First Stage - Second stage ... whose on first base?

[Deron Douglas]

I'm starting to explore turbine helis and I've been wondering what's meant by First Stage a and Second stage? I see that the second stage heli turbine has a gearbox connected.... is this it?

[Deron Douglas]

Hi, investigating my next big project and I came across this Hughes 500D:

http://www.heli-factory.com/modelle/hughes/hughes500emclaren/index.html

The turbine is a JetCat with PH5 gearbox.... this allows the exhaust to come out the rear end where it does in the actual 500D.

Two questions,

1 - doesn't this get too hot for the boom?
2 - Does Wren have a gear-box like this so I can do the same?
3 - OK..one extra... would this setup be a stage One and no stage two setup.

Thanks.

[cbergen]

That looks to be a PHT3 per the ECU in the pix. Which means it's a single stage (no "gearbox" just belt reduction), and the exhaust is routed out the back. You'll still need some sort of diverter (which I believe they have) or the thrust from the engine will push the heli forward in a hover, causing a "tail down" attitude.

Wren does not do a single stage heli version, they are either a thrust engine, a 2 stage Turboprop, or a 2 stage Heli with 90 degree gearbox.

A single stage is a thrust engine like used in Jet Airplanes, except there is some form of power takeoff from the front of the engine, whether by belts or gears, to reduce the 100,000 appx RPM to something more usable in a headspeed.

A 2 stage is a gas generator (the jet engine similar to the single stage) with the addition of an interstage by which the hot high pressure exhaust is blown at another turbine wheel, causing it to spin. The exhaust is then vented overboard with reduced heat and velocity. The second turbine wheel (2nd stage) is then connected by a shaft to either the Turboprop gearbox or the 90 degree heli gearbox.

The RPM of the second stage turbine wheel is appx 1/2 the gas generator, the gearbox is then further reduced by 1/4. Example, the turbine is spinning at 140,000 RPM, the 2nd stage is then spinning 70,000, the output of the gearbox is spinning 17,500. These numbers are appx as there are losses to contend with, but you get the idea.

Point is, there is NO direct connection between the Turbine shaft and the second stage, so you are not lugging down the turbine itself, wasting fuel and creating more heat....

The difficult part of this in a scale application is that you still have to route the exhaust overboard somehow, which is more complicated when the exhaust is coming out 2 sides and in the middle of the fuse....

The Wren dealer in Australia came up with a beautiful solution, putting the Turbine in the scale location of a Jet Ranger, on the top deck behind the mainshaft. Big sucker, awesome to see fly.

For the MD500 pictured, the setup shown is probably best, as long as you have the high velocity exhaust diverted somehow.

[Deron Douglas]

Thanks Chris,
Excellent post. It's understood now. I was blown away by this heli, but after further consideration it seems to me that the better way of entering the turbine market is to go with your Intrepid turbine heli. It seems that all the hard work (and thinking) is already done. I personally like kits, I like to "tinker" so that would be the route I will go soon.

Thanks for your help. :thumbup:

[lperagallo]

Ddragon,

I fly a Bergen Turbine and love it. Not to set off the JetCat boys, but in my opinion Wren is a great product. It runs beautifully and has pretty good fuel consumption. The engine fires up great and I have no issues with flameouts. My flying style is sport and I like the occasional loop, roll and stall turn. I am trying to get inverted down, but I haven't made it yet. Need more Sim time. From what I read, I probably am one of few that fly a turbine in this style as most like to fly scale like. I am practicing scale, but not as much as sport.

The Bergen is a nice heli to build and customer service is second to none. I've visited their facility twice and they have worked with me on both my Gasser and Turbine. On my turbine, within an hour it was torn down to kit form and we spent the day rebuilding it. Talk about major maintenance overhaul. We went over every part and replaced anything that was questionable. Talk about a smooth flying machine. It's great to get that kind of support and know that it's done right.

While weather here in Indy hasn't been very friendly this winter, I've managed to get out a few times. I will admit the turbine is hard to start at 30 degrees. It's also tough on the hands. But at least I've had the opportunity to get some stick time.

Good luck on your choice of machines.

Lou

[Deron Douglas]

Ddragon,

I fly a Bergen Turbine and love it. Not to set off the JetCat boys, but in my opinion Wren is a great product. It runs beautifully and has pretty good fuel consumption. The engine fires up great and I have no issues with flameouts. My flying style is sport and I like the occasional loop, roll and stall turn. I am trying to get inverted down, but I haven't made it yet. Need more Sim time. From what I read, I probably am one of few that fly a turbine in this style as most like to fly scale like. I am practicing scale, but not as much as sport.

The Bergen is a nice heli to build and customer service is second to none. I've visited their facility twice and they have worked with me on both my Gasser and Turbine. On my turbine, within an hour it was torn down to kit form and we spent the day rebuilding it. Talk about major maintenance overhaul. We went over every part and replaced anything that was questionable. Talk about a smooth flying machine. It's great to get that kind of support and know that it's done right.

While weather here in Indy hasn't been very friendly this winter, I've managed to get out a few times. I will admit the turbine is hard to start at 30 degrees. It's also tough on the hands. But at least I've had the opportunity to get some stick time.

Good luck on your choice of machines.

Lou

Thanks Lou :thumbup: