Modded FatBoy to use 4 18mm & 1 24mm.

[Fuddrucker]

I am modding a FatBoy to fly on several different motor configurations. On the largest config, it will use 4 18mm and one 24mm. I will post a couple of pics of the mount later. For those who have done this type of mod on a FatBoy, how much nose weight did you wind up adding?

On my first attempt I only changed the MM to a 24mm but did not add any nose weight. I called it Fat "E" Boy", stuffed a AT E18 in it and it went every which way but UP. Learned a little from that one and don't want it to happen again.

Thanks.

 

[GL-P]

Get a demo of Rocksim then visit EMRR. Great program!!! They have files for almost all Estes rockets. Then just load you rocket and find the CG. Add nose weight as necessary

 

[Fuddrucker]

Cool, I have the Rocksim 5 demo. I will give that a try.

Thanks.

 

[brianc]

Originally posted by GL-P
Get a demo of Rocksim then visit EMRR

RockSIM isn't really required if you haven't changed the rocket profile.

Just grab the <a href="https://www.rocketreviews.com/cgi-bin/search/searchall.cgi?fat+boy#CP">CP point from EMRR</a>, then add enough nose weight to ensure
the CG is 1-2 calibers in front of that.

 

[Stymye]

one way,
weigh the different motor configurations including motors (subtract the weight of a single 18mm motor) add that same weight to the nosecone.

 

[Elapid]

put the CG in the stock location or forward, and go for it!
i added an extra fin to my fatboy scratch-built to help out with my choice of 2 - 24mm, 4 - 18mm, 2 - 13mm cluster power.

i think i'll fly that at XPRS III!

 

[JRThro]

Originally posted by stymye
one way,
weigh the different motor configurations including motors (subtract the weight of a single 18mm motor) add that same weight to the nosecone.

That'll really only work if the stock CG is midway between the nose weight and the weight of the stock motor mount and motors. If the stock CG is closer to the motor end of the rocket than to the nose end, then you'll have to add more weight to the nose (that is, more weight than the added weight of the modified motor configuration with motors). If the stock CG is closer to the nose end of the rocket than to the motor end, then you'll have to add less weight to the nose.

What I have seen people suggest several times is this: build, or at least assemble, the Fat Boy stock, including the biggest motor it's designed for, and mark the location of the CG. Then build it your way, including all of the biggest motors that you've redesigned it for, then keep adding nose weight until the CG moves forward to the same location as the stock CG. If you haven't made any changes to the body or fins, then the new relationship between the CG and CP will be the same as they are for the stock Fat Boy.

 

[Fuddrucker]

Here is a pic of the MM I have been working on. With this config I figure I should be able to fly it five different ways.

1. On a single 24mm motor.
2. On 2 18mm motors across from each other without the 24mm.
3. On 2 18mm motors and a 24mm in the center.
4. On 4 18mm motors.
5. On 4 18mm motors and 1 24mm motor.

I am not to sure about number 2 configuration though since the 2 18mm motors will not be next to each other. Any thoughts?

 

[rabidsheeep]

it could work but if one doens't light it might be alittle unstable

 

[rocketdad0934]

with the three 18mm I added 1oz and it went real well once it sit only two of the three and it was a bit scary as the fatty went real unstable It was on the ground before the ejection charge went but no damage it was the 18mm booster that killed it