Spruce is a lot stronger , and ' whippier ' as in itll bend without snapping .
But its HEAVIER , about four times , Idealy you taper it , for spars .
Also a few hard ply or suchlike spacers , at the C S ribs . Preferably with radiused corners , or on the ply gussets .

You need damn good glue for any splices . Pre Glueing both faces .

P. S.

theres nice even straight close ( HEART TIMBER ) grained spruce , and horrible knotty stuff that may be lighter ,
and loose grained weavy wobbly grain sap timber . ' impurities ' weaken it .

The Close Even grain stuffs often hard to find , but if you want it to curve like a yacht mast , or whadeva , Its WHAT YOU NEED .

Get the scales out . dont use any knotted sections where theyre obviously weakened . Whip a few about like a fencing sword
& or sit em over a roundeed bench end and test the weight / deflection .

Thus we aspire to be all scientific in the selection . !

Knactually , ANY Spars , the deflection Test - wether its a finger tip or something sat on em that weighs something , gets MATCHED STRENGTH .
AND if we balace em in the middle , we'll see if one ends HEAVIER . Presumeably its stronger , if it has no FLAWS - so goes in the middle
of the aeroplane. not the ends .

( Tearing Hair Out Icon ) 

After considering pros and cons, all spars will be hard balsa.
I will weight everything and write down these weights in my Little Black Book.

Tiger's wing will be build using the Tom Morris three piece L.E and T.E method and the metal "L" shaped brackets supporting these edges.Tom Morris used wooden blocks and steel angles to hold these blocks in place.

This method was described in the Stunt news, Jan/Feb. 2000. Tom Morris used the Lincoln Log method but I will use the 1/16" balsa shear panels connecting the spars between ribs with grains at + - 45 degrees (ref: principle of diagonal tension). Four most inside and four most outside spaces between ribs will not have the shear panels but tension/compression truss like members, creating the triangular pattern.

Bee's wing will be created using the same method but I will remove some balsa from the inside of L.E between ribs to save weight.

The reason: Tiger will be exposed to serious vibrations of Ro-Jett76 and Bee will be electric therefore the vibrations and their effects will be much smaller.

Your comments and suggestions are welcome,

Regards,
Matt

 

After considering pros and cons, all spars will be hard balsa.
I will weight everything and write down these weights in my Little Black Book.

Tiger's wing will be build using the Tom Morris three piece L.E and T.E method and the metal "L" shaped brackets supporting these edges.Tom Morris used wooden blocks and steel angles to hold these blocks in place.

This method was described in the Stunt news, Jan/Feb. 2000. Tom Morris used the Lincoln Log method but I will use the 1/16" balsa shear panels connecting the spars between ribs with grains at + - 45 degrees (ref: principle of diagonal tension). Four most inside and four most outside spaces between ribs will not have the shear panels but tension/compression truss like members, creating the triangular pattern.

Bee's wing will be created using the same method but I will remove some balsa from the inside of L.E between ribs to save weight.

The reason: Tiger will be exposed to serious vibrations of Ro-Jett76 and Bee will be electric therefore the vibrations and their effects will be much smaller.

Your comments and suggestions are welcome,

Regards,
Matt

Hi Matt, Hears an idea for you. Get some Balsa (hard), some spruce and some bass wood all the same demention and make your "test" spars.

Then weigh them, and break them with a scale to see how many LBs each breaks at and what they weigh. This way you can pick the strongest (or not) weight to strength spar.

This way you can make an educated guess as to the best spar system for you.

Good luck, Jerry


PS: The late Bob Bayard of SBSS did this for glider wings and the results were amazing.

Since I'm just beginning a build of a Brodak Cardinal kit, I have a question regarding spar choice. I still pancake once in a while in my low Advanced pattern flying. Would any of you defer to the added strength of bass or spruce over the lighter weight of balsa with this one punishing reason in mind? I've not yet built a stunter that hasn't met the ground within its first year of practice sessions.
Wreckin' Rusty

Doctor's orders, okay, Doc.

In choosing the material for CL stunt wing spars, there are several things to consider.  Most wings for stunt ships are designed with a top and bottom spar.  Those spars do not necessarily need to be stiff to resist bending.  Instead, those spars are resisting either compression or tension as loads are imposed during maneuvers.  This assumes there is sufficient structure between the spars so that any bending force on the wing is transferred to the spars as compression or tension (i.e. sheer webbing).  This is why the I-Beamers are efficient as far as weight and strength are concerned.  I do not have the numbers to compare, but balsa is surprisingly efficient in compression and tension for its weight compared to other materials.  (Of course, the density of the balsa makes a difference with these numbers.)  It makes a lot more sense to build a wing with sufficiently supported balsa spars rather than down sizing the dimensions if spruce spars are used.  Unless the spruce spar dimensions are reduced drastically, there will still be a weight penalty for no real benefit in probably unneeded additional strength.

Now, when models with heavier wing loadings are built, like scale, spruce spars or otherwise reinforced wing structures using plywood, carbon, or other materials and choices in covering/skins can make sense.

Understanding that spars should be used to take compression and tension loads, the single spar used in the center of the wing airfoil used by the Ring Master is there to resist bending is not an efficient structure.

Keith

One thing with spruce , a party trick - covered in silk , is to put the fuse on your knee & pull the wing tips up and down about 3 in. ea. way .

Try this on someones balsa plane and  see what happens . 

 actually , you can get about a inch deflection , warily , on a balsa wing . Think in gusty air the ' more flexable ' spruce may absorb a bit of the shock more
and thus fly smoother . as long as its TORSIONALLY adequate .  As in Twist / incidence deflection .