Harer STC Vent System

[freightpilot27]

Re: Harer STC Vent System

Maybe I'm missing something.....
I understand the theory for the extra vent for the wing tanks. Redundant, but no argument there.

But the additional vent over the cabin is tied into the main tank. My drawing says "Use std. float type fuel quantity indicator and vented cap". Does this mean i retain the existing main tank cap? If so, wouldn't this defeat the purpose of the additional overhead vent? wouldn't all the head pressure be lost through the main tank cap vent?
I sure would like to retain the existing bobbing cork type indicator.

BUT-
Anyone know where I can get the parts to add the "float type fuel quantity indicator" If i need to go that route?

[barnstmr]

Re: Harer STC Vent System

You might be thinking of a "pressurized" vent system... meaning the air in the tank is elevated above outside air pressure. The Gilberti vent system is not a "pressurized" vent system... It has no provisions for increasing the air pressure acting on the fuel tank beyond ambient air pressure. I would call it instead an "equalized" vent system... meaning that the air pressure in the tanks is allowed to equalize to match the outside ambient pressure. Since all three tanks are tied together and are each tied to outside air... all of the air spaces have equal pressure.

"Head" refers to the fuel pressure delivered to the carburetor due to gravitational acceleration acting as a result of the specific gravity (weight) of the fuel in conjunction with it's vertical distance above the carburetor float level. (THAT WAS A MOUTHFUL for this Texas boy). In other words... pressure "head" is just the tendency of a liquid to flow down-hill. It has nothing to do with the air, unless you have a pressurized vent system.

[Hank Jarrett]

Re: Harer STC Vent System

If you have ever transferred fuel from the original wing tank to the main before it was half empty you will know why you can't use the cork and wire fuel quantity system. The fuel from the wings fills the main past full and fuel sprays around the wire and blows in a fine mist into the window! Never happened to me, but it did to the guy I bought one of my planes from. He "was" a smoker and had just Bogarted a butt out the window. He said his hand was still out the window when it was soaked in finely atomized fuel! It ruined his seats but he finally quit smoking. He said it terrified him beyond belief and the rest of his cigarettes followed the butt out the window.

If the wing tanks are hooked to the main without manual valves to do the transfer the main has to be able to hole the pressure head from the wing tanks! You also CAN'T open the main if there is fuel in the wings! Fuel will flow as soon as you open the cap on the main. From the pictures and diagrams I have seen here it looks like the wings and main work like one large tank with vent lines interconnecting them. If that is true, you would have to fuel from the wings and let it drain to the main or not use the wing tanks. The main cap has to be sealed with the cap on.

Another bad assumption I have been hearing is that the STC allows all the tanks to be at ambient pressure. That is NOT TRUE! The fuel system will be at the pressure the vents are seeing. If the vents are at the top of the windshield or on the wing fuel caps, that is LOWER than ambient. Remember? The wing LIFTS because the pressure is lower on top. That's where the vents are. That is also why the original wing caps had tubes bent to the front on them for ram pressure. The ram was needed to get the fuel to flow because the low pressure on top of the wing would stop fuel transfer without it.

Be REALLY CAREFUL if you are modifying your fuel system. These planes burn REALLY WELL in a 60 to 100 MPH wind in flight when fuel is being sprayed around. I have cleaned up after an in flight fire crash when I was doing crash investigations and it's NOT PRETTY! You won't burn long, but you will burn like a living candle. I can't imagine a worse way to die.

Hank

P.S.
By the way, I just changed out the fuel lines from the wing to the main on my 41 (putting my original wing tank system back in service). The fittings and tubes were cracked when I inspected them. Aircraft lines have 37* flares NOT 45*!!! The flaring tool is expensive, but so is making your charred remains presentable! I was told by one guy that the reason they use soft Aluminum is so you can push the 45* flare to 37* when you tighten the nut. He will NEVER TOUCH MY PLANE. I plan to hang the cracked fuel line on the wall in my hangar with the main tank fused fuel cut off valve as a reminder. That's right, my fuel shut off hasn't actually been working since I bought the plane! DO IT RIGHT OR GO FLY GLIDERS.

P.S.S.
USE THE RIGHT FUEL LINE TOO! Woody Clapp died in his Sopwith Triplane because he used copper fuel line (like the original). COPPER FATIGUES AND CRACKS, even seamless copper. IT's for WATER, not fuel!

Sorry, rant over. I just don't want to go to any funerals.

[barnstmr]

Re: Harer STC Vent System

Hank,
If you have not studied the STC drawings, you are missing out on some of the details. For example... the wing fuel caps have to be modified and they actually do have some RAM air effect. My description of the "ambient" is an over simplification for discussion sake. This system is designed and placarded to rely on the wing tank shut off valves to hold up wing tank fuel until there is adequate space in the main tank. Therefore it is supposed to retain the original vented cork/float/cap.

BOTTOM LINE: To all those installing STC # SA1-210, Certified Aeronautical Products (CAP) recommends that you strictly adhere to the STC drawing requirements. CAP does not authorize any deviations with respect to the fuel system. If you choose to deviate from the STC FAA approved data, use extreme caution and make sure you understand the system.

[Pearson]

Re: Harer STC Vent System

[QUOTE=barnstmr;60281]Hank,
If you have not studied the STC drawings, you are missing out on some of the details. For example... the wing fuel caps have to be modified and.... QUOTE]

Terry, I have studied the STC drawings and I STILL feel like I am missing out on some of the details. As I am sure you are aware, the drawings leave out a lot of detail. One of the areas I am scratching my head on is how to do the baggage area. The drawings show a piece of 1/4" thick wood along the sides at the top and bottom. The wood along the bottom is to glue interior fabric to. The wood along the top is for headliner bows. It has an inset that shows the bows going into the wood, but does not show how the wood is supposed to be attached to the airframe. I guess it is up to the individual to do as he chooses.

Another area is how it shows to attach a piece of sheet aluminum across the front of the baggage area. It shows attaching another piece of 1/4" thick wood to the tube across the back of the seat. But this is where you lace the seat sling. If the wood and a sheet of aluminum are there, how are you supposed to lace up the seat sling?

I have not seen anything regarding modifying the gas caps, other than welding the vent tubes to the filler necks. Is that what you were refering to as "modifying the gas caps"?

[barnstmr]

Re: Harer STC Vent System

I have not seen anything regarding modifying the gas caps, other than welding the vent tubes to the filler necks. Is that what you were refering to as "modifying the gas caps"?

Richard,
There is a separate STC drawing (G-160) for the fuel cap modification.

As for the baggage questions, this subject would probably be best for another thread... But I admit some of these items are vague... however I believe the method of attachment of the headliner may have been considered by Gilberti as a minor issue left up to the expertise of the installer in following routine interior installation shop practices. I do. This kind of thing falls under Minor alteration and needs only an "appropriately rated mechanic" following acceptable shop practices, and closed by a logbook entry.

One example is the upper wood supports for headliner bows. I recommend this could be attached to the frame by using doped strips of cotton fabric (or ceconite) tape approx 3/4 inch wide in a few locations. This was a common practice dating back to the early days. Waco's commonly had this method for attaching wooden brackets that support fuselage stringers. (I am guessing there may be a few former Waco production workers who later worked at Taylorcraft and surmising that this technique might have made its way from Troy to Alliance.) There are other methods for attaching this wood, but I can't think of a better way (cost-efficient, quick, easy, strong, little fabrication, few tools required, utilizes scrap materials).

[Hank Jarrett]

Re: Harer STC Vent System

[QUOTE=barnstmr;60281]
If you have not studied the STC drawings, you are missing out on some of the details.

I haven't seen the STC, just what has been posted here, which was starting to scare me. I never saw anything in the posts about keeping the shut off valves and that would have required sealing of the main tank (NOT the way I would have done it!)
I understand your use of "ambient" now and it all makes more sense with the simplification. I think some of my old documentation shows the curved vent tubes were added early on to solve a non transfer problem with the old wing caps. If you never transfer fuel unless the main is at least half empty the cork and wire float won't cause problems. Just make SURE there is 6 gal. of room in the main before you transfer!
Your "BOTTOM LINE" is what is key here. You need to STRICTLY ADHERE to the STC, but it sounds like maybe we need to get some photos here to help everyone who is trying to put the STC in see exactly how it should be done. The written instructions and drawings don't seem too clear to a lot of people. Not saying the STC isn't good, I have heard the exact opposite, but if we can eliminate some confusion on what it SHOULD look like maybe we can prevent an accident.
Who has it installed and can share some pictures?

Hank

[T-Rex]

Re: Harer STC Vent System

I've got a question on how another Harer equipped T-Craft is vented. There is no center vent, it appears to be plumbed like the second drawing. It uses Luscombe style ram air gas caps. The wing tank vent lines are welded to the foreword upper corner, and the main tank line has a welded bung with a tee in the rear (inst. panel) side of the tank. It has a float type fuel gauge in the cabin on top of glair shield. and uses a Cessna style vented fuel cap on the main tank. The pilot says there is no problem with fuel flow from the wings. What are the possible risks other than the obvious deviation from the STC.
Thanks, Brad

[N96337]

Re: Harer STC Vent System

I should have some pictures around here somewhere......

I do have a question though..... I always understood the drawing calling out to "use standard float type fuel indicator and vented cap" to mean what was a standard cap on the main tank of a Tcraft... the cork float and wire sticking out the vent in the top of the cap. Am I wrong here? I've never seen one done with a "gauge" like the F19 had..... ???
John

[Pearson]

Re: Harer STC Vent System

If anyone has a picture of how the added vent tube is mounted, it would be a big help.

[Laz]

Re: Harer STC Vent System

Having just completed the plumbing for my wing tank vent system to comply with the STC I can say with out any doubt or hesitation the whole thing is a bunch of crap. That being said I did as the STC required and install the redundant vent system connecting both wing tanks and the main fuel tank. The problem with the drawings provided with the STC is there is no real guidance or detain on how to position the lines around the aircraft structure and where to exit the wings with the vent lines. I did find a few photos of a F19 with the wing tank vents that showed how the Factory routed at least part of the system. They say you are suppose to weld a little piece of tube on the on the windshield area tube to rout the copper line . They do not show its actual location so I guess you just guess. My mechanic and I decided to use a clamp instead, since Murphy s law dictates we would have welded the tube in the wrong spot. I now have two wing vent caps, a vent in the main tank cap, plus the lines connecting them all. Add to this the plumbing of the wing tank fuel lines and you have about a weeks worth of work. Now on to my next post about the Oil pressure line routing.

[Robert Lees]

Re: Harer STC Vent System

Of course it's carp, because it's unnecessary, from an engineering perspective.

I run 100hp in my BC12D using the original fuel lines & cas caps and wire gauge in the front and no problem, even at extreme AoA.

The STC ought to be updated, but I should imagine this would be F****** expensive. Yes, that's what I said, FAA expensive .

[dejh22]

Re: Harer STC Vent System

Not to hi-jack this thread,but on the stc it calls out for small plates to be welded on to the wing strut attachment brackets. What thickness are they and at what length? I might be making new spars and will be installing the new bushings. I would also like to do the plates now while the wings are apart. Thanks!

[Guest]

Re: Harer STC Vent System

sent you a pm Dale so as to not hi-jack this thread

[N96337]

Re: Harer STC Vent System

I guess I must've missed something, as I didn't think it was such a huge deal to put the vent system in any of the ones I have done. I've been around Cubs and such that didn't have the redundant vent system and it always seemed like they were fussing with them to get the flow right....that being said, I've been around Tcraft's that didn't have it and they worked fine too... usually.
John