The “EYEBALL” Spherical Metal Grommet

BACKGROUND

The “Eyeball” was developed to solve a problem in the restoration of a 45-year-old aircraft. The aircraft is a 1953 Mooney Mite, a then state of the art aircraft with performance exceeding other aircraft of its class. Most of the structure is of wood, with some steel and aluminum in the cockpit and engine areas.

In most aircraft fire safety is a major concern. All have a “fire-wall” between the power plant and the rest of the structure. These are usually of carbon or stainless steel sheet, usually less than .020 inches thick, about three or four times the thickness of letter paper.
There must in all cases be intrusions through this fire-all such as engine controls (throttle, mixture, carburetor heat, etc.), and instrumentation wires, cables, and tubes such as oil temp, oil pressure, cylinder head temperature, fuel primer lines, etc..

Historically these were protected as they passed through the firewall using a rubber grommet, or in the case of the Mite by bringing them together in a bundle, wrapping them with asbestos sheet and fibers, then taping them, and putting this assembly through a large hole in the firewall.

All this is to retard any fire in the engine compartment that could migrate into the cockpit area where persons and fuel might be located.

In the case of the Mite, asbestos could no longer be safely used, and a single large hole to accommodate the above listed components was less safe and did not permit satisfactory routing of these components once into the crowded and complex engine compartment. The single hole bundled components pass-through required very tight turns of some of the cables and controls, which do not function well when turned through a small radius to reach their individual destinations. 

In the more conventional method of passing these components individually through rubber grommets, fire safety is compromised, and if an attempt is made to pass though the firewall at an angle other than perpendicular, to better route to the individual destination, the grommet fit is compromised and the grommet may itself sustain damage.

The Eyeball design addressed these issues by providing an all-metal (aluminum and stainless steel) device to pass individual components through the firewall, and allow this to pass through at angles up to 45 degrees from perpendicular and then positively lock into this position.

While this was developed to solve a Mite restoration issue, is was observed by aircraft enthusiasts who expressed interest in purchasing these devices for their use. Manufacturing and distribution was begun in 1996.

THE PRODUCT

On the left above is the original Eyeball “B” version. It is the least expensive and lightest model. The ball is of aluminum, and the other parts are stainless steel and aluminum, and the other parts are stainless steel and aluminum. It was found to be most adaptable for installation on new firewall construction where the required hole locations could be easily accessed and drilled.

Later, the “s” model was introduced with a hollowed steel ball to meet the heat exposure requirements on certificated aircraft. To date FAA approval for the use on certificated aircraft has not been addressed. The product does meet the heat requirements, and with the removal of some of the material internal to the ball, the weight increase of the steel is minute.

For aircraft that are being modified with the engine and accessories in place, the “one-hole” product was designed to allow mounting with a single firewall hole that could be made with a common thinwall electrical conduit punch. This product is all aluminum.

Use of these products in aircraft is limited by the Federal Aviation Agency (FAA) to the experimental (primarily home built) category. Occasional use in repair of renovation of certificated aircraft can be accommodated with appropriate paper work and local FAA approval.

“EYEBALL” Spherical Metal Grommet
				Use SE961B series for experimental aircraft. Use SE961S series for certified aircraft firewalls. TTP Series only requires one hole
ball matl. appx. wt. part no.	alumn. 0.10# SE961-	steel 1.11# SE961-	alumn. 0.12# TTP-
hole size				Applications
.125"	125B	125S	125	Oil pressure, primer
.188"	188B	188S	188	ACS cable, 730, 740, 1770, A1780 Bowden Cable
.218"	218B	218S	218	ACS cable, 700, 1340
.240"	240B	240S	240	750, 770, 780, 790, 800, 810, 820, 920, 930, 950, 960, 970, 1550, 1600, 1750, 1760, 1860, 1870, 1970
.250"	250B	250S	250	Tubing
.260"	260B	260S	260	Tachometer cable
.375"	375B	N/A	375	Tubing

The chart above shows the thru-hole sizes available and the approximate weight of each of the three models. A custom model is available to accommodate shielded magneto wire pairs. It is necessary to provide wire diameter with shield insulation removed, as there are many different sizes of magneto wire. By removing the shield insulation, the shield is grounded at the firewall, reducing radiated electrical interference.