Fuel Pump Operation

[CodyValkyrie]

I haven't heard back from my mechanic friend either. He's been super flaky lately, so it's been hard to get anything from the guy unless I physically go down to the airport and just ask him.

[Scott - A2A]

Les,

Thanks for posting that, and I'm getting the same feedback on my end.

Scott.

[ResidentEVO]

In the IO-520D I fly at work (on a Cessna 185 floatplane, so it should be close), for start we go

mixture rich
fuel pump on
throttle full for a few seconds to prime
throttle back to "cracked"
fuel pump off
mags to start.

Engine should start, and that's all I use the mechanical fuel pump for.

UNLESS, it's a hot as hell day, and we're climbing out heavy. I'm not sure how the Bonanza is, but in the 185, the CHTs go up, up, and up... even in a 100 mph climb. A trick to keep them a bit cooler is to turn on the fuel pump and dump fuel into the engine; burns cooler and makes a noticeable difference in the CHT on climbout.

I'm curious to see if this works in the Beech!

[Les Parson]

Below is additional fuel pump info received from a current F33 operator who has upgraded from -520 to the -550 engine. There is a also description of the single-speed and two-speed pumps used on certain models:

Some more research
-in early B36TC (turbocharged -36 model with a stretched wing/more fuel), TWO aux fuel pumps were installed - one for low pressure to combat fuel vapors at high altitude and/or high temps, exacerbated by the heat from the turbo the other is for high pressure, used for priming and emergencies. Eventually the two pumps were retrofitted with one low/high speed pump and one switch.
-all A36s and G36s after ‘84 have the same arrangement (off/Lo/hi) described above
-some early Debonairs (model 33, 4-seat, non-V tail) which upgraded to the IO550 engine (300hp) have also added the two speed pump as part of the STC (ironically, I just did that engine upgrade and kept the off/on switch)

Summary
-on/off (single speed) pumps are used for priming and engine-driven pump failures only. The failure checklist (memory) will call for its use.
-on two speed pumps, the HI position is used the exact same way as the single speed pump ON position described above - priming/primary pump failure. The LO position is used to overcome fuel flow fluctuations from vaporization in the fuel lines. This is indicated by fuel flow fluctuations or even engine power variations. The main concern is at high temps/high density altitudes on takeoff. However, with that said, there is a placard next to the pump switch to NOT use the pump (even in LO, except if there is a loss of fuel pressure). The only exception I could find is certain IO550 equipped Barons call for the pumps on LO during takeoffs above 90F.

So except for the Baron exception noted above, the electric fuel pump isn’t used for takeoff or landing except in case of emergency (loss of fuel pressure).

Let me know if you have any questions. BTW, all this info came from an instructor course I took presented by the American Bonanza Society.

[CodyValkyrie]

I just got a response from my friend who’s a longtime mechanic of Bonanzas. It’s hard to read, but it makes sense if you take your time.

“I was I will always refer you to the Poh but if you have a long enough Runway doing the board and take off with it on and make sure you have enough run off and then go back and doing the poor to take it off take off with it off and see if you feel a performance difference always follow the poh that's why they made it.”

Basically what he’s saying, from what I can gather, is that generally it’s not too big a deal, but it can make a difference under certain conditions. If you compare it on to off, especially on longer takeoffs, you’ll see a difference. He refers to the POH, so there you go. It should be off, which we’ve all established.

Edit: He probably was drunk when he wrote that, since he’s on vacation in Costa Rica, which makes it absolutely hilarious.