Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Boost pump use
- Thread starter g zero
- Start date
SmilingJack
Well Known Member
- pre-start
- takeoff
- landing
Same reason as jchang10
- takeoff
- landing
Same reason as jchang10
Yes, I do use the boost pump prior to takeoff and throughout the climb. I shut it off once cruising.
I also use it immediately before, during, and a short time after switching tanks which I strive to do every 30 mins in flight.
When landing, on downwind, I switch it (boost pump) on in case of the need for a go around.
Why, I was trained that way and it's on the checklist.
The reason as I undwrstand it is to ensure adequate fuel psi under full power takeoffs and go arounds.
This technique supplements the engine driven pump. Provides redundancy In case low psi due to the mechanical engine driven pump providing inadequate psi.
As for switching tanks, ensures positive psi from tank to engine driven pump.
But what do I know? Not much. I'm a 145 hour pilot in a new to me RV8. Someone, please correct me if I'm wrong and clarify.
I have a fuel injected RV-8.
Charlie
I also use it immediately before, during, and a short time after switching tanks which I strive to do every 30 mins in flight.
When landing, on downwind, I switch it (boost pump) on in case of the need for a go around.
Why, I was trained that way and it's on the checklist.
The reason as I undwrstand it is to ensure adequate fuel psi under full power takeoffs and go arounds.
This technique supplements the engine driven pump. Provides redundancy In case low psi due to the mechanical engine driven pump providing inadequate psi.
As for switching tanks, ensures positive psi from tank to engine driven pump.
But what do I know? Not much. I'm a 145 hour pilot in a new to me RV8. Someone, please correct me if I'm wrong and clarify.
I have a fuel injected RV-8.
Charlie
JohnInReno
Well Known Member
Lycoming or Continental
I use the boost pump before start, during take-off, and during landing.
I was confused at first by the reports of engine flooding caused by the boost pump resulting in engine failures. I believe the failure modes are related to the big Continentals with 2 positions for the electrical pumps.
Someone more knowledgeable please chime in.
I use the boost pump before start, during take-off, and during landing.
I was confused at first by the reports of engine flooding caused by the boost pump resulting in engine failures. I believe the failure modes are related to the big Continentals with 2 positions for the electrical pumps.
Someone more knowledgeable please chime in.
Not really. It provides a greater vacuum on the Tank to help purge any air that may be introduced after switching tanks. You may have air between the tank and the valve on the un-used side. The electric pumps typically provide more flow (GPH) than engine driven pumps and therefore help overcome the difficulty of pulling on an air entrained line. You want to keep the pump one for a minute or so after switching, as the air doesn't dissipate until it hits the carb or servo.
Larry
Last edited:
BillL
Well Known Member
Tom, the reason is a technical one. Fuel will vaporize if the absolute pressure is low enough and the temperature of the fuel is high enough.
So - if the boost pump is not on, the pressure drop from the fuel tank to the mechanical pump is proportional roughly to the square of the fuel flow. At takeoff, the fuel flow, full throttle, full rich, is at the maximum, so -therefore - is the pressure drop at the inlet of the mechanical pump. Just after rotation there is an uphill flow that adds to this pressure drop. This is the worst case for flow and pressure. Temperature and actual vapor pressure of the fuel is another matter.
If the fuel is at that high end of the vapor pressure, and combined with hot fuel on a hot day, maybe even a hot start, then this would be the most likely condition to create vapor due to "suction" (low absolute pressure) at the suction of the mechanical pump.
So, the condition of the fuel filter, size of the lines, altitude and temperatures all remain variables to address.
Keeping the boost pump on during TO is a precaution to avoid all the thinking and measurements and unknown variables.
I hope this makes sense. Other variables of the various ways people build the fuel system from tank to M. pump affect that pressure drop. Lycoming says -2psi is the max drop to the pump inlet. I have not quantified what this means terms of temperature tolerance (yet). My building takes priority.
Bill's response is on the money.
Temperature is a big player in this too - the fuel will vaporize at any point where the pressure is low enough and the temperature is high enough. Now consider that the mechanical fuel pump is bolted directly to the biggest heater you have in the airplane.
Start to see the issue?
The electric boost pump cannot help cool down the fuel, but it does raise the pressure high enough that creating vapor bubbles (leading to vapor-lock) is unlikely.
Temperature is a big player in this too - the fuel will vaporize at any point where the pressure is low enough and the temperature is high enough. Now consider that the mechanical fuel pump is bolted directly to the biggest heater you have in the airplane.
Start to see the issue?
The electric boost pump cannot help cool down the fuel, but it does raise the pressure high enough that creating vapor bubbles (leading to vapor-lock) is unlikely.
That is correct. It applies to the IO-520 for sure, not sure about the other Continental injected engines. I suspect the IO-550 is the same. Either way, it shouldn't cause the engine to flood and fail at power. In my experience it does cause it to run rough due to being excessively rich, but it does still provide ample power.
All that being said, it doesn't apply to RVs. Unless somebody wants to wake up the neighbours at 2850rpm from the IO-520 at take-off
Andy Hill
Well Known Member
Personally I do not, the system should run without it, and if there are issues with the Boost Pump off, at least you have a "tool in the box" to try and recover the power and land somewhere.
I am surprised by the number of people who do not use the electric pump for landing and takeoff, and as above, have to explain you are one failure from an accident. I await after takeoff until the view out of the window shows a forced landing likely successful, and say 1500'+, then turn it off.
rleffler
Well Known Member
Exactly!
I had this happen on my first flight. I had inadvertently overlooked the check list task to turn on the electric boost pump on take off. The engine just about died when I turned crosswind. As soon as I turn the boost pump on, fuel flow was back to normal, I aborted the plans for the first flight and immediately landed to figure out what happened.
N941WR
Legacy Member
To this I would add "Switching fuel tanks".
Exactly!
On takeoff, I turn off the fuel pump when at 1000' AGL and turn it back on again when I descend back to 1000' AGL for landing.
tadsargent
Well Known Member
You asked about inverted flight and the boost pump, yes I always leave the pump on. I can not allow a fuel related issue to occur.
