making your own cowlings in fibreglass

zodiacpugh · Post by **zodiacpugh** » Tue Jun 30, 2009 4:01 pm

I have been trying to find suitable cowlings for my Zodiac/UL power engine combination, with no luck and would like to try making them myself. What is my best plan of action, as I have no experience in this field at all? I have, however, built this aeroplane from plans and it is nearing completion.

Brian Hope · Post by **Brian Hope** » Tue Jun 30, 2009 5:21 pm

Is it Tom, sorry I'm hopeless with names. I have a number of friends who are pretty ace at the mouldless composite techniques used on Rutan designs, and they swear that the best way to go is to use urethane (?) foam in situ and carve, sand it to shape. When it is perfect, they glass over it, sometimes using Kevlar as well as glass cloth to make it as light as possible. The surface is then smoothed with lightweight, microballoon filler and the whole is removed from the aircraft and the foam dug out to leave the bare glass shell. It then has to be split, reinforced around the edges and oil door etc.
One of these guys is a regular poster so hopefully will come on and give a more detailed explanation.

zodiacpugh · Post by **zodiacpugh** » Tue Jun 30, 2009 9:18 pm

Thank you Brian for that information. Sounds like a good idea. Yes it is Tom and the Zodiac build is going really well.

Tom Pugh

Kevin Dilks · Post by **Kevin Dilks** » Wed Jul 01, 2009 8:54 am

I noticed on the latest zenair news letter that a cowl for a UL powered XL is available from Gus Warren in the US.
He is the ULI US dealer.
They also have a engine mount thats very long to help with the CG

Hope that helps.

cardiffrob · Post by **cardiffrob** » Thu Jul 02, 2009 2:54 pm

I was given some 2-part foam in tins. It is used to fill canoes with foam for buoyancy. Might be a cheaper option than builders foam.

Mix it in a plastic tub for 30 seconds and pour it on. It expands to about x8 and then sets like that blue foamy stuff in Vari-eze wings.

zodiacpugh · Post by **zodiacpugh** » Thu Jul 02, 2009 2:58 pm

Thanks all, for these interesting replies. I now have a lot of ideas to consider

Tom Pugh

gasax · Post by **gasax** » Thu Jul 02, 2009 4:02 pm

I've not made a cowling but I do have quite a bit of experience with building grp boats both mouled and mouldless.

Building the plug will take a serious amount of time. My advice would be to use a fabricated frame to get as close as possible to the final dimensions. Large 'blobs' of foam will require a huge amount of shaping and more importantly introduce the possibilities of asymmetry, which isn't a problem until you apply paint (usually after you have made the plug, the mould and the fist cowling...!) and then it can give you glaring defects from some angles.

Fitting even a poor cowling from someone else will take 20 to 50 hours. Making one - if it goes right first time - 200 plus. Making your own would allow a lot of issue to be addressed but it is a significant effort. Best of luck either way.