New (and first) 2 stage rocket - Looking for advice as we move along.

[Chad]

Second flight went a bit better. Booster recovery strategy was better and seems to work good. Probably going to shelve it until LDRS.

hey what did you use for adding the velocity and altitude gauge on your video?

 

[BABAR]

Congrats on a second successful flight!
Great video too

 

[BryRocket]

hey what did you use for adding the velocity and altitude gauge on your video?

Hey there, I use RaceRender 3 on my MAC. It isn't the greatest, but gets the job done.

 

[tollyman]

I am going to use a StrattologgerCF to handle the cute deploy on the booster and I'll have a chute release on that. I also stuck a spare EggFinderTX in it as well. **Neat find: If you set the Strattologger's main deploy altitude to something greater than will be achieved, it will fire at 1 sec after apogee.** So, I have two charges, one set at apogee (Drouge) and the other set at 9999' (Main). This should fire each at apogee but one with a 1s delay. That is my only redundancy for the booster. 1 computer, 1 battery but 2 chances to fire the deploy.

There is some serious epoxy going on in the IC that you'll notice. That is to hold the bulkplate in place. I've blown coupler bulkplates out with charges on my pistons in the past so I went a little crazy here hoping to prevent that.

I was always targeting a static stability of 2.5ish for the whole stack but I had designed it around using 2 CTI 4 grain motors. An interesting oversight on my part was the stability once I used a heavy 75mm CTI motor in the booster and then a lighter 2 grain 54mm in the sustainer. It was back heavy and the stability fell to below 2 (I think it was ~1.8-1.9). So, we get creative. I am using a 2 grain 54mm motor in a 4 grain case with 2 spacers and an Aeropack MD Fwd Closure adapter. I'm pretty sure it accepts 5/16th threads. I was already planning to use this for providing the forward retention of the motor into the sustainer. I ended up make a few ~550g weights out of the CTI 54mm packaging, some lead shot and aeropoxy with a plastic center tube. I was able to bolt these onto the all thread supplying the forward retention to simulate a larger motor and manipulate the sustainer's (and ultimately whole stack's) weight and CG. This moved loaded stack to 2.26 and the sustainer to 3.19. It will work much easier when I get to using 2 larger motors of the same weight. In the picture you'll see two weights. I ultimately went with just one. Two improved the stability even further but hey, we do still have to go high right? If I had planned better I guess I could have added both and went with a 3 grain 54mm for the sustainer. Here are some photos of that:

View attachment 357761 View attachment 357762 View attachment 357763 View attachment 357764 View attachment 357765 View attachment 357766

A stratologgers can also be directly programmed to have an apogee delay without having to set an altitude higher than what you will achieve. This will also result in a long constsnt beep during the start up sequence. I know this is an older post but thought id give my 2 cents. Im looking at making a 2 stage as well and this is a very good reference for me, thank you.

 

[BryRocket]

A stratologgers can also be directly programmed to have an apogee delay without having to set an altitude higher than what you will achieve. This will also result in a long constsnt beep during the start up sequence. I know this is an older post but thought id give my 2 cents. Im looking at making a 2 stage as well and this is a very good reference for me, thank you.

Hey there!

Yep, I use the programmable apogee delay on my SLs that are used as a backup in the sustainer. With the booster, I was trying to get 2 separate charges to fire with one SL. For this to work correctly, I set the main to an unattainable altitude. On this channel, it will fire at apogee with a 1 second delay. Thus, you get get one charge go off at apogee (from the apogee channel with no delay) and then you will get a second charge (from the Main channel) one second later. Not totally redundancy but it gives me a little extra protection.

 

[tollyman]

Hey there!

Yep, I use the programmable apogee delay on my SLs that are used as a backup in the sustainer. With the booster, I was trying to get 2 separate charges to fire with one SL. For this to work correctly, I set the main to an unattainable altitude. On this channel, it will fire at apogee with a 1 second delay. Thus, you get get one charge go off at apogee (from the apogee channel with no delay) and then you will get a second charge (from the Main channel) one second later. Not totally redundancy but it gives me a little extra protection.

I misunderstood what you were doing with the stratologger. That is actually really smart! Little bit of a loophole but hey whatever works. Have you done that method reliably? I didn't realize that stratologgers had that backup. IIRC stratologgers can only have drogue programmed to 9999ft as you had it, so a project over 10kft wouldn't work for this application as a 1s delay.

 

[BryRocket]

I misunderstood what you were doing with the stratologger. That is actually really smart! Little bit of a loophole but hey whatever works. Have you done that method reliably? I didn't realize that stratologgers had that backup. IIRC stratologgers can only have drogue programmed to 9999ft as you had it, so a project over 10kft wouldn't work for this application as a 1s delay.

I have used this method reliably two times.

You are correct, the max main altitude you can set is 9999’ so if your booster was to go higher than that, say 11k, you would get your drogue charge fired at apogee and then your main “backup” at 9999’. I’m flying it at LDRS with an M1540 in the booster and if I fire the stage separation charge at 1 second after burnout the booster shouldn’t go much higher than 8k’.

 

[BryRocket]

A few updates to wrap this thread up:

As mentioned, I had intended to prep this thing for LDRS. Prior to leaving, I met with Jim Jarvis again and we talked about the flight. As he was looking over everything he had some concern about the possibility of fin flutter and mid-flight disassembly of the sustainer if I approached the simulated velocities. We talked about a few different strategies. One being to cut some of the fin span off and the other being to do some type of reinforcement or lamination over the fins. Keep in mind that the rocket is fully painted and this is late Sunday night and I was set to leave Thursday mid-day for Kansas. And I have a real job and family. I really didn't want to cut some of the span off since it would compromise the stability of the rocket when used as a single stage (it didn't really change much as a stack and for this flight) but it seemed like the easiest to do with my time constraints. I didn't sleep all that good that night as I just pictured this thing coming unraveled in a few days. So, I grabbed the 80 grit sandpaper and went to town on the fin can and committed myself to the lamination process. I talked with Jim again and he gave me some great tips and pointers on how to go about this process to do it efficiently and to prevent delamination at high velocity. I have some experience with building carbon tubes and T2T applications and had everything on hand. The following pictures are from the modification. I didn't do a true T2T. I stopped about an inch short of the bevel so I could lay down some epoxy to the bevel and then smooth it all together. I managed to get the fin can sanded, cleaned and fully laminated that night on Monday. I let it cure in my car (Austin Texas where it was 101 outside) on Tuesday and then got it cleaned and painted. It felt MUCH stronger and I felt better about its chances of survival. It was a bit rushed so it isn't beautiful and the rocket didn't disassemble so I'm really glad Jim made the recommendation and that I had time to do it.

 

[BryRocket]

And lastly, the video of the flight. Very grateful to Jim for his help. It appears I started this project about 18-19 months ago and it has been a great learning experience. And how wonderful was LDRS!? Now on to the next project

 

[BryRocket]

Here are the other details and logic for the staging.

I wanted the sustainer ignition to be at 7 seconds after the booster burnout (4.5seconds). I assumed that the motor would take around 2 seconds to come up to pressure and ignite. This made my target for initiation of the igniter to be at 9.5 seconds. Simulation showed that the rocket would be at 6100' at 9.5 seconds so I programmed the Raven to fire there. My safety check was putting a qualifier that this altitude is reached in less than 11 seconds, giving myself a 1.5 second buffer. The rocket hit 6100' at 10.05 seconds and full pressurization was at 11.20 seconds where it responded with 20Gs of acceleration to Mach 1.7. Channel 3 was for the separation charge and channel 4 was for the staging.

 

[Cameron Anderson]

Congrats!
Great thread - I have been following for a while and it was great to see it all.

 

[Tobor]

Congratulations and well done.