Could you please explain how this counter works (in the picture)? I thought that it starts with propeller (so propeller starts moving so this counter), but seems it registers the pure flight - from take off to landing (is it so?). I just started lessons and of course I‘ll ask FI, but since I’m doing my homework now - your advice would be helpful. I don’t see this gauge in POH.
Your photo is not very clear but the gauge appears to be nearly identical to this VDO Hour Meter with sweep second hand. VDO is a German company and “betriebsstunden” means Hours of Operation in German.
The factory installed hour meter in DA-20 aircraft is prone to failures and I suspect your flight school added this VDO hour meter as a replacement. Most single engine aircraft use engine oil pressure to activate the hour meter.
That would in all likelyhood be a Hobbs meter. Hobbs meters are used to count operating hours, and there are actually quite many different ways it can be activated:
(list adapted from Wikipedia)
All of the above serve pretty much the same purpose, to keep track of the operating hours of the plane, but each has it's own "niche". For example verification of engine hours is important with regard of service intervals. Airspeed would give a pretty good reading on civilian flight hours, counted as from "stop to stop", "airborne" method would track "military flight hours" as they are measured as actual flying time (at least in my jurisdiction).
The specific thing with these meters is, that they have no user interface, so the pilot (or any other person for that matter) cannot tamper with the reading. The count is accumulative since the plane left the factory.
As for which type the meter is in your specific case, cannot be determined with the information you have provided.
That is a Tach Hour meter, if you look close at the image it even says "Tach Hours" under the number read out. This measure engine "tach" hours. Typically they are normalized to the cruise RPM of an engine. In other words if your DA-20 has a cruise RPM of 2300 then when you are running it at 2300 RPM the meter will work on a 1:1 ratio of hours. If you run the engine slower, the meter will clock hours slower and if you run it faster it will clock them at faster than your base rate.
There is a good overview on the different between tach time and hobbs time here.
Real world example from my past few flights. My club charges per tach hour so here are two examples of bills:
I went up to do some pattern work the other weekend. I put 1.1 on the hobbs but spent a chunk of time taxiing on the ground and coasting into some nice landings so I only ended up getting charged for 0.2 hours on the tach as I was well below cruise RPM for most of my flying.
On the contrary I took the same plane on a long XC a few weeks before and put 6.2 hours on the plane round trip and somewhere in the range of 5.9 tach hours since most of the flying was at cruise power.
