Thorp Air Command - T18.net

I'm starting the process of redesigning the fuel cap. I'd like some input. My plan is to make a retro fit capable system that will replace the current thermos type cap. The question is, how many of you have a cap that is flush with the top of the boot cowl? How many have a cap that is under some type of cover? Do I need to design the retro fit to be flush? Since we there is no supplier of the thermos gasket, I thought I'd design a system that can be installed into the original tank, but has threads and an O ring for a better seal and safety. Thoughts?
Cubes

Mr. Cubes : I have one of the tanks from Mike Archer . I started out using the ACS flush type cap with the rubber gasket and after the rubber gasket started to wear I had to go with the ACS "New Style" flush cap with a Viton O-ring as they no longer made the rubber gasket . Much to my surprise I had to slightly enlarge the current opening to fit in the "New Style" cap with the O-ring . Not a big deal as the tank was still out of the AC during the build . The new cap is the ACS flush cap P/N 10455 @ $38.00 . Now it appears Spruce has a cap (with O-ring) that is interchangeable with the old style rubber gasket cap . That ACS cap is $44.00 and the P/N is 10460 . Not sure how old this style of ACS cap is but it is a flush "twist to lock" cap . P/N 10600 @ $50.00 . Sort of partial to this one as it is a threaded unit . Not sure how it would work with a current tank retro fit ? The Usher flush cap P/N 05-01061 @ $44.00 is a possibility .

A flush cap with the option of a locking cap is my vote . Adding a lock seems to add another Benjamin to the cost .

RB

Like Rich, I too have gone to the ACS flush cap with O ring seal and lever. I too had to open the hole in the tank so it would fit.
I would like a lock-in cap, at least as good as a motorcycle cap. I would really like to be able to retro fit it without removing the tank, just remove the filler door and work thru the top...
Not Too Demanding, am I??
Bruce Finney posted his cap upgrade, but it is probably lost to us at the old server? Maybe Bruce could repost it. Thread in or Quarter Turn or Key lock caps are OK with me, I just want some assurance that the cap will say in place in the remote possibility the airplane ends upside down.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

I installed the Vans locking retro fit fuel caps (aircraft spruce pn 05-01006) in my header and wings tanks. http://www.aircraftspruce.com/catalog/a ... fitfc3.php

the retro fit fuel cap is too small for the fuel tank openings, so I cut out a ring of aluminum (3-1/16" outer diameter with 2" diameter hole....thus making the "ring") from .091 left over from my panel build. This ring allows the retro fit fuel cap to drop into the 2" hole of the ring and the ring's outer diameter sits in the existing fuel cap opening. I roughed up all mating surfaces, cleaned the mating surfaces with MEK and used proseal to attach the ring to the tank, and more proseal to attach the retro fit fuel cap to the ring. It looks good, is basically flush, and I don't think I could beat it out with a hammer if I had to.

Found this on a Van's site . One downside it appears to have some "plastic" parts ? I would certainly keep some spare parts on hand , including a spare O-ring ! I like the set up , just not the plastic or what appears to be plastic parts ?

RB

Hey, Jim. I ended up buying MEZ-PN6500 Bung and Cap from Summit. $25. Replaced the thermos cap.

I didn't make my existing opening bigger, so it's a tight squeeze to turn the cap by hand. I slotted the top of the cap and made a tool. Starting from scratch one would just make a bigger door.

Those flush caps look great! Hopefully there's a positive welded connection between the neck and the tank. If it's a gasketed joint then you have to be concerned about it coming apart in a crash.

The nice thing about a flush cap is you don't have to build a scupper.

D

I machined my own cap, fits the standard S-18 tank neck, has flat Neoprene gasket, uses Allen wrench about a 5/16", You will split the tank before you blow it off. Drop it on, turn a quarter turn and then a half turn on the allen, done. It is flush, can be run on a C&C lathe by the bucket full, it has 3- components, well if you count the gasket it has 4. Dan

heres my setup with pictures:
here is the fuel cap that will sit down in the ring that I made:


heres the old cap sitting next to the ring I fabricated which will sit on the lip you can see in the opening of the fuel tank.


here is the ring and cap both installed in the wing tank:


Here is my best effort at taking a picture of the header tank showing it is basically flush with the top of the outer lip:

Yeah, I'm not happy with what I see at ACS. I was thinking of something you actually thread onto your plane with an O ring on top to provide the seal. All these thermos ones are subject to popping off in a crash or heavy (screwed up) aerobatics.
Danny are you going to Sedona? I'd like to take another look at yours. I'll check out Les' again this week.

Still the question is, does it need to be flush?
Cubes

personally, I think a flush fuel cap would look much better than any other option.

Has anyone ever put the flush cap in the upper fuselage decking of a T-18 with a short, flexible hose to a filler neck on the tank itself, as is used in auto racing fuel cells?

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

We wish we were going to Sedona!! We are going to miss the Sedona schedule by about 2-weeks. Of Coarse that is not a Complaint thats just the way it is this year no harm done. Who knows, maybe some things will change and we will get to go!! I will try my best to post some pics( there is Rumor of a KVIS Gathering this year by the Way) Dan

My cap is under a door. A hidden hinge and flush latch makes it as clean as anything. I don't have a scupper, I've only f'ed it up once so far, but it was a good one and right after I washed it. Sometimes pax notice the smell of fuel after a fill up but that might be due to the oily rag I used to replace the fuel cap I lost on the way to Airventure (joke) I kind of like the smell of 100LL myself.

_________________
http://www.dixiefriedfabrication.com/

Mine is under a door. Makes positioning the tank so much easier. I use a cap like a model A radiator with a short neck. Hot rod stuff.

_________________
Bob Highley
N711SH
SN 835
KLAL

Here is my version of a fuel cap retrofit. I had a web page with all of this on it but comcast in their infinite wisdom did away with personal web pages, oh well.

Original installation when I bought my aircraft. I needed a 1/2" wrench to remove the cap and cover.


The new cap, it is an Mocal Aero 400 3" locking cap purchased from British American Transfer http://www.batinc.net/aero.htm, Aircraft Spruce also has them in their catalog. Why the 3"? because it would cover the hole left in the tank after I hacksawed the filler neck. I also purchased the mating mounting ring that has threaded nutserts on it. To install I used Permatex #2 sealant and the included screws and in 8 years have not had any leaks as far as I can tell.




I installed a door with a hidden hinge.



Why this cap? It is a quarter turn mechanical lock to keep the cap in the tank with an o-ring seal and a key lock to keep the fuel thieves at bay.

Just one more data point.

enjoy,

_________________
Bruce Finney
N18JF T-18C #262
Yelm, WA USA