Full Scale 100 lb Bomb

[PSLimo]

Hey Guy's,

I'm trying to build an exact replica 100 lb bomb. I have the scale fincan finished and it comes in at 3lbs and will be bolted to the frame.



The shell of the bomb is resin cast from the real deal. The screw in front fuse is going to be the access for the nose weight and recovery mount. The 8" shell will have a 4" tube run through it that will house MM and the rear eject like I've done before in an 8" Fat Man. I put a very simple file together to start with to see where the CP/CG ends up and got less than encouraging results, lol.



Any thoughts on moving forward with this one?

Thanks in advance,

Phil

 

[K'Tesh]

You could start with the SBR "THE BOMB!" kit...



And upscale it...
My sim can be found in my OR Files thread...

FWIW, I hope to build a full scale MK-82 SnakeEye and AIM-9L missile (reminders of my days as an Aircraft Armament Systems Specialist).

 

[bobby_hamill]

You might want to print up several "inert" tags and attach them to the model as you are transporting it ,
that would save some Police Officer from a heart attack or stroke when seeing it in your vehicle !!

Or better yet "Inert for training only"

 

[ljwilley]

Should look cool when you build it!

 

[bobby_hamill]

let me guess "tumble" recovery ?

 

[A Little Loud Labs]

We did something kinda similar, the box part of the fin will help the sim greatly.
Our Sim with the box:
Our Sim without:

I keep meaning to do a video for the modeling and sim but haven't yet, we 3d printed the nose, fin and the transition. It was rear ejection like your fat man. Flight vid: oat bomb flight

 

[jqavins]

I think that, one way or another, the sim is wrong. Because the real thing is stable. With the CP forward of the whole object, no amount of nose weight can possibly make it stable. So the model contradicts the empirical fact, and therefore the model is flawed.

And I think I see the problem. And I see a possible culprit. You've got four fins, but not the panels between them. You need to add a ring tail.

 

[Capt. Eric]

I think that, one way or another, the sim is wrong. Because the real thing is stable. With the CP forward of the whole object, no amount of nose weight can possibly make it stable. So the model contradicts the empirical fact, and therefore the model is flawed.

And I think I see the problem. And I see a possible culprit. You've got four fins, but not the panels between them. You need to add a ring tail.

Agree - the SIM has to be wrong. Just eyeballing it, the CP must be well aft of the center of the body. Probably don't need much nose weight.
You can always test its stability by, say, dropping it from an airplane from 20,000ft.

And instead of marking it "Inert for training only", I'd go with "Inert for Entertaining only".

 

[neil_w]

Yeah, the box is critical for stability. I’m still not sure how CO ended up so far forward, though. Care to share the ORK file?

 

[PSLimo]

Yeah, the box is critical for stability. I’m still not sure how CO ended up so far forward, though. Care to share the ORK file?

Here's the basic ork file I started with. I weighed the body and divided the weight between the seams for a NC, BT and TC for the mass overrides. When I added the tailcone the C/P flew forward. Those Bomb suspension lugs will be used for 1/2" launch lugs keeping the bombs scale in appearance.

 

[PSLimo]

I think that, one way or another, the sim is wrong. Because the real thing is stable. With the CP forward of the whole object, no amount of nose weight can possibly make it stable. So the model contradicts the empirical fact, and therefore the model is flawed.

And I think I see the problem. And I see a possible culprit. You've got four fins, but not the panels between them. You need to add a ring tail.

Correct, adding weight to the nose does nothing to move the CP.

 

[neil_w]

Here it is with the box. Unsurprisingly it looks much better. There are a couple of different ways to do the box, I chose the approach that seemed like it should be most accurate (but it's just a guess). I don't know the actual geometry of the box so you'll need to adjust it for accuracy.

Note that models like this are at best an approximation, but it has to be closer to reality than leaving the box out entirely.

 

[jqavins]

When I added the tailcone the C/P flew forward.

Yup, a tail cone will do that. On a "regular" rocket, a tail cone is great to reduce drag, bad for stability.

Those Bomb suspension lugs will be used for 1/2" launch lugs keeping the bombs scale in appearance.

Nice!

 

[PSLimo]

Here it is with the box. Unsurprisingly it looks much better. There are a couple of different ways to do the box, I chose the approach that seemed like it should be most accurate (but it's just a guess). I don't know the actual geometry of the box so you'll need to adjust it for accuracy.

Note that models like this are at best an approximation, but it has to be closer to reality than leaving the box out entirely.
View attachment 632520

Thank You!

Time to start building. Going to use a timer for deployment with rear eject to come down bomb style. plenty of room between the 54mm MM and the 4" coupler to house the electronics.

Phil

 

[cerving]

Just don't lose it, whoever finds it will panic big time. Good chance it would make the local news...

 

[cwbullet]

Here it is with the box. Unsurprisingly it looks much better. There are a couple of different ways to do the box, I chose the approach that seemed like it should be most accurate (but it's just a guess). I don't know the actual geometry of the box so you'll need to adjust it for accuracy.

Note that models like this are at best an approximation, but it has to be closer to reality than leaving the box out entirely.
View attachment 632520

Neil,

That design is the Bomb. I hate to use rocketry and bomb in the same sentence, but it is a nice design.

 

[rharshberger]

Should look cool when you build it!
View attachment 632345

yellow would be a real Explosive filler designation, light blue stripes and tip would be correct for a practice/dummy round.

 

[ljwilley]

Was just posting a picture of what it might look like. Just saying it will be cool!

 

[PSLimo]

It'll be hard to tell from the real deal once it's painted and lettered. Here's a dry fit of It so far:



I cut out a 4" hole in the rear to run a fiberglass BT through it.



I was going to replace the fuse bushing and screw in plug with PVC for the recovery attachment but might switch to cast to add a pound where it needs it.

 

[ljwilley]

awesome!

 

[PSLimo]

Looks like the easiest way to keep the build as scale as possible on the pad was to modify the square suspension lugs inserting a round collar and fly off a 1/2" rod.

 

[lr64]

I hope the replica isn't TOO exact. I suppose the Fat Man wouldn't have worked, even if it had been exact scale in all respects.

 

[PSLimo]

The 4" FG bodytube was a perfect fit and it's time to screw on the fincan.

I'd also like to give a shout out to Wildman Rocketry on the quality FG parts for this build. I ordered them Monday morning at 9am, received an email a couple hours later with a tracking number and the parts were delivered the next day. That's Wildman Prime delivery!

 

[Daddyisabar]

Thrust and nose weight will solve most of your problems!

I have this one stashed away in the garage in case the Ruskies come.


Now all I need is a real Corsair!



Launching off a 1/2" stainless rod will make all the old dudes soooo happy. Please get video.

 

[ljwilley]

Wow, this is looking great so far! Keep on posting pictures!

 

[BABAR]

You might want to print up several "inert" tags and attach them to the model as you are transporting it ,
that would save some Police Officer from a heart attack or stroke when seeing it in your vehicle !!

Or better yet "Inert for training only"

I’m guessing YOURS is not gonna be a park flyer and unlikely to have a ballistic recovery in someone’s backyard. Just in case…..

 

[jqavins]

Do you launch that with Diet Coke and Mentos?

 

[ljwilley]

That is cool!

 

[PSLimo]

Time for paint.

 

[crossfire]

Time for paint.

View attachment 633512

Just awesome. Do you fly at Bong?