GB2175651A

GB2175651A - Contra-rotating air screw propellers

Info

Publication number: GB2175651A
Application number: GB8513673A
Authority: GB
Inventors: Blyakhman Basya Petrovna; Galaev Vladimir Alexeevich; Kalyazhnov Vladi Vladimirovich; Kishalov Anatoly Nikolaevich; Kopalov Vladimir Sergeevich; Kulikov Evgeny Ivanovich; Larin Anatoly Ivanovich; Ostroukhov Stanislav Pavlovich; Poddubsky Valery Antonovich; Simonov Lev Alexeevich; Sukhorosov Jury Leonidovich; Chesnokov Boris Alexeevich; Yakovlev Alexandr Viktorovich; Vasiliev Valdimir Ivanovich
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-05-30
Filing date: 1985-05-30
Publication date: 1986-12-03
Also published as: GB8513673D0; DE3519226A1

Abstract

To improve the propulsive efficiency of a pair of coaxial, contra rotating propellers 5, 6, the number of blades 7 on one is different from the number of blades 8 on the other. <IMAGE>

Description

SPECIFICATION Aircraft power plant The present invention relates to aircraft industry and, more particularly, to aircraft power plants.

Most advantageously the present invention may be used on subsonic aeroplanes having gas-turbine engines with coaxial propellers and differential reduction gearboxes to divide engine power between the coaxial propellers non-uniformly.

The invention resides in that in an aircraft power plant in which output shafts of a differential reduction gearbox are mounted coaxially for contrarotation and each is provided with one row of blades making up coaxial propellers, according to the invention, the number of the blades arranged in one row is different from the number of the blades arranged in the other row.

The aircraft power plant according to the invention being comparatively simple in design makes it possible to increase the efficiency of the coaxial propellers and, consequently, to improve fuel economy of the aircraft.

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings wherein: Figure 1 is a side view representing schematically an aircraft power plant according to the invention; Figure 2 is a front view representing schematically a front row of blades; Figure 3 is a front view showing schematically a rear row of blades with the front row removed; Figure 4 shows the dependence of a profile lift coefficient Cy on a propeller radius ratio i; for propellers having equal and unequal numbers of blades in the front and rear rows; Figure 5 shows the dependence of an aerodynamic quality K on a standard propeller radius ratio for propellers having equal and unequal numbers of blades in the front and rear rows;; Figure 6 shows the dependence of an efficiency in a cruising flight on a ratio of powers N1/N2 for propellers with equal and unequal numbers of blades in the front and rear rows; Figure 7 shows the dependence of a propeller-thrust coefficient a on a power coefficient ss in the take-off conditions.

An aircraft power plant comprises a gasturbine engine 1 (Fig. 1) having a differential reduction gearbox 2. Coaxially arranged output shafts 3 and 4 of the differential reduction gearbox 2 mount fixedly hubs 5 and 6 respectively. The hubs 5 and 6 accommodate constant-speed units (not shown in the drawings).

Secured in the hub 5 are blades 7 (Fig. 2) making up a front row, and secured in the hub 6 are blades 8 (Fig. 3) making up a rear row. The front and rear rows of the blades 7, 8 form coaxial propellers. The front row includes eight blades 7, whereas the rear row includes six blades 8.

A number Ii of the blades 7 in the front row and a number 12 of the blades 8 in the rear row are selected from a condition i1 N1 12 N2 in order to load all the blades of the coaxial propellers substantially equally. In the embodiment described herein Ii is selected to be equal to 8 and 12, to 6, as the design of the differential reduction gearbox in the given embodiment determines the relation between powers on the shafts 3 and 4 N, -=1.5.

N2 The advantages of such selection of the number of blades will be better understood from the description of the aircraft power plant operation.

In the process of the aircraft power plant operation the front row of the blades 7 with the hub 5 and the shaft 3 and the rear row of the blades 8 with the hub 6 and the shaft 4 rotate in the opposite directions.

Fig. 4 shows the dependence of propeller blade section lift coefficients Cy on a propeller radius r=, R where r is the blade section radius, R is the blade maximum radius, for the prior art construction having the equal number of blades in both rows ill=12=8 and for the construction disclosed herein and having the unequal number of blades in the front and rear rows li=8 and 12=6.The relations Cy(q for the front row of the blades in both cases are the same and indicated by a curve 9; the relation Cy(F) for the rear row of the prior art propellers with ill=12=8 is indicated by a curve 10; the relation Cy(q for the rear row of the blades of the propellers disclosed herein with ill=8 and 12=6 is indicated by a curve 11. Fig. 5 shows the dependence of an aerodynamic quality K of propeller blade sections on a propeller radius ratio r, which corresponds to Fig. 4.The relation K(r).for the front row of the prior art and disclosed coaxial propellers are also the same and indicated by a curve 12; the relation K(r) for the rear row of the prior art propellers with ill=12=8 is indicated by a curve 13, the relation K(r) for the rear row of the diclosed propellers with ill=8 and 12=6 is indicated by a curve 14.

As seen from Figs. 4, 5, with N, -=1.5 N2 the use of equal numbers of blades in both rows with 11=12=8 results in that, as compared with the embodiment having unequal numbers of blades in the front and rear rows with 1,=8 and 12=6, the rear row blades work at a lower value of the aerodynamic quality K of the sections thereof. Consequently, the level of profile (and wave) losses on the rear row blades in the case 12=8 is higher than in the case 12=6.Accordingly, the efficiency of the coaxial propellers and, consequently, of the whole aircraft power plant in the case ill=8 and 12=6 is higher than in the case it=12=8. The example discussed herein reiates to the coaxial propellers with a diameter D=4 m for a flight at an altitude H= 11 km and a speed corresponding to a Mach number M=0.7, with an engine output shaft total power N1+N2=2800 kW and a power-topower ratio N1 -1.5.

N2 The calculations show that the efficiency of the coaxial propellers having the number of blades It=12=8 equals w1=85%, whereas the efficiency of the coaxial propellers with the number of blades ill=8 and 12=6 is =87%, i.e. is higher by 2%.

Effect of the Invention The experiments performed on a model power plant provided with the prior art coaxial propellers and with the coaxial propellers disclosed herein have confirmed the results of calculations. Fig. 6 shows curves 15 and 16 corresponding to the dependence of the efficiency of the prior art coaxial propellers with it =12=8 and of the disclosed coaxial propellers with 1,=8 and 12=6 on the power-topower ratio N, N2 under one and the same conditions of flight described hereinabove. The comparison shows that with N1 > 1 .2 N2 the coaxial propellers with unequal numbers of the blades in the front and rear rows (the curve 16) feature a higher efficiency.

It is also worthy of mention that the coaxial propellers having unequal numbers of the blades in the front and rear rows with 1,=8 and 12=6 are not inferior to the coaxial propellers having equal numbers of the blades it=12=8 in both rows in a take-off propellerthrust coefficient a up to the values of a power coefficient ss=1.2, which is higher than the design value B=0.9 for the propellers with a diameter D=4 m, which is illustrated by the test results given in Fig. 7 wherein a curve 17 corresponds to the coaxial propellers with 11=12=8, and a curve 18 corresponds to the coaxial propellers with 1,=8 and 12=6.

Claims

1. An aircraft power plant in which output shafts of a differential reduction gearbox are mounted coaxially for contrarotation and each is provided with a row of blades making up coaxial propellers; the number of the blades arranged in one row is different from the number of the blades arranged in the other row.

2. An aircraft power plant substantially as described hereinabove with reference to the accompanying drawings.