The dream of a small jet or turboprop?
I don't think the panache or aura of turbine whine and smell of kerosene will ever fade, especially a cheap turbine? May be it is like owning a P-51, may be attainable but never practical or cheap. Innodyn or not I don't think small turbines are practical in general and in a RV airframe a particular an even poorer match. Where do you see single engine turboprops, Cessna Caravan, Pilatus PC-12, SOCATA TBM-700 and Piper Meridian. There are some notable conversions of Dehavilland Otters and Beavers. So it seems the aerospace industry has sized the practical use to cabin class singles and utilitarian haulers.
I looked all the successful turbo prop experimentals an some factory planes, well successful is a relative term. I flew a Swearingen Metroliner SA227, so I know a little about turboprops. The Lancair Turbine program (projet) I think uses a Walter de-rated / flat rated 750 shaft HP engine. Not sure what the engine cost is but I thing engine and prop will be the better part of $150,000.
As far as other prop jets there was a Luscombe (yes a high wing taildragger) that was for sale as part of bankruptcy on the NET just a few weeks ago. It uses a small Solor APU engine rated up to about 160 HP. Its fuel burn is 1.3 lb/shp-hr. If you do the math it is quite a fuel flow and still makes less than a Lycoming O360. Innodyne claims some crazy 0.7 lb/shp-he efficiency? I remember seeing this Solor Propjet Luscombe at a few airshows in the late 90's. It was not practical as a power plant in general and much less for that airframe in particular.
Besides the 750shp Walter, the only other turbo props in contention I can think of are the Pratt & Whitney of Canada PT6's and The Garrett TPE 331's. They all come in at 600+ HP and typically 700+ HP (up to 1000shp). If less HP is needed or allowed on take off they flat rate it, which means the fuel controller reduce fuel to lower sea level HP. Since the engine is de-rated it can maintain that sea level power to a higher altitude, and which point power falls off with altitude. This kind of power will OVER POWERS most experimental aircraft. Obviously the RV with a 220mph Vne (that is TRUE AIRSPEED BY THE WAY NOT INDICATED) is not going to handle that kind power.
My choice if I could dream of a personal turbine engine would be a Pratt & Whitney PT6, but the cost and size would not make it suitable for a RV or even a Lanciair. The Walter (made in Eastern Europe) is of a similar design to the PT6 but cost less, so that is probably the reason Lancair supports the Walter as their turbine candidate. Either way you are looking at 500+ de-rated shp at least. A RV-x can not use that much power (Vne).
The nice thing about a PT6 (and Walter) is its a free turbine where the turbine the drives the gear box, that drives the prop, is separate and not mechanically connected to the "Gas Section" of the turbine. It is connected by hot gas only and the power turbine is FREE to spin independent of the GAS turbine. This allows the turbine to "spool up" with out immediately turning the prop. Direct drive turbines where the prop is mechanically connected to the gas section are harder to start and need big batteries (banks of batteries), since you have to turn the prop while starting as well as the "gas section". The Metro IV (Garrett TPE331) is like this and why you always see JUMP Cart's on airplanes using these engines. The jump cart provides extra battery power. You can start on internal battery only but it is hard on the batteries and the engine starts much hotter. The "battery" jump cart allows the engine to turn faster during start. Failure to turn a turbine fast enough during start, before adding fuel, can cause a HOT START and destroy the engine.
As far as pure jets, Greg Richter of Blue Mountain Avionics converted a GE T58 turbine normally used for Helicopters by removing the accessory case and using it for it's jet thrust alone, about 800lbs thrust. The article of Greg's Jet powered Cozy is in the EAA Sport Aviation Magazine this month or last month. The bottom line it works and works well, but Greg's last statement is it is NOT practical. The RV is not suitable for jet thrust obviously but the advantage of just chucking all the gear box and prop control is pretty obvious. Although not practical as Greg said the performance is of his JetCozy is impressive. However economy is not the hallmark of jet travel, especially in a two seat plane with little cargo/baggage.
That leads me to the Innodyn. First they have not done themselves any favor with some of the semi-data they have out there, which seems to defy normal efficiency by a factor of 2. Also the history of the company and promises others can speak to make me wary of purchasing one.
My conclusion is there is no chance a suitable small turbo prop engine in the 180-250 HP range is really possible (practical). THERE is an economy of scale. If you are going to make a true aircraft capable turbine designed for the purpose of being a power plant for an airplane, it is going to come in at least in 400 hp and more, like the 600 hp range. They will also cost well over $100,000. Also the RV is not big enough or have a high enough Vne to take advantage of turbine power. If you want a jet the Lancair/Walter seems to be one of the the best things on the market.
Can a RV use a de-rated 700HP engine? I doubt it, a Pressurized airframe like the Lancair is a better match. RV's are just NOT jet aircraft. The Jet Powered Cozy Greg Richter, although not really practical is a better match, in my opinion, than any turbine in a RV.
Now can Innodyn really make a 180-220HP turbine that is cheap, practical and safe. Well from what I know they have made some simplifications is design and systems to make it work at the "SCALE" or size they are at. Every turboprop is usually saddled with a heavy complicated gear box, hydraulic prop, torque measuring device (usually strain gages) and fuel controllers. All this stuff is complicated and expensive. Is it worth it to have all these items only for 200 HP? Innodyn has simplified the prop (no hydraulic prop), gear box (no torque measurement) and the fuel controller are all no doubt simplified.
You can put a turbine on anything:
http://www.aardvark.co.nz/pjet/turbinenuts.shtml
But that does not mean you should. If you want a Turbine Jet aircraft plan on at least 1/4 million dollars, not $80 grand. The RV will never be a great match for a turbine and practical turbo prop powerplant/props are at least +600HP. At this time I don't see Innodyn being practical. More important is safety. Is it safe?
Here is my idea for a cheap turbo prop engine prop set up. I would buy an wrecked TurboProp Aero Commander with two good Garrett TPE331's with a partner. We would part the plane out and use the two engines for two single engine projects. The airframe could be any high speed aircraft (Lancair), Thunder Mustang or may be a big heavy hauler bush plane designed for a IO540 and super size the plane. (If you can't go fast go heavy to take advantage of the HP.) You would get all the engine instruments, controllers, prop (you hope not damaged) and bits and pieces to make them run. PT6's are better but just too popular and you will pay a fortune. The TPE331 have been around and have got to the point of high reliability. The Dash 10 models are very good. These engines or variations are in Cessna Conquest, Aero Commanders, BAe Jet stream and Fairchild/Swearingen Metro. The latter commuter planes have higher HP versions up to 1200SHP with AWI (A-we). AWI is alcohol water injection.
I would never discourage anyone's JET DREAMS, but I think there is better ways to go and would go with a REAL aircraft turboprop and not this experimental set up.
George