adding weight to fly a big rocket in a small field

[Elapid]

i'm thinking that if i add about 10 oz of nose weight to my cheetah i can fly it on a big motor for my field size.
that would put it at about 19 oz total weight.

anything i should worry aobut besides a larger chute?

 

[EMRR]

Yes. Being over-stable. This may induce increased sensitivity to any wind (weathercocking). It also may increase the stability beyond 2 calibers, which has been known to be called "overdamping".

Just a thought...

Nick

 

[sandman]

The launch rod is keeping it traveling vertically for the first 3 feet.

The biggest fear is that it will head horizontal as soon as it leaves the launch rod. That's about 4 or 5 feet off of the ground...

That's just about window height of a car in the parking lot!
Or about head height of a 12 year old!

THAT is the biggest fear!

For a small field...use a small rocket and a small motor.

Please!

We don't want to read about it in the paper.

sandman

 

[Missileman]

At some point when nose weight becomes too much. The pendulumn effect tries to bring the heaviest point down.
Arodynamic forces try to compensate. Fins and speed become critical. A nasty wobble may occur.
Wind will be a major factor, even a light wind will have an effect.

 

[seo]

19 oz. means you need to trigger a FAR101, doesn't it?

Keep it under 16 oz. and no procedures required.

 

[Ryan S.]

you mean near horizontal?

If you are always going to launch in a small feild build your whole rocket heavier.

I am more afraid of a rocket coming straight down then horizontal.

 

[BlueNinja]

Maybe you caould add weight to the front AND back of the rocket somehow... That would keep it normally stable if the weights were equal... Or would it?

 

[Elapid]

simply adding any extra weight at the center of gravity should avoid any problems in that case...
i havent' been in college for 11 years, so i'm a little rusty on mechanics/fluid dynamics...it's all coming back, but i think i'll drag out my old text and brush up...

thanks for the replies!
and please correct me if i'm wrong!

 

[Elapid]

they make self-sticking lead weights for balancing fancy rims at the tire store...or even a ballast donut like a motor mount where you have access to the space between the body tube and the inner tube...add weight and secure the bulkhead...ejection charge still has a path... voila...

i'm sure there are as many methods as modelers.


i think if i stay within the lifting parameters of the motor and have a chute to accomodate, everything should be fine...
still a few more days to pick up tips.

 

[Neil]

Where are you going to get the bigger chute? im hoping you already have it... Itll be coming down pretty hard if you dont...

 

[fehskens]

I routinely use this strategy -- a lot of weight in the nose to increase static margin and reduce performance. I have had no more problem with weather cocking than with lighter models with smaller static margins. Stability and weather cocking are a lot more complicated than just static margin. Putting weight at the end of a long moment arm also increases the angular inertia, which actually makes the model more resistant to perturbations.

len.

 

[wwattles]

Originally posted by Blue_Ninja_150
Maybe you caould add weight to the front AND back of the rocket somehow... That would keep it normally stable if the weights were equal... Or would it?

It would, to a certain extent. The issue is that the CG moves forward throughout the duration of the boost. If you add the weight close to the CG with the unused motor, and use strip weights running longitudinally, it should be okay. You can get self-adhesive strip weights in the pinewood car section of your local hobby shop.

WW

 

[Elapid]

Originally posted by Neil
Where are you going to get the bigger chute? im hoping you already have it... Itll be coming down pretty hard if you dont...

i think i'll cut up my wife's car cover...maybe our old tent...


thanks for the info, fehskins!
i had a feeling the simplest method would have a large chance of success seeing as there are a lot of payload-carrying models that fly just fine with varying degrees of 'nose' weight.

i'll be needing to use a shorter delay than the recommended motor, which is part of my strategy; i got some motors with 4 second delays that wouldn't work so well with a stock-weight cheetah from what i can surmise