C-85 Upgrade - What else while the plane is down?

[Kerbs]

The 85 STC's tank venting can be improved via larger diameter forward pointing upper tank cap vents, and if a third non-pointing vented cap replaces the original wire gauge. Atlee Dodge sells both of the vented cap styles.

Edit: The STC calls for the main tank to be vented through the wing tank(s) with forward pointing wing tank vents fabricated. Fuel lines are sized according to expected demands for flow and the three gallon main tank minimum recommended for the F-19's and later advisable for earlier 85's and Strokers. In my experience exposed tank vents can become temporarily plugged by snow and insects so a backup vented cap on the main tank (with the vent protected from the elements) might be worthwhile. That's how mine's rigged.

http://www.fadodge.com/fuel-cap-for-180hp-piper/

http://www.fadodge.com/fuel-cap-vented/

Gary

Gary did you modify the existing wire gauge cap or purchase one of these? Just curious if you use a vented main tank cap how/what you use for fuel gauge. The addtional venting make sense given the increase in fuel consumption with the 85.

[PA1195]

Hello Stu. The changes were done by the previous owner(s) in accordance with Harer's STC SA1-210 Drawing list G-171. The wing and main tank caps installed are those linked above and are the equivalent of Taylorcraft's fuel system as it evolved from the early BC12D-85 through the later F-19. My installation is therefore the progressive equivalent of the 85hp and later F-19 fuel system...caps and vents with a Rochester (?) assembly fuel gauge mounted inside on the top of the tank. The later parts are listed here pages 6-9: https://www.univair.com/content/part...ile/index.html

For best advice contact Terry Bowden at CAP http://dc65stc.blogspot.com/p/stcs_06.html and discuss your pending fuel system design. I assume a wire gauge and cap is an acceptable alternative to the internal unit.

Gary

[astjp2]

Hello Stu. The changes were done by the previous owner(s) in accordance with Harer's STC SA1-210 Drawing list G-171. The wing and main tank caps installed are those linked above and are the equivalent of Taylorcraft's fuel system as it evolved from the early BC12D-85 through the later F-19. My installation is therefore the progressive equivalent of the 85hp and later F-19 fuel system...caps and vents with a Rochester (?) assembly fuel gauge mounted inside on the top of the tank. The later parts are listed here pages 6-9: https://www.univair.com/content/part...ile/index.html

For best advice contact Terry Bowden at CAP http://dc65stc.blogspot.com/p/stcs_06.html and discuss your pending fuel system design. I assume a wire gauge and cap is an acceptable alternative to the internal unit.

Gary

Nope, not if he wants to comply with the STC as written.

[PA1195]

Thanks Tim for the correction. https://www.taylorcraft.org/docs/Tay...anual_1985.pdf Page 5 shows main tank 0797-12 with flange for Rochester fuel gauge 6560-12 for 85hp.

My Gilberti/Harer STC doesn't specify that gauge mod but some pages or change orders may be missing. There is a drawing that shows the tank and welded flange 0797-9 but another does not. Atlee Dodge did mine and there's a yellow tag release for the welding of the flange 7 1/4" behind the filler neck per Taylorcraft's specs.

Please clarify.

Gary

[astjp2]

Yeah, you need the Rochester gauge, they use the venting from up by the wing to pressurize the tank to feed the engine. You need a quantity gauge and a way to vent the tank and a sealed cap accomplishes this with the boat gauge. If you have the cap with the cork on a stick, the tank supposedly will not have enough head pressure to supply the larger engine. It also does not have the problem with water dripping down the wire and contaminating the gas.

Realize though I do not have the STC paperwork to review, I am only going with what conversations I have had with people knowledgeable of the original design. I know that an o-200 will run with a 5/16" ID valve and -6 fuel line with a standard tank, but it can out climb the fuel's ability to feed the engine if the tank is low on gas, AOA can get pretty steep with a lot of power and just hanging on the prop.

[N96337]

BS! All my drawings show the stock, vented cap with the cork gauge. I've done about 5 of these and never seen nor heard of a problem. The drawings show the vents from the top, coming down and connecting in the filler neck of the main tank.
John

[PA1195]

Thanks Tim for the info...appreciated as always. I may have a partial set of parts list and full prints but they may be dated. Harer sold them and it's for my plane by N and S/N. My main tank cap is a vented Atlee unit and the wings are theirs for an O-360 Cub conversion. I may be loosing pressure with the vented cap but no problems so far. The Rochester gauge reads empty when there's 3 gallons left which the F-19 is placarded for as minimum fuel.

However....one of my drawings of the fuel system shows a main tank with the gauge base installed and externally vented.

I still suggest contacting Terry Bowden and let the current STC holder enlighten the rest of us on Gilberti and Harer's intent. That would be the final word as the STC SA1-210 may have evolved as parts became available. As noted the link in #19 lists the parts for an 85 and F-19 as being available.

Gary

[PA1195]

BS! All my drawings show the stock, vented cap with the cork gauge. I've done about 5 of these and never seen nor heard of a problem. The drawings show the vents from the top, coming down and connecting in the filler neck of the main tank.
John

Thanks John for that as well. Terry should be asked to confirm the requirements for gauging. It may be related to the option for 1500# GW when the plane is converted from CAR4 to CAR3 to a Model 19 via optional paperwork and added Flight Manual. I have a copy of the Manual and approval ($600 today) and it doesn't mention much relating to fuel gauges or changes thereto.

Edit: However TCDS 1A9 does list "fuel gauge" and "unusable fuel 18#" for the Model 19, for which models converted with -4 mounts and C-85 can be the equivalent. See Notes #1 and #2 for info on the Model 19.



Gary

[astjp2]

BS! All my drawings show the stock, vented cap with the cork gauge. I've done about 5 of these and never seen nor heard of a problem. The drawings show the vents from the top, coming down and connecting in the filler neck of the main tank.
John

Ok John, scan and email me a copy of the installation drawings, I have never actually seen them, only worked on airplanes that had the Rochester gauge installed. Much appreciated, Tim

[PA1195]

It's obviously time to unravel the STC by equivalent model and gross weight. Terry Bowden can. Ask.

Gary

[Kerbs]

Terry has provided the DER work for me to remove the vent line requirement on my install. I already had the correct fuel lines and valves from the wing tanks to the main tanks. If I remember correctly, he said the vent line requirement came from a confusion on the wing tanks feeding the engine, which they do not do. Obviously I want to make sure i have enough venting to the main tank but it sounded like the the wing tank to main tank vents were not needed for this. Curious to see what others find out.

[astjp2]

Maybe barnstmr will pitch in his comments on this topic

[N96337]

Here you go. Says right on it in big letters to use the standard float type gauge and vented cap. I don't know who told you different, but I'd verify any more advice from them!
John

[PA1195]

From here > https://www.taylorcraft.org/resources.html > under Letters & Articles of Historical Interest (#2 down) comes this Information on converting to 85hp. I assume it supersedes or at the least supplements Gilberti/Harer/CAP's 85hp and G/W conversion via STC SA1-210 Drawings and Specs G-171 and G-172. These are from my copies of that data. Please note the recommended change orders for the fuel system that amend DWG. No. G-133 that John copied in Post #28 that's also called out in both Dwg. No.'s G-171 and G-172. I'll post the relevant copies below and can forward them to personal e-mails.

Gary

[Robert Lees]

The required modified fuel system for the C85 upgrade is technically a load of hogwash.

I installed the 85 upgrade (with the stroker mods) into my aircraft here in the UK (long before Mr Bowden became involved) over 10 years ago, and from a technical and fuel-flow perspective, there is no reason for all the silly fuel gauges and balance pipes and so on.

It was probably done to satisfy some 1950's CAA (or FAA) requirement back in Jack Gilberti's day.

I still use the normal 1946 fuel tanks and cork float on the front, but I did "nod a wink" to the 3/8 pipes from the wings to the fuselage tank (quite why, I don't recall...probably I got some cheaper while I was rebuilding)

My fuel flow to the carb was all that interested me, and in the hangar, with the tailwheel on the ground, and the main gear hoisted 12" off the floor, the gravity fuel flow was still more than 150% of the carb requirement.