This stuff is all of great interest to me. I have a couple of comments that might be of interest to others.
For Robinson to put a diesel into the R44 he only has one engine option - a derivative of the SMA SR305-230.
www.smaengines.com
[Yes i'm aware of Zoche, but that program is a long way off]
The problem is that allthough the new engines have a higher TBO 3000hrs, include fuel injection and burn jet fuel which is an enormous advantage in Europe, the engines are extremely heavy. All of the helicopter manufacturers that have used piston engines over the years have had terrible trouble with the fact that even the trusty Lycomings are too heavy really for use in helicopters due to the unique sensitively of helicopters to airframe weight (Thrust Balances weight etc etc). This is hampered further still by the need for 'power in reserve' for helicopters - i.e in the R22's case that bit between 25-27 MAP that your NOT SUPPOSED TO USE but could if it was essential.
Couple this with the fact that helicopters have an extremely demanding duty cycle for engines and we are then faced with the grim reality that if we want our engines to reach overhaul, then they need to be sustantially derated ~ i.e Robinsons approach, 131hp from a 160/180hp engine for R22. [There are also altitude effects to be considered in non turbo'd engines.]
So.....what does all this mean for the R44........
Well if Mr R want's to use the SMA unit he would have to use the future derivative of the SMA 305-230 (which is only a 230hp unit), the 300hp unit with an increased compression ratio (from 17:1 for the 230hp unit, to 19:1 for the 300hp unit)
This engine is likely to weigh approx 250kg and be derated to 250hp for heli apprlications the non-fuel injected Lycoming used in the Raven 1 weighes 170kg - that 80 kg of extra dead weight using the diesel (A whole passenger)! There will of course be a saving in fuel weight of approximately - 10kg per hour flight-time of fuel carried - for a typical 2hr mission fuel load the deisel configuration is still heavier by 60kg. To add insult to injury, the SMA crank speed is slower so the transmission would need to be changed and the slower spinning elements would have to be beefed up to cope with the additional torque - more weight!
In summary while it is theoretically possible to produce a SMA powered R44 that would not result in too significant a loss of performance, it would be difficult, expensive, and is most unlikely to provide an extra seat (unless it was for show!), further, to get more weight out of the airframe 'other' things would have to be compramised.
I refer you to:....
Low Interia Rotor System
Lack of Crash Protection
Low Airframe TBO
Now a turbine, thats a different kettle of fish, but while that would be a dream from a weight and performance point of view (and could mean 5-seat with high performance, or six seats with contemporary performance) the cost would be substantial. The only sutable engine is the Roll Royce C250, nominally 370hp MAX Cont and 420 for 5 mins - That enough for 2 R44's WOW!
If Mr R decided to go for 6 seats, then i'm sure we would have the most cost effect and commerically viable 6-seater ever designed...I guess we'll have to wait and see!
PS: I heard a rumour that Mr 'R' has had a Jet A1 Tank and pump fitted at the factory!
CRAN
