Warranty Inspection

by James Ott in 912 / 914 Technical Questions 12 years ago

The mandatory 25 hour warranty inspection for my new 912ULS; is it based on 25 hours Hobbs time or engine tach time?

Jim

Re: Warranty Inspection

by bill martin » 12 years ago

bill martin

10 757 0

Jim,

According to the line maint. manual, you should not use the mechanical hour meter. See chapter 5-10-00, time definitions.

It sometimes gets complicated. Simple mechanical tachs don't actually count hours but revolutions and those don't match hours because speeds vary and hours don't. Some mechanical tachs don't start the odometer until it passes 1000RPMs. Hobbs meters come closer to actual hours if they are wired properly. If the hobbs is wired through an oil pressure switch, it will record hours only when the engine is running and you will get a more accurate indication of hours. If it is wired directly to the master switch (an old trick used by some FBOs when renting airplanes) it begins recording hours as soon as the master switch is turned on, even if the engine is not running.

If you have Flydat, E.I.S., properly wired Hobbs, etc., that is the reading to use. otherwise, use the mechanical tach. By the time you reach 25hrs., the difference in any of them will be slight. If you really want to play it safe, use the one that gets there first.

Bill.

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Re: Warranty Inspection

by Roger Lee » 12 years ago

Roger Lee

131 5.38k 5.44k

I'm with Bill.

Use Hobbs time. The mechanical tach is usually 15%-20% off because they are governed by engine rpm. The Hobbs works anytime the oil pressure is over 15 psi so the engine is running and it isn't affected by rpms so it records at a constant time.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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