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Correspondence

Correspondence November , 1933 AIRCRAFT ENGINEERING 265 The Editor invites letters for publication on matters of general interest to readers. No responsibility is, of course, accepted for the views expressed by correspondents RESEARC H ON LOW-DRAG COWLINGS engine functions satisfactorily with th e Townend of the salt bath, there is an indication of ring, as, of course, a radial engine must do possible technical progress but, in advocating To the Editor to-day in order to be a practicable proposition. pyrometric paints, are you not running the DEA R SIR,—In your issue of September 1933, Wit h the best forms of ring and on properly risk of spoiling what is otherwise a possibly particulars are given of some tests carried out designed bodies the drag of the combination is valuable bath ? on Bristol engines fitted with Townend rings, ver y low and at the same time th e engine inside While not claiming any very deep knowledge and some recommendations as to the type of th e ring is left completely bare without loss of or experience I had always understood tha t the ring to be fitted are made by tha t company. efficiency. reason why one adopts the salt bath in prefer­ Some of the statements made are, we think, We think it would be desirable to draw the ence to a furnace or muffle containing air or liable to cause misunderstanding. attentio n of your readers to the fact that the other gases is because the automatic circulation First, with regard to the influence of the cowlings recommended by the Bristol Company and convection of th e salt bath secures a virtual fitting of ring cowlings on the temperature of are the subject of patents in most countries. temperatur e equality in all parts so that, engines, it is not correct to say tha t flight tests The use of such cowlings, except in connection having brought the bath to a particular tem­ have proved tha t there is necessarily a marked with engines licensed by us, would be an perature, we may know tha t an y work immersed increase in engine temperature when these infringement. therein will be heated to tha t temperature. cowlings are fitted. Yours faithfully, The only exception t o this rule is that , as the I t is interesting in this connection to quote for BOULTON & PAUL LTD., upper surface of the bath must inevitably be a statement made by Mr. A. Nutt, Vice- J . D. NORTH, loosing heat and as heat is abstracted from the President of the Wright Aeronautical Corpora­ Director. bat h by the material immersed in it, there must tion, U.S.A., in discussing Mr. McKinnon be a continuous flow of heat through the walls Wood's paper on Engine Cooling Research, {In connection with Mr. North's suggestion of the bath from the source of heating, and reference the Journal of The Royal Aeronautical that cither Fig. 5 or the conclusions drawn from therefore there will be some temperature Society, September 1933, page 752 :— it require modification, we are informed by the gradient through and at the immediate surface " He did not agree with the statement that Bristol Aeroplane Company that in fact there of the wall of the bath. This gradient will be ' all the cowling rings tha t have been devised was an error in the numbering of the curves as steeper when the heat loss from the bath is increase the cylinder temperatures appre­ they appeared in the " Bristol Review," from greater and, therefore, for a given steady ciably.' As a matter of fact, both the cow­ which they were reproduced by us. We therefore temperatur e in the bath, the temperature of ling and rings tha t have been used here have reprint this figure below with the correct re­ th e wall will var y according to the heat input. definitely decreased the temperatures and it ferences for the curves, as now given us by the would be impossible to run these engines in Bristol Company. We have called Mr. North's I t would seem that, to put these paints on flight service satisfactorily unless both cow­ attention to this correction, which appears to th e wall of the bath is, therefore, to attempt ling and rings were used." modify the conclusions drawn. He, however, t o measure the temperature at the very place Furthermore , it has been usual for air- still wishes us to publish his letter.—EDITOR.] where we know there will b e th e largest variation cooled engines to be fitted with some sort of and where, if there are any differences at all, cowling over the crankcase and the lower part the y will certainly exist. of the cylinders. The use of the Townend ring The reason for using the bath being to heat as an alternative to these is hardly likely to certain pieces of material up to a certain increase th e engine temperature. temperatur e is it not more reasonable to insert some heat-sensitive device in the bath in I t is true that in many cases a slight rise practically the same way as the material will in engine temperature is found when the be inserted. This is the way that a properly Townend ring is fitted, but this is not always arranged electrical pyrometer does measure the due to a reduction of the air flow over the temperatur e and, since there are no special cylinders, e.g., in some cases it has been found technical difficulties in providing the electrical to arise from the effect of the smoothed air pyrometer for such work as is described, the flow on the air intake. Modification in the argumen t for the paints can only be one of carburation arrangements has satisfactorily cheapness in first cost. If the paints were reduced the temperatures. In any case this bette r than the pyrometer the case would be rise in temperature is small compared with different, but I suggest, for the reasons above, the temperature variations usually measured the y would be definitely inferior. They would between one cylinder and another on the same also be inferior in other directions, namely, that engine. watching the change of colour in the paints I t is curious that the statement is made would not be too easy and would not provide on page 211 that the summary of the information on a temperature scale. When a comparative wind speeds illustrated in Fig. 5 temperatur e departs from the figure desired, if shows clearly a marked drop in air speeds a pyrometer is used, the rate at which it is around the cylinders when ring cowlings arc departing can be estimated and from this the used. Actually the largest drop in air speed, operator can gauge the amount of reduction of particularly over the upper and most important hea t appropriate to bring the temperature back part of the cylinder, is between curves 1 an d 2, to the desired figure. This can only be done which is the effect of fitting the Bristol front with the aid of a pyrometer pointer moving exhaust ring only. over a temperature scale or an autograph It would, therefore, appear that, quite apart record continuously produced. from any considerations of the heat in the exhaust ring, the adverse aerodynamic effect on Returning to the question of cost, compared engine cooling of this exhaust ring is very with the value of the plant and of the material marked. When, however, as shown in Curve under treatment, even quite an elaborate (1) Bare engine. (2) Engine with long chord 4, a short chord Townend ring is added to this pyrometer outfit becomes " pett y cash " when ring and rear exhaust ring. (3) Engine with combination, the air flow is restored around the figured in terms of bath-hours on the basis of short chord ring and front exhaust ring. (4) upper part of the cylinder to such an extent interest and depreciation on first cost; which Engine with Bristol front exhaust ring. that the adverse effect of the Bristol front is the way in which all plant expenditures exhaust ring is almost neutralised. It would are figured by those who know their business. SALT BATHS FOR DURALUMIN appear, therefore, that either Fig. 5 or the conclusion drawn from it requires modification. To the Editor Yours faithfully, We are glad to be able to endorse very fully DEA R SIR,— I have been much interested by CHAS . E. FOSTER, F.Inst.P. the remarkabl e improvement in cooling on the th e article on this subject in your October Pegasus engine described in the article. The issue. Certainly, as regards the construction Letchworth, Herts. Foster Instrument:; Co. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Correspondence

Aircraft Engineering and Aerospace Technology , Volume 5 (11): 1 – Nov 1, 1933

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb029739
Publisher site
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Abstract

November , 1933 AIRCRAFT ENGINEERING 265 The Editor invites letters for publication on matters of general interest to readers. No responsibility is, of course, accepted for the views expressed by correspondents RESEARC H ON LOW-DRAG COWLINGS engine functions satisfactorily with th e Townend of the salt bath, there is an indication of ring, as, of course, a radial engine must do possible technical progress but, in advocating To the Editor to-day in order to be a practicable proposition. pyrometric paints, are you not running the DEA R SIR,—In your issue of September 1933, Wit h the best forms of ring and on properly risk of spoiling what is otherwise a possibly particulars are given of some tests carried out designed bodies the drag of the combination is valuable bath ? on Bristol engines fitted with Townend rings, ver y low and at the same time th e engine inside While not claiming any very deep knowledge and some recommendations as to the type of th e ring is left completely bare without loss of or experience I had always understood tha t the ring to be fitted are made by tha t company. efficiency. reason why one adopts the salt bath in prefer­ Some of the statements made are, we think, We think it would be desirable to draw the ence to a furnace or muffle containing air or liable to cause misunderstanding. attentio n of your readers to the fact that the other gases is because the automatic circulation First, with regard to the influence of the cowlings recommended by the Bristol Company and convection of th e salt bath secures a virtual fitting of ring cowlings on the temperature of are the subject of patents in most countries. temperatur e equality in all parts so that, engines, it is not correct to say tha t flight tests The use of such cowlings, except in connection having brought the bath to a particular tem­ have proved tha t there is necessarily a marked with engines licensed by us, would be an perature, we may know tha t an y work immersed increase in engine temperature when these infringement. therein will be heated to tha t temperature. cowlings are fitted. Yours faithfully, The only exception t o this rule is that , as the I t is interesting in this connection to quote for BOULTON & PAUL LTD., upper surface of the bath must inevitably be a statement made by Mr. A. Nutt, Vice- J . D. NORTH, loosing heat and as heat is abstracted from the President of the Wright Aeronautical Corpora­ Director. bat h by the material immersed in it, there must tion, U.S.A., in discussing Mr. McKinnon be a continuous flow of heat through the walls Wood's paper on Engine Cooling Research, {In connection with Mr. North's suggestion of the bath from the source of heating, and reference the Journal of The Royal Aeronautical that cither Fig. 5 or the conclusions drawn from therefore there will be some temperature Society, September 1933, page 752 :— it require modification, we are informed by the gradient through and at the immediate surface " He did not agree with the statement that Bristol Aeroplane Company that in fact there of the wall of the bath. This gradient will be ' all the cowling rings tha t have been devised was an error in the numbering of the curves as steeper when the heat loss from the bath is increase the cylinder temperatures appre­ they appeared in the " Bristol Review," from greater and, therefore, for a given steady ciably.' As a matter of fact, both the cow­ which they were reproduced by us. We therefore temperatur e in the bath, the temperature of ling and rings tha t have been used here have reprint this figure below with the correct re­ th e wall will var y according to the heat input. definitely decreased the temperatures and it ferences for the curves, as now given us by the would be impossible to run these engines in Bristol Company. We have called Mr. North's I t would seem that, to put these paints on flight service satisfactorily unless both cow­ attention to this correction, which appears to th e wall of the bath is, therefore, to attempt ling and rings were used." modify the conclusions drawn. He, however, t o measure the temperature at the very place Furthermore , it has been usual for air- still wishes us to publish his letter.—EDITOR.] where we know there will b e th e largest variation cooled engines to be fitted with some sort of and where, if there are any differences at all, cowling over the crankcase and the lower part the y will certainly exist. of the cylinders. The use of the Townend ring The reason for using the bath being to heat as an alternative to these is hardly likely to certain pieces of material up to a certain increase th e engine temperature. temperatur e is it not more reasonable to insert some heat-sensitive device in the bath in I t is true that in many cases a slight rise practically the same way as the material will in engine temperature is found when the be inserted. This is the way that a properly Townend ring is fitted, but this is not always arranged electrical pyrometer does measure the due to a reduction of the air flow over the temperatur e and, since there are no special cylinders, e.g., in some cases it has been found technical difficulties in providing the electrical to arise from the effect of the smoothed air pyrometer for such work as is described, the flow on the air intake. Modification in the argumen t for the paints can only be one of carburation arrangements has satisfactorily cheapness in first cost. If the paints were reduced the temperatures. In any case this bette r than the pyrometer the case would be rise in temperature is small compared with different, but I suggest, for the reasons above, the temperature variations usually measured the y would be definitely inferior. They would between one cylinder and another on the same also be inferior in other directions, namely, that engine. watching the change of colour in the paints I t is curious that the statement is made would not be too easy and would not provide on page 211 that the summary of the information on a temperature scale. When a comparative wind speeds illustrated in Fig. 5 temperatur e departs from the figure desired, if shows clearly a marked drop in air speeds a pyrometer is used, the rate at which it is around the cylinders when ring cowlings arc departing can be estimated and from this the used. Actually the largest drop in air speed, operator can gauge the amount of reduction of particularly over the upper and most important hea t appropriate to bring the temperature back part of the cylinder, is between curves 1 an d 2, to the desired figure. This can only be done which is the effect of fitting the Bristol front with the aid of a pyrometer pointer moving exhaust ring only. over a temperature scale or an autograph It would, therefore, appear that, quite apart record continuously produced. from any considerations of the heat in the exhaust ring, the adverse aerodynamic effect on Returning to the question of cost, compared engine cooling of this exhaust ring is very with the value of the plant and of the material marked. When, however, as shown in Curve under treatment, even quite an elaborate (1) Bare engine. (2) Engine with long chord 4, a short chord Townend ring is added to this pyrometer outfit becomes " pett y cash " when ring and rear exhaust ring. (3) Engine with combination, the air flow is restored around the figured in terms of bath-hours on the basis of short chord ring and front exhaust ring. (4) upper part of the cylinder to such an extent interest and depreciation on first cost; which Engine with Bristol front exhaust ring. that the adverse effect of the Bristol front is the way in which all plant expenditures exhaust ring is almost neutralised. It would are figured by those who know their business. SALT BATHS FOR DURALUMIN appear, therefore, that either Fig. 5 or the conclusion drawn from it requires modification. To the Editor Yours faithfully, We are glad to be able to endorse very fully DEA R SIR,— I have been much interested by CHAS . E. FOSTER, F.Inst.P. the remarkabl e improvement in cooling on the th e article on this subject in your October Pegasus engine described in the article. The issue. Certainly, as regards the construction Letchworth, Herts. Foster Instrument:; Co.

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: Nov 1, 1933

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