"Little Boy" Atomic Bomb -- 3D Printed Parts + BT-55/BT-20 tubes

[BigMacDaddy]

In recognition of the Oppenheimer movie coming out, I made a small "Little Boy" model rocket. Model is built around BT-55 & BT-20 body tubes and is designed to launch on a 13mm mini or 18mm engines. I will also try to make a BT-80/BT-55 scale version.

I opted to put 1oz in nose so that I could launch on a range of 18mm engines but I think it would be stable with 1/2oz for 13mm mini engines launches.

The boxtail is around 27% larger to help with stability (mainly me just rounding off numbers and letting it get a bit larger since it cannot hurt). For the BT-80 version I will try to keep the box tail closer to scale since I will have more length to work with (and parts should be proportionately lighter).

Test flights to come next...






This time period definitely represented a turning point in US and world history (not to mention dramatic advances in rocketry technology). I hope world leaders never forget the past or we may be doomed to repeat it.

 

[techrat]

Wow, that's a very little Little Boy. What's the yield on a bomb like that? 0.00001kt?

 

[Cape Byron]

Got any pink and blue paint for that?

 

[BigMacDaddy]

Got any pink and blue paint for that?

View attachment 594359

I was going to do a Barbie rocket but my wife pointed out that is not my niche...

 

[bjphoenix]

I was going to do a Barbie rocket but my wife pointed out that is not my niche...

We had a Barbie rocket at our last club launch- a level 1 attempt by a University student.

 

[BABAR]

In recognition of the Oppenheimer movie coming out, I made a small "Little Boy" model rocket. Model is built around BT-55 & BT-20 body tubes and is designed to launch on a 13mm mini or 18mm engines. I will also try to make a BT-80/BT-55 scale version.

I opted to put 1oz in nose so that I could launch on a range of 18mm engines but I think it would be stable with 1/2oz for 13mm mini engines launches.

The boxtail is around 27% larger to help with stability (mainly me just rounding off numbers and letting it get a bit larger since it cannot hurt). For the BT-80 version I will try to keep the box tail closer to scale since I will have more length to work with (and parts should be proportionately lighter).

Test flights to come next...

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This time period definitely represented a turning point in US and world history (not to mention dramatic advances in rocketry technology). I hope world leaders never forget the past or we may be doomed to repeat it.

this one will be an interesting flight.

I love box fins.

my first attempt had some issues
https://www.rocketryforum.com/threads/update-7-14-post-40-da-bomb-bigger-box-fins.167005/
second worked great
https://www.rocketryforum.com/threads/couple-flights-today-da-bomb-and-late-st-patrick’s-day-saucer.167674/#post-2165846

the box fins are functionally the fins. I am curious the effect your cross hatching ( I know, done to emulate the namesake) will have. On the negative side they may reduce flow and fin effectiveness. On the plus, if they do that the thing will act like a plate and have a ton of base drag.

yours is gonna be draggy as heck. Maybe a C5-3?

hope you get the same roll stability as I get from box fins. They make for a great camera rocket.

 

[BigMacDaddy]

this one will be an interesting flight.

I love box fins.

my first attempt had some issues
https://www.rocketryforum.com/threads/update-7-14-post-40-da-bomb-bigger-box-fins.167005/
second worked great
https://www.rocketryforum.com/threads/couple-flights-today-da-bomb-and-late-st-patrick’s-day-saucer.167674/#post-2165846

the box fins are functionally the fins. I am curious the effect your cross hatching ( I know, done to emulate the namesake) will have. On the negative side they may reduce flow and fin effectiveness. On the plus, if they do that the thing will act like a plate and have a ton of base drag.

yours is gonna be draggy as heck. Maybe a C5-3?

hope you get the same roll stability as I get from box fins. They make for a great camera rocket.

Thanks for sharing that -- innovative use of a bottle!

I do not know how far to trust Open Rocket CP calculations for the box fin... With pods I can get them to draw up correctly but I think there are issues with fins on pods and stability calculations. I have done some ring fins and some boxy-tails in the past (Fritz-X and a fictional Mortar round come to mind) but for the scale ones I just wind up going nose heavy. In this case there is the added complexity of the antennas that I assume will work a bit like forward fins.

Even w/ 1oz of nose weight this little guy is under 60g so should fly well on a B6-4. Agree about dragyness - there are even holes in the inside fins on the boxtail to add even more drag and turbulence.

I printed the parts for the BT-80 version last night and I am going to try to keep the boxtail scale on that version (and made from 2mm plywood).

Trying to get a number of rockets ready for testing -- lately I had been getting one rocket ready and rushing to test it but it is such a pain to pack everything up for 1 launch. Also we have a new car so I want to try strapping the launch rail to the roof so I do not scratch the interior with the rails.

 

[Hobie1dog]

Quite talented

 

[BABAR]

The far tailward launch lug will be okay if the tubing between the box fin can and the “bomb” (the “neck” if you will) is “hell for stout” as @lakeroadster likes to say.

Otherwise you have a problem with windy days if rocket is on pad /rod for long. Winds will push hard on the “bomb” and create a flex ion force at the neck. Potential is also there at deployment, if shock cord yanks nose sideways. Lot of inertia in that fin can. It bent my first rendition

 

[BigMacDaddy]

The far tailward launch lug will be okay if the tubing between the box fin can and the “bomb” (the “neck” if you will) is “hell for stout” as @lakeroadster likes to say.

Otherwise you have a problem with windy days if rocket is on pad /rod for long. Winds will push hard on the “bomb” and create a flex ion force at the neck. Potential is also there at deployment, if shock cord yanks nose sideways. Lot of inertia in that fin can. It bent my first rendition

Thanks - There is also a straw-style lug glued on the body tube against the antenna detail -- I just had not put it when I took pictures.

 

[ghostfather]

Now just upscale it for a 38mm or 54mm motor.... but you might have to go with something stronger for the box fins

 

[BigMacDaddy]

Now just upscale it for a 38mm or 54mm motor.... but you might have to go with something stronger for the box fins

I finished my BT-80 version with a 24mm motor. It has a BT-55 tube inside the boxtail so could easily take a 29mm motor mount.

 

[lakeroadster]

Have you launched any of these to see if they are stable? Seems like the fins are traveling in "the wake".

Should be interesting...

Fat Man had an alternate configuration of the fins that was called a "Parachute"... got any view from the rear?

​

 

[ghostfather]

Have you launched any of these to see if they are stable? Seems like the fins are traveling in "the wake".

Should be interesting...

Fat Man had an alternate configuration of the fins that was called a "Parachute"... got any view from the rear?

View attachment 597507​

Called the "California Parachute"

 

[ghostfather]

I finished my BT-80 version with a 24mm motor. It has a BT-55 tube inside the boxtail so could easily take a 29mm motor mount.

View attachment 597497

Nice looking, good job

 

[BigMacDaddy]

Nice looking, good job

Thank you!

 

[BABAR]

Have you launched any of these to see if they are stable? Seems like the fins are traveling in "the wake".

Should be interesting...

Fat Man had an alternate configuration of the fins that was called a "Parachute"... got any view from the rear?

​

I did a highly detailed 1-1 scale model of a Pepsi Bottle Bomb (although I altered the paint scheme.). fins not that different, flew fine.




Btw, consider tape a camera on it, makes a nice stable videocam launch bird.

 

[OverTheTop]

Nice model.

How robust are those UHF antenna features? Are they removable for flight?

 

[lakeroadster]

I did a highly detailed 1-1 scale model of a Pepsi Bottle Bomb (although I altered the paint scheme.). fins not that different, flew fine.

View attachment 598076


Btw, consider tape a camera on it, makes a nice stable videocam launch bird.

Your version, the fins stick out past the o.d. of the bottle....

 

[BABAR]

Your version, the fins stick out past the o.d. of the bottle....

True, I had the same concern you did.

You’ve done so many models I can’t keep track, but I think I remember you playing with gas stabilization. Would the rocket jet flow tend to cause a low pressure zone around the tail, INSIDE the box fin (essentially a square ring fin) and draw flow into the box?

 

[BigMacDaddy]

Nice model.

How robust are those UHF antenna features? Are they removable for flight?

In my model I glued them on, but you could slide them in and remove for flight.

I think it is going to land boxtail first but may break one if it flops over hard. Also they likely shift the CG forward some.

 

[lakeroadster]

True, I had the same concern you did.

You’ve done so many models I can’t keep track, but I think I remember you playing with gas stabilization. Would the rocket jet flow tend to cause a low pressure zone around the tail, INSIDE the box fin (essentially a square ring fin) and draw flow into the box?

Good question... it's unlikely.

A good swing test should confirm stability... and if that comes out bad then maybe give it a go anyways, away from other folks.

 

[BigMacDaddy]

Boxtail on the BT-80 version is scale (BT-55 was a bit large). Looks like it needs around 2.5-3oz of noseweight...

 

[BABAR]

Good question... it's unlikely.

A good swing test should confirm stability... and if that comes out bad then maybe give it a go anyways, away from other folks.

Did your gas stabilization models pass a swing test. My hypothesis is that if they did, they Gas Stabilization feature was at best redundant.

 

[DocSeuss]

I was going to do a Barbie rocket but my wife pointed out that is not my niche...

If she's good enough for Homer Hickam...

https://www.smithsonianmag.com/air-space-magazine/flights-amp-fancy-you-go-girl-28029113/
I can't figure out what the original source for this image is. They had one in the movie too that, as I recall, was based on this picture. Really, really fun; it looked like everyone making that movie was just having as much fun as possible the whole time.



I'd definitely love a BT-80 version; your work rules. I need to finish that F-104.

 

[lakeroadster]

Did your gas stabilization models pass a swing test. My hypothesis is that if they did, they Gas Stabilization feature was at best redundant.

No it did not.

 

[BigMacDaddy]

Wanted to share an update on this model -- I had a chance to fly these two last week as well (BT-55 and BT-80 scale). Both flew beautifully.

Video of the BT-80 version came out good but for the BT-55 version my 8yo was not up to his usual video quality (it has been a little while since we launched rockets so I think he forgot that the goal is to stay zoomed out and see the trajectory, no need to zoom in to see details).

Here is the video of the BT-55 version on a B6-4:


Here is the video of the BT-80 version on a D12-5:

 

[ljwilley]

Awesome!

 

[BigMacDaddy]

If she's good enough for Homer Hickam...

https://www.smithsonianmag.com/air-space-magazine/flights-amp-fancy-you-go-girl-28029113/
I can't figure out what the original source for this image is. They had one in the movie too that, as I recall, was based on this picture. Really, really fun; it looked like everyone making that movie was just having as much fun as possible the whole time.

View attachment 598642

I'd definitely love a BT-80 version; your work rules. I need to finish that F-104.

Thank you!

Found this interesting history of astronaut Barbie...
https://airandspace.si.edu/stories/editorial/barbie-astronaut-ages