AAPT Apparatus Competition, Entry Description

Introductory Laboratory Category

Apparatus Title: Fan Unit Construction using Ducted Fan

Abstract (50-75 words)

Inexpensive, lightweight ducted fan motor units for electric model airplanes allow a simpler and faster construction of fan units to supply a nearly constant force in mechanics experiments on force and motion¹. The duct serves as a shroud increasing the safety of operation. The lighter units facilitate experiments using the newer plastic PASCO dynamics carts.

Description:

Ducted fan unit construction

Robert Beck Clark² suggested experimenting with the use of an electric ducted fan intended for model airplane use. The homemade fan unit described here was designed for simple construction of such a fan unit. It costs more for parts and is less robust than the fan unit design described in the 1993 article by Morse, but is lighter and easier to assemble than that unit.

Parts list.

Ducted Fan GWS-EDF50 Electric Ducted Fan. From hobby shops or web-sites. List price about $20. May be found for less on sale. Some sources are: http://www.officeshops.com/gws/ducted_fans/

http://www.balsapr.com/catalog/parkFlyers/ductedFan.asp

http://www.aeromicro.com/Catalog/ducted_fan_systems_108649_products.htm

Battery Case with Switch

Radio Shack 270-40 holds 4 AA cells and has a built in slide switch. A similar part is available from Mouser Electronics and other suppliers.

Double Sided Mounting Tape

Duct tape

Wooden skewers

Corrugated plastic. From craft stores. 20 inch by 30 inch piece about $3.75

Construction

1.Cut 5 cm by 5.5 cm piece of corrugated plastic, with corrugations running along the short axis.

2. Cut two 5 cm strips of mounting tape.

3. Center the corrugated strip on the bottom of the battery case and mount it with corrugations paralleling the battery alignment. This serves to locate the battery holder on top of a low friction PASCO™ cart. (Other carts may require a different mounting system.)

4. Cut a 6 cm by 6 cm piece of corrugated plastic. Cut a piece of duct tape 20 cm long by about 2.5 cm wide. Stick the middle of the duct tape to the middle of the corrugated plastic, with the tape parallel to the corrugations. Use the duct tape to mount the ducted fan unit with the fan axis perpendicular to the corrugations. Be careful not to distort the duct when wrapping the tape over the ducted fan unit. (Alternative construction-make width of corrugated plastic about 3 cm. Use two nylon cable ties through corrugations to fasten duct unit on top- don’t over tighten or you will distort duct.)

5. Cut two 6 cm strips of mounting tape. Stick them to the bottom of the corrugated plastic and ducted fan assembly.

6. Mount the plastic and fan assembly on top of the battery case with corrugations running perpendicular to the battery alignment. Make sure you do not obstruct the switch. The fan blades should be farthest from the switch. See diagram.

7. Solder the battery pack leads to the fan leads, or use connectors of your choice. For a remote switch you will need to provide some kind of connector to allow you to break the circuit or provide a remote power source and switch. Use a closed circuit two conductor phone jack as in the first version, which also allows use of a timed switch, or you may use snap type battery connectors.

8. Fasten the fan unit to the cart with two strips of duct tape. You may gang three fan units together by using two wooden skewers passed through the corrugations on the plastic on the tops of the three battery cases. A rubber band around the ends of the skewers will keep the fan units from sliding off. (Fig. 2.)

Notes

1. Robert A. Morse, “Constant Acceleration: Experiments with a Fan-Driven Dynamics Cart”, Phys. Teach. 31, 436-438, (1993)

2. Robert Beck Clark, personal communication, (2003)