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

[astjp2]

Terry, would you please let the tribe know what the current fuel system modifications are if they were to commit to installing your stc as written without deviation? I have been asked by several members before, but I don’t have it on my airplane so I was not able to answer. Also what sort of deviations have people asked for? I know that a 5/16” id on the header tank valve and -6 lines along with 1/4” npt gascolator or equivalent per our previous conversation, but I am at a loss for any of the other mods necessary, thanks, Tim

[cbcfly]

Tim,
For a point of reference: I'm in the middle of completing the STC on my Taylorcraft. I am complying with the 5/16 ID valve, -6 lines, and 1/4 npt gascolator. I am getting a deviation for the vent system. Using vented caps (with forward facing tubes) on the wing tanks and the normal float gauge cap on the fuselage tank. No inter-tank venting. All coordinated with Terry.

[barnstmr]

The Current STC-Approved fuel system venting for C85 - both Configuration A (short mount) and Configuration B (long mount) - is
- main tank cap is standard vented cap with float type fuel gauge
- Optional for one or two wing tanks - at least one required.
- wing tank caps are vented type with vent facing forward.
- neck of each tank modified with soldered tube (for additional venting)
- all tubes in tank necks are interconnected with a tee above cockpit - upper part of tee has a L-shaped pitot style tube facing forward

As previously explained this configuration was defined to match the factory configuration of model 19 as delivered by the Feris'.

[N96337]

Tim,
For a point of reference: I'm in the middle of completing the STC on my Taylorcraft. I am complying with the 5/16 ID valve, -6 lines, and 1/4 npt gascolator. I am getting a deviation for the vent system. Using vented caps (with forward facing tubes) on the wing tanks and the normal float gauge cap on the fuselage tank. No inter-tank venting. All coordinated with Terry.

The deviation being no vent at the "T" on top as well as none going down to the main?
John

[cbcfly]

The necks of my two wing tanks do not have the soldered tube for extra venting, and consequently no T on top. There is no additional venting of the fuselage tank. Simply the hole in the cap that the float gauge goes through.

[PA1195]

John N96337 and I are discussing offline potential tests for fuel flow that an owner can do to confirm it's adequate for the existing system's design and horsepower. Under CAR4 and CAR3 the stated requirements for maximum fuel flow can be read by downloading and reading the fuel sections in respective documents. Thanks to Terry at CAP the range of fuel flow for the A-65 through O-200 can be determined here: https://app.box.com/s/gb9v3ss7ls

I suspect that available maximum fuel flow changes as the main tank is emptied due a gradual reduction in head pressure, and the potential for outlet unporting increases at high flight angles. The requirement for venting may also vary as fuel is consumed. There's a reason Taylorcraft specs a minimum useable fuel of 9 gallons in the main tank for the Model 19 and later aircraft until that tank was removed and replaced with only wing tankage.

Obviously the main tank's wire gauge and vent system works as certified. The question of adequate flow becomes important when the plane is modified and additional power increases demand for fuel. Follow the STC holder's recommendations and also confirm flow if desired.

Gary

[barnstmr]

If you want to repeat the test from which the 9 gallon unusable fuel was determined, it was a flight test. Go read FAA AC 23.8A or the predecessor CAM titled flight test guide for small airplanes. Look for the section called “determination of unusable fuel”. The other regulation y’all are talking about (regarding flow) is a static test which has a different purpose. And that is to ensure that flow rate has a minimum amount of margin over the Engine requirement.

[PA1195]

Thanks Terry for the information and link. FAA AC 23.8A in turn refers to AC 23.16A Subpart E Section 23.959 for "Unuseable Fuel supply" (https://www.faa.gov/documentLibrary/.../AC_23-16A.pdf). While flight tests are normal, it does suggest an alternative static test may be conducted: "Ground tests using equipment that accurately simulates the airplane fuel systems and in-flight effects may be used. Alternatively, the applicant may establish a conservative unusable fuel quantity and conduct necessary tests to show that engine malfunction will not occur." I do appreciate the two tests - inflight fuel system behavior and CAR4 and 3 minimum flow requirements. Section 23.955 above discusses determining fuel flow and head pressure limits if that's of interest.

There is a Taylorcraft BCS12D-4-85 in town whose fuel system mimics mine (closed main fuel cap, separate (original?) tank gauge, vent line to wing tanks, forward facing wing vent caps, and no single overheat vent). I've sent for the FAA records and will be interested to see what they contain. Somewhere in its lineage the current fuel system was installed. The question was it a Factory job or Gilberti's drawings from Post #29?

Gary

[astjp2]

Just get a fuselage, install the fuel system without the boot cowl, cut the fuselage off behind the "a" pillar, install an engine and mount, rotate to simulate flight AOA and determine when you do not get enough fuel flow, cut the fuselage off at the back of the baggage and you can do wing tanks too.

[PA1195]

Need more vent air - open the fuel valve on an empty wing tank. Might help.

Gary

[astjp2]

Need more vent air - open the fuel valve on an empty wing tank. Might help.

Gary

what happens if your wings are full and your header is 1/4 tank? Unfortunately systems design must be absolutely idiot proof so having a non standard procedure would not be the most prudent idea. There should be adequate venting with the cap by itself...

[PA1195]

what happens if your wings are full and your header is 1/4 tank?

Depends on how the main tank is vented and how much fuel remains in the main. If fuel from the wings displace air in the main that's ok as head pressure from fuel will build as the tank fills. But in the interim if the tank can unport due to a Vx WFO climb maybe nobody happy? Refill in level flight has meaning. Drains the wings low spot best and keeps fuel on the main outlet until level rises.

Gary

[astjp2]

Yeah true and you also need to be less than half a tank in the header before the transfer, over filling the tank sucks and stinks.

[PA1195]

Want to maybe never repeat a recurring engine stoppage and fatality in a Taylorcraft? Read this about a local F-19 that sadly had issues and finally took a toll. "the airplane had a history of unexplained power losses on takeoff" The carb was implicated but ???

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20050506X00563&AKey=1&RType=HTML&IType=FA

Gary