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Old 07-03-2006, 08:09 PM
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Default U/W Wunderlich prerotator

I'm going to be swapping out the electric pre-rotator on my Monarch for a Wunderlich style. The electric setup is simple and so-far reliable, but it doesn't have nearly the guts I need to deal with shorter fields.

I am specifically interested in the type of setup used on the Ultrawhites, since everyone seems to report good results with it. Here are some pics from an earlier thread - this setup eliminates the typical 90 degree bend in the flex shaft, and is likely more efficient as a result.

Does Dick Wunderlich sell the entire setup, or will I need to get the prop plate engagement components & engine mount bracket from Ernie?

If anyone has any of these parts for sale I'd love to hear from you.

Thanks
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Old 07-03-2006, 09:27 PM
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Ivan,

I believe that you will need to get the drive plate and lower bracket that attaches to the gearbox from Ernie.
I didn't see anything listed in my Wunderlich parts list (unless it's been recently added).

The upper Bendix assembly is the same one used on the Mac engines, and uses a reversing gear.

I've flown two Dominators with this setup, and it really spools the blades up.
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Old 07-04-2006, 09:18 AM
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Iven,
You can also buy the entire thing from dad.I think it just about the same price as if you bought the parts and assembled it yourself or just a bit more. This saves some aggrivation.
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Old 07-04-2006, 12:38 PM
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Thanks Mike I'll probably go that route.

I have a 582 and the UW comes with a 503, but I'm assuming they use the same gear box so the bracket should work fine for me.

The only other variable I can think of is the length of the flexible shaft. Does anyone know how long the UW's is?
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Old 07-04-2006, 01:53 PM
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I talked to Larry Neal a couple of weeks ago and he said that he had a prerotator for the butterfly that used belts and would bring the rotor nearly to flight RPM. You might want to call him and see if he has what you want designed for the Butterfly series.
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Old 07-04-2006, 02:31 PM
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Hey Alan, you're referring to Larry's Metro Launch System (MLS as he calls it). Its an engine-driven prerotator system, with a belt drive off the rear end of the engine. I saw it at Sun'n'Fun but he hadn't fully completed it at that time. According to Larry he can hit flight RPM and do a 15-foot roll takeoff, similar to the CarterCopter CCTD Trainer videos.

It looked to be a bit excessive for what I need, and perhaps a bit overly complex. The Wunderlich system is more of a tried and true solution, and its simpler. I will get some more details from Larry though before I make a final decision.
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Old 07-04-2006, 02:33 PM
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Iven, the pre rotator on the ultrawhite does work well, Best pre rotator I have used yet. It will work on 503 AND 582 engines as the engine is not a factor.... what is a factor is what type of gearbox the engine has on the end of it. Ernie uses the Wonderlick type on the Rotax B type gearbox and the Hydro type unit on rotax C type gearbox. You need to see what kind of gearbox you have first before ordering any parts.

You can have either gearbox on either model engine, so just cause it is a 582 does not mean it will have one type of gearbox automatically.
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Old 07-04-2006, 02:53 PM
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Default Question ...

Iven, please excuse me buttin' into your thread, but I have a relevant question.
Some time back I saw a picture of a Wonderlick type prerotator that engaged the power take-off drive on a 45* angle as opposed to 90* as depicted in the link above. Was that a gearbox work-around, or just another way of doing it. Any advantages or disadvantages?
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Old 07-04-2006, 02:54 PM
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Thanks Ron. I'm pretty sure I've got the B-box. I've attached a picture of it, can someone confirm? It looks like what the Rotax manual says a B-box should look like.
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Old 07-04-2006, 03:24 PM
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That would be a Rotax B type gearbox and it is installed the right way to add Ernies Ultrawhite pre rotator system.
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Old 07-04-2006, 05:42 PM
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Iven,

You said you have an electric prerotator, is it a soft start? Because I made one electric soft start and want to get moast information about it which could help to enhance my own one which get about 160RPM in about 15 seconds. It work well but if I can do better...

Rene
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Old 07-04-2006, 06:59 PM
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Hi Rene, mine does have a soft-start. The soft-start is achieved by running the current through a stainless steel tig welding wire, about 9" long and 1/8" diameter. I haven't measured it but I believe this resistor wire drops the voltage by at least 2-3 volts.

The full-power setting activates a common auto-parts solenoid to bypass the resistor wire.

My rotor tach doesn't read very reliably, but I would estimate that I'm getting no more than 150 rpm on a good day.

The battery is a lawn-tractor battery, weighing probably 30lbs. The battery is only good for a single full-prerotation takeoff. After that it will get the blades up to maybe 60 rpm.

If you want more RPM out of your prerotator, the way to go is probably a larger battery and possibly a different gear ratio to the ring gear.
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Old 07-04-2006, 07:00 PM
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160 is about the highest rrpm from a ele. pre-ro. Don't think you can get more.
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Old 07-04-2006, 07:48 PM
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160 rpm is about all you can usefully use anyhow, unless you have an aerial bulldozer that will stay planted.
Without pitch change, full power take-offs from a standing start are extremely poor practise and very hard on the mast and rotor system.
The ability to operate from short fields is more related to pilot experience than pre-rotation speed.
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Old 07-04-2006, 07:53 PM
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My soft start is electronically controlled with 10 power transistor 30amps each which act as a fast switch, so I send very shorts pulses and get pulses a little bit longer as te time past, the battery is a small 20 amp/hour and is good for several prerotation. At the end, Ialso use a relay to bypass my transistor but also to plug on a 2 volts added battery in serie which send 14 volts. Everything is set into a microcontroller which also calculate my rotor RPM, motor RPM, battery voltage , remaining fuel and distance etc... It work well for now.
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