"Deja Vu" - L2100X Submin to Mach 3.6 below 2500' AGL - Apogee at 21,000ft.

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tsbooska

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You already know what time it is. Rabble rouser tsbooska is back at it again with more memes and dreams that have turned into a reality. This one started with @Zertyme from his thread "Gas Gas Gas" - a K17-1800X submin to M3.3ish. I decided to build a version 2 of that rocket, as Julien intentionally left a good bit of safety margin in his design. I wanted to also double down on robust tracking and recovery, to try to get back this... thing... It was successfully flown and recovered at FAR on April 6th, with an apogee of 21,000 feet, and an estimated max speed of Mach 3.6. Videos and photos at the end of the thread.
 
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Next is the front end of the rocket. It features a machined aluminum forward closure that both seals the top of the motor in normal EMK fashio, as well as serving as a conical nose cone coupler, and as recovery packing space. Most of the recovery system packs in the forward closure. The avionics bay is a G10 sled that is attached to the tip using a machined aluminum adapter tip. The kevlar loops through a small hole in the sled. The avionics setup features a Featherweight GPS and an Easymini. My favorite combo.
1712792616993.png
 
I won't go into a ton of detail on the motor, but it's 7 grains of Propellant X in their long 25" EMK, the same case as the L1000 and K455. The first 5 grains are a 3/4" core, and the last two are 1.125. The burn is somewhat progressive, meaning that peak thrust occurs near the end of the burn, where the rocket is lightest.
 
I painted the stack as poorly as I could from an adhesion perspective, to get max mach rash, and loaded it up in the back of my car to bring to FAR!
 

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Prep the night before and morning of went well, and I launched at about 10 AM. The following pictures and videos are from @yellowkazoo , @Brainstormz123 , @vulpesjr , and well, show how FAST this thing went.
 

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Recovery popped as requested, and the main was tangled, which increased the speed from 35 ft/s to 50. Even then, that's a pretty easy and soft landing for this rocket, and it landed completely unharmed, 1.9 miles away. My Mach rash mission was completed, and the rocket now sits as a little memento in my shop/room. As for what's next? Well, the Mach number might just start with a 5.
 

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Congrats on the nominal flight!
Would you mind uploading your CAD design on GrabCad or other platforms so that other people can improve on the design?

One interesting point: for Deja Vu and Gas Gas Gas, the stability margin estimated by OpenRocket was negative near burnout. So here's a "comparison" between multiple simulation tools:
Position of the center of pressure from the nosecone tip at 0° AOA.
1712824535190.png

Cnalpha (Rogers Modified Barrowman in RAS)

1712824892001.png
 
Wow @tsbooska, what an amazing rocket and a great flight !

EDIT: oops ! I just now realized that this Q would be for @Zertyme !

Q: Why do the OpenRocket CP -vs- Mach and CN(a) -vs- Mach cut off at Mach = 3 ?

Do you know if that an inherent OR limitation or is it because the rocket + motor only sim'd to Mach 3 in OR ?

And ( EDIT: a Q for @tsbooska ) ...

I am about to build a primitive test rocket with HED using a Piranha Line Cutter so I can learn the gotchas ...

Q: Were you able to determine what caused your main to tangle ?

Thank you for sharing !

-- kjh
 
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kjhambrick said:
Wow @tsbooska, what an amazing rocket and a great flight !

EDIT: oops ! I just now realized that this Q would be for @Zertyme !

Q: Why do the OpenRocket CP -vs- Mach and CN(a) -vs- Mach cut off at Mach = 3 ?

Do you know if that an inherent OR limitation or is it because the rocket + motor only sim'd to Mach 3 in OR ?

And ( EDIT: a Q for @tsbooska ) ...

I am about to build a primitive test rocket with HED using a Piranha Line Cutter so I can learn the gotchas ...

Q: Were you able to determine what caused your main to tangle ?

Thank you for sharing !

-- kjh
Click to expand...
I took the data point in the components analysis in OR. The mach number slide only goes up Mach 3 and I didn't bother going above using the sim.
 
kjhambrick said:
Wow @tsbooska, what an amazing rocket and a great flight !

EDIT: oops ! I just now realized that this Q would be for @Zertyme !

Q: Why do the OpenRocket CP -vs- Mach and CN(a) -vs- Mach cut off at Mach = 3 ?

Do you know if that an inherent OR limitation or is it because the rocket + motor only sim'd to Mach 3 in OR ?

And ( EDIT: a Q for @tsbooska ) ...

I am about to build a primitive test rocket with HED using a Piranha Line Cutter so I can learn the gotchas ...

Q: Were you able to determine what caused your main to tangle ?

Thank you for sharing !

-- kjh
Click to expand...
So I use piranhas in a pretty weird way. I wrap the chute in a very small thin nomex, then put the piranha over that, then wrap the main nomex over all of that. This is so that it has the main nomex serving as a drogue, and so that it doesn't need to escape the nomex before deploying. In this config, the lines for the main weren't wrapped in the piranha's ziptie, and the ematch wire tangled around the main lines. The main deployed, but was effectively reefed. For next time, I'm going to wrap the main parachute lines in the zip tie as well, to reduce that failure mode, or just switch back to using a drogue, and wrapping the entire burrito of main with the cutter.
 

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