Electrical system and APU oddities

[Rongor]

According to the manual p 6-107: Powering on the APU requires a power source and aft fuel pump on

1. Just noticed I can shut the aft fuel pump off and still the APU keeps running. I can even restart the APU without any fuel pump switched on. Only requirement is an open APU shutoff valve.
2. When I disconnect ground power and switch off batteries, a running APU instantly shuts down automatically.

 

Manual claims the APU generates electrical power

1. How can I verify the generated current? The electrical systems panel is not functional (p 6-98), unlike in all the other helos.
2. On manual page 13-20, the APU is not even present in the electrical systems diagram, let alone as a source of power
3. Why does the APU shutdown when all other power sources are disconnected? If the APU generates power, the disconnection of other sources wouldn't matter.
4. The ABRIS needs AC to run. If I have a running APU with inverter on, ABRIS won't start. With batteries and inverter or DC ground power with inverter or switched off inverter with AC ground power, ABRIS starts. So whatever power the APU generates, it obviously doesn't feed into the electrical system. Is this correct?

 

Ground power indication

Manual on p 6-79, item 4: When DC ground power is on, lamp will be lit.

In my Blackshark, this lamp only is lit when both switches, DC ground switch and AC ground switch, are on. If one of these is off, lamp will not light. As long as AC ground is off, DC ground on doesn't light the lamp.

Special case: If batteries and the inverter are on, only the AC ground switch lights this lamp and the DC ground switch is ignored by it. Is this all so correct?

 

 

 

 

 

Edited October 28, 2021 by Rongor
I like editing stuff

[AlphaOneSix]

A.

1. In theory, if there is enough fuel in the line to start the APU, the fuel pump built into the APU could suck fuel without the help of a boost pump. It certainly works for the engines. I reality, in my experience, the APU will not finish its start sequence before it shut off from fuel starvation. Maybe the Ka-50 is a little more forgiving in this aspect, or maybe ED didn't model this particular requirement.

2. This is correct behavior. The APU on the Ka-50 is not set up to supply DC power.

B.

1. You can't, the gauges aren't modeled. Maybe BS4?

2. The APU is not a source of power in the Ka-50, and therefore is not mentioned in the electrical system.

3. The APU doesn't generate power, and so requires batteries or external power to be available in order to operate. I don't know what kind of shutoff valve is used in the Ka-50, but in the Mi-8, the APU solenoid valve is held open electrically, so removing power shuts the valve, stopping fuel flow to the APU. I don't know if this is the same valve the Ka-50 uses. I suspect that there are actually two valves, and the one that's like the Mi-8 valve is not shown on the fuel system schematic, since that's how the APU is shut down...pressing the APU off button removes power from the APU fuel solenoid valve (a different valve from the one that is operated from the right wall panel), causing it to close and shut off fuel to the APU. And that solenoid valve requires power to stay open.

4. This is correct, since the APU doesn't provide any electrical power.

C. 

It seems like the manual may be mislabeled and this is actually an AC ground power light. The behavior you described would be correct behavior if it was an AC ground power light and not DC. Maybe check the Russian version of the manual if you can get it? I don't have it. So either the manual is wrong and it's really an AC ground power light, or the aircraft modeling is wrong and it acts like an AC ground power light when it should be DC. To save your sanity, I think it would be best to assume it's an AC ground power light and that the manual is incorrect, because it (the sim or the manual) is not going to get fixed...or at least it's very unlikely to get fixed.