Tachometer problems

Sean, let's remember that a propeller in windmill is significantly more drag than one that is stopped in flight. In large prop aircraft the prop is put into a feather position to increase glide.  Just saying I still think the prop is the object we need to control. 

Cheers

Howdy Sean,

Hope all is well.

Quote:

"Just saying I still think the prop is the object we need to control."

I agree with RW on the prop importance which also directly affects the engine in several ways. Seeing the engine rpm in flight tells you several things vs seeing what rpm the prop is. I care more about the engine running and longevity over knowing what prop rpm on a gauge. Prop pitch the engine well and everything is good. Over pitch it and it can take its toll over time. Then it can get costly. Good prop pitch is like controlling your fuel mixture, proper spark plug temp range and gaps, balance on the prop, air intake and running rpm's. They all play a part in the big picture. Think of each one as a disease people could get. Like  contaminated blood (oil system), electric issues left unresolved (nervous system), smoking and doing things that cause cancer, ect..

They all play a part in our body over the many years so we try and do the right thing so we don't end our life too early.

So prop rpm and pitch understanding is important for longevity.

Jeff Blakeslee wrote:

Paul,

The fact that this has always been a problem makes me think it’s systemic rather than a part failure. I believe you need to know if Tecnam and/or Garmin has seen this on other Rotax powered aircraft using the GEA 71.  So, you may have to engage your Garmin dealer or Tecnam - as painful as that may be!  

With both engines now exhibiting this behavior this can’t be isolated to your aircraft.  The number of Rotax engines installed in certified aircraft with the G1000 must be very small, so this kind of thing has not had much chance to get worked out.  There are some folks on this site that are quite good with electronics, can you post a simple diagram of how the coils are wired to the GEA 71?  Maybe just markup one of the diagrams in the GEA 71 installation manual.  Good luck with this Paul.  

Sorry I guess I was maybe not clear that it is something that I noticed on another of our engines on another aircraft, a slight tick or instance where the tach showed a fluctuation that was clearly a false indication but hasn't been reported since it's first noted instance.   I am ready to run this engine to see if she's happy now that I have re configured the wire routing, I will keep this thread updated as for diagram, I will attach it here.

This is the old one and not the one brought to us by the avionics tech from Tecnam

Rotax Wizard wrote:

Sean, let's remember that a propeller in windmill is significantly more drag than one that is stopped in flight. In large prop aircraft the prop is put into a feather position to increase glide.  Just saying I still think the prop is the object we need to control. 

Cheers

As so often happens, the respondent addresses the detail, of the analogy,  while avoiding the principal message - No engine No prop.

While having no prop and an operating engine would be equally disastrous, my contention is that ; - The engine is the aircrafts primary means of leaving the ground & staying aloft. Its the engines motivation of the prop, which allows for all this.

I do not mean to suggest that the prop (along with all the other vital components of an aircraft) should be forgotten, somehow reduced in importance (no elevator control may see an early departure from this life).

Fact remains, in both direct drive & geared drive, the engine must be managed, in its own right. 

If we accept that, in an operating aircraft, engine speed is the main indicator of its health (who doesn't have a quickening of the heart, if there is an uncommanded change in engine note/smooth operation); 

In a direct drive the relationship between engine speed & prop is a no brainer - set either one & you have the other.

In a geared drive, set the engine speed, within its known (Rotax) parameters and you really don't need to be concerned with prop speed, as it will be a constant.

Should the prop be a Constant Speed /In Flight Adjustable - management of the propeller operation follows engine power setting/changes and we check/adjust for MAP, EGT & other parameters of the engine.

This weird (to me) idea, that a Rotax powered aircraft must be configures to simulate a direct drive engine/aircraft ,makes no sense at all and is driven by the need to conform to a perceived convention, that does not exist. In so doing misdirects the (student) pilot from the need to manage the all important power plant/engine, to the propeller. Much good this will do the pilot when the engine stops.

Tell me how I have this wrong.😈

1) Engine vs Prop rpm - it doesn't matter. Mph vs Knots vs Kph - it doesn't matter. kW vs HP - it doesn't matter. All convey the same information. If you're experimental, use whatever you want. Certified, and the units are specified in the Aircraft Flight Manual via the written specs and more definitively, the required panel markings. In the copy for a USA P2006t, rpm limits are placarded using prop rpm. Similarly so for the Diamond HK-36TC. Changing the manufacturer's default is not up to the owner/pilot without official blessing. 

2) To the OP's question: various feedback may point to the solution, IDK. But many many weird electrical problems I've dealt with turned out to be more with the grounding than the signal. Ground loops or noise on the ground itself can cause havoc, especially for long cable runs. 

3) The MT hydraulic prop is a not-quite constant speed prop. A typical Lycoming/Conti Hartzel/McCauley setup will give a rock solid rpm for any normal throttle setting. The MT, not so much, and least on the HK-36 I sampled. Set an rpm, change the throttle, and the rpm will vary, less so than it would for a fixed pitch, but it will vary and require tweaking after the change.