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How to install a hobbs/tach?

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1906

Joined: 30 Nov 2018
Posts: 58

Posted: Sun Dec 09, 2018 8:11 pm Post subject: How to install a hobbs/tach?

Is it possible to install some sort oil pressure switch on these?

My mechanic thought he had it, connected to I believe the oil dilution port but it didn't pick up enough pressure for the switch there...

dsavarese0812(at)bellsout
Guest

Posted: Mon Dec 10, 2018 4:08 am Post subject: How to install a hobbs/tach?

Oil dilution port is an INPUT to the oil pump. Not an OUTPUT.  Find the oil pressure line coming the oil pump and going to the triple instrument in the cockpit.  It is a flexible hose. 

Dennis



Sent from my iPad



 	  Quote: 	
		   On Dec 9, 2018, at 11:11 PM, 1906 <zmadwolf(at)gmail.com> wrote:

 

 

 

 Is it possible to install some sort oil pressure switch on these?

 My mechanic thought he had it, connected to I believe the oil dilution port but it didn't pick up enough pressure for the switch there...

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=486201#486201

Looigi

Joined: 20 Apr 2015
Posts: 80
Location: Christchurch, New Zealand

Posted: Mon Dec 10, 2018 11:21 am Post subject: Re: How to install a hobbs/tach?

Can I ask a stupid question..... Why would you want to?



My Yak is in a syndicate of 9 people, so we need to track flying time so Rob can send each of us his monthly hate mail.... the bill.



Given that the Yak needs a lot of time to get the engine oil up to temperature, especially in winter, I didn't want to use an oil pressure switch.  I needed to record flight time, not engine time because I didn't want guys to try and save themselves a few cents by short cutting the warm up only to cost us big bucks on engines.



I installed a Hobbs and a pressure switch.  The Hobbs has its own power supply, through a circuit breaker straight from the master switch and is turned on by a small pressure switch plumbed into the pitot system.  There was a convenient unused pipe behind the back seat where some sort of "flight data recorder" once was, and I just plugged into that.  When we were doing the bi-annual pitot test, I adjusted the switch to come on at about 60km/h airspeed.



If this sounds a solution to your problem, I can dig out the details of the switch I used.



I hope this helps,

Chris

cjpilot710(at)aol.com
Guest

Posted: Mon Dec 10, 2018 1:37 pm Post subject: How to install a hobbs/tach?

At the Collings Foundation, the B-24 Hobbs was hooked up to the landing gear strut.  With strut extended a switch powered the Hobbs meter.  The FAA seems to be happy with that. Jim "Pappy" Goolsby

 

 

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wlannon(at)shaw.ca
Guest

Posted: Mon Dec 10, 2018 7:44 pm Post subject: How to install a hobbs/tach?

Looigi;



While I have no concern with your choice for activating the Hobbs meter I do 

have a problem with your choice of power supply.



The battery master switch is there to activate the battery master relay 

which in turn powers the bus.  None of the bus load is carried through the 

switch which is sized for it's primary  purpose only.  The load you are 

adding may not be enough to cause a problem but I believe you are breaking a 

cardinal rule in aircraft electrical practice.

Since operation of the entire electrical system depends on the master relay 

the loss of it's power supply (the switch) means total elec. failure.  Any 

added elec. load should always be taken directly from the bus never from the 

master switch.



Walt



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Looigi

Joined: 20 Apr 2015
Posts: 80
Location: Christchurch, New Zealand

Posted: Tue Dec 11, 2018 12:08 am Post subject: Re: How to install a hobbs/tach?

Hi Walt,



Yep, I considered that.  Admittedly I am an engines and airframe man and I much prefer working on bits I can hit with a hammer.  



In my defence though..



The switch is very typically Russian and over rated to the max.  From memory, it has 10A marked on it, but don't quote me on that.



The Hobbs I am using has a 0.8mA draw at 12vdc (so 0.4mA at 24v) and the CB is mounted only a few inches away from the switch.  I can't remember the rating of the CB, but it was the smallest I could get.



Chris

1906

Joined: 30 Nov 2018
Posts: 58

Posted: Tue Dec 11, 2018 7:48 pm Post subject: Re: How to install a hobbs/tach?

I appreciate your input guys. My hobbs was connected to the engine instruments switch and any time I do some maintenance or troubleshooting, the thing just keeps adding time. How do you accurately maintain the actual time on the airplane for maintenance and resale purposes otherwise? That was my reasoning.

Viperdoc

Joined: 19 Apr 2014
Posts: 484
Location: 08A

Posted: Tue Dec 11, 2018 8:13 pm Post subject: How to install a hobbs/tach?

The aircraft originally did not have a Hobbs. The flight time was recorded in the a/c log books. Mine does not have a Hobbs. I keep up with flight time with a separate column in my log books. 

Doc



Sent from my iPad



 	  Quote: 	
		   On Dec 11, 2018, at 9:48 PM, 1906 <zmadwolf(at)gmail.com> wrote:

 

 

 

 I appreciate your input guys. My hobbs was connected to the engine instruments switch and any time I do some maintenance or troubleshooting, the thing just keeps adding time. How do you accurately maintain the actual time on the airplane for maintenance and resale purposes otherwise? That was my reasoning.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=486248#486248

_________________
Viperdoc

n13472(at)aol.com
Guest

Posted: Tue Dec 11, 2018 8:26 pm Post subject: How to install a hobbs/tach?

Hook it to one of the landing gear up lights. This way it is recording

flight time only.

unless you like to fly with the gear down?

Tom Elliott

CJ-6A NX63727

777 Quartz Ave

PMB 7004

Sandy Valley NV.

89019

Cell 541-297-5497

N13472(at)AOL.COM

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jbsoar(at)gmail.com
Guest

Posted: Tue Dec 11, 2018 11:00 pm Post subject: How to install a hobbs/tach?

There is a really good digital tachometer available that also counts engine hours.  Contact me off the forum for specifics.



On Tue, Dec 11, 2018 at 9:55 PM 1906 <zmadwolf(at)gmail.com (zmadwolf(at)gmail.com)> wrote:



 	  Quote: 	
		  --> Yak-List message posted by: "1906" <zmadwolf(at)gmail.com (zmadwolf(at)gmail.com)>

 

 I appreciate your input guys. My hobbs was connected to the engine instruments switch and any time I do some maintenance or troubleshooting, the thing just keeps adding time. How do you accurately maintain the actual time on the airplane for maintenance and resale purposes otherwise? That was my reasoning.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=486248#486248

 

 

 

 

 

 

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cjpilot710(at)aol.com
Guest

Posted: Sun Dec 16, 2018 2:19 pm Post subject: How to install a hobbs/tach?

The airlines don't really keep track of "Flight time" as much as they do "cycles".  Some of PAAs 747SP would be airborne as much as 20 hours per day but with just 2 cycles (1 takeoff 1 landing).  Replacement of things like landing gear was based on cycles.  I use the time off my electronic tach (engine running).  The B-24 I flew for the Collings foundation use the "squat switch" on the left landing gear to run a hobbs meter.  I personally don't remember anywhere in the regs (AND I CAN BE WRONG) where it says HOW the time would be determined for light aircraft.  It seems to me a timed cycle (ala gear switch) or engine running (electronic tach or oil pressure Hobbs) would be close enough.

 Jim "Pappy" Goolsby

 

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