Should I add nose weight?

[kelltym88]

Hello,

I have recently remade my Mega Mosquito and upgraded it to 29mm. Being a big fin, draggy rocket, is nose weight required? The CG is just about where the CP is? It is about 2" longer, so slightly stretched (like my waist line).

 

[jmasterj]

It's a 3FNC rocket, what does your sim say? You can use the base drag cone adjustment to get a better handle on the CP.

 

[sambatterman]

Use OpenRocket and on the nosecone, double-click and use the "Override" tab to add weight until the CP and CG look right. There's the weight you want.

 

[lakeroadster]

Hello,

I have recently remade my Mega Mosquito and upgraded it to 29mm. Being a big fin, draggy rocket, is nose weight required? The CG is just about where the CP is? It is about 2" longer, so slightly stretched (like my waist line).

That's a beauty! Well done.

I'd swing test it and see how it performs... add nose weight as req'd.

 

[Hobie1dog]

it sounds like you don't have Open Rocket sim program, so just do a swing test as shown above.

 

[Back_at_it]

If your fins are the stock size, The CP of that rocket with a two inch stretched body tube should be 10.625 down from the tip of the nose cone. I sim'ed it with an F15-8 in the tail and the CG was at the 14.85 mark which is more than stable at 1.48 without doing the base drag hack in OR.

Insert the largest motor you are going to using into the rocket. Pack the rocket with wadding, shock cord and parachute then check it's CG. If the CG is at the 14.5" or further forward then you are fine. This is measured from the tip of the nose cone.

If your CG is lower than 14.5" then add nose weight until you get to that point.

 

[lakeroadster]

If your fins are the stock size, The CP of that rocket with a two inch stretched body tube should be 10.625 down from the tip of the nose cone. I sim'ed it with an F15-8 in the tail and the CG was at the 14.85 mark which is more than stable at 1.48 without doing the base drag hack in OR.

Insert the largest motor you are going to using into the rocket. Pack the rocket with wadding, shock cord and parachute then check it's CG. If the CG is at the 14.5" or further forward then you are fine. This is measured from the tip of the nose cone.

If your CG is lower than 14.5" then add nose weight until you get to that point.

Lot's of variables you quite frankly don't know about @kelltym88 modifications, so your advice is problematic, at best.

 

[Back_at_it]

Lot's of variables you quite frankly don't know about @kelltym88 modifications, so your advice is problematic, at best.

How so?

We know the length of the body tube is approx. 2 inches longer than stock. We know the body tube is 2.6". Assuming the fins are stock shape then we have what we need to plug into OR to get a CP. From there it's just a matter of packing the rocket and testing and adjusting for CG. What am I missing?

 

[Buckeye]

I'll take Back-at_it's OR analysis over a swing test any day.

 

[rharshberger]

How so?

We know the length of the body tube is approx. 2 inches longer than stock. We know the body tube is 2.6". Assuming the fins are stock shape then we have what we need to plug into OR to get a CP. From there it's just a matter of packing the rocket and testing and adjusting for CG. What am I missing?

I think you pretty much dead on, based on the info the OP gave.

As for swing testing, I used to do it...but with OR and RocSim being as good as they are I now only do it when I feel the design is questionable (and even after swing testing treat the rocket like a poisonous snake).

 

[lakeroadster]

How so?

We know the length of the body tube is approx. 2 inches longer than stock. We know the body tube is 2.6". Assuming the fins are stock shape then we have what we need to plug into OR to get a CP. From there it's just a matter of packing the rocket and testing and adjusting for CG. What am I missing?

The choice of which 29mm motor he will use... and how he did the 29mm upgrade. I'm a glueaholic... and the fin can is always heavier than OR calculates.

Sure, it's hard to beat a simulation when it comes to stability. But accuracy matters.

 

[kelltym88]

Thanks guys for all the replies... I figured the biggest motor I would use would be a G64...if I got to that point... I do have some F-67's... I used basswood CR's and epoxy, coated really well. TTW fins, again with epoxy, so it is not stock by any means. Based on the responses, I will add some weight to see how it balances out.

Right now, with the casing in the CG is below the CP, but again, a 3-FNC draggy rocket... but I will proceed on the side of caution.

Thanks again.

 

[Steven]

This is what happens when I add nose weight.