Need some more experienced minds

[jenget]

I'm building my first higher altitude (above 10,000 ft) rocket. It's a 3" LOC Precision kit with some minor tweaks to it. Major concern: OpenRocket simulation shows it hitting Mach 1.5. The rocket is a phenolic tube, plastic nosecone, and 1/8 in plywood fins. I REALLY don't want it to shred. I'm smart enough to make sure I'm using a good strong epoxy when building it but I wasn't really expecting that result from the simulation. I ran the sim with an Aerotech K1050W (the largest 54mm RMS). Obviously, I don't NEED to use that motor, but I would like to eventually.

So the big question:
Is it safe to send this supersonic?

Can provide the OpenRocket file on request.

Thanks all!

 

[cbrarick]

Public Missiles claims that it's good at any speed. The landing, however can be an entirely different matter as it's pretty brittle

 

[Buckeye]

What is your objective of the flight? If it is an initial flight for altitude, then you can choose a lower thrust/longer burn motor and stay away from Mach transitions. This is probably not a heavy rocket, so you will be fine with lower thrust motors and be closer to their optimum mass for altitude.

If the objective is speed, shorter burn, and whoosh, bye-bye, then go for the K1050. You are probably ok with TTW fins and good fillets.

 

[ECayemberg]

I'm building my first higher altitude (above 10,000 ft) rocket. It's a 3" LOC Precision kit with some minor tweaks to it. Major concern: OpenRocket simulation shows it hitting Mach 1.5. The rocket is a phenolic tube, plastic nosecone, and 1/8 in plywood fins. I REALLY don't want it to shred. I'm smart enough to make sure I'm using a good strong epoxy when building it but I wasn't really expecting that result from the simulation. I ran the sim with an Aerotech K1050W (the largest 54mm RMS). Obviously, I don't NEED to use that motor, but I would like to eventually.

So the big question:
Is it safe to send this supersonic?

Can provide the OpenRocket file on request.

Thanks all!

I wouldn't be concerned with the phenolic tube and plastic nosecone.

1/8" ply fins likely need a bit of help to sustain a M1.5 flight. Option would be to replace with thicker material (3/16" or 1/4" would do....Loc can do this for you if you give them a call). Or do a layer or three of tip-to-tip fiberglass to the fin can area. What is the fin shape (or the kit?)

-Eric-

 

[mccordmw]

At mach 1.5, I'd be worried about fin flutter as your point of failure. You need to check them using Finsim. I would suspect they will need to be reinforced with fiberglass.

 

[dhbarr]

Have you simmed the Loki L-2050-LW or M-1378-LR? But anyhoo, how -long- you're at that speed really matters, as well as at what altitude.

 

[mpitfield]

I wouldn't be concerned with the phenolic tube and plastic nosecone.

1/8" ply fins likely need a bit of help to sustain a M1.5 flight. Option would be to replace with thicker material (3/16" or 1/4" would do....Loc can do this for you if you give them a call). Or do a layer or three of tip-to-tip fiberglass to the fin can area. What is the fin shape (or the kit?)

-Eric-

At mach 1.5, I'd be worried about fin flutter as your point of failure. You need to check them using Finsim. I would suspect they will need to be reinforced with fiberglass.

X3, I think your bonding is fine and phenolic is pretty durable tubing, but relatively brittle, it's the fin flutter that would concern me with that motor.

 

[cerving]

I'd replace the plywood fins with FG. 1/8" ply at mach 1.5 is asking for problems. The rest of the rocket is fine.

 

[Steve Shannon]

I'd replace the plywood fins with FG. 1/8" ply at mach 1.5 is asking for problems. The rest of the rocket is fine.

I would laminate the plywood fins with fiberglass and laminate the phenolic tube with fiberglass. The tube doesn't need it for flight, but as others have said it's brittle which can be a problem on landing or when transporting to a launch. With such lamination your rocket will last for years.


Steve Shannon

 

[REK]

I would laminate the plywood fins with fiberglass and laminate the phenolic tube with fiberglass. The tube doesn't need it for flight, but as others have said it's brittle which can be a problem on landing or when transporting to a launch. With such lamination your rocket will last for years.


Steve Shannon

Agreed here, nothing like adding some strength to make it last.


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[REK]

I'd suggest you glue your fins on well with either internal fillets or foaming it.

The rocket in the right (green and black paint) only went to Mach 1.2 and the fins layed waste to the blue tube. Huge mistake on my end for not gluing it to the motor mount, assuming it would hold to the outer tube.

Fin shape has a lot to do with the flutter effects going past the speed of sound.

Sent from my iPhone using Tapatalk

 

[jenget]

I appreciate everyone's help. It sounds like my main concern is actually the fins. So my next question is: should I completely replace the fins or laminate the plywood ones with fiberglass?

 

[Steve Shannon]

I appreciate everyone's help. It sounds like my main concern is actually the fins. So my next question is: should I completely replace the fins or laminate the plywood ones with fiberglass?

I have had 1/8 inch G10 fins crack along the root due to repeated Mach+ flights. If you do go with G10, go thicker, maybe 3/16".
Personally, I would just laminate the fins you have. Fiberglass laminated on plywood will be very stiff but still lighter than 3/16" G10.


Steve Shannon

 

[mpitfield]

I appreciate everyone's help. It sounds like my main concern is actually the fins. So my next question is: should I completely replace the fins or laminate the plywood ones with fiberglass?

Really your choice, either way if done correctly will accomplish what you need. However as pointed out you should try to perform an analysis using FinSim to get some data. Also if you have the equipment then laminating it may be more challenging and push your experience and knowledge forward as it is arguably more complex than replacing the fins with something heavier. If however you do not have the equipment or if you have other constraints then replacing the fins may be more convenient for you.

It also depends on what you have done already. If they are mounted then just reinforcing the part you see, base of the exposed fin to the tip, may help some but your TTW point is still weak so ideally you want the strength from the root to the tip.

 

[Oberon]

I could be wrong, but don't all LOC kits use standard glassine-coated kraft paper tubes, as opposed to phenolic? Or did you get a custom tube from somewhere else?

 

[SteadyMobbin]

I could be wrong, but don't all LOC kits use standard glassine-coated kraft paper tubes, as opposed to phenolic? Or did you get a custom tube from somewhere else?

+1 on this question as well. I've shredded a 3in LOC bird on a L1000, and shredded a 3in LOC bird that was entirely sleeved with coupler on a L1000.

 

[jenget]

I researched a little and found out I made a mistake. The body tube is glassine coated tube. Any suggestions?

 

[rharshberger]

I researched a little and found out I made a mistake. The body tube is glassine coated tube. Any suggestions?

If your going to fiberglass wrap the tube, make sure to peel off the glassine layer or the epoxy/fiberglass will not bond well to the tubing.

 

[markkoelsch]

If your going to fiberglass wrap the tube, make sure to peel off the glassine layer or the epoxy/fiberglass will not bond well to the tubing.

This is the truth. Peel the glassine off first. It will look rough, but that is ok as it is cardboard. You will get a good bond this way.

Next, get a single piece of fiberglass that will extend along one axis a couple inches over each tube end. Cut it long enough in the other direction to do 2 or 3 complete wraps of the tube.

Get good laminating epoxy ( I use Aeropoxy), some paint brushes. Mix the epoxy, and paint a very thin layer into the tube. Let sit for a couple minutes. Start to roll glass into the tube slowly working the glass into epoxy on tube with a paint brush with a little epoxy on/in it. You should see the glass go clear- keep looking for dry spots as you turn the tube. Once you get to the second wrap you will likely need to add a little epoxy to the first layer of glass. Keep rolling until done.

That is the basic version. You really only want enough epoxy that it were the cloth- more is fundamentally not adding strength- only weight. With this method the weave is visible though.

That said, you can use the same method but add additional epoxy at the end, and wrap it with other smooth materials to get a smoother surface. Prettier but a bit heavier. I cannot remember the name of said products right now though- been a really long week.

 

[rharshberger]

Another excellent epoxy is US Composites 635 with the medium hardener for laminating.

 

[markkoelsch]

I thought I might add this. Some of you know who Mick Kelly is, and some of you do not. Mick was one of the best composite rocket guys ever, and he started the Composite Rockets Group on Yahoo. He has since had to leave the hobby due to health reasons, and the group has become dormant. That said, I do have some of his files, and posted a couple to rocketryfiles.com (username and password guest). Follow the link below, and read a file called Micks tube method.doc - I promise it is worth it.

https://www.rocketryfiles.com/?p=home&d=Technicalarticles/

 

[Steve Shannon]

I thought I might add this. Some of you know who Mick Kelly is, and some of you do not. Mick was one of the best composite rocket guys ever, and he started the Composite Rockets Group on Yahoo. He has since had to leave the hobby due to health reasons, and the group has become dormant. That said, I do have some of his files, and posted a couple to rocketryfiles.com (username and password guest). Follow the link below, and read a file called Micks tube method.doc - I promise it is worth it.

https://www.rocketryfiles.com/?p=home&d=Technicalarticles/

Good link, Mark. When I first found Yahoo Composites Rocket Group I was in awe of Mick's articles. I never said anything; I was simply awestruck.
I hope Mick recovers and I really hope his health problems have nothing to do with composites.

 

[markkoelsch]

Steve, his issue were with his back. He had surgery to fix it, but at last reports he was still struggling.

 

[Steve Shannon]

Steve, his issue were with his back. He had surgery to fix it, but at last reports he was still struggling.

Back problems are more debilitating that many understand. I hope he improves.

 

[tfish]

here's one way to glass cardboard tubes..

[video=youtube;bjZNyXsd8gw]https://www.youtube.com/watch?v=bjZNyXsd8gw[/video]

Tony

 

[Spicer007]

I researched a little and found out I made a mistake. The body tube is glassine coated tube. Any suggestions?

Jenget,

Do you have a level 2 certification to fly a K1050W motor?

Most of the LOC 3.1" kits are only rated for motors up to J. They are heavy cardboard BT's, not phonetic. If you build following the kit directions,
the rocket will most likely shred at MK 1.5. Everything will have to be modified to survive a MK 1.5 flight.

My stock built LOC300 weighs only 3.1lbs with no motor. If I would fly it on a K1050W, it would reach about 13,000' and MK 1.85 and I bet I would not be able
to finding all the pieces after that flight...

 

[markkoelsch]

here's one way to glass cardboard tubes..

[video=youtube;bjZNyXsd8gw]https://www.youtube.com/watch?v=bjZNyXsd8gw[/video]

Tony

Tony, I was also going to mention you in another post, but did not have time last night. Very nice video.

 

[ksaves2]

I appreciate everyone's help. It sounds like my main concern is actually the fins. So my next question is: should I completely replace the fins or laminate the plywood ones with fiberglass?

I did surface mount 1/8" plywood on a LOC cardboard tube minimum diameter project for 38mm motors.
I used 2 oz. cloth on the fincan and did the 1/3rd, 2/3rds and full span lamination of the fincan.



Stuck a J motor, I believe a J350 and the rocket bound on the rail, shattered a Mayhem Rocketry rail guide to pieces, went to 8,600' and hit roughly 750mph on the EggTimer TRS.

I was shocked, just a few paint chips. My fault as the rail guide was tight on the rail and I
should'a pulled it off and used a cleaner launch rail.

It was a pain to pull off. Twelve pieces of 2 oz. cloth to cut. First layer, lays on can and goes 1/3rd the way up on the finspan. Second layer, I rotated the weave 45 degrees when I cut the piece and is lays on top of the 1st layer and goes 2/3rds the way up the finspan. Last layer is the same position as the 1st and goes tip to tip.

On the three fin rocket it's nine pieces of cloth.

EggTimer TRS flew it and it was single point dual deploy with an Archtype Rocketry
(now known as Prairie Twister?) cutting the zip tie to unfurl the main at 1000 feet.
Totally sight unseen, arrow straight (by the smoke trail) flight landed 1.66 miles away.

The TRS gave me the direction to start walking and a handheld Yagi antenna started pulling in an updated position after the rocket was on the ground, I still couldn't see it and had to walk closer. It was out in the open and obvious the main came out and it was a successful flight.
(Although my fault with the railguide)

The fin construction contributed to the structural survival of the rocket even though it
was a plywood fin root up against a cardboard tube! The 'glass lamination
really made a big difference. Kurt

 

[Binder Design]

If your going to fiberglass wrap the tube, make sure to peel off the glassine layer or the epoxy/fiberglass will not bond well to the tubing.

There is a trick I learned. The tube is stronger with the glassine left on but like you mentioned, epoxy doesn't bond well to the glossy surface. There is a simple way to degloss it. Wet down a sponge and squeeze out the water so it is not dripping wet. Then just wipe down the tube and dry it off with shop towels when you are done. No more gloss. Let it dry for a day or two before glassing to be sure it is good and dry.

 

[dixontj93060]

There is a trick I learned. The tube is stronger with the glassine left on but like you mentioned, epoxy doesn't bond well to the glossy surface. There is a simple way to degloss it. Wet down a sponge and squeeze out the water so it is not dripping wet. Then just wipe down the tube and dry it off with shop towels when you are done. No more gloss. Let it dry for a day or two before glassing to be sure it is good and dry.

That's a nice tip--I'm going to have to try that next time.