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I have been asked to provide my comments regarding the provisional E-36 Event. It has been suggested that it will do for free flight electric in general what P-30 did for free flight rubber and free flight in general. I could not agree more with the criteria of low cost and simplicity, which drove P-30 to such great popularity, alongside hand launch and catapult glider. Before he died Keith Hoover made this observation: "Perhaps we should consider free flight electric as more like rubber jobs than gas models." Besides the rate of climb, one of the greatest differences between rubber and gas is that in rubber no timer is needed to stop the prop before it finishes unwinding. But in 1991-92 Keith considered electric to be a "power" event, so included electric material in his "Power Book". Did this drive the thinking of free flighters to conceive of electrics ONLY as free flight models with timers? My free flight electric development work of the past several years makes it clear that limiting the CHARGE on the flight battery in lieu of timer usage is a totally feasible method, like LMR, of limiting performance to conditions, and offers advantages timers cannot, such as: 1. There is no transition problem, just as with a rubber job, making trimming easier for beginners. 2. Costs drop $21 to $70 per model. 3. A fast climb is still competitive, but no longer mandatory for competition. The following comments address the numbered items in the provisional E-36 announcement. E-36 RULES 1. Power source will be limited to use of 4 or less Nickel Cadmium (Nicad) cells or Nickel Metal Hydride (NI-MH) cells not to exceed 150 mAh each in capacity. Lithium Polymer (Li-Poly) cells will not be allowed, Limiting cell count has been found to be counterproductive to design flexibility; as with limiting battery weight, with the 36" span limit. Nor is a capacity limit needed. The span limit by itself is quite sufficient to limit performance, as exceeding optimums will not improve performance, but degrade it!! In general, putting cell count, capacity or weight limitations on the battery may well serve to produce models that climb poorly. I do agree with not allowing the use of lithium-polymer batteries. 2. A single electric motor, brushed type only, and will be restricted to those available from common sources. Gearing will be allowed. Except gearing is counterproductive to both criteria, low cost and simplicity, and, a $5.00 to $10.00 limit would keep motors out of the expensive arena and exclude outrunners. 3. The flyer will have the choice of experimenting with various types of propellers for maximum thrust and extended flight times. Direct drive motors do not need folding props (except for outrunners), as optimality is found with small low pitch props turning at high rpm's. Use of folders would again violate the cost and simplicity criteria. 4.Motor run times shall be limited to a maximum of 25 seconds. The flyer shall demonstrate the motor run time to the timer before flight if there is a question of the duration of running time. The motor run time shall be shortened to 15 seconds on the first fly-off flight and then to 10 seconds on the next and to 5 seconds on the third fly-off flight. All subsequent fly off flights will be limited to a 5 second motor run. Without timers, motor run is a function of the battery charge, and need not be timed seperately timed. Protests about over-runs would be a thing of the past. |
5. Flight time including motor run will be limited to 120 seconds. (Max=120). This shall include fly-off flights. Fine as is. 6. Wing Span of the model shall not exceed 36 inches of projected span. There will be no limitation on projected area. Okay as is. 7. The model including all flight item and in a ready to fly condition must weigh no less than 150 grams. A minimum model weight was found to be unecessary over 45 years ago in the standard gas events. Why should it add to processing tasks now? 8. Current AMA Free Flight rules will apply when flying this event. A maximum of two models shall be allowed per entry. When two models are allowed in any beginners event won't this tend to put kids who cannot afford a second model at a disadvantage? RATIONALES FOR RULES DECISIONS Nickel Cadmium and Nickel Hydride batteries are inexpensive and readily available at low cost. They can be charged with little or no danger to the flyer or others. Charging sources can be as inexpensive as common flashlight batteries and therefore also low in cost. At this time Lithium Polymer batteries and the necessary charging equipment is expensive and prone to safety issues when slightly damaged or incorrectly charged. I agree 1.Small inexpensive brushed motors are readily available from a large number of sources including discarded battery operated toothbrushes, electronic warehouses and discarded foam plastic model airplanes. This keeps the cost very low. It also encourages the flyer to test motor thrust, amperage and other characteristics. Gearing could be used to getthe maximum thrust from the system. Electric motors are the hardest part to understand; but let me try to share my insights: An optimal model has been found, by Chuck Groth, to have about 1/4 of its flying weight in the motor . Since most 36" models will weigh about 5 ounces, this gives a target motor weight of 5/4 or 1 1/4 ounces. Is this the size one gets out of his old automatic toothbrush or whatever? If it is to be direct drive, an optimal battery (also about 1/4 of flying weight) needs to drive a small, low pitch (4 1/2") around 12 to 17K rpm. Will the appliance motor do this? In my search for GOOD motors, I have tested perhaps 50 different kinds, but was satisfied with only three! The excellent E-38 was preceded by an E-35, which was the same size and made by the same manufacturer; but it took a 70 mah charge to get a 2 minute flight with it, while the E-38 did this with only a 50 mah charge! Which brings us to MY proposal: Before All Electronics (a surplus place) ran out of what I call the "E-38", (38 grams) I was able to accumulate over 300 of these great little motors and now I am ready to DONATE up to this amount to the NFFS, to be used for a beginners program! The only catch is that it must be based upon the limited charge (charge allotment) concept instead of limited motor run, to keep costs low (NO motor timer) and to maximize simplicity. The E-38 is an excellent motor for both 1/4A and small 1/2A sized models. For 1/4A I chose a design of about 200" (aspect ratio of 6 1/2 to 1) and use 3 "110" Sanyos, and a 250" climbing model for a 1/2A size with 6 "250" Sanyos. The weight of the 1/4A battery is 0.8 ounce, add the motor of 1.3 ounces (2.1 oz. total) and multiply by 2 for an initial flying weight estimate of 4.2 ounces . . . Similarly, the 1/2A battery is 2.1 ounces plus motor of 1.3 = 3.4 X 2 = 6.8 ounces total . . . With twice the cells, the electrical power input of the 1/2A is about 4 times that of the 1/4A. |