Atimeter question

Hi,

When setting the altimeter pressure also two triangular indexes move and on page 96 of the manual I found it is described what they mean and how they should be used. From what I understand they can be used to get the QFE for a higher landing place, correct? Reading the manual it is not clear for me how that should be done.

Best, Marcel

L-39 and MiG has similar.

When QNH is set in the pressure scale, indexes set normally, and helicopter at surface you will see a picture similar to Fig. 5.41. The altimeter will read true altitude and indexes show zero height.

If the pressure setting is adjusted downward the altimeter reading will decrease while the indexes will increase at the same time. By the time QFE setting is reach the altimeter will read zero and the indexes will show the pressure elevation. They will have exchanged values as shown Fig. 5.42.

Essentially index displays how wrong (below) your indicated altitude is below the correct altitude. If index says 200m then altimeter is showing 200m below actual altitude ASL. Naturally QFE setting makes your altimeter "wrong" the entire magnitude of the airfield elevation.

One benefit is that pressure scale is not marked the full range of the adjustment value. If the altimeter is turned beyond the marked scale to the blank area the only way to know the setting is by the indexes. In this way an extreme QFE in the blank area of the scale can be set.

The other benefit is estimating a QFE where QFE value is not known. E.g. if your indexes are set up for 500m elevation and new location is 800m then adjust pressure knob until index shows 800m. Then altimeter will read close to zero when landing at a location 800m ASL.

Of course the relationship between indexes and pressure scale must be set by technician for each flight. How this is done I don't know. There does not appear to be a control for the pilot to alter this.

Yes, get it. Thanks!