Cardboard tube DOES have its limits...

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AlnessW

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Sigh...

At OROC's Summer Skies launch last weekend, I shredded my old Excel Plus. I flew it on a K375NW, the Aerotech boost-sustain motor that goes in the 54/2560 case. (It boosts on a grain of Warp-9 propellant, then sustains on White Lightning.) Here is a link to my full launch report.

Per the photos below, the cardboard tube just folded under the high thrust, right below the ebay (not pictured). After 11 flights, the old airframe just gave up. The main chute also was reduced to shreds.

IMG_2440.jpg
shred.jpg

Video of shred with some amusing commentary...
https://picasaweb.google.com/104803...key=Gv1sRgCPqryJnejOv21gE#6041631378055414834

You'll notice that the sharp Warp-9 boost was what did the rocket in.
I emailed Mike Fisher and he pointed out that the last time he saw my rocket, it had dents in the airframe, and that those are what usually lead to shreds. Makes sense...

So you might say that "after over a year of searching, I finally found the limits of cardboard." ;) I like to push my rockets pretty hard, so the eventual shred of this rocket did not come as a huge surprise to me.
 
Sigh...

At OROC's Summer Skies launch last weekend, I shredded my old Excel Plus. I flew it on a K375NW, the Aerotech boost-sustain motor that goes in the 54/2560 case. (It boosts on a grain of Warp-9 propellant, then sustains on White Lightning.) Here is a link to my full launch report.

Per the photos below, the cardboard tube just folded under the high thrust, right below the ebay (not pictured). After 11 flights, the old airframe just gave up. The main chute also was reduced to shreds.

View attachment 179807
View attachment 179808

Video of shred with some amusing commentary...
https://picasaweb.google.com/104803...key=Gv1sRgCPqryJnejOv21gE#6041631378055414834

You'll notice that the sharp Warp-9 boost was what did the rocket in.
I emailed Mike Fisher and he pointed out that the last time he saw my rocket, it had dents in the airframe, and that those are what usually lead to shreds. Makes sense...

So you might say that "after over a year of searching, I finally found the limits of cardboard." ;) I like to push my rockets pretty hard, so the eventual shred of this rocket did not come as a huge surprise to me.

Any flight data you could post?
 
So you might say that "after over a year of searching, I finally found the limits of cardboard." ;)

You found the limits of mushy cardboard. All it takes is one crease in the airframe to weaken it. That K375 is no big deal in one of our kits that does not have damage. One reason for a pre-flight inspection with a critical eye for such things.

For creases like you had, there is a fairly simple fix. You soak the area in thin CA which will bring the integrity back. I probably should have mentioned that the last time I saw your rocket, but I didn't know you had big future plans for it.
 
You found the limits of mushy cardboard. All it takes is one crease in the airframe to weaken it. That K375 is no big deal in one of our kits that does not have damage. One reason for a pre-flight inspection with a critical eye for such things.

For creases like you had, there is a fairly simple fix. You soak the area in thin CA which will bring the integrity back. I probably should have mentioned that the last time I saw your rocket, but I didn't know you had big future plans for it.

Interesting to know! Indeed, my Galaxy and NXRS RTV are in much better shape than the Excel was, so I've pondered putting a K700W or maybe an L (like the L730 or L640) in one of them, but those longburn motors like the K270W and K250W are just as fun...

The CA trick - do you wick it into the airframe?
 
You can also line the inside of airframe with couplers epoxied in, will stiffen it up quite a bit. Did that to my Galaxy.
 
You can also line the inside of airframe with couplers epoxied in, will stiffen it up quite a bit. Did that to my Galaxy.
One of our local vendors (who stocks Mike's kits) suggests this, as well. I have also been thinking about building one of his new kits with a 75mm motor mount, and fully glassing the rocket.
 
Cheap and cheerful. The RalphCo Crayon bodies make a perfect "stiffy coupler" for those 4" airframes. I have one stuffed in my Excel Plus!
 
The CA trick - do you wick it into the airframe?

Yes. You can do it from the inside so you don't mess up your paint, but if you can do both sides, even better. To do the outside, you have to cut away the glassine, wick it in and sand smooth.
 
Cheap and cheerful. The RalphCo Crayon bodies make a perfect "stiffy coupler" for those 4" airframes. I have one stuffed in my Excel Plus!

Or just use our new HD couplers. Twice as thick walled as the old ones, as well as longer. And they fit better. The old ones were tight, so people sanded them which made them even thinner. These new couplers are even thicker than the airframe tubing.

I honestly believe that if one of our airframes was doubled up with these new couplers, it could withstand an M without fiberglass or carbon fiber wrap. I intend to try it at some point.
 
Cheap and cheerful. The RalphCo Crayon bodies make a perfect "stiffy coupler" for those 4" airframes. I have one stuffed in my Excel Plus!
I see that "Recycles RalphCo Crayons" is living up to his name... :wink:

Yes. You can do it from the inside so you don't mess up your paint, but if you can do both sides, even better. To do the outside, you have to cut away the glassine, wick it in and sand smooth.
Got it. Knowing me and paint I'd probably just do the inside...

Or just use our new HD couplers. Twice as thick walled as the old ones, as well as longer. And they fit better. The old ones were tight, so people sanded them which made them even thinner. These new couplers are even thicker than the airframe tubing.
The new couplers ARE really nice! Indeed, they fit perfectly whereas the old ones were shorter in length and very, very tight.

I honestly believe that if one of our airframes was doubled up with these new couplers, it could withstand an M without fiberglass or carbon fiber wrap. I intend to try it at some point.
Really!
Or should I say "Challenge accepted"...
 
Or just use our new HD couplers. Twice as thick walled as the old ones, as well as longer. And they fit better. The old ones were tight, so people sanded them which made them even thinner. These new couplers are even thicker than the airframe tubing.

I honestly believe that if one of our airframes was doubled up with these new couplers, it could withstand an M without fiberglass or carbon fiber wrap. I intend to try it at some point.

Mike, are these new couplers used in the av-bay offerings?
 
Interesting. I have a Lightning Bolt kit to build that I was thinking about glassing. Maybe I'll pick up a some of your HD couplers instead and build it that way.
 
Interesting. I have a Lightning Bolt kit to build that I was thinking about glassing. Maybe I'll pick up a some of your HD couplers instead and build it that way.

It will make the airframe over twice as strong. The stock airframe can handle K's and certain L's, so I don't see a problem with small M's, but we'll see.

I also have 75mm motor mount tubes and centering rings that I'll be adding to the web store, for those that want to build it with bigger mounts. For now, I still recommend fiberglass or CF wrap.
 
It will make the airframe over twice as strong. The stock airframe can handle K's and certain L's, so I don't see a problem with small M's, but we'll see.

I also have 75mm motor mount tubes and centering rings that I'll be adding to the web store, for those that want to build it with bigger mounts. For now, I still recommend fiberglass or CF wrap.

I would certainly want to do mine in 75mm regardless of how I'd reinforce the airframe, for sure. For the couplers - would you glue them in with Titebond?
 
Sorry about your Loss.
I've found that Papering a Body Tube with 110# Cardstock using TB II as the glue enhances its Rigidity to an incredible degree, as well as the previously mentioned adding of Couplers.
 
I would certainly want to do mine in 75mm regardless of how I'd reinforce the airframe, for sure. For the couplers - would you glue them in with Titebond?

Yes, titebond, but you have to thin it with water first. They'll grab if you don't. And if you go full length with the motor tube with plenty of centering rings, You won't have to worry about the booster section buckling.
 
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I assume that one would put these couplers in above the upper motor mount centering ring (assuming that the fin can section really doesn't need this extra support). Could you simply slide them all in and then only glue the upper most coupler? My thought is that that the other couplers would be held in place at the bottom by the centering ring and at the top by the glued in coupler. Thoughts?
 
Could you simply slide them all in and then only glue the upper most coupler? My thought is that that the other couplers would be held in place at the bottom by the centering ring and at the top by the glued in coupler. Thoughts?

The glue adds the axial strength. Otherwise, they are just floating and provide wall strength (radial) only.
 
If it were me, I'd line the whole booster section, then use the centering rings cut for the coupler ID X MMT OD. Probably overkill for the booster section, but we are talking M's here. No matter what, it will still come out to about half the weight of fiberglass tubing.
 
Understood. Thanks for your input on this. I'll probably work on this in the off-season.
 
Great suggestions, thanks! I think I'll probably do something like this for a winter build, as well.
 

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