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Jett heli motor?

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Old 08-10-2008, 08:31 PM
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Ramz
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Default Jett heli motor?

I know that JETT makes some of, if not the best small glow motors on the market today. I fly monstly giant scale aerobatics but I also dabble in nitro heli's and smaller glow planes. I was flying my Raptor today with an OS 50 Hyper and I got to thinking how neat it would be to have a JETT 60 in that thing. My questions is: has JETT ever thought about making a hot motor for a 50 size heli? I know alot of the heli guys can never get enough power and it would be great to have another, more powerful option for those of us who don't mind paying for performance.
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Old 08-11-2008, 08:28 AM
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Default RE: Jett heli motor?

Hi,

Thanks for writing...

Actually, Jett use to make a .50 and a .76 heli engine. They were discontunied about 7-8 years ago. (photo attached just as a reference)

The .50 actually worked out well ..... but the problem was that guys wanted an engine that "ran like an OS, but with more power".

This engine has more power, but that is why it does not run like an OS. Throttle and idle and stuff were great, but it is best suited for higher rpm applications. Was not long ago folks prefered low rotor speeds, and this engine was not suited for that.

To develop power, you increase rpm and gear it more. And you want to keep it at high RPM. (HP = rpm x torque) Folks were reluctant to do that. Also, the engine needs its own muffler tuned for the rpm range..... guys insisted on running the standard hatori and other heli mufflers. Plus, to make power, you burn fuel. Fuel consumption is higher than an OS ..... guys were not happy about that. At that point, you might as well have an OS.

The current Hyper 50 is a hell of an engine. You are probably best off sticking with that. The ring engine design seems to be prefered by heli pilots since it is not as sensitive to rapid changes in cylinder temperature.

In fact, I think the OS50 has more potential - same limitations the Jett power found needs to turn up (over 17,500-18,000 rpm) - geared appropriately supported by a good tuned exhaust that will keep it running up there. Again, folks are worried about fuel burn and noise. Both are byproducts of power.

Using the standard production SJ-60LX is possible. Dub still has the 90deg muffler adapters I think. But you will have to modify the fan/flywheel to mate with the Jett drive cone (not the same as the OS), drop at least one tooth on the pinion size, and you would want to fabricate your own over-size heat sink for the head.

You are welcome to try one of the engines... there are more than a few helicopters flying with Jett power today. But keep in mind the R&D activities and necessary modifications to the helicopter are up to you. You want to gear a SJ-50 or SJ-60LX engine so it runs around 19,000 rpm.

One other problem I ran into when I tested a SJ-50 in a helicopter a few years ago - the engine power stripped the main gear when I aborted out of an autorotation .... idle to full torque with an unloaded rotor and it was history. My goof there.

I trust this helps answer your question

Bob
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Old 08-11-2008, 09:18 PM
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Default RE: Jett heli motor?

Bob: thanks for the reply. I had no idea that JETT made a heli motor.

I know their are many heli pilots who are perfectly happy with a less powerful heli motor (TT50 for example) and who will never really use all the power that is available to them and those people, like you said, would never benefit from having a JETT. When I fly my heli I always fly with a headspeed of about 2000 about 99% of the time (motor running around 16000 I believe). I would have thought that a 60LX heli motor with a JETT tuned muffler built to fit in to the modern heli's (raptors, Trex 600's, Vibe 50, etc) without any mods would sell really well. I know I would definately give it a try. And like you say, it wouldn't really take much modification of the motor itself to make it work. I personally don't care how much fuel it burns or how noisy it is but I do care how user friendly it is and how much reliable power it makes.

Just my .02
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Old 08-12-2008, 10:57 AM
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Default RE: Jett heli motor?


the mods are part of the problem.

You can not really modify the Jett engine to fit where the OS mounts. The crankshaft and drive collar are larger and it does not use a conventional threaded shaft. So you have to machine the flywheel to match the engine.

As I noted, a few helis are flying well with Jett power. As long as you get the gearing right to allow the engine to really unload, its a load of power. It just takes the R&D work on the pilots end to make it work.

But trying to provide a plug-n-play helicopter engine at this point would result in endless emails from the "ARF" crowd and a bunch of burnt up engines. Just not worth it.
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