Fuel Pumps?

[Joni]

They dont work, do they? I noticed there is no effect in turning them off :(

[Priller]

The wing boost pumps can be turned off to prevent the fuel from being burned while using droptanks. Main boost pumps can be turned off for a short period of time before the engine eventually dies. Both pumps for that engine have to be shut off for it to die tho.

 

I do not know if the engine is being modeled with some sort of mechanical fuel pump or if it is just burning the fuel and/or pressure that was in the line before it dies.

[Joni]

thought that too, but i flew 50 mins with the 4 pumps off and nothing happened.............

[Priller]

thought that too, but i flew 50 mins with the 4 pumps off and nothing happened.............

 

Before this last update I was testing for fuel burn in the A-10C using droptanks etc. At that time it took just a few minutes for that engine to die at full power settings. I would guess a engine driven mechanical fuel pump is being modeled to allow you to continue flying without electrical power or due to damage.

 

I will test if I get the same result.

[PFunk1606688187]

Emergency procedures from the -1:

 

MAIN BOOST PUMP FAILURE

 

Failure of either main fuselage boost pumps, indicated by the

applicable L or R MAIN PUMP caution light coming on, will

have no effect on engine operation while fuel is being pressure

fed from the wing tanks. When the wing tank boost pumps are

not operating, fuel will suction-feed from the main tanks to an al-titude of approximately 10,000 feet. Above this altitude, engine

operation could become erratic;however, placing the crossfeed

switch to CROSSFEED will supply the engines with fuel under

pressure from any operating boost pump and allow continued

operation above 10,000 feet.

Warning

Dual engine flameout may occur during negative

g flight after approximately 5seconds with one

main boost pump inoperative,or off.

Caution

In the event an engine is suction-feeding due to a

failed boost pump, the affected engine will suc-tion-feed from the failed tank for all power set-tings above idle up to 10,000 feet (most cases,

20,000 feet).

 

I don't see any reason why the engines should fail if you have no boost pumps as long as you're not doing harsh maneuvering and stay within correct altitude constraints, but I haven't tested the sim's representation of this. You only need the boost pumps to start the engines and even then you can start all engines with the DC boost pump that is energized when the APU is turned on which feeds the left fuel system. It can be made to feed the right system by opening the crossfeed valve.

[Priller]

Emergency procedures from the -1:

 

 

 

I don't see any reason why the engines should fail if you have no boost pumps as long as you're not doing harsh maneuvering and stay within correct altitude constraints, but I haven't tested the sim's representation of this. You only need the boost pumps to start the engines and even then you can start all engines with the DC boost pump that is energized when the APU is turned on which feeds the left fuel system. It can be made to feed the right system by opening the crossfeed valve.

 

I was able to turn off all the pumps. Climb to 21,500ft with the crossfeed off then go to 350+. Able to then go to 450 in a dive all the way to sea level. I did +8 G and -2G without issue. I tried high AOA at speed and as slow as 100mph. I was unable to get either engine to shutoff .

[PFunk1606688187]

Then its likely not modeled to have any degree of volatility and assumes perfect suction feeding.

[QuiGon]

According to Prillers earlier comment it was implemented in earlier versions. So that would be a step back? Why should the devs take this feature out of the game?

[StandingCow]

This would be a good question for Snoopy.

 

Since they are just boost pumps my assumption is that they only help out when the engine cannot pull fuel itself (not running), such as in startup. Did you try going inverted and seeing if the engines cut out quicker without the boost pumps going?

 

I am talking out of my ass here and making a lot of assumptions, so take it with a grain of salt.

[Snoopy]

This would be a good question for Snoopy.

 

P*Funk basically covered it above. Only thing to add is:

 

• The DC fuel pump is energized if there is no fuel pressure from the left main tank boost pump (my guess why Priller's engines didn't shut down per this post)
  

[Joni]

i started both engines without any pumps

[Deezle]

Did you have crossfeed on? I've never had the right engine start with the pumps off.

[Joni]

I had everything off

[Wrecking Crew]

I just tested this on the A-10C with a cold start. If the four fuel switches are left off the right engine will spin up but the gauges -- TEMP, % RPM and PSI will not come up to nominal, i.e.: the right engine is not operating correctly.

 

WC

[Wrecking Crew]

Then I turned on the four Boost Pump switches but the right engine still did not catch -- the Engine Start indicator was on this whole time. Then I shut down the right engine (throttle back to its stop) and tried to restart it and it did -- the pumps were on then.

 

I saw something else, though --

I can start the left engine w/o the Boost Pumps, then turn on the pumps for 10 seconds then turn them off, and then the right engine will start even though the four Boost Pumps are off.

 

WC

[Joni]

mmmm there is something strange going on here.

 

 

should i report this as a bug?

[FSKRipper]

I'm not sure what would happen in the real AC but my experience this evening was that after switching on battery, Inverter (stby) and APU I was able to start the left engine without boost pumps. I never got the APU Gen warning and when switching the right engine to idle, it won't spool up.

 

Maybe a bug, maybe the right behaviour. Snoopy or the devs could tell...

[Snoopy]

I just tested this on the A-10C with a cold start. If the four fuel switches are left off the right engine will spin up but the gauges -- TEMP, % RPM and PSI will not come up to nominal, i.e.: the right engine is not operating correctly.

 

WC

 

The engine will spin because of bleed air but won't ignite.

 

I'm not sure what would happen in the real AC but my experience this evening was that after switching on battery, Inverter (stby) and APU I was able to start the left engine without boost pumps. I never got the APU Gen warning and when switching the right engine to idle, it won't spool up.

 

Maybe a bug, maybe the right behaviour. Snoopy or the devs could tell...

 

The DC fuel pump will allow #1 to start.

Edited September 4, 2015 by Snoopy

[Joni]

The DC fuel pump will allow #1 to start.

 

would you explain how it works?

[FSKRipper]

Thanks Snoopy, can't comment on the flight tests but ground behaviour seems ok if you confirm it. :thumbup:

[Wrecking Crew]

The APU Gen *must* be on for the whole sequence to begin, i.e., Left Engine start. The APU needs to spin up to ~100% before turning on the APU Gen or the APU will bog down.

 

WC

[Wrecking Crew]

The DC Fuel pump starts with the battery (or the Battery Inverter). This is the fuel pump that feeds to APU, too.

 

WC

[Joni]

and why cant it feed the right engine?

[Snoopy]

and why cant it feed the right engine?

 

Because the DC pump is in the left main tank that feeds #1. If you do a search you'll find that this has been discussed many times.

[PFunk1606688187]

I shoulda just attached this from the get go. Staring at diagrams makes me feel like a little kid again. :D

 

Incidentally I just tested it and you can start the right engine with the crossfeed open and all boost pumps off. If you shut the crossfeed immediately after the engine start cycle light extinguishes you'll get a right fuel pressure warning and the right engine will shut down. How much of that is realistic is beyond me.