Mach 3.5 Loki L Altitude Record Attempt Build

[watheyak]

Hey everybody,

There's a ton of really cool high performance build threads happening right now, so I though I'd pile on. This project has been in the works for literally years. I bought a Loki 54/4000 case right when Scott at Loki Research released it. My intention from the very beginning was to set the Tripoli L altitude record with a Loki L-2050. About that same time I was given a large amount of prepreg carbon fiber by fellow club member and Darrel Burris. A project was started, but at the time, I didn't have the expertise or finances to really do it correctly. The project honestly scared me a bit. I had seen that motor destroy quite a few rockets, and I needed to take a step back and re-think this.

Fast forward to about a year ago, I started devising a whole new plan, still borrowing some ideas from the old project. I learned some basic CAD (Fusion 360), acquired a 3D printer and continued to hone my composites knowledge and skills through rocketry and other hobbies. Some of this design was blatantly stolen from the likes of Jim Jarvis, Nic Lottering and AstroAnon. Sprinkle in some John Coker and Tony Alcocer, and G_T as well.

This is essentially a flying case with a motor-diameter nosecone. The only commercially available parts are the motor hardware, electronics and parachute. Due to the high speed expected, there is no paint, and all the epoxy and other materials are capable of withstanding high temperature. The fin cores and leading edges are high temp G-11 and the nosecone is made with Cotronics high temp epoxy. For added cool factor and strictly aesthetic reasons, the nosecone is also 2x2 Kevlar twill. Hopefully it'll look pretty neato.

There has already been quite a few versions of both the fin can and nosecone. Mistakes have been made and learned from. The nosecone has already flown to Mach 3+ on a Loki L-1040 and survived the aerodynamic loads and heating unscathed. (the landing not so much) I think It's time that I can take what I've learned through all the previous iterations and make the parts for the L record attempt via an L-2050.

Here are two threads that have been running concurrently leading up to where I'm at now. In case you're really bored and want some background in why I'm doing what I'm doing.

Cutting Carbon Fiber with a Cricut Vinyl Cutter

So I've been struggling with how to keep leading edges and tip to tip reinforcements intact during high speed (M2.7+) flights. Mach 3.7 in this particular project. I've been doing lots of combing through threads here, a flight or two of my own that illustrated what not to do, and some laying...

www.rocketryforum.com

Molding a Nosecone Using a Pressure Bladder

Hi all, I'm about to move into some unfamiliar territory, at least for me. I'm going to try and mold a nosecone for a sub-minimum-diameter project using a pressure bladder inside the mold. This isn't a new technique. R/C discus launch glider folks have been making fuselages this way for a while...

www.rocketryforum.com

Here's some pics of what I'm working from-

















First up, gotta make a tube....

 

[watheyak]

The tube in this case is made from the uni-directional prepreg. It's 6 layers of alternating 0/90 layers. It's .024" wall thickness and weighs about 30 grams. The mandrel is a from the telescoping antenna mast tubes from DX Engineering.

Cutting the pieces-


Mylar surface release. This is really just to get rid of the ridges created by the shrink tape I'm using for compression.


The releases. They work better than any release I've ever used.


Getting the first wrap on there tight and straight is the hardest part of this whole build....


Adding one of the 90 layers in there.


Spiral wrapping the shrinky tape.




Out of the oven, moment of truth...


Turned out pretty nice. Trim the ends and a quick sand and attach some fins!

 

[Conway Stevens]

Looks quite fun and interesting. Will be following. Good luck on the build.

 

[Neutronium95]

I've been waiting for this. I've felt like the L2050 should smash the current record, and I'm so happy to see someone finally doing it. If it survives the flight, do you have any plans to refly it on the M1378? IIRC that should have a pretty good shot at the M record.

 

[watheyak]

I've been waiting for this. I've felt like the L2050 should smash the current record, and I'm so happy to see someone finally doing it. If it survives the flight, do you have any plans to refly it on the M1378? IIRC that should have a pretty good shot at the M record.

The thought has crossed my mind. Usually rockets that go this fast are pretty much single use. Or at least the Mach rash puts a serious damper on their aerodynamics. But I'm encouraged by what I say with the nosecone on the L-1040 flight. So we'll see. I'm getting pretty fast at making these parts, so even if it's not so pretty when it comes back, a reflight on the M still isn't out of the question.

 

[watheyak]

The fins for this are machined from G-11. It has a max temperature of around 335 degrees F and is hard and dense. I arrived at this after seeing regular G-10 survive high-Mach flights good as new. In addition to flight loads, they also needs to withstand the temperature of the oven while the prepreg reinforcements cure. This was a major hurdle that caused a couple do-overs in the previous iterations. Fingers crossed for a fins that aren't crispy and warped this time around.

The leading and trailing edges have a generous bevel, and a pocket is routed from the center of the plate, allowing the tip to tip reinforcement to be recessed, out of the slipstream. This will prevent any sort of seam or step at the leading edge to soften and spilt due to aerodynamic loads and heating. This is one of the ideas I stole from the "what would I have done differently" post in A5tro Anon's N-5800 thread a few years back.

[L3] Composite N5800 Flying Case, ~67kft MSL, M3.5

Great flight...write up & detailed build . I enjoyed it immensely & re-enforced some of my decisions on my project. Thank you & party on!!! Just one more thing......after this fight & reflecting on it. What would you change or modify, if anything? [there's usually some tweek...LOl]

www.rocketryforum.com

Here's a CAD drawing and pics of the actual part-






I used a Macklin guillotine for the alignment. Something else I arrived at after limited success with other methods. The small size and odd shape make these fine not want to play nice with other alignment methods.



All four fins attached. Fillets next.

 

[watheyak]

Concurrently with the fins, I've been making the nosecone. I had some goals for this that allowed me to borrow from another hobby of mine, RC sailplanes. While I haven't flown RC in a long time, I still keep up with the current tech, and this is where I got my start in composites fabrication in the first place.

I wanted there to me compaction of layers, a smooth inside for av-bay O-ring seal, and a decent fiber to resin ratio. I also wanted it to look cool, hence the Kevlar. Goes nice with the Loki blue!

To achieve all this, I decided to use a pressure bladder mold. A strong and stout mold was built, and a latex balloon was used as the bladder. The mold weighs close to 50lbs, contains nearly a gallon of epoxy, 8 feet of 1" steel, a and a bag of sand. All tinted to a calming teal color. The plug was turned by Charlie Ogino of Carolina Composites, long, long ago. It's since been refinished, re-coated and polished. It's a 7:1 Von Karmann profile with an integral 3" extension.

The layup consists of 2X2 Kevlar twill, satin weave S-glass and satin weave Kevlar. G_T Gerald helped with some of the specifics here. The epoxy is Cotronics 4461, good to 500F.

If you suffer from insomnia and would like to nerd out on the entire mold build process and all the successive versions of the nosecone, the thread is here-

Molding a Nosecone Using a Pressure Bladder

Hi all, I'm about to move into some unfamiliar territory, at least for me. I'm going to try and mold a nosecone for a sub-minimum-diameter project using a pressure bladder inside the mold. This isn't a new technique. R/C discus launch glider folks have been making fuselages this way for a while...

www.rocketryforum.com

Here's some pics from the nosecone that will be used for the flight. Fresh out of the mold moments ago.

Mold halves cleaned and Frekoted. Oooh Buttery.


Bladder connections and bladder. This one ran at 35psi.







The layup. This is actually from a practice part and is messy. I learned and used a staggered wet seam layup.




Bolted together. Those bolts are a pain as they get glued in by all the excess epoxy that gets squeezed out. If I make any more of these nosecones I'm going to move to a clamp system. Now I know why I kept seeing that method in my research.


Ready to come out of the mold. Oh the suspense.


To be continued...

 

[watheyak]

Mold halves split Notice all the extra epoxy that was squeezed out.


Pulling out the bladder. It's like picking a big booger. Very satisfying.




Turned out pretty OK. Totally useable. No pinholes, also thanks to suggestions from G_T Gerald.


Now for trimming, tip and internal coupler.

 

[mlrtime99]

Agreed on the kevlar, great look!

 

[rfjustin]

Fantastic!

 

[Wayco]

They just keep getting better and better!
Now, about those recoveries.....

 

[watheyak]

The last nosecone had a phenolic tip. The person who made that tip is busy putting his superb skills to much better use making super secret aerospace parts.

I had the idea to print the tip on my resin printer from high temp resin. The high temp SLA resins are usually meant for injection molds for rapid prototyping, but so far the parts I've made seem like it's pretty tough stuff. I had a tip print that didn't turn out so hot, so I'm going to abuse it a bit to get a better feel for how it'll hold up.

The first resin I tried is Siraya Sculpt. It's good to ~350°F and a nice gray color.

 

[Michael Wilson]

Looks great! That nosecone is an absolute beauty, though id be concerned about the 3d printed tip. Earlier this year i wanted to do this, but then i got slapped in the face by reality Glad some one else is doing it though, that casing was meant to do crazy flights like this.

 

[watheyak]

Looks great! That nosecone is an absolute beauty, though id be concerned about the 3d printed tip. Earlier this year i wanted to do this, but then i got slapped in the face by reality Glad some one else is doing it though, that casing was meant to do crazy flights like this.

Thanks!

I'm not necessarily 100% sold on the 3D printed tip, either. I'm definitely interested in what you or anyone else has to say about it.

 

[Nytrunner]

Thanks!

I'm not necessarily 100% sold on the 3D printed tip, either. I'm definitely interested in what you or anyone else has to say about it.

To paraphrasing my materials professor "I'd confidently hang from a pullup bar made from true 3d printed material, but not from anything extruded from those glorified hot glue guns mascarading as 3d printers"

 

[Michael Wilson]

Thanks!

I'm not necessarily 100% sold on the 3D printed tip, either. I'm definitely interested in what you or anyone else has to say about it.

Id be very skeptical that itd hold up, i think itd be a much safer bet going with your composite tip or a new metal one as they have been proven.
Are you going to use an ablative? Or do you think that the g11 will protect it?

 

[watheyak]

To paraphrasing my materials professor "I'd confidently hang from a pullup bar made from true 3d printed material, but not from anything extruded from those glorified hot glue guns mascarading as 3d printers"

I agree about the hot glue guns. This is a liquid resin SLA printer, however. Also not known for strength necessarily. But it won't melt and there are no bond line issues.

I'm going to put the part through some torture and report back.

 

[Michael Wilson]

I agree about the hot glue guns. This is a liquid resin SLA printer, however. Also not known for strength necessarily. But it won't melt and there are no bond line issues.

I'm going to put the part through some torture and report back.

Will be waiting eagerly!

 

[watheyak]

Id be very skeptical that itd hold up, i think itd be a much safer bet going with your composite tip or a new metal one as they have been proven.
Are you going to use an ablative? Or do you think that the g11 will protect it?

No ablative. I actually thought that maybe "No Habla...tive" might be a funny name for the rocket.

I feel that the max service temps of the G11, prepreg and high temp epoxy will be greater than and aerodynamic heating.

 

[OverTheTop]

Nice project here!

The spec sheet for the SLA resin gives you the rated temperature and you can calculate the total temperature at the tip to see what margin you have. There are some really great resins out nowadays.

You may want to consider a slightly blunter tip that might stand up to the flight stresses more predictably.

 

[AeroAggie]

Well done, Scott! Where do you plan to launch from? I have a very similar project coming together slowly. Would be awesome to see a couple of these go off back to back if the timing is right (who knows what 2021 holds in store...).

 

[steveh.jae]

The thought has crossed my mind. Usually rockets that go this fast are pretty much single use. Or at least the Mach rash puts a serious damper on their aerodynamics. But I'm encouraged by what I say with the nosecone on the L-1040 flight. So we'll see. I'm getting pretty fast at making these parts, so even if it's not so pretty when it comes back, a reflight on the M still isn't out of the question.

Do Mach+ flights fray the high heat carbon fiber plate?

 

[Zertyme]

Subscribed!
Are you still using the same roll of TenCate M40JB prepreg? Have you noticed any change in the stiffness/tackiness of the prepreg after all those years?

 

[Nytrunner]

Do Mach+ flights fray the high heat carbon fiber plate?

Below ~M2.5-2.7, not really. Above that, chances increase

 

[pbahorich]

No ablative. I actually thought that maybe "No Habla...tive" might be a funny name for the rocket.

I feel that the max service temps of the G11, prepreg and high temp epoxy will be greater than and aerodynamic heating.

Have you calculated the stagnation temperature at that Mach number to see what the aerodynamic heating could be?

 

[watheyak]

They just keep getting better and better!
Now, about those recoveries.....

Thanks Wayne!

So next launch I'm gonna fly an EZI-65 on motor eject for mojo replenishment! Much needed. I'm pretty excited about it, actually.

Also, I'm hoping I got all the kinks worked out of this particular system. It was such a fluky thing that caused the "half-eject" last launch.

 

[steveh.jae]

Below ~M2.5-2.7, not really. Above that, chances increase

Thanks

 

[watheyak]

Well done, Scott! Where do you plan to launch from? I have a very similar project coming together slowly. Would be awesome to see a couple of these go off back to back if the timing is right (who knows what 2021 holds in store...).

If it's done in time, it will fly at the January TRAPHX launch here in Phoenix. We'll see how much I can get accomplished before then.

 

[watheyak]

Nice project here!

The spec sheet for the SLA resin gives you the rated temperature and you can calculate the total temperature at the tip to see what margin you have. There are some really great resins out nowadays.

You may want to consider a slightly blunter tip that might stand up to the flight stresses more predictably.

Thanks!

I think you're right, the tip came out a bit thinner than it looked on the screen. It might not even survive the ride to the launch site, lol.

 

[watheyak]

Have you calculated the stagnation temperature at that Mach number to see what the aerodynamic heating could be?

Well, no, not exactly. Years ago there was quite a bit of discussion about this surrounding some other rockets expected to reach high Mach numbers. Some other discussions were had with engineering types I know personally. Math was even done, I think. A ballpark figure of just over 300°F was decided in both cases if I remember correctly. Possibly as much as 350°F for a very short time.

Perhaps it's time I revisit this for real. I am not an engineer, I'm a pilot. We're practically forbidden from doing any math that doesn't involve a 3:1 ratio. But I do have an understanding of the variables involved. I suppose we need to know airspeed, air density, air temperature. Boil all that down to true airspeed? Reynolds number? Then material comes into play, correct?

There is also a calculator that's been around for a while. It seems to spit out some things that don't make a ton of sense to my pilot brain. It also seems to come up with unusually high numbers.

https://www.aerospaceweb.org/design/scripts/atmosphere/

I would appreciate and pointers from anyone who is familiar with what's involved, and has the patience for a little hand-holding to guide me through this.