Reducing Weight of Plywood Internal Frame?

[jmmome]

Inspired to build a 5 feet tall version of the Kaboom Krewe's "Space Oddity". Initially plan to use a center frame of 24" diameter plywood with a 4" dia Blue Tube as the motor/chute tube. Probably two other plywood smaller dia. frames forward and aft, with cut styrofoam filling out the shape.

Don't want it to weigh several hundred pounds like the original...lol. My thought was to take out some of the plywood without sacrificing the structural integrity. Would you suggest "wheel-spokes-hub" plywood removal; simply using a hole drill to remove 3" or 4" holes from the plywood; some other method?

Mike Momenee
TRA#12430 L3

 

[Andrew_ASC]

This was one design approach method to reduce weight not taken by my university but we did do some “internet digging” on the subject of weight reductions. You could easily make a skeleton structure. I personally remember choosing reducing tube diameters for less drag force for altitude. Anyways your project isn’t about maximizing altitude. If you got real creative I think there’s this dope glue that makes paper material rock hard used in aircraft construction methods and for balsa gliders. I thought this cal poly design was pretty elegant at reducing weight.

https://digitalcommons.calpoly.edu/...com/&httpsredir=1&article=1106&context=aerosp

Thought you might find some info useful in there despite that being a multistage. I just don’t see why a design has to weigh several hundred pounds like that. You could have ribs and connect outer members and save a bunch of weight then just skin it with cloth and dope it. Especially when it’s a big draggy subsonic model.

 

[jmmome]

Thanks! I actually did something similar a couple of years ago with my McDonnell Douglas "Delta Clipper" pyramid-shaped rocket. It came in at 45 pounds (hence the back brace) but about 10 pounds of that was nose weight. The inside was three plywood squares epoxied to the motor/chute tube running through their centers, and the four corners were delineated by 1/2" PVC pipe. The outside was skinned with fiberglass.

I'll check into the dope glue, since that would help to reduce weight by eliminating the fiberglass.

It was already suggested on Facebook that I may want to make the "Space Oddity" fins even larger, since the rocket was close to not stable. But what a
fun launch it was to watch (on video)!



Mike Momenee
TRA#12430 L3

 

[Andrew_ASC]

https://www.vintagemodelcompany.com/how-to-cover-your-model-with-tissue.html

Eze Dope is a brand name of the glue used. All I really remember about dope glue from using it on balsa kits as a kid was it was highly flammable when wet and emitting vapors. Haven’t touched that stuff in years.

I could imagine one would save a great deal of weight and expense comparing to fiberglass or foam methods.

And if anyone thinks that’s a bad idea let me know lol. Just tossing low weight low cost ideas out there. I want to say in aviation sense the WW2 Corsair fighter plane has 400 mph level flight speed and its tail horizontal stabilizer fin was of same construction. Hawker Hurricane being a british fighter of tube and fabric design Also. There’s even modern kit planes like carbon cub that use fabric covering cf tubes. Fins I would want to be fiberglass or plywood or some other normal HPR material. The skin really doesn’t do much structurally so it all depends on frame design.

Heck I was tempted to buy a giant balsa ME163 Komet kit last week and convert it to HPR rocket glider but I found a EPO foam kit cheaper. The only bad thing I’m imagining about doped fabric in rocketry is if the exhaust flame hits the fabric it’s uhhh toast or if recovery is hard irregular surface might pierce skin.

I guess another way would be build a foam core then make a fiberglass shell structure then delete core. Where skin would be all structural. But that seems expensive and heavy. The only other weirder thing I’ve seen done was burt Rutan layering composite skin over styrofoam for kit planes like Long Ez. He shedded a bunch of weight in his designs doing that. Anyways out of ideas for now.