Balsa wood sizes

[Pleiades]

ok so i need to make a list of all the balsa wood that i need for wright stuff and elevated bridge. i'm new to balsa wood so i dont really know about the grains and the sizes of wood. can someone please tell me what size i need, what grain type, and how much of it?

[carneyf1d]

there are three types of grain: a,b,c. They are differenciated because of the cut which is used on the tree. A grain is very flexible, where C grain is stiff and strong. B is somewhere in the middle. Balsa also has a density measured in lbs/cubic ft. It is crucial that you get light density balsa for wright stuff. For more questions, feel free to pm me.

[jander14indoor]

OK, do some research on the old list, MUCH discussion of balsa wood use for Wright Stuff planes there.

Some links (from Google, there are more of course) to balsa wood grain, density, etc.
http://www.skyhooks.ca/balsa.htm
http://www.rcscalebuilder.com/tutorials ... alsa_1.htm

As to sizes and specific weights for your plane, it depends on the plan. Again, much discussion on the old forum, spend some time there.

But, as a start, your goal is to select sizes and densities that give you an exactly 7.000000001 gm (a little joke there, but as close to 7 gm as you can build and measure) plane. You figure that out by making up a spreadsheet with EVERY part in your plane listed with weights. Adjust the balsa density and wood size until your plane weighs 6.5 gm or so. Get to 7 gm with clay to adjust balance.

From experience, if you are getting a stock of wood to work with, you'll need some 7-9 lb/ft3 1/16 sheet stock for spar and wing posts (typically A-grain), 7 lb/ft3 1/32 sheet stock for ribs (typically C-grain), and the lightest (4-5 lb/ft3) ¼ inch stock you can find for the motor stick (B-grain might be nice here, but A is fine). Hold the sheets up to the light and make sure the grain is STRAIGHT. Put anything wavy back for the unsuspecting.

Oh, and learn how to use a stripper. Avoid pre cut sticks you'll have NO idea what the grain is like.

I can't advise you on wood sizes for bridges, but what I just recommended for Wright Stuff is probably a good starting point. Though I doubt you will use much of the ¼ inch stock. You may also need less dense 1/32 and 1/16 sheets for the bridge as min weight is the goal vs target weight for Wright Stuff. I've heard some comments about some members being bass or spruce wood, but the balsa will get you started.

Jeff Anderson
Livonia, MI

[carneyf1d]

i slightly disagree with jander14indoor...
First, dont build .5 grams underweight, instead maybe only .1 or so. as long as you keep weighing your parts throughout you should be fine. The extra .4 grams can go into making a stronger motor stick, long tail boom, or simply spacing the wing and stab farther apart by lengthening the wing struts...you decide
Second, ribs should be made of the lightest material you can find. At least this is my preference.
Third, rolled motor sticks are best with c-grained balsa. Since C is the least flexible. You can improvise on this a little since the tube walls can be fairly thick. For solid motor sticks, i hold the sheet up to a light and chose the brightest area of the sheet. This is usually the least dense area in the sheet. Solid motor sticks can also be tapered to each ends, saving unnecessary weight.
I've always used hobby shop wood -- until i got to f1d's -- and it is possible to find decent enough wood since you are allowed 7 grams. SO planes can be built like tanks. My planes consisted of 3/32 by 1/8 L.E. spars and 1/16 by 3/32 T.E spars. They were extremely light weight but still strong. You can sand down the front of the L.E. so that it comes to a point and is a little more aerodynamic. The ribs were around 1/16 but made from the lightest balsa i could find. With a 1 gram wing and a .6 gram stab that were built like a tank, and 2.1 gram broad blade prop, i had much room to play with the weights and sizes of the motor stick and tail boom.

[Pleiades]

thanks guys =) i was just thinking about this - since this year there is no maximum wing chord i would obvioulsy want a big one. Since the center of gravity is supposed to be right behind the wing [from my understanding] inorder to achieve that wouldnt i need to lengthen the motorstick and/or tailboom since my wing now has a larger mass? wouldnt lengthening them also add to the mass? or do i have enough mass to work with?

[carneyf1d]

im working on a model right now. i have everything built, i just need to get the gym to fly it. the stab is limited, so im not sure how big of a wing you can have. my stab weighs about .4 grams. on the wing the major weight comes from the spars (at least for me) so lengthening the ribs shouldnt add too much weight. the covering weight shouldnt make too much of a difference. I would save that .1 gram ballast to determine the center of gravity. I have a pennyplane that works best with the CoG at 75% of wing chord, yet my last year scioly plane worked best at the back post of the wing. Just experiment a little.

[carneyf1d]

also, there are several ways of minimizing mass in the plane. tapering everything helps, rolling tubes, maybe you can even find a loophole in the rules to use light weight wires such at music wire to strengthen small/light/weak wing mounts. There are many more. If you need them, just message me.

[jander14indoor]

I hate pushing back on an experienced F1D flyer(These guys build 1.1 gm planes that fly 30 minutes! My longest ever flight was a 3 gm penny plane at 10 minutes.), but for new builders, rolled motor sticks are orerkill on the smaller SO planes at 7 gm. As to light ribs, heck, I didn't use anything less than 7-8 lb/ft3 wood on last years bigger SO planes except the motor stick.

Now, if you are one of those experienced builders, follow carneyf1d's advice, your times WILL improve.

As to aiming for a 6.5 or 6.9 gm plane, depends on your level of confidence. But carneyf1d did hit a key point, if you aren't building with a scale next to you, you won't get there. He's also right, the best place for weight is in wood structure, not ballast. But absolutely evil is any weight above the minimum 7 gm.

On your question about enough mass for a large chord, you have LOTS of room. Its EASY if you plan and build with a scale. Students hit target weight with tissue covering and a much larger 50 cm by 10 cm wing in years past. If you don't plan, you'll have a 15 gm lead sled and be competing in the race to the floor.

Jeff Anderson
Livonia, MI

[gh]

Using wire is definitely illegal and unnecessary. With 7 grams at your disposal (maybe 8 for Division B), you'll do fine by using 1/16″ square basswood for wingposts.

Rolling tubes does indeed have lot of advantages, but will also introduce several problems. For example, your plane can be significantly longer, which allows you to reduce the size of your stab (since more length means more leverage), decreasing drag. You will also get more torque out of your rubber, since it will be stretched out longer. In addition, transportation is a snap, because the stick and boom are detachable.

This is a picture of my plane from the 2007 season:

Click on image for more info

However, tubes are a pain to make, and I still have not got down the art of mounting the rear hook and wing tissue tubes. Rolled sticks do not bow as much as solid sticks do, though with the amount of torque you get from WS-width rubber, you do get some bowing. Solid sticks are your best bet for lower ceilings for that reason.

One more thing. Mr. Anderson is right: rolling is just way overkill unless you're sure it will help you. That plane I linked to was 5.6 grams (1.4 grams underweight) even with 1/8″ leading edge spars, basswood wingposts, and an overall length of 37″. I probably could have built to the same length with solid stick and boom, instead and save a lot of time, albeit with a lower weight margin.

[carneyf1d]

hey, nice lookin plane you got there. I'm more of a wing tip person rather than dihedral though For me, lengthy planes is not my personal choice. At nats i flew a 14" compact droop boom. But for some others, they try to maximize length as much as possible. With the unlimited wing chord this year, i dont think it's a bad choice. I know that weight shouldnt be an issue, but why not stretch the limit with these planes... make it as long as possible... Stretch the distance from wing to stab so there is less air interference, and use all the weight for a purpose. I wouldnt risk structural integrity, but why not experiment with different lengths. And gh they did say wire isnt allowed...however they made an exception when connecting different parts of the plane. you could possibly get away with it if you convinced them it served that purpose as well. Granted, it isnt very necessary, but i was just making note of it as ways to save weight.