stunthanger.com
General control line discussion => Open Forum => Topic started by: Tim Wescott on August 26, 2010, 11:52:05 AM
-
I used to design that in almost exclusively for wing spars in gliders and RC projects, but now it seems hard to find.
Why isn't it used in CL? Do folks feel it's too heavy, even after accounting for its greater strength and using smaller pieces? Or did it just never catch on?
And does anyone know who sells it other than Sig and Aircraft Spruce & Specialty?
-
Wicks, www.wicksaircraft.com/ .
-
This might not be for everyone, but I cut my own spruce spars. The wood is free for me, and my son has a very complete woodworking shop with all the right machine tools.
I used to get spruce pieces at the LHS, but they seldom had any stock that was straight.
Floyd
-
If you can saw your own, Alaska Cedar is a great substitute. It's yellow, not red. Our NW F1A team member and Boeing Stress Engineer, Jim Walters used it. I think I may still have a slab of it around. Someplace... :P Steve
-
out of curiosity, why use spruce at all ? and for what parts ?
-
It has a better strength to weight ratio than balsa, and is very shatter resistant. So it's a good material to use for wing spars that'll get a lot of punishment.
-
It has a better strength to weight ratio than balsa, and is very shatter resistant. So it's a good material to use for wing spars that'll get a lot of punishment.
So, if you were going to use spruce for the spars in a design that called for 1/4" square balsa, what size spruce would you substitute ?
-
So, if you were going to use spruce for the spars in a design that called for 1/4" square balsa, what size spruce would you substitute ?
1/4 x 1/8, maybe 1/4 x 3/16 if I wanted to make it stouter at the same time.
-
y1 y1 y1 y1 y1
Tim:
I've been using spruce in many difference area in my CL Stunt ships for about the last 8 - 10 years. Each new ship I expand the spruce construction a little further. Very happy with the results. #^ #^ #^ #^ #^
Gene
-
What ever happened to Bic Brannon? He had a take apart Barnstormer he used to bring to VSC each year in a small carry on type case. Was very little balsa in it. Kept hoping he would do a construction article on it. It was also very light. H^^
-
Spruce is used a lot outside of North America. We've been spoiled with abundant supplies of balsa here. If you look at East Eurpean or Chinese model construction, they use spruce for all stress members.
1/4 x1/4 balsa spar can easily be substituted with a spruce spar half its thickness: 1/4 x 1/8. Just make sure to stand the spar up(narrow end up).
-
It has a better strength to weight ratio than balsa, and is very shatter resistant. So it's a good material to use for wing spars that'll get a lot of punishment.
UUUhhhh...
Sorry Tim but spruce does not have a better strength to weight ratio than balsa...in fact almost no materials do. Spruce makes good spars because it's simply harder and less fragile. It's also easier to find in straight pieces in small square sizes.
Randy Cuberly.
-
Tom Morris has been a long time advocate for using spruce in C/L stunters. Also smaller size balsa (for things like fuselagfe sides) than most people think is "necessary". Personally, I have used 3/32nd in place of 1/8th in a LOT of my planes. Especially the ".35" size stunters. My Geo Juno (modified Saturn) uses 3/32nd sides and is now powered with a PA 61 on pipe. Nary a problem after 14 years! ;D
The Spacehound I built from European planes called for spruce spars. it is a fairly thin plane with minimal LE sheeting. And, it is necessary to use the spruce unless you use a bigger balsa spar. ;D (speaking from personal {bad} experience! LOL!! )
But, we DO tend to overbuild in the wrong places, most of the time.......
Big Bear
-
The strength to weight issue is interesting. "aircraft" spruce does very well because the FAA has strict specifications for the density, number of growth rings per inch, lack of knots or deformities, etc. Generally, a larger, lower density piece of balsa will have better strength to weight and better stiffness than other woods in model applications. Go to too low a density, grain and firmness of the wood become very important. Mush soft 4 lb. wood will not be very strong. But if it is firm, has a definite grain, and isn't abused otherwise, it has the best strength/weight of any wood.
Balsa, especially low density wood, is prone to wind checking, which is cracks across the grain in the wood(usually nearly invisible) which make it useless for anything but carving blocks. Other wood can also get wind checked, so take a close look at any spars and try bending and pulling on the wood. A wind-checked piece will break very easily with no strings or sign of anything going across the break. Just a more or less flat across break that looks like it was almost cut(which it almost has since the wood fibers are mostly already broken).
Overall, the strength of a piece of wood is primarily proportional to its density. Heavy dense wood is stronger than lighter, less dense wood, across the board for a given cross section. But carefully selected wood with straight grain and no defects can easily be twice as strong as a poorly selected piece. So a spruce spar will be pretty much the same strength as a balsa spar of the same weight(not the same dimensions).