First Attempt at 2 Stage HPR

[cthunter01]

I've built LPR multistage rockets that use Estes black powder motors before, but never anything at the mid or high power level that utilize composite motors. I enjoy launching multistage rockets, and enjoy building and flying HPR rockets, but have never combined the two before and would like to attempt that this year.

I've been working on a design for a 3 inch diameter 2-stage rocket with 38mm motor mounts in both stages, and would appreciate some feedback on what I've come up with so far. I'm attaching an OpenRocket design file with a few motor configurations as well. My local club has a waiver to 12k ft, and there are a few clubs a little further away with higher waivers if lower flights are all successful and I'm feeling adventurous.

Here are some extra data points about this design:

1. I would like to use a small BP charge to separate the stages about 1 second after 1st stage burnout. I would do it at first stage burnout except that I want to account for any residual thrust from the booster motor so as to not run into the sustainer after separation. I plan on using a Missileworks RRC2L as a timer (because I already have a couple, but thoughts on something better are welcome) in the booster to control that separation, as well as deploy the booster parachute at apogee. Motor deploy can be a backup to deploy the parachute if something happens with the electronics.

2. The sustainer will be have a redundant DD setup for recovery. I plan to use the Aux channel on a Missileworks RRC3 to ignite the sustainer motor a few seconds after the booster burns out and separates. Then use the main and drogue channels for DD. The backup will be a Missileworks RRC2.

3. I initially thought about using drag separation, but after searching the forums it didn't seem reliable. So I decided to use a small BP charge to separate them, and can use some shear pins to hold the stages together during boost.

4. The sustainer can be flown on its own.

5. The parachutes in the design file are just to get the descent speeds approximately right. If you have thoughts on specific parachutes or whatnot that would be great.

6. I'm using lipo batteries for the electronics.

7. Do you have any pointers on specific igniters?

 

[cthunter01]

To add, I have a JLCR I can put on the booster parachute so it doesn’t drift too far. I may need to upsize the sustainer main chute to account for the possibility that the booster doesn’t separate and the whole assembly comes down in one piece safely

 

[boatgeek]

Reviewing the Eggtimer Proton/Quantum airstarts guide is pretty helpful even if you're not using their products. They have some pretty good guidance on motor selection, settings, etc. My advice below is based on relatively limited experience, but it worked for me. For my first couple of flights, I wasn't really seeking altitude so I had the separation charge at 0.5s after burnout and sustainer ignition 0.5s after that. My booster motor was a fast-shutoff motor that didn't have a long tail on the thrust curve so I wasn't too worried about thrust continuing for longer.

1. I think the separation charge is a good idea. I didn't get drag separation on mine before the separation charge went.
2. Sounds good.
3. I wouldn't include shear pins mainly because that's one more thing to do at the pad and the consequences of early separation are minimal. You won't be able to put your igniter in until you get out to the pad area (or other remote prep area), so you'll need to take your booster off for prep. It's always a hassle getting things lined up in the field. Worst case is that you do get drag separation and the separation charge doesn't do anything. If you don't have shear pins, the separation charge can be very small as well.
4. That's a nice feature.
5. What's your ground hit speed for both stages separately and the stages together under the main?
6. Seems legit.
7. I used CTI motors, so the supplied ematch was plenty.

 

[mikec]

7. I used CTI motors, so the supplied ematch was plenty.

+1. There are many ways to make AT motors work (you probably can't use stock AT igniters because they use a lot of current, so you need something lower-current but with enough oomph to work) but the CTI motors just come that way standard.

 

[waltr]

Reading the Eggtimer air start manuals is a good idea since Cris goes over a lot of what if's and how to's that can be applied regardless of which computer used.
Agree with every thing baotgeek posted.

Also, there are a number of good threads discussing air starts here in this forum topic. All worth reading and many cover various safety aspects of setting up an air start 2 stage at the range.

I have been using AT motors so make igiters using 40ga nichrome and Quickburst Procast. A 2S LiPo easily fires these but did have one flight where the sustainer took 4 seconds to come up to pressure, By them the rocket peaked and nosed over. Sustained properled the down down through a tree. Not pretty. Velocity, altitude or tilt lock-outs would not have prevented this since the igniter fired at the correct time with rocket pointed up.

 

[cthunter01]

Thanks for the feedback and info!

I'm checking out the Eggtimer documentation, which is quite good. I may look into actually getting a Proton in the future, as it looks pretty capable, and the the wifi arming is quite nice. And I like the idea of soldering it together myself, sounds fun.

I'm targeting a ground hit velocity of between 4 and 5 m/s. Right now they're at 4.7 m/s or so each. That's nominal however, not if the booster is still attached to the sustainer. If that happens then for sure it'd hit faster, and I'll have to go back and sim that. I'll upsize the sustainer main to account for that possibility.

And good call on the shear pins with the interstage coupler. I don't think they're necessary, so I won't use them. I still do like the idea of the stages staying together until I intentionally separate them though. Maybe that's me being overly concerned. What are your thoughts on using some masking tape on the ISC to provide that fit, like you might do with a nosecone?

I have been using AT motors so make igiters using 40ga nichrome and Quickburst Procast. A 2S LiPo easily fires these but did have one flight where the sustainer took 4 seconds to come up to pressure, By them the rocket peaked and nosed over. Sustained properled the down down through a tree. Not pretty. Velocity, altitude or tilt lock-outs would not have prevented this since the igniter fired at the correct time with rocket pointed up.

That's my biggest concern honestly. And why I asked about igniters specifically. I plan on using CTI hardware, but I've still had motors take several seconds to come up to pressure on the pad on the ground, which I really don't want to happen in the air.

 

[waltr]

The best thing is to have plenty of air speed at 1st stage burn out. This helps ensure the rocket maintains an upward vector until 2nd stage motor comes up to pressure.
Starting with minimum delay is good until you get a good feel for what the rocket will do.
When you run simulations, try longer delays to 2nd stage ignition to check this. Look at velocity.

If the booster motor burns out then the stages can separate without issues. It is rare to drag separate so do not think this should be a concern.
Greater concern is ensure recovery deploys on each stage even when separation or ignition does not go as planned.
My last 2-stage flight the Proton did not fire the igniter but did fire separation charge. Booster deployed chute and the drogue then main deployed on the sustainer. Disappointing flight but all parts came down safely.

CTI motors are a favorite for upper stages since then use an Ematch and a starter pellet is in the propellant core.

I have been running a D15 in the sustainer, G74 in booster. We have a smallish field and my biggest worry is the sustain fires with rocket horizontal which then flies into the next county. Maybe run a very small motor in 2nd stage. since it already has air speed you don't need a lot of thrust in the 2nd stage. Also keeps peak altitude lower.
Again, play with this is the sim.

 

[boatgeek]

Thanks for the feedback and info!

I'm checking out the Eggtimer documentation, which is quite good. I may look into actually getting a Proton in the future, as it looks pretty capable, and the the wifi arming is quite nice. And I like the idea of soldering it together myself, sounds fun.

I'm targeting a ground hit velocity of between 4 and 5 m/s. Right now they're at 4.7 m/s or so each. That's nominal however, not if the booster is still attached to the sustainer. If that happens then for sure it'd hit faster, and I'll have to go back and sim that. I'll upsize the sustainer main to account for that possibility.

And good call on the shear pins with the interstage coupler. I don't think they're necessary, so I won't use them. I still do like the idea of the stages staying together until I intentionally separate them though. Maybe that's me being overly concerned. What are your thoughts on using some masking tape on the ISC to provide that fit, like you might do with a nosecone?


That's my biggest concern honestly. And why I asked about igniters specifically. I plan on using CTI hardware, but I've still had motors take several seconds to come up to pressure on the pad on the ground, which I really don't want to happen in the air.

The Proton is a nice unit. If you haven't soldered before, I'd suggest building a Quark first to gain skills. It's more or less the same price as a learn-to-solder kit and you get a working altimeter out of it. I used the Proton on my 2-stage--you might want to read over my flight programming details if you use a Proton. I had a few kinks that I needed to work out.

4-5 m/s is nice and slow. I wouldn't have too much heartburn about up to 7 m/s unless you're landing on hard surfaces like pavement.

I would use masking tape until it doesn't wobble, but I'm not that concerned about having it tight like a nose cone. If you do that, you'll definitely want to ground test the separation charge.

Somewhere on TRF, Jim Jarvis put together a list of which CTI propellants were easiest to light. IIRC, BT, WT, and RL were high on the list and WH, GR, and SS were lower. That said, 38mm motors seem to come up to pressure pretty fast.

 

[waltr]

A Quark is a good first build and could be used in the booster ISC to have electronic deployment at apogee. Later a Cable Cutter can be used for Main deploy at 600-300 feet.

Have you flown any DD? If not then I recommend build and fly DD the start learning about using electronics for deployment. There is a lot to go wrong with DD and a lot more with air start.

 

[TRWXXA]

Sounds like you're planning A LOT of delay after booster burnout -- 1 sec. for separation charge and "a few seconds" for sustainer ignition.

Remember, that your rocket will be decelerating that whole time, and probably starting to weathervane, before the sustainer ignites. I'd pop that seperation charge right at motor burnout, or at the point just after the simulation shows the rocket ceasing to accelerate. I'd fire the sustainer ignition at that point too, because it's going to take a little time for that motor to come up to pressure.

On my first staged flight I had the upper stage ignition set for 1 sec. after burnout. The nearly 3 second coast I got looked REALLY cool, but it felt like an eternity, as I wached the rocket slow down and start to point upwind. I cut it down to 0 sec. after that.

If you really want altitude, then you'll need to cut down on that delay anyway. Ditch the booster as soon as vertical acceleration goes to zero. I used the sustainer motor as my "speration charge". It'd just singe the paint on the interstage coupler a little.

 

[Jmhepworth]

On your first launch, I suggest you separate about a half second after expected motor burnout. You don’t need to worry about the booster colliding with the sustainer. Also, sheer pins between stages is a bad idea. If you drag separate before the separation charge fires, so what? Because you want to see it all happen, start the sustainer a couple of seconds after motor burnout. That will cost you altitude, but on the first launch you want to see everything happen. You can add coast time later (until you get to the 17 seconds or so that Kip Daugirdiss did on his 293,000 ft flight). If you want to use Aerotech motors, a pyrodex pellet at the top of the sustainer motor increases the likelihood that the sustainer lights. That’s what I do and I’ve lit 100% of my sustainers when the ematch lit. The complexity of a high power two stage is what makes it fun. Make and use a checklist, especially at the pad.

 

[OverTheTop]

Consider using an altimeter with tilt detection. The new Blue Raven looks like a reasonably-priced unit for the capabilities it carries.

https://www.featherweightaltimeters.com/blue-raven-altimeter.html

 

[BABAR]

The new Blue Raven looks like a reasonably-priced unit for the capabilities it carries.

https://www.featherweightaltimeters.com/blue-raven-altimeter.html

This is one of the statements that keeps me very satisfied as an L-0.

 

[OverTheTop]

This is one of the statements that keeps me very satisfied as an L-0.

Why is that?

 

[BABAR]

Why is that?

I have great admiration for HPR rocketeers. Among other things, HPR requires advanced skills in building rockets that handle more stress, often electronics, and most (not all) fly far higher by at least a couple orders of magnitude higher and this require tracking skills and devices (almost certainly in a two stage high power build that would employ this nice and electronic device.) waivers required too. I’m sure there’s far more I’m just ignorant of. All this comes at a far higher cost.

For the $175 for this fantastic altimeter, I can build, finish, motor and fly somewhere between 3 and 8 low power scratch birds, and if I lose one (or more!) for whatever reason I don’t have quite the financial hit. And something tells me the final financial “pad ready cost” for the rocket that uses this will be at least double the cost of the altimeter.

Emphasize this is just the way I personally am wired (or in case of electronics, where for the most part my most advanced device is my Pratt Go-Box ignition system —- “unwired.”)

Everyone in rocketry for an extended period finds the thing or things that “pay off” in satisfaction for the time, mental and physical effort, and $$ for them. Also travel time and costs are likely higher for HPR as the fields are fewer and far between. Having been to one NSL, it was clear from the HPR folks it was a heck of a rush for them to see their birds perform!

For a LPR Odd-Roc fan like me, $175 buys a lot of duct tape and dental floss! And when one of my birds does particularly well I think I get a decent personal fraction of the “HPR rush” feeling at a much lower cost.

Lots of different roads and destinations in rocketry, that’s why we have so many forum subsections.

 

[OverTheTop]

Fair enough. To each their own. Rocketry is a bit like skiing. It doesn't matter how you get down the hill as long as you have fun.

 

[BABAR]

Fair enough. To each their own. Rocketry is a bit like skiing. It doesn't matter how you get down the hill as long as you have fun.

Yeah, but you gotta be safe, too. There are definitely some ways down the hill better than others!

 

[OverTheTop]

Yes, always should do it safely.

I will keep my snowboarder jokes to myself, too.

 

[b.wieting]

I have great admiration for HPR rocketeers. Among other things, HPR requires advanced skills in building rockets that handle more stress, often electronics, and most (not all) fly far higher by at least a couple orders of magnitude higher and this require tracking skills and devices (almost certainly in a two stage high power build that would employ this nice and electronic device.) waivers required too. I’m sure there’s far more I’m just ignorant of. All this comes at a far higher cost.

For the $175 for this fantastic altimeter, I can build, finish, motor and fly somewhere between 3 and 8 low power scratch birds, and if I lose one (or more!) for whatever reason I don’t have quite the financial hit. And something tells me the final financial “pad ready cost” for the rocket that uses this will be at least double the cost of the altimeter.

Emphasize this is just the way I personally am wired (or in case of electronics, where for the most part my most advanced device is my Pratt Go-Box ignition system —- “unwired.”)

Everyone in rocketry for an extended period finds the thing or things that “pay off” in satisfaction for the time, mental and physical effort, and $$ for them. Also travel time and costs are likely higher for HPR as the fields are fewer and far between. Having been to one NSL, it was clear from the HPR folks it was a heck of a rush for them to see their birds perform!

For a LPR Odd-Roc fan like me, $175 buys a lot of duct tape and dental floss! And when one of my birds does particularly well I think I get a decent personal fraction of the “HPR rush” feeling at a much lower cost.

Lots of different roads and destinations in rocketry, that’s why we have so many forum subsections.

I have great admiration for HPR rocketeers. Among other things, HPR requires advanced skills in building rockets that handle more stress, often electronics, and most (not all) fly far higher by at least a couple orders of magnitude higher and this require tracking skills and devices (almost certainly in a two stage high power build that would employ this nice and electronic device.) waivers required too. I’m sure there’s far more I’m just ignorant of. All this comes at a far higher cost.

For the $175 for this fantastic altimeter, I can build, finish, motor and fly somewhere between 3 and 8 low power scratch birds, and if I lose one (or more!) for whatever reason I don’t have quite the financial hit. And something tells me the final financial “pad ready cost” for the rocket that uses this will be at least double the cost of the altimeter.

Emphasize this is just the way I personally am wired (or in case of electronics, where for the most part my most advanced device is my Pratt Go-Box ignition system —- “unwired.”)

Everyone in rocketry for an extended period finds the thing or things that “pay off” in satisfaction for the time, mental and physical effort, and $$ for them. Also travel time and costs are likely higher for HPR as the fields are fewer and far between. Having been to one NSL, it was clear from the HPR folks it was a heck of a rush for them to see their birds perform!

For a LPR Odd-Roc fan like me, $175 buys a lot of duct tape and dental floss! And when one of my birds does particularly well I think I get a decent personal fraction of the “HPR rush” feeling at a much lower cost.

Lots of different roads and destinations in rocketry, that’s why we have so many forum subsections.

I wish Estes still made the Tomcat. Now that I’ve increased the size of the elevators on my (twice repaired) knockoff, I think I’ll risk a flight at Rocstock.