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Jul 22, 2019, 01:11 PM
Marion
Thread OP
Thank you Bruce. You always have excellent insight into such things.
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Jul 22, 2019, 05:40 PM
Registered User
I'll use Bass over Spruce anyday... and do. I've never lost a plane due to a spar failure ever.

Bruce is right about the most important part of choosing ANY spar material, and that is, it needs to be straight grained.
My personal rule is that if there is any grain drift, that one end of the grain goes at least 24 inches before dropping off the other side.
Jul 23, 2019, 07:04 AM
Registered User
A friend of mine built one of these out of pine about 30 years ago. Still flies it.

Pine, spruce, bass, balsa, fir - lots of stuff you could build airplanes out of. Iíve built planes out of all kinds of different woods as well as cardboard and foam board. Made spars from hardware store yardsticks. Why limit yourself? Itís a hobby.
Jul 23, 2019, 08:20 AM
Registered User
Here is the Yardstick. I was going to make one of these when the plan came out. Got a weedwacker motor ready. It was just too big for my shop. https://aerofred.com/details.php?image_id=96944 I think Sitka spruce is no more special than any other run of the mill spruce. It is used in aircraft because the trees are very tall with no branches to create knots. That is important on a full sized plane with a 30 ft. spar. A model spar can be selected carefully with no issues.
Jul 23, 2019, 08:32 AM
AndyKunz's Avatar
It's also used in aircraft because it grows very slowly in the cold climate, giving very tight ring spacing (making it stronger).

Andy
Jul 23, 2019, 08:58 AM
An itch?. Scratch build.
eflightray's Avatar
Can't beat a Spruce Goose Bruce.

(always wanted to say that )

.
Jul 23, 2019, 11:10 AM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by Treeline
......My personal rule is that if there is any grain drift, that one end of the grain goes at least 24 inches before dropping off the other side.
I think you might even be more demanding on runout than I am... On thin pieces 24" from one side to the other would be excellent. But I feel like something more like 16 to 18" would be decent enough on something like 1/8 x 1/4" stock. And magnifying that to something like 1/4 x 1/2 that makes it more like 32 to 36". So depending on what size we're looking at 24" for a grain line to run from one side to the other is a nice number to keep in mind.

Of course ideally there's at least one grain line that runs the whole length of the spar.

Ray, you missed out the bain of my childhood... Bruce the Moose.... We all watched a lot of Rocky and Bullwinkle back then and my brother or sister got onto that one.....

Speaking of the Spruce Goose.... I've been down to see it a couple of times during my drives down to the FF meets in Oregon. It's been a few years now though. I think I'll add a day to the trip and hit up the museum again this year. It really is a magnificent thing to see and walk around and go inside.
Jul 23, 2019, 02:54 PM
AndyKunz's Avatar
I always loved Rocky & Bullwinkle, and Boris & Natasha, and the Pink Panther, ...

Andy
Jul 23, 2019, 03:13 PM
Marion
Thread OP
I took an opportunity to tour the Spruce Goose once in Longbeach. I think it was moved up the coast sometime afterwards.. I think..
Marion
Jul 23, 2019, 03:26 PM
Registered User
The one major factor that companies like BUSA and Sig turned to Basswood is the cost of aircraft grade spruce. From what I've read, Sitka spruce is becoming scarce for some reason, or the demand has decimated the Sitka forests much like the heavy demand for balsa used for wind generator vanes.
There is very little difference in performance but you would notice the difference in costs.
Jul 23, 2019, 03:33 PM
Registered User
Quote:
Originally Posted by jollyroger
The one major factor that companies like BUSA and Sig turned to Basswood is the cost of aircraft grade spruce. From what I've read, Sitka spruce is becoming scarce for some reason, or the demand has decimated the Sitka forests much like the heavy demand for balsa used for wind generator vanes.
There is very little difference in performance but you would notice the difference in costs.
I donít know how much of the demand it represents, but Sitka is very popular for musical instruments as well. I suspect more of it goes there than to aircraft use.
Jul 23, 2019, 06:00 PM
Registered User
Quote:
Originally Posted by Marion
Thanks for all your thoughts. The model is a yet-to-be built Ultra Stick. About 60 inch wingspan. Sounds l like I'll use whichever the local hobby shop has in stock.
Marion

The original Ugly Stick by Phil Kraft …… also with 60" wingspan, used 1/4" by 1/2" balsa spars with the same as a doubler out to just into the three rib bay.

https://outerzone.co.uk/plan_details.asp?ID=1253

I would think that the time tested Kraft design/construction materials and dimensions are "good enough".
My rule thumb for substituting balsa where hard wood spars are called for in the plans is to double the cross section in balsa.... this is fairly easy to do in many designs such as the Ugly Stik, less so with thinner glider wings.

Easily cut from 1/4" balsa sheet; use a denser balsa sheet to ease your mind if you want (smiley)

I prefer to orient the long side of spars horizontally though. And add balsa webbing between the top and bottom spars almost three quarters of the way to the wing tips.


Michael in Ontario, Canada
Last edited by 2michaely; Jul 24, 2019 at 11:26 AM. Reason: spelling
Jul 23, 2019, 07:20 PM
AndyKunz's Avatar
Quote:
Originally Posted by Marion
I took an opportunity to tour the Spruce Goose once in Longbeach. I think it was moved up the coast sometime afterwards.. I think..
Marion
It's at the Evergreen museum in Oregon. A friend was just there last week with his kids.

I'd love to see that thing in person myself.

Andy
Jul 24, 2019, 06:28 AM
Registered User
Captain Dunsel's Avatar
I recall that Jensen's kit for the Ugly Stik specified NOT to use iron-on coverings, due to their not being as strong as silk & dope. That might've been because it came out when the original (wet) Monokote was the primary iron-on covering. A modern Ugly Stik shouldn't be as heavy as the original, but I'd still use spruce or bass spars, just in case.

CD
Jul 24, 2019, 07:49 AM
Ft Lauderdale
Number_6's Avatar
Jelutong, Tupelo, Walnut, Mahogany, Ash, Oak, Brazilian Rosewood, and Maple are some of the woods I have accumulated over the years as a woodcarver.

While not easy, or cheap to obtain, jelutong and tupelo are strong, non-splintering woods that could be used effectively in place of basswood. IF...you already have them, they are long enough for what you need, and you can rip/crosscut yourself.

Talking about model plane use here, not human flight.
Last edited by Number_6; Jul 24, 2019 at 01:38 PM.


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