Author Topic: A point on the P38l fuel system (Read 540 times)

Hazard69 · « **on:** January 04, 2004, 04:02:58 PM »

Just a few things ive noticed.
In planes like the P51 as fuel is selected it is first put in the main wing tanks before the aux tank. Presume as it reduces the aircrafts manoeverability. But then why is it that in the P38 for any fuel selection the same fuel is put in all tanks.
25% all 4 tanks at 25%
50% all 4 again 50% and so on.

Now the aux tanks are located in the outer wings. Fuel in that serves to reduce an already low roll rate. Thats why the two aux tanks are burnt first. My question is why not have it like this:-
25% LM n RM at 50%
50% LM n RM at 100%
75% LM n RM at 100% n LA n RA at 50%
100% LM, RM, LA and RA all at 100%

This serves to help improve the P38s roll rate even with higher fuel levels remaining......

Also, all american aircaft......P40, P47, P51 have 75 gallon ext tanks. The P47 actually has an option between 75 and 150 gallon ext tanks. Why doesnt the P38 have a similar option, of two 75 or 150 gallon ext tanks rather than the single or twin 150 gallon tanks?

Ack-Ack · « **Reply #1 on:** January 04, 2004, 04:11:36 PM »

You don't have to bother with the fuel system in the P-38, keep it on auto-fuel.

ack-ack

Widewing · « **Reply #2 on:** January 04, 2004, 05:23:32 PM »

Skuzzy is likely to move this to Aircraft and Vehicles, but to answer your last question; the P-38 required tanks designed specifically for its particular shackle design. The 160 gallon tanks were standard, with 310 gallon tanks as optional. However, the 310 gallon tanks were never used in the ETO or MTO. Use in the SWPA was not commonplace either, due to the increased risk of these large tanks striking the tail when released.

The standard 150 gallon paper tanks and 75 gallon aluminum tanks were not usable on the P-38.

HTC doesn't model the P-38 tanks as 160 gallon, but rather as 150 gallons, which is actually closer to the truly usable amount contained in the 160 gal. tanks.

My regards,

Widewing

Seeker · « **Reply #3 on:** January 04, 2004, 05:46:27 PM »

The auto fuel switching is designed to preserve the aircrafts centre of gravity.

Wing tanks are largely irrelevant to this.

Hazard69 · « **Reply #4 on:** January 05, 2004, 03:34:59 PM »

Originally posted by Widewing
The standard 150 gallon paper tanks and 75 gallon aluminum tanks were not usable on the P-38.
Thanks for clearing tht up Widewing.

Originally posted by Ack-Ack
You don't have to bother with the fuel system in the P-38, keep it on auto-fuel.
Originally posted by Seeker
The auto fuel switching is designed to preserve the aircrafts centre of gravity.

I agree and I always fly with auto-fuel on. But this is not my point. My query is not about how fuel is used in the P38.
My query is with why is fuel loaded in this unusual manner in the P38. Fuel in outer wing tanks increases the aircraft's moment of inertia and thus making the P38 harder to roll. My query was that why instead of loading equal amounts (in % of course) of fuel in all the seperate tanks, why isnt fuel loaded first into the inboard main tanks and then as fuel load is increased is also loaded in to the auxiliary tanks (as its done in the P51).

AIRCRAFT AND VEHICLES FORUM!.......Hmmm....Now why didnt I think of putting it there......must have been drunk...lol

moot · « **Reply #5 on:** January 05, 2004, 03:43:04 PM »

same thing with some other planes, P47, 190A, ta152.. The aux or wing tanks are filled at the same % as every other tank.

Wing tanks happen to brake reaaaal easy when full on the 152, the aux (and aft) tank is a pain in the rear with the 190A and P47..

I asked HT about it and he replied it was "not as simple as you envision", so it's probably so.

Octavius · « **Reply #6 on:** January 05, 2004, 04:49:51 PM »

Moot, did you ask before or after this thread?

Punting that one for good measure.

leitwolf · « **Reply #7 on:** January 05, 2004, 06:04:49 PM »

Quote

Fuel in outer wing tanks increases the aircraft's moment of inertia and thus making the P38 harder to roll.

I dont know the actual reason but you can see it as an incentive to manage fuel manually.
It gives a slight edge over automatic fuel tank selection just like manual trim has tiny advantages over combat trim at the brink of a stall. Regarding fuel.. the difference is pronounced in some planes (every Fw190 and Ta152) and in some planes there's no difference at all (P51s and of course planes with only one tank - most Spitfire Marks and the 109s).
I'm not too sure about the 38 though.. it's so huge that even if the effect is modeled it's probably not worth the effort - plus the lightning is already invincible on auto

Ouch · « **Reply #8 on:** January 06, 2004, 11:27:01 AM »

(I know I'm gonna get slammed if I'm wrong, but)

IIRC, the AUX and Main tanks are parrallel in the wing. What I mean is that they are both in line with the direction of the aircrafts travel, rather than one farther out in the wing than the other. Thus there should be no difference in roll rate for having all the fuel in one tank (main) or two tanks (main+aux).

It DOES make a small difference in the center of gravity along the flight path, but it's pretty negligable.

(Damn, my spelling is so bad you'd think I worked for HT.)

Ouch out.

moot · « **Reply #9 on:** January 06, 2004, 06:36:25 PM »

a while before that. Was when HT and co still came around in blue.

deSelys · « **Reply #10 on:** January 07, 2004, 03:31:09 AM »

Quote

Originally posted by Ouch
(I know I'm gonna get slammed if I'm wrong, but)

IIRC, the AUX and Main tanks are parrallel in the wing. What I mean is that they are both in line with the direction of the aircrafts travel, rather than one farther out in the wing than the other. Thus there should be no difference in roll rate for having all the fuel in one tank (main) or two tanks (main+aux).

It DOES make a small difference in the center of gravity along the flight path, but it's pretty negligable.

(Damn, my spelling is so bad you'd think I worked for HT.)

Ouch out.

Sorry you're seriously wrong here. To demonstrate it, try to rotate a certain weight in your hand. Then you tie 2 objects approx 1/2 weight of the 1st to the ends of i.e. a ruler, you hold the ruler on its center section and you try to rotate it again. Weight is about the same (bar the ruler), CG is still in your hand, but the roll momentum is much greater (and is a relation of the weight of the objects, and of the length of the ruler). Or even better, you make yourself turn as fast as possible on your office chair (when your boss is out, that is

), with your arms along your body. Then you extend your arms. You'll see that your 'roll-rate' will immediately decrease.

Auto-fuel indeed keeps CG where the plane is well balanced, and drains outer fuel tanks first to help roll-rate. So you don't have any advantage by selecting the fuel tanks yourself. The only way to improve roll rate would be another repartition of fuel loadout as suggested in the 1st post.

moot · « **Reply #11 on:** January 07, 2004, 06:27:56 AM »

deSelsys, he's saying the tanks are not along the wing span, but placed one to the front of the plane, and the other in the rear of the wing, relatively.

Unless he's confused, which I doubt since everyone knows pulling your feet in while spinning the chair you sit on accelerates the rotation.

deSelys · « **Reply #12 on:** January 07, 2004, 07:00:40 AM »

Oops yes sorry... I pounced on him without reading carefully.

Then IMO you're right Ouch. Sorry again.