R-1 rpm underreading

[FlyingDude]

Hi guys,

Any pireps on R-1 rpm module underreading and potential issues? What were the causes and fixes?
ps: Prop rpm is fine: checked with laser tach.

 Thanks a lot.

[toto]

So the RPM on the display matches the prop RPM as verified with an optical gauge? What’s the underread?

[FlyingDude]

About 5% lower. 950 for 1000; 1900 for 2000; 2550 for 2700…

[PT20J]

Tachometer reads revolutions/minute. The mag pickup counts revolutions since the mag is geared to the engine. The unit must have an internal time base to measure a minute. It is possible for them to be off just as your Timex can lose or gain time. This would be a factory repair. It's also possible that the pulses from the mags are getting lost if you have a bad connection, but since it connects to both mags this seems less likely, But I would check all the connections just in case.

Skip

[Marauder]

Hi guys,
Any pireps on R-1 rpm module underreading and potential issues? What were the causes and fixes?
ps: Prop rpm is fine: checked with laser tach.
 Thanks a lot.

I’ve been flying behind an R-1 for the past 8 years. Mine has been rock solid. There are a couple of insulators on the brown and orange wires. I would make sure these are in place and not loose. The round connector should be checked as well.

If you don’t see something obvious, give EI a call. They are very helpful. Good luck!


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[FlyingDude]

5 hours ago, Marauder said:

I’ve been flying behind an R-1 for the past 8 years. Mine has been rock solid

Thanks for the pirep.  Have you verified your R-1's readings against a laser tach?  

Yeah, the decoupling resistors are installed correctly (they call them insulators...)  I verified the resistance on the orange and brown wires from the connector to ground with the mags OFF (i.e. grounded).  I also made sure that the connector is also installed properly.  It has a sleeve ring that you turn and it clicks when the connector halves are engaged.  I don't know: you think the internal terminals may be getting loose and as they shake due to aircraft vibrations, they may be changing their impedance?  That would change the waveform and throw a wrench in the internal measurements.  But again, 2700rpm is 45Hz.  That's a really slow waveform...  It shouldn't be that fickle...

I'll try re-routing the harness...  Maybe it's picking up some electromagnetic noise from other avionics?

[Marauder]

Thanks for the pirep.  Have you verified your R-1's readings against a laser tach?  
Yeah, the decoupling resistors are installed correctly (they call them insulators...)  I verified the resistance on the orange and brown wires from the connector to ground with the mags OFF (i.e. grounded).  I also made sure that the connector is also installed properly.  It has a sleeve ring that you turn and it clicks when the connector halves are engaged.  I don't know: you think the internal terminals may be getting loose and as they shake due to aircraft vibrations, they may be changing their impedance?  That would change the waveform and throw a wrench in the internal measurements.  But again, 2700rpm is 45Hz.  That's a really slow waveform...  It shouldn't be that fickle...
I'll try re-routing the harness...  Maybe it's picking up some electromagnetic noise from other avionics?

I personally haven’t measured it, but when I had my prop balanced once they measured the RPM with some sort of optical gizmo. The R-1 is my second tachometer in the plane. I also have a JPI 900. Between the two of them, I don’t see more than 20 RPM difference.

I looked up the spec on it. It’s built with a 1% accuracy on a 10 RPM readout under TSO 49a. I’m wondering if the difference between the actual prop speed and the R-1 has something to do with the mags. You would think there would be a 1:1 correlation between the prop speed and the mag rotation but maybe some of what you are seeing is due to a difference between the two.

As I mentioned, I’d give them a call. Their technical staff is great. I had a problem with my MP-1 instrument after some avionics work and they clued me in quickly what to look for and how to correct it (the shop hooked up the manifold line to the wrong port).




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[FlyingDude]

27 minutes ago, Marauder said:

I’m wondering if the difference between the actual prop speed and the R-1 has something to do with the mags. You would think there would be a 1:1 correlation between the prop speed and the mag rotation but maybe some of what you are seeing is due to a difference between the two.

How could that happen?  You have 1 spark per rotation per mag...  If some spark events are missed, then you'd get engine roughness, right?  

Yeah, I'll call them... It's still 7:30 in Oregon, so I'll wait a few hours 

[oregon87]

Typically, installing an isolator (required for magneto ignition) of the wrong value would result in one of two conditions.  First, too small of an isolator value would result in jumpy and high readings as the R-1 would be picking up the noise near the bottom of the p-leads pulsed signal.  The isolator would not be attenuating the signal enough to where the R-1 is only capturing the peak, registering one pulse.  Conversely, if too large of an isolator is installed, the RPM indication will typically be low or even 0 at lower power settings, slowly becoming erratic and more accurate at higher power settings.

Is this a new installation?  Safe to assume the aircraft is equipped with two magnetos?  If you have a serial number of the R-1, I'd like to review its original configuration to make sure it was set up correctly for the aircraft it is installed in.

If it is not a new installation and has been functioning well previously, has any work been done on the aircraft recently?

[carusoam]

@FlyingDude

Dude, Did you see the note from our EI guy above?

 

Go MS!

Best regards,

-a-

[FlyingDude]

@carusoam  Hey A,

Thank you for following up 

Yeah, I saw that and called EI.  I talked to an engineer on the phone and I will send the unit in for repair/overhaul...