Estimating Tacho Time
 

Hi chaps, can anyone estimate tacho time for a 152 at 7 hours flight time?

FS :ok:

Tacho time is equal to 1 hour at a set RPM. The RPM should be in the POH. On some aircraft it is possible to bimble about for 1:20 actual time for 1:00 Tacho provided you run at 55%. Conversely if you are at 10,000 ft you will probably get 45min to 1 hour Tacho.

Rod1

It could be as low as 5.6 tacho going by 0.8 tacho/ flight hour. It could also be quite a bit higher than that though depending on the actual duration of the flight and the ground taxi.

tacho time is usually set to read correctly at the typical cruise RPM of 2300. RPM less than that will result in the time under reading and over that will result in over reading (ie it will count hours faster than true time). However the tach itself must be accurate and it is not unusual to see a tach errors of over 100 RPM as almost nobody does a static RPM check.

Well, as petty as it will sound, the hour counter portion of the tachometer will always be very accurate, as it is simply counting engine revolutions by direct drive and gears. It is the pointers which are notoriously unreliable for RPM, as they are adjustable.

I suggest that any of this is really not relevent in the context of logging piloting time though... It all averages out in the end, and that extra .5 of an hour over a year, does not mean much in the context of skill.