Please Help!

How do you make a rocket go higher without changing the motor. I am building the Alpha rocket. I have experience with model rockets but there is a contest. Please Help!

An Aerotech D21 Single Use Motor will fit that Bird.

We are not aloud to change the motor only the body shape and weight.

Airfoiling, or at least putting a knife edge on the edges of the fins can reduce quite a bit of drag, as well as substituting the launch lug for a tower, and using a piston to get every possible newton second out of the motor. You can also polish the body of the rocket, the fins, and the nosecone to get the smoothest surface possible, reducing skin friction. Also, building the rocket as light as possible (or at least as close to the optimal weight as possible(use Openrocket to determine that)) other than that, using a minimum diameter rocket (an 18mm motor in an 18mm tube) will give you much more altitude. Also, leave off the decals. They add weight and drag.

Welcome to the forum!

There are three basic forces acting on a rocket in flight.

1) Thrust from the motor upward - you said we can't change that.

2) Gravity pulling the rocket downward - you can't change gravity, but you can decrease how much is has to pull on.

3) Air pushes back on the rocket, resisting it's movement - decrease the diameter or change the shape of the rocket, or make the rocket smoother.

That's the basics.

+1 on TopRamen's idea. Not for the contest, but afterwards... Have you ever seen a rocket teleport? A D21 will put it to 1700 ft. reeeaal quick!

Nate

In addition to smooth surfaces, etc. optimize your rocket to damp any oscillations quickly without adding additional fin surface area. Any oscillations of angle attack is energy spent pointing a direction other than straight up.


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+1 on everything above.
seal and foil the fins-you may be able to trim a bit off the ends.
no paint
do a cg/cp check to see if you can trim some body tube off
see if you can hollow out the nose cone a bit, then seal, buff and wax (it if is made of balsa-I keep forgetting this is the age of plastics.)
don't overglue.
You have to remember that competition models 'push the boundries' and aren't really designed to fly repeatedly. Any kit is over-engineered for safety and to some extent crash-worthiness. By doing these mods you are reducing these parameters for the 'contest'.

There might actually be an optimum weight. There maybe an Apogee e-zine article on this. You see just making it light is not necessarily the key, because the deceleration during the coasting phase due to air drag will be higher for a light rocket. You could go to the Apogee website and look to see if there is an issue on this subject, but there are over 200 issues. If you have a simulation computer code like Open Rocket or Rocsim, you could run the model with different weights and see which one goes the highest.

Use elliptical fins. Boat tail. Change out the parachute for a streamer. In the Estes publication TR-11 they devote a great deal of space on how to get an Alpha to go higher. I have a copy but I understand it's available online.

aerostadt said:

There might actually be an optimum weight.

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A 'naked' Estes A, B, C, motor is already beyond optimum mass. Make the rocket as light as possible

Ditto the suggestions on finding the optimal weight (yes, you may actually be too light), and making it as aerodynamic as possible. +1 on a tail cone? That will help it slip through the air easier. +1 on a launch tower or piston launcher (I don't know squat about piston launchers). You may be able to replace balsa fins with very thin plywood (1/16" or thinner). You can also change the shape of the fin.

I am surprised no one has asked yet: How are you determining altitude?

A 'naked' Estes A, B, C, motor is already beyond optimum mass. Make the rocket as light as possible

Click to expand...

This is a valid point. There is some information in Apogee "Peak of Flight" issue no. 84 that helps explain optimum mass, but this issue might confuse some people. There is more information in Apogee Technical Publication #15 (1999), but I don't see it on their website. On page 16 of this report it states that the optimum mass for an Estes Alpha with an Apogee C10 motor is 30.25 g, but this is just a little bit over 1 ounce, which is very light.

The original request doesn't really give very much information. It is not clear what is the rocket or the motor and as CZ Brat says the request makes no mention of how the user is going to check altitude.

nute said:

, as well as substituting the launch lug for a tower, and using a piston to get every possible newton second out of the motor.

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If you don't want to do a piston launcher or tower then follow the advise of the angry launch lug - see posts 10~12 about cutting the lug at a 45 degree angle
https://www.rocketryforum.com/showthread.php?69216-The-Angry-Launch-Lug&highlight=angry

I seem to recall that I read about some college kids that were given an Alpha to optimize for maximum height and the Alpha ended up looking a lot like an Estes Sprint when they were finished.

+1 on cutting the launch lug so that the ends are at a 45 degree angle. Maybe mount the launch lug in the fillet area of one of the fins, and make sure the fins are on very straight to minimize any spin that the fins may induce. Spinning will rob the rocket of height.

David

Astronot said:

I seem to recall that I read about some college kids that were given an Alpha to optimize for maximum height and the Alpha ended up looking a lot like an Estes Sprint when they were finished.

+1 on cutting the launch lug so that the ends are at a 45 degree angle. Maybe mount the launch lug in the fillet area of one of the fins, and make sure the fins are on very straight to minimize any spin that the fins may induce. Spinning will rob the rocket of height.

David

Click to expand...

Agreed. The Astron Sprint has elliptical fins and a boat tail. Both reduce drag greatly. Airfoiled clipped delta fins are almost as low drag and easier to make.

I would eliminate the launch lug all together and use a tower. Adding a piston launcher to the tower would be the ultimate.

Bob