Mini Fat Boy - 18mm Upgrade - CG Question?

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GregGleason

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I am working on an Estes Mini Fat Boy with one of my children. I have made a mod to convert it from 13mm to 18mm, so it can fly on B6's.

However, I am not sure what the CG should be, since I am certain that it has change due to adding more mass to the aft.

Does anyone know where the CG should be?

Greg
 
Before the "official" kit came out, I made one using a Baby Bertha kit, and an 18mm mount. With 0.25 oz nose weight, OR says it has around 0.5 calibers stability. It flies fine.
 
Thanks for the data point.

I forgot about using OpenRocket to check the stability.

Greg
 
Keep in mind that the stability assumptions used in sims assume a relatively long body to the diameter. And in this rocket you will have a lot of base drag. This is why one might be fine with only a half caliber stability.
 
I didn't know you could do this... modify a mini fat boy to accept A-B-C size motors?
If I knew that, I wouldn't have repaired it so quickly, but tried to tear out the motor mount
and insert something larger after my CATO last club launch.
(Darn A10-3T motors! Went up like a roman candle! No delay at all!)
 
when I bought mine, all the tubes were more than a tad oval, so I cut a bt60 an inch longer than stock (6.75"), gave it an 18mm mmt, and added 10g of nose weight. flies well on B6-4s, almost out of sight on a 'Big C6-5'. I also use a top flight thin mil 12" chute for recovery.
Rex
 
Keep in mind that the stability assumptions used in sims assume a relatively long body to the diameter. And in this rocket you will have a lot of base drag. This is why one might be fine with only a half caliber stability.

Thanks for the reminder. I don't usually fly "squatesque" rockets so this is a little new for me.

I didn't know you could do this... modify a mini fat boy to accept A-B-C size motors?
If I knew that, I wouldn't have repaired it so quickly, but tried to tear out the motor mount
and insert something larger after my CATO last club launch.
(Darn A10-3T motors! Went up like a roman candle! No delay at all!)

All you need are new centering rings and an 18mm motor tube. It's not a difficult mod, you just don't have a lot of room in the airframe for recovery once it's done.

when I bought mine, all the tubes were more than a tad oval, so I cut a bt60 an inch longer than stock (6.75"), gave it an 18mm mmt, and added 10g of nose weight. flies well on B6-4s, almost out of sight on a 'Big C6-5'. I also use a top flight thin mil 12" chute for recovery.
Rex

Thanks for the data point Rex. I was thinking that a C6 would give it quite a ride!

Greg
 
OR says about 800', I suppose if one wanted to lose it, that a D10 might do the trick :).
Rex
 
I modified an original fat boy to 29mm flys great on a H-225.Next one is going to be 54mm with soda can motor.
 
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