Quantcast

Bigger Daddy CG

The Rocketry Forum

Help Support The Rocketry Forum:

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
I've just loaded up my Bigger Daddy with 4 x D12-7's and found the CG. It is 13.5cm from the base of the bodytube , is this stable ?

[/newbie mode on] Could someone explain please , where the CG should be for a rocket to be stable [\newbie mode off]

Karl
 

firemanup

Well-Known Member
Joined
May 2, 2002
Messages
1,305
Reaction score
79
The general rule of thumb requires the knowledge of the CP (center of pressure) of the rocket.

At least one caliber of stability is what's wanted, a caliber being the same length as the diameter of the rocket...

So to put this all together, you want the CG one caliber above or toward the nose, of the CP.

In a 3" rocket that has the CP 20" from the nosecone, if the CG was 17" from the nosecone it would then have one caliber of stability.. CG 14" from the nosecone and you have two calibers of stability...

EMRR has several listings in the CP library for the big daddy, they all put the CP between 14 and 15" from the nosecone.. You want your CG to be about 11 or 12" from the tip of the nosecone..for one caliber of stability....
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Well I've just the digital callipers and found out that my CG is 19.152" from the tip of the nosecone . So this mean I need more noseweight?
Karl
 

Zonker

Well-Known Member
Joined
Jan 21, 2004
Messages
45
Reaction score
0
Yes. I just finished my 4x24mm big daddy and I had to add 4 oz to the nose to get the CG right. Depending on how you've built yours, you may need to add a little more or a little less.

Zonker
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Hmmm! This thing weigh's so much allready Im not sure it's even gonna be worth modding it for 4 x 24mm's :(
 

Zonker

Well-Known Member
Joined
Jan 21, 2004
Messages
45
Reaction score
0
I ran into the same problem. The most powerful motors I can get in my area are Ds, so the only way to get more power was to cluster. As you mentioned, the downside is the weight....my big daddy is a pig. I have yet to launch mine, but I'm not expecting a lot of altitude (it simmed to 900ft, but I think that's being optimistic). Once I find a place to launch, I'll give it a shot and let you know what happens.

Zonker
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Maybe Ill have to come up with a Big Daddy 2 Stage design with some spare 3" tubing.....;)
 

Elapid

Well-Known Member
Joined
May 2, 2009
Messages
1,734
Reaction score
0
the Big Daddy is the only rocket i've built basically stock!
hehehhe!
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,468
Reaction score
5
Totally Tubular now has the 3" tube for the Big Daddy.

He mistakenly marked it a BT-100 IT IS NOT A BT-100!

It is an old NCR size tube and the same size as the Pro Series 4 engine cluster Patriot Missle.

http://www.dars.org/jimz/est2066.htm

THAT would be a neat clone to do since it uses the Big Daddy nose cone too!

sandman
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Sweet Sandman! Im sure my mate has that rocket , he does have a Estes 4 24mm Patriot......!
Yep the tube im getting is gonna be a TT 3" tube that is listed on the Apo11o website here.
It is actually called the Big Daddy tube , and the specs are :

ID
2.217

OD
2.175

Wall
0.021

Legnth
34.00

Weight
75.330

EDIT:

The Big Daddy is not the same as BT-80 , and if i where to make a 2stage BB , the biggest coupler I can get is to couple BT-80 :-/
 

qMaxx

Well-Known Member
Joined
May 6, 2004
Messages
107
Reaction score
0
Originally posted by Karl
Sweet Sandman! Im sure my mate has that rocket , he does have a Estes 4 24mm Patriot......!
Yep the tube im getting is gonna be a TT 3" tube that is listed on the Apo11o website here.
It is actually called the Big Daddy tube , and the specs are :

ID
2.217

OD
2.175

Wall
0.021

Legnth
34.00

Weight
75.330

EDIT:

The Big Daddy is not the same as BT-80 , and if i where to make a 2stage BB , the biggest coupler I can get is to couple BT-80 :-/
You might want to check those dimensions you listed again...those are the specs for BT-70 tubing...not to mention you mixed up the ID with the OD :D

As for a coupler, just cut off a couple inches of the tube you're using, slice it lengthwise, overlap it inside the tube you want it to fit inside of, mark the overlap, cut off the excess, then glue it in place as a coupler.
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,468
Reaction score
5
Totally Tubular has the tube as a T-100 tube and it's exactly the same as the Big Daddy tube...I have one here in my hands.

I just think the specs. on the Apo11o web site are a misprint. It is 3.00" O.D.

It's thicker too to match the Big Daddy nose cone.
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Hmmm Im not sure that there is any way to add a booster to the Big Daddy , at the aft centering ring , theres no space to fit a coupler.Unless you cut the booster BT up , so the fins can sit in them?
 

qMaxx

Well-Known Member
Joined
May 6, 2004
Messages
107
Reaction score
0
Originally posted by Karl
Hmmm Im not sure that there is any way to add a booster to the Big Daddy , at the aft centering ring , theres no space to fit a coupler.Unless you cut the booster BT up , so the fins can sit in them?
Try putting 3/16" launch lugs in the centering rings, then gluing 3/16" dowels in the booster to line up with and slip into the lugs. You could even use a small coupler section that would just stick out of the booster 1/4" or so, just to maintain alignment of the stages.
 
Top