Hypothetical fuel question for the Cherokee Six.

The Six has 4 tanks, and mains are to be burned down before tips to reduce the wing bending moment.

If one wanted to go on a short flight carrying minimal fuel (say 2 hours) and keep two tanks completely empty, would you keep the mains empty or the tips?

I am thinking drain down the mains to empty and just utilize the tips as there are no takeoff/landing restrictions using any of the available tanks. Any issues with doing so?

The Six I’m familiar with has 17 gallon tip tanks. A two hour flight probably burns 30 gallons. 4 gallons isn’t enough legal reserve, and it may not be useable anyway. If you want to cut it really close using just the tips, you create one of two situations. Either you burn one tank dry, or you have your reserve (tiny already) split between two tanks. So mains empty doesn’t work, at least for me.

Understood, let me rephrase. If i only wanted to carry 34 gallons of fuel using two tanks which tanks would be the best solution to use.

If you are looking for 34 gallons, just fill the main tanks (inboard wing tanks) to the tabs. In my six I only fill the tips if I need the range on long flights.

I don’t think it really matters much with 34 gallons but just playing devils advocate... but wouldn’t keeping the mains empty and the tips full reduce wing bending moment?

Only reduces the bending moment when in flight, increases it when taxing around and landing. So, if the strip is short requiring a firm landing or surface is rough during taxi it may be more damaging to the wing to carry the fuel outboard. If I remember correctly, and I very possibly could be wrong, the wing is certified to 3.5 g's positive and only -2.0 g's negative. Me, I would carry the fuel inboard.

Tim

Scott -

Your initial thought it correct. If you want minimal fuel in a 6 you use the tips. This is per the POH, not internet speculation. I often use only tips or only partial tips if doing a short flight (<1hr). Around here I tend to give myself a minimum of 1hour reserve, so I plan on having at least the equivalent of one tip tank in reserve. You won’t even notice that weight in a good six.

That being said, if you want to use the mains I’m sure it’s fine, just not by the book. The wings on a Cherokee are very robust, we twist the hell out of them on both rough strips and high winds day in and day out for tens of thousands of hours. So I doubt the wings will fall off if you land a little bouncy with fuel in the tips, or catch some turbulence with fuel in the mains.

One of the interesting factoids is that while the earlier 6s had 4 tanks accessible by a 5 position selector, newer 6 variants had 4 tanks but only a 3 position selector--the outboard tanks drained into the inboard tanks. So I speculate that although the earlier POH definitely said to burn off the inboard tanks first before burning from the outboards, it really doesn't make a whole lot of difference regarding stresses to the structure of the wing--unless Piper materially changed that structure on newer models, which I don't think that they did beyond changing from the Hershey bar to a tapered plan form. Either way, the 6 variants, all of them, are hell for stout airplanes. The 6-260 that I have some hours in was a veritable tank, about as solid (if kinda ugly) as any airplane I've flown.

Cary

Thats a good point Cary, the ‘79s had the hershey bar wing and the 3 position switch and I am not aware of any structural change... if that is the case I guess Piper concluded it was good enough.

I was curious so I looked it up. Minimum fuel should be carried in the tip tanks. The main tanks are inboard of the main landing gear so with no fuel in the tip tanks but fuel in the main tanks the compression load on the top wing skin is increased when on the ground. A hard landing in this situation can buckle the top wing skin. Having fuel in the tip tank and nothing in the main tanks reduces the compression load on the top wing skin inboard of the main landing gear. Piper increased the thickness of the top wing skin at some point thus eliminating this potential issue.

We always leave the tips empty or min fuel and use the mains for 3hr. - short trips. One reason is the fuel pick-ups in the mains will burn the tanks dry down to about two cups of fuel. I have proven this in our ship. This is in a Pathfinder which may be different.