24mm Fat Boy

[rocketgroupmike]

I've substituted an E-size motor mount in my Fat Boy and found the CP to be 8.25" from the nose. With a rocket this shape, do I need the CG to be a full caliber in front of the CP?

 

[wwattles]

If you haven't changed the external configuration of the rocket (fin size/shape, nose cone shape, BT length, etc), the CP should still be the same as it would have been had you built it stock.

Did you, perhaps, mean that the CG was 8.25" from the nose?

In any case, the Fat Boy is just about the epitome of the "short/fat" rocket, where base drag plays a significant role in stability. My amateur recommendation would be to put enough noseweight into it so that the CG comes out close to where it is when built stock. It's gonna be a little more sluggish off the pad due to the extra weight, but the stability margin will be the same as the stock kit, which is nicely balanced.

You should be able to get the stock CP/CG locations from EMRR.

WW

 

[tazzdevl1]

I built my FB with a 7X18mm cluster mount from Sunward. I had to put 6 ounces of weight in the nose cone to make it balance correctly. CG for my FB X7 is about 1.6 calibers ahead of the CP. You will also need a larger chute to handle the added weight. Cutting off the base of the nose cone will give you some added room for that bigger chute.

Cliff

 

[JeffS]

I'm also finishing up a 24mm Fat Boy, and it will have less than one caliber stability. My 3x18 cluster also had less than one caliber stability, and it flew fine, as long as all three motors lit .

My 24mm Boy will have 1.5 oz of nose weight, which gives it .75 caliber. See attached pic. Also, refer to this article on wind instability.

Can anybody build just one Fat Boy?

 

[Stuck Fingers]

I just read the wind instability article.

Perhaps we should use the LENGTH of the rocket as the basis of our stability ratio rather than the Diameter.

Maybe we should be saying that the CG is 10% of the length of the rocket ahead of the CP instead of 1 diameter ahead?
Note the 10% was a random number pulled from rectal storage and NOT a proposed value to use.

 

[JeffS]

Hmm, I don't know about applying a 10 percent rule for all rockets. It would be interesting to see how the numbers work out.
Remember that two of the rockets in the article were extreme in terms of the ratio of length to diameter. Certainly the 1 plus caliber of stability works for most rockets most of the time. I would say, when in doubt, always go for 1+ caliber of stability.

 

[Rob Fisher]

Can someone please explain to me the reason that Estes would put such a popular rocket, especially the KING of bashing that the Fatboy is OOP? It just defies logic as far as I'm concerned!

 

[rocketgroupmike]

Thanks all, I should have mentioned that the 8.25" CP was via RockSim. I'm not sure why I came up with a quarter inch farther forward from JeffS, I'm guessing it's because I never added a launch lug or paid attention to the finish of any parts, just did a quick outline sim. (EMRR agrees with JeffS, 8.5")

"QUOTE" Can anybody build just one Fat Boy?

JeffS, I came across that very question as I pondered the paint scheme of my FB. Having recently built a WAC Corporal, I've got enough black and yellow spray cans, and I've always loved my old Goblin. Then my mind went GOONY, and Fat Red Max, Fat WAC, etc. started flashing by... Looks like I picked a bad day to quit getting loaded! hahaha!

 

[WShoreRockets]

Originally posted by Rob Fisher
Can someone please explain to me the reason that Estes would put such a popular rocket, especially the KING of bashing that the Fatboy is OOP? It just defies logic as far as I'm concerned!

I have a feeling that its going to get a makeover, like the Big Daddy did in 2005.

Bob

 

[TeenRocketNerd]

yeah, but it'll probly have a new name, b/c "fat" will be to confrontational, and is too demeaning. It will be the "big boned boy" or the "obese boy" I bet you're right about them getting a "facelift" though, atleast, I hope you're right, and I hope that I'm wrong about the name

 

[Rob Fisher]

As far as a PC version of the Fatboy goes, I'm kinda partial to "The Heavy Boy".

 

[metalwizard]

Originally posted by Stuck Fingers
..... random number pulled from rectal storage and NOT.......

now thats the funniest way to get past the censors..... lmfao.

by the way my fat boy is stock, except for the "E" mount, and nicer chute. no extra nose weight. and flies fine.

 

[rocketgroupmike]

Metalwizard, that's exactly what I wanted to hear, as that is my plan for my FB. The only other thing I had in mind was a bit of fin reinforcement, as my kit came with less than premium, slightly mottled-looking balsa. I guess I'm looking for lightest; easiest; strongest; in that order.

 

[metalwizard]

mike, my chute is big and heavy, and has lots of 1/4 nylon "schock" cord, so if you build it "stock" w E mount, and dont up do your recovery, or if you beef up your fins (i wish i had, the balsa is beat up now) you may need to add a little nose weight. remember on a small rocket nothing beats a swing test...

 

[trogdor]

Originally posted by Rob Fisher
As far as a PC version of the Fatboy goes, I'm kinda partial to "The Heavy Boy".

Husky Boy is the new name...

 

[Skippy]

Originally posted by Trogdor
Husky Boy is the new name...

It's a Star Wars tie in: Obese One Cannoli














I'll go now...

 

[Rob Fisher]

Originally posted by Trogdor
Husky Boy is the new name...

LOL! The word "husky" reminds me of when I was a kid & my Mom took us to Sears to buy new toughskins jeans to wear for the new school year. The toughskins came in a "husky" size for fat kids. They also came in every color of the rainbow.

 

[rocketgroupmike]

Ok, so back to my rocket... any suggestions for fin reinforcement or paint scheme?

 

[rocketgroupmike]

Or has anyone flown a rocket like this?

 

[Stuck Fingers]

I would pick up some full size sheets of Avery label paper from Office Depot. Stick it on the outside of fins. Fast easy and no sealer required.

 

[kelltym88]

I made a 24mm FB (only for "D" motors though) and didn't add any nose weight or reinforce the fins or anything. Flew great till I lost it over some houses showing off for the kids. With an "E" , just add a little clay to the nose, should be fine. Don't forget pictures.


As for paint, on my 3x24mm FB I painted the NC copper and the body I used Krylons "hammered" grey. Made it look like a bullet.

Here's a link to a picture of it:https://www.rocketryforum.com/showthread.php?s=&threadid=6519&highlight=bullet

 

[Rob Fisher]

I built a 24mm D size "Husky Boy" & didn't add any nose-weight. It flew perfectly fine about the first 6 times & then on the 7th launch it went completely unstable, chased it's tail a few times & then slammed into the ground & broke apart!
I WOULD NOT SKIP ON THE NOSE WEIGHT! I had to learn my lesson the hard way & the worst part about it was that it was at an SLRA launch with many people watching!
Here's a pic of my non-existant 24mm Fatboy:

 

[powderburner]

If you put in a bigger motor, the rocket will go higher.

If it goes higher (with the same parachute), it will drift further in the wind.

If you don't want it to drift further, you might use a smaller chute.

If you use a smaller chute, it will land harder (higher sink rate combined with heavier weight)

If it lands harder, you probably need to beef up the fins a bit.

I like to add a strip of something stronger than balsa to the fin trailing edges. I don't worry about streamlining on the FB (just look at it, do you think streamlining will really help?) so I just glue on something like a strip of spruce or some of that bamboo skewer they sell in the grocery store. Makes the fins a LOT more durable around my part of the country (lots of hard and rocky soil)

 

[Bowhunter]

Originally posted by Rob Fisher
I built a 24mm D size "Husky Boy" & didn't add any nose-weight. It flew perfectly fine about the first 6 times & then on the 7th launch it went completely unstable, chased it's tail a few times & then slammed into the ground & broke apart!
I WOULD NOT SKIP ON THE NOSE WEIGHT! I had to learn my lesson the hard way & the worst part about it was that it was at an SLRA launch with many people watching!
Here's a pic of my non-existant 24mm Fatboy:

Hey Rob that FatBoy looks familier and you know how heavy my 4x24mm FatBoy nose is. Its back together and ready to fly agian

 

[Rob Fisher]

Originally posted by Bowhunter
Hey Rob that FatBoy looks familier and you know how heavy my 4x24mm FatBoy nose is. Its back together and ready to fly agian

-Speaking of nose-weight, OMG! Bow could use his Fatboy for a boat anchor! I couldn't believe that it still flew as high as it did!

 

[Bowhunter]

I need to get looking for another FatBoy Cause I need to stick a 29mmt in it

 

[Tucker5246]

Originally posted by rocketgroupmike
Ok, so back to my rocket... any suggestions for fin reinforcement or paint scheme?

Here is a pic of ours. It has a 4x18mm motor mount with aprox. 2.5oz of nose weight. Has yet to be flown, the 3/16 launch rod should be delivered tomorrow. Looking forward to flying it.

Edit: I forgot to say that the fins were lamintated with tracing paper and diluted Elemers glue.

Keith

I do have another one in the package, its getting a 24mm mount.

 

[RimfireJim]

Originally posted by kelltym88

As for paint, on my 3x24mm FB I painted the NC copper and the body I used Krylons "hammered" grey. Made it look like a bullet.

Here's a link to a picture of it:https://www.rocketryforum.com/showthread.php?s=&threadid=6519&highlight=bullet

Hey! That's what I'm planning to do with one of my FBs, after someone suggested it on the Scratchbuilding forum (see my post "150 cal BMG"). I'm going to use clear plastic for the fins, paint the "case" brass, and I'm thinking about wrapping it with a second, slit BT-80 tube to create the "step" where the NC/bullet meets the BT/case. It's not the right length/diameter ratio for a .45 ACP cartridge; closer to a .38 Special.

-Jim

 

[RimfireJim]

Originally posted by Stuck Fingers
I would pick up some full size sheets of Avery label paper from Office Depot. Stick it on the outside of fins. Fast easy and no sealer required.

I've been using the Avery label paper technique on the last dozen or so rockets I've built, and I've always soaked it with thin CA that I squeegee on with a credit card. I sand it lightly with 320 grit after the CA cures to get it smooth again, though it never comes out as good as it was before the CA. I've always been a little nervous about the adhesion of the paper to the balsa w/o the CA, especially at the edges. Is the CA an unnecessary step? Can I just seal the paper with CA at the tip and trailing edges?
-Jim

 

[RimfireJim]

Originally posted by Bowhunter
I need to get looking for another FatBoy Cause I need to stick a 29mmt in it

My locals Michaels store still has them in stock; I picked up another one with this week's 40% off coupon. Came to $10.19 plus tax. Bought one recently from hobbylinc.com for $12.09. Tempted to pick up another one from Michaels. I had co-workers bring in their coupons for me. Dangerous!
-Jim