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Old 12-03-2019, 06:17 PM   #6
Theodore42
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Join Date: Dec 2018
Location: Texas
Posts: 45
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Quote:
Originally Posted by grafspee View Post
Looks like late models had vapor return to fuselage tank
Question is, is -25 and -30 late version or early version.
Looking at booster pump switch i assuming that we have later version because of 2 position switch
There is a note in that manual on p22:
"In later planes the vapor return goes to the fuselage tank instead of the left wing tank. With these planes, use the fuselage tank first. However, the only way of finding out to which tank the return is connected is to ask the engineering officer." Or, in our case, the DCS manual

Quote:
Originally Posted by Weta43 View Post
Perhaps just incorrectly sitting in the tank it was drawn from - in which case the end result has no effect on range, weight or performance, only on the proportion of time you have to select the left tank to keep fuel evenly distributed.

A bug, or an oversight, but a very insignificant one.
It's important for a few reasons:

Firstly and simply, the startup checklist says to start from whichever tank has the vapor return line. So we are all ritualistically simulating this act but we can't experience the negative effects for failing to follow the checklist (wasting fuel). If it is 10 gallons per hour, that is kind of a big deal.

However, there is also the matter of fuel management:

If you are keeping a schedule of switching between external wing tanks and then internal wing tanks, you may end up with a lot more fuel in the vapor return tank than you have scheduled. Probably not the kind of thing that would get noticed unless you are flying a LONG time, but if 10 gallons per hour is the maximum.... it could make relevant an understanding how much fuel is going back to the vapor return tank.

MOST importantly, however, is that the checklist says simply to start up and take off with the vapor return tank. If you have a full fuselage and external tanks, then you are switching to the fuselage tank asap to prevent reversibility. Then you are switching to the external wing tanks so you can drop them if need be. That is a LOT of time spent returning vapor to the vapor return tank... And if it is full then you are losing fuel.

Anyway, I was going to do some testing last weekend to verify that there is/isn't any vapor return but... you know.... that F-16 module
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