NSL 2024: A 24" Diameter 1/6th SpaceX Dragon Pad Abort Test

[bandman444]

I am very excited to announce an exceptionally cool project that @jpoehlman and I are working on together.

Some may know that I happen to have an affinity for short and fat rockets. A couple years ago I started progress toward a 1/6th scale Falcon 9. Turns out, that is very hard. At over 38ft tall, the structural design to keep it from folding on itself was an intense challenge. A scale model showing internal structure and materials was made 7.5" in diameter, but never flown. I always loved the idea of having a scale capsule with crew seats, cockpit screens, and a couple scale astronauts. With a 360 camera on board it would have been so cool to make happen. But alas, I've got a million other projects in work and so scope was decreased to work on more projects.

That is when the idea of just flying the crew capsule came from. I remember a few years back watching the Pad Abort test and thinking about whether or not a model that shape could be stable. Attached to the trunk it had decently large fins that perhaps could make it stable enough to work.

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Another fact that it had going for it was that the motors were all located on the forward end of the rocket, this would push the center of gravity forward again helping with stability.

With the motors up front, it leaves the back end completely empty and easy enough to make very lightweight.​

Due to my previous work toward a large Falcon 9 model, I found a pretty sweet CAD model of the Dragon and Trunk and it became the basis for the outer design of the rocket.

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I really wanted this to maintain a relatively scale appearance in flight, so an 8 motor cluster was a must have. As you can see, the Super Draco engines are packed 2 wide in 4 separate nacelles. At the moment we are not planning to drill out the locations for the RCS packs, but we will probably paint them in.

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The next major question was how I was going to build it. My mind immediately jumped to 3D printing as a way to get the complex outer shape. Then I would fiberglass it for strength and handling protection.

The trunk section could be made easily from a single piece of 24 inch diameter sonotube.


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That left the major design work to be the motor mounts and Recovery sections. Another particularly challenging element to this project would be the rail guide attachment. Because the rocket is so big in diameter I was worried that we would have a big challenge keeping the rail buttons attached especially if a single motor or two did not light perfectly. That was when I came up with the idea to run a rail through the middle of the rocket you will notice that it is not included in the renderings above as the details are still being worked on.

Two 3d printed sections​

Unfortunately I do not have a 3D printer big enough to print a 24 inch diameter rocket in. So I needed to break the model up into smaller pieces this includes three layers with four pieces per layer, and a single nose cap piece. I brought a couple pieces that I had printed to a local club meeting, and that was when @jpoehlman stepped up and volunteered to help. Little did he know that he was volunteering to join the project and has been instrumental in keeping me focused and a great resource for construction ideas and manufacturing plans.

Notice that you can see the motor mount sections in the second row of pieces.​

After roughly a month of printing time and god knows how many spools of filament, we had completed all of the 3D printed pieces necessary for a majority of the capsule.

This is how most of the mock ups looked like. Since parts were printed on different printers, and using different filament, most joints weren't perfect, but they were generally all good enough without major tweaking.​

 

[bandman444]

Now that 3D printed parts were finished, it was time to assemble the capsule. The first thing we did was CA all of the sections together.

@jpoehlman sliding in another segment ahead of CA gluing.​

Due to warping and other printing irregularities the base was not perfectly circular. To counteract this we glued up the sections around a circular ring form. Which was a leftover test centering ring piece for project Sasquatch made out of MDF.

Me looking very happy with how things are going.​

Do to having all hands on deck for the fiberglassing process, I don't have a lot of pictures of us actually laying up the capsule. However the process we used was pretty straightforward where we used a large piece of butcher paper to create a template of 1/4 the surface. We used the templates to cut out different shaped pieces of fiberglass. After that, we wetted out the fiberglass flat on the table then peeled it up and stuck it to the outside of the rocket. This allowed us to ensure the entire piece of cloth was fully wetted out and made it a lot easier to see when laid flat versus against a white 3D printed shell. After all the fiberglass was applied we squeegeed the vehicle to make sure there were no air pockets and that the fiberglass was flush.

The black sharpie lines are on the fabric to show us where to cut along the template. We then added a couple inches all around to make sure we had plenty of fiberglass overlap



Over all the fiberglass turned out pretty good.
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Next up will be fiberglassing the motor mounts into the capsule, and starting the design and construction of the av-bay/recovery-bay/rail attachment sections. Stay tuned, we've got some fun stuff coming up!

 

[jpoehlman]

Thanks for pulling me into the fun project @bandman444 , No way I would have started something like this on my own. I can't wait to see this thing fly, and if nothing else, excitement is guaranteed.

Since we're planning to fly this at NSL West, plans include a pair of Spud-ronauts as this thing has such a close resemblance to the NSL logo:

 

[burkefj]

Only question I have is how confident are you of lighting all of the motors or at least enough for avoiding significant asymmetric thrust causing cartwheeling?

 

[vulpesjr]

Is this using Warp 9 motors? What's the thrust to weight off the pad? What are you using for igniters?

 

[Neutronium95]

Is this using Warp 9 motors? What's the thrust to weight off the pad? What are you using for igniters?

The NSL featured projects page says that it's flying on I40s. That seems to impose a pretty strict weight limit. If all of them ignite, the loaded weight needs to be less than 14 pounds to have a 5:1 twr. And all eight motors weigh about 6 pounds.

 

[jpoehlman]

Is this using Warp 9 motors? What's the thrust to weight off the pad? What are you using for igniters?

tentative plan is to use 8x Aerotech I40N Warp 9 motors. We're estimating 40 LBS which get to an initial thrust to weight of ~4.64:1 with the I40N having an .5 sec spike to get off the pad. Final build weight will make some determinations, but the 3D parts totaled 6.6 lbs. If all motors light, there will be 9.5 seconds of 2:1 to sustain the boost. Igniters options are still under review. The I40 has a nozzle is just big enough for a standard e-match though.

 

[jpoehlman]

Only question I have is how confident are you of lighting all of the motors or at least enough for avoiding significant asymmetric thrust causing cartwheeling?

Getting all / enough motors light is definitely a concern. We'll want this on an away pad for sure. We will validate each starter, and build a robust electrical solution to ensure current and voltage has a definitive and validated path to the starters. While success cannot be assured, human safety is of highest concern. Spud-ronaut survivability I'd rate at 60%

 

[cerving]

Dip the ematches lightly in ProCast or similar pyrogen. It doesn't take a whole lot to light eight ematches... or Warp9, either.

 

[jpoehlman]

The NSL featured projects page says that it's flying on I40s. That seems to impose a pretty strict weight limit. If all of them ignite, the loaded weight needs to be less than 14 pounds to have a 5:1 twr. And all eight motors weigh about 6 pounds.

The I40's have an initial kick to help get off the pad:

 

[Gus]

I know a bit more than most about flying a Pad Abort model. I was also at the actual SpaceX Pad Abort flight as well as the actual MLAS flight.

Simultaneous ignition of 8 H motors, and the absolute necessity of lighting all of them, is a significant challenge. But there are other issues just as daunting.

The center of gravity of these very short pad abort models makes them phenomenally susceptible to wind. I restrict my Apollo Pad Abort model to D motors, and only very light winds, because it arcs significantly right off the pad in even the most minor wind. Using E motors would allow it to complete the arc and hit the ground under power. The tractor design of these models exacerbates that problem. The 10 second duration of burn of the I motors in your model is a real concern for that reason as well.

Similarly, the MLAS is remarkably wind susceptible even though its four canted motors are at the base of the trunk. A very short burn jackhammer boost off the pad is OK, but longer burns, even for that model, are very problematic. I suspect the same for yours. 10 seconds of thrust is really concerning.

Have you actually flown a subscale boilerplate using black powder motors to check for this issue, and others? I’m also interested in what testing you’ve done on the strength and precise alignment of your motor mounts. The slightly canted thrust of these motors reduces your overall lift ability. Also, the relatively shallow cant suggests they will likely impinge upon the sides of the capsule. 10 seconds of flame along all four sides of that capsule could be a real problem. If one of your motor mounts lets loose or you have a Cato, the lengthy burn of those motors is really concerning.

Not to be Debbie downer here, but I have more experience flying this type of model than anyone I know and your model really concerns me. I love it, but it really concerns me.

Steve

 

[Gus]

 

[Gus]

Apollo Pad Abort 1 flying on two D12-3's and two D12-5's .

 

[bandman444]

I know a bit more than most about flying a Pad Abort model. I was also at the actual SpaceX Pad Abort flight as well as the actual MLAS flight.

Simultaneous ignition of 8 H motors, and the absolute necessity of lighting all of them, is a significant challenge. But there are other issues just as daunting.

The center of gravity of these very short pad abort models makes them phenomenally susceptible to wind. I restrict my Apollo Pad Abort model to D motors, and only very light winds, because it arcs significantly right off the pad in even the most minor wind. Using E motors would allow it to complete the arc and hit the ground under power. The tractor design of these models exacerbates that problem. The 10 second duration of burn of the I motors in your model is a real concern for that reason as well.

Similarly, the MLAS is remarkably wind susceptible even though its four canted motors are at the base of the trunk. A very short burn jackhammer boost off the pad is OK, but longer burns, even for that model, are very problematic. I suspect the same for yours. 10 seconds of thrust is really concerning.

Have you actually flown a subscale boilerplate using black powder motors to check for this issue, and others? I’m also interested in what testing you’ve done on the strength and precise alignment of your motor mounts. The slightly canted thrust of these motors reduces your overall lift ability. Also, the relatively shallow cant suggests they will likely impinge upon the sides of the capsule. 10 seconds of flame along all four sides of that capsule could be a real problem. If one of your motor mounts lets loose or you have a Cato, the lengthy burn of those motors is really concerning.

Not to be Debbie downer here, but I have more experience flying this type of model than anyone I know and your model really concerns me. I love it, but it really concerns me.

Steve

Thanks so much for the great comments.

I have multiple flights worth of experience with high power clustered flights with a couple 5 and 7 motor O impulse motors. The I40 motors offer an interesting challenge and opportunity. Unlike my other large clusters, there just isn’t room for redundant ematches. This means that the BKNO3V dipped ematches we will be using will be the only ignition source for each motor. Thankfully regular ematches do fit. Warp 9 is also not an extremely difficult propellant to ignite, so while I believe a bare ematch right against the propellant should work really well, the dipped igniters should be better.

We do have a boiler plate BP powered model in works for confidence and stability verification. Thanks again to the extreme base drag and the cg shift thanks to the tractor motors, I’m quite confident it will be stable. But I agree completely with “trust but verify”, hence the subscale test model.

Since we are using electronic ejection and are never traveling really fast, I’m quite confident that if we end up at a high angle of attack, recovery success is still pretty likely.

Another thing that helps me sleep at night (and would if I were an RSO), is that this rocket is physically large, and quite impressive. This makes a heads up flight inevitable, from a safety point of view, personnel safety is number one. I honestly believe this flight is a low risk for a big rocket, with low apogee, and easily visibility, the mostly hard it can do is to itself. I don’t think complete failure is likely though thanks to the safety measures, design considerations, and test plan.


I also reserve the right to make changes along the way as necessary to increase safety and project success.

This is not a model that will be tolerant of winds. While a maximum wind condition allowance has not been calculated, it will, and will be rigidly adhered to.

Thanks for your post and its contribution toward the success of our project.

 

[Gus]

Bryce,

Thanks for taking my comments in the spirit they were meant. Really hoping the flight goes well. And bummed I won't be there to watch it. Rooting for you on this one and your handicapped flights.

Steve

 

[Daddyisabar]

Canted tractor motors rock! Widely spaced pods rock! Yes Mr. RSO, it's just an ignition issue. High Power oddrocs...ROCK! Stubby oddrocs with centerline rods/rails rock!

San Louis Valley is the place to go. Flown many high powered, canted tractor motored, oddroc abominations there. All smiles and few, if any stink eyes at altitude. A gangster, I mean oddroc flying paradise. We sell motors at a discount price living in an oddroc paradise.

Early morning launch for calm conditions. The real high power guys are still in bed after a hard night of partying. Limited spectators, a good thing! Early oddroc flyer gets the pad assignment!




A little shaping of your rocket with tractor motor flame in flight is a good thing! All natural as it was meant to be! Yeah, right, safe 3-4FNC rule.



NSL is not as good as thier normal launches, too busy, especially when getting that first oddroc flight dialed in. But it will do. And the satisfaction is greater I guess. I can't get no...


Look at that idiot flying a silly oddroc on 3xE12 4! He needs 3xE12 0 with a modicum of BP on top...is that even legal? That first time flight was for the birds. Did he even to a computer sim? Another no delay oddroc abomination. Better luck next time. It's a hard knocks life for the oddroc flyer.

 

[Daddyisabar]

The local clubs have some good power (cluster boxes.) I don't need another wanna be rocket scientist, I need a good electrician! When they all must light at the same time. Who you gonna call?




I would love to see you lower power demo model.

With all that lovely space down low is it/could it be rear eject?

Weight up top Good.
Weight on bottom Bad.
Will we see some heavy sonotube peeling?

 

[Daddyisabar]

Only question I have is how confident are you of lighting all of the motors or at least enough for avoiding significant asymmetric thrust causing cartwheeling?

Like Voilet Beauregarde is Tim Burton's Willy Wonka, CONFIDENCE IS KEY! Ummmm, here comes the dessert...it's blueberry pie!

Send immediately to the juicing room!

It can be done, no dejuicing required!

Love me some awesome clustering technique coupled with scale beauty.

 

[Daddyisabar]

Thanks for pulling me into the fun project @bandman444 , No way I would have started something like this on my own. I can't wait to see this thing fly, and if nothing else, excitement is guaranteed.

Since we're planning to fly this at NSL West, plans include a pair of Spud-ronauts as this thing has such a close resemblance to the NSL logo: View attachment 636821

Twin tater nose weight! No tater water for fuel though.

 

[Daddyisabar]

Getting juice to all of those awesome, widely spaced tractors motors looks hard. I have used one of these, but they aren't real cool or good for your hipster image.

Bitchin clip whips take forever to hook up at the pad. Hey cluster Prima Donna, are you done with your hookups already? Decent, safe 3-4FNC flyers need to launch.

Honey, I'm on the phone and I know the old car won't start...Dude, I have the wiring harness for an awesome clip whip!

 

[jpoehlman]

This week, we made some progress on the 1/12 scale boiler plate / proof of concept version. The model needed a serious weightless program to get under 1500 gram limit to fly as a class 1 model rocket. The trunk section was the easiest component to put on a diet. Reducing after weight has the added benefit of moving the CG forward too. We reduce the trunk's tube cross section and thinned the fins to be closer to scale. The trunk 3d printed weight was reduced from 686g to 409g:



I can also confirm, the ABS filament definitely has warping issue! The print was done in a full enclosure (non-heated).

Net result of the weight loss program resulted in a dry mass of 1074g, giving plenty of margin for motors and recovery. The sections of the 1/12 scale are now epoxied together. The nose cone needs a bit more sanding to provide sliding clearance.

Here's the scale comparison of the 1/6th and 1/12th scale versions:

 

[Gus]

Wow! Great work! That’s a heckuva weight reduction. What motors are you planning to use to fly the 1/12 scale on?

 

[Daddyisabar]

As to the central rail and possible asymmetric thrust you might consider eliminating rail buttons/guides all together. They will just want to bind up with any tourqe. I had one launch where a slight delay in one tractor motor igniting and the resulting asymmetric thrust slightly bound the rocket on the thick rod, making the problem even worse. And this was with toy motor F15s.

A super strong rod planted in the ground will do. Don't need a blast defector. But would that set up just be too uncool? Image is important but those darn tractors make you think backwards and unconventional.

 

[jpoehlman]

We did fly the 1/12th scale flight proof of concept prototype at the WAC (Washington Aerospace Club) 60 Acres launch yesterday, April 6th. Flight was powered by 8x Quest Q-jet FJ. Due to on hand availability, we had a variety of impulse and delays comprised of 4x D16-4, 2x D16-6, 2x C13-6.

Fly recap is in the works, but here is an image from the flight:




More later this week after the eclipse.

 

[Gus]

Fantastic! Huge step getting that up in the air. Looking forward to the recap. Enjoy the eclipse.

Steve.

 

[jpoehlman]

Wow! Great work! That’s a heckuva weight reduction. What motors are you planning to use to fly the 1/12 scale on?

Initial thought was Estes C6-3's, but the Quest Q-Jet D16 & C13 increased thrust offered a much high thurst to weight margin in case of partical ignition....... and I had them on hand.

 

[Daddyisabar]

Different motors! Wow, I am super impressed. Awesome job! Best ever! Congratulations on the flight!

Any video?

 

[jpoehlman]

So, test flight 1 was not exactly ideal, here's the full frame image:



and yes, we have video: Dragon Flight 1

So, what did we learn?

Key contributions to the flight profile:

1. Marginal current supply from the launch system battery / GSE to the ignitors
2. ¼” launch rod flexibility allowed 1st set of motors to induce angular momentum
3. Ignitor generational differences combine with #1 lead to delayed ignition
4. Wind speed and direction, based on smoke drift and tumble weed, the dragon flew into the wind…. Likely did not help, but not sure it was a significant factor.

What are our corrective measures:

1. Build a high current relay solution to ensure significant current is supplied to ignitors. It should include a inline 30 Amp fuse in case of short circuit.
2. Correct model to accommodate 1010 rail
3. Next flight should have identical ignitors, if motor generations vary, equally distribute ignitors
4. Need to determine and define flight limits especially for 1/6th scale

More details on test flight 2 in the coming days........

 

[Daddyisabar]

Wow! It's a hard knocks life for the oddroc flyer. You have an awesome club.

I would just put a pole/pipe in the ground with a short, very loose centerline lug. You don't want buttons binding up in a rail groove. I use 1/2" 6' stainless rod for my abominations. That might not even be enough for the big one.

Cluster box available from George at SCORE/COSROCS. I'm sure he would bring it to NSL.

Good clustering techniques a must.

Good conditions a must.

It's just an ignition issue.

Good luck.

 

[krislhull]

I wasnt at 60 Acres for the first test, but I was at the Sod Farm last week for the second, and that is a fun rocket to watch fly! It will always keep you on your toes!

Its looking good!