Workbench 2.0, Two-Stage 100K+ Build Thread and More

BDB said:

Looks great! Do you think heat from the engine would be a problem for the electronics (or possibly melting the mounts, if you made them out of PLA)?

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I don't think so as long as there's an air gap between the forward closure and the PLA material.

You could do a heat transfer calc or just tape some PLA to the forward closure of your next flight. Be sure to share your results if you do!

Ok I will post about the interstage tonight.

Recently, I have been focusing on the design of a new pad and picking a new first stage motor given the situation at CTI.

The motor picked for this flight is an N2501 from CTI. It is by no means an amazing motor when looking at its relatively low ISP of 180s. But it makes makes up for it with total impulse by maxing out 15,300Ns 6G case. It also has good peak thrust of 800lbf and a decent burn time of 6 seconds. These attributes make it the best option for a first stage motor.

The options from Aerotech are not as appealing to me. The 6G motors available from Aerotech are:
N1000 (take off thrust too low even at 10:1 ratio risking off vertical flight)
N2000 (low total impulse 1900Ns less than the CTI N2501)
N3300 (short burn, 1200Ns less impulse)

Both the N2000 and N3300 give me 15-20k less altitude than the original CTI N2501. I hear Aerotech is coming out with some new products this summer so maybe the options will expand.

Hi Kip,

One possibility might be the Loki Research N-4550 Blue. According to the Loki FB page: "It was about 16,600Ns stuffed into a 98/12,500 case with 7,295g of propellant".

It was pretty wicked in person, I can tell you that!

ChuckH said:

Hi Kip,

One possibility might be the Loki Research N-4550 Blue. According to the Loki FB page: "It was about 16,600Ns stuffed into a 98/12,500 case with 7,295g of propellant".

It was pretty wicked in person, I can tell you that!

Click to expand...

Wow that could work! But I checked their Facebook and didn't see anything regarding that motor. If only I had Loki hardware...

I'm guessing an ISP of around 230s (impressive), burn time of 3.5 sec.

Kip_Daugirdas said:

Wow that could work! But I checked their Facebook and didn't see anything regarding that motor. If only I had Loki hardware...

I'm guessing an ISP of around 230s (impressive), burn time of 3.5 sec.

Click to expand...

It flew at Airfest last year so the post was from September 18:

https://www.facebook.com/plugins/po...cebook.com/LokiResearch/posts/412021975653958

Kip_Daugirdas said:

Ok I will post about the interstage tonight.

Recently, I have been focusing on the design of a new pad and picking a new first stage motor given the situation at CTI.

The motor picked for this flight is an N2501 from CTI. It is by no means an amazing motor when looking at its relatively low ISP of 180s. But it makes makes up for it with total impulse by maxing out 15,300Ns 6G case. It also has good peak thrust of 800lbf and a decent burn time of 6 seconds. These attributes make it the best option for a first stage motor.

The options from Aerotech are not as appealing to me. The 6G motors available from Aerotech are:
N1000 (take off thrust too low even at 10:1 ratio risking off vertical flight)
N2000 (low total impulse 1900Ns less than the CTI N2501)
N3300 (short burn, 1200Ns less impulse)

Both the N2000 and N3300 give me 15-20k less altitude than the original CTI N2501. I hear Aerotech is coming out with some new products this summer so maybe the options will expand.

Click to expand...

The N1000 is an amazing motor and more than capable of boosting a 4in/3in two stage over 100k. In fact it was ripping off rail buttons, sending the whole deal off vertical, and still topped 100k, estimating over 125k for a straight flight. That same group is trying an N3300 booster too but has yet to have a successful flight with that configuration. Altitude is not expected to drop too much but we will see. The N2000, I would probably avoid.

There is also a 98mm single use O, which is reportedly 55 inches long, but certification is taking a while. I believe any other N reloads will not happen until that one is on the market.

The N1000 is tempting.

But I'm worried about gravity turning/weather cocking for these reasons:
1) Lower peak thrust at takeoff makes the rocket more sensitive to wind.
2) Gravity turning. The longer the entire stack is in flight the more prone it is to this phenomenon. Any slop between stages or bending of the airframe can initiate a turn or worse prolong a turn pushing the flight further from vertical.

I feel much better dumping the booster ASAP and coasting with the sustainer to the same altitude that the N1000 would've pushed me. I have momentum on my side (heavy upper stage due to loaded motor), drag is cut in half and the upper stage is short and stout (reducing any impulses to initiate a g-turn). I'm 80% confident this is the right approach. Particularly after my "dart" flight with this rocket last year. But I could be persuaded otherwise.

Note: I have a narrow off vertical angle to stay within (+\-15 deg) otherwise I'll have staging lockout.

I heard Aeropac switched to N3300 too...I'm guessing for the reasons stated above?

Kip_Daugirdas said:

The N1000 is tempting.

But I'm worried about gravity turning/weather cocking for these reasons:
1) Lower peak thrust at takeoff makes the rocket more sensitive to wind.
2) Gravity turning. The longer the entire stack is in flight the more prone it is to this phenomenon. Any slop between stages or bending of the airframe can initiate a turn or worse prolong a turn pushing the flight further from vertical.

I feel much better dumping the booster ASAP and coasting with the sustainer to the same altitude that the N1000 would've pushed me. I have momentum on my side (heavy upper stage due to loaded motor), drag is cut in half and the upper stage is short and stout (reducing any impulses to initiate a g-turn). I'm 80% confident this is the right approach. Particularly after my "dart" flight with this rocket last year. But I could be persuaded otherwise.

Note: I have a narrow off vertical angle to stay within (+\-15 deg) otherwise I'll have staging lockout.

I heard Aeropac switched to N3300 too...I'm guessing for the reasons stated above?

Click to expand...

I meant to say, sorry if any of that sounded like me telling you what to do. That was not my intent at all, only trying to share my experiences.

Honestly a big part of their interest in the N3300 over N1000 is simply cost. The belief was that coasting with all that weight, the higher speed would likely yield similar results. Sadly this is still unknown as the last flight in that configuration resulted in a corkscrewing sustainer. It is important to remember that one of the core goals of the project is repeatable flights for payloads at modest costs, so knocking $100 off a motor is significant especially for the school and nonprofit interests.

One of the central beliefs of the project is that going too fast, too low, kills performance. Get up a bit higher, the air thins, and higher speed has higher coasting reward. So the N3300 curve bulging in the middle still offers some of the N1000 benefit, but like I said the theory still needs to be verified!

Have you compared liftoff weight with theirs? I am looking at about 61lbs depending on motor choice. Oh, and I like that 15 degree staging lockout.

watermelonman said:

I meant to say, sorry if any of that sounded like me telling you what to do. That was not my intent at all, only trying to share my experiences.

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No you're good I didn't take it that way at all I do agree that flying a long-burn motor gets you more altitude because you minimize drag but the primary benefit comes at the sustainer motor and not so much at the booster.

I ran a few combinations of motors in RASAero II for my rocket:
N1000 to M685, 135,123 ft
N3300 to M685, 128,452 ft
N1000 to M1850, 111,841 ft

The difference between using an N3300 versus an N1000 (both 14K Ns motors) with an M685 sustainer is only 6,500 ft. Whereas if I flew the N1000 and switched my sustainer motor to a M1850 (a shorter burn 7.5K Ns motor) I loose 23,000 ft in altitude.

If I was counting dollars, I'd fly a N2501 (same price as a N3300):
N2501 to M685, 143,690 ft

Loaded the rocket is 56.7 lbs on an N3300 and 58.25 lbs with an N1000. A touch lighter, but I don't know if that savings is at the booster or sustainer stages. I've convinced myself into a N3300 which I will purchase if CTI's production line is still affected come mid-August.

Awesome, sounds like you have a great plan! I have to admit, I want an N2501 too. Hopefully the limited production they mentioned this morning starts with the classics and whites.

Yes, the altitude to speed ratio is way more important for the sustainer, but has kind of remained a mantra for the group. Next chance I will get some more specific weight breakdowns and we can compare. I am definitely interested in where the extra pounds went, as the basic materials and techniques all look the same.

Kip,

How high would your two stager on an N2000 to an M685? Not sure why the N2000 would not be a good choice for a booster motor considering current CTI availability.

Thank you,

rfjustin said:

Kip,

How high would your two stager on an N2000 to an M685? Not sure why the N2000 would not be a good choice for a booster motor considering current CTI availability.

Thank you,

Click to expand...

N2000 to M685: 122,854 ft

watermelonman said:

Hopefully the limited production they mentioned this morning starts with the classics and whites.

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Where did you hear such wonderful news?!

Kip_Daugirdas said:

Where did you hear such wonderful news?!

Click to expand...

https://drive.google.com/file/d/0B61IjVuE29dETURvaXdQRHNULTg/view?pref=2&pli=1

Interstage:
The interstage is pretty simple. It houses no electronics and it's basically two concentric tubes with an aerodynamic transition.

The internal tube was rolled on a 75mm casing using the method Jim Jarvis outlined in one of his tutorials. The reason why I made a custom tube was for a tight fit between the interstage and the sustainer (5.5" of upper stage motor casing slides into the interstage).


The outside tube is a filament wound carbon fiber coupler. I went with carbon because I had one laying around and it was a tight fit with the booster airframe. ~.002" undersized.

The motor mount tube was centered using plywood centering rings. The aft ring has a fiberglass ring glued to it with four 6-32 PEM nuts pressed in for retaining the aft bulkplate. The centering rings were machined on the CNC using Finnish plywood which is more dimensionally stable and flatter than Baltic birch.



The aft bulkplate is machined out of .250" thick G-10. Mounted to it is the PVC stage separation BP canister and the rope-guide recovery anchor.


The transition is machined out of aluminum and bonded to the interstage. I stepped the transition with 100 iterations. It turned out okay (see pic below). I was in a rush and had to nail this part the first time so I did not attempt offsetting the tailstock to machine the taper. But the result would've been much nicer.


All in all the interstage weighs 1.5 lbs And is a huge improvement over the outdated one I made 10 years ago on the left in the pic below.


Next up: Sustainer avionics
Followed payload bay and recovery setup.

Question to those following this thread:

How fast has anyone pushed HTR-212 laminating resin?

I ask because I have time this summer to apply Cotronics to the leading edges but I'm trying to determine if it's even necessary. HTR is good to 300F.

In your answers please state the peak velocity, what altitude it occurred, fin thickness and leading edge shape (angle if wedge airfoil).

Thanks for the help/insight!

Kip_Daugirdas said:

Question to those following this thread:

How fast has anyone pushed HTR-212 laminating resin?

I ask because I have time this summer to apply Cotronics to the leading edges but I'm trying to determine if it's even necessary. HTR is good to 300F.

In your answers please state the peak velocity, what altitude it occurred, fin thickness and leading edge shape (angle if wedge airfoil).

Thanks for the help/insight!

Click to expand...

I'll be pushing it to M3.5-4 at Balls this year. However, it's under a layer of ablative. Its my opinion that it's better to properly protect your layup then just selecting a high heat epoxy and hoping for the best. Clay (from Bountiful) uses it and he's about to go out and fly some fast stuff with it in a few weeks. (M3+ territory)

Alex

How are you bonding the aluminum transition to the remainder of the assembly?

Random Flying Object said:

How are you bonding the aluminum transition to the remainder of the assembly?

Click to expand...

First thing first, I put down a veil of thin 3oz fiberglass on all carbon surfaces that were going to be bonded to the aluminum. This was to ensure galvanic corrosion wouldn't occur. I machined the aluminum after doing this to ensure a proper fit.

I cleaned the aluminum with denatured alcohol. Surface prepped the bonding surfaces of the aluminum with 220 grit sandpaper and scored the bonding surfaces with a couple passes of 60 grit then cleaned again with denatured alcohol. The carbon coupler tubes were prepped the same way. I made sure to bond the parts within 20 minutes of prepping to avoid oxidation issues with the aluminum. I used Aeropoxy ES6209 structural adhesive.

Be careful with this stuff it's thick like cold maple syrup and doesn't let air pockets to easily escape. I had to drill a few holes in the coupler centering ring to help the trapped air escape while sliding the aluminum transition on. The aluminum transition has a jog in the bonded surface where it goes from 3" to 4" and this creates an air seal with thick epoxy. The trapped air doesn't allow you to fully seat the transition down no matter how hard you push.

Also when parts are taking a high shear load, make sure you have around .010" of play so you can get a proper bond line thickness of .005" all the way around for maximum strength. If your bond line is too thin (<.002) or too thick (>.015) bond strength drops off quickly!

Aksrockets said:

I'll be pushing it to M3.5-4 at Balls this year. However, it's under a layer of ablative. Its my opinion that it's better to properly protect your layup then just selecting a high heat epoxy and hoping for the best. Clay (from Bountiful) uses it and he's about to go out and fly some fast stuff with it in a few weeks. (M3+ territory)

Alex

Click to expand...

I have never used ablative, do you reapply it between flights? Does it chip or crack easily on landing? If I get the sustainer back after the first flight, I want to re-prep and fly again the next day.

Is Clay (we haven't met) flying with HTR bare and no coatings?

Thanks! -kip

Kip_Daugirdas said:

First thing first, I put down a veil of thin 3oz fiberglass on all carbon surfaces that were going to be bonded to the aluminum. This was to ensure galvanic corrosion wouldn't occur. I machined the aluminum after doing this to ensure a proper fit.

I cleaned the aluminum with denatured alcohol. Surface prepped the bonding surfaces of the aluminum with 220 grit sandpaper and scored the bonding surfaces with a couple passes of 60 grit then cleaned again with denatured alcohol. The carbon coupler tubes were prepped the same way. I made sure to bond the parts within 20 minutes of prepping to avoid oxidation issues with the aluminum. I used Aeropoxy ES6209 structural adhesive.

Be careful with this stuff it's thick like cold maple syrup and doesn't let air pockets to easily escape. I had to drill a few holes in the coupler centering ring to help the trapped air escape while sliding the aluminum transition on. The aluminum transition has a jog in the bonded surface where it goes from 3" to 4" and this creates an air seal with thick epoxy. The trapped air doesn't allow you to fully seat the transition down no matter how hard you push.

Also when parts are taking a high shear load, make sure you have around .010" of play so you can get a proper bond line thickness of .005" all the way around for maximum strength. If your bond line is too thin (<.002) or too thick (>.015) bond strength drops off quickly!

Click to expand...

If you run in to a situation were you need to bond a metal to a composite on future projects I have an alternative for you. I can apply a conversion coating to your aluminum part that will allow the use of thinner epoxy systems, prevent the need for abrasion and greatly increase shear strength.

Sustainer Avionics:
2 Altus Metrum Easy Megas
1 Rocket Hunter Transmitter

I like using CAD to optimize the electronics layout and keep things short.




The Easy Megas use two lipo batteries each. One for pyro and the other to run the board. The rocket hunter is mounted in the same carrier/mount as the batteries. The carrier was 3D printed.

Pictures speak louder than words so I will just post those.

Payload:
- Two GoPro Hero 2s one taking 940p video and the other camera was taking an 11 megapixel picture every second after liftoff.
- Beeline GPS for tracking
- Arduino setup to run the time lapse GoPro.
- High altitude charge canister 1/4" NPT tubing screwed into the aluminum aft bulk head.

CAD:

Alright time to get this guy ready to fly. Two things need to get done.

1.) Cotronics leading edge cap on sustainer
2.) Repaint sustainer airframe (fins remain naked) with high temp Rustoleum.

I decided I would experiment with a Cotronics 4525 cap on the leading edge. To make the wedge I'm using the method Jim outlined in his 3 stage thread. Tonight I did a test fin to try out the method which is using two sheets of Mylar to make a wedge. My airfoil given my super thin fins is not the regular 10 deg but closer to 5 deg...so quite sharp. When using his method I had issues keeping the Mylar in the wedge shape - it kept wanting to flatten out. So I forced it into a wedge by adding some masking tape over the top of the two pieces to keep them together. Not sure if this is going to work but it looks ok. Any suggestions? Not sure how I am going to make the nice transition from the cap to the fillet either at the moment.


Test fin

I'm still debating if this cap is even necessary. The rocket will be pushing Mach 3 at around 30k ft and the fin profile is already thinner than most rockets of this type. So high altitude coupled with thin cross section = less drag and less heat.

Max thickness towards the middle of the fin.

Right behind the wedge.

We'll see how the test fin turns out tomorrow. Till then I'll think of better ways for doing this.

I have done quite a few rockets where the cotronics is just painted on instead of built up. That would be much easier for you and take less time. You might paint on three thin layers going a little further past the leading edge each time - maybe 1/8, 3/16, 1/4. Sand each layer lightly and carefully, and before it gets too set up (it's a pain to sand once fully cured). You can wipe on a little laminating epoxy at the end if you want it to look nice. Be sure to give it a heat cure before you fly. A version of the method was in my Part 1 article.

https://www.rocketryfiles.com/files/Technicalarticles/Jim Jarvis Carbon-Tutorial/carbon-guide.pdf

Jim

Thanks Jim, I'm likely just going to go the paint-on route.

It says to post cure at 250F one hour and 1 hr at 350F. I wouldn't want to push my oven much past 200. What did you post cure at Jim?

Kip_Daugirdas said:

Thanks Jim, I'm likely just going to go the paint-on route.

It says to post cure at 250F one hour and 1 hr at 350F. I wouldn't want to push my oven much past 200. What did you post cure at Jim?

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Actually, my oven only goes to 200. I found out once, though, that if you don't post cure, the epoxy won't hold up at all.

Jim

JimJarvis50 said:

Actually, my oven only goes to 200. I found out once, though, that if you don't post cure, the epoxy won't hold up at all.

Jim

Click to expand...

So I'll do a 1hr hold at 150 and a 1 hr hold at 200?

Kip_Daugirdas said:

So I'll do a 1hr hold at 150 and a 1 hr hold at 200?

Click to expand...

I'd probably let it cook for a bit longer.

Jim

MarkH said:

Look at some of Nic Lottering's flights, I think that is his name, goes by cryoscum on the Autralian rocketry forum. He has had some mach 3+ flights with no coatings other than 2k urethane automotive paint, with barely any damage to the fin can. I think the hardness of the paint is key, and it is the sand blasting effect of the air and not so much the heat, that abrades the fin can at these moderately high mach 3 speeds.

I was going to test that theory with a M2245 MD flight with 2k paint this year at XPRS, but my motor purchase fell through. I flew nearly the same rocket on an M2245 to about mach 2.9 last year at Aeronaut with only bare cotronics 4461 and header paint, and it got abraded pretty badly.

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Mark thanks for the data point this kind of stuff is very useful! What got abraded bad the paint or the Cotronics? What altitude did the rocket hit M 2.9? Fin thickness? I think this info will really help peeps designing. Thanks in advance!