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Glassed Tubes Data

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BDB

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To determine the optimal amount of FG wrap to apply to the BT of my L2 rocket, I decided to perform a kind of systematic study. The data is summarized here.

View attachment Glassed Tubes Test.xlsx


Layup Method


I started by cutting 2" lengths of 4" LOC tubing. I peeled the glassine layer and applied one or two wraps of 2, 4, and 6 oz FG cloth to them. I am a beginner at this technique, but I tried to follow the method shown by tfish in his YouTube video. I used peel ply to get a smooth finish, but did not vacuum bag the layups.


Texture

The peel ply made for a very smooth finish. Shown below are tubes reinforced with 6 oz + 2 oz, 6 oz + 4 oz, 6 oz + 6 oz glass wraps. The fine weave is only slightly smoother to the touch. I'm pretty sure that a good coat of primer and paint would completely cover the minuscule texture difference.

textures.jpg


Materials

fiberglass fabric
6 oz E-glass: from West Marine
4 oz E-glass:
http://www.fibreglast.com/product/4_...erglass_Fabric
2 oz E-glass: http://www.fibreglast.com/product/2_...erglass_Fabric

laminating epoxy
US Composites 635 epoxy with medium hardener: http://www.uscomposites.com/epoxy.html

peel ply
teflon-coated release fabric: https://www.aircraftspruce.com/catal...lickkey=131669


Strength Testing

To test the strength of the glassed tubes, I constructed a super-simple press. I applied 10 lbs of force to the top of the press and measured the distortion of the tube using a digital caliper.

test stand.jpgtest stand with caliper.jpgtest stand with control tube.jpg


Flight Simulations

I weighed each of the tubes before and after the layups and calculated the % increase in mass. I then extrapolated these data to predict the weight of a standard LOC IV kit with the different layups and simulated flights with Loki H144 and I405 motors using OpenRocket and the rocksim file for the kit from the Apogee Components website.

I'll save my interpretations of these data for a later post, but I really want to hear the comments from the members of this forum. In essence, the change in the mass of the BT reduces the apogee with the H144 by up to 20%, but the apogee with the I405 is nearly identical, even though the dry weight of the rocket has doubled.
 
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dhbarr

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I'll save my interpretations of these data for a later post, but I really want to hear the comments from the members of this forum. In essence, the change in the mass of the BT reduces the apogee with the H144 by up to 20%, but the apogee with the I405 is nearly identical, even though the dry weight of the rocket has doubled.
Sounds like for the I405 maybe dry weight A was on one side of the optimal-altitude-mass, and dry weight B on t'other?

For A, a light rocket takes off fast and punches a hole in the sky, but peters out relatively soon after burnout. It doesn't mass much in comparison to the wind.

For B, a slightly thicker significantly heavier rocket lumbers off the pad, relatively speaking. It never achieves the G's or top speed of A, but due to it's stoutness it coasts to about the same height.

There's probably a mid-point on I405 weight where the light-ness and the coast-ness are balanced, yielding a higher overall altitude. The H144 of course has a different story.
 

Handeman

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Yes, what dhbarr said.

Each rocket and motor combination will have an optimum total weight to get to it's highest apogee.

It would be interesting to see that data as compared to the J-320 and J712 in a 38/720 and the K-627 and K-1127 in the 38/1200.
 

KenRico

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Thanks !

Very simple , but very descriptive .

I did a single wrap of the Mege Der Red Max tube with 6 oz glass , but did not record the weight . At the time I had the same size Blue Tube and a FW Fiberglass tube all about 22 inches long. The Blue Tube weighed 25% more than my newly single wrapped tube and the FW FG tube weight almost twice as much . When flown the tube held up to a K400 VM and a K550 ST without issue , although my built up fins imploded on the K550 ST .

For fin slotting the wrapped tube seemed easier and much tighter slot than what I was able to acheive with the blue tube also . The tube is flexible and has some elasticity , should help with the fall over and transportation dings .

Kenny
 

BDB

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It would be interesting to see that data as compared to the J-320 and J712 in a 38/720 and the K-627 and K-1127 in the 38/1200.
Here is the OR predicted data for a standard LOC IV rocket with various amounts of glass on the tube. I simulated flights with the Loki motors that Handeman suggested as well as the H144 and I405 (the most fun you can have without a hazmat fee.)

View attachment Glassed Tubes Test.xlsx (updated file including the LOC IV simulations and a few random simulations for my L2 Binder Design Terrordactyl)

Loki H&I data for LOC IV.png

Loki J data for LOC IV.png

Loki K data for LOC IV.png

The H144 does not have sufficient thrust to overcome the effect of the added mass, so its performance declines as more glass is added to the tube. It appears that the optimal mass of the rocket for the I405 is achieved around 8 oz of glass [(4 oz + 4 oz) or (6 oz + 2 oz)], and the other motors with more thrust do not even reach optimal mass with 12 oz of glass applied to the rocket.

It is amazing to me how the high thrust motors continue to increase in altitude as the weight is added. I have read about optimal mass calculations but had never appreciated them until now. It is also worth noting that the average velocity uniformly is reduced as mass is added. These data aren't plotted but can be easily seen in the spreadsheet.

The only point to consider then is the effect of the weight on the velocity off the rod. Nearly all of the motor/rocket combinations tested had velocities off of a 6' rail >100 ft/s. The H90 and G69 (data not in spreadsheet) had velocities off the rod of 55 ft/s and 45 ft/s, respectively, for a rocket with two 6 oz wraps of FG, so that represents the lower limit of safe flying for these reinforced airframes.
 
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BDB

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As seen in the pictures in the first post, unreinforced tubes are very weak. Even a single wrap of 4 oz glass provides a huge increase in rigidity, though this added strength comes at the expense of mass. The data shown is not true destructive testing, so it is impossible to know what the actual strength of the glassed tubes are, but it is safe to say that two layers of 6 oz cloth are significantly more strong that unreinforced LOC tubing. And as previously mentioned, the added weight does not necessarily inhibit performance.

Strength Data.png

I think there is a press in my building that would be capable of measuring the absolute strength of these materials. If not, my friend, coworker and fellow rocket addict, Al B., devised a homebrew method involving a scissor jack and a bathroom scale that just might work. If I can use the press, or if I can find the time to construct a homemade press, I'll report actual destructive testing data. But in the mean time, I think these data are instructive.
 
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BDB

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Based on the data it appears that one does not need to be overly concerned with the weight added by reinforcing a tube with fiberglass. The only exceptions to this would be if one was designing a rocket to be flown on low thrust motors. Going forward I will likely wrap most of my airframes in two wraps of 6 oz FG. This was the strongest of the materials tested, and, so long as the layup is finished with teflon peel ply, the resulting airframe has a smooth surface. Surprisingly, the added weight actually increases the performance of the rocket in terms of altitude, though it does decrease the performance of the rocket in terms of velocity and acceleration.
 

rharshberger

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Based on the data it appears that one does not need to be overly concerned with the weight added by reinforcing a tube with fiberglass. The only exceptions to this would be if one was designing a rocket to be flown on low thrust motors. Going forward I will likely wrap most of my airframes in two wraps of 6 oz FG. This was the strongest of the materials tested, and, so long as the layup is finished with teflon peel ply, the resulting airframe has a smooth surface. Surprisingly, the added weight actually increases the performance of the rocket in terms of altitude, though it does decrease the performance of the rocket in terms of velocity and acceleration.
Its that optimal weight thing coming back into play again, too light and it gets less altitude but starts off teleporting, too heavy less altitude and less velocity, just the right weight and acceleration is smooth and the rocket coasts higher to get max altitude. Thanks for doing this little study.
 

Handeman

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Based on the data it appears that one does not need to be overly concerned with the weight added by reinforcing a tube with fiberglass. The only exceptions to this would be if one was designing a rocket to be flown on low thrust motors.
I agree with that and would add, if you are designing to use low thrust motors, you probably don't need the re-enforcement of glass anyway.

The first rocket I glassed the LOC tubes on was my L2 cert rocket in 2009. I used two layers of 6 oz glass. That rocket will be making it's 35th, and probably 36th, and 37th flights this coming weekend. Most likely on K motors. It's flown Mach 1.2, landed on drogue only, hung on power lines, bounced off hard packed clay roads and survived a lot of transport to and from the field. Even if the glass layers did significantly lower performance, I would still glass the tubes for the longevity it's given me!
 

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