MISCELLANEOUS TECHNICAL TOPICS
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Takeoff ROG) or Hand Launch? Speed 400 models and 1/2A sized planes in general are skittish on takeoff. Since Speed 400 rules do not require takeoff (ROG) there is no point doing it. With a good hand launch the clock starts with the plane already at 6 ft. altitude and at full climb speed. For a takeoff the clock starts with the plane stationary at zero altitude and about to meander down the runway as it accelerates to climb speed. A hand launch will gain you at least 10 seconds. For style watch Ed Hamler. |
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Where to Land Your Speed 400 plane is not a disposable ARF -- it is a valuable piece of craftsmanship. If you have any reservations at all about landing it on the runway -- then don't. Head for the tall grass. In windy weather it will safely "catch" your plane and protect it from the wind. |
Tall Grass on the far side of the runway is a necessary part of our Old Timer field. It provides an alternate, safe, and legal landing area for Old Timers, particularly when it is windy.
Batteries You could save weight using a little 500 mAh LiPo, but it the voltage will drop seriously when the motor starts pulling 10 to12A or more, and the rpm will sag. At the other extreme, Dave Harding used a 4000 mAh LiPo which is surely an overkill.
The best battery is a matter of personal preference. Or it's how much extra weight you need to meet the 16 oz. rule and the 8 oz./sq. ft rule (see international rules below).
Last year Dick Irwin, Nick Kelez and I used Thunder Power 2s 1320 mAh LiPo's, (based on Dick's testing) with a 6 x 4 prop turning at 10,000 to 11,000 rpm. It weighs 2.5 oz including connectors. This gave a good climb. In fact it gave three good 2-minute climbs -- great for three practice flights without removing the battery. The pack is rated at 13C which means up to a continuous 19A is Ok.
Wing Loading Example Rich Minnick's Diamond Demon has 320 sq. in. wing area. The minimum allowed weight is 8 x 320/144 oz = 17.8oz. The weight without battery is 14.4 oz so an additional 3.4 oz is needed. So it will carry the Thunder Power 2s 1320 mAh LiPo(2.5 oz) and still be 0.9 oz short. So there is still room for a power switch and a few pennies.
Connectors The little red GWS jst connectors are great at 3A, but get hot at 5A. They start to fry and may self destruct at 10A leaving you without power or radio. The standard Deans connectors are reliable but awkward in a small plane. The miniature Deans connectors are easier and good for 25A. So too are the 2 mm bullet connectors, and you only have to remove one to act as a switch.
Switches Many planes require the wing to be removed and then replaced after plugging in the battery. When hawks (or models) suddenly appear circling over the field it is time to launch immediately. This where a switch or external plug pays off. The 10 A Radio Shack switch # 275-325 is small and light. To verify it is a good one, run the motor at full power for a minute. A good switch will remain cool
Center of Gravity for under-cambered wings is generally much further back, typically 50% or more of the chord (wing width). Mount the battery with Velcro so that it has a 2 in. range of position. Too far forward requires excessive up-trim during glide. Moving back progressively improves the glide but eventually reduces the stability. Find the best battery position and mark it clearly.