I am trying to gain an understanding of the crossfeed system. The POH prohibits the use of both crossfeeds on at the same time. I would have thought, that the engines would still be fed, but from opposite sides..... also, if one wanted to drain one tank, could they opperate both engines from one tank via the crossfeed?

Thanks,
larry

Hi Larry, On my PA30 I don't think you can use both crossfeeds simultaneously. The selector switch won't work that way. When the selector is turned to a crossfeed, the opposite crossfeed is locked out. I personally can't think of any emergency where you would need to crossfeed right tank to left engine while at the same time crossfeeding left tank to right engine. Someone else may know more about this than me. I'm interested in why you would think you might need to do that?

I can't answer your second question about taking off using only one main tank to feed both engines. Someone with more knowledge can help with that one.

Clear Skies,
Gomer

Thanks. I didnt know that the other one was locked out. i dont know of a time when it would be needed, I just didn't understand why you could not.

larry

Think of it this way - the gas has to come from somewhere.
The fuel selector determines the where SOMEWHERE is ie the left main
You can feed the right engine from the left main if the RIGHT selector is pointed to the crossfeed and therefore the left main.
Does that help?

 

The crossfeed system works by feeding fuel from one fuel selector to the other fuel selector. If both fuel selectors are drawing from each other, then neither is drawing from a tank.

Thanks for the explantion Kristin. That makes sense. The other systems that I am familair with would draw from the tank itself, not via the opposite fuel selctor.

Thanks again,
larry

The Aztecs and IIRC, the Navajos, just open up a line in between the two engine feed lines. With the Aztec, the connection is down stream of the aux pump so you can even prime one engine from the opposite side. There are some Aztec operators I have run into that advocate taking off and landing with the crossfeed open so that there are two feeding sources. I haven't adopted that as I haven't tested it enough to be confident that it might not cause other problems.

The Comanche, with two tanks in each wing complicates crossfeed. In a Seneca or a Seminole, there is only one tank in each wing so the valve arrangement is simpler. In effect, each fuel selector has right, left, and off. It is just that the are labelled ON, OFF, and CROSSFEED instead.

I would also question if the line from one main tank would be able to supply both selectors and engines at maximum power.
I'll have to try it.

Clarence

Clarence,

I should try that sometime as a safe altitude and see if it does provide adequate flow.

Clarence,

If the question was, does, as an example, the left main successfully feed both engines when the right selector is pointed in crossfeed at full power. the answer is Yes - at least i know it works in my 39-10.