They hold everything together, the fins, the motor and the nose.
It depends on what type of rocket you are building.
To build a model rocket you will need a chemical rocket engine, some cardboard tubes, glue, a long rubberband, a garbage bag and a lot more. You can find a complete list of supplies here: http://www.ehow.com/how_2308899_build-model-rocket.html
The body tube of a rocket is there for friction. As the rocket comes back down the body tube along with the fins are there to slow it down. Also the longer the body tube the faster your rocket will go. The body tube gives it a narrow edge.
about one-forth of the height of the size of the rocket.
Normally model rockets are made from kits you buy at a hobby store. The most famous maker of model rocket kits is a company named Estes. Visit links below. The other option is to build it from scratch. One great way to build from scratch is to purchase the Designer's Special from Estes. It contains an assortment of body tubes, nose cones, and centering rings. Just make sure to use an 18mm. diameter tube for the engine (usually will need to be 2.5in long) and that the Center of Gravity of the Rocket is at least one body diameter ahead of the Center of Pressure and you'll be fine. You can find the Center of Gravity by balancing the rocket with everything in it, and you can find the Center of Pressure of the rocket by balancing a cardboard silhouette of your rocket, or you can find both before you build the rocket by using a simulator like Rocket Modeler II (http://www.grc.nasa.gov/WWW/k-12/rocket/rktsim.html) or RockSim (http://www.apogeerockets.com/rocksim.asp).
You use a Launch Lug, Parachute, Removable Solid Rocket Engine, Parachute Lines, Fins, Body Tubes, Nose Cone Payload (removable), Engine Mount (fixed), Shock cord, and Recovery Wadding.
It is the main part of the rocket that everything else is built off of. The central piece.
i like to use balsa for fins; paper tubes for the body and balsa or plastic for the nose.
Modern model rocket fuel is a solid fuel.
A rocket body tube is the center of a rocket; also the piece that holds the rocket together.
In a real rocket, there is short a time in atmosphere and the aerodynamics are less important. In a model rocket, all flight in the atmosphere and the aerodynamics are very important. In a real rocket, it has a liquid or solid rocket engine and a large propellant mass fraction. In a model rocket, it has a solid rocket engine and a small propellant mass fraction . In a real rocket, there are four forces during atmospheric flight. In a model rocket, there are four forces throughout flight. In a real rocket, there is a long powered flight . In a model rocket, it has a very short powered flight . In a real rocket, it has passive stability and active control . In a model rocket, it has passive stability and no control. In a real rocket, it has expensive materials such as aluminum, titanium, and nickel alloy. In a model rocket, it has inexpensive materials such as balsa, cardboard, and plastic. In a real model, there is a high speed and the heating is very important. In a model rocket there is low speed and the heating is not important.
He invented the rocket in 1926