Fuel tank selector cock

[Dingeme]

I updated the spitfire accusim core to 1.5.2. Not sure what previous core update was installed, but it was an much older one.

The technique I use to be aware of when the Mk II top tank was out of fuel, was to fly with the top tank fuel cock ON and bottom tank fuel cock OFF. So when the top tank was empty, the fuel pressure would drop and I switched the bottom tank fuel cock on. This was an easy way to be aware of when the top tank had ran out of fuel.

With the new core update I'm running with the top fuel tank selector ON and bottom OFF and when the top fuel tank reaches 0% the engine does not starve of fuel. The bottom fuel tank capacity just continues to drop (100->99%). At first I thought this was some leftover fuel from in the fuel system lines running to the engine, but even when flying 5 min on empty top tank with top tank selector ON, and bottom tank selector OFF the spitfire keeps taking fuel from the bottom tank. When I have both fuel selector cocks to OFF the fuel pressure start to drop and the engine sputters after a little while due to fuel starvation before it dies.



In the picture of the Mk I (tested this both on Mk II and Mk I) the top fuel cock is on, bottom fuel cock is off, top tank is empty and the engine has been running from the bottom tank.

According to the the schematic from the spitfire fuel system and combined with the quote from Killratio from another thread the spitfire should starve of fuel when the top tank if empty and top tank fuel selector cock is ON and bottom fuel selector cock is OFF.

1. Both cocks OFF... fuel will not feed to engine but fuel WILL feed top to bottom (say if bottom is holed badly).
2. Both cocks on..fuel feeds from both tanks to the engine as required to keep up pressure. Fuel ALSO drains from Top to Bottom as bottom tank is used.
3. Top cock off...fuel feeds from bottom tank to engine but fuel STILL drains from top to bottom to replenish.
4. Top cock on, bottom off .. fuel feeds to engine from top tank, bottom tank stays full.

You can see from the above that fuel starvation is only possible in cases 1 and 4.

Darryl

Is this the correct behavior for the fuel system?

[francesco.doenz]

Dear Dingeme,
Being not at all into mechanics, I understand the fuel system as explained by Darryl, but what I never understood is the connection without stopcock between both tanks, because as described by Darryl in situation one, if the lower tank is badly shot up it will leak inspite of the selfsealing mechanism and BOTH tanks will end up empty, EVEN IF THE UPPER STOPCOCK IS CLOSED!? It seems to me impossible to isolate the tanks because of this connection, inspite of it being written in the airpublication 1565A, under the heading "fuel cock controls and contents gauge" where it is stated: Either tank can be isolated, if necessary.!?
Would be interesting to get the opinion of an expert in this forum! Already many thanks!

[francesco.doenz]

Sorry, this topic has in part already been discussed here

http://a2asimulations.com/forum/viewtop ... 78&t=32839

but the question how to isolate the two tanks remains unsolved!?

[Killratio]

I've been out of testing pretty much for the "final stage" due to other commitments in RL.

Simple answer is that the fuel setup as described in my original post is correct. If the new "flow" is as described by the OP, then something has changed (I think fuel was messed with to fix a filter problem) and needs looking at.


The bottom tank can NOT be isolated from the top tank but can be isolated from the engine. So an empty top tank and the bottom tank shut off WILL stop the engine. Fuel will leak from the top tank if holed but when empty, obviously that will stop. If the bottom tank WERE holed, then the whole lot top and bottom would drain.

That is why the bottom tank has heavy self sealing capability.


D

[francesco.doenz]

Thanks once more for your input Killratio, but for a newbie the reasoning for putting this connection without a stopcock between the two tanks remains hard to understand, if this connection did not exist it would have been so easy to isolate the two tanks!

[Killratio]

Francesco,

You are looking for logic in British Engineering..NOT a foregone conclusion I'm afraid

The main thing to remember here is that we are looking at essentially the very first Marque of Spit. The Mk II is nothing but a Mk I with a different engine to improve a bit of performance in a desperate situation. No real "redesign" was undertaken, just bang on the newly available engine.

These two are the only ones of 24 marques to have the top tank operated by a separate cock. When the design WAS re-thought, the superfluous nature of that control was acknowledged and it was removed. I believe the two tanks were split to fit around the internal structure, not to provide "two tanks" per se. If a single tank would have fit there, that is what would have been used. Apparently removing and working on the tanks was a major pain, so a single odd shaped tank would have been impossible to put in and pull out without pulling the whole front end of the aircraft off.

cheers


Darryl

[Dingeme]

Just applied the 07-15-2014 update and the fuel cock behavior is still the same. Are there any plans to change them back in a next update, or is it to deep in the code. It kills the immersion abit when you have to wait until the top tank is empty and the bottom tank is below full before you can know you have used up all of the upper fuel. Offcourse the shift+3 menu helps, but it feels like cheating

[Scott - A2A]

Dingeme,

Nice catch. We may be days away from a Cherokee update, but I just did this fix and tested it and it seems to work well and as expected. So this should be in the next update. Thanks for posting.

Scott.

[Dingeme]

Awesome, thank you for the heads up. This was in my opinion the only thing missing from making the Spitfire perfect. Can't wait to suddenly have my engine cut out because I forgot the lower fuel tank cock and not watching the fuel pressure.