Harer wing tank vent

[Laz]

I am rebuilding my 46 BC12D and have purchased the Harer STC. My plane always had two wing tanks. I am perplexed about the redundant fuel vent system that is included in the plans. I will comply with the STC but have doubts about what was actually intended. I have the following observations from the STC plans and paperwork Any help with the following would be greatly appreciated.

1. Taylorcaft never used this extra vent system and relied on the vented fuel caps my airplane has always had. Why are they needed now?
2. The STC drawing G-133 has a “Schematic Layout _vent Line” in that drawing it has a note “See Dwg G-170. G-170 has been eliminated in the revision to the STC. That lists the drawings to be used in the conversion.
3. There is also a “vent kit” drawing in the Packet of plans I received form Mr. Harer. It clearly shows a main fuel tank that is different that the one on Dwg G-133. It appears to be used with a main tank that has a place for a different fuel gauge than the cork and wire that my plane had.
4. The plans also come with a drawing of how to modify fuel caps for the wing tank to make them vented. Dwg G-160.
5. G-133 shows both wing tanks installed in the wings with the original Taylorcraft style vents in the cap and NO additional vent lines installed.

My own interpretation of the above conflicts in the plans is this. Taylorcraft built and certified the wing tanks without this vent system. Most Cubs I know with 85 and 90 hp engines just use the plane old fuel cap with wire gauge and no addition vent other than caps. Since drawing G-170 was eliminated that had something to do with the fuel venting system. Is it possible that just vented wing caps were all that was intended unless you had the internal gauge in the main tank and a non vented main tank. In which case the venting system would be needed. I have seen at least one Main tank like this and it appears that with the Internal gauge a venting port was installed on the top of the tank.

Sorry for all the long detail, but I do not like the fuel vent system and not that keen on the Soldered fittings in the filler neck.

[VictorBravo]

Re: Harer wing tank vent

Sorry for all the long detail, but I do not like the fuel vent system and not that keen on the Soldered fittings in the filler neck.

You mean you have doubts about holding a soldering torch flame con a fuel tank?!? Sheeesh, no guts!

I think that the complex Harer venting system was actually designed to provide some extra vent pressure on top of the main tank fuel level. I don't like it either, but if I recall correctly the new system wouldallow ram air from the upper wing tank cap pitots to further pressurize the main tank, by way of the aux vent lines that run down the windshield and are soldered into the main tank.

There's probably a better cleaner way to accomplish this, but alas....

[Ragwing nut]

Re: Harer wing tank vent

The extra wing tank vents are not needed as our F-21 did fine without them from the factory. It did have the header tank pressure vent. I would feel differently about this if there was no header tank. Wing tanks are merely auxilary fuel and have no need for extra pressure to the tank. However, if the STC says to put it there, put it there.

[N96337]

Re: Harer wing tank vent

Laz,
You can always apply for a field approval for a deviation to the STC. I'd be totally suprised if you got it, but you could always try. I had a Tcraft with the 2 wing tanks come in here without the vent system, and he said it was pretty much a toss of the coin if they'd drain properly when needed. We installed the vent system as per the STC and it made a world of difference! The owner was impressed and says now they never miss a beat. My Tcraft didn't have the vent system as per the STC and they both seemed to work just fine, but it WILL have the approved vent system when it goes back together. Think about it this way...if something happened and the STC wasn't followed to the letter (such as the vent system not modified as they show) your insurance company has a wonderful "out", as you're aircraft is now technically not airworthy, not to mention that the FAA is going to have a wonderful time with you, even if it's maybe not directly related to the problem. It's alot easier to just spend the couple hours and put the system in the way the STC calls out, and not worry. Besides, what harm will it do to have a bit of extra vent?
John

[Laz]

Re: Harer wing tank vent

Thanks so much for the reply. Whe you installed the vent system per the STC Which diagram did you use. Mine has two. One with a extra intake vent mounted in the center above the cabin, although it does not say where. The other shows no such extra vent. Also did your STC come with Dwg G-170 mine did not. It is referenced in the drwing on G-133. at an arrow pointing to the main tank filler neck.

How did you solder the copper tube to the steel filler necks. Any help and tips are always appreciated. soldering does not seem to be a very stong way to attach something that will carry fuel tank fumes thru the cabin.

I agree that it should be installed. However I am frustrated with lack of clarity in the STC drawings. Did you use the Vented Caps that were in the STC?

Thanks to all that replied

Mike

[Ragwing nut]

Re: Harer wing tank vent

I have modified several caps to the prints and have found they don't work very well which is why I think they have the other vent. I think the design is very poor in how it is closed at the front where maximum pressure would be and have the 2 holes on each side. I am almost positive that the air gets trapped in the larger tube and does very little to pressurize the tank. The vent in the roof is on the left side. THe header tank vent goes up the left diagonal tube, tees into the wing tanks, and then goes out the top.

Soldering is plenty strong if done correctly, but if you have aluminum wing tanks you will have to weld the tube on.

[N96337]

Re: Harer wing tank vent

Thanks so much for the reply. Whe you installed the vent system per the STC Which diagram did you use. Mine has two. One with a extra intake vent mounted in the center above the cabin, although it does not say where. The other shows no such extra vent. Also did your STC come with Dwg G-170 mine did not. It is referenced in the drwing on G-133. at an arrow pointing to the main tank filler neck.

How did you solder the copper tube to the steel filler necks. Any help and tips are always appreciated. soldering does not seem to be a very stong way to attach something that will carry fuel tank fumes thru the cabin.

I agree that it should be installed. However I am frustrated with lack of clarity in the STC drawings. Did you use the Vented Caps that were in the STC?

Thanks to all that replied

Mike

Mike,
If you look at the drawing list, revision B, dated 4-7-71, it says they deleted G-128, G-129, and G-170
I always just layed the 1/4" line down there so it didn't interfere with the boot cowl and marked the hole, then drilled it and inserted the line to just protrude through the filler neck, and solder it in.

As far as the confusion on G-133, the drawing on the left is showing the vent system, and the top vent is shown in the center of the fuselage. The drawing on the right is showing the fuel transfer lines only.... could that be part of the confusion, or am I not understanding you?

Yes, I definately used the vented caps as per the STC. My Tcraft had the other style vent tubes (1/8" tube out the top, pointed into the wind) on it when I bought it.

Hope this helped,
John