Airborne time counter, diff pressure operated

Hobbs can run off the electrical system, oil pressure, airspeed sensing vane, or alternators coming online. Why do you want to use oil pressure? Usually rental planes do that…

Do you have a GTX-328 of GTX-330, that one could sense take-off and start the timer. You would still have to stop it manually or use the squat switch if available.

There are several kits available for pressure sending, pitot would be best / most accurate. Oil pressure and alternator would already start when you start your engine.

Hi Gary,

we use the Winter Flying Hours Counter in our aircraft (http://www.winter-instruments.de/#!flugstundenzhler—-flying-hours-counter/c6zs). It starts counting above around 60 kph when connected to total pressure.You can get it at Siebert
for instance.

USFlyer wrote:

Why do you want to use oil pressure? Usually rental planes do that…

We found it is much more sensible to use flight time instead of hobbs (engine running time) for rental / school ops, as well as for partial ownership accounting. This is, what is usually used in my area.

A differential pressure switch which compares the pitot pressure with the static pressure is described here (search for “differential”).

What sort of timer you can connect that to is another matter, but there are countless options in the industrial control market; everybody and their dog is making what is called e.g. a running hour meter, like this

To install one in a certified aircraft the instrument needs to be certified which basically means TSOd. There is a point of view that it merely needs to comply with TSO; discussed here recently, but that is of little help in practice.

My diff switch (above) feeds the GTX330 and auto switches it between GND and AIR modes. It also feeds the Avidyne TAS605 box.

Would a GTX330 fed from such a switch needs a manual action to terminate the timing?

Logging airborne time only is a nice way to do things because

• you get the maintenance time directly
• billing pilots is fair, if you add a bit for taxi time (removes the incentive to rev up the engine before moving and then thrash the thing to the runway)

but obviously to get the same overall income you have to charge a bit more per hour than somebody charging for brakes-off to brakes-on

Are those Winter instruments certified? I know this is a trivial issue (like a certified sunshade) but if somebody wants to give you a hard time and they are looking for a way to do it…

You could also use a handheld GPS with track log function, like the old Garmin 96 (or similar, not sure they still make these). They start to count when airspeed is above 40kts or so, IOW pretty much t/o to landing on a typical SEP.

Peter wrote:

Would a GTX330 fed from such a switch needs a manual action to terminate the timing?

No. That is only the case when you don’t have any external switches installed. Pressure switch or squat switch can operate the timer, from start to stop.
When you have only encoder hooked up to the GTX-330 it has automatic airborne detection, based on the encoder signal, As it only knows pressure altitude according standard atmosphere, it doesn’t know field elevation and altitude above the airfield, so it can not determine landing.

Peter wrote:

To install one in a certified aircraft the instrument needs to be certified which basically means TSOd. There is a point of view that it merely needs to comply with TSO; discussed here recently, but that is of little help in practice.

Under EASA it must be approved for installation. There isn’t a need for (E)TSO, there are other ways to show it is suiteable for the intended use.

Doesn’t Skydemon also do this?

For a differential pressure switch (unapproved of course) the easiest to get is the flue pressure switch from a gas appliance like a fanned flue heating boiler

I suspect one big issue in this is it being tamper-proof.

That rules out the GTX330 / Ipad / etc approaches.

They need an hour meter which cannot be reset.

When I used to rent out my TB20 (and bear in mind I was quite fussy about who flew it) one of the biggest issues was people fiddling the flight times. And the biggest fiddlers were instructors… no kidding! They knew all the tricks.