Upward Propensity: My Level 2 rocket

[CCotner]

I go to Harvey Mudd College in Claremont, CA (east of Los Angeles).

As do I.

Limit motor size and thrust. REJECTED

Ahahahahahahaha NEVER COMPROMISE THRUST

So, I'm going to reinforce the fins with tip-to-tip fiberglass. Straight from tip to tip. In fact, I'm going to literally run G10 from one fin tip to the next to prevent the fins from twisting. It's going to be a beam section in the shape of a V with a wooden dowel glued in between to prevent them from fluttering on their own.

Ok, I know there are pictures, but this I got to see. I don't have class till 10 tomorrow; on my way down to the lab now!

 

[CarVac]

Real tip-to-tip fiberglass. None of that skinny, weak, cloth nonsense.

I tacked them on with 5-minute epoxy and then applied Aeropoxy ES6209 to the joints (it's currently sitting on its tail so the fillets aren't going anywhere). The stiffness has dramatically increased, and stability hasn't been sacrificed. Just from the airspeed of walking down the hallway it exhibits a dramatic tendency to orient itself in the direction of walking.

Overall, so far, it weighs about 5.5 pounds. That's a bit on the heavy side for my 48" Spherachute, but it's well-built enough for me to not worry about landing damage.

 

[Aksrockets]

This is turning out to be a very interesting build, Carvac! Interesting choice with the "tip to tip". Good luck with the L2. I can't wait to see how this turns out.

Alex

 

[MasonH]

Well, you certainly get points for originality. Keep it up!

 

[CarVac]

yo man i herd you liek reinforcement so i put reinforcement on my reinforcement...

I'm epoxying wooden dowels between the fin fillets and the nearly-tip-to-tip fiberglass in order to prevent them from vibrating and cracking the epoxy joints between the fiberglass and carbon fins. Hopefully.

Perhaps it'll be safe to fly on a non-moonburning K now.

 

[bobkrech]

I go to Harvey Mudd College in Claremont, CA (east of Los Angeles).



Aside from that: The news from today.

I decided that I would grab the Apogee article on fin flutter and plug the numbers from my fins into the formula. Seeing the formula, I was surprised, because I expected the mass of the fin (and thus its resonant frequency) to have some sort of influence on the results, but there's nary a sign of it. Nor is there any mention of sweep. I guess it does have to do more with the characteristics of the forcing functions, but I don't know why wing sweep isn't taken into account for that.

The result varies depending on what the effective shear modulus of my foam-cored CF fins are. I wasn't sure, but this page (https://www.performance-composites.com/carbonfibre/mechanicalproperties_2.asp) gives two results for the in-plane shear modulus: 5 GPa and 33 GPa, depending on whether the fiber is oriented 90/0 degrees or 45/45, respectively, with respect to the direction of stress.

With these two values, I get ~.35 Mach and ~.9 Mach. The former is more likely, since my fins aren't completely CF, but my fins have a very large amount of 45/45 in the layup so it might be somewhere in between.


So. 1/3 of the speed of sound. That's an awfully limiting speed for a fairly lightweight 54mm rocket. Here I'll enumerate a few options I had.

1. Limit motor size and thrust. REJECTED
2. Add mass. REJECTED because I do want to be able to fly on smaller motors on occasion, and because it's largely assembled already.
3. Add drag. Unlikely to affect top speed too much unless I mount a saucer the size of the fins on the bottom of the rocket, so it's not going to work great.
4. Reinforce fins somehow.

So, I'm going to reinforce the fins with tip-to-tip fiberglass. Straight from tip to tip. In fact, I'm going to literally run G10 from one fin tip to the next to prevent the fins from twisting. It's going to be a beam section in the shape of a V with a wooden dowel glued in between to prevent them from fluttering on their own.

Fun side benefit: more drag, so it'll stay lower on the big, long-burning motors I intend to fly this on.

I have a couple of design questions for you.

Greater stiffness leads to higher flutter speeds so why didn't you use a thicker core material for the fins since the core material is very light weight and 0.1" is a very thin cross-section for such a larger fin and stiffness increases with the cube of thickness?

Carbon fiber composite is aproximately 3 times stronger and stiffer than fiberglass so why would you choose to use fiberglass instead of carbon fiber for a tip to tip lamination?

Bob

 

[CarVac]

I have a couple of design questions for you.

Greater stiffness leads to higher flutter speeds so why didn't you use a thicker core material for the fins since the core material is very light weight and 0.1" is a very thin cross-section for such a larger fin and stiffness increases with the cube of thickness?

Carbon fiber composite is aproximately 3 times stronger and stiffer than fiberglass so why would you choose to use fiberglass instead of carbon fiber for a tip to tip lamination?

Bob

The fins were made a year ago; making them thicker, even only adding core thickness, would dramatically increase weight.

The fiberglass is not tip-to-tip lamination, but rather a spar. Take a look at my pictures. Had I had carbon fiber sheet on hand, I would have used that instead.

 

[CarVac]

From left to right: Giga Drill Breaker, Upward Propensity sans nosecone, and a 5-gallon bucket of PTM&W 5712 high-temperature laminating epoxy. No, Troj, I'm not going to fly the epoxy bucket.

This photo is just to give you a sense of scale for the fins and the associated support structure.


Interesting things to see from this angle: Inside the avionics bay is a 1/4 sector of a centering ring. This acts as a bayonet mount for the avionics sled, which has a slot cut out of the side.

I insert the sled oriented vertically in this photo's viewpoint, and then twist it so that the tab fits into the slot.

The sled takes no load itself, so this little bayonet mount prevents me from needing to use a screwdriver or rivets or anything like that to retain it.



In fact, I'm planning on making this a screwdriver-less assembly. The altimeter will be powered on by putting header pins together, and I have brass thumbscrews which act as terminal blocks on the avionics bay itself, which I'll document once I finish it tomorrow.

 

[CCotner]

No, Troj, I'm not going to fly the epoxy bucket.

*snort*

I can't wait. This is going to be special, no matter how it turns out.

As some point, isn't this just going to become a grid fin rocket? =p

 

[CarVac]

I kinda didn't give an update after the first flight... I launched it on an I357T.

It was super windy so all of the reinforcement popped off on landing and a few fillets cracked. On the plus side, my toolless design worked great; it was incredibly refreshing to not worry about where I left the darned screwdriver.

The fins are still on strong, so I am reattaching the reinforcement better: this time the fin-to-reinforcement joint will be fiberglassed, as will the meta-reinforcement-to-reinforcement joint. The meta-reinforcement will be full-on plywood this time instead of piddling little dowels. The only problem is that now my friends are telling me to reinforce the reinforcement for the reinforcement.

Based on my experience with the first flight, I'm gonna just do single-deploy from now on. The I357 only went 750 feet, much lower than expected. When I tuned the sims based on the results of that flight, the result was that a CTI K400 G would only go ~3000 feet, easily low enough for single deploy without tracking.

This rocket is turning out to be a sweet sport rocket: low-n-slow on a mid K due to obscene drag, but the capability to fly on a relatively small motor due to the light weight.

 

[CarVac]

I level 2'd today with this rocket on a J420 Redline. It turned out that the reinforcement strakes make a mean whistle: all of the way until ejection (which for some reason happened slightly before apogee), and with the whistle pitch proportional to airspeed.

It sounded like a rocket coming in ballistic, except it happened on the way up! Perhaps that's this rocket's way of living up to its name?


Video and photos later.

 

[MasonH]

Congrats on the cert!

 

[bill2654]

Way to go on the level 2 cert! Wheres the pics?

 

[CCotner]

Way to go on the level 2 cert! Wheres the pics?

I have them, he took video. Coming later.

 

[o1d_dude]

Gratz on the L2. Nice choice on the red motor.

 

[CarVac]

VIDEO:

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

 

[skyviper73]

Congratulations! Love the sound!

 

[MasonH]

You got the low part, need to work on the slow part!!

 

[CarVac]

You got the low part, need to work on the slow part!!

It's slow by my standards. It leaps off the pad because it's not that heavy (7.4 pounds loaded with the J), but the ridiculous drag really limits the top speed.

 

[CarVac]

Photos:

Not too hard to spot.

The shock cord to the nose is really, really long. By my standards.

Stuck the landing! Here you can see that I didn't reinforce the reinforcement, and it was fine. Instead I have small wooden blocks tucked into the corners of the joints which greatly, greatly increase the bond area.

 

[CarVac]

This time, I chose a motor that completely drowned out the whistle, though it was still spectacular: the CTI I100 Red Longburn.

Just as simulated, it burned all of the way to apogee.

[video=youtube;shPTzQ1zhpk]https://www.youtube.com/watch?v=shPTzQ1zhpk[/video]

It only went 1673 feet, but it seemed much higher than that...

 

[CarVac]

I did not post the results of the last flight, but one of the reinforcements fell off on landing.

So, on the Saturday of LDRS, the day after launching Bare Necessities, I glued it back on with Aeropoxy ES6209. Instead of waiting 24 hours, though, the intense desert heat and sun let me fly in a mere 5 hours.

I wanted to fly an I435T, but upon a brief consultation with CCotner ("The Dark Matter, of course") I flew it on a K456DM. Pretty epic, and it only went 2580 ft. Video later when I have non-phone internet.

Then, on Sunday I acquired a DMS J270 White Lightning and flew it on that. No video of that launch, unfortunately.

 

[RocketRob]

Beautiful rocket man!

 

[CarVac]

[video=youtube;D1IAlKDarQA]https://www.youtube.com/watch?v=D1IAlKDarQA[/video]

 

[CarVac]

Prepping U.P. (which is pointing down)

With single-throat 54mm AT motors, the nozzle opening ends up flush with the bottom of the rocket. This would not be true of Medusa nozzles, though.

Dark Matter always makes spectacular photos, especially when combined with the horizontal plate blast deflector...

Photos courtesy Allison Mis

 

[CarVac]

I'm gluing up the fin reinforcement again, and tomorrow I shall wire the av-bay up anew, this time for an EasyMini. Hopefully I'll fly it on Saturday.

 

[CarVac]

I flew it twice. Two great flights, one great landing.

Unfortunately, it stuck a fin in an odd way on the second landing, dislodging it (actually pulling straight out from the root).

It seems that while the spread-weave CF is supposedly good for ultimate material strength, it may be worse for bonding to than standard twill CF: the Aeropoxy glue joints peeled fibers off of the surface of the fin.

 

[codysmith]

That is a truly amazing rocket. It looks awesome and it's flights are beautiful.

 

[CarVac]

I've posted some photos of it flying before in other threads, but I might as well put them here as well.

These are both Loki I316 Spitfires, flying to about 1090 feet. The first is on an overcast day so the sparks look brighter.

H144 Loki White, to 525 feet.

This is it descending on its new 60" Spherachutes LT which packs into nearly the same space as the old 48" normal Spherachute. And now it doesn't lose the tip-to-tip fiberglass on every other landing anymore!


EDIT: Oh and an artsy shot of the business end.