Silver Eagle

The problem with all of the Allison turboprops is that the engine doesn't have any power at altitude. In most cases the turbo recip at 25,000 ft will fly right on by going 20 kts or more faster.... These engines have about 500 hp at takeoff, but the cruise power is a lot lower than that, and when you go up at altitude you end up with a lot less power than turbocharged recip. Notice that O&N quotes the maximum cruise speed at only 16,000 ft, and the best fuel consumption at 23,000 ft... That isn't an accident. At the lower altitude you will be sucking fuel more like 25+ghp and the range is down to 800 miles (with an IFR reserve). If you go higher you save fuel but the speed drops off.

If you want the lower maintenance and better reliability of the turbine you are going to pay for it with a lot higher fuel consumption and lower speed at altitude... Not a trade that a lot of folks are willing to take....

The new RR500 engine is even worse, it only has a cruise power of 320 hp at sea level. That's why they haven't made any sales yet.

All of the Allision conversions only make sense if you are putting the engine into an unpressurized aircraft and don't intend on flying high enough to need oxygen. So if you want to do a Bonanza conversion it might make sense. If you do that you will suck about 60% more fuel, but you will have more high and hot takeoff power and things like that.

The cost of the engine is about 3x that of new turbocharged recip, but it lasts about 2x as long between overhauls. Overhauls of the recip are an order of magnitude less, so the real cost of engines for the recip is actually about half that of running the turbine in a $/hr without considering the 60% higher cost of fuel.

If you have the money look at the Rocket conversions of a Malibu, they are a lot more capable airplane than the Silver Eagle.

While it is a nice airplane the Silver Eagle just doesn't make much sense from the standpoint of whay you get in performance for what it costs you to buy and fly it. That's why they haven't blackend the sky with them. If you have a P210 and love your airplane you might want to do it, but it is a pretty weak airplane in terms of performance for the $.

 

The problem is, there aren't any other turbines that make sense in the P210. The PT6 is too long as is the Walter. You would have to do a lot of reconfiguration of the nose and nose gear to get it to work. The Allison makes sense because it is short, but the engine isn't strong enough to do the job.

I am partial to high wing aircraft too, having owned a 182RG for a lot of years and it was a great airplane.

The 210 has some additional disadvantages in terms of weight and balance so it isn't all sweetness and light in that department

 

Most auto engines aren't really designed for an aviation (or a marine for that matter) duty cycle. In a car you spend most of the time at 15% power or less. When you start running an auto engine at 75% power it becomes very difficult to get the heat out of the heads and piston areas. The result is oil burning and coking and ring sticking as well as distress to the areas near the exhaust valve and port. The Theilert engine was a Mercedes diesel and they had to totally rework the cylinder head to get it to live, and there were realibility issues with the reduction gear train. In the end they were nowhere near the TBO they wanted and went under as a result of high warranty costs. Even with that the engine was a throwaway. That is, it was so used up that it couldn't be overhauled after it reached it's time limit.

A better bet would be to take a large auto engine and rework it for reliability and then only run it at prop speed (no gearbox, running at 2400 rpm) and you might have a chance to make it live 2,000 hours with a power output of around 250 hp. Problem is it won't be any lighter than a Lycosarus. It would likely be cheaper, but it woudn't be a certified engine and who knows what the reliability would really be. The long time aviation engines (Lyc and Conti) are actually pretty good in terms of what they do for the money you spend. While lots of folks say they are really old engines, they were really pretty well engineered at the time, and have in most cases been developed and improved a lot over the years.

In short, if is was really easy to design a much lighter, more reliable piston engine, somebody would have done it by now.

I had a lot of hope for the Deltahawk diesel, because, to me, a 2 stroke diesel made a lot of sense. My guess is that they are having reliability problems with a piston ported 2 stroke (cylinder wall scuffing around the exhaust port and consequent ring failures are common to that design), and that 2 stroke with valves (like a Jimmy diesel) would be a better solution. But the net result is that the power to weight ratio of all of these engines ends up close to that of a Lyc so what is the incentive to replace it?

I have heard from (insert any and every airframe OEM here) and they are all desperate for a heavy fuel engine for Europe and the third world. Avgas isn't an issue here, but they really need an engine that runs on JetA, and are willing to spend more for it if they could get one.

 

A friend of mine had a P210 with the Silver Eagle turbine conversion, and he told me that the only big difference was on climbing, but once up to the altittude, the cruise speed was pretty much the same, but he was burning much more fuel, he regreted having the conversion done.

 

It depends on what you want to do with it. The Meridian is nice but way overpriced in terms of performance, as is the TBM. The problem is the cost of the engine (P&W is raping their customers since there isn't any competition) drives up the aircraft cost and net result is a pretty expensive airplane for what it does. The Meridian is $1.6m the last time I looked and the TBM is $2.6m. The TBM beats most of the VLJ's in terms of payload and range and doesn't require a jet rating, so if you are stepping up from a high performance single the cost of transition is a lot lower. OTOH it isn't a jet and, but the DOC is about half of a jet....

Nothing is cheap in this world. Like I said earlier the JetProp Malibu conversion makes about the most sense in terms of airplane/$ since Malibu's with run out engines are (in a relative sense) fairly cheap.