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Bowhunter

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Would a 4 C-6 cluster be concidered mid-power?
 

Bowhunter

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Its Done the finish didnt turn out the way I wanted it to.
 

SwingWing

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That should be a fun flier.
How much nose weight did you have to add?
 

Bowhunter

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I got to go to the store tomarrow and get some modeling clay Ill let ya know later
 

Fore Check

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For nose weight, get some of the Duck brand "Poster Putty" in the "business supplies" section at Wal-Mart. It's blue in color, and looks like two sheets of four strips of blue clay. It's the stuff you hang posters and such to a wall with without using nails and stuff. It comes in a 2 oz. package, so each "strip" (there being 8 "strips" in a package) is about 1/4 oz.)

It weighs about as much as modeling clay (for the same volume,) costs a little less, is easier to work with, and takes *forever* to dry out. Even when it does, it's "stuck" when dry. Heck, it's deisgned to be sticky, so when you push it up in the front of your nose cone, good luck getting it out!



On the other hand - it appears you have some epoxy on hand. You *could* simply get some lead fishing weights, drop in them in the nose cone, and pour some epoxy in to fix them there forever. You probably have a fishing tackle box with a few lead split-shot sinkers hiding in your garage somewhere. Lead sinkers make superb nose ballast.
 

Fore Check

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By the way, after downloading the RocSim file off EMRR for the Fatboy, modifying it to be a 4 x 18mm C6-7 cluster, I had to add 2.5 oz. of nose weight to acheive a stability caliber of 0.60 Barrowman (which is 175% of the acceptable minimum according to Galejs' paper regarding the stability of short stubby rockets vs. long skinny ones.)

With 2.5 oz of nose weight and 4 x C6-7's, RSim predicts 1361 ft. altititude, with an optimum delay of 6.91 seconds (so use the C6-7, rather than the C6-5.)
 

Bowhunter

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It Died but what a way to go things just flew everywhere. Oh well it was fun
 

Bowhunter

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It got hung on the pad then ripped off the LL then lawn darted and ejection charge blew out the side of the BT. It was fun tho
 

Ryan S.

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wow sounds pretty spectacular


sounds like my barracuda except the ejection charges didnt blow mine up
 

Rob Fisher

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Time to go to wallyworld & getcha another $8.00 fatboy
 

crashinj

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I check my Wallyworld everytime I go but haven't seen a Fatboy there in sometime. If someone happened to pick me up a couple I'd gladly pay for them plus postage. All the Fatboy postings makes me want to play.

CrashinJ
 

kenobi65

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Originally posted by Bowhunter
It got hung on the pad then ripped off the LL
Sounds like you may have suffered a Bernoulli lock. How far off the blast shield was the bottom of the rocket?
 

Bowhunter

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I may beable to repair it. Ill get on it in the morrning
 

Ryan S.

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Originally posted by kenobi65
Sounds like you may have suffered a Bernoulli lock. How far off the blast shield was the bottom of the rocket?
I thought it was the Krushnik effect. Hmm wasnt bernoulli the guy who discovered as the speed of a fluid increases its density decreases. I thought the Krushnik effect was when the motor was near the pad and the engines were somewhat up in the rocket and the high speed gases pulled the air out of the back of the rocket causnig a vacuum and if to close to the pad this vacuum would hold the rocket down

It could have just bound up on the rod, which often happens, and if it ripped off the lug and then took off then I think this is probaby what happened

I could be confused...about Krushnik and Bernoulli hmm
 

Bowhunter

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Well I got the job done I just got in from retreiving it but it went up about 100' then made a 90deg. turn hauled A*S I need a longer shock cord I had seperation and I put more nose weight in it and then I went to my motor box and discovered I only had 3 c's left well its time to make a trip to wallyworld. But the good thing is I saved it from death and gave it life agian. (ITS ALIVE!! ITS ALIVE!!!!!)
 

loopy

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Congratulations! It's kinda like the Phoenix (mythical, not Estes) Fat Boy! lol
 

powderburner

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The so-called Krushnik effect is caused by setting a motor nozzle too deeply inside the back end of a BT, causing the motor exhaust to basically cancel itself and significantly reducing thrust. You would have to position your nozzle approximately one "BT diameter" (or more) forward of the edge of the BT before this effect shows up.

The Bernoulli principle states that as flow velocity increases, pressure is reduced. This can appear in the form of 'launcher lock' when a nozzle is positioned on (or very close to) the blast plate and the motor exhaust is forced to squirt out radially. This can reduce pressure enough to 'suck' the rocket down onto the blast plate during the motor burn.

If you built your Fat Boy anywhere close to the instructions (motor mount in the correct location, fins on the right places and pointed in the right direction, etc) then you probably did not have either one of these effects take place.

Were you by any chance using one of those two-piece Estes launch rods that come with the starter specials? If so, toss it and go buy a piece of 1/8 or 5/32 music wire from your local hobby shop. The joint in Estes rods can result in a small misalignment between the two halves, but it can be enough to snag a rocket.

Check the tips of your launch rod to make sure there are no burrs from dropping or tapping the rod on concrete----if you find any burrs there, file them off. Keep your launch rod clean and free of rust with an occasional wipe-down with an oily cloth. Scrub dirt and exhaust deposits off with a piece of steel wool (we keep these items in our field box, don't we?). If the launch rod gets bent or corroded, replace it.


Boy---now that I read it again, this sounds kind of dictatorial and just a bit harsh. Really didn't mean it that way.
 

Bowhunter

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That was cool it did good at the ellsberry launch. I launched it four times but all 4 motors fired together twice it was fun i had to do some epoxy work on it alittle but no real problems
 

Bowhunter

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The Bowhunters gives our sympathy to Dr. Don and my heart completely shattered when the Amraam had its problem also
 

rocketdad0934

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WOW sorry dr don to bad.
so I modified my faat boy to a three 18mm cluster after retriving the body tube from a tree (thank you elmers glue) and then purchased another kit (walmart) It flew real good without any additional nose wieght, now I have built a single engine booster stage from the left over parts in the kit. the problem is I have not built or don't own a two stage rocket and would like the info on how to set up and make this thing go. lighting the three engines from the one. what do I need?? what is the trick?????:D
 

powderburner

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Originally posted by rocketdad0934
. . . would like the info on how to . . . make this thing go. lighting the three engines from the one. what do I need??
Are the three upper stage motors arranged in a tight cluster or are they spread out?

It is going to be a bit of a challenge to deliver the burn-through from a single booster motor to three upper stage nozzles. Here is an application where you may need some of that 'quick match' stuff to accomplish what you want to do.
 

rocketdad0934

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yes it is a very tight triangle cluster with the three fat boy wings unaltered holding every thing in place with only the top centering ring to work the ejection charge so I made the booster stage to be about 4 inches in length and assembled the wings and motor assembly per the directions. the stage coupler goes from the top of the single motor to the bottom of the wings of the rocket. I fire proofed the wings around the motors with elmers as the directions in the richter rechter said so it should withstand the blast of the booster. what is the "quick match and where do I get it???
 

Bowhunter

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I know this is an old thread but I got another fat boy kit and I just happen to have a few 4-24mm cluster CR's that fits the BT. Well here I go agian man I cant help it:D
 

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