Cowl bumps again

[senior]

Re: Cowl bumps again

Has anybody tried Wag-Aero's PA-11 bumps?
They seem like a reasonably priced alternative to most others I've seen!

http://store.wagaero.com/product_inf...oducts_id=8075

UPDATE: These bumps fit very well with a little massaging to fit the cowl curve!
Although advertised at $25 if two or more purchased &
price confirmed by phone before purchase,
when the order was recieved they charged the single unit price of $36.
Not worth the argument

[KewFlyer]

Re: Cowl bumps again

Part of my T-craft stash...White ones are plastic, other two pair are aluminum and tapered (hard to tell in the pic). I have a couple of styles of small bumps mounted on cowls at home. Thinking about trying to make a couple of molds and bucks and trying my hand at pounding a few out for guys at my field. I kinda prefer the small ones (x 4) on one of the cowls at home....actually prefer none at all (43319 has no bumps).

Stumpy.
Would you consider selling the metal 10" or the 12" bumps. Im currenlty using old and deteriorated Ercoupe cans and I'm not getting good connections between the leads and the plugs...even at time, intermitent..... which translates to engine misbehaving.

thanks

Ralph

[Hank Jarrett]

Re: Cowl bumps again

Randy,
Just went through the old messages in this thread and noticed my response to you didn't post. Ping me with a message and I will try to remember to get some better photos of the bumps. Most of them I WOULD NOT put on a plane since they are cracked and damaged, but they would be good for making molds for fiberglass or a Bondo buck to make a metal one.

Hank

Hank: I would buy bumps from either 1st or 2nd pic if you would consider removing & shipping?

[senior]

Re: Cowl bumps again

I broke down & purchased a set from Wag Areo.
Individual price was ok but they offered a deal if you bought two or more.
I even confirmed with lady on phone.... placed my order & got NO discount
Oh well they do the job, & certainly look better than two holes with plugs stuck thru!

I considered making a set from fiberglass but pondered whether they would crack or break due to flexing of the cowl on opening & closing.

[Hank Jarrett]

Re: Cowl bumps again

They will crack. Even the flexible plastic ones I have are all cracked. The BEST way is to make a buck from ones you like and tap out aluminum ones, but I have a few of those with cracks too.

Hank

[Mark Julicher]

Re: Cowl bumps again

I made a decent set of spark plug fairings from fiberglass, but they were about 1/8 inch thick when completed. I used them a long time and they did not crack. I also hammer-formed a set from aluminum - takes patience but it worked.

If you go the hammer form route, a Bondo mold works just fine. Use 3003 H-0 aluminum, .050 thickness. The metal is going to work harden so beginning with soft metal is an advantage. I'm assuming you are going to make the "Canoes" and not the"Tear Drops" in this explanation. The deep corners are going to thin out considerably, meaning as much as .015 thinner than the original metal, so you need to begin with beefy metal .

If you merely lay a piece of flat aluminum over a female mold and hammer it, the edges will wrinkle up dramatically as you push metal down into the cavity. In order to minimize this, clamp the edges to the mold so that these edge flanges are captured and restrained from deeply wrinkling. You don't want to clamp the edges too tight because the metal has to move somewhat as you work it down into the cavity, but if you can reduce the wrinkles it is a big help. You can make a plywood frame and use it to clamp/capture the edges, or you can just use a bunch of C clamps with suitably wide feet.

After you work metal down a ways and it is apparent that no more metal will be drawn from the edges down into the cavity, then you should trim the edges to a little over their desired finished width. This will save some work.

A 490 degree Tempil stick and a propane torch will let you anneal the deep corners if you need to do so. Work hardening is relieved this way to reduce chances of cracking the areas that are hammered the most. The advanced tin smith may not have to anneal at all, but I am not there yet.

If you are super patient, you can get a good result from just hammering; however, you can also sand the exterior to achieve a pleasing final contour because using .050 metal you started with enough thickness to to allow a bit of sanding. Accomplished metal smiths usually won't sand - but it is an option for we amateurs.