THE POWER FACTOR AND L/D RATIO
For a soaring glider or duration model when gliding the total power factor, Cl1 5/Cp should be as high as possible. The most suitable wing profile is that with a high section power factor, Cl’ VQj. This may be calculated from the wind tunnel results.
The table opposite indicates the method. A pocket calculator should be used to speed the work. The section 1/d ratio is also worked out in the tables. This gives a general idea of the profile’s efficiency, while the minimum drag coefficient indicates the potential of the aerofoil for high speed flight A low «у at low q is essential for a speed model wing.
THE BEST ANGLE OF CLIMB
It is assumed here that a duration power model has enough power available to achieve any desired angle of climb. The problem is to know which angle of climb, at maximum power, will give the best rate of ascent
A COMPARISON OF TWO AEROFOILS AT Re 100.000
1 
2 
3 
4 
5 
6 
GOTTINGEN 801 
Re 100000 (KRAEMER 

C1 
cd 
‘Vcj 
q3 
AT 
V7/cd 
TEST) l 
FROM 
FROM 
Column (1) 
(Cold))3 
JCo (4) 
Col (5) 

TEST 
TEST 
Column (2) 
Col (2) 

0.4 
0.0289 
13.84 
0.064 
0.253 
8.754 

0.5 
0.0241 
20.75 
0.125 
0.3535 
14.668 

0.6 
10.02181 
27.75 
0.216 
0.4648 
21.32 
Min Cd at Cj0.6 
0.7 
0.0220 
31.82 
0.343 
0.5857 
26.53 

0.8 
0.0240 
33.33 
0.512 
0.7156 
29.82 

0.9 
0.0260 
34.62 
0.729 
0.854 
32.85 

1.0 
0.0300 
33.33 
1.000 
1.000 
33.33 

1.1 
0.0317 
34.70 
1.331 
1.154 
36.40 

1.2 
0.034 
1 35.291 
1.728 
1.315 
38.68 
Max 1/d at q 1.2 
1.3 
0.0378 
34.39 
2.197 
1.482 
ПЙШ] 
Max power factor, c j 1.3 
1.4 
0.0518 
27.03 
2.744 
1.656 
31.20 

0.4 
0.0222 
18.02 
0.064 
0.253 
11.396 
107,000 G. Muessman Test 
0.5 
ІЙ.0221І 
22.62 
0.125 
0.3535 
15.995 
Min. C^atcj 0.5 
0.6 
0.0222 
27.03 
0.216 
0.4648 
20.936 

0.7 
0.0223 
31.39 
0.343 
0.5857 
26.26 

0.8 
0.0224 
35.71 
0.512 
0.7156 
31.95 

0.9 
0.0235 
138.301 
0.129 
0.854 
36.34 
Max l/d at cj 0.9 
1.0 
0.0265 
37.74 
1.000 
1.000 
Г37Л7І 
Max 
1.135 
0.0400 
28.37 
1.462 
1.209 
30.23 
Starting from level flight trim, the power is increased step by step. In level flight, as already seen:
Lift (Level flight) = Lo = W = *pV*SCL This may be rearranged to give an equation for speed:
V2 (level flight) = V02 = W/V4pSCL
In the climb Lift (Climb) = Lc = W Cos в Also, if Vc = speed along the inclined flight path then
Lc = 14pVc2SCl =W Cos в
Rearranging this in turn to obtain equation for Vc2, Vc2 = W Cos 0/WpSCL – From the foregoing:
Vc2 = (WCos flj ^ / W = WCos в ISpSCL
V02 WpSCL/ : [^pSCl/ WpSCL W
which cancels down to:
rrr = Cos в and soгг— = y/CosB
*0* ’’O
(This is on the assumption that Cl remains unchanged, i. e. the model is not retrimmed.) In the small diagram Figure A3, Vc, the flight speed along the inclined path, is

Fig. АЗ The best angle of climb for a highpowered model
represented by a line at angle 9 to the horizontal. The length of this line is proportional to Vc = V0 x VCos 9
The rate of climb on this diagram is proportional to the length of the line marked C. From basic trigonometry,
^= Sin 9 or C = Vc Sin 9 *c
And therefore:
C = V0 x v/Cos 9 x Sin 9
For a particular model and trim condition, V0 is constant The factor /Cos 9 x Sin 9 may easily be worked out with the aid of standard tables of Sine and Cosine, for any value of climb angle, 9. The result may be plotted against 9, as has been done in Figure 4.6. The maximum rate of climb is then found to occur when the graphed curved reaches its maximum close to 55 degrees. The result is approximate. Departures of four or five degrees either way make little difference. The practical trimming procedure is thus to aim at achieving the desired climb angle by adjustments of trim, wing camber, flaps etc. then to ensure that the engine propeller combination yields maximum thrust at that angle.
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