Special limiting valve

[Mobius_cz]

From the manual :

"The pipe that feeds from the drop tank to the rear tank actually connects to a special limiting valve, mounted in the rear tank. If the plane carries a drop tank, that limiting valve will only open when the rear tank content drops below 240 liters.

 

At first, no fuel is consumed from the drop tank, because the limiting valve is closed. So in the beginning fuel will be consumed from the rear tank, until its level drops to 240 liters. Only then, the limiting valve will open and allow fuel from the drop tank to feed into the rear tank. When the drop tank is empty, the fuel level in the rear tank will drop below 240 liters – this is the indication that the drop tank is empty".

 

If i understand that correctly you will use from rear tank 52l of fuel then fuel indicator stops at 240l and "special limiting valve" allow fuel to flow from the drop tank to rear tank but rear tank still remains on 240l until drop tank is used.

 

What is the point of this valve? Avoiding over pressure the rear tank, maintain the same pressure during consuming drop tank? This is really interesting.

[fastfreddie]

Unsure of the engineering reasons for doing it this way but you can tell if the drop tank is empty when the rear tank level falls below the 240l mark.

[Random]

Suspect its for CoG reasons. Get the rear tank down to a level where the CoG is in a favourable position without the drop tank. So if engaged by the enemy you ditch the tank and have less to worry about with the CoG.

[ZaltysZ]

Probably the point is to move CoG forward as quickly as possible.

[Yo-Yo]

From the manual :

 

 

If i understand that correctly you will use from rear tank 52l of fuel then fuel indicator stops at 240l and "special limiting valve" allow fuel to flow from the drop tank to rear tank but rear tank still remains on 240l until drop tank is used.

 

What is the point of this valve? Avoiding over pressure the rear tank, maintain the same pressure during consuming drop tank? This is really interesting.

 

To spend drop tank fuel first. And, yes, maintaining CG not so far aft. But not much.