FREE FLIGHT INDOOR
Bud Tenny, Box 830545, Richardson TX 75083
CONTEST DIRECTOR Alert
- CDs who fly in events where they officiate must appoint another CD to officiate, including processing of the model(s) to be flown, while they fly.
- Record-breaking flights made as part of the contest may be timed by one person.
- Record attempts aside from the contest flights, made with the permission of the CD, must have two timers, neither of whom is the CD of record.
Loose Ends
Previous columns reported on efforts to make a more-sensitive scale to support research in weights of different adhesives and methods of building (for example) laminated wing ribs and laminated outlines. The force multiplier for my electronic balance will easily give a 10:1 multiplication, but so far has been slightly erratic during calibration. I have yet to shield the mechanism from moving air, so no final results are available. If air drafts are not the problem, then there may be too much backlash in the pivot mechanism.
Appropriate software is available to handle the data generated by the paddle-wheel rubber tester previously reported. Before the software could be installed, my computer(s) were infected by a really nasty virus, which showed a lot of projects!
Indoor Group
At one time the Indoor Group numbered more than 140 persons who had registered with me. They received late-breaking news, such as Steve Brown's one-hour flight, shortly after it happened. Clubs holding Indoor events sent announcements to me via E-mail or snail mail (address at top of column) for posting to members of the Indoor Group and on an Indoor Web page.
In August 1998, a server crash at my Internet Service Provider wiped out the list. After it was mostly rebuilt, I got an ugly virus on my computers and lost it again. It has finally been rebuilt again, and I have better control over the situation. However, I don't have a way to verify how complete the new list is. If you got dropped from the old list or want to be added now, register by sending an E-mail to [email protected]. Come join us!
Rubber Motor Storage — A Reminder
Several years ago we had a big flap over rapid deterioration of rubber between seasons or even between flying sessions. The problem was solved by changing the type of envelope used for storing motors.
Tony Italiano reported the following in an issue of Free Flight, credited to Flightmasters by way of correspondence from Boyd Felstead of Australia:
There has been concern by rubber modelers, especially Indoor ones, of rubber deterioration when stored in plastic or paper envelopes. The Australians have found that the culprit is polyvinyl chloride (PVC) which is out-gassing vinyl chloride (VC) from the plastic bag. VC is bad for rubber as well as being a carcinogenic element (which may be disputed). Some plastic bags are made from PVC and polyethylene.
Manufacturers may call their bags, say, polyethylene or polyester, but the formula has dozens of variations in the recipe. Bags made from polyester, however, are chemically inert and will not harm rubber. Polyester bags are called "oven" bags which melt at approximately 280°C or 536°F. It is advised that rubber be stored in polyester bags, but do not overwrap with a polythene bag, as the molecules of VC gas will penetrate through the polyester bag and "chew" up your selected rubber!
A simple test is that polyethylene (polyethene) smells like a burnt candle when ignited, whereas PVC has an acid smell when burned.
There is an alternative: transparent paper envelopes (called glassine) used by stamp collectors. They are available from stamp shops and the Postal Service.
Dynamic Prop/Rubber Tester
Previous columns have reported on various flights Bob Wilder has made with his record-holding Indoor RC Electric Duration model. I have reported on and shown photos of some of Bob's extensive test facility where he evaluated motors, batteries, and props in pursuit of his excellent flight times. I have also reported on Jim Clem's Indoor prop test facility. Both those test setups tested the props in static mode—not moving through the air.
We know that a prop "unloads" (turns faster with the same torque input) when it begins to move—but we really don't know how much. I built a swing-arm tester that tests props while moving.
The first tests to be run are on one of Bob Wilder's prop/motor combos, as powered by a regulated current source with selectable output levels of 125 mA, 186 mA, 249 mA, and 296 mA. The aerodynamic drag of the swing arm will be approximated in the calibration runs with the bare arm, and with drag plates of 15 and 30 square inches respectively.
Various combinations of drive current and drag give a range of 1.37 seconds per revolution and 4.396 seconds per revolution. The velocity range for the propeller goes from 6.99 feet per second (fps) (bare arm and 296 mA) to 2.18 fps with the 30-square-inch drag plate and 125 mA drive.
After calibration runs that Wilder can use to correlate with his data, a motorstick will be substituted for the motor assembly. Future tests begin with half-gram test motors driving a standard prop. In this mode, the quality of various batches of rubber can be compared.
Another test mode would use standard motors to compare different props. The actual rig is large enough that I didn't have room enough in my house to get it all in one shot. A composite photo shows the 60-inch boom, which is static-balanced for each test setup. On the left, note the motor with a 3 x 5 note card (15-square-inch drag plate). A six-volt battery pack and the current regulator form part of the counterbalance; a glob of modeling clay is used for fine balance.
The swing arm boom is assembled from precision square styrene tubes glued together, a styrene upright and 1/8 x 3/8 spruce supports stiffen the center part of the boom, and a single adjustable upright tensions a length of sewing thread that supports the outer end of the boom at the motor. The base is constructed from 3/4" square hard balsa.
A photo shows the top of the base. A hard balsa triangular support holds a thrust bearing cut from tin can stock and drilled for a close fit with the .0625" music wire shaft. A lower hard balsa plate is drilled to fit the shaft. A nylon bead bears on the thrust bearing and supports the styrene boom. Bearing friction is so low in this setup that the boom weathervanes easily in drafts from fans and air conditioners.
The battery pack and current regulator units are attached using double-stick tape, as are the drag plates. The motor power wires are attached using Scotch® tape.
The motor has polarized leads; instead of a switch to control power, one power lead is unplugged to turn off the motor.
Another photo shows the motor, which mounts on an L-shaped bracket of 1/16" square spruce strips that plug into the boom. A common toothpick locks the motor mount in place. A similar arrangement will mount the motor stick for tests using half-gram motors. For the rubber-based testing, a small computer board will periodically measure and record prop rpm and boom rotation speed throughout the entire motor run. These data will be correlated with data taken from the rubber test rig reported on in a previous column.
m.a.
Transcribed from original scans by AI. Minor OCR errors may remain.
