Hello all
I've recently installed my MGL fuel flow senders( duel tanks - left and right) into my aircraft Rotax 912 ULS, I installed the 2mm jets into the flow meters. My fuel flow is 21 liters an hour at 5500 rpm on the Rotax 912 (As measured after 1 hour flight by refilling the tanks back to full). I've had to adjust the K factor on the FF4 fuel flow gauge down to approximately 970 and 1100 respectively to get the 21 l/h showing on the FF4 gauge , which seems a far cry from the 7000 k factor. The gauges were reading 3.6 and 7.0 before any adjustments.(K factor 7000)
My question is this, was this the correct jet or should I go to the 1mm jet (3 to 30 liter per minute)?
Any advice would be appreciated.
Also my range and and time does not display (No reading displayed) using calculated fuel level or float sender, how do I get this to work?
Thank you.
MGL fuel flow meter Jets
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Re: MGL fuel flow meter Jets
K factor is the number of pulses your flow meter produces for a given quantity of liquid passing through it.
Nothing more - nothing less. In our case we work in liters - and our sender with a 2mm jet correctly installed - you get about 7000 pulses per liter within the flow range as noted in the doc that comes with it.
You are dealing with a liquid. It's non compressible under normal circumstances. There are many things that can affect the number of pulses resulting in incorrect readings. The doc mentions a few. The flow must be straight - if you have a bend in the pipe just before the sender - guess what happens - yes your flow is no longer linear but rotates. This affects the speed at which the little impeller rotates. That means the number of pulses will be less in this case - but due to the yet - the effect is not dramatic - it's more noticeable for larger jets or no jet (often used for fuel hungry turbines).
Fuel shunting - this happens if your fuel flow is not steady. Fuel instead goes backwards and forwards through your sender all the time. You can imagine what that does to the rotation of the impeller. This is caused by fuel pumps. Some have non-return valves, some don't and some have valves that no longer work properly. Fuel pumps, many of them anyway, create pressure pulses - they are stroked pumps. Often the fuel is forced into the fuel system but has nowhere to go - float valves (in case of carbs) are closed, the bowls are full. If you have elastic fuel lines somewhere - rubber fuel lines or similar - they simply expand and take up the excess fuel - during the pumps down stroke - the fuel gets shunted back where it came from.
Some fuel pumps have dampers internally to help minimize this effect - others nothing at all.
Shunting completely screws around with your flow sender - you will get really weird readings greatly affected by the length of lines and the rate the pump if working at.
In some cases we have had the impellers stop turning - only seen this on (some) new aircraft with fiberglass wing tanks - some chemical wax or similar is leached out and settles on the sapphire bearings eventually stopping the impeller from turning freely. The sender can easily be opened and cleaned if this happens.
If your flow is very low the force on the impeller paddles is also very low - you need to be aware of friction - you can play with our sender to see what happens. Put it on its side (outlet and inlet at same level or slight incline) blow through it - notice how long it takes until the impeller stops. There is almost zero friction. Now do the same but rotated so the spindle going through the impeller is horizontal - now the spindle rests on the bearings - friction is much higher and the impeller stops much sooner - OK it's not really that bad - once liquid is inside the sender we have a lubricant so this effect is much less. But take it into account for your mounting. Also mount your system in such a way that there can never be vapor or air trapped inside the sender - any bubbles that can't go anywhere will severely affect your reading.
Finally - if you want your FF-4 to show range - you need to connect a GPS receiver (see manual). It needs to know how fast you are going.
Nothing more - nothing less. In our case we work in liters - and our sender with a 2mm jet correctly installed - you get about 7000 pulses per liter within the flow range as noted in the doc that comes with it.
You are dealing with a liquid. It's non compressible under normal circumstances. There are many things that can affect the number of pulses resulting in incorrect readings. The doc mentions a few. The flow must be straight - if you have a bend in the pipe just before the sender - guess what happens - yes your flow is no longer linear but rotates. This affects the speed at which the little impeller rotates. That means the number of pulses will be less in this case - but due to the yet - the effect is not dramatic - it's more noticeable for larger jets or no jet (often used for fuel hungry turbines).
Fuel shunting - this happens if your fuel flow is not steady. Fuel instead goes backwards and forwards through your sender all the time. You can imagine what that does to the rotation of the impeller. This is caused by fuel pumps. Some have non-return valves, some don't and some have valves that no longer work properly. Fuel pumps, many of them anyway, create pressure pulses - they are stroked pumps. Often the fuel is forced into the fuel system but has nowhere to go - float valves (in case of carbs) are closed, the bowls are full. If you have elastic fuel lines somewhere - rubber fuel lines or similar - they simply expand and take up the excess fuel - during the pumps down stroke - the fuel gets shunted back where it came from.
Some fuel pumps have dampers internally to help minimize this effect - others nothing at all.
Shunting completely screws around with your flow sender - you will get really weird readings greatly affected by the length of lines and the rate the pump if working at.
In some cases we have had the impellers stop turning - only seen this on (some) new aircraft with fiberglass wing tanks - some chemical wax or similar is leached out and settles on the sapphire bearings eventually stopping the impeller from turning freely. The sender can easily be opened and cleaned if this happens.
If your flow is very low the force on the impeller paddles is also very low - you need to be aware of friction - you can play with our sender to see what happens. Put it on its side (outlet and inlet at same level or slight incline) blow through it - notice how long it takes until the impeller stops. There is almost zero friction. Now do the same but rotated so the spindle going through the impeller is horizontal - now the spindle rests on the bearings - friction is much higher and the impeller stops much sooner - OK it's not really that bad - once liquid is inside the sender we have a lubricant so this effect is much less. But take it into account for your mounting. Also mount your system in such a way that there can never be vapor or air trapped inside the sender - any bubbles that can't go anywhere will severely affect your reading.
Finally - if you want your FF-4 to show range - you need to connect a GPS receiver (see manual). It needs to know how fast you are going.