HELP!-Wing Spars

[BStaley]

I am trying to finish a Chris Williams Petrel. Being British, the plans call for the rectangular steel bar/brass tube set-up for the spars. There are 2 for the wings. I'm sure there is enough strength in the vertical load but does anyone have any experience with these in the lateral loads from towing? I don't want to go thru all the work to build this and have it fail-like my Reiher. If I need to change the set-up now is the time to decide before I build the wings. Thanks-Bill

[Tom]

Do yourself a favor and pitch the steel blades before you even consider putting them into the wings.....a 7075 3/4" round aluminum joiner will work much better.

[lenb]

I double second what Tom says, and he knows!!!! He's the spar man when it comes to sailplane wings. Throw out the thought of blade joiners and go with a round aluminum.
I've personally have seen those blade joiners fail on three occasions.

Oh, wait a minute, it was four times!!

Len

[BStaley]

Thanks for the info. Where is a good source for the aluminum or steel spars? Bill

[Tango Juliet]

I had the same question/issue with my T21 build. I was also advised to go with the round aluminum bar and brass sleeves.

- 1/2" x 19.5" long - solid 7075 aluminum rod stock available from www.onlinemetals.com
- 17/32" x 12" K&S brass tubing

[Tom]

Thanks for the info. Where is a good source for the aluminum or steel spars? Bill

Do not use steel for the joiner.....steel rusts, is heavier then aluminum, and is not as strong. Go aluminum round joiner with either brass or carbon receiver tubes you can buy or roll your own from fiberglass......

[BStaley]

Got it. Thanks for all the help-now to the trash can...