HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 25, 2014, 11:54 AM
They call me Spock
United States, TN, Knoxville
Joined Jun 2013
179 Posts
Discussion
Wing Spars

I need some direction on wing spars. I am building a 60" Kfm3 with dihedral (BBAP1). The first one I built ended up with twist in it. The plane was difficult to fly so I tore the wing apart and am rebuilding. I have my new spar but it is also warped. I havent attached any foam yet. What do you guys do to straighten spars or install them such that wings are not warped or twisted?
dmanuel is offline Find More Posts by dmanuel
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 25, 2014, 12:42 PM
Registered User
Los Angeles, CA
Joined Mar 2004
1,253 Posts
Quote:
Originally Posted by dmanuel View Post
I need some direction on wing spars. I am building a 60" Kfm3 with dihedral (BBAP1). The first one I built ended up with twist in it. The plane was difficult to fly so I tore the wing apart and am rebuilding. I have my new spar but it is also warped. I havent attached any foam yet. What do you guys do to straighten spars or install them such that wings are not warped or twisted?
What kind of a wing soar do you gave now that is warped. I use carbon tube or the solid carbon rods. If your spar is warped, you probably need to get a new one
lv2soar is offline Find More Posts by lv2soar
Reply With Quote
Old Jan 25, 2014, 12:47 PM
They call me Spock
United States, TN, Knoxville
Joined Jun 2013
179 Posts
I am using wooden dowels. I have wondered if CF might not be a better choice, but I have never worked with it. So then my questions shift to how do you cut it? Join two pieces? Attach to foam?
dmanuel is offline Find More Posts by dmanuel
Reply With Quote
Old Jan 25, 2014, 12:53 PM
Registered User
Canada
Joined Nov 2000
7,068 Posts
Dowels are notoriously bad for warpages. Avoid them.
Square/rectangular spruce is a far better material for spars, as is Carbon tube, but at 5x the price of the spruce.
Ca glues Ca very well, but use the foam safe variety on your foamy wing
Bare is offline Find More Posts by Bare
Reply With Quote
Old Jan 25, 2014, 12:54 PM
Registered User
Los Angeles, CA
Joined Mar 2004
1,253 Posts
Quote:
Originally Posted by dmanuel View Post
I am using wooden dowels. I have wondered if CF might not be a better choice, but I have never worked with it. So then my questions shift to how do you cut it? Join two pieces? Attach to foam?

Not sure how long is your wing span. Wood dowels warp over time due to temperature change.

Use one piece for the length of the wing. ie: if your wing is 36" long, you can use a 32" long carbon spar. Give and take. I cut my carbon spar with a sharp knife by scoring it. Out the knife on where you want to cut and score it back and forth, then you can bend it to snap it apart. Some people use a Dremel. E careful not to breathe in the dust.
lv2soar is offline Find More Posts by lv2soar
Reply With Quote
Old Jan 25, 2014, 02:12 PM
Registered User
Joined Apr 2013
590 Posts
At 60" span, I would trust only CF tube. The wood dowels are half the strength for double the weight - even if you get ones that aren't warped. The CF tubes can be joined with short metal rods that have an outer diameter that is very close to the inner diameter of the CF tubes - epoxy them in place.
I would go with a flat wing at the root (no dihedral) and have angled winglets at the outboard end of each wing. This achieves the desired roll stability without compromising the strength at the root (the root is, of course, the point that gets the most stress - ask me how I know ). So that 30-something inch CF tube would span about 15 inches of each wing at the root and then additional CF tubes added outward on each wing with short metal rods joining them.
nuteman is offline Find More Posts by nuteman
RCG Plus Member
Latest blog entry: My youtube channel
Reply With Quote
Old Jan 25, 2014, 02:23 PM
serial scratchbuilder
Granted's Avatar
Canada, BC, Mission
Joined Sep 2012
1,339 Posts
My favorite source for cheap spars right now is fiberglass hoop-skirt boning. The stuff is round, available in black or white and comes in 20' lengths in sizes from 1/16" to 1/4". The 1/4" is most expensive at about $.60 per foot.
Granted is online now Find More Posts by Granted
Reply With Quote
Old Jan 25, 2014, 02:59 PM
Registered User
Joined Apr 2013
590 Posts
Quote:
Originally Posted by Granted View Post
My favorite source for cheap spars right now is fiberglass hoop-skirt boning. The stuff is round, available in black or white and comes in 20' lengths in sizes from 1/16" to 1/4". The 1/4" is most expensive at about $.60 per foot.
Where do you buy those? I've been looking for something a bit cheaper than CF.
Can they be ordered online?
nuteman is offline Find More Posts by nuteman
RCG Plus Member
Latest blog entry: My youtube channel
Reply With Quote
Old Jan 25, 2014, 03:06 PM
They call me Spock
United States, TN, Knoxville
Joined Jun 2013
179 Posts
Quote:
Originally Posted by nuteman View Post
I would go with a flat wing at the root (no dihedral) and have angled winglets at the outboard end of each wing. This achieves the desired roll stability without compromising the strength at the root.
Since the plans I am using don't specify this and this is my second scratchbuild, I would like more detail on how to accomplish this. I like the idea.
dmanuel is offline Find More Posts by dmanuel
Reply With Quote
Old Jan 25, 2014, 04:48 PM
serial scratchbuilder
Granted's Avatar
Canada, BC, Mission
Joined Sep 2012
1,339 Posts
Quote:
Originally Posted by nuteman View Post
Where do you buy those? I've been looking for something a bit cheaper than CF.
Can they be ordered online?
I get mine from cosplaysupplies.com
http://www.cosplaysupplies.com/store.php?s=G0II
Granted is online now Find More Posts by Granted
Reply With Quote
Old Jan 25, 2014, 08:22 PM
Registered User
Joined Apr 2013
590 Posts
Quote:
Originally Posted by Granted View Post
I get mine from cosplaysupplies.com
http://www.cosplaysupplies.com/store.php?s=G0II
Thanks!
nuteman is offline Find More Posts by nuteman
RCG Plus Member
Latest blog entry: My youtube channel
Reply With Quote
Old Jan 25, 2014, 08:28 PM
Registered User
Joined Apr 2013
590 Posts
Quote:
Originally Posted by dmanuel View Post
Since the plans I am using don't specify this and this is my second scratchbuild, I would like more detail on how to accomplish this. I like the idea.
There are probably scores of examples on this site alone, but here's one that I did using that approach (see link below), so you get an idea of what it looks like. The spar was placed just as I described above.
I also recall seeing a couple of really detailed videos (I think one was on ExperimentalAirlines youtube channel form Ed) that show exactly how to lay in the spar across the root - for both un-swept and swept wings.

Tips for RC Twin Boom Pusher (7 min 55 sec)
nuteman is offline Find More Posts by nuteman
RCG Plus Member
Latest blog entry: My youtube channel
Reply With Quote
Old Jan 25, 2014, 08:32 PM
RC Adddict
Wilfor's Avatar
Canada, BC, Williams Lake
Joined Jan 2010
4,268 Posts
Quote:
Originally Posted by dmanuel View Post
Since the plans I am using don't specify this and this is my second scratchbuild, I would like more detail on how to accomplish this. I like the idea.


Not a 60" Wing but this is what you want .. Jack says it best

http://www.rcgroups.com/forums/showthread.php?t=1474665
Wilfor is offline Find More Posts by Wilfor
Reply With Quote
Old Jan 25, 2014, 08:34 PM
treefinder
springer's Avatar
SE MI
Joined Oct 2004
9,748 Posts
If you hav wood available to you you can laminate two or three layers to take out bows and bends in the wood strips. Also, arrow shafts are good for spars. Get them at sporting goods or Walmart.
springer is offline Find More Posts by springer
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold carbon fiber wing spar tube psychoticflyer Aircraft - General - Miscellaneous (FS/W) 0 Jan 05, 2014 11:10 AM
Sold 3DHS 65" Vyper Wings/Bags/Carbon Spar, $70.00 CNICFLY Aircraft - Electric - Airplanes (FS/W) 1 Nov 22, 2013 08:27 AM
Help! Uni carbon wing spars / wing rods DLGjunkyard Hand Launch 27 Nov 11, 2013 01:05 PM
Discussion Hawk Sky Replacement Wing Carbon Spar FPVdude Foamies (Kits) 0 Nov 03, 2013 12:54 PM
Building a 20" wing.....Spar or no spar????? azfrench Flying Wings 4 Aug 21, 2004 07:53 AM