Yeah, but the Continental diesel doesn’t have enough power to be an alternative. They think 172, 182 is the market, but it’s not. It’s all the turbo IO-540/IO-520 powered singles and twins that need a replacement. The P210’s, the Bonanzas, the Barons, the Aerostars, the 340’s, 414’s, Malibus.
Yes, if Cirrus offers a factory diesel, it will probably sell well. But as a retrofit?I don’t see it in great numbers.
The Continental diesel offers 300hp today. I expect it will scale to 350hp and more. You might mix it up with the 4 cylinder Continental diesel producing 155hp.
You don’t need to replace a 350hp AVGAS burner with a 350hp diesel as the diesel offers much more torque which is what’s relevant for takeoff. At altitude you need to provide enough boost for the diesel to keep its power and it can outperform an AVGAS engine with higher nominal HP.
That doesn’t really leave the EPS engine with much of a market I believe.
achimha wrote:
You don’t need to replace a 350hp AVGAS burner with a 350hp diesel as the diesel offers much more torque which is what’s relevant for takeoff.
350HP at a given RPM are 350HP, regardless of how the engine produces it.
At altitude you need to provide enough boost for the diesel to keep its power and it can outperform an AVGAS engine with higher nominal HP
You are referring to turbo-diesel engines, which the thielert/continental are? They of course perform better than a normally aspirated avgas engine, but the specimens currently in production have a critical altitude in the low 100’s, so perform worse than the corresponding AVGAS burners.
The main issue remains – to be successful, these engines need volume, and that means OEM, not retrofit. Thielert/Austro managed it with Diamond and the military, whichever engine Cirrus ends up using will make it if the aircraft does, and the same applies to Cessna. Or a military cross-application, if the manufacturer can be bothered.
Cobalt wrote:
350HP at a given RPM are 350HP, regardless of how the engine produces it
Unless equipped with a fixed pitch propeller, with RPM accordingly limited for takeoff… but no, you don’t see a lot of 350 HP planes with an airspeed range narrow enough to allow a fixed pitch propeller, so low rpm torque becomes irrelevant: the engine doesn’t run at reduced rpm for takeoff or climb, or any other time that you would like high percentage power.
The torque (flat power versus rpm) issue is relevant when comparing takeoff and climb performance for high speed (e.g. Rotax or similar) 100 HP engines with other lower rpm 100 HP engines when both are driving a fixed pitch propeller. This is why a C150 when re-engined with a Rotax 912 also needs the addition of a variable pitch propeller. Another example is the Lycoming 65 HP engine, which failed in the market as a result of insufficient low end torque, regardless of making the same peak power as the A65 Continental that was sold in vast quantity. But with a variable pitch propeller it doesn’t matter…
Cobalt wrote:
The main issue remains – to be successful, these engines need volume, and that means OEM, not retrofit. Thielert/Austro managed it with Diamond and the military, whichever engine Cirrus ends up using will make it if the aircraft does, and the same applies to Cessna. Or a military cross-application, if the manufacturer can be bothered.
The main factor that has allowed development of the Thielert engine to reliable operation (pre-Chinese ownership) was US Army money, and the Army’s need for single fuel operation for a tactical (read small, moderate power) UAV in remote and hostile places. The Air Force didn’t care as much about fuel for their high altitude, long endurance aircraft and needed higher power/weight performance so allowed Rotax engines from 1988 on, although no longer on new aircraft today. Today, I think the US military is moving to turbines for larger UAVs plus very small tactical UAVs and although you can never say never, for those reasons I think it’s unlikely there will be US military demand for a 350 HP reciprocating engine of any kind. The funding mechanism that allowed the US AIr Force EPS engine lab testing referenced above was a Broad Agency Announcement which generally means it’s contractor proposed and not associated with an existing program. I think the Air Force motivation would have been to recommission their high altitude test lab, using project money instead of capital.
Quite important how the engine delivers the HP – cf the most obvious difference between the DB605 and the Jumo 211 Messerschmitt 109…
Silvaire wrote:
This is why a C150 when re-engined with a Rotax 912 also needs the addition of a variable pitch propeller.
It’s more a matter of design principles IMO.The 150/152 is already under powered with the 110 HP Lycoming as it is. Putting an even less powerful engine like the Rotax 912 ULS will make it comparable to the 100 HP Continental engine (on the 150). Anyway, a 912 UL (80 hp) is designed to be used on MTOW 450 kg microlights. Later the slightly larger ULS came (100 hp), more suitable for MTOW up to 600 kg, all fixed pitch. The MTOW of the C-150 is 750 kg or something, more like a VLA or TMG. 100 HP starts to become on the weak side no matter what at that weight, so typically these aircraft have variable pitch and usually also the 914 (turbo) with 115 HP.
LeSving wrote:
The 150/152 is already under powered with the 110 HP Lycoming as it is.
Whut? Tens of thousands of them flying around over gross (obese CFIs) every day, needing almost no runway. This is one aircraft that is definitely not underpowered with its standard engine.
Of course Silvaire is right that a low torque engine such as Rotax needs a variable pitch prop to replace a high torque direct drive engine of the same HP. Thanks to the variable pitch propeller, the 160hp Lycoming of the C172 could be replaced by the heavier 135hp Thielert engine with overall comparable performance (a bit more takeoff run but better speed at altitude due to the turbo).
achimha wrote:
Thanks to the variable pitch propeller, the 160hp Lycoming of the C172 could be replaced by the heavier 135hp Thielert engine with overall comparable performance (a bit more takeoff run but better speed at altitude due to the turbo).
You can also install an STC’d variable pitch propeller on the Lycoming, I happen to have one on my O-320 
The variable pitch propeller negates the effect of low rpm torque on either engine and makes sea level performance of two engines with the same power rating identical. 135 HP provides much less excess power available for climb than 160 HP, assuming both have VP propellers, so the 135 HP engine will then produce much lower climb rates at or near sea level, particularly if it’s a heavier engine.
Separate from that, a turbo on any engine usefully increases performance over 8000 ft DA. Over some altitude the otherwise underpowered, heavy turbo Diesel will equal or better the Lycoming normally aspirated engine in aircraft performance. Whether that’s important depends on whether you fly that high, or (more importantly to me) take off that high.
Re turbos many people probably don’t think much about how high Rotax engines fly, how often, for how long, or what it may have taken to make it workable without a pilot Link
Silvaire wrote:
Re turbos many people probably don’t think much about how high Rotax engines fly, how often
According to Rotax in a conversation I had with them on the AERO in spring the Rotax-Turbo 914 is sold in big numbers in gyrocopters where a high power output is required in the mission profile of these aircraft. There are also many (grass)airfields in Europe, where the extra boost is highly appreciated, especially in summer or on an upslope at MTOM. Given the prices of aircraft other than the basic-microlights the additional cost of the Turbo becomes neglectable.
There must be a reason why Rotax (>50.000 aircraft-engines produced) introduced the 915iS-Turbo and one could see quite some airframes at the fair having it installed even before its certification. That said I think, that the 915iS is too heavy (even the 912iS is) for most of the microlights as long as there’s no massively increased MTOM.
BTW I like flying in the flightlevels with my 914 :-)
achimha wrote:
restarting a turbine in flight is far from trivial
It certainly isn’t anything difficult in a CJ with the Williams engines. Just press the starter, bring the power lever to idle at the appropriate moment, and the starting sequence occurs
