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Spar strength - 1/22/2003 11:04:35 PM   
Mendes



Posts: 477
Joined: 1/8/2002
From: Ottawa, ON, CANADA
Status: offline 		I am in the midst of planning my construction project for next (yes next) winter.

It is going to be a Hostetler Pitts S-1-11B enlarged to 55%. The wingspan will be slightly under 10', a BIG plane. I am looking for opinions on what type of spars to use, specifically, does it make sense to use a material like carbon fibre to add strength.

I am currently building a 42% bipe which doesn't use any composites at all. But at 55% and I am projecting around 60 lbs, I am hoping to be able to use a combination of lighter wood and composites to keep weight down.

Also, where else can I use composites to save weight? Other than the obvious landing gear, and spinner etc....

Thoughts?
       Post #: 1

Spar strength - 1/24/2003 10:10:07 PM   
r1morris


 

Posts: 327
Joined: 5/9/2002
From: Las Vegas, NV, USA
Status: offline 		55% is getting into areas of loads and stresses not normally associated with model aircraft. If your not an engineer,the next best thing is to look into the practices of the home built light aircraft groups. Your completed project will more then likely be more successful constructed using full scale building tech-nicks and materials. Your talking about reproducing an aerobatic aircraft. high G maneuver could pull up to 10 G's in high stress areas.
Think of it this way . If your completed aircraft came out at 100 pounds and pulled 10 G's thats 1000 pounds of force.
Several years ago I witnessed a 50% Ultimate fly at the QSAA event in Las Vegas. Evin at 50% the aircraft was built more like the Full size then a model. Good luck

< Message edited by r1morris -- Jan 24 2003 5:23PM >

(in reply to Mendes)
       Post #: 2

Spar strength - 1/27/2003 12:32:13 PM   
Giant Scale



Posts: 856
Joined: 6/8/2002
From: Baltimore, MD, USA
Status: offline 		If you want to make a flat wing spar like those found in full size gliders(they must stand lots of g's) you can use end grain balsa. Start with an endgrain balsa core(ie the grain is oriented from top of wing to bottom, not spanwise). Cap the spar top and bottom with graphlite carbon rod. Then wrap the entire spar with biaxial fiberglass so the weave looks like an X or fiberglass cut on the bias. Reinforce the root end with some CF cloth, laminate and vaccum bag the whole thing. The result will be a spar considerably stronger than any plywood or hardwood spar. Spars of this type are used in full size gliders and will
withstand considerable g forces. I am working on a 50% CAP-232 and will use this type of spar system to replace a heavy plywood wing spar. The wings are balsa covered foam core with CF spar.

(in reply to Mendes)
       Post #: 3

Spar strength - 1/28/2003 9:36:21 PM   
Mendes



Posts: 477
Joined: 1/8/2002
From: Ottawa, ON, CANADA
Status: offline 		[QUOTE]Originally posted by Giant Scale
If you want to make a flat wing spar like those found in full size gliders(they must stand lots of g's) you can use end grain balsa. Start with an endgrain balsa core(ie the grain is oriented from top of wing to bottom, not spanwise). Cap the spar top and bottom with graphlite carbon rod. Then wrap the entire spar with biaxial fiberglass so the weave looks like an X or fiberglass cut on the bias. Reinforce the root end with some CF cloth, laminate and vaccum bag the whole thing. The result will be a spar considerably stronger than any plywood or hardwood spar. Spars of this type are used in full size gliders and will
withstand considerable g forces. I am working on a 50% CAP-232 and will use this type of spar system to replace a heavy plywood wing spar. The wings are balsa covered foam core with CF spar. [/QUOTE]

Thanks for the info! That is what I was looking for. I am also considering a plywood box spar. I think that, in the end, I will make up three or four different types of spars and perform some stress tests.

As big as this plane will be, a standard spruce spar will be strong enough, it is the weight savings that interest me.

Composites really interest me, I think some vaccum bagging equipment will make it's way to my workshop soon.

(in reply to Mendes)
       Post #: 4

Spar strength - 1/29/2003 8:28:45 AM   
Giant Scale



Posts: 856
Joined: 6/8/2002
From: Baltimore, MD, USA
Status: offline 		Rich,
To learn more about spar building check out
this link
http://www.continuo.com/marske/carbon/carbon.htm

He makes various strength comparisons of wood spars, wood/composite and full composite spars. When I first started thinking about wing spars my initial reaction was that a spar must be thick and heavy to be strong. After a lengthy phone conversation with Jim, I realized I was wrong. A properly designed spar will be lighter and much much stronger than an all wood spar. If you can spare the time give him a call, the graphlite carbon he sells is amazing stuff, and he has a wealth of design knowledge. Let me know what you think of the article.

(in reply to Mendes)
       Post #: 5

Spar strength - 1/29/2003 9:16:33 AM   
Mendes



Posts: 477
Joined: 1/8/2002
From: Ottawa, ON, CANADA
Status: offline 		[QUOTE]Originally posted by Giant Scale
Rich,
To learn more about spar building check out
this link
http://www.continuo.com/marske/carbon/carbon.htm

He makes various strength comparisons of wood spars, wood/composite and full composite spars. When I first started thinking about wing spars my initial reaction was that a spar must be thick and heavy to be strong. After a lengthy phone conversation with Jim, I realized I was wrong. A properly designed spar will be lighter and much much stronger than an all wood spar. If you can spare the time give him a call, the graphlite carbon he sells is amazing stuff, and he has a wealth of design knowledge. Let me know what you think of the article. [/QUOTE]

That graphlite is amazing! Looks like it is the only way to go if you want a light design. I will give him a call for sure, I would love to hear his input on my project.

Thanks again, you have been a great help!

Keep me posted on your 50% Cap progress.

(in reply to Mendes)
       Post #: 6

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