I know on equipment a certain rpm has a 1:1 correlation to real time. I would assume the same for aircraft. Where would this point be?
Thanks Gary

At rated time for the tach hour meter..my old 170 actually had graduations on the tach indicated this..I believe for the C-145 it was at 2500 RPM. So once you were in cruise at 2500 RPM the Hobbs meter and the Tach would track the same time. If you where renting a plane and charged by the Hobbs you were paying more than if you were charged by time on the tach. The tach hour meter is gear driven and if you spent a lot of time idling, this time cost you less from the tach vs. the Hobbs meter as the Hobbs is litterally an hour meter..it runs as soon as the power to it is turned on..even if the engine is not running.
HC

Thanks Ernie
I got some flyin to do today, I'll do some checking and see what I get.
Have a good weekend
Gary

I have a Horizon P-1000. I should compare it to real time and see if it is based on rpm's or Hobbs time.

Most of my "logged" hours have been from tach readings, up until the last 3-4 years. As I am shutting down, I look at my Garmin 696's flight log. It is always 10-15% higher then the tach, depending on how I flew. At 24 squared, it shows 10% extra.

The Horizon P-1000 registers real time at 800 RPM and above.

Joe

My Dynon uses two tachs. One is engine run time and the other is a trip meter that kicks in when I am over about 1500 rpm or so. Too bad for us that engine tbo hour ratings got a lot shorter when they made the switch to hobb style tachs. Not that engines have to be over hauled at recommended TBO's but how about it shortening real time inspection intervals or the effect on commercial operators.

Our farm equipment used to be mechanical driven too. An hours work was an hour at rated hp pto speed, like the old aircraft steam gauge tachs, and people would brag about getting 10,000 hrs on a tractor but with the new hobb style hr meters that is nothing anymore. The combines are using two tachs now to keep track of engine time and the second for the separating time. The 2388 I just bought shows 2000 total engine time and the separator shows only 1400 separating hours. I thought there must be a mistake until I talked to the previous owner and found they let the engine idle all night during cold weather to avoid cold starts in low temps the next morning, like a semi. Better than having the road time I guess.

Used to fly some single engine charter and ocassionally would rent the 150, 172 or Arrow where I worked. Would open the throttle for takeoff and never retard it till approach. That was the Boss's orders. Less tach time than Hobbs.

Gene

Gary, it depends on your tach and it should say on the data plate or tag on the back of your unit.

My tach equals the 60 minute clock @ 2550 rpm. When I got the plane, it had an old Cessna tach that clicked off one hour at 2350 rpm which was too low for me and my Lycoming 0-360. What does it matter you ask??? Well, I track engine and airframe time off the tach and 2550rpm is my normal cruise setting and I dont want to do any more math or conversions than I have to. With the old tach, I would click off an hour of airframe time in 50 minutes sometimes. Works for me.

As noted above, one can use a watch, hobbs, tach, garmin etc.....

Well, I just got back. 5 hours on my watch, 4 on the Garmin, and 4.2 on the tach. I can't seem to run at a constant RPM for more than a couple minutes , so I guess I'll never know as far as my application goes.
But the tack and Garmin were fairly close. RPM's were in the 2300-2500, most of the time.
Gary