Current production specs for the CH-53K detail the legacy nylon grommet MS21266 for anti chafe and anti-arc protection. It requires a slow, multi-step install that is both time consuming and costly.
An alternative is Spring-Fast grommet M22529/2 that applies simply and quickly with finger pressure. We estimate that switching could save Sikorsky $3.338 million over the life of the CH53-K program. The details are below.
The Insignificant Grommet?
While grommet edging is a small component of any aircraft; its impact on the EWIS is far larger than their size. It protects aircraft wiring from chafe that can result in arcing, sparking and fires. However, chafe creates a far bigger more low level issue than extreme cases of arcing and sparking.
NAVAIR research shows that when aircraft are designated as AOG (Aircraft on Ground) or NORS (Non Operational Ready Status), the biggest single reason – 37% – was wiring discrepancies due to chafe. Chafe is a significant drag on readiness, availability and efficiency – for the military or commercial aviation.
Our cost analysis is based on a trade study format. For the CH-53K it assumes: 196 are produced through 2029, 292 penetrations per aircraft, a wrap rate of $200, an NRE of $12,680.
The table below shows the top level break down of the costs and savings: direct labor and materials, WIP consumables (safety glasses, Scotch-Brite, wipes, cheesecloth etc) and nonrecurring costs for the change.
M22529/2 already has NAVAIR approval and is fully qualified as an FAA approved replacement part.
Why the Savings Are So Significant
Key features of the M22529/2 drive a far lower direct labor install cost:
- Snap in place installation without adhesive
- Superior retentive strength without adhesive
- Immediate wire/harness routing – no fixturing or cure time delays
Issues with the Old Legacy MS21266 Grommet
- Preparation and application is a multi-step process.
- Multiple items for application & technician safety have to be collected before install.
- Edge prep is needed: light abrasion with Scotch-brite & cleaning with IPA or an acetone wipe to ensure proper adhesion.
- Nylon grommets have no inherent retentive strength and tend to straighten and disbond, so are glued to an edge using Pliobond –a single stage, MEK solvent based, air cure adhesive. While Pliobond is considered a contact cement, in almost all cases, MS21266 requires “fixturing” – pieces of masking tape hold it in place until the adhesive cures.
- Any excess adhesive after curing has to be cleaned with a MEK solvent and elbow grease.
- Disbonding means the work often has to be redone adding to the cost of poor quality.
This may have been state-of-the-art when the S-56 was being built, but now it is an anachronism.
M22529/2 –The Better Way
- M22529/2 is a high performance grommet that has a polymer coating on an ultra thin CRES substrate that snaps into place with finger pressure.
- It is a caterpillar style grommet with opposing finger-like castles that exert a compression force which create static friction for retention without glue.
- It has passed 20/20/20 G static load tests even when 4 castles are removed to provide clearance for a p-clamp riveted clip used on some penetrations.
- M22529/2 also virtually eliminates the large FOD footprint of shop consumables (gloves, cheese cloth, adhesive, tape) required for the glued nylon grommet.
This single component switch offers significant multimillion $ savings, improved efficiency and best in class performance.
Indeed recently we had a specification success when after several weeks of testing similar products; Sikorsky Aircraft approved an EC (Engineering Change) mandating the use of M22592/2 on specific fittings subjected to severe vibration on the US Army UH-60M program – a testament to the product's high performance.