Jumpy RPM-indication

[lalnaes]

I have two 10' SkyViews and on today's flight I noticed that the RPM-indication on the right screen was jumping vigorously. Wwere the left screen was indicating a constant 4500 RPM the right needle was alternating between 4000 and 4800 and anything between. Almost like there was a bad contact on the transducer, but then the right indicator ought to jump as well. Any ideas what might cause this?

 

[thibault]

I have also seen and reported this here on the forum. Only response I got back was, "hmm, haven't seen that before".

 

[dynonsupport]

We're aware of this issue and hunting it down. Thanks for your patience.

 

[thibault]

Here is a suggestion that might cut down on chatter that keeps reporting the same issues over and over.

I presume that you have a formal S/W Trouble Report system. How about letting us have access to it. Other companies do this. For example Flight Prep lets users originate trouble tickets and watch their progress. Those of us who have signed non-disclosure agreements can view all the trouble tickets. Others can only see their own. The need for privacy is related to concern about competitors.

If nothing else, users should at least be able to look up what things are acknowledged and being worked, such as this one. As it is, the only way to know if an item is already being worked is to search the whole forum for it.

Thanks.

 

[Ron_B]

First flight on our RV-10 today. We thought we had a high rpm and would require a governor adjustment. We made a second flight with an optical tachometer and had a top RPM of 2680. Our Skyview would fluctuate up to 3000 RPM before we could slow it down to 2700. This glitch explains our situation.
Ron

 

[Ron_B]

Dynon
Any update on a fix for this yet? After 18 hrs, ours is still reading over 3000 rpm with a 2700 rpm max engine (IO-540), with all controls forward as in take off and initial climb. With a constant speed prop if we lower the prop control (reduce prop RPM) just a touch so the prop rpm is below 2700 rpm the reading reads correctly. It just needs a touch of movement to make the reading stabilize and be correct. Seems odd behaviour?
Ron

 

[dynonsupport]

Ron,
The only bug we know of is a totally wrong RPM on one screen in a multi screen system.

Your error sounds like something we have seen before, which is mentioned in the install guide. You likely need to increase the resistors between the P-leads and the SkyView. For some reason the mags on a 6 cylinder put out a lot more voltage and cause issues sometimes, but these are easily resolved.

 

[Ron_B]

Thanks I was wandering about that and got confused with the post and thought this was our problem. We will get on the resistors.
Ron

 

[RICHAWK]

I have exactly the same issue with an IO-540 (jumpy readings and overeading around 2600 and up it goes to 2900-3000. I have 150k in each lead. I can't get the aircraft cleared for flight because of a lack of reliable rpm gauge. Are we supposed to increase above 150k ? If so how much ?

Richard

 

[dynonsupport]

Basically, go bigger. 250K, 300K, whatever it takes to stop the jumpiness. One caveat. Only go bigger if this only happens only at high RPM. There is a bug that we're chasing which manifests itself as jumpy RPM on usually just one of two SkyView screens, which can happen at any RPM. So if it happens at moderate RPM too, and only at times, it may be that bug.

 

[RICHAWK]

OK bigger it is. I'll report back in a couple of days.


Richard

 

[RICHAWK]

I have now tried resistor values in a continuous range from 30k to 530k by using twin variable resistors. At the lower value resistances I get really stable results but the rpm over reads. Increasing the values enough to make the top end rpm correct, results in no readings at all below about 1500rpm and extremely erratic readings in between. In short there is not a single value that will satisfy the whole rpm range (Factory Lycoming IO-540 with Slick mags.) Finding this really odd as presumably this aspect of previous Dynon products worked OK. Over to you Dynon !

Richard(still grounded)

 

[jakej]

Richard

What's your PPR ?

Jake J

 

[RICHAWK]

Jake,

Funny you should ask that. I set the engine to Lyc 260hp in the belief it gave the correct default PPR. When I checked today it is set to 1 pulse per rev which doesnt seem correct ?

Richard

 

[jakej]

Try the standard settings as given in the D120 manuals ie 1/4 or 1/2 or total number of cylinders eg 1.5, 3.0 or 6.0

HTH

Jake J

 

[RICHAWK]

Jake,

Should get time to try again tomorrow. It looks like it should be set to 3 and back to the beginning trying resistors from 30k up.

Richard

 

[RICHAWK]

Well it turns out I was trying to solve the wrong problem. The PR that works with an IO-540 turns out to be 1.5. With that set correctly the resistor value 0f 30k is fine. Good accurate RPMs and as steady as a rock. Would be a help to future users if the PR data for common engines was included in the manual.

Richard

 

[jakej]

Glad you're smiling again.

Jake J