radios and fuel pumps

I was reading the "Wall Panel" section of the manual and was doing some testing and found some discrepancies.

First, it says the radios and datalink can't work without AC power. I tried switching off the DC to AC inverter but the radio still seemed to work. Engines were off so the AC generators weren't operating.

Second, the manual says the APU is fed by the rear fuel tank. I turned off the rear tank boost pump but the APU was still able to start (cross-feed switch off). As an aside, the engine fuel feed logic seemed to work as expected.

I can verify the first issue with the radio. Either it's implemented incorrectly, or the manual is incorrect and it's supposed to be DC power instead of AC power. I'm leaning towards the latter, as it wouldn't be too useful for a helicopter to not be able to communicate if the inverter goes out.

As for the APU, I can't reproduce it. Are you starting the APU, and then turning off the boost pump? If so, the suction from the APU will keep fuel flowing into it. If you're turning off the aft fuel pump prior to starting the APU, then the APU sound should play, but the temperature won't increase, and the APU will die after a short while.

I can verify the first issue with the radio. Either it's implemented incorrectly, or the manual is incorrect and it's supposed to be DC power instead of AC power. I'm leaning towards the latter, as it wouldn't be too useful for a helicopter to not be able to communicate if the inverter goes out.

As for the APU, I can't reproduce it. Are you starting the APU, and then turning off the boost pump? If so, the suction from the APU will keep fuel flowing into it. If you're turning off the aft fuel pump prior to starting the APU, then the APU sound should play, but the temperature won't increase, and the APU will die after a short while.

Thanks for the reply.

Not sure. I think in the A-10C, the inverter has to be on to work the radios so maybe the same thing.

 

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Do you really think it's a good idea to compare an American plane to a Russian helicopter?! Try to compare it with the Mi-8, but not even this comparison can be guarantied.

Edit: Now at home and checked it: The Radios are DC power supplied via the DC emergency bus (directly fed from the batteries)

The following power consumers are supplied by the DC emergency buses (in case both

generators and rectifiers fail):

 POS-500B inverter to supply the AC consumers

 Communication equipment: VHF radios, intercom

 Radar altimeter

 IFF responder

Black Shark manual page 471, chapter 13-21

Electricity doesn't care what country it's in or who designed the thing it flows through. ;)

Kidding aside, every radio I've ever seen in an aircraft has been powered by DC. From any country.

I've never even heard of an AC radio, is that even possible?