Flying model rockets is a relatively
and inexpensive way for students
to learn the basics of forces and
the response of a vehicle to external forces.
Students can also learn some of the basics of full scale
rocket operation and performance.
On this slide we compare and contrast
A model rocket is subjected to four
thrust, and lift and drag.
The same forces operate on a full scale rocket as it moves through the atmosphere.
of a full scale rocket takes it out of the atmosphere as quickly as possible.
Therefore, the aerodynamic lift and drag are less important for
a full scale rocket relative to a model rocket.
The magnitude of the aerodynamic forces depend on the
and air density
to near zero at the edge of the atmosphere.
For model rockets, the entire flight is conducted in the lower atmosphere
and the aerodynamic effects are very important.
both model rockets and full scale rockets use a
rocket propulsion system.
Model rockets employ a variety of small
solid rocket engines. There are some larger
"amateur" rockets which use liquid or hybrid engines, but these are intended
for older, more experienced rocket builders and are not discussed at this site.
Full scale rockets may employ either
rocket engines. On full scale rockets, solid
engines are often used as
during the first minutes of flight, with liquid
engines used for sustainers and upper stages.
For a model rocket, the propellant is a small fraction of the weight of the
entire rocket, typically, 10 - 15%. For a full scale rocket the propellant
represents a large mass fraction of the weight of the vehicle, typically,80 - 85%. Part of the reason for this difference is that model rocket engines
very quickly, usually less than
two seconds. A full scale rocket engine may fire for 10 minutes to get into orbit.
During flight both model rockets and full scale rockets must provide some systemof stability and control. Stability indicates that if the flight path is
slightly perturbed, the rocket will return to the previous path and not fly
erratically. Control is the ability to maneuver the rocket during flight.Both models and full scale rockets are designed with
passive stability within the atmosphere. The "passive"
part means that the rocket will return to the flight path without moving any
control surfaces. The conditions for stability are that the
center of gravity must be located above the
center of pressure. Model rockets have no provisions for
control. After the rocket leaves the
launch rail, it can go anywhere. You watch a
model rocket fly; you can't control it. Model rockets often turn into the
wind, in a maneuver called
because of aerodynamic forces on the stability fins.
Real rockets use very sophisticated instrumentation, computers, and high speed
actuators for flight control.
The early V2 had
small vanes in the rocket nozzle which would deflect the thrust during flight.
Most full scale rockets use a system called
in which the
whole nozzle is rotated while the engine is firing.
Model rockets fly at relatively low speeds (<250 mph) so aerodynamic heating is
not a concern. Model rockets are made of inexpensive
like balsa wood, cardboard, or plastic.
Full scale rockets fly very fast (> 10,000 mph) so aerodynamic heating is a big
concern. Exotic, expensive materials are used in the construction of real rockets;
materials like titanium, and nickel alloys. On some rockets, like the Space Shuttle
external tank (ET), special insulating material is applied to the metal skin to
prevent damage due to aerodynamic heating. That's why the ET is orange-colored.
Types of Rockets:
Full Scale Rockets:
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