Metro-Launch

Doug Riley

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Joined
Jan 11, 2004
Messages
6,487
Larry Neal's Metro-Launch is a powerful prerotator for use on Rotax 2-stroke engines. The design goes its own way, compared to almost all other gyro prespinners.

It takes power directly off the mag end of the Rotax crankshaft -- bypassing the slip joint built into the Rotax gearbox. It uses a single big, long V-belt to bring power to the rotorhead. It has a soft-start feature that uses a consumer-grade 12 v. tire inflator to fill a tiny air cylinder that, in turn, gradually tensions the drive belt. All the stepping-down of crankshaft RPM to rotor RPM takes place via a heavy reduction unit hung from the rotorhead torque bar. The weight is enough to eliminate the trim spring.

A friend of mine has a Butterfly equipped with one of these beasts. I've flown it a number of times over several years. It easily brings the rotor past 200 RPM, providing instant nosewheel lift once you release brakes. So, as a prerotator, it's pretty potent.

I worry about the longevity of the unit, though. A welded-on bushing on the upper unit has broken off (crummy welding). My friend had it re-welded. The lower unit attaches to the Rotax crankcase with long, spindly bolts threaded into the pot-metal case. Then there's the unusual load it puts into the "wrong" end of the crank.

So, questions for those few others who have a Metro-Launch: How has it help up? For how many hours? What has failed over time? Any evidence of crankshaft misalignment (from the wrong-end loading)?

Thanks for your responses.
 

Jazzenjohn

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Oct 9, 2004
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Milan Mich.
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I've designed, built, and flown 4 different ultralight gyros. Amassing parts for a 2 place now.
Total Flight Time
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Christine had some issues with her Metro launch prerotator including a broken pitch pivot bolt which I believe was partly a result of the out of round pulley putting a powerful torsional vibrating load on it.
 

wolfy

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Dec 19, 2013
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western australia
I remember looking at a butterfly a while back, I can't remember whether it had metro launch but the rest of the machine had some good ideas but I think poorly executed for longevity reasons.

wolfy
 

DANNAL

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Apr 23, 2009
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Warfordsburg PA
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C172
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Found these photos in an old file. Never had a problem with mine but I didn't run it that hard.
 

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DANNAL

Newbie
Joined
Apr 23, 2009
Messages
17
Location
Warfordsburg PA
Aircraft
C172
Total Flight Time
300
Doug. You mentioned that a spring was not needed, and yes the one that came with the base kit was not going to work. When I test flew it without a spring I found that something was still needed so as you can see in the picture I added a longer, smaller gauge spring that had a softer more linear pull. Also, the upgrade kit had a small battery to run the pump because my engine was pull start (no battery) but I found that was not necessary, the stator/regulator was up to the task.
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,487
Sounds right on the trim spring. Dan's Butterfly had far too much aft pull at cruise, even though the spring was set to go sloppy loose with back stick.

Dan took the spring off altogether, and that was a wee bit TOO little tension. She will creep up to 60-65 on climb if you neglect to hold backpressure. That speed reduces rate-of-climb as compared to the optimal 45-50. So a long, soft spring may be perfect.

Interesting about running the airpump right off the mag.

I'm also still anxious to hear what, if anything, has BROKEN on Metro-launch units in the field.
 
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