What's your Largest motor in LP tubing?

[Walldiver7]

I've been playing with larger and larger motors in cardboard low power tubing for a while. My experimentation was driven by a competitive event that my section holds once a year. So far, I've successfully launched CTI G126 motors in 1.64" LP tubing (Estes type.. 0.021" thickness, I think). I've had no problems putting these rockets up into the 5K range. I'm considering launching a CTI H399 (29mm) in this same type of tubing, BUT have reservations about it holding up to that type of acceleration. The sim for my latest design shows it leaving the rod at 133fps with the H399. The peak thrust of the G126 was around 38lbs, while the peak thrust of the H399 is around 123lbs... huge difference.

What's the largest motor you've launched in LP tubing?

 

[Walldiver7]

While waiting for a response... I decided to do some testing. I took a 2.125" piece of BT-60 tubing and started stacking plate weights on it. That's 60lbs... and although I don't have the picture to prove it, it held 90lbs before I quit.

According to OpenRocket, my rocket will experience a 100 G boost. Will BT-60 tubing survive?

 

[rstaff3]

There is one way to find out for sure

I've only tried up to a G80 in BT-60 and a G106 in BT101. In my experience, the fins come off before the tube fails. Fiberglassing is cheating.

 

[REK]

There is one way to find out for sure

I've only tried up to a G80 in BT-60 and a G106 in BT101. In my experience, the fins come off before the tube fails. Fiberglassing is cheating.

Cheating thats funny lol. Agreed though, fins fail first before body tubes do.


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[markkoelsch]

There is one way to find out for sure

I've only tried up to a G80 in BT-60 and a G106 in BT101. In my experience, the fins come off before the tube fails. Fiberglassing is cheating.

Cheating? It is better to have said rocket survive, and if glass with do it then that is the ticket.

 

[blackjack2564]

Line tubing with couplers.

Fin are going to be the issue.

 

[MClark]

I did some very long burn H and I motors (30-40 seconds) in Estes tubing and nose cones.

 

[Handeman]

I've had an Estes Leviathan I've flown on H128W, H165R, H180W and H250G. I did use epoxy to attach the fins and a piece of 1/8" tubular Kevlar glued to the MMT as a shock cord anchor. The Stock shock cord was tied to the Kevlar.

It finally failed on a H128W when the chute deployed at motor burn out. The Kevlar zippered the tube to the forward CR and the tube actually tore in half. The elastic ripped near the knot with the Kevlar. The chute and the fins are fine.

 

[dmgrime]

Flown the BT60 based star orbiter stock (wood glue only) on an economax G74-9W....only issue was transonic shredded the balsa fins. Tubes were fine. Rebuilt with basswood fins to fly again this spring on same motor.

 

[dhbarr]

Most assuredly TTW vs SM matters here more than most places.

My thinking in this area has been around 29MMT, full length coupler, BT longer than coupler by NC shoulder length, wood fillets.

Essentially it would be three paper tubes laminated together w/ slow epoxy ( don't try PU or wood ), w/ bass or ply fins attached w/ woodglue.

 

[neil_w]

Most assuredly TTW vs SM matters here more than most places.

My thinking in this area has been around 29MMT, full length coupler, BT longer than coupler by NC shoulder length, wood fillets.

Essentially it would be three paper tubes laminated together w/ slow epoxy ( don't try PU or wood ), w/ bass or ply fins attached w/ woodglue.

Wow, full length coupler makes it a really thick tube. I'd imagine that to be low on the list of items likely to give way. Dunno how heavy coupler + BT is compared to alternatives. Actually seems like overkill to me, but should certainly be about as durable as you could want.

 

[dhbarr]

I243 in paper . The only two reasons for the third layer in my mindsim are a) the general unavailability of NCs that fit couplers and b) you might get enough pressure on the nose to shove it into the tube.

 

[Walldiver7]

Yes,... and I've been putting skins (paper) on my basswood fins to add a bit more integrity.

Flown the BT60 based star orbiter stock (wood glue only) on an economax G74-9W....only issue was transonic shredded the balsa fins. Tubes were fine. Rebuilt with basswood fins to fly again this spring on same motor.

 

[Walldiver7]

Line tubing with couplers.

Fin are going to be the issue.

I did give your idea some thought.... and at that point, that's when the testing began. With the tube able to handle 90lbs, I'm fairly confident that the compressional strength of the tube will handle the "crusher" (the CTI H399). But, I will likely go with a longer MMT to add some strength to the lower portion of the airframe. As far as fins go, I will use papered TTW basswood fins. One of my secondary objectives is to keep this rocket light enough that it can fly on E motors at my local site. And like one poster mentioned above...... glassing is cheating. lol

 

[Tramper Al]

In thinking about the low power parts most vulnerable to high thrust and speeds, what do you all think about the (F- or G-composite designed) Enerjet 1340 fin can that is reproduced on the Estes Eliminator? If the plastic fins themselves could handle F- or G-composite speeds in a lightweight low power rocket like the Eliminator or 1340 clone, would the fin can to BT adhesive be the weak point? Would epoxy suffice, after roughing up both BT and plastic? Or would some kind of through the wall modification be necessary?

 

[rstaff3]

Cheating? It is better to have said rocket survive, and if glass with do it then that is the ticket.

Seeing what the raw tubes can take seemed to be the question. Asking what glassed Estes tubing can withstand makes no sense.

 

[Mr G]

Put up a close-to-stock Estes Partizon on an Aerotech I200W to over 4,000 feet with no issues. See post #103 at https://www.rocketryforum.com/showt...izon-build-challenge/page4&highlight=partizon. Peak thrust of an I200 is 104 lbs.

 

[Bat-mite]

My Mega Der Red Max was built stock, and I put an I204 in it.

 

[emckee]

this is a fun idea, but you need to define what "low power cardboard tubing" means... I've got cardboard rockets that I use with high powered motors, such as a K375, etc, but personally, I don't think that counts because it's not standard Estes tubing. Are there "stock" tube options from Estes for 29mm? Their motor mount tubing isn't quite BT55 or BT56, so I'm not sure I'd count that either... What about a 29mm MMT inside Estes tubing? etc...

I think you also need to define some configuration parameters. A cylinder is a very strong structure in terms of bearing load. The OP's stacking of weights on a short length of BT60 demonstrates that. However, the strength of the tubing depends heavily on the fact that the stress is applied axially. Once you start loading off-axis, strength drops precipitously. This is why so many superroc's (a term which I apply to extremely high L-D ratio rockets) buckle under thrust. You get off-axis loading from wind, etc, which causes bending or oscillation in the tube, which then buckles under the thrust loading from the motor, because two halves of the rocket are pointed in different directions.

set your boundary conditions, then ask again

 

[cerving]

I've used both BT55 and BT60 tubing with small H's and through-tube 1/8" basswood fins, they hold up fine. I generally run coupler stock up the tube to stiffen the booster ahead of the payload bay. Of course, I haven't tried an H410 with one...

I'll echo the previously noted comments, it's the fins that are going to shred not the body tube. Balsa isn't going to hold up beyond maybe 400 or 500 fps, and if you're crazy enough to go trans-sonic with something like this the basswood fins won't hold up either. Once you get to that point, you should be looking at 38mm FG rockets, not hacking up Estes kits.

 

[dhbarr]

Specifically, the fins are likely to strip right off the tube, taking some layers of it with them.

 

[claytonbirchenough]

this is a fun idea, but you need to define what "low power cardboard tubing" means... I've got cardboard rockets that I use with high powered motors, such as a K375, etc, but personally, I don't think that counts because it's not standard Estes tubing. Are there "stock" tube options from Estes for 29mm? Their motor mount tubing isn't quite BT55 or BT56, so I'm not sure I'd count that either... What about a 29mm MMT inside Estes tubing? etc...

I think you also need to define some configuration parameters. A cylinder is a very strong structure in terms of bearing load. The OP's stacking of weights on a short length of BT60 demonstrates that. However, the strength of the tubing depends heavily on the fact that the stress is applied axially. Once you start loading off-axis, strength drops precipitously. This is why so many superroc's (a term which I apply to extremely high L-D ratio rockets) buckle under thrust. You get off-axis loading from wind, etc, which causes bending or oscillation in the tube, which then buckles under the thrust loading from the motor, because two halves of the rocket are pointed in different directions.

set your boundary conditions, then ask again

I'm kind of with emckee on the stacking the weights on the tube doesn't make for a very good kind of approximation, especially since the tube used was so small. I am by no means well versed in the subject of buckling, but it does depend on the length of the tube/support used. If you go to the Wikipedia article on buckling and then look at the columns section, I think it explains really well what I'm trying to explain

 

[Nytrunner]

I'm kind of with emckee on the stacking the weights on the tube doesn't make for a very good kind of approximation, especially since the tube used was so small. I am by no means well versed in the subject of buckling, but it does depend on the length of the tube/support used. If you go to the Wikipedia article on buckling and then look at the columns section, I think it explains really well what I'm trying to explain

^^What he said. Buckling is a second failure mode for things under compression. The tubes strength will decrease as it's unsupported length increases. Which I assume is why people are talking about glassing and coupler tube reinforcements.

Look around a little, Mccordmw (spelling?) Did a thread with a great spreadsheet for some basic info on tube failure strength that takes buckling into account for several materials.

 

[Initiator001]

In thinking about the low power parts most vulnerable to high thrust and speeds, what do you all think about the (F- or G-composite designed) Enerjet 1340 fin can that is reproduced on the Estes Eliminator? If the plastic fins themselves could handle F- or G-composite speeds in a lightweight low power rocket like the Eliminator or 1340 clone, would the fin can to BT adhesive be the weak point? Would epoxy suffice, after roughing up both BT and plastic? Or would some kind of through the wall modification be necessary?

The Enerjet fin can will not hold up under transonic velocities.
The fins are too thin and will flex too much at that speed.

When Matt Steele was working for Estes the company was going to bring out a low-cost ($49.99 SRP) mid-power starter set called the Orbit Starter Set.
It would feature a rocket named Orbit that would use the Enerjet fincan. It was a long/tall rocket and would fly on an NCRBE DarkStar F62-9 motor.
Matt told me they had to add weight/mass to the model otherwise the fins would vibrate at high velocities and break away.

 

[sl98]

Yes,... and I've been putting skins (paper) on my basswood fins to add a bit more integrity.

Apogee advertises that you can achieve supersonic by papering balsa wood and surface mount:

https://www.apogeerockets.com/downloads/Technical_Publications/Tech_Pub_29.pdf

 

[Walldiver7]

^^What he said. Buckling is a second failure mode for things under compression. The tubes strength will decrease as it's unsupported length increases. Which I assume is why people are talking about glassing and coupler tube reinforcements.

Look around a little, Mccordmw (spelling?) Did a thread with a great spreadsheet for some basic info on tube failure strength that takes buckling into account for several materials.

The tube's strength won't decrease,... but with a longer tube, other forces acting on the tube/airframe will be more prominent, which could lead to failure. The test I preformed was to determine it's compressional strength only.

 

[Walldiver7]

Apogee advertises that you can achieve supersonic by papering balsa wood and surface mount:

https://www.apogeerockets.com/downloads/Technical_Publications/Tech_Pub_29.pdf

Yes ........... and, to add a bit more insurance (hope? ha!) that my fins might stay with my rocket under the acceleration of the H399, I will install mine TTW.

 

[Walldiver7]

this is a fun idea, but you need to define what "low power cardboard tubing" means... I've got cardboard rockets that I use with high powered motors, such as a K375, etc, but personally, I don't think that counts because it's not standard Estes tubing. Are there "stock" tube options from Estes for 29mm? Their motor mount tubing isn't quite BT55 or BT56, so I'm not sure I'd count that either... What about a 29mm MMT inside Estes tubing? etc...

I think you also need to define some configuration parameters. A cylinder is a very strong structure in terms of bearing load. The OP's stacking of weights on a short length of BT60 demonstrates that. However, the strength of the tubing depends heavily on the fact that the stress is applied axially. Once you start loading off-axis, strength drops precipitously. This is why so many superroc's (a term which I apply to extremely high L-D ratio rockets) buckle under thrust. You get off-axis loading from wind, etc, which causes bending or oscillation in the tube, which then buckles under the thrust loading from the motor, because two halves of the rocket are pointed in different directions.

set your boundary conditions, then ask again

Point taken.... Originally the focus was only to question the compressional strength of the BT-60 airframe. The question I added at the end concerning .. "will it survive" did open other factors that must be considered.

 

[tbonerocketeer]

Flew a fat boy on a H48 and an H45...still going up on the last one.

 

[Walldiver7]

Flew a fat boy on a H48 and an H45...still going up on the last one.

"still going up on the last one." Lol...