Drilling out balsa nosecones?

[Grant_Edwards]

Do people bother drilling out large balsa nosecones to save on weight?

I'm building a FlisKits D-Nelson Tomahawk, and the nosecone weighs about the same as the rest of the rocket (sans engine). It is a big nosecone, but it seemed particularly heavy. With eye-screw it was 22g.



So I decided to hollow it out. For that you need something to hold the nosecone vertically on a drill press. I cut up a scrap piece of ceder and drilled holes through the pieces (progressively smaller after the first two):



After being wrapped in a paper towel, the nosecone fit snugly into the jig. After removing the screw-eye, I drilled out about half the length of the nosecone with a 3/4" forstner bit. Then I glued a scrap of light plywood across the hole to provide an attachment point. How much weight did I save?

About 5-6 grams.

Not really worth the effort, but I had to try it to see how it would work.

I probably could have used a slightly larger bit, or drilled farther after switching to a smaller bit, but it would have been a pretty small incremental improvement.

 

[jqavins]

So many models need nose weight that losing some in this way can sometimes be the very thing you don't want to do. Often, the reason to drill a nose cone is to make room for clay or some such.

 

[Alan15578]

I did that in the late 60's, early 70's, for contest rockets, mostly BT5 and BT20 sized. I also did a large BT65 egg capsule, but that took a lot of additional hand carving and sanding.

 

[Grant_Edwards]

So many models need nose weight that losing some in this way can sometimes be the very thing you don't want to do. Often, the reason to drill a nose cone is to make room for clay or some such.

Yes, that's true, but this rocket is so over-stable, that it's not a problem.

After my "ligtening" OR says stability is 3.9 cal (using measured CG and simulated CP) with the heaviest engine I'll ever use. With the full-fat nosecone it was about 4.5 cal.

That's simulating with simple flat fins that match the profile of the actual combination tube/fins. The real tube/fins should move the CP back even further compared to the simulated flat fins.

According to OR, I could take the nosecone's weight down to almost 0 and still be stable.

 

[Grant_Edwards]

I'm beginning to suspect my scale is a bit off. According the the OR database, that nosecone was supposed to weight about 10g. I suppose it could have been made from an unusually dense block of balsa. I don't think I've got that much filler on it...

 

[lakeroadster]

Do people bother drilling out large balsa nosecones to save on weight?

I drill them out and tap them to..... add weight..

 

[neil_w]

I'm beginning to suspect my scale is a bit off. According the the OR database, that nosecone was supposed to weight about 10g. I suppose it could have been made from an unusually dense block of balsa. I don't think I've got that much filler on it...

Balsa density varies *enormously*. That seems easily possible.

 

[lakeroadster]

Balsa Density varies from 0.06 to 0.09 oz/in3

Open Rocket uses .098 oz/in3

 

[neil_w]

Balsa Density varies from 0.00011 to 0.00016 10³ kg/m³

That is far too narrow a range. Here's a table of densities from this page: https://www.modelaviation.com/balsa

That's almost a factor of four variation from lightest to heaviest. I've inadvertently purchased pieces near to both ends of that scale, neither of which I would wish on my worst rocket-building enemies. That's what taught me to bring my scale with me when buying.

 

[lakeroadster]

That is far too narrow a range. Here's a table of densities from this page: https://www.modelaviation.com/balsa
View attachment 493504
That's almost a factor of four variation from lightest to heaviest. I've inadvertently purchased pieces near to both ends of that scale, neither of which I would wish on my worst rocket-building enemies. That's what taught me to bring my scale with me when buying.

I revised my post. But I gotta ask... are you buying balsa by Cu-Ft?

 

[neil_w]

I revised my post.

I wasn't talking about the location of the decimal point (although your new location looks much better ); rather, your numbers show only about a 33% range in density. Actual variation is much wider than that. Where did you get those numbers?

Edit: here's another chart showing a full 4x variation in density: https://www.auszac.com/pdf/Balsa_Sheet_Density_chart.pdf

 

[jqavins]

[N]either of which I would wish on my worst rocket-building enemies.

Nonsense. You have no rocket building enemies.

 

[neil_w]

Nonsense. You have no rocket building enemies.

You don't know the dark secrets of my past.

 

[Bowman]

I'm beginning to suspect my scale is a bit off. According the the OR database, that nosecone was supposed to weight about 10g. I suppose it could have been made from an unusually dense block of balsa. I don't think I've got that much filler on it...

How much does the screw-eye weigh?

 

[Grant_Edwards]

How much does the screw-eye weigh?

According to my scale around a half a gram (with some glue and wood still stuck to it). The resolution of my scale is 1 gram, and the reading toggles between 0 and 1.

I need to get a smaller scale...

 

[lakeroadster]

Actual variation is much wider than that. Where did you get those numbers?

All these sources reflect the same numbers I posted... The Engineering Toolbox Matmach Easy Calculation My Math Tables

You state "Actual Variation", but I wonder if the data you are referencing is from companies that are modifying the balsa in some manner to make it lighter, or growing a variant and that standard balsa doesn't have such a wide range?

Thinking through this, one would have to also realize that the strength of such balsa would also have the same wide variations.

 

[Back_at_it]

I drill them out generally to ADD weight. I don't bother reducing weight in the nose cone of most models. I have limited areas to fly so those times that I do want big altitude I just stuff a larger motor in it.

 

[Grant_Edwards]

Being overly weight conscious during construction is a permanent side effect of building electric RC airplanes back in the day when brushed motors and NiCd batteries were the only choice. The brushed motors were so inefficient and the batteries had such a low energy density that to get flight times longer than a couple minutes you had to build the rest of the plane with components that had negative weights.

 

[Funkworks]

By drilling out the nose cone, you can screw an eye bolt deep inside to move the CG closer to the nose cone. After you hook in the shock cord, you can also add more weight if needed by epoxying in anything heavier than balsa.

 

[Back_at_it]

I have hollowed out about an inch deep portion of a 3in balsa version of the super big bertha nosecone then drilled a 1 inch diameter hole about 2 inches deep. The 2 inch deep hole was filled with a hard wood dowel rod as I needed a solid place to anchor my screw eye. The 1 inch recess was to allow for adjustable nose weight. Basically remove the screw eye, add weight and go.