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prkaye

Well Known Member
I have the Dynon D-180. I have the float fuel senders and did the calibration procedure, but the fuel gauges just don't provide me with any level of accuracy, and when they just start to get into the yellow region my tanks are almost empty. I do have a fuel flow sender and use the Dynon for Fuel flow display.

I hadn't got around to looking at using the Dynon "Fuel Computer" until recently. I had *hoped* that the fuel computer would use the fuel flow value to continuously subtract the appropriate quantity from the full value, thereby providing you with a much more accurate fuel quantity information. Of course this would require you to tell the dynon which tank you were running off at all times. From what I read in the manual, the Dynon fuel computer does *not* do this, however, and it appears I am stuck with the fuel gauges. Have I missed something?
 
FUEL'S GAME

I think you are begining to understand that you never know exactly how much is in the tank until the engine starts to cough. Reserve is always suppose to be just that, held in reserve. Most gauges are not that great be it GA or experimental. The sight gauges were nice in some old a/c but there is unusable in every system. Learn the settings that give you 7.5 gph or 8.5 or 14.2. We are supposed to fly by time. Trying to fly down to the last 20 minutes of total fuel is a fools game. I lost a friend in an aircraft who bet his life on that and lost. John Denver took off in a long eazy that could fly 10 plus hours on a load of fuel and crashed trying to switch to fuel in another tank. My -6 will fly for 4 hours easy with reserve. Why push your luck? The weather 500+ miles from your departure airport is seldom the same and you must always have fuel to reach an alternate.
 
Funny how so many threads quickly fill-up with common basic safety principles being rehashed in as many different ways as people can find words to articulate them.

Clearly, flying till you're out of gas is a bad idea and everybody knows that a pilot should always visually check the fuel level before takeoff and not plan to fly longer than the known fuel allows with a healthy reserve. Everybody learns this as a student pilot, and we get reminders of the importance of this principle when accidents happen like the ones you mentioned.

However, I think everyone can agree that having reliable in-flight fuel quantity information can at least sometimes be a good and useful thing :rolleyes: . So getting back to the actual topic of my thread, which was the Dynon Fuel computer system... am i correct that the Dynon does not provide the feature I described? Do later versions of Dynon products provide this?
 
Fuel flow sensor installed?

Do you have a fuel flow sensor installed? If so the Dynon totalizes the flow very accurately to display gph, mpg, fuel used, fuel remaining... Assuming you start from a known level, typically full. The totalizer does not interact with the level sensors. The level float arms might be sticking on the indents that make up the rheostat, or perhaps more likely they were a bit sticky when you did the initial calibration giving you bad data... take a look at the resistance values throughout the float range (generaly 0-16 gallons) and graph them... it should be reasonably linear... You should be able to edit the sensor data in the Dynon directly to reflect a best fit from your graphed data to adjust for any recorded points that are obviously in error.
 
If so the Dynon totalizes the flow very accurately to display gph, mpg, fuel used, fuel remaining...
Click to expand...

This is what I was looking for. Yes, as I mentioned in my original post I do have a fuel flow sensor (it's a Red Cube) and I display my fuel flow on the EMS at all times. However, I couldn't find anythign in the manual describing how to tell the Dynon which tank it is using at any given time so as to display fuel remaining in each tank independently, based on fuel-flow computations and not on the fuel level sender. Does the Dynon not allow you to do this?
 
Change your paradigm...

The totalizer needs a known starting point that YOU provide... The fuel computer does NOT use the level sonsor data. You set up what your total fuel is and then indicate when the tanks are full... the totalizer does not know or care where the fuel comes from... it is just accounting for the fuel that flows through it.
 
Right. That's what I suspected. It would be nice if it allowed for independent totalizers for each tank, with a way to select which tank you're running on at any given time. You tell it when you fill both tanks, and you always tell it which tank you're running on. Then it would do exactly what you describe except it would do it for each tank independently. This would be an easy thing to add to the software (doing exactly what you describe, except for each tank independently). The only downside would be if you switch your fuel selector and forget to change the setting on the dynon, the dynon would be subtracting the fuel value from the wrong tank.
 
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prkaye said:
........ However, I couldn't find anythign in the manual describing how to tell the Dynon which tank it is using at any given time so as to display fuel remaining in each tank independently, based on fuel-flow computations and not on the fuel level sender. Does the Dynon not allow you to do this?
Click to expand...

Correct. Dynon does NOT do this.
 
Check your float calibration...

I think that you have an issue with your floats... my tank floats display within a gallon or so in their range; plenty accurate for tank level... my totalizer is accurate to about a tenth of a gallon. Check your float calibration.
 
Page 6-14 in the install manual...
Is this what you're looking for?
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No. That doesn't answer my question about whether the Dynon will allow you to do the totalizer thing independently for each tank. However, Brian and Stephen have confirmed my understandign that the answer is NO. A real shame, because this functionality would only require a software update, and the extra code would be pretty simple (essentially duplicating the code they already have for the totalizer and modifying the interface).
 
???

If you use the totalizer to display tank level you would end up ignoring the only mechanical measure of actual fuel and would not account for undocumented changes in level... from a leak, draining sumps, syphoned away, or more typically from adding fuel and forgetting to hit the reset. Even though the tank levels might not be as accurate as they could be they are from a real mechanical reading rather than a derived virtual value; that's a good thing for redundancy in a critical system.

For anyone; if your level sensors are significantly in error, check the calibration data.
 
and would not account for undocumented changes in level... from a leak, draining sumps, syphoned away
Click to expand...

Good point there. But you're not objecting to the capability, really - just to its potential for misuse. By your observations, obviously one would want to only use this capability supplement visual checks and the fuel gauges.

I generally think more information is better, but as with anything, if the information isn't properly managed and combined with other sources, it can certainly be mis-used. I certainly wasn't advocating using fuel totalizers as the *sole* mechanism for fuel management.

For anyone; if your level sensors are significantly in error, check the calibration data.
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Yeah, I should probably drain the tanks one of these days and re-do my calibration procedure. I just need to find a time when nobody will mind me hogging the fuel pumps for the time required to do this.
 
When you calibrated your tanks was the airplane in flying attitude? My Dynon is right on the money on fuel level and fuel flow. When I fill up I can tell you within 1/10gal how much it will take. How do you expect the Dynon to tell you fuel flow and total from each tank when the transducer is between the engine and fuel selector. You would have to have two transducers one one each side before the fuel selector to do that.
 
fuel level

I agree with Yakdriver, my float senders and Dynon are very accurate in staight and level flight, the best of any airplane I have owned. They are totally inaccurate on the ground because of the tailwheel attitude. They are totally inaccurate in flight if not in co-ordinated flight, the ball off center will also show how the fuel sloshes over to one side of the tank affecting what the fuel float sees. Does your airplane fly ball-in-center? If not, correct that first. If I run a tank in flight until it shows four gallons, it will take 16+ gallons to fill. Drain your tanks, level your airplane and recalibrate. Your setup should really work great. Unless you had a faulty sensor connection on one tank, I doubt you would have that problem with both tanks.
 
The fuel flow, with the proper K factor, is VERY accurate. After you've filled tanks a few times and feel comfortable that it IS accurate, you can use it to help adjust your fuel gauges. Simply run on one tank only, burn X amount of fuel and then adjust the sender value till you match what you know is in there. Say you use 9 gallons in one tank, adjust the gauge till it reads half. Look at other values and if they are not fairly linear adjust those also.
Right down the current values before you start. If they are not accurate now, you've got nothing to lose and it's easier than a full re-calibrate.
 
It might be simple to press a button for left tank or right tank. But what if you forget...and people will. The TOTAL fuel as based up the fuel flow hardware/software is very accurate once the K-factor is calibrated.

Then you can use ops procedures to ensure that you know how much is in a tank.

Example: Run ten gallons (use fuel remaining from the fuel totalizer) then switch tanks. Once you have run ten gallons from each tank you have about one hour duration in each tank and can select how low you will go on the remaining fuel before you switch tanks.

My guess is that this is a far better solution that what you wish to do.
 
Step to calibrate

For those that have done the Dynon fuel gage calibration can you tell me the steps. I need to do this soon. Instruction book says follow on screen directions. I want to make a checklist for this so I don't tie up the pump longer than I have to. I know level the plane first then what, two gal at a time, is a helper to man the fuel nozzle a good idea? Can I record this stuff inside the Dynon and get it later? If you can give me a summary of the steps it would be greatly appreciated. Thanks for the help.

Cheers
 
The physical location of the float sensors and dihedral of the wing will prevent accurate fuel level readings above about 16gals per tank as the floats will be at their highest point at 16gals (RV8 tanks).

I had a helper push the buttons on the screen as I added the fuel. If your calibration is the first time the tanks have been full since construction I recommend you give the wing a good rap with the palm of your hand just above the float location. Do this after each 2 gal addition prior to pushing any buttons. This helps ensure the senders break free of any residual friction present after sitting in a fixed position for several years. If you don't do this you'll likely get a very flat calibration curve which will be totally inaccurate.
 
I have the D-120 engine monitor in the -10, probably all the same circuitry as your 180 and is super accurate, regarding remaining fuel and fuel at the arrival waypoint. The tank gauges are also very accurate and I check the fuel added every time I gas up and it's within tenths of what it said remained.

All that's important is fuel remaining to me, not which tank it's in...that's my job.:)

Best,
 
Mike-

Make sure you give time for the fuel to settle before pushing any buttons on the Dynon. Depending on your tank construction and how much proseal may have been used around the relief notches in the ribs, it can take a while for the fuel to flow to the inboard bay where the senders are. (You'll see the resistance value on the screen gradually change until things settle.) Doing this generally takes about 10 minutes or so per tank, so I would recommend using the fuel pump at a time when others are not likely to be using it. Whatever you do, don't hurry it though. And, yes, a helper is a good thing unless a lineboy is there filling for you.

If you want to see how it works, go ahead and do a practice run on calibrating the Dynon just to see how the buttons work. You can then cancel that practice attempt out once you get to the real thing. It is, in fact, probably going to tell you to add two gallons at a time, pressing a button after each 2. At the very end of the process, Dynon will give you a chance to record all the resistance values for your records. Make your self chart with 3 columns: the first for gallons at 2g intervals up to the capacity of the tank, a column for the resistance levels associated with those gallon numbers, and a column for your dip tube level at each. Related to the third column, remember also to dip the tank at each interval. That way you can calibrate your dip tube at the same time. (For your first few flights you're going to want to trust the dip tube more than the Dynon, especially until you see if your K-factor is accurate for your setup.) Finally, note Ken's comment above: be aware that if you have float senders, they'll only indicate up to about 14 gallons (at least on the RV-9) depending on how much travel you bent into the wire holding the float. Above that, your fuel level display will simply say "14+" or whatever the max value it is. For the RV-8 it sounds like that number is more like 16.

Hope this helps. Good luck.
 
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I've calibrated mine a couple of times and they still tell me that there is more fuel than I really have at the low end. I have capacitive sensors.

To answer your questions:

-A helper is not required. I used one the first time I caled but not the other times.

-There is a terminology issue with the cal that got me once but I can't remember exactly what it was. It was something along the lines of the screen showing the words "fuel add" vs "fuel added". Like I said, I can't exactly remember but the issue with my brain was understanding if I added fuel, then press the button, or press the button, then add fuel. This was an issue at the end of the cal when the tanks were full. There is a point at which you tell the Dynon that the tank is now full. If you press the button at the wrong time, it will think that you have 2 gallons less than you actually have. Now you need to burn off all that fuel and then do it all over. Ask me how I know.

On the day you plan to calibrate, do a short dry run in the hangar so you understand when to press the button.

-After each two gallons, make sure you allow enough time for the Dynon to be ready for more gas. It will tell you on the screen but I found that you can easily jump off the wing and start filling the next two gallons before it's ready.

-It will most likely ask you during each 2 gallons of gas if you actually added fuel. Maybe that's only with capacitance gauges but it basically says that it didn't see a whole lot of change during those 2 gallons and it's just checking to make sure you actually did it. This seems to be normal behavior.

Good luck.
 
Gas Can

RVG8tor said:
For those that have done the Dynon fuel gage calibration can you tell me the steps. ..........If you can give me a summary of the steps it would be greatly appreciated. Thanks for the help.

Cheers
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Mike,

For the fuel calibration you start with an empty tank and the calibration screen up for the appropriate tank. You will then add two gallons at a time and tell the Dynon you did so. It then churns away for 15 seconds of so before the next step. As you get to the top the floats stop rising. The Dynon will ask you "Did you really add fuel because the value didn't change?" You just say yes and move on.

I did it with a six gallon fuel can I marked in 2 gallon increments. Once done with one tank I drained the fuel out for the other tank. It's not the most expeditious way but I didn't want to take a tail stand over to the pump area and tie it up for too long, and I didn't want full fuel for first flight.

If you had a helper it would be great. One person could sit in the cockpit and push buttons after the fuel settled down. If you do it by yourself, I'd figure something to hold the nozzle while you go to the cockpit and advance the steps. Laying it on the ground would not be cool.

Don
 
Great Help

Thanks guy for all the input I am getting the procedure now. I also ran across some posts from 2009 so I have a good feel for what I need to do.

One thing I read on another post is this; since the full resistance value starts at around 15 gal for the RV 8, did you guys still add fuel on steps after this or did you just push the button as if you had. It seems adding more fuel serves no purpose but maybe there is some small change the instrument can detect.

I like the idea of calibrating a dip stick but I have to have the plane in an inflight attitude for the calibration but for preflight fuel level checks it would be in its normal on the ground attitude. Now I have the nose wheel so not a big difference but this could be significant for a tail wheel plane.

Cheers
 
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