# Building Big, Light Rockets

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#### kalsow

##### Well-Known Member
I am on a quest to figure out how to build large rockets (8-24-inch diameters) that are extremely lightweight. They are not Mach busters or altitude-record setters, but they are fun to watch and cheap-ish to fly.

This note is to report on a little experiment I ran looking for better airframe wall materials. The perfect material would be cheap, light, stiff, strong, readily available, and easy to work. Unobtainium!

Executive Summary

For my application, cardboard wrap is probably a good replacement for honeycomb core.

Raw Materials

I used the following materials to construct test samples.

[F] Fiberglass – 6 oz, plain-weave, E-glass. Commonly available in 50-inch widths for about $5/yd. [E] Epoxy – U.S. Composites 635 thin resin with 3:1 hardener.$72/gallon kit.

[C] Cardboard wrap – Single faced corrugated cardboard with 1/4-inch A-flutes. I got a 12-inch x 250-foot(!) roll from Staples for about $25. [H] Aramid honeycomb – 1/4-inch thick, 3/16-inch cells. I can get a 4’x8’ sheet locally from Express Composites for$145.

Test Samples

I prepared the following six samples. Each was a flat plank, 4 inches wide and 12 inches long.

[F] – One ply of fiberglass, saturated with epoxy.

[F+C] – One ply of fiberglass, saturated with epoxy and bonded to the corrugated side of the cardboard wrap. The entire corrugated side of the cardboard was painted with epoxy. The flat side was left untreated. The corrugations run parallel to the long side of the plank.

[F+C+E] – The same as [F+C] with the flat side of the cardboard also painted with epoxy.

[F+C+F] – The same as [F+C+E] with an additional ply of fiberglass bonded to the flat side of the cardboard.

[F+H] – One ply of fiberglass, saturated with epoxy and bonded to a section of honeycomb. A thin layer of epoxy thickened with U.S. Composites Faring Filler was squeegeed on the fiberglass to get decent bonding with the honeycomb.

[F+H+F] – Like [F+H] but with a layer of fiberglass bonded to both sides of the honeycomb.

Test Procedure

Each test sample spanned an 8-inch gap. A bucket was suspended in the middle of the sample. The bucket was filled with water until the sample collapsed and fell through the gap. To prevent the bucket handle from cutting into the sample, a 1.5-inch x 4-inch strip of plywood was put between the sample and the handle. When the sample finally gave way the bucket, water, and plywood strip were weighed. This measured weight is the “breaking weight”.

Results

Here are the measured results. The most interesting results are that adding cardboard [F+C] is 1000 times stronger than just the fiberglass [F] and that honeycomb core is only 3 (or maybe 5) times as strong as cardboard core but it is 45 times as expensive.

 Sample Weight Cost Breaking Weight Breaking Weight / Weight Breaking Weight / Cost oz / ft^2 $/ ft^2 oz oz / (oz/ft^2) oz / ($ / ft^2) F 1.10 0.40 0.2 v 0.19 0.52 F+C 2.88 0.50 221 76.8 442 F+C+E 3.12 0.50 276 88.5 552 F+C+F 4.18 0.90 330 78.8 366 F+H 3.49 4.87 95 27.2 20 F+H+F 5.53 5.27 900 162.8 171

The reported costs do not include the epoxy. I only used a few ounces of resin for the entire test.

In the [F] test I did not use the pail and water setup. A single U.S. quarter was enough to break the sample.

In the [F+H] test the sample was severely deformed but did not fall through. I believe the unfished side of the honeycomb snagged the wood that formed the edges of the gap.

In the [F+H+F] test the sample did not break. My bucket did not hold enough water. Adding a bunch of other weights helped but didn’t get there. With the reported 900 oz of weight the sample was sagging a little, maybe 1/4-inch.

Future Work / Exercises for the Reader

I tested the resistance of the materials to bending in one direction. The walls of a rocket experience both lateral and longitudinal forces. Both directions should be tested. My guess is that in the long direction the cardboard cores are actually stronger than the honeycomb.

I tested the asymmetric samples (F+C, F+C+E, F+H) with the fiberglass (in compression) on top of the core material. The results may differ if the fiberglass (in tension) was below the core material.

Rocket walls are pipes, not flat planks. A next step would be to build tube sections (say 8-inch diameter by 12-inch long) and test them.

I did not try to measure partial deformations of the samples. A proper materials testing set up would be able to capture the deformation as a function of weight.

Pictures

Cardboard wrap

Prepared test samples

Test sample with little deformation

Highly stressed test sample

#### K'Tesh

##### OpenRocket Chuck Norris
I seem to remember Frank Burke built up some foam rockets in the 8" diameter.... A Falcon missile IIRC.

#### crossfire

What year was that? Was it at 3 Oaks. I think I was there.

#### krislhull

##### L2
As Jim mentioned above, Frank Burke. of Dynasoar Rocketry fame, has built some large lightweight rockets. Both his Atlas and Titan rockets are 7 or 8" in diameter, and fly on 29mm motors. I believe he has a few threads on there where he outlines how he built them. Frank is a regular at my local club, and we also have another member, Jim Pommert, who is known for large and lightweight rockets. I believe he has a 6ft tall 5.5" bird that is FAR101 compliant, if I am remembering right.

#### burkefj

##### Well-Known Member
TRF Supporter
My largest is a 10" diameter by 7' tall atlas, not counting chute, altimeter or motor it weighs 4.5 pounds, the test 3
examples above are much heavier than what I used but may be stronger. Flies on H and I motors. I focused on compression testing, a 1' half section at 8 or 10" diameter would hold 75 pounds in compression.

Last edited:

#### OverTheTop

##### Well-Known Member
Great set of experiments. It is about the only way to prove how strong a composite is. Looking forward to seeing what this turns into .

#### David Schwantz

##### Well-Known Member
Should the testing not be in compression though?

#### Kelly

##### Usually remembers to get the pointy end up
Cool stuff. It would be interesting to see a competition based on something like, "largest rocket (in volume?) flown on an 'H' motor".

#### jrap330

##### Retired Engineer, NAR # 76940
I am on a quest to figure out how to build large rockets (8-24-inch diameters) that are extremely lightweight. They are not Mach busters or altitude-record setters, but they are fun to watch and cheap-ish to fly.

This note is to report on a little experiment I ran looking for better airframe wall materials. The perfect material would be cheap, light, stiff, strong, readily available, and easy to work. Unobtainium!

Executive Summary

For my application, cardboard wrap is probably a good replacement for honeycomb core.

Raw Materials

I used the following materials to construct test samples.

[F] Fiberglass – 6 oz, plain-weave, E-glass. Commonly available in 50-inch widths for about $5/yd. [E] Epoxy – U.S. Composites 635 thin resin with 3:1 hardener.$72/gallon kit.

[C] Cardboard wrap – Single faced corrugated cardboard with 1/4-inch A-flutes. I got a 12-inch x 250-foot(!) roll from Staples for about $25. [H] Aramid honeycomb – 1/4-inch thick, 3/16-inch cells. I can get a 4’x8’ sheet locally from Express Composites for$145.

Test Samples

I prepared the following six samples. Each was a flat plank, 4 inches wide and 12 inches long.

[F] – One ply of fiberglass, saturated with epoxy.

[F+C] – One ply of fiberglass, saturated with epoxy and bonded to the corrugated side of the cardboard wrap. The entire corrugated side of the cardboard was painted with epoxy. The flat side was left untreated. The corrugations run parallel to the long side of the plank.

[F+C+E] – The same as [F+C] with the flat side of the cardboard also painted with epoxy.

[F+C+F] – The same as [F+C+E] with an additional ply of fiberglass bonded to the flat side of the cardboard.

[F+H] – One ply of fiberglass, saturated with epoxy and bonded to a section of honeycomb. A thin layer of epoxy thickened with U.S. Composites Faring Filler was squeegeed on the fiberglass to get decent bonding with the honeycomb.

[F+H+F] – Like [F+H] but with a layer of fiberglass bonded to both sides of the honeycomb.

Test Procedure

Each test sample spanned an 8-inch gap. A bucket was suspended in the middle of the sample. The bucket was filled with water until the sample collapsed and fell through the gap. To prevent the bucket handle from cutting into the sample, a 1.5-inch x 4-inch strip of plywood was put between the sample and the handle. When the sample finally gave way the bucket, water, and plywood strip were weighed. This measured weight is the “breaking weight”.

Results

Here are the measured results. The most interesting results are that adding cardboard [F+C] is 1000 times stronger than just the fiberglass [F] and that honeycomb core is only 3 (or maybe 5) times as strong as cardboard core but it is 45 times as expensive.

 Sample Weight Cost Breaking Weight Breaking Weight / Weight Breaking Weight / Cost oz / ft^2 $/ ft^2 oz oz / (oz/ft^2) oz / ($ / ft^2) F 1.10 0.40 0.2 v 0.19 0.52 F+C 2.88 0.50 221 76.8 442 F+C+E 3.12 0.50 276 88.5 552 F+C+F 4.18 0.90 330 78.8 366 F+H 3.49 4.87 95 27.2 20 F+H+F 5.53 5.27 900 162.8 171

The reported costs do not include the epoxy. I only used a few ounces of resin for the entire test.

In the [F] test I did not use the pail and water setup. A single U.S. quarter was enough to break the sample.

In the [F+H] test the sample was severely deformed but did not fall through. I believe the unfished side of the honeycomb snagged the wood that formed the edges of the gap.

In the [F+H+F] test the sample did not break. My bucket did not hold enough water. Adding a bunch of other weights helped but didn’t get there. With the reported 900 oz of weight the sample was sagging a little, maybe 1/4-inch.

Future Work / Exercises for the Reader

I tested the resistance of the materials to bending in one direction. The walls of a rocket experience both lateral and longitudinal forces. Both directions should be tested. My guess is that in the long direction the cardboard cores are actually stronger than the honeycomb.

I tested the asymmetric samples (F+C, F+C+E, F+H) with the fiberglass (in compression) on top of the core material. The results may differ if the fiberglass (in tension) was below the core material.

Rocket walls are pipes, not flat planks. A next step would be to build tube sections (say 8-inch diameter by 12-inch long) and test them.

I did not try to measure partial deformations of the samples. A proper materials testing set up would be able to capture the deformation as a function of weight.

Pictures

Cardboard wrap
View attachment 417782

Prepared test samples
View attachment 417783
Test sample with little deformation
View attachment 417784
Highly stressed test sample
View attachment 417785

#### Red Phenix

##### Well-Known Member
Karl Hemphill and I launched the xflrs6 - from the Tin Tin moon shot series - on several m and then an n motor. The rocket weighed around 31kg with 75 mm m1850 motor. Construction was
foam with a vinyl overwrap. You could fly this rocket on a very high thrust k, or l motor - aligned with your lower cost very much larger rocket philosophy.
The xflrs-6 was the little brother of the 1:1 scale V2 that Australia’s Victoria Rocketry flew. That nearly 40 foot tall rocket launched on an O25000 and comprised an internal skeleton of aluminium, a foam overlay, and a vinyl wrap. Good luck with your upscale.

btw - karl is threatening to make a 2:1 V2 rocket on a cluster of O motors. construction would be modified from the 1:1 V2 Flown previously.

That's awesome!