Heidmann, Marcus F

English

NASA Technical Reports Server

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By Marcus P, Heidmann 
+ Lewis Flight Propulsion Laboratory 
Cleveland, Obi0 
Washington 
September 1949 
https://ntrs.nasa.gov/search.jsp?R=19930082628 2020-06-17T22:15:59+00:00Z
NATIONAL ADVISORY CO- FOR AEROX'iAUI'ICS 
TECHIJICAL mTE 1951 
METHOD OF -hTG COmDITIOEJs OF 
OF AN TURBINE-PROPELIJER CWLI?JATION 
By Marcus F. Heidmann 
S m Y  
The characteristics of a turbine and a propeller were inve 
tigated to determine the conditions of maximum-efficiency operation 
when utilized as an independent turbine-propeller combination. The 
procedure used to determine the conditions of maxirmun efficiency . 
and the speed ratio between the turbine and the propeller is illus- 
trated. This procedure involved the use of a method of matching 
turbines and propellers. 
By the use of this method, the conditions for maximum-efficiency 
operation can be defined by turbine-inlet temperature, pressure ratio, 
and propeller speed for each flight condition. 
these parametars is adaptable to independent control of turbine- 
propeller speed when interaction between the turbine-propeller com- 
bination and the gas generator is either nonexistent or when the 
effects of interaction can be sufficiently damped. 
The relation between 
INTRODUCTION 
An independent turbine-propeller combination constitutes a 
component of an aircraft-propulsion system that may be used with 
any type of gas-generating unit supplying the necessary gas-energy 
conditions for the turbine. This component is independent in the 
sense that there is no mechanical drive between the gas generator 
and the turbine-propeller combinations. One of the characteristics 
of such a propulsion system is the absence of a fixed ratio between 
turbine-propeller speed and gas-generator speed. This character- I 
istic can be,utilized to realize efficient over-all performance by 
operating both the generator and the turbine-propeller combination 
at speeds resulting in maximum efficiency for any given power out- 
put. 
defined as maximum-efficiency operation. 
Operation along a curve of maximum-efficiency conditions is 
An analysis of an independent turbine-propeller combination 
The conducted at the NACA Lewis laboratory is presented herein. 
speed ratio for maximum-efficiency operation and the resulting 
2 aACA "N 1951 
control relation are determined over a range of turbine-inlet and 
flight conditions. The conditions for maximum-efficiency operation 
and the control of the turbine-propeller combination are discussed. 
The procedure used in the analysis involved the application of a 
method for matching turbines and propellers at various speed ratios. 
In the analysis, the characteristics of a representative gas 
turbine andpropeller were used. 
turbine and propeller was assumed constant with no gearing losses 
and the outlet static pressure of the turbine was assumedto be 
equal to the ambient pressure. 
The speed ratio of the coupled 
METHOD OF ANALYSIS 
Turbine and propeller characteristics. - The individual per- 
formance characteristics of the turbine and the propeller are shown 
in figures 1 and 2, respectively, 
propeller, a value of blade speed exists for each operating con- 
dition that defines operation at maximum efficiency, For the tur- 
bine,as shown in fijpre 1, maximum-efficiency operation is defined 
by the maximum efficiencies for each pressure ratio, MFurimum- 
efficiency operation of the propeller at any flight velocity 
(fig. 2) occurs at the minimum-horsepower conditions at constant 
thrust. In the turbine, each maximum-efficiency condition at con- 
stant thermal dynamic input and altitude determines only one value 
of speed and horsepower. Similarly, for the propeller at constant 
flight velocity and altitude, maximum-efficiency operation is 
defined by a relation of speed and horsepower. 
however, for a turbine-propeller combination operating with a 
fixed speed ratio, that these relations of speed and horsepower 
will coincide for all operating conditions, Actually, for any 
value of transmitted horsepower, the speed for maximum-efficiency. 
operation w i l l  occur somewhere between that defined by only the 
turbine and the propeller. 
For both the turbine and the 
It is improbable, 
Determination of masrimum combined efficiency, - The maximum- 
combined-efficiency conditions can be obtained and most simply 
illustrated by representing both turbine and propeller character- 
istics on the same coordinate systems. The coordinates selected 
were blade speed and horsepower divided by altitude-density ratio. 
In making the representation, all the parameters were calculated 
as percentage of reference values and the reference values of tur- 
bine and propeller horsepower were made equal to each other. With 
this representation, the turbine characteristics at altitudes of 
sea level and 40,000 feet are shown in figure 3 and the propeller 
characteristics for flight velocities of 200, 400, and 600 miles 
per hour are shown in figure 4. 
NACA TN 1951 3 
In the independent turbine-propeller cornbination, the horse- 
power of the turbine equals the horsepower of the propeller and the 
ratio of blade speeds is constant. 
4 are presented on log-log plots, the characteristics resulting 
from coupling the turbine and the propeller could be obtained by 
superimposing the turbine characteristics on the propeller char- 
acteristics under the stated conditions. 
impossible, however, without a known speed ratio. The selection 
of a speed ratio is dependent on a number of factors andlimita- 
tions that may be characteristic of the installation. 
analysis, the general case will be assumed in which a gas gener- 
ator delivers gas at increasing pressure with increasing tempera- 
ture. A speed ratio will be selectedthat compromises between the 
condition of maximum efficiency at low pressure ratio and tempera- 
ture, and the condition of maximum efficiency at high pressure 
ratio and temperature for all the assumed flight conditions. 
Inasmch as both figures 3 and 
This superimposition is 
In this 
The >est approximate over-all efficiency is obtained with a 
ratio of percentage turbine-blade speed to percentage propeller- 
blade speed of 2.4. With this percentage speed ratio, the char- 
acteristics of the coupled turbine and propeller are shown in 
figure 5 for flight velocities of 200, 400, and 600 miles per 
hour at altitudes of sea level and 40,000 feet. 
Control relation for maximum efficiency. - Maximum-efficiency 
operating conditions can be obtained from figure 5 for each pPes- 
sure ratio and temperature under the various flight conditions 
investigated. Maximum-efficiency operation is defined by the 
points of tangency of the temperature and thrust curves. From 
inspection, these points were obtained and plotted in figure 6, 
which shows the change of propeller-blade speed with turbine- 
inlet temperature for each pressure ratio and flight condition. 
All parameters required to define maximum-efficiency operation 
are presented in figure 6. This figure indicates the parameters 
and the relation that may be incorporated into the design of a 
control for the turbine-propeller combination. 
RESULTS AND DISCUSSION 
For the propeller and turbine data used and the flight conditions 
investigated, figure 6 shows the effect of flight velocity and altitude 
on the relation of parameters for maximum-efficiency operation to be 
small. In reality, turbine operating conditions influence the maximum 
over-all efficiency t0.a greater extent than the propeller operating 
conditions. Flight velocity and altitude, which contribute to propeller 
performance, therefore had little effect on the curves of figure 6. 
4 MACA TN 1951 
The dependence on turbine characteristics may be attributed t o  the 
fact  that the angle of attack of the propeller may be adjustedby 
means of a pitch-angle change, whereas such an adjustment is impos- 
sible fo r  the turbine. As a result of the small effect of flight 
conditions on the maximurn-efficiency relation, a single curve was 
drawn through al l  the points a t  each pressure ratio. 
propeller uharacteristics with decreasing velocity indicates that 
such a generalization below a flight velocity of 200 miles per how 
may be impossible. 
The trend in  
A t  a flight velocity of 600 miles per hour, only the high- 
power conditions were considered. The propeller a t  low power was 
extremely inefficient and, inasmuch as maximm-eff'iciency operation 
f o r  l o w  power a t  600 miles per hour has l i t t l e  practical applica- 
tion, this power range was not investigated. 
The performance results of this analysis are applicable only t o  
the propeller and turbine data assumed. 
problem may indicate a greater effect of f l ight condition on the 
relation presented in  figure 6 .  
(fig. 2 )  represent the low-speed characteristics of a propeller and 
were used t o  i l lustrate the method of obtaining maximum-efficiency 
operating conditions. Other propeller and turbine data may lead t o  
a different relation of the parameters. 
is  applicable to  any combination of turbine and propeller 'data and 
the same parameters w i l l  determine the desired operating condition. 
The procedure used t o  obtain the operating conditions 'for 
highest over-all efficiency imolved the use of a method of match- 
ing turbines and propellers, In this analysis, a turbine and a 
propeller of known power ratings were assumed. From the blade- 
speed ratio that was obtained, a rotary speed ratio may be cal- 
culated dependent on the diameters of the turbine and the propeller. 
The characteristics of' a propeller of a specific diameter are shown 
i n  figure 2, 
by i ts  characteristics i n  figure 1. 
therefore dependent on turbine diameter. 
ra t io  is l e f t  t o  the designer providing that in  selecting a turbine 
diameter, hub-to-tip diameter ratio of the turbine remains constant 
and stress and other design limitations are not exceeded. 
method of mtching is also applicable when using propeller char- 
acteristics corrected for propeller diameter. 
diameter can remain unevaluated u n t i l  af'ter the components are 
matched, 
selecting a turbine diameter, a propeller diameter, and a gear 
ratio that w i l l  give performance most nearly approaching any 
specified performance e 
An extensive analysis of the 
The propeller characteristics assumed 
The general method, however, 
A specific turbine- diameter, however, is not implied 
The rotary speed rat io  is 
The selection of this 
The 
The propeller 
Th i s  method of matching therefore provides a mans of 
NACA mJ 1951 5 
I-' 
I-J 
@3 w 
Two general methods are possible for the control of turbine- 
propeller speed: 
gas-generator component or the control of the turbine-propeller 
and the generator may be interrelated. 
ent on the characteristics of the complete propulsion system. 
The speed may be controlled independently of the 
The method used is depend- 
With independent control of the turbine-propeller combination, 
the control is concerned only with the available power and flight 
conditions from which the desired operating condition is deter- 
mined and no knowledge of the operating condition of the generator 
component is assumed. 
for satisfactory control by this method. 
interaction between the turbine-propeller combination and the gas 
generator is either nonexistent or that the effects of the com- 
bination can be sufficiently damped to allow a condition of stable 
equilibrium to be obtained. With interaction, a change in turbine- 
propeller speed will possibly, for example, alter mass flow through 
the propulsion system and thereby change the temperature, the pres- 
sure, and the power delivered by the generator component. 
operating condition as determined from the available power will 
change and an additional change in speed is required again to 
obtain a desired operating condition. 
action could lead to completely unstable operation. A more complete 
analysis of interaction and its relation to the control is described 
in reference 1. 
One important condition must be met, however, 
It is necessary that 
The 
Such a condition of inter- 
A control in which the turbine-propeller combination and the 
generator component are interrelated would consist of a system in 
which the turbine-propeller operation is scheduled in accordance 
with the operating condition of the generator. If the effect of 
interaction cannot be sufficiently damped, this type of control 
is required. Such a method of control can be investigated only 
through an analysis -of the complete propulsion system. 
The relation of parameters for maximumefficiency shown in 
figure 6 readily lends itself to the independent control of a 
turbine-propeller combination. In these curves, the relation 
between blade speed and temperature is substantially linear and 
the slope of the curve is approximately constant for all pressure 
ratios, Independent control requires the condition of either no 
interaction or of sufficient damping of its effects where inter- 
action occurs. 
the systemto maintain critical flow in the turbine nozzle of the 
turbine-propeller combination under all operating conditions, 
turbine assumed in this analysis meets this requirement over a wide 
range of power conditions and it is assumed that a generator com- 
ponent delivering the desired available power can be developed. 
One method of obtaining no interaction is to design 
The 
6 NACA TN 1951 
From a measurement of turbine-inlet temperature and pressure 
ratio, the required propeller speed under any flight condition is 
determined as indicated in figure 6. One possible oontml B y s t e m  
based on this relation would consist of a mechanism for changing 
the propeller-blade angle, the mechanism being actuated by an 
adjustable-speed governor for maintaining the propeller speed at 
a value determined by measured values of turbine-inlet temperature 
and the pressure ratio. 
SUPIMAKP OF RESULTS 
From an investigation of an independent turbine-propeller com- 
bination, it was found that the conditions for maximum efficiency 
can be obtained by the use of a method of matching turbine and 
propeller characteristics, 
ciency operation can be satisfactorily represented by a relation of 
turbine-inlet temperature, pressure ratio, and propeller speed for 
each flight velocity and altitude. The described reration is adapt- 
able to independent control of turbine-propeller speed when inter- 
action between the turbine-propeller combination and the gas generator 
is either nonexistent or where its effects can be sufficiently damped, 
By the use of this method, maxirmun effi- 
Lewis Flight Propulsion Laboratory, 
IVational Advisow Committee for Aeronautics, 
Cleveland, Ohio, Msrch 18, 1949. 
NACA Tm 1951 
APPENDIX - SYMBOLS 
7 
The following symbols are used in the figures referred to in 
the analysis: 
propeller thrust, lb 
horsepower 
ratio of turbine-inlet pressure to turbine-outlet pressure 
turbine-inlet temperature, % 
flight velocity, ft/sec 
propeller-blade tip speed, ft/sec 
turbine-blade tip speed, ft/sec 
gas flow, lb/sec 
propeller-blade angle, deg 
ratio of turbine-inlet pressure to sea-level ambient pressure 
(total to static) 
ratio of turbine-inlet temperature to sea-level anibient 
temperature 
ratio of altitude density to sea-level density 
1. Boksenbom, Aaron S., and Hood, Richard: General Algebraic 
Method Applied to Control Analysis of Complex Engine Types. 
NACA TN 1908, 1949. 
NACA T N  1951 
NACA TN 1951 9 
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0 0  0 
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0 0  I n *  
IO NACA TN 1951 
. lool=l= 90 
60 7 0 ~  
3 0 ~  
i n l e t  
;eyperature ,  
(percent   turbine^^ 1 
- loo t  
~ 
0 50 60 
Turbine-blade speed, v t ,  percent  
90 
Figure 3. - Turbine c h a r a c t e r i s t i c s  o f  a l t i t u d e s  o f  sea 
level and 40,000 f e e t  w i t h  expansion t o  atmospheric 
pre  s s u r e  
N A C A  T N  1951 
E 
P r o p e l l e r  -blade speed, vp, per  cen t  
( a )  F l i g h t  v e l o c i t y ,  200 miles  pe r  hour. 
Figure 4 .  - P r o p e l l e r  c h a r a c t e r i s t i c s  a t  cons t an t  f l i g h t  
v e l o c i t y  . 
12 NACA TN 1951 
lllii 50 60 '
Prope l l e r -b l ade  speed, vp, pe rcen t  
(b) F l i g h t  v e l o c i t y ,  400 miles per hour.  
-I 
Figure 4. - Continued. P r o p e l l e r  c h a r a c t e r i s t i c s  a t  cons t an t  f l i g h t  v e l o c i t y .  
NACA TN 1951 13 
30 
20 
30 40 50 
P r o p e l l e r  -blade speed, vp, pe rcen t  
( e )  F l i g h t  v e l o c i t y ,  600 m i l e s  per  hour. 
I 
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i 
f 
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Figure 4.  - Concluded. P r o p e l l e r  c h a r a c t e r i s t i c s  a t  cons t an t  flight ve loc icy .  
14 NACA TN 1951 
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Propel ler-blade speed, vp, percent  
I I I I I 1 1 1  
30 40 50 60 70 80 90 100 
Turbine-blade speed, vt ,  percent  
( a )  Al t i t ude ,  sea l e v e l ;  f l igh t  ve loc i ty ,  
200 mi les  per  hour. 
F igure  5. - Performance c h a r a c t e r i s t i c s  of independent 
tu rb ine-propel le r  combinat ion. 
N A C A  TN 1951 15 
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Propeller-blade speed, vp, percent  
I l l  
30 40 50 60 70 80 90 100 
Turbine-blade speed, vt, percent  
(b) Alt i tude ,  sea l e v e l ;  f l i g h t  v e l o c i t y ,  400 miles  per  hour. 
Figure 5. - Continued. Performance c h a r a c t e r i s t i c s  of independent tu rb ine-  
pr  ope l l e r  combination. 
16 NACA TN 195'1 
100 
90 
80 
70 
60 
50 
40 
I 
_ _  - - - - si 
- c -- 
,_----- 
-e-. 
_/-- * - 
1 I I I I I 
10 20 30 40 50 60 70 
I I I I I I I I  
Propel ler-blade speed, vp, percent  
30 40 50 60 70 80 90 100 
Turbine-blade speed, v t ,  percent  
( c )  A l t i t ude ,  sea l e v e l ;  f l i g h t  ve loc i ty ,  600 m i l e s  per  hour. 
Figure 5. - Continued. Performance c h a r a c t e r i s t i c s  of independent tu rb ine-  
p rope l l e r  comb i n a t  ion. 
NACA TN 1951 17 
Propel ler-blade speed, vp, percent  
I I I I I 1 I 1  
30 40 50 60 70 80 90 100 
Turbine -blade speed, vt , percent  
( d )  A l t i t u d e ,  40,000 f e e t :  f l i g h t  v e l o c i t y ,  
Figure 5. - Continued. Performance c h a r a c t e r i s t i c s  of  
200 mi les  per hour. 
independent tu rb ine  -pro pe l l e  r combination. 
18 NACA TN 1951 
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_ - - -  - -  
I 
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e -  - - - -  
c -  _ -  - -  
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Propel ler-blade speed, vp, percent  
30 40 50 60 70 80 90 100 
Turbine-blade speed, vt ,  percent  
I I I I I I l l  
( e )  Al t i tude ,  40,000 f e e t ;  f l i g h t  v e l o c i t y ,  400 miles  per hour. 
Figure 5. - Continued. Performance c h a r a c t e r i s t i c s  of independent tu rb ine-  
prope 1 l e r  comb f n8 t ion. 
NACA TN 1951 19 
I I I I I I 1 
10 20 30 40 50 60 70 80 
Propel ler-blade speed, vp, percent  
I I I I I 1 1 1  
30 40 50 60 70 80 90 100 
Turbine-blade speed, v t ,  percent  
(f) Al t i tude ,  40,000 f e e t ;  f l igh t  ve loc i ty ,  600 mi l e s  per  hour. 
Figure 5. - Concluded. Performance c h a r a c t e r i s t i c s  of independent tu rb ine-  
pro pe l l e r  comb ina t ion. 
20 
I= 
90 
~ 100 
Turbine- in le t  temperature,  T, percent  
Figure 6. - Control  r e l a t i o n  f o r  maximum ope ra t ing  e f f i c i e n c y  
of independent t u r b i n e  -propel le r  combina t ion. 
NACA-Langley - 9-29-49 - loo0 


Method of determining conditions of maximum efficiency of an independent turbine-propeller combination

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