Hobbs Meter

[Bill Hertzel]

I am having trouble getting the Hobbs and Tach meters to operate correctly.

My RPM 1 setup is as follows...
100%RPM= 5800
Display = 6000
Hobbs Minimum RPM = 1000
Hobbs TACH 100% RPM = 5000

The engine is a 912is monitored through an MGL RDAC-CAN.

The problem...
With the Engine stopped and the Lanes OFF, the RDAC-CAN sends default data.
The RPM default is reported as 9001 rpm as the indicator that the RDAC is not receiving CAN Data from the engine.
The HOBBS meter falsely starts running as it sees an RPM above the minimum.
And the TACH Meter runs at nearly double speed because it thinks the rpm is 9001!

The second problem...
The HOBBS only ticks off 0.01 hours (36 sec.) for every 144 seconds.
It is running at exactly 1/4 speed.

I could multiply the Hobbs by 4 as a workaround, but the meters running when the engine is OFF is a No-Go!

[rainier]

What EFIS are you running ?
I know this was something reported in the past so current systems handle this correctly.
If you have something with an iBOX make sure you update it to the current firmware.

[Bill Hertzel]

I have an 8.5" Explorer iEFIS Lite that monitors a Rotax 912is engine via an RDAC-CAN

System Status Info...
iEFIS G3 Version A 1.1.0.3
FlightOps Version A 1.0.0.3
Serial: 170400177

[rainier]

The lite (if you are running current firmware) will not count the hobbs or tach if the RPM reads the 9001 code.

[Bill Hertzel]

Rainier,
Thanks for the response.
I know we both believe that the Hobbs should NOT be Counting with a 9001rpm, but it is.
It might be fooling you because it is running at 1/4 speed and it takes 2:24 minutes to get the first 0.01 tick to show up.

This is on a live, installed iEFIS not the SIM.

I set up a screen with the Hobbs,Tack and RPM next to the Stopwatch. Attached are two montage photos showing the results.

Photo A shows the Firmware status and the RPM/Hobbs setup screens.
The bottom photo shows the Hobbs still at Zero after 6 minutes with the lane active and the RPM at Zero as expected.
The Bottom Right Shows the Hobbs after 6 minutes with the lanes OFF and the RPM displaying 9001.
The Hobbs has ticked off 0.02 (Should have been 0.10) and with the TACH running (9001/2500) 3.6 times faster at 0.10 (Should be 0.36)
Both times are 4 x slower than expected.

MGL_Hobbs_A.jpg (255.07 KiB) Viewed 6513 times

Photo B ...
The Top Left photo shows Zero on both timers just after turning OFF the lanes to produce the 9001 RPM.
The Top Right Photo Shows that after 2:20 the Hobbs is still at zero. It ticked to 0.01 at 2:24.
The Bottom Right photo shows that at 2:36 The Hobbs has ticked to 0.01. Should have been 0.04 by this time.
The Bottom Left photo shows that after 24 minutes (0.40 hours) the Hobbs has finally made it to 0.10 with the TACH at 0.36 as it is running 3.6x faster.

MGL_Hobbs_B.jpg (240.49 KiB) Viewed 6513 times

It is strange that the timers are running 4 time too slow at the default 9001 RPM.
I was not able to operate the engine at Running RPM to confirm that the timers operate at correct speed under real world conditions.

If I am doing something wrong, I will be happy to admit it and correct the problem.

[rainier]

The Hobbs tach RPM is set way too low - your 100% RPM for a 912 should be around 5400.

Can you please install www.mglavionics.co.za/Beta/EXP3.BIN (That is version 1.1.0.5). Just want to make sure we are on the same page.
Also please check if you get the CAN RDAC diagnostics in the diagnostics menu - you can see all the diagnostic information from the 912 ECU.
The EFIS uses the presence of this information to detect if it has a CAN/CAN RDAC connected and only then does it look for the 9001 code to skip the hobbs calculations.

[Bill Hertzel]

FYI, I intentionally set the TACH 100% point unrealistically low only for testing purposes.
This has confirmed that it is being calculated based on 9001 rpm.
- - -
The BIN file installed successfully and Ver. 1.1.0.5 is current.
The diagnostic screen shows "RDAC is connected" and RPM1 = 9001
I do not see anywhere it specifically shows a "CAN RDAC".

I do NOT have an external iBOX even though it shows "iBOX is Connected".
I assume this is the Internal iBOX within the iEFIS LITE.

The HOBBS is still running at 1/4 speed at 9001rpm and Stopped at Zero rpm.
No change!

MGL_Hobbs_C.jpg (213.68 KiB) Viewed 6492 times

[rainier]

Thanks for trying that out.

Are you not seeing a diagnostics option for "CAN RDAC 1 ECU status information" ?

[Bill Hertzel]

How could I not keep seeing that! Embarrased!!!
YES! "CAN RDAC 1 ECU" and #2 are there big as day!

MGL_Hobbs_D.jpg (241.93 KiB) Viewed 6474 times

The RPM Toggles from 9001 to Zero with thes Lanes ON.

MGL_Hobbs_E.jpg (236.63 KiB) Viewed 6474 times

And the Lane status for both sides are available.

MGL_Hobbs_F.jpg (231.02 KiB) Viewed 6474 times

May I suggest that the Question is Not why the Hobbs is running at 9001 RPM but WHY is it running at 1/4 real time speed???
Answering that might lead to the solution quicker.
- - -

To the forum members,
Is there anyone else with a 912is engine that can confirm that your Hobbs meter runs with the lanes OFF and the RPM showing 9001.
Watch the HOBBS for 8 minutes. The number should not change. If you see it change 00.03 hrs or 00:02 minutes, speak up.
Even negative result reports will be helpful.

[bkc]

Bill, sorry I am a few months late with a response. I have a 912is and can confirm that the Hobbs on my iEFIS (challenger lite) runs with the lanes off and RPM at 9001 at about 1/4 rate. I am not flying yet so this hasn't bothered me too much since it doesn't matter if I reset the EFIS Hobbs by removing the power from the EFIS. However, this appears to be a bug in the software. I have the latest firmware update (G3).