3 of 3 people found the following review helpful
Reality is amazing!,
This review is from: Simple Science of Flight (Paperback)
Tennekes' book is a real treasure in its field! The author's strength lies in explaining in a comprehensible manner which flight parameters are essential for flying objects in general and by using easy to understand comparison examples he shows that there are many connections between the "design principles" of birds and airplanes. The revised version contains many new interesting facts and considering the price/quality ratio there is no better opportunity to fight the financial crisis than by buying this book!.
The reason that I take the opportunity to write a bit more is to question some points which would, in my opinion, deserve closer consideration when preparing the (I hope) next issue. Where civil aviation is concerned, a favourite victim for comparison is the motorcar. Tennekes (with Delft aeronautical background), who otherwise is known for his emphasis on a sound scientific approach, also relies in some examples upon arbitrary comparisons with cars. What always appears to be forgotten is that civil aviation transport has totally different basic requirements when compared to private motorcar use. To give an example, just think about the situation in which all motorcar drivers would have to comply with the same strict employment standards as applied to pilots; no doubt already for reasons of filtering out all risky drivers and alcohol abstention (at least during flight) an enormous leap in road safety improvement would be the result. Indeed roads would be quite empty too! In so far, not only is the efficiency comparison on page 177 between the General Electric90-115B engine and "a motorcar consuming 7 Litres/h at 100Km/h" in itself highly arbitrary because for such a high efficiency engine rather the AUDI A2 consuming less than 3 Litres/h at 100Km/h should be chosen, but because operating conditions and the size of the engine are important parameters for its efficiency potential a large engine should be compared to an engine of equal output and operating conditions. The Wärtsilä-Sulzer RTA96-C of comparable maximum output (81.3 MW), driving the Emma Mærsk containership (cost 145M$, see Wikipedia) capable of transporting 11,000 containers of 14 Tons each, also achieves over 50% thermal efficiency at cruise speed, even without the advantage of a -50°C ambient temperature. As a matter of interest, the newest, biggest and most efficient Boeing 747-8F Jumbo Jet (cost 150M$), having a freight capacity of 134 tons, would need more than 1100 long distance freight transport flights to transport such container volume. Thus even when doing one long-distance flight per day it would need almost three years to do the same as the Emma Mærsk does in one voyage! I hope this example shows the absurdity of arbitrary comparisons. Focusing on the specific purpose of use, almost every means of transport, if well designed and used in an intelligent manner can have high productivity, efficiency and safety for its specific use. Diversity in nature as shown in the book, but also the individual success stories of the Boeing 747, the TGV, the Emma Mærsk, as well as that of the bus, motorcar and even helicopters speak for themselves.
In relation to the Carnot cycle it is mentioned on page 169 that cold intake air and extremely high turbine temperatures make for superior engine efficiency. I am sure that the author knows that these temperatures only indicate an efficiency potential. On page 176 fanjets are mentioned together with their compression ratio, without making it clear that the high bypass ratio helps to increase the propulsive efficiency, while the high pressure ratio helps to increase the thermal efficiency. It would have been nicer if the engine efficiency parameters and their interaction would have been more extensively explained (and better in relation to the Brayton cycle).
These remarks are not intended to narrow Tennekes' accomplishment; considering the audience addressed it is extremely difficult to find an optimum between too much or not enough theory and I find the present balance already remarkably good.