FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1945
1945 - 1815.PDF
100 . FUGHT ' SEPTEMBER 13TII, 1945 DE FLEX-REACTION PROPULSION Fig. 4- (Below) Complete reversal 0 dow at right angles to flightdirection. introduced in the circuit, and it E-ili be noted from the superimposed force diagram that the reactive pro- pulsion force generated is negative, If. it acts as drag, from formula? Fig. 3 shows the case for a 90 deg. ;nd, and it will be observed from Sic force diagram and the reversed osition of the bend in relation to the direction of flight, that (positive propulsive force is generated, from formula; (2) tid (3). The reaction stresses indicated by arrow Y in he force diagram have no propulsive effect'and are taken fire of in the structure of the machine. The value of the isultant reaction force depends upon the velocity of the as stream and the sine of the angle c. [Fig. 4 shows a complete reversal in the flow of the gas. peam. In this case no propulsive force or drag is generated. p the flowing gas stream and the resultant stress, indicated arrow Y, is again opposed by .the structure of the lachine. In this case, however, the force indicated by' !ro\v Y is double the similar force created in the 90 deg. Flow Path through Machine , " Ihese elements can now be combined into an example "jch will be illustrative of practical designs which are; follow. Fig. 5 indicates the complete flow path of the is stream through the machine, together with the reactions endered. The air enters a double-sided centrifugal air npressor and is turned through 90 deg. to emerge iaily. Thus no thrust forces are created at the com- ssor entry, since the deflection reactions balance each On Ieaving'the compressor the air is turned through 5 deg, ni a rearward direction,-and a forwardly acting '"ion force is thus created ; the air velocity at this - is assumed to be 200 feet per second. ubsequently, the air passes through the combustion Km, where its velocity is increased to an assumed ol 1,000 feet per second. Its thermal energy content ^creased, as well as its mass, by the addition of fuel. , emerging from the combustion system the gas stream [turned outwardly through 85 deg. and its velocity is eased in the bend to 2,000 feet per second, accompanied a corresponding decrease in its energy content. 1 will be noticed that this bend is similar to the bend w on Fig. 4, and that its effect on the thrust is but . ^e gases are now, however, flowing radially in direction required to- drive the radial-flow turbine/ f" ™ turn drives the air compressor. The gases finally -rge irom the periphery of the turbine at about 1,400 feet second and are immediately turned rearwardly through- ng'e of about 116 deg. In the bend the gas velocity 'creased to i;62o feet per second, and it is from this oend defied ion that the grcatci part, almost the Fig. 5. Flow path through jet propulsion unit ; double-entry radia compressor and radiai turbine. Eat whole, of the effective iorwardly-acting thrust is obtained. Having now discussed the reactions which occur at the . respective bends, it remains to investigate them individually and collectively from a detailed thrust point of view,., basing all our calculations on standard sea level atmospheric conditions. Commencing at the outlet of the air com- pressor, the positive static thrust generated at the 65 deg. bend is "given by :— \V K = — (V, cos a) + (V3 cos b) .. . W - = — (Va cos 32A dcg.) + (V3 cos 321 deg.) \V= — (200 x -8434) + (200,x -8434) • "x \v • • ~ . — — (i65-6S + I68-6S) ' . = ;O3io5 X 337-36 < = 10-5 lb. and the thrust component will be :— , T = R sin c = R sin 49 deg. = IO'5 X '7547 -.77 lb. The combustion system and its pipework is inclined at 15 deg. to the horizontal line of level flight. Injecting •018 lb. of fuel per pound of air per second into the combus- tion system, the velocity of the gases is increased from 200 to 1,000 feet per secom,, ,,.nd the increase in momentum will be 1,000-200 = .Son feet per second. The resultant propulsion force generated will be :— . = — x Soo = -0316 x 800 .". . a = 25-2S lb. • ';;'• •• and the resultant thrust component will be :— "-. r: T = R cose . v - . '• .,'-'. = R cos 15 deg. ' \ • ' ...Y~. - '•" = 25-28 x -9059. .: . • • . • " ' / = 24-4 1b. ••••• • • • , The negative thrust at the 85 deg. bend will be:— R « _ (V2 cos «) -f (V3 cos b) -•••' ',-.•;• • 8 - , . - •. •'.:>.- :
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
