Mini Fat Boy/ Larger 18mm engine conversion

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aviserated

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My original mini fat boy that uses the mini engine is a pretty boring 250' low level flight, so i decided to build another one which use the larger A,B,C 18mm engines. Went to hobby lobby and purchased the baby bertha kit ($7.98 dollars) and converted it to mini fat boy by cutting the body tube shorter and trimming back of nose cone for more recovery room. Also had to cut out fins to match mini fat boy. This new rocket flies perfectly strait and lots higher. Compaired to mini engines the larger engines are lots more fun. Rocket flies slightly higher using A engines, Twice as high using B engines and out of sight using C engines.

I super glued a piece of 1/8" plywood in nose cone to tie shock cord to. Gorilla mounting putty (4.5 squares) was applied to inside tip of nose cone using 3/8" dowel rod. With heavier/larger Estes C65 engine installed CG is 2 13/16" measured from bottom tube edge.
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Donnager

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I thought it was near mandatory to up size Estes motor mounts. Of course, I might just like walking a lot.

I built my mini fat boy to fly 18mm stuff. I also made an adapter to fly the smaller motors. If you get an Estes Designer Special it will have enough parts to up size many Estes kits for a while, and give you templates to make more.

I like your nose cone mods.
 

Back_at_it

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Did the same to mine. Tossed the 13mm mount in the box of parts and built an 18mm mount. Flies great with no added nose weight.

Really likes the B6-6 motors.
 

aviserated

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There is so much misinformation in the forums. One guy said to put half ounze of nose weight in rocket. This is way too much. I am also sure it would fly without any nose weight added at all. But what about D size motors...is more nose weight needed?
 

dr wogz

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There is so much misinformation in the forums. One guy said to put half ounze of nose weight in rocket. This is way too much. I am also sure it would fly without any nose weight added at all. But what about D size motors...is more nose weight needed?
sim it & find out.. I would expect so.. (The Estes Goblin requires some nose weight, same with the Bullpup..)
 

CalebJ

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There is so much misinformation in the forums. One guy said to put half ounze of nose weight in rocket. This is way too much. I am also sure it would fly without any nose weight added at all. But what about D size motors...is more nose weight needed?
How do you know it's misinformation?
Did you measure it carefully like you did with the epoxy covered paper fins?

If you're going to call people out for misinformation, at least show up with evidence.
 

Back_at_it

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There is so much misinformation in the forums. One guy said to put half ounze of nose weight in rocket. This is way too much. I am also sure it would fly without any nose weight added at all. But what about D size motors...is more nose weight needed?
With the 18mm motor mount "MINE" didn't need nose weight. I have gotten good straight flights every time but keep in mind that I don't fly in anything over 5mph winds and I have a 48in launch rod for my smaller rockets so they are moving pretty fast by the time they leave the rod.

A 24mm motor would require a fair bit of nose weight to make it stable. I'd thin you would need at least 1/2oz maybe more.
 

aviserated

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Where can I find a one piece 48" launch rod. The Estes two piece rods are adequate, but looking for better.
 

CalebJ

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Any hardware store.
 

aviserated

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I know I can get 36" length 1/8" or 3/32" diameter, but the 48" may be a problem.
 

CalebJ

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Don't use 1/8 for a rod that long. Step up to a bigger lug.
 

CalebJ

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You still haven't explained why you think the half ounce of nose weight suggested by others was misinformation, by the way.
 

CalebJ

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That's not an answer.

You called it misinformation long before that. What is your stability margin without it? It's pretty bold to tell someone else they're posting misinformation without providing the slightest reasoning.
 

aviserated

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OK I used way less than 1/2 oz and rocket flew fine. Is that enough...wtf?
 

Back_at_it

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I know I can get 36" length 1/8" or 3/32" diameter, but the 48" may be a problem.
My local Lowe’s and Home Depot both sell 1/8" and 3/16" rod in 48” sections. They also have 1/4" in 72" sections.

Estes stock rods are too short in my opinion and I never liked the two piece design.

I have not had any issues with rod whip using the 48" sections so the length is fine even for 1/8" rod.
 
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icyclops

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There is so much misinformation in the forums. One guy said to put half ounze of nose weight in rocket. This is way too much. I am also sure it would fly without any nose weight added at all. But what about D size motors...is more nose weight needed?
No, just use a nylon 18” chute and lots of wadding....I have built and launched mine with Estes 24mm D12-5 with good results....have to walk a bit further for recovery but due to the drag of that Roc it flys just fine. Also, I cut the bottom off the nosecone, trimmed it and glued it further up into the nosecone to allow more room for the chute, elastic shock cord and still retain the original cone eyelet.... so it moves all that weight further up due to that....no more nose weight required.
 

aviserated

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With a D motor I bet it would be impossible to see rocket without the 18 chute. Roughly how high does it fly using D power? Would you use a steamer?
 

Back_at_it

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With a D motor I bet it would be impossible to see rocket without the 18 chute. Roughly how high does it fly using D power? Would you use a steamer?

You would never see it again. It's out of sight on a B6 motor. The amount of nose weight you would need would ridiculous. Stick to 18mm motors.
 
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icyclops

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With a D motor I bet it would be impossible to see rocket without the 18 chute. Roughly how high does it fly using D power? Would you use a steamer?
With a D12 it just goes barely out of sight. There is a lot of drag with that nosecone and stubby body....but it does fly straight. On a cloudless day you can see the tracking smoke and ejection puff. I don’t use altimeters so have no idea how high. I just know with the 18” chute I use I don’t need to add any nose weight as I mentioned previously with slight mods to the cone. Hope this helps.
 

icyclops

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Ooops sorry, I did not read the title correctly....I was talking about the original FatBoy using the NC80 roundish cone....sorry.
 

Sooner Boomer

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I'm prone to using really long streamers rather than parachutes on this sort of up-conversion. I've got a Baby Bertha I fly on BP 29mm motors. It has 3/4 oz nose weight, and a 10' crepe paper ribbon for recovery. It peaks at over 2000 feet, way up there. The long streamer helps see it on the way down, and find it on the ground. It could use less nose weight to fly on these motors, but I also want to get stupid some day and fly on a composite motor.
 

rklapp

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I swapped out the 13mm with an 18mm. I kept the streamer. It worked with the A8-3 but not with C6-5.


I then added NC weight and was awesome.

 

aviserated

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I have two mini fat boys, one original with mini engine engine. And one with the larger 18 mm conversion. I was told to balance the 18 mm rocket to the same center of gravity as original mini with motors installed. It only took 1/8 oz of putty in nose cone to balance and rocket flies great. Used rubber band and paper clip to find CG of both rockets. Fun simple project.
 
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