3. The flyer will have the choice of experimenting with various types of propellers for maximum thrust and extended flight times.
Most flyers I know will ask a winner what prop works best rather than experiment himself --- It's easier.
4. Flight times and fly-off times are kept to 2 minutes to stay within the boundaries of most free flight fields. Motor run times are cut drastically to prevent fly-off flights from exceeding the field boundaries and to limit the number of fly-off flights. This will make it imperative for the flyer to learn how to use motor timing devices that will be accurate. Such devices as the Moffset types or the present "Smoothie" timers are readily available and inexpensive and easy to install.
I agree with retaining 2 minute limit for flyoff flights
The parallel to reduced motor runs for flyoff flights, with the charge allotment approach, is to FURTHER limit the charge (in mah). This is much simpler for the beginning flyer, as a timer does not have to be reset. The "Smoothie" timer I got to try added $70 to the model's cost, and was so tiny I could not sucessfully solder wires to it without "bridging". I finally called on electronics tech to repair it for me. The mosfet timers I have tried slow the motor, don't have a sharp cutof, and are severely ampere limited.
5. Many of the currently available kits, including those designed for 1/4 A, Nostalgia, 1/4A Old Time Gas and even small rubber models will make an excellent basis for this size model. Modification to make the model electric powered will be minimal. This is the weight of a 1/4 A payload model which has the same wingspansuggested by these rules. Performance should be comparable. The weight will ensure a dependable, consistent model without resorting to high technology or extraordinary modeling skills, Use of AMA rules governing safety and flight lines procedures etc. will apply.
I agree re: the availability of kits, further: Minimum weight is not needed -- 36" span restriction alone determines OPTIMUM battery and weight.
Entry level electrics should not need timers, to minimize cost and complexity. This is easily done with the limited charge concept. Once beginners become experts, they may well want to "graduate" to the limited motor run electric events.
MISCELLANEOUS
A. Getting an accurate charge allotment to each contestant for each flight: Relatively inexpensive chargers are commercially available, that can be used by contest management to charge each contestant's flight battery just before each flight. Fifty mah is the E-38 charge that has been found by repeated testing to routinely provide 2 minute flights for a good model, regardless of cell count. Charging takes less than one minute. First, the motor is switched on to bleed off any residual charge in the battery, then the charger is connected to the battery with the switch off. A visual display indicates the accumulated charge, and the charger is disconnected when the allowed charge is reached. This must be done manually now, but the electronic experts tell me it can be done automatically in the future. All that would be needed then is to dial in the desired charge and hit a start button.
B. Adjusting the charge downward for flyoff flights: One way to increase the difficulty of maxing is to reduce the charge allotment 10% of the basic for each flight after "maxing out". Thus the 4th flight might be given a charge of 90% of 50 mah, or 45 mah; the 5th flight 80% (40 mah); and so forth til the max is not made.
C. LER/LMR events vs. charge allotment: Because of the physics involved, any Limited Engine Run/Limited Motor Run event asks, basically, "Who has the fastest climb?" More accurately, the contest is to find the model with the greatest climb/glide ratio; and it is easier to improve the climb than the glide. Opposed to this is the charge allotment, where climb rae is not as impotant as height achieved on the limited battery charge -- It's more of an efficiency thing. Exhaustive testing has demonstrated that fast climbers may do as well, but have no advantage.
D. The cell count variable: The chart below summarizes tests runon the SAME model with cell counts from 2 to 6 where only the cell count was changed. Altogether 25 timed flights wre made, with the same mah charge; the shortest flight being 103 seconds and the longest 154 seconds. Average times were taken for each number of cells and plotted as below. As expected, rates of climb varied considerably, but the tests with fewer cells RAN longer on the same charge, and the model got almost as high. Every attempt was made to insure all flights wre made in dead air.
E. Reason for one specific motor explained: I've found that a mere 5% or so of the motors tested provide good performance. The rest are wimpy, and the climb performance is poor. It would seem that expecting semi-interested FF'ers to search for the one best motor for an event when it has already been founf is unrealistic. Instead, why doesn't the NFFS offer a kit, to include motor, prop, wire and perhaps battery, to all interested, and give a price-break to the kids? Such a kit would include simplified instructions that require no special electrical knowledge by the recipient. If this were done, the playing field would be level. The danger if different motor designs were allowed is best seen by the math involved in the hypothetical example that follows, where a few assumptions are made only for simplicity and clarity.
The most basic formulas in volved here are (1) amperes (current) = Voltage (pressure)/resistance (in ohms); and (2) wattage (power) = amps X volts. When the resistance is unknown, it may be found from (1) by volts/amps. Also, the 59 mah charge is really .05 ampere-hours, or 3 ampere-minutes, which is easier to use =. . . In other words, the standard charge put on the flight battery (assuming 100% efficiency) should be enough o run the motor for 1 minute at a drain of 3 amps or 1/2 minute at 6 amps. Let's also assume that one NiCad cell, under load of the motor, provides 1.0 volt.
Now let's also say our specific motor, driven by 3 cells, consumes 3.5 amps and the power input is (3v X 3.5a) 10.5 watts. The motor's resistance, R, is found by dividing the 3v by the 3.5a, or .857 ohms, from equation (1). With 3 cells the motor can run .86 minute, about 52 seconds (3 ampere-minutes/3.5 amps).
Should we now DOUBLE the cells to 6, the amps and volts BOTH double, as the R stays the same, the power goes to 42 watts, 4 times what it was! (6v X 7a). At the doubled current the run-time on the same 50 mah charge becomes 1/2 of what it was, or about 26 seconds ... And the hardest thing to understand is that the flight time is almost the SAME, on either 3 or 6 cells, as measured at flight test! ... But this may be true ONLY when using the same motor design.