acobra

My Feedback: (40)

[sm=confused.gif] OK, I hope this is the right place to post this. I have a Joe Saitta 82" Me 173 that weighs under 10 lbs. and flys fast and aerobatic. I broke the main spar (don't ask) and it looks like it is Maple or (?). I can't find any maple locally to cut a new one but have axcess to some good straight grain spruce that was a main spar in a full size champ that I bought at an airport sale along with other woods, I can cut this spar to the size I need (29" X 3/4" X 1/2") for the model spar. My question is " What do you think of this?" [>:]

Augie11

I believe maple is stronger but then again, spruce worked for the Wright brothers.

Laird SS

If you go with the spruce, why not consider gluing some carbon fiber strips to the top and bottom edges of the spar for added stiffness. You could cut the spruce a little bit smaller to account for the strips if necessary.

Just a thought.

Rodney

You should be fine with the Spruce.

CoosBayLumber

My Feedback: (1)

I think so too. Maple is usually used for engine mounts, as it does not like to soak up the oils.
Spruce WILL soak them up.

In a wing, spruce is preferred as normally oil does not get in there.


Wm.

TedMo

there is no comparison between maple and spruce, maple is far stronger so I would not go with spruce for the main spar. You should be able to find maple in any cabinet shop. You could use birch or oak also about the same weight and strength as the maple. Spruce is not good for your use it is a softwood like pine, fir, cedar. Wright brothers used it mainly to save weight and realized it would not be stressed as it will be in your plane.

Rodney

Spruce is nearly as strong as maple when you compare members of equal weight and, in the ability to absorb shock loads, spruce is superior. Your spruce spars will serve every bit as well as the maple and will be lighter.

acobra

My Feedback: (40)

This is really close grain spruce. There are 13 "grain rings?" in just 3/4" Of course the grain would run vertically. Im leaning toward the spruce.
Frank

BMatthews

Go with the spruce. The original spar is highly unlikely to have been maple in any event. More likely a European equivalent of spruce, pine or bass. Also that spruce stock is going to have a far more striaght line grain structure. On the other hand maple tends to have far more waves in the grain. I'd trust a tight straight grain spruce spar far more than I'd trust a maple spar that has severe grain runout issues. And this is assuming it really is maple which I highly doubt.

acobra

My Feedback: (40)

I doubt it's Maple also after looking closer and cuting it with my pocket knife, it just cuts to easy.
Frank

aerowoof

probably bass

shootnstarz

In the cabinet business there are two types of maple. One is a rock hard wood used in butcher block, engine and landing gear mounts and props. The other is a lighter colored softer maple comparable to poplar. IMHO neither is acceptable for use as spars.

Spruce is by far the strongest wood per weight and is a very long grained wood that gives it it's superior strenght, while weighing not much more than heavy balsa. The biggest problem with aircraft grade spruce is the cost, that stuff doesn't grow on trees you know.

I am having trouble finding any spruce that doesn't cost nearly $100 for a 5' 2x6. The main national supplier is very expensive and frankly hasn't returned any emails and was almost to the point of rudeness when I called and inquired about their bundle deal. Guess they just don't have time to mess with small orders.

Until I find a source of aircraft spruce I'll be using heavy balsa and carbon fiber tape for spars.

Rick,
Pensacola, FL

acobra

My Feedback: (40)

Thank's all. I'm going with the spruce. What I have must be the softer maple shootnstarz talked obout because one of my original thoughts was poplar. Spruce it will be.

Frank

Rodney

If you can not get spruce try pine. If you have a lumber yard that will let you select the stock, you can often find some close and straight grained pine boards that can be ripped into pretty nice spar stock, I do it all the time and I'll bet you can not tell the difference between them and spruce ones in either looks or strength. It just takes a lot of looking and choosing those boards with little or no pitch and nice close straight grain.

fokker fan

I've used pine as well, but I've found it to be much heavier than spruce. I've now gone back to spruce for spars but still use pine where I need small blocks of hardwood (harder than balsa anyway) for mounting things like servos, struts, etc.

marwen1

My Feedback: (6)

Maple, Pine, Bass, etc.

Maple is a deciduous HARDWOOD, so is the Bass but no where near the hardness of the maple.

PINE is an EVERGREEN, soft, and sappy.

An alternative that is readily available and a split between both ends is POPLAR. A DECIDUOUS tree, but is considared to be a medium hardwood. It's a lot like bass.

marwen1

BMatthews

Shootnstarz, to call the softer maple the equivalent of bass is a bit of a rash comparison. Yeah, it's softer but even the soft maple, unless it's a really bad bit of wood, is still very much a hard wood to work. I've used some to make a table and a few lathe turned bowls and it required pretty serious working when doing the hand work portions. Even the soft maple is USUALLY far, far harder than bass or even aircraft spruce.

I'm thinking bass wood or, since it's from Europe, possibly their pine like linden wood.

Michaelj2k

Douglas fir is the next selection under spruce for aircraft construction.

shootnstarz

First, I didn't compare soft maple to basswood, I compared it to poplar. Didn't even mention basswood in my post.

Second, I own a cabinet shop and work with all these types of wood daily and have for over 25 years. I buy soft maple in 300 to 500 board foot lots for cabinets and I don't see much variations in weight and density of this wood. Variations in color, yes. I think I may possibly know of what I speak :-)

Rock maple is a whole other critter, very hard and very dense. Great for cutting boards and propellers. Poplar is denser than basswood and just under soft maple. It does have some variations in density from piece to piece but not a great deal.

I'd go with spruce if you can find it, fir as a second choice. Just make sure the grain is straight with no runout. I also use 14 lb balsa for spars on smaller planes. A little CF tape never hurts either.

Rick
Pensacola, FL

ARUP

Hi- use carbon fibre tube! Lighter and stronger! Carbon Dragon for source. I'm sure there are others. Good luck

carlosponti

My Feedback: (1)

the way i can tell maple apart is what i refer to as ray flecks they are small(minuscule) compared to oak. on the face grain one of the adjacent faces will have a little showing of the ray flecks. they are straight and run with the grain. as a hobby i woodwork and only have access to oak maple walnut pine and poplar for that hobby. I haven't ran into any that would use maple for spar material, not saying there isn't just none that I have seen. for the planes I have built i was fine with spruce or basswood for a spar. carbon fiber is nice but too expensive for the airplanes i would build since i build mostly sport airplanes.