balsa strength

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AfterBurners

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Is it possible to build a rocket using balsa fins/wings and reinforcing the balsa to fly on 38s? I'm considering using hardwood around all leading edges and papering the fins/wings. I also plan on hand sanding airfoils on each piece.

Feedback appreciated. I'm just trying to keep the weight down. Also considering a phenolic airframe.
 
I've heard of a lot of people modding the MDRM for 38mm (or flying them with high power motors including "H" motors)... It has a built up balsa ply fin... So, I think you're safe there.
 
I've heard of a lot of people modding the MDRM for 38mm (or flying them with high power motors including "H" motors)... It has a built up balsa ply fin... So, I think you're safe there.

I'm considering the same type of guy construction cutting out sections of the ply to reduce weight. Just need to decide he thickness of the balsa so I can sand the airfoils without gin through the ply section.
 
You really don't need to change materials on the leading edge if you would move from paper laminate to a lightweight fiberglass cloth. I have done it a number of times. Put up an I161 on a highly-modified minimum diameter Estes Patriot years ago.
 
Based on some past & other experiences, I would say "yes' as well.

Frame up the fin in balsa (like the MDRM or an R/C plane's wing) and fill the voids with Styrofoam, then sheet with balsa.

Frame up the fin in balsa (like the MDRM or an R/C plane's wing) and fill the voids with Styrofoam, then sheet with thin ply (like, 1/16" or 1/32")

As above, and paper, or glass them, or even Monokote (that stuff can add a tremendous amount of strength!)

Use basswood sticks instead of balsa stick to frame up the fins.

Poke many many many tiny holes (pin holes) in the sheets / skins, and coat / flood with thin CA.

Use thick ply (like 1/4") and 'swiss cheese it' with many many holes (to lighten it) then sheet with balsa.

Go exotic, and make a 3-ply balsa sandwich, then vacuum bag it with either aramid, glass, or carbon fiber outer skin..

'Hot wire' cut fin cores, and then sheet with balsa or thin ply. Lightening holes can be added to eh foam cores.. Add hardwood tips & roots, LE & TE edges pieces..
 
Is it possible to build a rocket using balsa fins/wings and reinforcing the balsa to fly on 38s? I'm considering using hardwood around all leading edges and papering the fins/wings. I also plan on hand sanding airfoils on each piece.

Feedback appreciated. I'm just trying to keep the weight down. Also considering a phenolic airframe.

I would discuss it with the club's RSO before building it. No sense building something that the RSO won't let you launch.
 
Use a skeletonized 1/8" plywood fin core with thin balsa skins, paper the exposed surfaces. Saves weight and makes a strong fin. Balsa will handle some H motors and some I motors it has a lot to do with fin profile, velocity, span and fin flutter.
 
Use a skeletonized 1/8" plywood fin core with thin balsa skins, paper the exposed surfaces. Saves weight and makes a strong fin. Balsa will handle some H motors and some I motors it has a lot to do with fin profile, velocity, span and fin flutter.

This is going to be an L2 bird going up on a J500 more than likely.
 
Keep in mind that Balsa has a very wide range of strength available. It varies from pretty punky junk, all the way up to equivalent to Spruce. It is available in multiple grain orientations. I'm not sure where to get the higher density end now though. When I got balsa (not for a few years) I got it from Balsa USA. Expect 50% to be out of spec, but that's about the best we can do now. The really good stuff goes to wind turbine blades.

All just FYI.

Gerald
 
Keep in mind that Balsa has a very wide range of strength available. It varies from pretty punky junk, all the way up to equivalent to Spruce. It is available in multiple grain orientations. I'm not sure where to get the higher density end now though. When I got balsa (not for a few years) I got it from Balsa USA. Expect 50% to be out of spec, but that's about the best we can do now. The really good stuff goes to wind turbine blades.

All just FYI.

Gerald

National balsa is where I normally buy
 
Our Dragonfly has balsa fins and flies on 75mm and 98mm motors. The root chord is ~12" and the semi-span is ~28". They are .5" end-grain balsa cores with 1.3mm carbon fiber skins, but they are still balsa....
 
Our Dragonfly has balsa fins and flies on 75mm and 98mm motors. The root chord is ~12" and the semi-span is ~28". They are .5" end-grain balsa cores with 1.3mm carbon fiber skins, but they are still balsa....
Now we are talking a balsa composite, far different than the plain balsa the OP seems to be inquiring about. Unless I misunderstood the intent. IMO a balsa composite fin would be strong enough ( end grain balsa with vacumm bagged fg or cf skins), but plain balsa similar to what LPR kits use would be a negative.
 
So by papering do you mean coating a fabric skin in liquid dope similar to skeleton model aircraft kits of balsa? With spar and sheets vertical aligned with an outward decreasing taper? You can make a relatively light structure stiff. The issue is I don't think balsa in that application is appropriate on a model rocket unless the airfoil and material thicknesses were drastically increased with a very stiff spar of non balsa. It would be hard to model the structure to find when it fails. You could crush test it if you wanted. Compressibility starts above Mach 0.3.

I really think it depends on the rocket performance you intend for the balsa airfoil.. Others posted better ways to do a composite balsa fin with higher strength. If it's a H motor two grainer with a massive tube diameter going rather slowly in
subsonic with overbuilt fins it'll probably survive just fine.
 
If you made it 2-3ft diameter it would travel very slowly and very low on a j500. You could probably use a balsa skeleton and paper in such a wonky low performance application as long as the motor mount was up to it. You'd have to nerf the HPR motor performance into LPR flight territory by using creative amounts of drag force to counter the thrust.
 
I've seen cardboard boxes fly on K motors. 200-300ff completely subsonic.
 
So by papering do you mean coating a fabric skin in liquid dope similar to skeleton model aircraft kits of balsa? With spar and sheets vertical aligned with an outward decreasing taper? You can make a relatively light structure stiff. The issue is I don't think balsa in that application is appropriate on a model rocket unless the airfoil and material thicknesses were drastically increased with a very stiff spar of non balsa. It would be hard to model the structure to find when it fails. You could crush test it if you wanted. Compressibility starts above Mach 0.3.

I really think it depends on the rocket performance you intend for the balsa airfoil.. Others posted better ways to do a composite balsa fin with higher strength. If it's a H motor two grainer with a massive tube diameter going rather slowly in
subsonic with overbuilt fins it'll probably survive just fine.
Literally paper whether glued or self adhesive label paper on sheet balsa. Nothing complicated or fancy.
 
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