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04-11-2015, 10:58 AM | #1 (permalink) |
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Join Date: Mar 2015
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138mm Blades on a Blade 120 SR
So, just an idea to toy around with.
Just because I can, I am looking for new blades for my 120SR (fun little thing). I see Zeal has some 138mm blades (out of stock). Has anyone every stretched the blades on a 120SR with luck? I checked clearance between the tail rotor and the main blades and it already looks tight with the 120mm blades at the extreme ends. I don't want to end up with a chopped up tail blade on the first flight. Thanks! |
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07-05-2015, 03:26 PM | #2 (permalink) |
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Join Date: Sep 2013
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To do this you would need,
Longer FP blades longer tail boom more power First you would need longer fixed pitch blades. Walkera had some fixed pitch machines that were a little larger, you could also get a set of coaxial blades. As long as they rotate the right direction, have pitch built in, and have a standard grip they should work. I would try to go no more than 20 mm longer, light as possible, and at least as strong as stock. The width of the blade, and the amount of pitch (twist) it has are also considerations. wider blades have more drag and need more power, more twist means more lift at a lower rpm. It might be favorable to find blades with the same or slightly less pitch. Less pitch will increase the hover rpm, in general more rpm = more power from the motor. To little pitch and the motor hits peak rpm before making enough lift. Too many variables to be sure, I would get a couple different sets of blades that are in the ball park. Next you will need a longer cf tube, 3mm diameter I think as well as a little shrink wrap to hold the wires to the outside of the stretch boom. The cf tube should be longer by the same amount the blades are I would add about 5-10mm extra to account for the possibility of heavier blades causing the tail to overcome more torque. For example if the stock blades are 115mm from bolt hole to tip and the blzdes you get measure 128 from root to tip then you would add 13mm+7mm for good measure, so you would cut a piece of CF tube 20 mm longer than than the factory boom. The tail motor wire should be long enough to reach when twisted around and shrink wrapped to the tail boom. You will have to file the flat onto the ends of the boom which is discussed in a few places here on HF. Finally you will need more power to spin the bigger blades, there is an Extreme brushed ball bearing motor for the 120sr (do not get the one for the blade CX 4 it is a 2s motor). You should also get some more powerful batteries 600 mah 30c are offered, but with the extra weight on the tail a lipo around 700-900 mah might balance better asteroid designs has a battery mount for the 120 to allow you to use the larger cells. Other power options include, adding a 2s speed control for the main motor. A small 2s brushed esc, and an extreme motor for the cx4 could work, and the motor would bolt straight up. A more popular option tends to be going brushless, a 2s lipo, 12 amp esc and BL motor of the proper kv would definitely provide the power to spin longer blades and possibly overpower the tail requiring it to be upgraded as well. At the end of the day you still have a flybarred FP heli. Anything above and beyond what can be done with the stock tail motor, high C lipos, and the extreme motor for the 120sr, is probably more trouble than its worth. Especially with the 200 srx now available. Good luck and enjoy.
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