Adding a second fuel flow sensor

[seagull]

My fuel flow numbers run high at full throttle during the first part of my flights with a full tank and climbing, as much as 6.5 gph. I know the numbers are wrong since I have done actual refill after an hour and it is around 5.0 - 5.5. I am not sure what causes the high readings, bad fuel sensor, more return flow because of more head pressure, cold flow sensor.

My average gph flying 2 people and a dog at 115kts, 5400 rpm for a full tank, 3.5 hrs, measured by refilling in the same location is repeadly 4.33 gph. My Dynon flow rate reads 4.3 after the first hour of flying but it shows excessive total use because of the first hour is high.

In any case I was thinking if there was a sensor reading the return flow back to the tank and subtracting it from the total there would be a more acurate total and no need for a K factor.

I was wondering if anyone has done 2 sensors.

 

[Ernie]

I installed two sensors on my 12. My results it diour that it didn't do much to improve the reported flowrate. Now I have too adjust two correction factors instead of one.

 

[seagull]

I installed two sensors on my 12. My results it diour that it didn't do much to improve the reported flowrate. Now I have too adjust two correction factors instead of one.

I may be wrong but I thought the Dynon had a way to subtract the return flow from the total flow That should eliminate the K factors completely.

 

[rvbuilder2002]

I may be wrong but I thought the Dynon had a way to subtract the return flow from the total flow That should eliminate the K factors completely.

The D-180 EFIS did.
The Skyview EFIS does not.

 

[j4cbo]

The D-180 EFIS did.
The Skyview EFIS does not.

Eh? From page 7-62 of the latest SkyView installation guide:

 

[rvbuilder2002]

Eh? From page 7-62 of the latest SkyView installation guide:

A standard build RV-12ULS installation (this is the RV-12 forum).

 

[seagull]

A standard build RV-12ULS installation (this is the RV-12 forum).

Scott, can you explain what you mean, I’m confused.

 

[Piper J3]

A lot of talk about fuel flow calculation not being exactly correct... Remember older Cessna float-style fuel gauges in the wing-root where you basically have no idea how much fuel you actually have onboard? Or, electric analog gauges in Pipers that were worthless?

EMS fuel gauge has hysteresis built-in to accurately depict fuel quantity remaining even when fuel is sloshing around in the tank. My RV-12 has four methods to determine fuel quantity. I can stick the tank, sight gage on side of tank, Mueller float gage on top of tank which can be seen in-flight, and very accurate EMS fuel gage. If I ever run out of fuel, someone should shoot me…
-

 

[seagull]

I appreciate all the replies for why I don't need to do this. Nobody addressed the original question, "has anyone done two flow sensors".

According to Dynon pin 19 can be setup to subtract the return flow.

My follow up question if someone had added the return sensor was "where did you physically put it".

My purpose of a second sensor is not to prevent running out of fuel. It is to know the exact flow at any phase of flight. I have noticed by cycling the electric pump the reported flow rate changes signifigantly although the engine doesn't skip a beat. One possible benefit would be if vaporlock should occur the actual flow rate would drop to zero. I could set up an alarm that would give me a 15 second warning the carb bowls are about to run empty. The original post described a 6.5 gph flow rate, although inaccurate it concerned me that I may have fuel going somewhere other than into the engine. Using a second sensor would read the same but I could trust that reading over an estimated system of one sensor.

 

[seagull]

I bought the second FT-60 (red cube), this is the same model already in the plane. I’ll be installing it during my conditional at the end of the month to read the flow returning to the tank.

What is interesting is the manufacturers instructions, “ If the aircraft has a fuel pump(s), the flow transducer MUST be installed downstream of the last fuel pump. Installing the transducer upstream of the fuel pump(s) can cause vapor lock and jumpy / inaccurate readings”

The current transducer is in between the two fuel pumps, not what the mfg recommends.

 

[seagull]

…..another part of the instructions says “This transducer must be suspended between flexible hoses on the inlet and exiting ports. The hoses must be supported within 6 inches of the transducer”. The transducer in mine is solid mounted on metal lines.

 

[rvbuilder2002]

I bought the second FT-60 (red cube), this is the same model already in the plane. I’ll be installing it during my conditional at the end of the month to read the flow returning to the tank.

What is interesting is the manufacturers instructions, “ If the aircraft has a fuel pump(s), the flow transducer MUST be installed downstream of the last fuel pump. Installing the transducer upstream of the fuel pump(s) can cause vapor lock and jumpy / inaccurate readings”

The current transducer is in between the two fuel pumps, not what the mfg recommends.

…..another part of the instructions says “This transducer must be suspended between flexible hoses on the inlet and exiting ports. The hoses must be supported within 6 inches of the transducer”. The transducer in mine is solid mounted on metal lines.

The system as designed and detailed in the KAI is well tested and proven by the design team and many 100's of other RV-12 owners.

Since yours is an experimental version you can modify the system any way you like.
While doing so, keep in mind the number one cause of engine stoppage in experimental aircraft accidents is fuel system related. I imagine all of the builders of the aircraft involved in such accidents thought the had a good idea.

 

[seagull]

Hey Scott, I wasn’t saying YOU designed it wrong, don’t take it personal. I have 1300 flawless flight hours on mine…….. but I have seen inaccuracies in the readings given by the flow sensor, and talked to other -12 owners that have seen the same. The mfg has recommendations, Vans went against those recommendations and it has worked…… mostly.

As always thank you for your positive input on this forum.

 

[Avanza]

Accurate readings

There is lots of instructions on where to mount the red cube.
What is important is to understand that the red cube will only provide correct
fuel readings if there is 100 % fuel in the line.
As long as there is 100 % fuel (NO bubbles), the red cube can be mounted
anywhere in the line.
High temperature, 90 deg fittings (pressure drop) or vibration may produce bad readings.
Fire sleeve, cooling air, no 90 fittings (low pressure drop), no vibration will
increase the likelihood of 100% fuel in the line.

Good luck

 

[Piper J3]

I guess I just don’t understand the fascination with wanting to know fuel burn rate and tank level with extreme accuracy... So, what if your burning 4.85 gph instead of 5.01? The legacy RV-12 with Moeller float gage has excellent redundancy to inform pilot of amount of fuel onboard. The pilot can easily view the Mueller gage over their right shoulder in-flight to verify the EMS fuel gage. I have an item on my preflight checklist to compare Mueller/EMS fuel gages before flight. I have never seen a mismatch in the two fuel quantity reporting methods. This adds tremendously to the comfort level when making in-route decisions. Much better than aircraft with fuel “hidden from view” in wing tanks, and almost as good as Piper Cub, with fuel level wire directly in front of windscreen. However, lots of people have run Piper Cubs out of fuel with poor decision making.

Personally, I would not add any more complexity to the ULS fuel delivery system. Two carburetors, two fuel pumps, fuel flow transducer, fuel delivery rail on top of hot tightly-cowled engine… A lot of things need to work correctly to keep engine purring along. I have had vapor lock on takeoff and I can tell you it’s not a pleasant experience.

I say…. fly the airplane safely and enjoy the scenery whisking by at 115 knots…..

 

[seagull]

Avanza,
My comment was the manufactuer of the sensor said where and how to mount it, Vans decided to do something totally against the manufactuers design in mounting and placement. Whether it has been working correctly for 10,000 flight hours or not was not my point. Don't shoot the messenger.

Piper J3,
If you read my posts you would quit saying I have a facination with fuel level. I have said many times that my interest is knowing the usage in different phases of flight. Your obsession with vapor lock is one of of the driving concerns. Knowing accurate fuel flow would warn of an impeding vapor lock situation 15 seconds before the engine starves itself of fuel.

 

[rvbuilder2002]

Hey Scott, I wasn’t saying YOU designed it wrong, don’t take it personal. I have 1300 flawless flight hours on mine…….. but I have seen inaccuracies in the readings given by the flow sensor, and talked to other -12 owners that have seen the same. The mfg has recommendations, Vans went against those recommendations and it has worked…… mostly.

As always thank you for your positive input on this forum.

No problem... wasn't taking it that way.
My point was that manufacturers recommendations are often general info for the masses (such as people designing their own fuel system) and often say that as an OEM the aircraft manufacturer is responsible for the system design and testing. This even applies to the Rotax engine installation as stated by Rotax in the installation documentation.

Point being, if it is installed differently from the basic install info it doesn't necessarily mean it is wrong.

 

[Piper J3]

Knowing accurate fuel flow would warn of an impeding vapor lock situation 15 seconds before the engine starves itself of fuel.

Be sure to let us know how that works out....

And... what would you do during the 15 seconds prior to engine shaking itself loose from the airframe?

 

[seagull]

Be sure to let us know how that works out....

And... what would you do during the 15 seconds prior to engine shaking itself loose from the airframe?

Jim you are so cynical. If vapor lock occurs on climb out, the most dangerous point of a flight, the fuel will quit flowing into the carb bowls. At that point the flow sensor will report no flow. The engine will run normally producing full power, not rough, until the fuel in the carb bowl is exhausted. In that 15 seconds or even 5 seconds, I would stabilize flight and look for a suitable landing site. That is an amazing amount of time when an emergency occurs.

 

[Piper J3]

The problem with vapor lock on 912ULS is one carb / fuel line will boil its fuel and the other carb will continue to make 100% power. The imbalance will be so rough that the best thing to do is to reduce power – not a good option, but the best option. So, even if the “EMS lady voice” announces “reduced fuel flow” it won’t be too comforting… Cynical maybe, but I like to deal with real world…

 

[seagull]

Jim, you may have had vaporlock in one carburetor feed line but that is NOT the most common place to get it. Vaporlock is the fuel boiling and turning into a gas inside the fuel line, low pressure is a contribuiting factor to help the fuel boil. The lowest fuel pressure area inside the cowl is before the mechanical pump not after it. If vaporlock occurs before the mechanical pump both carburetors are affected. For only one feed line to lock up would be very rare if the routing is per Rotax / Vans suggestions.

I have had vaporlock once sitting on the ground In Palm Desert, the engine got very rough, one carb starving then followed the other and quit. It was like someone pulled the fuel valve.

Real world is if I can get a 15 second warning that my engine is about to give me problems I'm not going to turn it down.