Andrew Porter's point regarding rotary engines with an 'energy transfer efficiency' of 70 per cent (Letters, 12 February) had me puzzled.
If Mr Porter is familiar with Carnot's theorem then it isn't obvious from his description. Converting up and down motion to rotary motion actually works quite well, and having a restricted speed range on its own is not going to affect efficiency.
The implication is that a rotary engine will be unrestricted — either at the bottom or top end of the range. Rather odd.
Robin Herrick
Wick, Caithness
Rotary puzzle
Water Sector Talent Exodus Could Cripple The Sector
Maybe if things are essential for the running of a country and we want to pay a fair price we should be running these utilities on a not for profit...