IO550g limited to 2450RPM?

[r0ckst4r]

I recently had a JPI 830 EDM installed and noticed that I seem to be limited to 2450 RPM and not 2500.  I checked it against the factory tach and on closer inspection it seems like I have been there all along and have never noticed it.  Is this a variation that occurred from the factory or is this something that can be modified by an A&P?

[LANCECASPER]

The answer is in your POH under section II, Limitations. If you decided to get a JPI 900 or 930 (both certified replacements), JPI would need a picture of the page that shows instrument markings. Your limit is 2500 on the 280hp Ovation. (There’s a $5000 STC to bring it up to 2700 rpm with a modified prop governor, the correct prop and a Tach that’s redlined at 2700)





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[r0ckst4r]

I think I didn't phrase this appropriately.  I think I've always been limited to 2450 RPM with full throttle.  I just didn't notice the small hash marks on the factory tach.  Not talking about the programming of the JPI unit or redlines, just the hard limit on the IO550g which is supposed to be 2500.  I go full throttle and all I get is 2450 RPM.

[N201MKTurbo]

You just need to adjust the stop screw on the prop governor. I may shorten your takeoff roll by 5 feet or so.

[r0ckst4r]

1 hour ago, N201MKTurbo said:

You just need to adjust the stop screw on the prop governor. I may shorten your takeoff roll by 5 feet or so.

I figured it was something like that.  I will let my A&P know at my upcoming annual that it should be 2500 RPM.  Thank you.

[A64Pilot]

3 hours ago, r0ckst4r said:

I figured it was something like that.  I will let my A&P know at my upcoming annual that it should be 2500 RPM.  Thank you.

It could be if your prop control is completely bottoming out a cable travel adjustment is needed and not the governor.

I have that issue and need to get off my Butt and adjust it, you should have “cushion” on all the controls, that is the controls should hit the stops at the engine but there should still be travel available in the cockpit. Mine bottoms out so I think my issue isn’t prop governor adjustment.

Your A&P or you should validate actual prop RPM too, it’s not unlikely that your tach could be off a smidge, cheap optical tachometers are available.

There are cheaper ones out there but if this is like the one I had decades ago it has setting for a two and three blade prop.

They are astonishingly accurate, you can even validate them by using the two blade prop setting, point it a a florescent light, it should return an RPM of 3600 as in the US our power frequency is 60Hz and 60 x 60 = 3600. 

https://www.chiefaircraft.com/radio-control/builder-supplies-tools/han-156.html?gad_source=1&gclid=Cj0KCQiAwP6sBhDAARIsAPfK_wYVhDLTf9DlxP-bFzM6nj8aCAkuuKvQmFhDbQR3joNg-n_RONVNSPYaAki3EALw_wcB

I bet there is an App too, but I’ve seen Apps that accuracy wasn’t close for other things so who knows?

[EricJ]

4 hours ago, r0ckst4r said:

I figured it was something like that.  I will let my A&P know at my upcoming annual that it should be 2500 RPM.  Thank you.

2450 is within the typical tach accuracy of 2500.    He might want to put an optical tach on the prop and see whether it is your governor or your tach.   Otherwise that's often close enough for most folks.  Getting it to exactly 2500 can be a fair amount of work for not much benefit if you're already getting to 2450.

That said, it may be worth making sure that the prop cable is getting full travel at the governor.   That's another common issue.

[Pinecone]

JPI is going to be pretty accurate as it uses pulses off the mag to determine RPM.

FYI, if you need to set any of the redline limits on your 830, you can do that yourself.  You should have the printed manual, but if not, it is available on JPI site.

One thing, if you are set for 2500 on your engine, and the JPI redline is 2500, you will get a red indication on every take off, since you are at 2500.  So you need to set the JPI to redline at 2510.

[hoot777]

Just checked my M20 G with a strode meter since I have a new top prop and Pinnacle Major overhaul. The old steam tach is reading about 100 rpm’s high. I think I read somewhere that a tach can be 3% off at normal cruise power. Any experts out there. Engine running great

[carusoam]

5 hours ago, hoot777 said:

Just checked my M20 G with a strode meter since I have a new top prop and Pinnacle Major overhaul. The old steam tach is reading about 100 rpm’s high. I think I read somewhere that a tach can be 3% off at normal cruise power. Any experts out there. Engine running great

bust out the smart phone app, and audibly determine actual rpm!

know if your engine has been set-up using the ship’s tach, or something more reliable…

accuracy at the high end is important for T/O power…

accuracy at the low end is important for landing distance…

If you fly by the book numbers… the instruments need to be accurate to get book numbers…

New EI tach and MP gauges to match the new engine is a great idea…!  

 

Briefly…

I have studied the rpm discussion pretty closely a decade ago… when going from O1 to O3 power…

RPM 1: 2500, 280hp, 25gph, T/O length 1200’….       IO550(g), stock Macaulay

RPM 2: 2700, 310hp, 28gph, T/O 800’…                     IO550(n), Acclaim TopProp

 

 

For comparison, I also collected data riding in @Cris’s Screamin’ Eagle.  I wasn’t going to pay for the O3 power, if I couldn’t measure it to know it was real…

Distance measured using WAAS gps for accuracy.  CloudAhoy app.

10% more horsepower….

1/3 less runway used…!!!

 

keep in mind…. These rough numbers don’t account for the big improvement in ‘excess power’ that is used for acceleration, T/O distance, and climb rate….

 

 

For max T/O distance… you wouldn’t want to be 100 rpm low.

For engine reliability/wear… you wouldn’t want to be 100rpm high.

It is good to calibrate your tach.  At least know how far off it is using an rpm app.

 

Checklist items…

• MP
• RPM
• FF

If all three meet your spec., you are developing full HP!  GO!  
 

There may also be  a seat of the pants difference with all of the horses running… depending on your seat’s sensitivity.

PP thoughts only,

-a-

[carusoam]

An example where the importance of RPM is shown…

My favorite airport, 2k’ long runway…

O3 power… off the ground before the halfway point.  If not, stop!

O1 power… trees start getting bigger in the windshield before being off the ground.   Stopping distance is getting really small…

 

Economically… the 200rpm cost something like 20amu back in the day… prop, STC, and install…

If your gov is set too low, and you are missing 100rpm… about 5%hp.

Get with your favorite mechanic for a low cost power boost.

Instrument and power accuracy are important on short fields.

 

PP thoughts only…

 

Best regards,

-a-

[carusoam]

Scary way to look at the same challenge…

 

(purely hypothetical situation)

Same plane, and runway… and we’re bringing the family along..

for some reason, my engine is only 10% off its max hp that day…. What could possibly happen?

T/O distance is 1200’ instead of 800’…. A huge 50% increase!

What if I load the plane up to MGTW?

It’s hot out, whole family is heading to the beach…?

 

The whole runway is getting shorter, and the 50/70 rule is jamming up in the brain…. Stopping distance is getting tiny.

 

expect rpm being off by 100…

• important if the engine is not set up correctly…
• less important if the tach has aged, and data is false.

 

mechanical tachs, with the speedometer cable… can get a nice accuracy improvement with a new cable…

PP thoughts only…

Best regards,

-a-

[hoot777]

Thanks guys. I’ve measured the tac with a test box or whatever you want to call it. I’m definitely 100 low or indicating 100 rpm more than actual.  I’ll talk with my mechanic about the cable. Good discussion and brings up the point about not hanging our hats on book numbers that were created by a “Perfect” plane. AOPA recommends doubling required runway for safety. 135 pilots add a factor also and airlines are always correcting bad instruments.

[carusoam]

On 1/15/2024 at 7:38 AM, hoot777 said:

Thanks guys. I’ve measured the tac with a test box or whatever you want to call it. I’m definitely 100 low or indicating 100 rpm more than actual.  I’ll talk with my mechanic about the cable. Good discussion and brings up the point about not hanging our hats on book numbers that were created by a “Perfect” plane. AOPA recommends doubling required runway for safety. 135 pilots add a factor also and airlines are always correcting bad instruments.

I nice rough way to measure performance against book numbers…

1) use a long runway…

2) Use CoudAhoy app..

3) supply CloudAhoy with WAAS data.

 

it is better to have a bad instrument and have good power….. than have a good instrument reading, and have bad power….

getting a modern tach is relatively low dollar upgrade, if able…

 

 

[rickseeman]

On 1/14/2024 at 9:42 AM, carusoam said:

bust out the smart phone app, and audibly determine actual rpm!

 

Which app should I get for this? Thanks