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Dakota 24 gallon tanks with CC headerless STC

Dick Williams

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Idaho
We want to put the Dakota 24 gallon tanks on a 180hp certified Cub that already has the Cub Crafters no header fuel selector both STC. The verbiage in the CC STC states that we must placard the useable fuel at 21 gallons. Is this legal mumbo jumbo or are we really going to have 6 unusable gallons? Hardly worth the money if that's the case. I've heard it may have to do with unusual attitudes, or the size of the fuel line at full power. Does anyone out there know the real story? If we can get close to the 24 gallons in straight and level flight we would be happy.
 
We want to put the Dakota 24 gallon tanks on a 180hp certified Cub that already has the Cub Crafters no header fuel selector both STC. The verbiage in the CC STC states that we must placard the useable fuel at 21 gallons. Is this legal mumbo jumbo or are we really going to have 6 unusable gallons? Hardly worth the money if that's the case. I've heard it may have to do with unusual attitudes, or the size of the fuel line at full power. Does anyone out there know the real story? If we can get close to the 24 gallons in straight and level flight we would be happy.

Sounds like you are mixing STCs. Not sure what the CC headerless STC says so can’t comment but when adding multiple STCs on the same airplane the installed has to determine the interrelationship won’t introduce any unairworthy conditions.


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To pile on Dick's question...If anyone has flown the Dakota 24 tanks without a header, did the experienced usable fuel (or unusable) seem affected by fuel selector valve placement during any aggressive maneuvering (extreme pitch, bank, sideslip)?
 
Best takes for using all the fuel were the ones in the Arctic Tern Interstate. I am surprised none like that are in cubs around here.
 
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I believe if you do a steep enough climb you can get the rear to the tank low enough that with less than 3 gal you can starve the engine of fuel. I did it running the Right tank only with about that much fuel and held in a steep climb to see what kind of decay in the feet per min climb I would get. I got about 2,000 ft when the engine started to cough. It has been a few years since I have done that anyone else have that happen? Just dropped the nose it was happy. Kind of like the early Cessna with rear fuel feed only, you can cough the engine in a prolonged nose down decent with low fuel. In that case you pick the nose up.
DENNY
 
I would talk to Dakota Cub. They have their own headerless STC that is identical to CC but uses Dakota Cub gascolator and fuel selector. There is some unusable fuel but I don't remember it being 6 gallons. There is less usable fuel when you look at how the system is designed vs the header tank left-right-off system where you always have a few gallons of gas in that header tank no matter what the attitude of the aircraft is. Think of being low and unporting a fuel pick up.
 
While I don't know the why in this case, the test would have been done in the most adverse situation. So assume this: one tank shut off, the airplane flown in a skid until the engine sputters, shut off the low tank and turn on the full tank...measure the amount remaining in the low tank. Multiply that number by two because two tanks. Is that number 6 gallons?

I have two 24 gallon tanks in my EAB Cub and have flown it until the pucker factor gets high. During that low level time I'm careful to not do any unusual attitude flying. My pucker factor exceeds 6 gallons remaining. The sight gage has shown not very much remaining and it does indicate to the bottom of the tank...when level. 6 gallons is 45 minutes...isn't that the required reserve?

I suspect with the CC STC, if it were flown coordinated without steep nose up or down attitudes, you could use most all of the fuel.
 
I just looked in the flight manual supplement for the Dakota Cub Headerless Fuel system in my Super Cub with 18 gallon wing tanks and each tank is placarded as 17 gallons usable.
 
I am not sure you can combine STCs in a way that replaces parts specified in one STC with parts from another. It could be that the Dakota STC uses the same valves and plumbing, and that they would give you their STC if you just bought their tanks?

You can combine STCs that interfere with each other (Sportsman and VGs come to mind) but say you choose Micro for the wing and AMD for the empennage? I think that might not work legally. Gas tank quantity would have no effect on the flow, but legally it might be problematic.

As usual, opinion.
 
Thank you for the responses. We have found that the testing for the STC involved maximum angle of attack and are confident that st. & lvl. flight will give more useable. But we will flight test after installation and post results.
 
Was the original STC and test done with just one tank fuel line, like the original Cubs? Perhaps since that STC was done with the header tanks that was part of it. As soon as we add two fuel pickup lines from each tank it affects the fuel unporting issues.

I am not knowledgeable like Steve Pierce but I seem to remember that the early cubs only had one fuel pickup port per tank. Yes? No?

Thanks

Bill
 
Not as smart as Steve but I do have a 1951 cub. The right tank has a rear only feed with a return/vent line that feeds into the top of the site gage. Both lines go to the rear header tank then single line to the fuel valve. The left tank has both front and rear feed to the header tank, the front feed is labeled vent. From front header single line to fuel valve. I believe they stayed that way through out the entire production. If I am going to work on a tank (usually fuel drain issue) I run it until the engine coughs, try to bank and get any extra out cough again and there is little to no fuel left. 1959 Cessna 180 tanks drained through the gascolator also had very little fuel in tanks. I do all sorts of turns/banks/slips with only a fuel gallons of fuel in the right tank with no problems other than that steep VX climb I mentioned I suspect the rear header tank is protecting me from myself. Interesting to see how it would perform without one. Considering two header thanks up front with new build.
DENNY
 
The right tank has a rear only feed with a return/vent line that feeds into the top of the site gage. Both lines go to the rear header tank then single line to the fuel valve. The left tank has both front and rear feed to the header tank, the front feed is labeled vent. Considering two header thanks up front with new build.
DENNY
Is your plane placarded to use the left tank only for take off and landing?

If your new Cub has two outlets on both tanks, you shouldn't need any header tanks. Mine has no headers and no issues.
 
Frankly, other than adding a bit more complexity (four more fuel line connections and the two header tanks themselves) I have never seen any down side to the header tanks in the original Cub configuration. The Cubs I've flown had a single aft pickup on the right wing, and fore and aft pickups in the left wing.

MTV
 
Dick, I have a '54 Cub with exactly this combination since 2009. I've never unported a tank, even in steep turns. OTOH, I don't do steep climbs after takeoff with less than 6 gals remaining. I view it as a reserve - I don't plan to use it, but if I have to, I know I can make to the next stop as long as I don't maneuver aggressively.
 
Is your plane placarded to use the left tank only for take off and landing?

If your new Cub has two outlets on both tanks, you shouldn't need any header tanks. Mine has no headers and no issues.
No placard in my cub, My Pacer which was similar fuel system without header tanks had a right tank restriction Placard but not the cub. My IA has a front and rear feed on both tanks and no header tank system and flys like myself Right or Left tank only no both, he also reports no issues with any maneuvers. It is just that hard low fuel VX climb that makes me wonder a rear header tank won't help in that case so both would have to be in the front. I normally avoid hard Vx but you never know what a flight might bring ya. Next time you get down to 2-3 gal in a tank isolate it and see if you can cough it with a hard Vx prolonged climb, it would be a lot simpler without header tanks.
DENNY
 
This is good to know. We have put an order in for the tanks and are planning an installation this fall. We will flight test it ourselves.
 
Just a suggestion, but if you have the old style fuel valve and gascolator you may want to give Dakota Cub a call. I believe that if you buy new tanks, valve and gascolator, they will throw in their STC paperwork for the headerless system for free. That way you’re not mixing STC’s. The valve is very nice.
 
Just a suggestion, but if you have the old style fuel valve and gascolator you may want to give Dakota Cub a call. I believe that if you buy new tanks, valve and gascolator, they will throw in their STC paperwork for the headerless system for free. That way you’re not mixing STC’s. The valve is very nice.
Fuel valve and gascolator, don't have to buy their tanks.

The headerless system was flight tested at crazy attitudes on the Super 18.
 
Fuel valve and gascolator, don't have to buy their tanks.

The headerless system was flight tested at crazy attitudes on the Super 18.
Correct - do not have to use the Dakota Cub tanks but you do need the fuel valve, gascolator, 2 fuel tank bungs and snorkel/pressure vented caps with the STC.
 
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