fuel system aux tank on 1969 Turbo

[jcthomas]

I just purchased a 1969 T337. A debate is brewing as to how the aux tanks function. The articles from the previous site said you can't get the aux fuel from a NORMALLY ASPIRATED ENGINE if you run the mains dry. I have been flying my plane the way it is stated ( after an hour switch one tank and then fifteen later switch the other, etc.).

When you look at the POH from Cessna, it does show a diagram of the fuel system which shows the pumps in a different configuration than the article diagram.

Perhaps GMAS or someone can clarify the difference.

Thanks,

JT

[FRED-E]

Jcthomas

I believe in your aircraft the AUX pump is feed by MAIN or AUX tanks because it is Turbocharged. In my plane (337B) it is only feed by the MAIN tanks because it is normally aspirated. I don't know why they did that.
Fred N358

[FRED-E]

Jcthomas
Let me try to send a schematic.
Fred N358

[Ernie Martin]

JC:

I wrote the fuel-management article which you can access from www.SkymasterUS.com, but it's for a normally aspirated 337. My quick analysis of the figure you posted suggests that indeed you can draw fuel from the auxiliary tanks after you run the mains dry in a Turbo model. That's because the auxiliary fuel pump is AFTER the fuel selector switch, so it pulls fuel from whichever tank you've selected. In the normally aspirated models, however, notice in your figure that the aux pump only draws from the main tank. And, as you know, you've got to have the aux pump if there are voids in the line (which, as you know from my article, will occur if you drain one tank dry).

Ernie

[jcthomas]

Thanks for the information. It will cost me dinner, but on the other hand, I felt safe doing it the other way.


I love the plane and it did a great job coming to its home in Indiana, PA from Seattle, WA. The paint scheme is one of a kind and I didn't buy it for the paint. It is pink and white with love child flowers on it from the 60's. It makes great conversation when I land. I am always asking the onlookers if they are having flashbacks!

thanks again

John

[Paul Sharp]

They're right. My turbo is the same way; doesn't have the hangup they're talking about and you can get fuel simply by switching - speeding up the access with the electrical fuel pumps.

[jcthomas]

Paul thanks for the info. I would be interested in how you manage the fuel.

[Paul Sharp]

Here's my basic approach: I keep the mains full at all times, having them topped off after landing each time. If I have used the aux. tanks I plan to run them dry each time (I simply switch back to the main tank when each engine starts to sputter). Then when I land I not only get the mains topped off but have them add 7 gals. to each aux. tank. That way I always have some "insurance" in case I do something stupid.

If I'm going on a trip where I want range and don't have to worry about the weight trade-off, I call ahead and have them top off the aux. tanks.

Note the standard caveat, however, that you always want to burn off an hour's fuel from the mains before switching to the aux. tanks or you'll be sending fuel out the overflow into the atmosphere - losing gas, money, and flying endurance time.

As to settings, I usually set for about 70% or even 75% power, due to the fact that what studying I've done in past years tends to indicate that getting there faster usually ends up saving on all-around costs in the long run. But if I ever think I might possibly get to where reserves would be stretched at all I simply throttle back until I reach a fuel stop.