It’s just different design of turbines. This jet drawing – like all big jets – is a dual stage axial turbine. Piston engine with turbo-compressor has a single stage centrifugal turbine.
Maybe we’ll even see some 250 to 300 hp turbines anytime soon.
I am convinced we will not. It doesn’t make sense (efficiency) and the potential market is tiny while development is very, very expensive.
The midsize PT6A is now in the 1m usd price range I hear.
The side discussion of turbocharged vs. turbine engines reminded me of the most bizarre airworthiness directive I have seen: on Piper Comanche 260TC, it mandated a removal of the “TURBO” decal from the cowling because of several occurrences of misfueling with Jet-A instead of avgas.
Eagle20 wrote:
Since when is a Rotax 915iS a Turbine engine? It’s a small geared and turbocharged 4 cylinder engine and it cannot sustain 140hp for long periods of time, you would only use the full 140 for a short time during take-off. Also, there’s no point in trying to compare this engine typically used to power ULM/LSA aircraft and a Turbine engine. They simply aren’t comparable. There’s no point in trying to build a Turbine to power the same aircraft you would normally use a Rotax 915 for, the result would be disastrously uneconomical if possible at all.
First things first, I didn’t say that the 915iS was a turbine engine, just that the performance of the finished aircraft would be similar to a 915iS as they are using a 140HP turbine hence I don’t think it’s the Heron, rather the TP-R90 seen in a Robin DR401.
The comparison with the 915iS is relevant because both provide the same sort of max rated power, both are the same approximate weight. The performance – including fuel consumption – is supposed to be similar – around 28 – 32 liters per hour. For those who want a light aircraft powered by Jet A1 without the reliability / maintenance issues of (eg) a CDI 155 diesel engine, it’s a solution.
The best thing you can all do is head by their stand at the Aero and see the finished product before it’s delivered
Eagle20 wrote:
I my opinion if you really really want an engine of that size to burn jet-A, you should go for a diesel, like an SMA, Continental or Austro engine, or a straight converted automotive diesel engine. it’s the only thing that would makes sense.
The main issues I see are a) the complexity coupled with the potential unreliability of such a motor and b) the weight – 85Kg for a small 140HP turbine or 135Kg for the Continental CD155.
The client in Africa wants to carry a massive photo camera to take photos of wildlife on the ground, that 50kg weight saving is highly beneficial, ignoring the 3000 hour TBO compared to 2100 TBR….
Sorry for the misunderstanding and blown up side discussion. I will go look for this little turbine at Aero Friedrichshafen. I’m still skeptic though :)
I agree CDI and even Austro engines aren’t what they should be either, just the fact they have a TBR alone.
Austro kept the steel case so they would be more economical and could be overhauled, but for whatever reason (my guess is they just make more money on selling new ones) they don’t overhaul them anymore.
I’d still prefer a good reliable avgas burning Lycoming or Continental.
Eagle20 wrote:
I’d still prefer a good reliable avgas burning Lycoming or Continental.
until Avgas becomes unavailable due to lead concerns – or has a universal no lead alternative been certified? Either way, I’m very happy with my 912iS, for fuel consumption alone, it’s unbeatable….
has a universal no lead alternative been certified?
It has, but in addition to licensing G100UL production, the developer is demanding an additional one time licensing fee from every aircraft that wishes to buy it. This is resulting in an ongoing stalemate between market and developer.
I’m very happy with my 912iS, for fuel consumption alone, it’s unbeatable
If you limit the choice of engines to gasoline powered engines currently in certified production that may be accurate because given the tiny cylinders it can run a compression ratio of 10.8:1. However it may not be true given the friction wasting RPM at which it runs.
Here is some efficiency data for different engines. The Rotax 914 (which is related but likely not as good as your 912iS) has the same efficiency as a carburated Lycoming O-235. An injected angle valve Lycoming IO-720 is listed as having higher efficiency, 34% versus 30%, while making four times as much power. It could be that the 912iS is comparable in efficiency at a smaller power output.
That’s only half of the story. A Lycosaur has good efficiency at one single point of rpm and load, and it requires careful fiddling by the pilot at that point to achieve OK efficiency. The 912 iS is optimized for all loads and rpms and achieves good efficiency every time without the pilot having to do a single thing. In practice they are not comparable. The 912 iS is far ahead.
Austro kept the steel case so they would be more economical and could be overhauled, but for whatever reason (my guess is they just make more money on selling new ones) they don’t overhaul them anymore.
Because the labor cost of overhaul highly exceeds the labor cost of building new engine and any savings accomplished with reusing used parts on overhauled engine is just a peanuts and can’t cover this difference. So, what once started as the advantage of Austro just disappeared and both Austro and CD are TBR at similar price with CD having 300 hours TBR more – 2100 vs 1800.
