Wildman 4" Dink Nosecone Ballast

[davdue]

My Dink has the Polycarbonate nosecone with the plastic tip. What do you all suggest for ballast. Per OR I need about 12 oz of weight to even get 0.57 caliber stability. The stability vs time plot shows it is pretty stable but I don't know if I should believe that. I have always had over 1.0 on all my rockets. With the eyebolt into the nosecone tip I can't really just pore epoxy and BB's in the tip. I tried 1-1/4 X 1/4 fender washers but 6 of them is only about 2 oz. Any ideas? This will fly on the AT J180T at LDRS. Attached is the latest OR file with overrides for quite a few of the items that I can weigh individually.

 

[David Schwantz]

Get longer threaded eyebolt, pour lead shot into MMT tube with eyebolt sticking through. Add epoxy. Secure with fender washer.

 

[davdue]

Get longer threaded eyebolt, pour lead shot into MMT tube with eyebolt sticking through. Add epoxy. Secure with fender washer.

Sounds but one thing I failed to mention in my post is that this is HED rocket so the main is in the nosecone with little room for weight. I guess it shouldn't take too much room for 10-12 oz of shot. I will have to try packing the chute and see how much room is available at the tip for weight.

Any ideas on what the lowest stability margin I should have?

 

[Nytrunner]

What's the length of the rocket? It's a stubby if I recall correctly (L/w less than 10)

For Stubbies/Superrocs, shoot for between 8-15% body length. The "caliber" approach is less applicable

 

[davdue]

What's the length of the rocket? It's a stubby if I recall correctly (L/w less than 10)

For Stubbies/Superrocs, shoot for between 8-15% body length. The "caliber" approach is less applicable

Yeah total length is 36.5” on a 4” rocket. But tip to bottom of booster tube is 34.5”

So 8% of 34.5 is 2.76” and 15% is 5.18”

So I am guessing that is the distance the CG is in front of CP? If so, 16 oz will get me 8.6%

With that much weight I am concerned about the nosecone shear pins during drogue deploy with main deploying at apogee.

 

[Nytrunner]

So I am guessing that is the distance the CG is in front of CP?

Right.

Hmm, that does sound like a lot. Sounds like the stability sims are lending support though. Sounds like a prime opportunity to exercise L3 flier judgment

 

[WILDMANRS]

My Dink has the Polycarbonate nosecone with the plastic tip. What do you all suggest for ballast. Per OR I need about 12 oz of weight to even get 0.57 caliber stability. The stability vs time plot shows it is pretty stable but I don't know if I should believe that. I have always had over 1.0 on all my rockets. With the eyebolt into the nosecone tip I can't really just pore epoxy and BB's in the tip. I tried 1-1/4 X 1/4 fender washers but 6 of them is only about 2 oz. Any ideas? This will fly on the AT J180T at LDRS. Attached is the latest OR file with overrides for quite a few of the items that I can weigh individually.

The 12 oz of nose weight should be plenty .
As far as the room up there attach the chute directly to the avbay an just use a couple yards of 1/4 Kevlar to attach the nose cone to the avbay .
The chute always comes out then and you save a ton of room on shock cord ..
Plus all of your weight is up front in the cone.

 

[davdue]

Right.

Hmm, that does sound like a lot. Sounds like the stability sims are lending support though. Sounds like a prime opportunity to exercise L3 flier judgment

Lol. I have never built a short stubby rocket before so that is why didn't necessarily trust my L3 flier judgement.

The 12 oz of nose weight should be plenty .
As far as the room up there attach the chute directly to the avbay an just use a couple yards of 1/4 Kevlar to attach the nose cone to the avbay .
The chute always comes out then and you save a ton of room on shock cord ..
Plus all of your weight is up front in the cone.

Thanks Tim. I have a 3 loop One Bad Hawk 1/4" Kevlar harness from Teddy and was planning on using it just like you suggested. The bad thing is I won't have the reload until I pick it up at LDRS so the first opportunity to check the CG will be at the rocket pasture. Well if I need to add weight I can always make it with epoxy out there. Lord knows there will be enough heat to get it to cure quickly. See ya at the pasture.

 

[jd2cylman]

Lol. I have never built a short stubby rocket before so that is why didn't necessarily trust my L3 flier judgement.



Thanks Tim. I have a 3 loop One Bad Hawk 1/4" Kevlar harness from Teddy and was planning on using it just like you suggested. The bad thing is I won't have the reload until I pick it up at LDRS so the first opportunity to check the CG will be at the rocket pasture. Well if I need to add weight I can always make it with epoxy out there. Lord knows there will be enough heat to get it to cure quickly. See ya at the pasture.

Look up the biggest and smallest motor you'll ever use in Thrust Curve. It should give you a loaded weight for each. Use a sack of BB"s or rocks or small children that weigh the same and fit in the same area of your mmt. Then you should be able to check your CG. Note: the children will be a little harder to pack in the same volume...

 

[davdue]

I understand jd2cylman. I was saying that I wouldn’t be able to physically check the CG until LDRS. I’ll have the weight already to go before then.