How to choose a cruise RPM for tach time on JPI 930

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readytocopy995

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We have a JPI 930 in our partnership 182. We just went from a O470R to an O470U with the 252hp STC (higher redline). What would be an appropriate cruise RPM for our tach timer to be based off of? I don't think there's any requirement for this to be x vs y. Obviously it's to our advantage maintenance wise to be higher, but then people will also probably fly it harder and burn more fuel.
 
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readytocopy995 said:
We have a JPI 930 in our shared 182. We just went from a O470R to an O470U with the 252hp STC (higher redline). What would be an appropriate cruise RPM for our tach timer to be based off of? I don't think there's any requirement for this to be x vs y. Obviously it's to our advantage maintenance wise to be higher, but then people will also probably fly it harder and burn more fuel.
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Just wondering how easy it is to program that. Does it require some kind of password so not just anyone at anytime could do it?
 
Stewartb said:
Memory says 2300.
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That's what I thought it was when we had the R engine. But we had an ordinary tach at that time so not sure.

Rgbeard said:
2,400 seems kinda fast, to me, for a cruise RPM but do what the POH says.
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That's my thinking as well, 2400 too fast. The redline on the standard U engine is 2400 rpm but we have the John Jewell STC which increases it to 2625 rpm. There is not a "proper" supplement for the POH which tells us the cruise settings, which is kind of the issue of how I can't decide how to set it.

EdFred said:
Leave it at what is it at now. You're still gonna cruise at what you're gonna cruise at.
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We are starting from scratch, new JPI. So we have to decide.

luvflyin said:
Just wondering how easy it is to program that. Does it require some kind of password so not just anyone at anytime could do it?
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You can make it whatever you want but after 10 hours it can't be changed. So clever pilots can't just set it to 2800 rpm before the flight and save on the tach billing ;-)
 
If you order the correct tach through Mitchell it'll be set at 2300. That applies to almost all Cessnas. My engine can run continuously at 2700 and my tach is set at 2300.
 
I got a new 830 sitting in a box for now, and reading the instructions, it says you have limited hours after initial installation to set up the RPMs for tach-time before it locks that setting. Look up the 930 and see if it’s different.
 
455 Bravo Uniform said:
I got a new 830 sitting in a box for now, and reading the instructions, it says you have limited hours after initial installation to set up the RPMs for tach-time before it locks that setting. Look up the 930 and see if it’s different.
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yes, i mentioned this above. after 10 hours you can't change the tach settings. but how do you decide what tach setting to use? POH says cruise is 2100-2625 rpm. so do i just pick one? on what basis?
 
readytocopy995 said:
yes, i mentioned this above. after 10 hours you can't change the tach settings. but how do you decide what tach setting to use? POH says cruise is 2100-2625 rpm. so do i just pick one? on what basis?
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Sorry. I was advised to pick the RPM that *I* cruise at to set it. Pick the driver that whips the horse the hardest and use that RPM.
 
Cruise power 55%, 65%, 75% is based on altitude. My archer has a chart on the visor that gives the various RPM settings for a given cruise power settings based on altitude.
 
Don't most 2700RPM redline tachometers true at 2500RPM? And 2400RPM tachometers at 2200?

If you're off by 100RPM then you're off somewhere in the range of 1/23-1/26 which is ~4%. Is that a big deal?
 
Joe_B1 said:
Cruise power 55%, 65%, 75% is based on altitude. My archer has a chart on the visor that gives the various RPM settings for a given cruise power settings based on altitude.
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I appreciate the input but I feel like people aren't reading my post at all. I know how to set for cruise power in an airplane. I'm trying to figure out how somebody decides what speed to base the tach rpm off of

asicer said:
Don't most 2700RPM redline tachometers true at 2500RPM? And 2400RPM tachometers at 2200?

If you're off by 100RPM then you're off somewhere in the range of 1/23-1/26 which is ~4%. Is that a big deal?
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This sounds about right, but again is there some literature somewhere on how to determine what the overhaul is based off of? "2000 hours" for TBO is different if that's based on 2k hours of operation at 2200 rpm or 2400 rpm.

MauleSkinner said:
Set it at 1500 RPM…your overhauls will last a lot longer! :D
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o_O

Stewartb said:
Bass-ackwards. Setting ot higher than true will slow the tach time. I hope whomever might buy this plane in the future is reading this thread.
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Yeah don't worry I'm not setting it at something stupid. POH supplement says green arc is 2100-2625 rpm. So what do I do? Split the difference? Conservative value like 2200 rpm? More modest 2350 rpm? Surely somebody has run across this issue before.
 
Stewartb said:
Bass-ackwards. Setting ot higher than true will slow the tach time. I hope whomever might buy this plane in the future is reading this thread.
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Nope. Think about it. Set it for 1500, but it spins at 2500. Meaning that it shows 67% more hours than true hours.
Result: "My engine made it well past 3000 hours before it started making metal."
Reality: Engine still only had 2000 true hours on it.

Sort of like setting an odometer to km/h and calling it miles.
 
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You should set it at whatever you normally cruise at.
I generally cruise io470k at 2450, so I would set it at 2450 as that will give you a true indication of how many hours you have been using the engine between oil changes etc.

You *can* cruise at 2100 rpm but do you? You *can* cruise at 2650 but do you?
The goal is to have an accurate estimate of the wear and tear on the engine, so set it where it will be most close to accurate.

The point is that if you're just putting around at 2100rpm there's very little load on the engine so it's not wearing as quickly as it would at cruise rpm so the hours read lower. Opposite is also true, during full power maneuvering it will read higher than true "time in use". At cruise it will be a 1:1 ratio.
 
readytocopy995 said:
"2000 hours" for TBO is different if that's based on 2k hours of operation at 2200 rpm or 2400 rpm.
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Again, if you're off by 100RPM then you'd be at 1920 hours or 2080 hours instead of 2000. Is that a big deal?
 
EdFred said:
Nope. Think about it. Set it for 1500, but it spins at 2500. Meaning that it shows 67% more hours than true hours.
Result: "My engine made it well past 3000 hours before it started making metal."
Reality: Engine still only had 2000 true hours on it.

Sort of like setting an odometer to km/h and calling it miles.
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you are saying the same thing as the person you are arguing with. he’s saying setting it higher slows down the tach timer, and you’re saying no setting it lower speeds it up. same thing.

but the engine doesn’t care about “true” hours. it cares about wear which is a function of rpm. setting the tach timer at 2000 rpm or 2400 rpm doesnt change when it will be a bad engine but it changes billing, mx, ad compliance, etc
 
readytocopy995 said:
you are saying the same thing as the person you are arguing with. he’s saying setting it higher slows down the tach timer, and you’re saying no setting it lower speeds it up. same thing.
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Someone said set it at 1500 because OHs will last longer, meaning the tach will say it has 3500ish when it has run about 2000 of real time - and the theoretical metal making time. He said that's backwards. It's not.
 
MauleSkinner said:
Set it at 1500 RPM…your overhauls will last a lot longer! :D
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Stewartb said:
Bass-ackwards. Setting ot higher than true will slow the tach time. I hope whomever might buy this plane in the future is reading this thread.
Click to expand...

EdFred said:
Nope. Think about it. Set it for 1500, but it spins at 2500. Meaning that it shows 67% more hours than true hours.
Result: "My engine made it well past 3000 hours before it started making metal."
Reality: Engine still only had 2000 true hours on it.

Sort of like setting an odometer to km/h and calling it miles.
Click to expand...

EdFred said:
Someone said set it at 1500 because OHs will last longer, meaning the tach will say it has 3500ish when it has run about 2000 of real time - and the theoretical metal making time. He said that's backwards. It's not.
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You're all saying the same thing but from a different perspective. The confusion is from MauleSkinner saying "your overhauls will last a lot longer"

Stewardb, as I first did, seems to have taken that as "you will take longer to get to TBO" but I think MauleSkinner was actually saying "your tach timer will read much higher by the time you need to overhaul" meaning you can "make it" to 3000 hours but in reality it's not been that many. Which is what you're saying. Everybody is right
 
readytocopy995 said:
You're all saying the same thing but from a different perspective. The confusion is from MauleSkinner saying "your overhauls will last a lot longer"

Stewardb, as I first did, seems to have taken that as "you will take longer to get to TBO" but I think MauleSkinner was actually saying "your tach timer will read much higher by the time you need to overhaul" meaning you can "make it" to 3000 hours but in reality it's not been that many. Which is what you're saying. Everybody is right
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Ignore my statement about 1500 RPM and all subsequent responses to it…they seem to be confusing you when you’re severely overthinking it already.
 
MauleSkinner said:
Ignore my statement about 1500 RPM and all subsequent responses to it…they seem to be confusing you when you’re severely overthinking it already.
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but i'm an engineer, there must be a reason or paper behind every single decision on a selecting a number!
 
You are using a constant speed prop I presume...set it to whatever rpm you set the prop for cruise rpm that is recommended for your engine/prop combo.
 
Doug Reid said:
You are using a constant speed prop I presume...set it to whatever rpm you set the prop for cruise rpm that is recommended for your engine/prop combo.
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indeed it has a constant speed prop. but there is not a single rpm for cruise, it's a range of 2100-2625 rpm. hence me asking the question...what to choose. we settled at around 2350 rpm as most will probably cruise 2300-2400 rpm but was just surprised there is not more specific guidance on what rpm setting these tbo figures assume
 
I am sure there is a C182 guru somewhere that can help. I know on my C195 there are several engines that were used back in the day. I believe they all ran similar rpm settings in cruise, with the primary advantage being power available for takeoff. Sounds like you made a good choice with 2350.
 
Since it’s not able to be changed ever after ten hours I would set it just below the lowest recommended cruise rpm in the performance charts. That way you know ot will always record any operation that is putting load on the engine regardless of who is flying.
 
Stewartb said:
If you order the correct tach through Mitchell it'll be set at 2300. That applies to almost all Cessnas. My engine can run continuously at 2700 and my tach is set at 2300.
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The FG Cardinal is 2566, the Cardinal RG is 2400... not sure about almost all Cessnas...

I'd look up the spec for your airframe!

Paul
 
Tarheelpilot said:
Since it’s not able to be changed ever after ten hours I would set it just below the lowest recommended cruise rpm in the performance charts. That way you know ot will always record any operation that is putting load on the engine regardless of who is flying.
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That's not how it works... it's not a threshold, it's a calculation factor for revolutions divided by factor equals minutes of flight.

Paul
 
PaulMillner said:
That's not how it works... it's not a threshold, it's a calculation factor for revolutions divided by factor equals minutes of flight.

Paul
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That sounds like a Rube Goldberg solution.

if it’s asking for cruise rpm and it’s as you described I would expect there to be rather precise guidance from the manufacturer on how to determine the magic number.
 
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