is 1 m and using the vertical pressure distribution in the Standard Atmosphere Model. The measurement process takes 1 second. The timer doesn't beep or carry out any other activities during altimeter recalibration and when the measurements are being taken during the flight. In consequence you must select measurement times when neither servo is required to move for at least the next second. In a addition an altitude measurement must not be made within two seconds of the DT time. Altitude measurements are saved to non-volatile flash memory only after DT so don't switch off the timer before it has carried out its DT actions.

Recording altitude data

The SETUP program must contain the line:

alt 1.000

This parameter corrects for altimeter gain and should be present even if the altimeter is not fitted. It is set by direct measurement: for example, you measure a building with a known altitude (40 m) and you get 39 m from the altimeter. Setting the alt parameter to alt 1.026 will correct the measured altitudes. Of course, its best to do this several times.

The FLIGHT program must contain the line:

alt 004 060

for altitude measurements to be recorded. It sets the two times in seconds when the timer will measure altitudes during the flight. This example records times at 4 seconds and 60 seconds after launch. If the altimeter is not fitted the values should be left as they were set in the FLIGHT program received with the timer.

Reading altitudes from the timer

There are 3 commands that handle stored altitudes:

• read the last flight
• read all flights in the memory
• clear the memory.

If you read the last flight (-la), you get 1 block of information containing 3 lines:

If you read all the flights (-fu), you get 1 block of information containing 2 lines for each flight:

If you clear the memory (-ls), all the information about the altitudes delete and after this next flight writes as number 1.