rccarguy
Veteran
Location: Boston MA
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| So hey this helicopter is cool but pain of a butt to tune too. Anyways anybody have one of these pegasus 18?
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Not a Pegasus, but same engine setup in a Protech 450 IC...
  
The Protech is classified as a 450, but it's a bit bigger. You can see it in the picture sitting between a Trex 450 and Raptor 30 for a size comparison. I've compared it to a Trex 500 as well and it's pretty much right in the middle in terms of size.
Yes, the OS 18 is tricky to tune when used in a heli. First it's an ABC engine, unlike the ringed engines built specifically for heli's, an ABC is a lot more sensitive to temperature variations, too much and you lose power quickly, not enough and it won't produce peak power. Other issue is that these engines rev a lot higher than what you normally see in a heli. The OS 50 in my Raptor Titan makes max power around 17,000 rpm, the OS 18 CVR in the Protech makes max power at 28,000 rpm, you cannot tune by sound as the 18 will always sound like it's over revving compared to what you hear from a ringed heli engine.
I find I have to intentionally run the engine on the rich side and use VERY conservative throttle curves to keep the engine from overspeeding, it can happen very quickly. If I remember right, idle-up 1 is set to run between 60 to 75% with the main needle set about 2 clicks too rich, anything with a higher curve limit or leaner setting will overspeed the engine every time the head unloads especially in breezy conditions when going from + to - pitch. It would be much easier if I could figure out a way to use a govenor or rev limiter, but take a look at the picture and you'll see it's all but impossible on the Protech. If you can fit one on the Pegasus, I'd highly recommend it, it will definitely help keep the engine running at a consistant RPM without having to tweak curves and needle settings.
That said, the Protech Zoom comes with an 12 size engine, I had to do a bit of machining on the OS 18 to make it work, but it transformed the little beast from a novelty into something you can actually fly with confidence when its running right. Best part is, a gallon of nitro will last for weeks with the little engine 
XCell Spectra G
Radikal G20
Some obsolete nitro helis too... |
info on this post about the Pegasus......
Stan
