M1147 Tank AMP Round (3D Printed Parts + Body Tubes + Plywood)

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BigMacDaddy

BigMacDaddy

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I posted about this elsewhere but wanted to get some feedback on the design before I print larger.

Thanks to @lakeroadster for posting the video that made me aware of this tank round. Cool looking model that was not too complex (and seemed aerodynamic rocketry-wise). My first version is made w/ a BT-80 + BT-50 tubes + 3D printed parts + plywood fins (my MO). Should be launchable on C5-3 or D12-5 engines and I guess I will load an 18" or 24" chute in there (could also use an E12-6 but I setup the motor mount for shorter engines).

I am planning to make a 1:1 scale version with a 4C ice tea canister so wanted to get feedback before doing so (will be 129mm so bit larger than 1:1).
  • What do you guys think of the design? Any changes / improvements / suggestions? I did modify the fins for a new version (the flight part of the video seems to show more streamlined fins than the static close-up picture I grabbed from the video).
  • Do you think I need a launch lug near the rear / fins? I currently just have the rail-lug in the middle.
  • Any thoughts on mechanism to make fins open automatically if someone was doing a tube launch?
Here are the inspirational pictures of the prototype:
1658751984200.png
1658752007461.png

Here is my 1.0 design and 1.1 build as well as latest design (just fins have changed I think). Last picture also shows the 4C canister version vs. the BT-80 version::
1658751654490.png
1658751694870.png
1658751939844.png

Thanks in advance for any feedback!!!
 
BigMacDaddy said:
  • What do you guys think of the design? Any changes / improvements / suggestions? I did modify the fins for a new version (the flight part of the video seems to show more streamlined fins than the static close-up picture I grabbed from the video).
  • Do you think I need a launch lug near the rear / fins? I currently just have the rail-lug in the middle.
  • Any thoughts on mechanism to make fins open automatically if someone was doing a tube launch?


Thanks in advance for any feedback!!!
Click to expand...
That's a great looking model. Well done.

  • I'm betting this would be a great rocket to fly on a composite motor.
  • Where's the CG? I'm thinking one launch lug should be fine.
  • Rubber bands for the fins. Shouldn't take a lot of force to hold them open, during flight the drag will keep them there once the rubber bands get them past center.
 
lakeroadster said:
That's a great looking model. Well done.

  • I'm betting this would be a great rocket to fly on a composite motor.
  • Where's the CG? I'm thinking one launch lug should be fine.
  • Rubber bands for the fins. Shouldn't take a lot of force to hold them open, during flight the drag will keep them there once the rubber bands get them past center.
Click to expand...

Thanks so much... Here is the OR sim --

1658754442458.png
 
BigMacDaddy said:
Haha... I will leave the tube launches to @lakeroadster

I just got really excited about making the full scale version but do not want to spend a couple of days printing unless I am 100% final - so trying to avoid obvious oversights.
Click to expand...

Really, all you need is a piece of pvc pipe. It's not rocket science... well, you know. :dontknow:

I think I'd design the fins so they hinge, just to allow for a future tube launch. Then temporarily attach the launch lug with tape, or better yet put the launch lug inside the body tube. Then you can silo launch it after you get a couple of launch rod flights under your belt.
 
With an incentive fin mechanism, you could maybe launch it from the fins closed position, using a rod. So tube launch, w/o the tube. Would require some testing obviously. Maybe a small drag-inducing fin tip that is high-drag when the fins are forward/closed and low-drag when in the open position? The high drag tips could cause the fins to open as it accelerates.
 
Joshua Smith said:
With an incentive fin mechanism, you could maybe launch it from the fins closed position, using a rod. So tube launch, w/o the tube. Would require some testing obviously. Maybe a small drag-inducing fin tip that is high-drag when the fins are forward/closed and low-drag when in the open position? The high drag tips could cause the fins to open as it accelerates.
Click to expand...

Could also have motor burn through a string that was holding fins closed so they snap open just before launch (maybe).
 
I have an RPG rocket with folding fins. They open as soon as the rocket starts to move. And tube launch is cool. I also have a 60mm mortar round that is tube launched. And now the Spiny Thing. The RPG was supposed to be tube launched but the folding fin pivots ended up too wide. You could try a rubber band or a piece of string around the fins and attach another string to the pad. As the rocket goes up the string pulls whatever is holding the fins closed off. And your rocket looks great. Very nice work.
 
I always love seeing cool designs like these and would definitely be interested in getting one - so you know the customer base is here.
I would paint mine with a blue stripe (which signifies a training round and would make it much safer if I displayed it in my office at work.)
 
teepot said:
You could try a rubber band or a piece of string around the fins and attach another string to the pad. As the rocket goes up the string pulls whatever is holding the fins closed off. And your rocket looks great. Very nice work.
Click to expand...
That's similar to what I was thinking. A ring like a one inch long piece of pipe - maybe literally that - which holds the fins like a belt so they spring open when they clear it. Really, that's just like clearing the muzzle of a tube launcher, but only the last inch of tube is there.
 
cls said:
So cool! Did you use a big chute? No damage to any fins? I guess the grass helps somewhat.
Click to expand...

Thank you so much.

I cannot recall what size chute but there is plenty of room in the BT-80 tube. Does not need any nose weight so was quite light. Fins survived the launch fine (they are plywood so quite durable).

Sadly I had accidentally glued one fin into the mount (CA glue that I was using quite far away ran down and wicked into the seam). It broke when I tried to free it so that it could fold again so I need to CNC a replacement.
 
Last edited:
Ok great. Looking forward to seeing the tube launch!
 
How “loose” are the hinges? i know the design looks for a round wrap string or band around the forward lateral fin edges when ”stowed”, if The hinges are very loose, an ELASTIC burn string spiraled around the fins with both ends crossed right under the rocket nozzle should work, especially if associated with small “fin-lits” at the forward lateral edges of the stowed fins. they will be perpendicular to flight path when stowed, HIGH drag, lateral position should force the fin out and down before it leaves the rod once burn elastic string is severed. When deployed, they are parallel with flight path so far less drag and strongly positive effect on CP.


in those cases where I have replaced burn strings with ELASTIC, I have found much more success two ways. First, regular string tends to come loose a bit between the time it is tied and the time the rocket is launched, elastic stays tight.

Second, when elastic burns through, the inherent elasticity tends to pull it away from the structure. All my Helis and Airbrakers use rubber bands, essentially elastic burn strings, to keep things together (and actually doubles as an engine block at times when I use motor eject) which in this case are crossed in FRONT of the motor casing, the stretched bands are very strong but reliably “snap” and release when touched by ejection charge.
 
BABAR said:
How “loose” are the hinges? i know the design looks for a round wrap string or band around the forward lateral fin edges when ”stowed”, if The hinges are very loose, an ELASTIC burn string spiraled around the fins with both ends crossed right under the rocket nozzle should work, especially if associated with small “fin-lits” at the forward lateral edges of the stowed fins. they will be perpendicular to flight path when stowed, HIGH drag, lateral position should force the fin out and down before it leaves the rod once burn elastic string is severed. When deployed, they are parallel with flight path so far less drag and strongly positive effect on CP.


in those cases where I have replaced burn strings with ELASTIC, I have found much more success two ways. First, regular string tends to come loose a bit between the time it is tied and the time the rocket is launched, elastic stays tight.

Second, when elastic burns through, the inherent elasticity tends to pull it away from the structure. All my Helis and Airbrakers use rubber bands, essentially elastic burn strings, to keep things together (and actually doubles as an engine block at times when I use motor eject) which in this case are crossed in FRONT of the motor casing, the stretched bands are very strong but reliably “snap” and release when touched by ejection charge.
Click to expand...

Depends on how you assemble, etc... The fins move easily backwards with little resistance but I did not want them bouncing around in the slot since that would tend to make things less stable / straight-flying. I included some ideas about how to make them tighter or looser depending on what you prefer in the build notes.

I was thinking you could maybe wrap a rubber band around a pair of fins and around the rear engine mount (either around fin, both band parts around rear mount, and around other fin or around both fins and then around motor mount). That should be sufficient to open the fins. It also would probably not put too much resistance on a smooth tube used for launching. The fins are slightly larger than the nose cone when folded so ideally tube would fit snug against fins when folded.

I think you could also use a double torsion spring if you had the right sized one -- might need slightly larger axles / fin mounts / bamboo sticks.
 
KSoldier said:
Any updates on this project? Flight tests?
Click to expand...
There is a flight video up above on a C5-3 (I posted it below again). I have not tested on a 24mm D12 or E12 but simulation seems to show it would work (although cannot recall if it needed nose weight).



I have a number of these kits in stock now -- https://www.facebook.com/Radical.Rocketry/

Also Jim Horstrup shared some pictures of his build of my kit -- much better finishing than my prototype...

1671771761583.jpeg

1671771782904.jpeg
 
Kris T shared a couple of his videos of the M1147 launching on D12 and E12 engines. Apparently it flew "straight as an arrow" on both but "really liked the thrust" of the E12. [Looks like the same video but I think they are different]
 

Attachments

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    1.1 MB
BigMacDaddy said:
I posted about this elsewhere but wanted to get some feedback on the design before I print larger.

Thanks to @lakeroadster for posting the video that made me aware of this tank round. Cool looking model that was not too complex (and seemed aerodynamic rocketry-wise). My first version is made w/ a BT-80 + BT-50 tubes + 3D printed parts + plywood fins (my MO). Should be launchable on C5-3 or D12-5 engines and I guess I will load an 18" or 24" chute in there (could also use an E12-6 but I setup the motor mount for shorter engines).

I am planning to make a 1:1 scale version with a 4C ice tea canister so wanted to get feedback before doing so (will be 129mm so bit larger than 1:1).
  • What do you guys think of the design? Any changes / improvements / suggestions? I did modify the fins for a new version (the flight part of the video seems to show more streamlined fins than the static close-up picture I grabbed from the video).
  • Do you think I need a launch lug near the rear / fins? I currently just have the rail-lug in the middle.
  • Any thoughts on mechanism to make fins open automatically if someone was doing a tube launch?
Here are the inspirational pictures of the prototype:
View attachment 529405
View attachment 529406

Here is my 1.0 design and 1.1 build as well as latest design (just fins have changed I think). Last picture also shows the 4C canister version vs. the BT-80 version::
View attachment 529402
View attachment 529403
View attachment 529404

Thanks in advance for any feedback!!!
Click to expand...
I'm trying to do this as well i keep on getting stuck on the hinge for the fins how should i do it
 
BigMacDaddy said:
Not totally sure what you are asking but I tend to use dowels (bamboo skewers, 2mm copper rods, etc...) as hinge pins since 3D printed parts are not particularly strong as a pin.
Click to expand...
Inserting myself into the conversation briefly 😉, I've entertained a few alternatives, but haven't found anything I thought would really work. I bought a box of all-metal thumb tacks. It might work, but they are a much smaller diameter so they'd be very loose. Oh, I should add that I'm clinging to the idea that I can launch it with the fins up and the acceleration would drop them down.
 

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