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Tach hours, K Factor etc

mike newall

Well Known Member
Sponsor
Running through testing and a couple of questions to 12 ers.

Dynon Skyview - legacy install - 1 upload from Vans (2017)

Is there a way to display or record tacho hours rather than Hobbs ? Never used Hobbs, always Tacho hours but can't find it in the set up.

K Factor - we are indicating 10 gph which I think is a tad high !!! Does anyone have ballpark K Factor numbers for a standard red cube Rotax install please.

Re pitched the prop to pin 2 setting, will test this week and checking the skins for wing low. Other than that, all going swimmingly :D

Getting an annoying buzzing that is obvious on the YouTube vid. Cycles at 2 second intervals, coming out of the intercom as it disappears in ISO. We have run for 2.5 hours now so the Dynon back up battery won't be fully charged - any factor ?

Suggestions welcomed.
 
I have been using 107,510 as my K-factor for the past 300+ hours. This value tracks well with my actual fuel use. My flights typically average about one hour in length -- if you take many multi-hour flights your K-factor might be different. I find quite a bit of variance in the indicated fuel flow (gph) value in flight but at the end of the flight the overall fuel consumption numbers are very close (e.g., within 0.1 - 0.2 gallons per 4.5 gallons used).
 
Going from memory at work now, in the set up menus are a variety of options to add/change the data points and locations on the various screens. The reason Hobbs is important is that service requirements for the Rotax are based on engine hours, which will always be higher than tach. Hence the need to track Hobbs.
 
As Steve said, Rotax requires that all maint. be done relative to Hobbs time.
It will be important that maint entries in the maint records are listed as hobbs time if you ever file a warranty claim, etc.
For this reason, the ability to configure tach time is not enabled, if you are using Van's settings file.
 
If your GALS (or LTRS) USED reads higher than you expect,
increase the K-factor.
Try setting the K factor while cruising at 5000 RPM so that GPH equals 4.9
 
Computing a K-factor value adjustment doesn't require a guess.....

It is a simple math problem and the formula is usually supplied with the documentation for any unit that does fuel flow.

Make a flight that will burn enough fuel to give you a good data point ( couple hrs). Start with the tank filled to a point you can accurately refill to, and the fuel computer gallons used value zeroed out.

After the flight, refill the tank to the same level to get an actual fuel used value.

Multiply the computer indicated fuel used times the current K factor, then divide by the total gallons actually used.

Computer indicated Fuel used X Current K Factor / Actual Gallons Used = New K factor

Program the new K Factor into the unit.

Do another flight to check the accuracy.
If it is still off slightly, do another computation using the new data. It will usually be within 0.1 gal per hr or so after two adjustments.
 
Last edited:
As Steve said, Rotax requires that all maint. be done relative to Hobbs time.
It will be important that maint entries in the maint records are listed as hobbs time if you ever file a warranty claim, etc.
For this reason, the ability to configure tach time is not enabled, if you are using Van's settings file.


Thanks Gents - still getting used to these whizzy little motors ;-)

Will look into K Factor next time it stops raining !
 
not to change the subject.. but on the rv-12iS (fuel-injection), does it also use a flow sensor? or does the fuel-used info come directly from the rotax electronics (since it should know exactly how much fuel it injected into the engine).
 
As for the intercom buzz, make sure the mic jacks are isolated from the airframe with insulating step washers. If there is a music jack, disconnect it.
 
I would go down that route, except for the fact the buzz is regular.

Bzzz..........Bzzz.........Bzzz........

About every 2 seconds.

Not loud but a PITA
 
I think I have figured it out........

So, because the flight testing is being done at a non fuelled airstrip, I decided to use the direct reading gauge for flight testing and then go to a gassed airfield with min fuel, drain down and then be able to safely dispense fuel gallon by gallon.

Now, the annoying buzz is directly in time with a warning thingy on the Dynon and I am now wondering if they have set up two levels of alarm - low level attention getter and OMG - yo, gunna perish boy ! It is the only uncleared alarm because the Dynon thinks I have no gas !

Will ask Dynon and report back further.
 
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