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If I was wanting to attach an electric starter motor as a pre-rotator to a benson copy gimbal head, where do I drill and where don't I drill? Hate to make a fatal mistake and weaken it.
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G'Day, CamelI'm no expert, but I did take your concern into account when I designed my pr-rotator system. I mounted a 0.5 inch alloy plate above my torque tube and used the main bolt, rear bolts and drilled 2 extra bolts to the front. By designing it this way I feel I actually strengthend the torque tube.The only thing left is the rotor brake, which due to this design will be unconventional. See Attached Pic's. Hope this helps !!!Regards Sam. [
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Thanks Sam. Good pics showing the mounting points. I have been told to use a Rosco ring gear on my head. Any one got his number?Sam's set up looks pretty good can anyone beat it??
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Ross Symes number is (08) 8087 6569
Safe Flying ... ding Good judgment comes from experience and experience comes from bad judgment
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Camel this set up is from a Butterfly Monark, and is very similar to mine !!!Sam. []Image Insert:
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Any reason why you have the starter motor on the side??BrianYou never know how far you can go, till you get there !
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Brian, Speaking to many pilots that have had a starter on the front of the torque tube, have described feeling exessive stick vibration, and by moving it to the side, it has vanished.The other reason I mounted it this way was my ring gear is custom made and very small. This will allow a faster final speed during pre-rotation, but also cause the starter to foul with the front of the assembly if mounted on the forward end of the torque tube. So without a choice, it was side, or buy a new ring gear.Regards Sam.
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Thanks Sam and Ding. Will call Rosco next week.I have a LAME mate who has lent me a reostat-he calls them a carbon pile. He sais that you can initiate a very controllable pre-rotation- totally removing the "snap" by having a seperate circuit engage the starter solenoid and then use the seperate carbon pile controlled power input to slowly introduce the power for prerotation. Simply putting finger pressure on the pile feeds in more "power"(im pretty vague on the lingo of electricians)and thus a soft controllable start right to full spin up. Maby even using a smaller still ring gear.Cam
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Cam,Terminology is good enough for this forum, when you apply the pressure to the carbon it forms more contacts in itself and thus has less resistance to the current, means more amperage and more power to pre rotator. As discussed elswhere on the forum (hub bars) there are some cautions you should apply with such pre rotators, you seem in part to be aware of the issues. Check the bolt pattern on your hub bar, if the teeter bolt holes are in compression due to the inertia of the blades being rotated it should be ok, if the holes are in tension, judicious care is required to be taken or if your hub bar has been machined for thickness anywhere (in contrast to being drilled) I would be inspecting it on a very frequent basis for cracks of any kind.Hope this helps,Nic.
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Thanks Sam, my pre rotator is in front and I get plenty of shake. Could be worth trying putting it on the side for a comparision.BrianYou never know how far you can go, till you get there !
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Cam there has been alot of discussion on this forum re. soft starting of electrical pre-rotators.***********Here is my 2 cents worth.*********** This is a great idea, and would limit the amount of torque exerted onto the mast, and so on. The problem with all these soft starting suggestions are, they all require some sort of variable resistance being placed in series with the starter. This is the only way you can vary the speed of a dc motor. This means, heat, weight, fire hazard, expence, and another thing that could fail.I am a sparky by trade, and I feel a simple flick of the blades prior to engagement of the pre-rotator, is the simplest, safest, lightest, and most reliable method.Regards Sam.
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While trying to resolve a continuing stick shake issue...The pre-rotator was at the front. It was removed entirely and the shake reduced somewhat. It was then re mounted to the rear with no perceptible increase in shake compared to being off entirely. Conclusion in this case was that mounted in the front makes an existing shake worse but at the rear doesn't seem to matter. Haven't tried side mounting yet []Dave
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I feel that stick shake is increased by the fitting of a pre rotator and then if your rotors arent very well balanced, then the shake gets a lot worse. The rotors have a big say in shake.BrianYou never know how far you can go, till you get there !
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Right on Brian. Waddles' Monarch had stick shake with his first set of rotors. The front mounted pre-rotator was removed and the shake disappeared. However, there was no stick shake when the pre-rotator was reinstalled with a new rotor.Daj
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Thanks for all this info fellas. Seems that an electric pre-rotator mounted on the front side of the mast accentuates any resonance in the rotor system into somthing more noticable.As per Nic's comments mu rotors are MCCutchens and I think hub bar bolts are in double shear.(But nobody quote me on that. So any further comments on where exactly to drill the torque tube to mount the mounting plate/bracket??Cheers, Cam
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