Has the Dakota Cub fuel valve changed your fuel management?

[ysifly2]

I installed a Dakota Cub valve several months ago. I did some initial checks at the time and then continued my old practice of flying on individual tanks with no problems.

Last weekend I decided to leave the fuel selector on both. I started with full tanks, flew 1 hour, ate lunch and then a 1 hour return. I noticed that the fuel gauges were tracking very differently so I sticked the tanks when I landed. Surprise I had 6 gallons in the left tank and 12 gallons in the right tank.

I'm sure there is some more flow resistance from the right tank, but I didn't expect this much difference. Is this normal? Should I be looking for some partial blockage from the right tank?

BTW, the next morning the left tank had 8 gallons and the right tank had 10 gallons. So I suspect the wings aren't exactly level.

My normal practice was to take off on left, the switch to right in level and cycle between the two every set period of time...
I have recently installed the Dakota Cub valve, but not yet flow with it (very soon though!)... but will plan the same L-R-L-R approach to fuel management, especially for cross-country flights.
it was also noted in the following thread:
http://www.shortwingpipers.org/forum...ll=1#post97448
but, during the install as I was filling each tank 4-gallons at a time to calibrate the fuel gauge and checking for any leaks,

I found (measured) that the tanks will cross-feed and equalize when in the OFF position.

Another normal practice is to always stick my tanks to read the levels within each tank prior to take off, but will be very cautious to not use the OFF position when parked at a transient airport where I don't intend to get fuel. If I had been managing fuel by time in each tank, I could see an instance where one may land with 'some' fuel in the right tank and a 'known' quantity of an hour in the left tank say, and park with the valve in OFF and have half of the fuel in the left tank level to the right tank.


Bryan

[Tp109]

If the dakota valve is connecting the tanks in the both position also like the mall valve does, you want to be very careful about running the right tank dry and then switching to the left tank and not the both position.

[deandayton]

If the dakota valve is connecting the tanks in the both position also like the mall valve does, you want to be very careful about running the right tank dry and then switching to the left tank and not the both position.

I'm not sure what the Maule valve does, but you've got me curious. Why shouldn't you switch to the left tank after running the right dry?

[ysifly2]

What he intended was that if you run the right tank dry... you should be sure to absolutely select the left tank on the valve (i.e. Do not select both if you had run the right tank dry).
Theoretically, if you ran the right tank dry and then switched to both, up to half of the fuel in the left tank could equalize to the right tank... question / concern is how that impacts with the "level flight only on right tank" limitation.


Sent from my iPhone using Tapatalk

[deandayton]

Ah, now I understand. Thanks

[walt.buskey]

As I've had too many other things to fix (and too many other not-plane-related things to do), I haven't yet flown with the DC valve, but have had the same experience when I was checking for leaks after installation: a relatively slow cross-feed when the valve is in the OFF position. I say slow because I had a leak on one side and started to drain the 5 gallons I'd put in, only to find my 5 gallon can wasn't nearly big enough. (!) A bit of a surprise there. Draining was painfully slow until I just went to the other tank to drain there as well. It wasn't til later I realized I should have selected only the leaking side.

I also didn't care for the original valve and chose to eliminate the AD associated with it. The DC valve is almost pretty enough (if you love machines and quality work, I suppose..) to put in an art museum. When 57A gets back together, my plan is also to use L-R-L-R fuel management while cruising, perhaps the BOTH when in pattern, but to always stick tanks first before any take-off.

Also replaced the original struts with sealed units, to eliminate another PITA AD. Figured both mods were good investments.

Walt

[Tp109]

What he intended was that if you run the right tank dry... you should be sure to absolutely select the left tank on the valve (i.e. Do not select both if you had run the right tank dry).
Theoretically, if you ran the right tank dry and then switched to both, up to half of the fuel in the left tank could equalize to the right tank... question / concern is how that impacts with the "level flight only on right tank" limitation.


Sent from my iPhone using Tapatalk

Correct, that's what I meant. With the Maule or the Piper valve if modified with the extra hole in the plug for both, if you takeoff with an empty right tank and a full left tank and select BOTH once airborn, it only takes 20 minutes for that fuel to equalize. If you run R dry and had 8 gals in the L when you switched to R, when R runs dry if you select BOTH instead of L you will be at 3 gallons in each tank within about 10 minutes. With all 8 in L you should have an hour before you are gliding, but in BOTH you transferred usable fuel into the right tank which may not be usable in a nose high attitude, where it would in the L tank.

Say you had planned to for the switch to L 30 minutes out from landing which gives you 30 minutes reserve. The safety issue here is the R tank plumbing, gravity will always try to keep L and R equal, but the L side feeds the engine faster than the R side in flight, by the time you get to the pattern where you transition to nose high attitude where you need the L tank aft fuel pickup, you will be close to fumes in the L tank, now landing is looking good until captain Blind who never clears final before taking the runway to takoff pulls out onto the runway as you are bringing the throttle to idle at 100 feet, now you gas it and begin your nose high attitude go around and your engine quits with 3 gallons of fuel in the Right tank

[Glen Geller]

Say you had planned to for the switch to L 30 minutes out from landing which gives you 30 minutes reserve. The safety issue here is the R tank plumbing, gravity will always try to keep L and R equal, but the L side feeds the engine faster than the R side in flight, by the time you get to the pattern where you transition to nose high attitude where you need the L tank aft fuel pickup, you will be close to fumes in the L tank, now landing is looking good until captain Blind who never clears final before taking the runway to takoff pulls out onto the runway as you are bringing the throttle to idle at 100 feet, now you gas it and begin your nose high attitude go around and your engine quits with 3 gallons of fuel in the Right tank

This is a compelling argument for using the conventional L-R-OFF fuel valve on a PA-2X with normal fuel plumbing configuration.
And I know about Captain Blind, he flies an RV6 out of KSPB in Scappoose OR.
We have another name for him...

GG

[Pacer42Z]

This is a compelling argument for using the conventional L-R-OFF fuel valve on a PA-2X with normal fuel plumbing configuration.
And I know about Captain Blind, he flies an RV6 out of KSPB in Scappoose OR.
We have another name for him...

GG

I agree with Glen, besides that I have four wing tanks, I think the original plumbing is actually quite intuitive. If I don't use my two extra wing tanks, I take off on the right main and fly it half empty, then on the left main until half empty, then back to the right until it is empty and back on the left and start looking for a place to land.
Draining out of both (main) tanks at the same time you may notice too late that you better find a place to land.

Juergen
Pacer N3342Z

[Glen Geller]

I agree with Glen

That's rare in my life. Thanks.

One other thing I forgot, I have the 8 gallon aux tank under the rear seat.
When the right tank is at 1/3 full it can be used to pump fuel up into it, takes about 20 minutes in level flight.
Changing other valves and fuel management might be too much for me to handle.

GG