D180 RPM issues

[xc]

I am running a D180 with Rotax 912s.
The RPM values were fine for the first year of activity, but are under reading by at least 1000-2000 rpm (but without fluctuating ie a straight consistent under-reading).
Wiring has been checked and shows no signs of any damage or wear.

The supplier of the D180 is no longer in business and if the D180 is removed, the aircraft will be grounded.

Any suggestions or help would be welcome.
Thanks, Nic

 

[dynonsupport]

Has the pulses per revolution been changed at all? Other than that, there's no real way for the D180 to break in a way that it would count only some of the pulses, but not all.

You might check and see if there's a 30K resistor installed on the tach wire. For Lycomings this is normal, but for the 912 unneeded. The added resistance could conceivably cause pulses from the trigger coil to be lost, but we'd expect that you'd have seen this behavior all along.

 

[xc]

Thanks for the reply.

The D180 RPM display worked fine for more than 200 hours of flying. Now at full power, RPM is around 3500 instead of 5500+

This phenomenon is worse in cold weather, and occasionally works OK for a short while.

As rpm is critical to good engine health I would appreciate some assistance on this issue to resolve the problem.

Can you send me a spare D180 for a swap out ?

Many thanks, Nic

Has the pulses per revolution been changed at all? Other than that, there's no real way for the D180 to break in a way that it would count only some of the pulses, but not all.

You might check and see if there's a 30K resistor installed on the tach wire. For Lycomings this is normal, but for the 912 unneeded. The added resistance could conceivably cause pulses from the trigger coil to be lost, but we'd expect that you'd have seen this behavior all along.

 

[xc]

On 24th of January the Dynon tech support emailed me to say that with the Rotax 912s, I should install a 30K resistor in the rpm line. Are you now contradicting this specific previous Dynon technical advise ?

This is very frustrating and time consuming especially given that the system worked fine without a resistor for the first 200 hours ??

Please can you provide some customer support on this issue, I really do not wish to ground the aircraft to resolve the problem.

Nic

You might check and see if there's a 30K resistor installed on the tach wire. For Lycomings this is normal, but for the 912 unneeded. The added resistance could conceivably cause pulses from the trigger coil to be lost, but we'd expect that you'd have seen this behavior all along.

 

[dynonsupport]

Sorry for the confusion. You caught some in-between advice.

Our installation guides have forever said to use a 30K resistor with Rotax engines. They're not strictly needed in this installation though, and many many customers have installed with the resistor without ill-effect. However, after noticing some scattered reports of customers seeing erroneously low RPMs we tweaked to the fact that the addition of said resistor could be causing this issue for some customers. We'll update the manual with in the next revision to remove this resistor requirement (SkyView has already been updated).

Until then, the vast majority of customers will be fine either way, based on customer reports. But, if someone is reporting that their RPM is low, and fluctuating, especially (despite having the correct PPR set), removal of this resistor is advised.

The advice is generically the same for any engine. If RPM is jittering high (when PPR is known to be correct), add resistance to cut the voltage and reduce "phantom" RPM. If it's jittering low, lower it. This raises the voltage that the EMS sees.

On magneto'd engines, customers shouldn't need to go beneath 30K though. If anything, they may need to add resistance in our experience.

 

[Steve_G]

I have the same problem with my D-180 (Vans RV9A). The RPMs are too low but then all of a sudden the RPM's will increase to expected values. I have a Lycoming O-320, 30k resistors and wiring looks okay. I believe this has been happening all along (about 100 hrs). Here's an example - yesterday I was crusing at 150kts IAS with a RPM of 1890 and fuel flow of 6.4 GPH. Then - with no change in prop sound or air speed it went to 2350 RPM and 7.7 GPH. It seems that on start-up and take-off I get wrong values but after it runs for a while it corrects. But not every time. Any help appreciated.

 

[dynonsupport]

The fact that both tach and fuel flow are acting up makes me think something might be off with your system clock. Look at how fast second count on the clock when this happens. Are they running slower than they should (you may need to compare against a different clock to notice the difference)? If so, that might explain it, but we would need to see the unit to repair it.

 

[Steve_G]

Yes, forgot to mention that the clock is wrong. I set the local time and that seems to be okay but the zulu is off by 12hrs. The unit is connect to a Garmin 430 via the HS34. The 430 clock is okay. Is there anything else I should check? Thanks.

 

[PhantomPholly]

If the unit is connected via ARINC to the HS34, you should be getting time updates from the GPS. Check for a time zone setting both on the GPS and on the Dynon setups.

 

[Steve_G]

If I have to return the unit how long does it usually take to get it back? Right now the plane is a 2.5 hr drive away at the paint shop. I have no problem driving there to test/remove the unit and that would work out great since the plane is already tied up. Note: It will be probably another 3 weeks (possibly longer) at the paint shop. Thanks.

 

[dynonsupport]

The unit will need to come back here to fix the clock issue. Once here, our typical turn time internally is 5-10 business days. Give us a call at 425-402-0433 or email support at dynonavionics dot com to set up an RMA.

 

[xc]

OK latest on Dynon 180 RPM issues with Rotax 912s.

Recap - worked fine for a couple of hundred hours, then started to read low values espeically in cold weather.

Dynon support suggested a 30K resistor, which just gave consistent low values and then suggested removing the resistor when this didn't work.

The system now gives correct values to around 4,000 rpm then erratic readings above this.

Strangely enough the Dynon also gives a proper readout for the first 30 seconds or so after take-off ie, a solid 5400rpm - but then goes haywire, fluctuating between low and high values.

Reducing the engine power to below 4000 rpm settles the display until power is increased - when once again all goes haywire.

I have tried:
a) Complete brand New Dynon 180 with no improvement (so display is ok).
b) Changing input from Left RPM to Right RPM input - no improvement.
c) Changing to screened cable for the rpm input line.
d) Running a new earth to the engine from a centralised instrument earth.

Other readings such as oil pressure all read correctly.

It would be really good to resolve this problem as the alternative is to fit an analogue rpm display.

Any assistance appreciated. Cheers, Nic