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Aviation History
1961
1961 - 0219.PDF
FLIGHT, 17 February 1961 219 TCA and JP.4 An Airline's Defence of Wide-cut Fuel Questioned BY J. W. RICKARD SO at long last Trans-Canada Airlines have decided to riskcoming out into the open with their case for JP.4 [Flight,January 13, page 51]. So far, so good; but whatever else \r purports to be it is certainly not a reply to my article (Ref 1,overleaf), whose every point they have ignored. Was it not of Miss Carmichael that Dr Johnson said: "WhenI tried to talk tight and close, she was all wiggle-waggle, and try s> I might I could not force her to be categorical"? Quiteobviously, TCA have no intention of being categorical either, this in view of the two very cleverly worded paragraphs (Nos 14and 15) from which they deduce that controversy is futile on account of the situation being slightly complex. Others, however,ate prepared to thread a way through the complexities in an attempt to arrive at the truth; and because of this it becomesnecessary to refute yet again some of the statements which TCA (and others) keep on serving up in defence of a bad case. I shall therefore consider under separate headings the technicalpoints raised both in TCA's article and in Mr Dyment's separate statement prepared for the Montreal Star [Flight, January 13,page 51], but before doing so it is necessary to deal with one of the questions TCA ask of the "anti-JP.4 brigade." They ask, implicitly, if we would ban all piston-engined flying.We would not. Our aim derives solely from the principle that each type of aircraft shall offer to the public the maximum amountof safety of which it is capable. To use JP.4 in a turbine-powered aircraft is a denial of this principle. As for the standard of safety with gasoline being "acceptable"to the travelling public, this is probably so, though only because nothing better has been available. But now that we have thekerosine-fuelled transport, any burning to death of planeloads of people through failure to use kerosine is going to be considered—to make an understatement—most unacceptable. The Crash-fire Risk TCA contradict themselves. In para 5they state that they had no doubt of the superiority of kerosine in "one type of accident." In para 15 they say that they acceptthe conclusions of the NACA crash-fire programme which, they tell us, "demonstrated scientifically that enhanced crash-safetycannot be achieved through choice of fuel." These NACA tests (Ref 2) are so often cited as evidence againstkerosine that some elaboration is necessary at this point (I presume Mr Dyment is referring to the formation of fuel mist when hetalks about fuel "splashing"). Agreed, if an aircraft after crashing is enveloped in fuel mist and this mist ignites, there will be adisastrous fire from which no one can hope to escape, regardless of the type of fuel. But the NACA tests were so staged as toproduce deliberately the maximum amount of mist. This was done by breaching the tank leading edges with conveniently placedstanchions so as to leave large forward-facing orifices through which fuel was projected under the impetus of deceleration.Certainly this can occur in a real crash, but Mr Dyment is quite wrong to imply that it is typical of the majority of survivablecrashes. How otherwise can be explained-away the fact that in at least five of the accidents listed in Ref 1 (to which must nowbe added the Electra at La Guardia and the DC-8 at Idlewild), aircraft struck the ground, sometimes with violence, and caughtfire, but that still substantial numbers of people were able to walk out? Also, if ignition does not occur immediately, a quite moderatewind can render a mist innocuous within a few seconds, whereas the danger from spontaneous ignition and electrical arcing remainsfor a considerable time. While spontaneous ignition, and ignition from burning engineand hydraulic oils, are probably the commonest causes of fuel fires in a crash, what justification has Mr Dyment for minimizingthe dangers of electrical arcing by saying that "the electrical system noes out in a crash"? Crash switches, when fitted, do not alwayshave the opportunity to work; and, as most accidents are unpre- meditated, manual switching-out of the electrics is rarely possible.Sparking from abrasion on concrete surfaces is also prevalent in some crashes: the Comet landing at Madrid on its wheel-lessundercarriage gave a spectacular demonstration of this. Spontaneous Ignition It is correct to state that the spontaneousignition temperature of JP.4 is higher than that of kerosine, but every authority which has tested the two fuels has come up witha different answer as to the magnitude of the difference. Mr Dyment, in order to make his case, quotes a figure of 222 °C'400CF), whereas another authority puts the difference as low as 3.5°C (6°F) (Ref 4). In Ref 1 I quoted the result of an inves-tigation carried out by the Douglas Company (Ref 5). This showed y difference of 100°C (180°F) in favour of JP.4 under specifiedconditions. I believe this to be the very maximum order of difference to be found in a powerplant. In any case, as Mr Dyment well knows, the NACA tests showedthat engine-surface temperatures in a crash were high enough to ignite all fuels in current use. In the tests with jet-engined aircraftdescribed in Ref 3, the JP.4 fuel caught fire without the slightest difficulty. In connection with spontaneous ignition temperature, it is ofinterest to note that the Technical Department of Sabena, another JP.4-burning airline which claims to have made an exhaustivestudy of fuels, disagrees with TCA. They, Sabena, state that "for both fuels this (the s.i.t.) is situated at an identical point, i.e.,350°C." Fuel Freeze-point When TCA state that the kerosine availablein Canada in 1955 would have jeopardized safety and reliability, I must presume they are saying that a —40' freeze-point kerosineis unsuitable for their Viscount operations. Notwithstanding the much-vaunted Canadian winter, if they want us to believe thisthey will have to produce some evidence. On how many occasions have they had fuel temperatures fall to — 40 ? Also it is a gross exaggeration to assert that time has shownthe —40° kerosine to be inadequate for jet aircraft. Most US domestic operators use this fuel, and in their first 18 months ofoperation the lowest recorded fuel temperature ».t the completion of a trans-continental flight was —37°C (—34.5°F) (Ref 6). Time has, however, confirmed that the —40° kerosine isunsuitable for long range over-water operation, especially with the slower jets, and to meet this situation the — 50°C ( —58°F)freeze-point kerosine was introduced some years ago. JP.4 and the CHI Companies Are TCA unaware that JP.4 isan excellent refinery balancer? If it cannot be sold the industry will have a surplus of light ends on its hands, hence the inevitabledownward trend in the price of JP.4. TCA need reminding that eminent fuel technologists of the Esso Export and Shell Companieshave over the years made claims identical with those now being pressed by us of the "ami-JP.4 brigade" (Ref 7). Engine Restarting Restarting an engine in flight can generallybe accomplished a few seconds earlier with JP.4 than with kerosine, but this cannot make the slightest difference to the safety of theaircraft. Mr Dyment has gone out of his way to suggest that restarting may not be possible at all with kerosine. So far asBritish engines are concerned, this is nonsense. One does hear, however, that some non-British engines are reluctant to restartat altitude with kerosine; I have yet to learn that this has jeopardized safety, although it may well cause inconvenience.What such engines need, of course, is not JP.4 but further development. Combustion TCA list the various manifestations of combus-tion-system troubles—e.g., carbon deposits, high component-tem- peratures, smoke generation—and then state that these things areworse with kerosine. British engines, which have been developed primarily on kerosine, do not noticeably suffer from these troubles.The development of many non-British engines, however, has been carried out on JP.4, with the result that, at their present stage ofdevelopment, these engines may exhibit some of these maladies when running on kerosine. But if kerosine jeopardizes the reli-ability of an engine to the extent Mr Dyment claims, I would expect the engine type-certificate to quote two overhaul lives, alonger one for JP.4 and a shorter one for kerosine. I am not aware that this is so in the case of any engine. To get this thing into perspective it is worth quoting the viewof American Airlines, who have first-hand experience of American turbine engines (which TCA have not). I quote from Ref 6:"Since engine manufacturers had generally believed JP.4 would be the US commercial jet fuel, engine manufacturers had concen-trated on that fuel and had little service experience with kerosine. But mechanically, jet engines apparently have tolerated whateverdifferences exist between kerosine and JP.4 with little distress." Calorific Value Agreed, the calorific value per unit mass ofJP.4 is higher than that of kerosine, but if TCA think the difference amounts to 1 per cent, then they are gravely mistaken and havenot taken the trouble to ascertain the facts. According to informa- tion supplied by the Esso Company last year, average calorificvalues for North American kerosine and JP.4 are 18,600 BThU/lb and 18,700 BThU/lb respectively. This is a difference of 0.5 percent, so their claimed seven-passenger advantage can be straight- away cut to three-and-a-half passengers. In order to achieve thisadvantage in switching from kerosine to JP.4, one would need a big jet aircraft flying for rather less than maximum range butwith some 17,000 Imp gal of fuel aboard; passenger accommoda- tion would be limited by weight. It would be interesting to knowhow often these circumstances arise in practice. In this matter of payload and take-off weight, TCA contradict
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