Bob's Mods

Here are some fairly simple modifications sent in by Bob Grimstead. They have been carried out on his RF-4, but many could be used on other Fourniers.


1. Aerobatic fuel cap.

Valve is from Stromberg CD 150 carburettor needle valve

2 Aileron gap seal tape

Standard glider stuff nearly doubles roll-rate, but lowers Va. Be very careful using full aileron at speed! Greatly helps in a roll-off-the-top.
5. Breather oil catch tank.
Made out of standard Australian, thin-walled, pressed steel gutter down pipe, and sealed with homebuilders' fuel tank sealant 'Proseal'. It just nestles neatly between exhausts, engine mounts and firewall.
6. Cockpit Ventilation
These vents probably would not need CAA/PFA approval. They just use Scat ducting from the wing-root vents, crossed over behind the instrument panel to blow in your face on a hot day. The P-clips were cut with scissors from black plastic Shell oil bottles. It is very important to fit them with pop-rivets or very short screws, so as not to puncture the tyre.
7. Cranked Stick
The cranked stick is a much bigger deal. Made by cutting the original diagonally (very carefully) and fitting in a five-inch piece of one-inch 4130. Got it wleded by an approved welder, of course. Kinda important it doesn't come un-glued! Makes the stick slightly longer for better leverage, as wells as more easily enabling full forward stick ( like, while inverted). Very useful for aerobatics if, like me, you have short arms.
8. Engine cooling mod
Filling the upper cowling half with quick-form foam has significantly reduced engine temperatures, by smoothing the airflow into the cowling. This is a Limbach suggested improvement, (Technical Bulletin 44.1).
9. Photographic Mounts

The camera bracket is made from four inches of general-purpose square section steel extrusion (patio tubing again), but could easily be folded from a single sheet of steel or aluminium, approximately ten inches by four. The only important dimension is the gap, which has to fit the thickness of the double-walled fuselage side. (You have to remove the fibreglass inner liner, if you still have one.) I have fitted rubber anti-abrasion strips, so as not to damage the paintwork. The bracket slides into place, to butt up against the canopy lock lever's little pin, and is held securely in place by the closed canopy.

The material has to be quite thick and rigid, to stay in shape against the 130-knot airflow at 6g. This one is fine. I have filmed my five minute sequence several times. The camera should be quite small, to minimise the drag, and therefore twisting on the bracket.

I slip the camera's lanyard over the canopy locking handle, as added security.

The wing-tip camera mount. It bolts through the balsa wing-tip, using the original smoke pod mounts. Smoke pod wiring from the cockpit button fires off the Olympus OM-2's motor drive. Not of great interest to the majority, but takes brilliant photos. The material is 'patio tubing' square-section, thin-walled, general-purpose domestic structural extruded steel tubing.
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