Sealant Groove For Fuel Boundary 1

[Aviator9]

Hello everyone,

I would ask you what is the advantage of groove applying to upper and lower flanges of spar/rib structures that form fuel boundary of wings. As far as I see, Eurofighter, F-16 and F-35 fighter jets have this groove to inject sealant without removing upper/lower skin. Is there any more requirement for it, such as preventing fuel leakage, blocking seperation of sealant? Or could it be designed the wing without groove channel?

 

[WKTaylor]

Kadir60...

I am familiar with injectable sealant grooves for wing integral tank sealing on F-15s... but I'm pretty sure that F-16s have adhesive-bonded/fastened joints for wings and fuselages sealing. Hmmm I'll have to check out F-16 sealing methods in latest pubs... to be certain [grooves may be back-up in the wings].

I have NO idea as to what 'system' the F-22 and F-35 use for integral tank sealing.

Just about every aspect of integral tank design with sealant grooves is explained/illustrated in the following documents...

AFWAL-TR-87-3078 AIRCRAFT INTEGRAL FUEL TANK DESIGN HANDBOOK

SAE-AIR4069 Sealing of Integral Fuel Tanks [DoD accepted]

AGARD R-771 Fuel Tank Technology

NOTE. F-15s had grooves running-down fastener-lines... with widened [spot-faced] areas at each fastener location to allow sealant to flow-around the fastener shank. Special fasteners were installed along the grooves... widely spaced... that had hollow-shanks with cross-drilled holes which aligned with the centers of the grooves when tightened down... and had a removable plug in the center of the flush head [injection port]. A special non-curing silicone sealant was injected into these fasteners VERY carefully and slowly, under low pressure to attain a seal thru the length of the joint... or to re-seal a 'leaker'. Over-pressuring with sealant could cause a joint to open-up under pressure and be a real problem... squirting uncured-sealant in the tank. Some jets were very leaky and high maintenance... others hardly ever leaked and stayed-off maintenance radar... I knew the 'leaker' tail-numbers by heart.

NOTE. The hollow injection-fasteners were prone to in-service failure [heads or shanks breaking]... which was another maintenance headache.

Typical groove injection/non-curing current-generation sealants are as follows...

AMS3283 Sealing Compound, Polysulfide Non-Curing, Groove Injection Temperature and Fuel Resistant

AMS3376 Sealing Compound, Non-Curing, Fluorosilicone Groove Injection Temperature and Fuel Resistant

NOTE. I'm pretty sure that the use of leak detection colored dyes [typical MIL-PRF-81298] are prohibited in these style tanks.



Regards, Wil Taylor

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[Aviator9]

Thank you for your detalied reply, Mr Taylor.

At F-16 wing, the groove channel has been used between two rows of fasteners for fuel tank sealing and sealant is injectable by holes on upper/lower skins. So, if there's a leakage at any area, they can prevent fuel leakage by injecting seal to that area without removing skins.

By the way,SAE-AIR4069 document contains so detailed information about fuel tank sealing. Thank you kindly for references.