Will a Hobbs work?

[Sensible]

I need to keep track of actual flying time of a Motor Glider. The Tach is absolutely no use since it only records engine hours and even those inacurately so when the aircrfta is gliding, there is no record of airtime. I am guessing that a Hobbs would also be connected to the engine oil pressure system by way of a switch. Is it possible to fit a hobbs directly say off of the electrical system so that a more accurate record of actual flying time is able to be recorded? Can anyone explain how a Hobbs actually works?

Any ideas would be most welcome and as the glider is on a CofA would a licensed engineer have to fit it?

[Speedtape]

Electrically driven, switched by an oil pressure switch (normally) and although not necessary for a licensed engineer to fit one, it will require raising of a minor modification and certification by an appropriately authorised (read LAE) person.

[WideBodiedEng]

Have the hobbs powered by an airspeed switch. Then it will record t/o to t/d. Anything off the oil pressure is daft as the engine will be shut down most of the time. Alternative would be on the landing gear. Like a squat switch if the LG would accept it.

[aerodesigner]

Widebodiedeng is right.

A weight-on-wheels switch would be both most accurate and reliable.

[Sensible]

Thanks very much for the input, the only problem is that it's an old Venture and the wheels don't retract. the air pressure switch idea seems the only alternative. Presumably tapping into the ASI feed is a no no! I guess a separate hole will need to be formed into the nose of the glider and presumably that is going to need to be approved by the CAA and a licenced engineer to fit it?

[PlasticPro]

I have seen a Hoobs connected to a standard, externally mounted stall warner switch. As the A/C takes off the Hobbs starts recording - switching off as you land therefore only recording airborne time.

Plasticpro

[I.C.Nosignal]

the wheels do not need to retract , a weight on wheels system can work on oleo extension, ie as the shock strut extends on rotation the switch makes, on touchdown the strut compresses and the switch breaks, a proximity switch on one of the leg torque link is probably the easiest way to go

[Sensible]

Thanks very much for that idea, extremely useful!

[Rocket2]

Sensible
We have a hobbs fed off the (sole) pitot line on our clapped out club Falke/Venture - why do you perceive a problem? Works well, but then if you switch off the battery master.......!