8KCAB Fuel line component below vent?

Big Ed

N50247 - '79 Super D
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Jul 20, 2020
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387
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Tampa, FL
Anybody have any idea what the heck this is? It is a hard point under the fabric. I have not noticed it on any other 7 or 8 series aircraft. Based on location I am guessing it is related to the fuel lines or sump. On my aircraft, it protrudes beyond the surface plane of the fabric and creates a stress point. The avgas from the vent above it has trashed the dope, and the fabric stress and UV are damaging the fabric. Gonna have to be repaired soon; might get away with stripping and re-doping, but I suspect I'll need to cut out that area and patch with heavy duty fabric and anti-chafing tape. Is there any way I can fix the protruberance?

protrusion.jpg
 

BB57

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Feb 20, 2020
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187
The vent above it isn't a fuel vent, It's the static port. There is one on each side, so that you have a neutral ambient pressure source even when slipping the aircraft. If there were just one, the airspeed reading would change due to positive or negative pressure on the port in a slip.

With two it can average the pressure and give you a stable ambient pressure to compare with the impact air pressure entering the pitot tube.
 

BB57

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Feb 20, 2020
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If you wiggle your way into the baggage compartment you can remove the lower rear panel (there are probably two winged quarter turn fasteners at the bottom corners). Once that panel is removed you can see the entire tail section and you can identify what that protrusion is.

While you are there, also inspect the battery as it should be inspected after every 50 hours in normal flight and after every 10 hours of aerobatic flight. Leaky battery acid or broken supports or fasteners are things you want to find before something bad happens. A friend of mine rolled a Supercub into a ball after battery acid leaked on a control cable and caused it to break.

I'm due for an oil change, air filter change and battery inspection in .7 hours, so weather permitting I plan to warm the oil up doing stop and goes in the pattern this evening and then drain the oil. I can get a picture of my tail section when I inspect the battery tomorrow afternoon and post it.
 

BB57

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I changed the oil yesterday and then knocked some items off the punch list (replaced the worn scat tubing from the alt air to the air box, added missing scat tubing from the baffle blast tube to the generator, added a third Camloc fastener in each cowl door and switched to winged Camlocs in the process, and installed blind nuts in the cowl for the air filter assembly so that the lower cowl no longer has to be removed to change the air filter).

I also removed the panel in the rear of the baggage compartment to inspect the battery and grab some pictures as promised.

You can see the tubing running to the right side static port here.

118608427_1714883062003928_7989145848524663881_n.jpg

And here is a picture looking more or less back to front showing the former from the other side.
118631652_1714883005337267_1424809069078555220_n.jpg

I have a similar slight protrusion in the fabric (just no hole) and it's also caused by that former.
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
387
Location
Tampa, FL
OK, thanks, that makes sense. That would explain the vertical cracking above the longeron on mine. The former is not quite offset enough from the fabric and vibrates against it when flying.
 

aftCG

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Apr 3, 2018
Messages
442
Location
Tacoma, WA
Having had GoPro cameras on my plane for some time, you might be shocked how much the fuselage fabric vibrates during takeoff and climb. Same with the underside of the wings in the propwash .
Can't help with the rest. My static port is collocated with my pitot under the right wing. And my plane has four winged camlocs on each cowl door.
 

BB57

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.../

/...And my plane has four winged camlocs on each cowl door.
All of the pre-'74 Citabrias with the large cowl doors had 4 fasteners. IAC Technical Tips Volume 1 discusses adding additional fasteners:

"Back to the first problem — that cowl door blowing open. This is a common problem with early (pre 1974) Citabrias and was mentioned in the March 1976 issue of Sport Aerobatics. The cure of this problem is simply to add additional fasteners to the cowl doors. There are several brands of fasteners to choose from, but Dzus fasteners are probably the most readily available. The standard Citabria cowl door fasteners are Dzus AJW wing-type fasteners and, of the Dzus line, these may be the most "uncommon" type. A more common Dzus is the "oval head" design. The parts needed to install oval head Dzus on early Citabria cowl doors are:

AJ5-50 Fasteners
GA5-375 Grommets
S5A-200 Springs

While having a cowling door come open may seem to be a minor problem, an IAC member who had the right cowl door latches open during a snap roll and the entire right door blow off pointed out: 'There was no further damage to the aircraft but during some maneuvers this could be a threat to the windshield.' "


I can't speak to what may have been standard but my early 1967 7KCAB had Camloc slotted fasteners on it when I bought it. I stayed with the Camloc fasteners but swapped the four 4002-11 slotted studs for 4002-11W winged studs. The two new fasteners also needed a 40004-G grommet, a MSR4T retaining ring, and a 214-16N receptacle. The first one took about 30 minutes to install while we measured, planned, remeasured, and then started drilling. The second one took about 10 minutes. Cheap insurance to keep the cowl door from coming off and potentially hitting something, or just coming open and beating the cowling up.

You can see a scratch under the rear fastener when a previous owner or pilot slipped with a screw driver while fastening the cowl with the old slotted fasteners. Winged fasteners make a lot more sense.

118608427_1714857578673143_4675630057425934252_n.jpg

The same volume also discusses the requirement for a dual lap belt and the (previous) problem of adding a second belt to comply with IAC requirements:

"For United States Citabria owners, good news has
again emanated from Washington. We have received
clearance from Mr. Charlie Schuck, FAA Flight Standards
Service, to install a second safety belt in Citabrias
without a lengthy Supplemental Type Certificate process.
According to the new 1974 IAC Contest Rules,
second belts will be required in all aircraft to compete.
To help out the owners of Standard category aircraft in
this regard, IAC has been working closely with FAA
over the past several months to make this process easier.
The method that is approved requires a TSO'd metal-to-
metal buckle type seat belt and a placard installed in the
aircraft that the belt must be properly stowed while not
in use. In addition, replacement of the lower bolt that
holds the rear seat support to the air frame with "AN"
bolts of sufficient length to accommodate the seat belt
hardware will be necessary. This is a simple, easy to
install operation and will increase the aerobatic safety of
this aircraft."
 

Bob Turner

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Apr 4, 2018
Messages
1,259
So one TSO'd belt, and the other can be high quality, like Silver Parachute?
 

BB57

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Feb 20, 2020
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So one TSO'd belt, and the other can be high quality, like Silver Parachute?
That's a good question. I think the way it's written in the IAC Technical Tips is ambiguous.

The FAA requires each seat have an "approved" seat belt. The IAC requires a second seat belt which is not an FAA requirement, and on any ramp check the FAA inspector would just look for an installed and approved seat belt for each installed seat. As long as one of them is approved, the seat belt requirement is met.

The Technical Tips article indicates that the FAA requires a TSO approved belt be installed to the seat attachment bolt with a suitable AN bolt, if a STC is to be avoided.

The IAC summary doesn't say you couldn't remove the original approved seat belt, but it's just a summary, and I have not seen the actual guidance letter. If the guidance letter isn't explicit on the subject, it would not violate the specific wording of the guidance (since any ambiguity goes against the author), but it would probably violate the intent of the guidance.

-----

A related issue is missing TSO tags. I know Air Tran got dumped on as some of their seat belts were missing TSO tags or had illegible tags and the Feds insisted the tags be replaced. The FAA approved Air Tran doing their own maintenance on them so they could replace their own tags. For most GA aircraft owners however that isn't an option and the odds of finding a shop that will put a TSO tag on a belt that comes in with a missing or illegible tag is slim to none.

I'm also not clear how this all affects old aircraft - like a 1967 7KCAB with what appear to be 3" military belts. When did the TSO requirement come in for lap belts? "Approved" shoulder harnesses became a requirement in 1986 and my impression is the FAA views anything as an improvement for a pre-1986 aircraft. How do they view lap belts?
 
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