Flying model rockets is a relatively
and inexpensive way for students
to learn the basics of forces and the
of a vehicle to external forces.
Any rocket is subjected to
four forces in flight;
thrust, and the
lift and drag.
There are many different types of model rockets.
An interesting variation of the two-liter
is the whoosh rocket.
This version of the whoosh rocket was developed by Roger Storm
of Fairview High School and Mark Skor of North Royalton High School;
both high schools are located in suburbs of Cleveland, Ohio.
The standard bottle rocket uses a two liter soda bottle as the
of the rocket, and pressurized water as the propellant.
The whoosh rocket replaces the heavy water with a much lighter, combustible,
alcohol-air mixture. The pressurization of the bottle occurs during the
of the alcohol. Because the exhaust products are much lighter than water,
the whoosh rocket does not
as much thrust as a water rocket, and the flight trajectory more
closely resembles a
than a water rocket
trajectory. Although the whoosh rocket does not
normally fly higher than 50 feet, it is instructional for students because
the thrust is generated by the combustion of a liquid fuel.
On the figure we show the launching of a whoosh rocket using a model rocket
launch pad. A straw is attached to the side of a two liter soda bottle
to guide the rocket along the rail during ignition.
The bottle cap is drilled to create a 3/8 inch hole which serves as
the rocket nozzle. Two or three drops
of rubbing alcohol are placed in the empty bottle and the bottle is shaken to
mix the alcohol with the air in the bottle. The rocket is then slid unto the
launch rail and an igniter is placed near the nozzle exit. As the flame from
igniter rises up through the nozzle, the mixture is ignited. Inside the
bottle a chemical reaction occurs which converts the alcohol and the
oxygen into carbon dioxide, water, and heat as described by this
2 C3H7OH + 9 O2 -> 6 CO2 + 8 H2O + heat
The reaction occurs very fast
and the heating of the exhaust gases produces high pressure in the bottle.
The exhaust gas is pushed out the hole in the cap and this produces
thrust as described by Newton's
When the thrust is greater than the weight of the bottle, the rocket
accelerates up the rail as described by Newton's
The powered portion of the flight of a whoosh rocket is quite short because
of the speed of the chemical reaction. The
majority of the
occurs with weight and drag being the only forces on the rocket.
WARNING - Extreme care must be exercised in flying a whoosh rocket and students
must be supervised when using this type of rocket. Do not attempt to build
and fly this rocket without the assistance of your teacher. Only use soda
bottles for the frame. Soda bottles are designed to withstand the pressure
associated with carbonated liquids. Water bottles are not strong enough
to withstand the pressure of combustion and may explode. The cap of the
bottle must be drilled to produce a nozzle for the rocket. Do not make
the nozzle hole smaller than 3/8 inch because this can produce excessive
pressure in the bottle during combustion resulting in explosion of the
bottle. Use only rubbing alcohol (isopropyl alcohol) for the fuel. Other
types of fuel may cause the bottle to explode. Because the fuel is highly
flammable, be sure to have a fire extinguisher available, keep the fuel
containers capped when not in use, use safety glasses, and only fire the
rocket outdoors in an isolated location. The rocket may be hot to the touch
when it lands, so exercise caution in retrieving the rocket.
Types of Rockets:
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