Piston vs Turbine

[Tim B.]

I have been seeing where different pilots are chaning out the engine that a set of plans might call for and replacing them with something else. I was wondering if someone could give me a quick and dirty run down on some of this stuff.

I see where a scorpion-II is using a Subaru engine modification. I maybe looking at this wrong, but is this a regular car engine? If so, how big (size and weight) is ok to use in a helicopter?

I have also been told about some pilots / builders changing from piston engines to turbine on their helicopters. It seems like the Solar T62 (Chinook APU) is the most popular, or that is all I have came across so far. Not really knowing much about turbines... YET, how do you compair those to piston engines in horsepower.

Has anyone ever attempted a twin engine helicopter or is this a never never no area with the FAA?

[HobbyCAD]

Originally Posted by Tim B.

I see where a scorpion-II is using a Subaru engine modification. I maybe looking at this wrong, but is this a regular car engine? If so, how big (size and weight) is ok to use in a helicopter?

It's not simply about putting in an engine. You can easily go to the basic mathematics, and figure out roughly how much HP you are going to need to make your contraption fly. Then you have to find an engine that will give you that, plus a bit more for performance. You will need to go around the calculation loop a couple of times, to figure what you need.

Next step, no use if you need say 60hp, but you add a ton of an engine that delivers 60hp. A Subaru engine + cooling weighs a LOT, now you need another 50hp extra to lift that. So you end up gaining nothing, in fact you loose, for you now need a beefed up rotor system to pick up the ton of mechanics, just to lift up "yours truely". Sit down, think it all out, do your homework, end up doing it right the first time.

Jon, I'm not critisizing your build, but geeze, he seems to have had to wring out every little bit of HP, with masses of heat to now get rid of, out of that Subaru engine of his, all to get that little Scorpion up into the air. OK, Jon is having a whale of a time doing it, I suggest you spend a bit more time to introduce more weight efficient components into the build.

Apologies Jon, I'm not insulting your intelligence, neither your build, I'm voicing my opinion.

Originally Posted by Tim B.

I have also been told about some pilots / builders changing from piston engines to turbine on their helicopters. It seems like the Solar T62 (Chinook APU) is the most popular, or that is all I have came across so far. Not really knowing much about turbines... YET, how do you compair those to piston engines in horsepower.

What better to have a double whammy of a thrill, flying a helicopter, as well as having it be powered by a gas turbine! That smell of kerosine.... It's like the sound of a throaty radial, the feel of a [censored]. I once owned 4 x T62-32's, been there, done that.... I regulary want to buy them back, for they are still stored in the loft where I delivered them to.

In my mind, there is only one little gas turbine that is suited to use in small experimental helicopters, and that is the T62 family of power generators. They were designed for high duty cycle use, the other little APU/GPU/ Air Start units were designed to start, do their job, and be shut down in minutes, before they heat up and destroy themselves. The T62's were designed for semi continuous use. Thus perfect to use as a powerplant in a small heli.

But there is a price to pay, they were used in the domain of the older military machines. The supply is limited. So with a limited number available, and having to supply the worldwide demand for experimental powerplants, the number of available units are drying up FAST. The second issue, they were not mass produced, and spared are not available on the open market. So if you damage one, you have to purchase another complete machine, to have spares.

Another problem, these little turbines are VERY thirsty, so it is costly to operate. Now, is it all worth it, installing an engine that is as scarce as hens teeth, will cost an arm and a leg to repair, and cost a lot to run, just for the nostalgic turbine feel? Man, I cannot answer the question myself, for if I had an easy way to go turbine, I would !!!!

Originally Posted by Tim B.

Has anyone ever attempted a twin engine helicopter or is this a never never no area with the FAA?

For someone that I interpret is in the learning stages of crawling, may I respectfully suggest you learn to walk, before you attempt to run.

[Tim B.]

Hobbycad -

Thanks for your reply.

On the Subaru engine, I understand it has to be heavy along with coolant and then beefed up parts just to mount it, drive the enlarged rotor system and such. I was just wondering if there is a "class" of engines that seem to be popular. I know I am not going to attempt to mount a rotor system and a seat on a huge helicopter turbine like I did to my car. I was just thinking there is no use in reinventing the wheel when someone has already figured out that a small 2 stroke chain saw engine is not enough and the engine from a Caterpillar 797 Series might be a tad too much.

I am not looking for someone to do all the math for me. However, observing others and paying attention to their "lessons learned" is always a plus. I know there are rpm and torque issues to be worked out. I also know, once you start farting around with changing engines, you might need to start looking into gear boxes and such to make sure all the parts are spinning at the desired rpm for what you want it to do. Then I might want to pay attention to strength of mounting, drive shafts, is everything staying cool enough, ect, ect.

I have seen a lot of videos on the different helicopters (mostly Helicycle and Mosquito XET) with the Solar T62 turbines. I just have not seen much, if any, of someone using any other turbine engine.

As far as the question about multi engine helicopters, I ask this because I have seen multi engine fixed wing designs but no rotary wing design. I am not trying to walk or run, just scooting across the floor before I crawl. At this point, I am doing good to roll over on my own. I think if I ever attempted a multi engine aircraft, it would be fixed wing... sticking to something I know a little more about.

[vickijohnk]

Tim B, The Marine Corps had a twin engine S-56/H-37 in the sixties. It was a "BUFF" if I ever saw one. John K

[brett s]

I'll second the T62 as being the only small turbine I'd touch - those things are pretty bulletproof, the downside is they are very thirsty. I operated & maintained them for several years in CH-47's...

A second engine adds another order of magnitude of complexity to your drivetrain, not to mention weight & expense. As yourself this - if you can't maintain flight on one of them, why bother? In a small homebuilt helicopter that's probably exactly where you'll end up.

[WaspAir]

Originally Posted by Tim B.

As far as the question about multi engine helicopters, I ask this because I have seen multi engine fixed wing designs but no rotary wing design.

The S-56 shown above is a rare example of a multi-engine piston helicopter with a pair of huge R2800 P&W Double Wasp engines.

Multi-turbines are very, very common, with just about every manufacture making them (examples from many of the big names listed below).

Three engine turbine helicopters include at least:
Agusta Westland AW 101 Merlin (formerly EH101)
Sikorsky CH53 E Super Stallion

Twin engine turbine helicopters are everywhere, including:
Augusta A109
Eurocopter EC 135
MD Explorer
Bell 412
Sikorsky S-76
Westland Lynx
Kamov KA-60
Mil Mi-26
PZL Swidnik W-3
NHIndustries NH-90
Boeing CH-47

For multi-engine SMALL piston helicopters, there isn't much, but for one recent attempt you can look up the Skyline SL-222, with a pair of little Hirth three cylinder engines:

http://www.skyline.ua/development_eng.html#

http://youtu.be/vcMGhi6UtXU

[Wiplash]

According to Wikipedia, the T62 puts out 60 to 150hp.

Would 150hp be enough for a small 2 place heli?

[Wiplash]

http://www.laehelicopterscyprus.com/index.html

Here ya go, have a look at this.

[Tim B.]

Originally Posted by Wiplash

http://www.laehelicopterscyprus.com/index.html

Here ya go, have a look at this.

That is VERY intresting... glad to see this on the Ultrasport 496T helicopter. Kind of gets my mind cranking a little.

But an attempt like that for me is some time off as of now. Just kind of researching and daydreaming some. Maybe try that on a 3rd or 4th project.

The Skyline SL-222, I am just not sure about that one. Guess so far there has just not been a need for a multi engine small homebuilt helicopter. And that kind of answers my question as to why I have not seen any kits or plans to date.

[hillberg]

Twin power plants,single power plant, yep-Let the fun start.

[bryancobb]

Originally Posted by Wiplash

According to Wikipedia, the T62 puts out 60 to 150hp.

Would 150hp be enough for a small 2 place heli?

10 HP needed for every 100# of takeoff weight on most helicopters.

[Tim B.]

Originally Posted by bryancobb

10 HP needed for every 100# of takeoff weight on most helicopters.

This is exactally one of the questions I had, but did not word it correctly.


Hillberg-
Are those your projects?


The way people (including me) love the sound / smell of turbines, I could just imagine that "Cobra" with a pair of T62's.