Recommended time between oil changes is 25 hours. Is that tach time or clock time? I noticed that since I've flown 39.2 hours tach time, I've flown 50.4 hours clock time.
Anne.
Recommended time between oil changes is 25 hours. Is that tach time or clock time? I noticed that since I've flown 39.2 hours tach time, I've flown 50.4 hours clock time.
Anne.
Baloney is still baloney, no matter how thin you slice it.
TACH for sure as this is "engine time"
sj
Anne,
All maintenance associated with the engine is based on tach time, not on Hobbs or clock time.
MTV
Tach time is set to accumulate differently for different engines. A Cub tach turns time at a different rate than a Cessna tach, based on average cruise rpm, I believe. I was taught that tach time multiplied by 1.2 (generally) should equal Hobbs time. I'm sure some guys cheat and put incorrect tachs into their planes to allow the engines times to accumulate at a slower rate.
For what it's worth.
SB
Stewart,
The "1.2" only works on short flights. We use it in flight instructing. If you do that on a cross country flight, you will find the tach and hours to be about the same before the math. As you pointed out, different engines are "clocked" at different RPMS. If you have a constant speed prop, you could run around at 25" manifold pressure at 2000rpm and get a lot more TBO life... at least on paper...
sj
To further answer Anne, for oil changes, err to the shorter interval. More changes are more better. The three month rule usually is in play before 25 hours tach time for private folks.
SB
The interval I use is both the tach time and the calendar. Once a month or 25hrs which ever comes first. My cub burns 40wt at a rate of 1qt for 9hrs of time. I usually change when it needs the second quart. I use straight weight and it is inexpensive to change frequently.pak
Anne,
Change your oil every 3 months or 25 hours which ever comes first. And besure to change just before you stop flying for the winter if that is you fly much less during the winter. Go read the Lycoming link under the Cams thread.
Hobbs time is the same as flight time normally. It reads true time from the time you start the engine till you shut it off. This is for the pilot logging time "chock to chock".
Aircraft maintenance is normally done by time in service, the time from the gear off the runway till it touches again. This is closest to tach time. it barely runs at idle, is a little fast at take-off and about right at cruise.
Oil changes are recommended by time in service or calender.
I recommend one more oil change than the manufacturer per 100 hrs. It's cheep insurance. No filter plan 20 hrs. Spin on filter plan 35 hrs. If you go a little over you are still in the manufacturers recommendations. If you can't afford one more oil change per 100 hrs than recommended you can't afford to fly.
Somebody correct me if I'm wrong, but my understanding is that the Hobbs runs anytime the master switch is on (unless you have an oil pressure switch installed) and keeps time like any clock. As there is no "clock" in the tach it is counting revolutions. The difference in tachs between airplanes is that some will match clock time at a certain RPM and others will match at a different RPM. If you let your engine idle for a long period of time it will record less time on the tach than if it runs at a high RPM. Therefore if I cruise at 2350 RPM and you cruise at 2500 RPM you will accumulate more time on the tach than I will for the same "clock" time. Did anybody understand that?
Oh by the way, one of the reasons that all engine maintenance is performed off of the tach time is that if you forget to turn off your master switch you will probably have to change your oil twice before the battery goeas dead.
As I understand it, what you stated is true. But, the tach records time based upon the engine that it is calibrated to. When I bought my tach for the 12, the instrument company asked what the airframe was that I was using the tach for, and they sold me a tach that was appropriate for that airframe/engine. My Cessna tach records tach time based upon higher RPMs than my Piper. If I was to put a Cessna-rated tach in my 12, the tach time would register less time than it should. I jokingly (well, kind of jokingly) asked if they would sell me a Cessna tach for my 12, and they said no.
SB
Could of just ordered a Michell RT11 from Spruce if you want a 2566 tach. the RT7 is 2300.
Can we expand a little on this thread? It seems to me from all I have read that the hardest thing on the oil and engine too is lack of use. I have read of folks changing the oil on the road on a long trip, ie ten days flying 4 plus hours a day, because they hit 25 hours. It would seem to me that you could safely go a little further between changes when using the plane so regularly, at least til you got home (assuming you didn't fly 90 hours or something). Thoughts?
Bill
I have a friend that flies pipeline. They fly over a hundred hours a month and change their oil every 100 hrs. Some of their engines are past the 3000 hr mark since major. My folks flew their 150hp Clipper toAK a few years ago and had the oil changed when they got their. I think they were just shy of 50 hrs. Oil is one of the cheapest things that go into an airplane.
Steve Pierce
"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
Henry Ford
The other issue to remember when talking about oil change intervals is the operating temperature of the engine oil. The manufacturers recommend that you run your oil temp at greater than about 180 degrees on every flight, for at least 20 to 30 minutes or more.
The purpose of this is to "boil off" the moisture which resides in the oil and engine. Moisture is one thing that kills engines.
Engine oil additives "wear out" with use, so eventually, all the goodies (like the additive that helps multi vis oil change viscosity) that the oil manufacturer put in your oil will lose their effectiveness, but the stuff will still lubricate the engine adequately.
Best plan of all is to change the oil frequently, both to keep the additives working well, and to get rid of as much moisture as possible.
MTV
Each engine saturates its oil at different lengths of use. Blow by, time since overhaul, and other factors affect this time. Basically when your oil becomes saturated with junk the engine consumption will increase noticably. The trick is to change before you get to this point.
Consumption is subject to many factors, this is a genuine can of worms.
How did they keep engine and airframe time when my 46 12 came out of the factory? My tach has no meter.
Thanks for the replies, folks. It's almost time to change the oil again.
Anne.
Baloney is still baloney, no matter how thin you slice it.
fortysix12,
If you look at your early logbooks, you'll find that the pilot logged every flight in the aircraft logbooks. This was logged takeoff to landing, and was considered acceptable for maintenance purposes, I believe.
Don't know when this practice ended, but it probably coincided with the advent of recording tachs.
MTV
Another question. A very reliable engineer type suggests that oil filters are better at filtering after 25 hours (please correct me, reliable engineer type), so he changes the oil every 25 hours, but the filter every 50 hours.
I would like to hear some opinions on this matter.
Randy
Lycoming Operator's Manual [0-320 & IO-320 Series] states oil changes 25 hrs with a Note "Intervals between oil changes can be increased as much as 100% on engines equipped with full flow oil filters - provided the element is replaced each 50 hours of operation."
They have a service bulletin that allows 10% TBO extension on frequently flown engines based on condition. [135 operators that are bound to the TBO times]
Sandy
Sandy
Randy, my thinking on what your talking about is when the filter starts plugging up so to speak the restriction is even greater in the filter which would inturn even catch the smaller particles after time. If that would be good or bad i really dont know. As long as you have oil pressure and its not pushing the bypass of its seat probably wont hurt anything. Is the oil pressure read after the filtered oil or before on yours?
You know, I am not sure where, in line, the oil pressure read occurs.
I believe your thinking on oil filter function is correct. The engineer I alude to is none other than Darrel Starr, who is one terrific engineer and one who really doesn't leave much to chance. His explanation is similar to your logic, tempdoug. He was a lead engineer at Caterpillar (Darrel, correct me if I am wrong) for years, and he explained to me that the oil filter begins to plug up a bit during the first several hours of operation, and there is a point (25 hours?) when it really begins functioning well...hence his suggestion to change the filter at 50 hours. Sandy, your contribution supports that notion, and I appreciate your inputs.
Randy
Randy, your statements are substantially as I related to you from a test run at Caterpillar years ago, remember I'm retired so this info is getting old. The only thing I would change is that in the tests I remember, the filter was a long long way from plugging up but had caught some particles to the point where the effective micron particle catch improved. That is why I change oil at 25 hrs and filters at 50 hrs. And at 50 hrs when I cut apart the filter I really don't see any "sludge" so I'm certain that I am not anywhere close to plugging the filter.
Back to the tach discussion -- I have an EI digital tach that doesn't record anything below 1200 rpm then operates like an hour meter once recording above 1200 rpm. It seems to be a fair representation of engine use.
Last edited by Darrel Starr; 09-10-2011 at 01:47 PM.
When a prang seems inevitable, endeavor to strike the softest, cheapest object in the vicinity, as slowly and gently as possible.— advice given to RAF pilots during W.W.II.
I always changed both my oil and filter every 50 tach hours. My gps "log book" feature almost always had 5 hours when the tach showed 4 during my long pipeline routes if I ran at 23/2300 with an O-360.
Those who pound their guns into plows, will plow for those who do not.
Patrol Guy, what was your average fuel consumption in US gallons at 23/2300, please?
So, not to get too far off course, but to throw one more twist into this conversation, when you are logging flight hours, are you logging by tach time or by hobbs time? Since my "antique" (anything older than me has to be an antique) supercub only has a tach meter that is what I have been recording in my logbook.
Am I shorting myself 20% of my legitimately logged flight hours?
"What we obtain too cheap we esteem too little!
King Brown, Sorry I just saw your question. It's been so long since I figured it. I always planned for 10 gph, but it takes 24/2400 to burn that much. 23 sqrd is probably around 9 gph. I know when flying in Alaska with a bunch of 150 hp super cubs (19/2100), I am usually in the middle of the pack as far as who used the most.
Those who pound their guns into plows, will plow for those who do not.
Here's the guidance for "flight time" from FAR 1.1:Originally Posted by dalec
So, not to get too far off course, but to throw one more twist into this conversation, when you are logging flight hours, are you logging by tach time or by hobbs time? Since my "antique" (anything older than me has to be an antique) supercub only has a tach meter that is what I have been recording in my logbook.
Am I shorting myself 20% of my legitimately logged flight hours?
Flight time means:
(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; or
(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.
The regulations don't propose precisely HOW you measure that time, but I suspect most lawyers would successfully argue that you'd use a clock, not a tachometer-hour meter.
MTV
Mike V.
Thanks for the clarification and sorry for the thread drift.
"What we obtain too cheap we esteem too little!
Oil breaks down in 25-30 hours. That is straight from a chemist that specialized in aviation oils. The filter has nothing to do with the oil other than getting out slightly larger particles. I change my oil every 25-30 hours after finding water in rocker covers, pitted cams, rust on crankshafts etc. Good clean oil is the cheapest insurance in my opinion and I think Cam Guard is second.
Steve Pierce
"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
Henry Ford
I think i read in a cub clues that Don Swords dosent recommend camguard in the 4 cylinder continentals, anyone know why? doug
Don Swords also said at a Cub Clues Forum I attended at Sun & Fun that he has crankshafts that were damaged from using auto fuel. I take what he says with a grain of salt. Having researched Cam Guard and the chemistry behind it I don't see any reason it doesn't benefit any air cooled aircraft piston engine.
Steve Pierce
"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it."
Henry Ford
Steve, after posting what i did i went to find what i had seen. in cub clues number 165 on page 14 4th paragraph down on right side of page. Not to use camguard on breakin, so my take on this is it thins the oil? this was at sentimental journey. doug
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