Aesir,
A few years ago, when the SMA305 series first appeared (along with the other aero-diesels) I looked into them in rather a lot of detail with regards to using them to power light helicopters. I found that I couldn't satisfy myself sufficiently that you could expect to produce a diesel engine light enough while maintaining the level of reliability and cost-effectiveness that people seem to be claiming for the demanding helicopter duty cycle. Sure you can do it, with some expensive materials and clever engineering, but then you end up with an engine costing as much as an equivalent turbine and I know which I would rather have powering my machine!
For those that are interested an early report on the subject is given in NASA CP-3260, by Alex Brouwers, in April 1980, whom studied a configuration not dissimilar from that subsequently developed (but not brought to market yet) by Zoche. The report clearly highlights both the well published benefits and many of the technical challenges in the field that to my knowledge have simply not been addressed. Furthermore, the literature is littered with accounts of companies both automotive and aeronautical attempting to 'get the weight out' of diesel engines and failing miserably; running into enormous technical problems! Has anybody wondered why SMA, Wilksch, Zoche, DieselAir and Deltahawk Diesel have all been ‘developing’ engines for over ten years, even with their doubtless capability and credentials? Or why both Lycomming (with Detriot Diesel) and Continental (NASA GAP Project) have abandoned their efforts? There are some very good reasons I assure you…
I know I keep hammering on with the same point, but you simply cannot escape the fact that helicopters have one of the most demanding duty cycles of any application for engines, not least of which is the requirement for engines with and extremely high power-to-weight ratio (i.e. turbines optimised for the application). Diesel engines occupy the opposite end of the P/W spectrum, having one of the lowest power-to-weight ratios, so where is the sense in trying that! This is a simple fact that if ignored will lead to an expensive, underpowered, underperforming, bulkly white elephant. (No pun intended.)
I will follow the MK Project with great interest and dearly hope, for their sake, to be found to be incorrect.
Best Wishes
CRAN
PS: Would you really want an engine in your helicopter that had absolutely nothing in reserve? No spare couple of inches of MAP! No five min or 30sec rating?