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Fuel Boost Pump Basics

mfleming

Well Known Member
Patron
The Airflow boost pump in now installed in my RV-7 with a fuel injected engine.

Basic questions not found through a search:

  • Preferred method for priming on the first pump start-up?
  • Can I torque all the B-nuts now or will I have to loosen some of them during first start-up?
  • How did you ensure the fuel system and pump delivers the required fuel flow?

If I missed a good thread about this please point to it ;)
 
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I have attached a fuel flow test that is required in Canada. It is pretty self explanatory. You should do the test at the discharge of the fuel line that goes into the fuel servo.

I would think you can torque all of your B nuts at this point.

I usually prime between 3 - 4 seconds.
 

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Thanks everyone, I've torqued all the fittings and look forward to being at the priming stage
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If the system is dry, I prefer to blow a little air in the fuel tank vent (be careful) and let the fuel flow either out the eng pump or servo inlet line. Running the pump even for a short period of time without fuel is not good for the pump.
 
If the system is dry, I prefer to blow a little air in the fuel tank vent (be careful) and let the fuel flow either out the eng pump or servo inlet line. Running the pump even for a short period of time without fuel is not good for the pump.

Great tip Walt.

Having spent a lifetime in the oil & gas business I understand being careful with air & fuel… Not to mention turning my nice airfoil shaped tank into a balloon :eek:
 
I did several with no pressure and by the sound, it primed within 3-5 seconds. We had 5 gallons in the tanks and plane level initially.

The system was pressurized with 30 psi air and closed to check for leaks. Leas were found in each of our tests. One was on the pump, it was replaced. Even a small suction leak will affect inflight performance at higher temperature. As a practical matter, the entire system can not be pressure tested, so the clear tubing covers more of the variables.

When you run the test, I recommend you add a valve to control output pressure to the recommended engine operating range for the flow test. Pumps vary volume with pressure - you should also have know this :)

We added a clear section of tubing to see if there were bubbles entrained from a

The Airflow pump should exceed all specifications.
 
...
The system was pressurized with 30 psi air and closed to check for leaks...
Hi Bill, I assume you excluded the fuel tanks for this test, just in case it's not clear to everyone who might try this.

You mentioned clear tubing - where did you put that? And did you pressurize from the servo inlet back to the closed fuel valve, or all the way from tank inlet to servo?
 
Max Climb Angle - for MDRA

Just wondering if I can tack on a question about Max Climb Angle. My plan is to hold down the tail on the RV-9A which gives me about 15-16 degrees on the deck. For the MDRA fuel flow test they look for max climb angle plus 5 degrees.
If the intent is to deliver fuel to the servo is it sufficient extend the line up (probably about 8-10" - I'll calculate later at the hangar for actual) to simulate the additional angle or is there something else that suggests the aircraft must actually be at 20 degrees?

Thanks.
 
Just wondering if I can tack on a question about Max Climb Angle. My plan is to hold down the tail on the RV-9A which gives me about 15-16 degrees on the deck. For the MDRA fuel flow test they look for max climb angle plus 5 degrees.
If the intent is to deliver fuel to the servo is it sufficient extend the line up (probably about 8-10" - I'll calculate later at the hangar for actual) to simulate the additional angle or is there something else that suggests the aircraft must actually be at 20 degrees?

Thanks.

Please see attached MDRA fuel test procedures. It states ...

For this test, the aircraft should be positioned in the MAXIMUM ANGLE OF CLIMB and only have the minimum fuel as per the weight and balance report. (MD-RA Form C17E).


Pump systems. The fuel flow rate must exceed 125 percent of the takeoff fuel consumption of the engine.


The full procedure can be found here.

https://www.md-ra.com/docs/C14E_Fuel_Flow_Report.pdf


I don't see where it is required to be +5 degrees greater than max climb angle.

I used 15 degrees for the test.
 
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Just wondering if I can tack on a question about Max Climb Angle. My plan is to hold down the tail on the RV-9A which gives me about 15-16 degrees on the deck. For the MDRA fuel flow test they look for max climb angle plus 5 degrees.
If the intent is to deliver fuel to the servo is it sufficient extend the line up (probably about 8-10" - I'll calculate later at the hangar for actual) to simulate the additional angle or is there something else that suggests the aircraft must actually be at 20 degrees?

Thanks.

That would be a good solution to increase the angle during your test.
 
too many docs

Please see attached MDRA fuel test procedures. It states ...

For this test, the aircraft should be positioned in the MAXIMUM ANGLE OF CLIMB and only have the minimum fuel as per the weight and balance report. (MD-RA Form C17E).


Pump systems. The fuel flow rate must exceed 125 percent of the takeoff fuel consumption of the engine.


The full procedure can be found here.

https://www.md-ra.com/docs/C14E_Fuel_Flow_Report.pdf


I don't see where it is required to be +5 degrees greater than max climb angle.

I used 15 degrees for the test.



Awe ****. See, that's what happens when you are reading too many things at once. The 5 degree reference is actually from the FAA reference "place the aircraft’s nose at an angle 5 degrees above the highest anticipated climb
angle.", which was also part of an EAA presentation I watched last year. Somehow my brain cobbled the 2 together.

Thanks for the correction.
 
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