6" Tubefin level 3 build

sugardaddy · Jan 11, 2013

Hi Guys,
I have decided to take the plunge and go for my L3. My rocket of choice will be a scratch built 6" tube fin made from Blue Tube.
Since i did my L2 on "Going Postal" a 3" duel deployment tube fin, I felt I needed to do the same for L3. My cert flight will be made on a Gorilla M1665WC.
This isnt going to br a masterpiece or anything like that, I'm just building a monster tube fin design to pass a cert flight.
Pics are coming up.

Danny

sugardaddy · Jan 11, 2013

Here are all the pieces ready for assembly. The AV Bay and nose cone were already done from a previous build.

MasonH · Jan 11, 2013

Do you have a file, or at least some specs?

sugardaddy · Jan 11, 2013

The First thing i did was cut the fins out using a band saw. The fins have a total length of 12" and tapper to the trailing edge about 35 degrees.

The fins needed to be cut at an angle on one side so i made a jig to hold the tube while sliding it past the blade.

Here you can see where i attached a guide to set the distance from the blade.

Then a cradle was made to hold the tubes at the set angle.

sugardaddy · Jan 11, 2013

I did. I have a rocksim file, but i have a new computer and i'll need to find my old hard drive and get it. I'll try and look for it tonight.

maxvelocity · Jan 11, 2013

I saw a blue tube tube fin shred on an M. Not sure which M hopefully he will chime in and give some advice.

sugardaddy · Jan 11, 2013

The next thing i did was cut 3 centering rings from 1/2" aircraft ply and cut a 24" MMT. The MMT is also made from Blue Tube.

Time to glue it all together. I started with the fins. I clamped body tube to the table and placed a fin on each side and epoxied/clamped them to the body tube. This insures that the fins are perfectly parallel to the body.
I originally wanted the fins to tapper on both ends for a sleeker look, but i couldnt find a way to cut angles on both ends of the tube while keeping both cuts dead center of eachother. Since i could only cut one side i had to decide either tapper the leading or the trailing edge. Because i have built a lot of tube fin rockets, i've learned that when the fins are flat across the bottom they get damaged easier. Rockets almost always land at an angle. On a tube fin, that means a fin is going to take the whole impact on its tip causing it to crush or crinkle over time. I decided to tapper the trailing edge so that then the rocket lands, more if the fin will absorb the impact leaving no damage. (Thats the idea anyways)

Then, its just a matter of continuing arounf the body tube epoxying fins together and filling filllets as i go around.

Here she is with all her fins attached. I will be adding a couple of machine screws to each fin later.

Danny

MasonH · Jan 11, 2013

Why do some tubes look shinier than others? Sealant, epoxy, glass, what?

sugardaddy · Jan 11, 2013

maxvelocity said:
I saw a blue tube tube fin shred on an M. Not sure which M hopefully he will chime in and give some advice.

I'm not building this thing to be a runway model. She's got some meat on her bones. I'm expecting it to weigh about 30lbs or so. I am also considering using the gorilla M745. It should be a bit more gentle on the fins. Its going to come down to what the weather is like the day of the launch.

Danny

sugardaddy · Jan 11, 2013

MasonH said:
Why do some tubes look shinier than others? Sealant, epoxy, glass, what?

Some of the fins were made from recycling an old 6" rocket the landed a bit too hard to fly again. It was already prepped with sanding sealer.

CarVac · Jan 11, 2013

maxvelocity said:
I saw a blue tube tube fin shred on an M. Not sure which M hopefully he will chime in and give some advice.

I think it was an M2020 Imax...I remember the thread.

sugardaddy · Jan 11, 2013

Next up is adding the MMT. I started be gluing the middle ring to the MMT I then reinforced it with chopped FG and epoxy on both sides.

Next I epoxied the middle ring and MMT assembly to the booster. I then filled each end with 4lbs expandable foam and epoxied the end centering rings in place.

This is what happens if you take too long to pour the foam. I was .032 seconds away from ruining the entire rocket by getting foam all over it. I instead left a trail of foam thru the house, the driveway, the yard and all over my hands.

JStitz · Jan 11, 2013

Danny, do you have a 1/2" centering ring at the top of the tube fins for a screw point?
Honestly, I would have done your fins upside down with the taper on top..just my :2:
And..the bottom should be screwed into the bottom ring also...Just sayin' if this will see an "M"
(knowing me I would have screwed back from the mmt into the tubes also..but that is me.IMHO.

John

sugardaddy · Jan 11, 2013

Hi John,
I agree, It would definately loof better with the tapper at the top. All my other tube fin rockets are that way. I wanted to try them like this to see if i can lessen the damage done when landing.
I do have the middle ring lined up with the top of the fins. I plan to run #8 machine screws through them to help support the fins.

Danny

JStitz · Jan 11, 2013

Exactly..It all helps to keep it together.Screws don't weigh much. LOL.
I have even remembered where I put screws in and glassed over it.(forgetting and re-discovering...bad signs of aging) :wink:

sugardaddy · Jan 11, 2013

Here Is what i gave so far. I still need to add the altimeters to the AV bay and attach the motor retainer. For retention, I'm using the Aeropak bolt on retainer.
I a friend that said he wants to paint it for me so on monday i'm dropping it off with him. I plan to fly this Feb 2 at the Tripoli Ft Myers club.

AHansom · Jan 12, 2013

Very nice build. How soon are you going to do the cert flight? Unfortunately I was the one who built a 6" Kraken out of Blue Tube and then ripped the fins off using a M-2020. Even though there both tube fin rockets I'm not sure they will act the same. I think a design were all the tube fins touch each other helps support them from oscillating and causing a failure.

sugardaddy · Jan 12, 2013

I'll be flying it on Feb 2.
I've always wondered how strong the fins were on a Kraken. I guess you found the limit. I feel pretty confident that these fins will hold. There is a lot of surface contact for the epoxy to grab on to.

Danny

cjl · Jan 12, 2013

AHansom said:
Very nice build. How soon are you going to do the cert flight? Unfortunately I was the one who built a 6" Kraken out of Blue Tube and then ripped the fins off using a M-2020. Even though there both tube fin rockets I'm not sure they will act the same. I think a design were all the tube fins touch each other helps support them from oscillating and causing a failure.

Fascinating - I've wondered for some time about tubefin shreds. Any idea how fast it was going when it came apart?

beezwax · Jan 12, 2013

sugardaddy said:
I originally wanted the fins to tapper on both ends for a sleeker look, but i couldnt find a way to cut angles on both ends of the tube while keeping both cuts dead center of eachother.

Looking at your jig, if you doubled it you could flip it and get a second precise cut. This is going to be much harder to describe in words than on the back of a napkin but I'll try and if it doesn't make sense let me know and I'll make a sketch...

Right now your jig is like a cradle or a saddle that the tube sits in, with a small block under it turned at a set angle to the cradle, which rides against your fence and gives you a repeatable miter cut. Instead of a cradle, if you made a square box that exactly fit your tube (ie outside diameter of your tube is the measurement of the inside square) and then put a second small block on top as another miter rail you could flip it and make your second cut. This would give you two miter cuts that are converging (trapezoidal) which I assume is what you want. If for some reason you wanted a parallelogram you'd flip your jig horizontally instead of vertically and wouldn't need to double it as I'm describing.

So, for this to work:
1) you have to clamp or screw the tube inside the box so that it can't shift, even when flipped
2) if you want your two miter cuts to be the same angle (forming an isosceles trapezoid shape) then you have to make sure your two miter guide blocks are exactly in line with each other on either side of the box...on the other hand if you wanted you could easily choose to set a different angle for top and bottom, and be able to repeat that shape reliably for each tube fin.

Did that make any sense? I know your rocket is already built but I thought I'd throw this idea out there in case you ever want to try it on another build. Good luck with your cert flight!

bill2654 · Jan 12, 2013

Good to see you back and posting again Danny. I'll be watching this thread. Good luck on your level 3.

3stoogesrocketry · Jan 12, 2013

Good luck Danny . You should fly it on the 19th in tampa . At least down in ft myers theres no water for you to land in lol .

Eric

boomtube · Jan 12, 2013

Why do the tubes of your 6” dia. Rocket all have Blue Tube 2.0” printed on the inside?

troj · Jan 12, 2013

Cool build -- ring fins and tube fins are cool!

If you're worried about airframe stress, I'd say a long burn motor, like the M745, isn't your best option -- I'd go for a mid-range burn, instead.

A really hard hitting motor gives it a whack, but it's short lived. A long burn motor doesn't hit it as hard, but often the peak velocity is higher, which causes its own problems.

If you want a Gorilla motor in that same case, I think the M1355RT would be a better choice.

Have you run any sims, to see what your peak velocity will be with various motors in that case?

-Kevin

troj · Jan 12, 2013

boomtube said:
Why do the tubes of your 6” dia. Rocket all have Blue Tube 2.0” printed on the inside?

That's "Blue Tube 2.0" as in "version 2.0," not "2.0 inches"

The first version of Blue Tube had problems if it sat in the sun. The guy who first brought it to market worked with the manufacturer to change something in how it's made, to solve that problem. Thus, Blue Tube 2.0 was born.

-Kevin

-Kevin

AHansom · Jan 12, 2013

sugardaddy said:
I'll be flying it on Feb 2.
I've always wondered how strong the fins were on a Kraken. I guess you found the limit. I feel pretty confident that these fins will hold. There is a lot of surface contact for the epoxy to grab on to.

Im thinking yours will be stronger because of the side contact with the other fins. On mine it wasn't the bond that failed it was the the tube itself shredded apart. I had about a 1.5" wide attachment and still have a few layers of Blue Tube attached to the airframe. I also put a few screws and large headed pop rivets along the joint but I don't think they helped much because there still there.

AHansom · Jan 12, 2013

cjl said:
Fascinating - I've wondered for some time about tubefin shreds. Any idea how fast it was going when it came apart?

I think it was going close to Mach and still had another second or more burn to go

I bet you were a little worried before you launched yours.

View attachment 1414OSkraken.FIPa

o1d_dude · Jan 12, 2013

Larry Brand's published max velocity for any of his tube fin rockets was 650 mph. Anything faster tended to separate the tubefins from the body tube.

"Yes, Virginia. There is such a thing as tubefin flutter." According to Larry.

mcderek · Jan 13, 2013

One answer to getting close to Mach with a tube fin is to use the same motor and build the rocket bigger:y:

Cool tube fin!

sugardaddy · Jan 13, 2013

beezwax said:
Looking at your jig, if you doubled it you could flip it and get a second precise cut. This is going to be much harder to describe in words than on the back of a napkin but I'll try and if it doesn't make sense let me know and I'll make a sketch...

Right now your jig is like a cradle or a saddle that the tube sits in, with a small block under it turned at a set angle to the cradle, which rides against your fence and gives you a repeatable miter cut. Instead of a cradle, if you made a square box that exactly fit your tube (ie outside diameter of your tube is the measurement of the inside square) and then put a second small block on top as another miter rail you could flip it and make your second cut. This would give you two miter cuts that are converging (trapezoidal) which I assume is what you want. If for some reason you wanted a parallelogram you'd flip your jig horizontally instead of vertically and wouldn't need to double it as I'm describing.

So, for this to work:
1) you have to clamp or screw the tube inside the box so that it can't shift, even when flipped
2) if you want your two miter cuts to be the same angle (forming an isosceles trapezoid shape) then you have to make sure your two miter guide blocks are exactly in line with each other on either side of the box...on the other hand if you wanted you could easily choose to set a different angle for top and bottom, and be able to repeat that shape reliably for each tube fin.

Did that make any sense? I know your rocket is already built but I thought I'd throw this idea out there in case you ever want to try it on another build. Good luck with your cert flight!

It make perfect sense. I think i'll try the boxed tube holder idea next time. Its easy enough and that would do the trick.

Danny

6" Tubefin level 3 build

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