fuel issues without really trying

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ghostflyer
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fuel issues without really trying

Post by ghostflyer »

Left departing airport with 160 liters for a 2.5 hour trip . Planned to land with about 60 liters left . Trip only took 2.4 hours . About 20 miles from home a fuel check was done again and fuel tank gauges showed what i expected and the fuel computer showed that there was 68 liters left . All good . descent commenced and passed over a small airfield not far from our home airfield. Gave a inbound call and started my landing checks. glanced at the fuel gauges again and to my shock all gauges showed empty and then the engine coughed , A quick relook and the left hand tank showed a little fuel . selected that tank and engine fired back to life. No circuit pattern for me, a straight in approach. Checked the fuel computer and showed 60 liters left. Landed ok [not the best landing but under a heap of stress].
Taxied up to the hangar and found a fuel cap missing. I checked the quanity and caps before departing .Found a some bits of the cap in the tank after a close inspection . The caps were no older than 3 years old . On the inspection in the hangar one tank totally dry and the other had 10 liters in it. so with out a tank cap one tank will empty out and the other will transfer fuel across.
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GAHorn
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Re: fuel issues without really trying

Post by GAHorn »

Yes, the fuel filler caps are in a "low pressure" area and in normal flight, fuel will be siphoned out and overboard. It's also been noticed with cracked/dried cap-gaskets. The correct, vented caps (Cessna) has a one-way check-valve incorporated into the vent. Some aftermarket caps will allow fuel to be sucked overboard.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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n2582d
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Re: fuel issues without really trying

Post by n2582d »

Ghostflyer, I assume you did not have the cap chained to wing. That'll get your attention when the cap comes off or is accidentally left off! Don't ask me how I know. :oops:

Here's my idea to prevent a lost cap from causing fuel from the opposite tank to siphon out. Two of these check valves could be mounted in the overhead cross vent, one on either side of the gooseneck vent. Andair makes a similar valve. They would also prevent fuel from vomiting out the gooseneck in a steep dive and during braking on landing. I think they might help the chronic problem a lot of Cessna's have with uneven fuel feeding between the left and right tanks -- not sure about this -- that might have more to do with how the caps are sealed and vented. Of course the challenge would be approval.
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Gary
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johneeb
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Re: fuel issues without really trying

Post by johneeb »

Gary,
Would you also put one in each supply line to keep those lines from cross feeding (assuming the fuel valve is in both).
John E. Barrett
aka. Johneb

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n2582d
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Re: fuel issues without really trying

Post by n2582d »

John, Good point -- flapper valves in the cross vent line wouldn't change the pressure differential between the tanks with a leaky or missing cap on one side. With only a bleeder hole in the valve it might actually exacerbate the difference by not allowing the tanks to vent as freely via the gooseneck. Having check valves in the main fuel line would prevent fuel from one tank from back flowing into the other tank with a missing cap but I don't think it would prevent uneven feeding from tanks with different head pressures.

So my amended solution for the missing cap problem? 1.) If possible have caps that have tabs that align with the slipstream. It's easier to detect whether they are on tight during preflight of after refueling. On the original style caps one could paint alignment marks that would serve the same purpose. 2.) My initial 170 checkout was by an veteran MAF pilot. He taught me, as part of the after-takeoff checklist, to look back at the inboard trailing edges of both wings for fuel. Generally, a fuel cap is going to be gone because the fueler forgot to put it on after fueling. I think a cap coming off late in a flight, like what happened to Ghostflyer, is unusual. 3.) Select the fullest tank and land ASAP.

Now, if money is no issue, there's this low fuel level detector you could install if you could get it approved.
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Gary
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johneeb
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Re: fuel issues without really trying

Post by johneeb »

Gary,
If money were no object we could bring back the Flight Engineer position and he could monitor all these systems in our oh so complicated 170s. :lol:
John E. Barrett
aka. Johneb

Sent from my "Cray Super Computer"
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GAHorn
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Re: fuel issues without really trying

Post by GAHorn »

Those check valves likely have "cracking pressures" which would defeat any use of them in a venting system. (and of course, the recertification of the fuel system is something that not even Cessna wanted to undertake, obvously...)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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