An anonymous forum to allow you to share those moments in flying that caused you concern. You can post without registering a username, registered users can log out to post
By Joe Dell
#1471917
Yesterday. Cherokee Six. 260. Mains to tabs. Tips full. Flew the first of three legs on left main, switching to right main before landing.
Flew the second (30 minute) leg with right main selected.
Took off on final leg on right main with the intention of running that tank down to match what remained in the left main before going to tips.

About fifteen minutes or so after levelling off in the cruise, the engineer in the right seat commented that the right tip indicator had packed in and was reading zero. I said he'd have to sort that out back at base. Clue missed.

Ten minutes later the engine starts to surge. I immediately switched the fuel boost pump on and check fuel selector. Right tank is selected and there's plenty of fuel in it. Engineer says he suspects a fuel flow problem or over lean mixture. EGT high. Mixture returned to full rich and carb heat on. There's a definite improvement. Boost pump switched off. Engine stops.

Pump back on. Left tip selected and we start to breathe again.
On landing the right tip is empty. Fuel selector found to be a bit vague . On right tip when apparently indicating right main.
Pilot changing his name to Homer. :oops:
By Joe Dell
#1471944
It's SOP.

In order to keep the airplane in best lateral trim during cruise flight, the fuel should be used alternately from each main tanks, and when they are nearly exhausted, from each tip tank. It is recommended that one main tank be used for one hour after takeoff; the other main tank used until nearly exhausted, then return to the first main tank. When nearly exhausted, turn to one tip tank and alternate at one-half hour intervals to maintain lateral trim. Turn electric fuel pump ON when switching tanks.
==============================
User avatar
By Flyin'Dutch'
#1533872
Joe Dell wrote:It's SOP.


Is that Piper POH SOP or own SOP?

It is some time since I flew an older PA32 with the omniselector for each of the tanks but cannot remember that sequence from the POH.

My home grown SOP is not to rely on fuel which has to be transferred from somewhere else by means of a pump, when no other fuel is available.

I.e. in the Maule I would transfer the wingtip fuel to the mains as soon as there was enough space in the main tanks.
By cockney steve
#1533886
Quick question ! Why would you leave the tip tanks to last?....My thinking is that the moment of leverage will be much larger than an inboard tank, therefore, getting the weight inboard ASAP should improve stability? Await enlightenment .
By ChrisRowland
#1533900
Some gliders have inboard and outboard water ballast tanks, the recommendation is to dump the inner tanks first because this reduces the bending load on the wings compared with dumping the outers but not the inners.
By riverrock
#1533935
The whole wing produces lift. It will need to "pull up" the fuselage and fuel (or ballast).
It will bend more, if all of the weight it is pulling up is attached to one end of the wing (the inboard end) rather than more evenly distributed, by moving some of the fuel (or ballast) further out.
By cotterpot
#1533951
Thanks - After pondering further - it's not illegal I believe - I thought it might be something like that, although with tapered wings there is less lift towards the ends?

I'm out of my depth here :oops:
User avatar
By T67M
#1534060
As I recall, airliners with body tank (eg 747) burn the fuel in the body first, leaving the wing tanks until later to minimise the wing bending effect. I imagine main vs tip tanks is a similar logic.
By malcolmfrost
#1534084
Indeed, the 747-400 has 2 outer tanks (12500 kg fuel each), 2 inner (35000 kg each) a centre wing tank (60000kg) and a horizontal stabilizer tank (10000 kg), all numbers from memory!
Assuming full tanks, the stabilizer fuel is used first ( due to trim issues you have to land after about 6 hours if you can't get it out) then the centre wing feeds all 4 engines. The engines are then fed from the inner wing tanks until all the wing tanks have 12500 kg when the feed is switched to "tank to engine" and each tank feeds 1 engine, until you are left with about 2500 in each tank, which is normal Reserve+ Diversion +contingency.