Trial bump-cowl fit

[ksatter26]

While waiting for my replacement lift strut inserts (5+ weeks now), I thought I'd take a look at how i might mount the fiberglass bump-cowling provided by Chris. I really like the look, but it seems to me that some serious modifications will have to be made.

(1) The picture is a rough placement of the cowl WITHOUT the seriously large air filter box mounted to the carburetor. It will be necessary to make a cutout through the starboard side to extend the box thru the side between the nose and the lateral portion of the cowl cheek.

(2) Looking inside the cowl, I can see that in changing the location of the radiator a new 90 degree cooling hose mounting fixture actually raises the hose such that very little (if any) clearance exists between the hose and the top, port side of the cowl. I can probably add some anti-shafe tape and tweek the placement to get a little clearance for the hose. The same problem exist in almost the same location for the spark plug wire/cap.

(3) The routing of the exhaust system on the port side also creates a rather tight fit against the cowl. Since this will get rather warm, I'm certain that yet another clearance hole will have to be made in the cowl here as well.

I'm not very good at fiberglass work so I'm not looking forward to these modification ... especially since I have no special means of accurately locating these holes and no pattern for them.

Moving this work to the back burner so I won't even drill out the mounting tabs and install the 10-32 rivnuts as yet. I look forward to hearing from anyone out there with any suggestions.

[Badland-F5 Pilot]

I'm sure I'm going to run into a similar issue. I would like something more of the looks of the Carbon Cub. I also have zero experience with fiberglass. Plus since the F-23 is a boxer style engine, well, it's going to be interesting to see what I can come up with.

Oh, the joys of building your own stuff!

[ksatter26]

I tried this for a simple cub-type cowl for my original 75HP Franklin Fly Baby project ( lost to hurricane Katrina).

It's a messy job with a LOT of shaping, sanding, and finishing. It worked fairly well. Gelcoat finishing would have made a nicer finish. I've also used spray foam to shape the throat of an air-scoop between the Viking 110 engine and firewall-forward kit cowl. Again a messy job. Shaping much tougher than the actual fiber -glassing.

Https://www.instructables.com/new-cowlo ... -aircraft/

[Badland-F5 Pilot]

I tried this for a simple cub-type cowl for my original 75HP Franklin Fly Baby project ( lost to hurricane Katrina).

It's a messy job with a LOT of shaping, sanding, and finishing. It worked fairly well. Gelcoat finishing would have made a nicer finish. I've also used spray foam to shape the throat of an air-scoop between the Viking 110 engine and firewall-forward kit cowl. Again a messy job. Shaping much tougher than the actual fiber -glassing.

Https://www.instructables.com/new-cowlo ... -aircraft/

I found it - https://www.instructables.com/New-cowli ... -aircraft/

Thanks! I saw a video on YT of a guy trying this. Unfortunately he only did the first steps of wrapping the engine and putting on the foam, never completing the process (or I didn't find his additional video which is always possible). I was also thinking of using some of the pink board foam from Home Depot and shaping sort of like what Terry Adair did for his Aford-A-Plane https://www.youtube.com/watch?v=LCzPNauv5Kg&t=7s. I'm thinking to make a plug like Terry did using foam board instead of wood. Then use liquid foam to fill in the plug. Once shaped and sanded to the contour that looks like it'll work I would cover with fiberglass. This would be a test piece. Removing the fiberglass from the plug I will test fit it to the plane, make adjustments on the plug as needed, and repeat the process. Eventually (hopefully with only two or three tries) I'll have the plug set up right. The last steps will be to carbon fiber the plug and hopefully when done I'll have a custom cowl. Any suggestions?

Bummer on the loss of the Fly Baby.

Thanks for the link and ideas. I've bookmarked the page in my Flying URL folder.

[ksatter26]

Styrene based foams are generally easier to sand/shape ... but dissolve in polyester resin and gasoline. This is helpful if you use EPOXY as you can use gasoline to "melt-out" the foam foam as the gasoline does not dissolve the epoxy. TEST your foam! I made an epoxy 3 25 gallon header tank for the 701 that way. came out ok (ugly as all get-out, but functional ... I trashed it for an aluminum one that a local guy sold me cheap).

I've also used micro-balloons in the epoxy as my own form of sandable bondo. The epoxy mixture (as with the bondo) is pretty thick so I really like the Polyprime idea for finishing.

I also reinforce mounting locations by glassing in large diameter washers, a piece of 0.016" 6061T6, or thin wire mesh (on the inside)

Get ready for LOTS of shaping and sanding. WEAR A MASK! I like the green styrene foams (from a local florist) ... you can use one piece of the foam to sand the other (creating twice a much dust). Wrapping with saran-wrap is good. Sealing with wax is time consuming for larger areas. Remember the styrene foam can be melted out with gasoline.

I'm definitely no expert, but in a pinch I'd try it again. Luckily, I really like the bubble-cowl that Chris offers, though it looks like I'll have to do some serious mods to fit the Polini 303. The Polini documentation raves about the efficiency of the air-filter box, but it is bulky an really destroys the contour of the cowl. Chris says to replace it with a small motorcycle filter. I found one on Amazon that has only a 2" projection. It should fit nicely into the cowl. I ordered one for testing.

Once again awaiting lift strut inserts ... I thought of just drilling out the 5/16-18's to 25/64" then tapping for a 3/8-24 thread. This means purchasing 4 3/8" rod-end bearings ($6.60 each from McMaster-Carr). I may run this by Chris. Should work, they're rated at 6,300 lbs.