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Difference between CC & Dakota headerless designs? Exp PA18 Fuel system decisions

J

JohnnyR

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AK, ME - what time of year is it?
Does anyone have the install drawings for the CC and the Dakota headerless fuel system (PA18) they can share?

Any commentary on differences between them is welcomed!

Am currently planning fuel system for Legend PA18 with Atlee 30.5g tanks, and there is musing at the Legend factory that a crossover tube may not be needed. There is also a suggestion to just go with simple on-off valves for each tank instead of a single L-R-Both-Off.

I am of the thinking that if a vented cap gets clogged, a tank could be deformed/collapse from the fuel/air draw. Always thought the crossover tube, even with its potential sidehill parking issues of draining from one tank to another, was a good idea to equalize the pressure.

J
 
If you wanted the crossover vent just put outboard vent ports like Skywagon mentioned then whatever valve you want. Best of both worlds. DENNY
 
On another note I know the older Atlee tanks had a outboard vent that came out the bottom of the tank. Does yours still have that? DENNY
 
My Cub’s fuel vents are Cessna style.

If running on Both is it possible to collapse a tank if one vent is blocked? I wouldn’t think so, and a guy should recognize one tank is emptying before he runs out on the one tank.
 

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The vent is high on the outboard side. Like Cessna, it uses a one-way check valve so fuel doesn’t find a way out.
 
I wonder about the check valve when the fuel tank is heated and everything tries to expand and vapor pressure increases. Does it maybe have a tiny hole for that purpose?
 
Standard vented caps. They cover the expansion problem while the under-wing vents allow higher flow rates for bigger engines.
 
stewartb said:
The vent is high on the outboard side. Like Cessna, it uses a one-way check valve so fuel doesn’t find a way out.
Click to expand...

Something like this? Opens at 1.5 psi according to the specs.
Marty57

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stewartb said:
The vent is high on the outboard side. Like Cessna, it uses a one-way check valve so fuel doesn’t find a way out.
Click to expand...
Those Cessna valves are notorious leakers when the tanks are full. It could just be because of their flapper design? Also the Cessna tanks have a cross vent tube which is open inside the tanks on the outboard ends. So when the tanks are full with one wing low, the fuel does flow across ship and overboard until the level goes down a bit.

Did you ever wonder how the fuel tanks are vented in the long wings on an airliner? The vent is connected to the tank at the outboard end of the tank, the vent tube then goes all the way across ship to the other wing tip where the vent exits under the wing. No cross flow at any wing angle. There is also a small collector tank at the outlet in case there is any overflow.

If stewart's vent was connected to the top forward inboard corner of the tank with the vent mounted where it is, he wouldn't need the check valve. Fuel being as viscous as it is can work it's way through some of the best valves.
 
JohnnyR said:
Does anyone have the install drawings for the CC and the Dakota headerless fuel system (PA18) they can share?

Any commentary on differences between them is welcomed!

Am currently planning fuel system for Legend PA18 with Atlee 30.5g tanks, and there is musing at the Legend factory that a crossover tube may not be needed. There is also a suggestion to just go with simple on-off valves for each tank instead of a single L-R-Both-Off.

I am of the thinking that if a vented cap gets clogged, a tank could be deformed/collapse from the fuel/air draw. Always thought the crossover tube, even with its potential sidehill parking issues of draining from one tank to another, was a good idea to equalize the pressure.

J
Click to expand...
CC and DC headerless fuel systems are identical in respect to plumbing. Only difference is the DC system calls out their fuel valve and gascolator.
 
I'm sure it has been mentioned somewhere already - for the simple inboard cross vent line a shutoff valve in the crossover line can be used to stop the side hill parking issue. And if you forget it in the closed position not really a big deal 99% of the time.
 
I’ve never had a drip from my fuel vents in either airplane. The Cessna usually doesn’t get the tanks filled but the Cub does.

Fuel cross-feed in my planes occurs from the fuel valve being on both. Easy to prevent but I’ve never bothered with it on the average slopes I park on. My valves stay on both unless shut off for maintenance.
 
KevinJ said:
Is there much difference between DC’s gascolator and Steve’s gascolator?
Click to expand...
The DC gascolator has the capacity for larger tanks than the standard Steve's.
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Johnny, what's your target fuel flow? Mine was 30gph and I met that with a little extra. Flow is dependent on venting. Don't short yourself.
 
Gordon Misch said:
I wonder about the check valve when the fuel tank is heated and everything tries to expand and vapor pressure increases. Does it maybe have a tiny hole for that purpose?
Click to expand...
There is a pin hole in the flapper valve. The line is supposed to rise after exiting the tank to reduce dripping.

Cessna vented caps only let air in.

Sent from my SM-G965U1 using SuperCub.Org mobile app
 
Difference between CC & Dakota headerless designs? Exp PA18 Fuel system decisions

Steve Pierce said:
The DC gascolator has the capacity for larger tanks than the standard Steve's.
View attachment 63373

View attachment 63374
Click to expand...

Both have the same 3oz bowl sediment capacity Steve. The only thing DC did different is the bowl retention with the screw..

FAA regulations is 1 fluid oz per 20 gallon main tank size. 3 fluid oz is good for up to 60 gallon main take capacity.

I have an optional 4 oz bowl for even larger fuel tanks up to 80 gallons.

Brian.
 
I've got a header less system with no crossover or both valve. I had a vent failure cause fuel starvation. Fortunately it happened on landing. The tank was collapsed to the point that I couldn't get a grip on the cap. I pushed up the drain to let air in, got a new cap, and so far so good. It was a good lesson!
 
There is a reason for the balance vent tube between tanks and the forward facing Fuel caps that pressurize the tank.

There is good reasoning for all these features. I installed it because these features make sense to me.

Everyone always seems to have a better Idea but these ones are proven.
 
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Steve's Aircraft (Brian) said:
Both have the same 3oz bowl sediment capacity Steve. The only thing DC did different is the bowl retention with the screw..

FAA regulations is 1 fluid oz per 20 gallon main tank size. 3 fluid oz is good for up to 60 gallon main take capacity.

I have an optional 4 oz bowl for even larger fuel tanks up to 80 gallons.

Brian.
Click to expand...
I was thinking DC told me they made their bowl with more capacity, maybe it was more capacity than the original. I remember working on a Super Cub with Atlee tanks and two gascolators and replacing it with your larger capacity bowl. It is easier to get the cotter pin retaining the bowl on your gascolator than the screw on the Dakota Cub gascolator.
 
Steve Pierce said:
I was thinking DC told me they made their bowl with more capacity, maybe it was more capacity than the original. I remember working on a Super Cub with Atlee tanks and two gascolators and replacing it with your larger capacity bowl. It is easier to get the cotter pin retaining the bowl on your gascolator than the screw on the Dakota Cub gascolator.
Click to expand...

Original Piper is 2oz. We went with 3oz because when we were developing the STC we wanted to match Husky bowl size and have it on the first AML.

Brian.
 
I have not been able to get a hold of DC to see if steves gascolator will be acceptable under their STC

I know CC stc will not accept the DC fuel valve.

The Dilema was we have the DC fuel valve with the Steves larger Gascolator and the CC STC

Unfortunately I did not have the STC to read before I bought it. At least the 24 gallon tanks are accepted under the CC stc
 
Dog said:
I have not been able to get a hold of DC to see if steves gascolator will be acceptable under their STC

I know CC stc will not accept the DC fuel valve.

The Dilema was we have the DC fuel valve with the Steves larger Gascolator and the CC STC

Unfortunately I did not have the STC to read before I bought it. At least the 24 gallon tanks are accepted under the CC stc
Click to expand...
I have installed DC fuel valve in a Cub Crafters fuel system. The CC fuel system is installed under one STC and the DC valve is installed under another STC. It is up to the installer to verify that one STC does not negatively impact the other. Dakota Cub developed their own headerless fuel system STC to sell their fuel valve and gascolator. They give you the STC when you buy the parts. The STC was developed out of the certified Super 18. Mark (the owner) is a machinist and didn't want he type certified airplane to be dependant on a vendor gascolator when he could build his own.
 
Some questions on fuel system design:

I'm curious - How would a "Both" valve reliably ensure fuel flow from a tank with a blocked forward facing pressure cap if there was no crossover tube or other secondary venting provided for the tank?

Couldn't the system be forced to only pull air off the "unblocked" empty tank on the other side because pulling from the "blocked" tank after sufficient vacuum was formed would require air to travel back through fuel in the feed lines of the blocked tank? See the areas marked with red arrows for sections that could completely cut off flow with an airlock.

Seems like in order to safely capitalize on the benefits of the L/R/Both/Off valve, there needs to be a secondary vent system. Ram air fuel caps can suffer from icing, bug invasion, etc., as can any venting, but to rely on just one source of equalization?

CC-Dakota headerless tube routing.jpeg
 

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You have just described several good reasons for installing a cross vent line. If there is any potential for vent blockage in your use of the plane, then absolutely install a cross vent. Make certain you connect it to the outboard ends of the tanks to ensure only air cross feeds.
 
The main reason for the cross vent tube is that if one tank runs empty and you do not have the cross vent tube the air pressure from the empty tank will go down the fuel line and push against the remaining fuel in the opposite tank - reducing or even stoping the flow. The cross vent will allow the top and bottom pressure to equal out to allow the remaining fuel to flow to the carb.
 
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