Page:EB1922 - Volume 30.djvu/69

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39
AERONAUTICS


TABLE A. Details of the Principal Engines Available in 1918 for Service.

Country

Engine

Type

H.P.

Weight

R.P.M.

Wt. per H.P.

Great Britain

Beardmore

6 cyl. W.C.

170

592

1350

4-85

Green

6 ' W.C

170

585

1350

3-99

"

12 ' Vee W.C

300

990

1300

3-85

Rolls Royce Eagle

12 ' Vee W.C. .

360

947

1800

3'i8

Falcon . . .

12 Vee W.C

275

715

2000

3-15

" Napier Lion .

12 ' broad-arrow

456

850

1925

2-41

Sunbeam Arab ....

8 ' Vee W.C

220

524

2IOO

2-93

Maori ....

12 " Vee W.C

280

720

2IOO

3-32

Siddeley Puma . . . .

6 " W.C.

290

635

1650

2-74

B.H.P

6 " W.C

254

604

I4OO

2-93

R.A.F

12 " VeeA.C

1 60

639

I8OO

4-00

B.R.I. . . . ' .

9 " Rotary A.C. .

150

410

1250

2-78

B.R.2 A.B.C. Dragonfly

9 ' Rotary A.C. . 9 ' Radial A.C.

224 294

496 651

1200 1650

2-21 2-22

Cosmos Mercury

14 " Radial A.C.

315

582

I8OO

I-8 4

France .

Hispano Suiza ....

8 cyl. Vee W.C

217

484

2OOO

2- 7 8

" 11

8 " Vee W.C

315

558

2OOO

2-33

Renault

12 " Vee W.C

245

924

1300

4-32

Lorraine Dietrich

8 " Vee W.C

215

834

1450

3-4

Canton Unne ....

9 " Radial W.C. .

255

840

1300

4-13

Anzani

10 ' Radial A.C. . .

125

522

I2OO

4-17

Le Rhone

9 ' Rotary A.C.

130

330

1250

2-54

Clerget

9 ' Rotary ....

125

37

1250

2-96

Mono-Gnome ....

9 ' Rotary .

105

260

I2OO

2-48

it "

9 ' Rotary ....

154

313

1300

2-03

Italy .

Fiat

6 cyl. Vertical W.C. .

317

910

I6OO

3-42

"

12 " Vee W.C

400

805

226O

2-57

Isotta Fraschini ....

6 " Vertical W.C. .

190

574 .

1450

3-57

14 11

6 " Vertical W.C. .

300

662

1650

2-76

Tosi

12 " Vee W.C

410

904

I6OO

2-76

Spa

6 " Vertical W.C. .

230

507

I6OO

2-76

Anzani

12 ' Radial A.C.

too

386

1320

3-86

Germany

Austro Daimler ....

6 cyl. Vertical W.C. .

200

728

I4OO

4-19

Benz

6 " Vertical W.C. .

163

592

I2OO

4-19

"

6 " Vertical W.C. .

235

846

1400

4-17

Maybach

6 " Vertical W.C. .

200


it

6 " Vertical W.C. .

300

891

1400

3-52

Mercedes

6 " Vertical W.C. .

164

618

I4OO

4-3i

6 " Vertical W.C. .

252

93

I40O

4-36

(2) A greater uniformity of temperature throughout the cylinder, and therefore less tendency to distortion.

(3) Generally, greater reliability and higher efficiency.

These advantages could justly be claimed over the earlier types of air-cooled engines ; to-day they are less clear. Thus the first claim is only justified where great attention is paid to the design and arrangement of the jackets and circulating systems. Measurements confirm claim (2), but also show that the lack of uniformity is not necessarily a serious matter, while troubles from overheated exhaust valves have recently been more prevalent on water-cooled than on the modern air-cooled type.

For the air-cooled engine is claimed :

(1) Smaller weight per H.P. of the complete power unit.

(2) No danger of water freezing on gliding from great heights, or when standing.

(3) Reduced vulnerability in war service and easier installation.

(4) Special adaptability for use under widely differing atmospheric temperatures, and for the tropics.

(5) Better adaptability for application of some supercharging device to give constant power at heights.

Claim (l) is a matter of demonstration, the usual weight allow- ance for water-cooling being 0-6 Ib. per H.P. while the very best is 0-4 Ib. per H.P. Claim (2) is admissible to the extent that if freezing be prevented by the use of some other liquid, such as a mixture of alcohol and water, the alcohol evaporates unless the temperature of the fluid is kept below about 70 C. which increases the radiator size.

There is undoubtedly a future for the air-cooled engine of the fixed-cylinder type up to a certain size of cylinder. What this limit of size may be is not known at present. Cylinders of 8-in. bore by lo-in. stroke developing over too H.P. have been made and proved to be possible, and investigations on cylinders up to 10 in. in diameter are in progress. Twelve 6-inch cylinders would give 600 H.P., a useful size at present, and an 800 or 900 B.H.P. air-cooled engine is certainly feasible.

Design of Air-Cooled Cylinders. The useof aluminium alloyforthe cylinder heads has largely conduced to these results. In a normal design the middle portion of the head is the hottest point because the flow of cooling air and the placing of fins at this point is impeded by the inlet and the exhaust valve ports and valve gear. Most of the heat has to be conducted outwards till dissipated from the periphery of the combustion head, and the aluminium alloy effects this well, both because its conductivity is 3-5 times greater than the steel, and

because being 0-4 of the density of steel it may be used in ample thickness.

Such a cylinder must be of composite construction, since the valve seats and the working surface of the cylinder barrel must be of some harder material than aluminium. The valve seats may consist of rings of steel or of bronze, and these may be either cast or expanded into position. Tests appear to favour a steel barrel with integral cooling fins, screwed into an aluminium head for diameters as large as eight inches.

Arrangement of Cylinders. Aero engines may be subdivided according to the arrangement of their cylinders, into the following types:

(1) Single line engines suitable for water-cooling.

(2) Vee engines suitable for water- or air-cooling.

(3) Broad arrow engines suitable for water-cooling.

(4) Radial engines fixed cylinders ; air-cooling.

(5) Rotary engines suitable for air-cooling.

The general arrangement of these types is shown in fig. 22.

The straight line engine (a), with six or eight cylinders in line, offers a low hea,d resistance and is accessible. On the other hand its fore-and-aft length is large. The crank-shaft and crank-case are long, and hence the type is heavy.

In the Vee type engine (6) two lines of cylinders are used inclined to each other to form a Vee in elevation, and the corresponding port and starboard cylinders operate a common crank-pin. Weight is saved on crank-shaft, case, and valve gear.

In the Broad Arrow (c) three lines of cylinders are used as above with further weight saving.

In the Radial engine (d) economy of crank-shaft and case is carried to its logical conclusion. The cylinders are mounted in one plane at equal angular intervals around the crank-shaft. All the connecting rods operate on a single crank-pin. The small fore-and-aft length of the engine helps the aeroplane designer but its considerable diameter may hamper him.

To obtain explosion impulses at equal intervals throughout each revolution an odd number of cylinders must be used, the usual number being seven or nine. Where a larger power is required two rows of cylinders may be used, operating a two-throw crank-shaft. The radial cylinders may be stationary or rotating. In the latter case the airscrew is mounted on a continuation of the rotating crank- case. The rotating cylinder engine is quite unsuited for water- cooling. Although the radial engine with fixed cylinders is not well