Speed 400 Bench-Tests

from

Peter Harries

  

To Silentflight index

 

Electric Power

Speed 400 motors have become extremely popular as a source of power in electric models. For small, very fast models (e.g. pylon racers) these motors are used without gearboxes and Table 1 contains relevant performance data for 2 readily available folding prop systems.

Table 2 provides information for 2.33:1 geared systems such as those available from Graupner, Aeronaut and MFA. Similar data can be made available for alternative geared 400 systems and for certain Speed 500 and 600 systems.

 

Table 1: Current/thrust/efflux data for direct drive 400 6v motors with different props.

 Battery 7 cells  Prop  Current (amps)  Thrust (oz)  RPM  Calc. Efflux (mph)
 AA/SCR  G 6x3 F  12.0  7.0  12,000  34
   R 6x3.5 F  10.5  8.5  13,800  45
 AA/AE  G 6x3 F  10.0  5.0  10,800  31
   R 6x3.5 F   9.5  6.5  12,400  41

G= Graupner: R=Robbe: F = folding

 

Table 2: Current/thrust/efflux data for 2.33:1 geared 400 6v motors with different props and battery types.

 Battery 7 cells  Prop  Current (amps)  Thrust (oz.)  RPM  Calc. Efflux (mph)
 AR/SCR  A 9.5x5 F  9.0  13.0 6,800 32
   A 9x6.5 F 11.0 10.0 6,000 37
   A 10x7 F 12.0 13.5 5,700 38
   A 10.5x6 F 11.0 14.5 5,300 30
   G 11x8 CPF 12.5 16.0 5,000 38
   G 8x4 SP 6.6 10.0 8,300 31
   G 9x5 SP 8.0 12.0 7,200 34
           
 AA/AE  A 9.5x5 F 8.0 11.5  6,500  31
   A 9x6.5 F 10.0 8.0 5,600 35
   A 10x7 F 10.5 11.5 5,200 34
   A 10.5 F 10.0 12.0 4,900 28
   G 11x8 CPF 10.5 13.5 4,600 35
   G 8x4 SP 6.0 9.0 7,800 30
   G 9x5 SP 7.0 11.0 6,800 32

A = Aeronaut, G = Graupner, CP = Camprop, SP = Slimprop, F = folding.

 

Typical weights for 7 cell battery packs (grams)

 AR/SCR  Weight  AA/AE  Weight
 500 AR  133  600 AA  154
 700 AR  189  700 AA  156
 800 AR  224  600 AE  126
 1700 SCR  392 1400AE  210

 

In order to select a power train for a given model aircraft from the data in tables 1 and 2, the following information is of relevance.

1. Static Thrust

The ratio of static thrust to the all up weight (auw) of the aircraft will have a significant bearing on performance.

 Static thrust =  25% of auw -  hand launch, approx. 15 degree climb
   33% -  rog from tarmac, approx. 30 degree climb from hand
   50% -  instant take off, approx. 45 degree climb from hand
   100% -

 vertical climb, no wings required!

 

2. Calculated efflux velocity

The calculated efflux velocity (mph) = rpm x pitch (in inches), divided by 1,056

For normal flight characteristics, select a power train with efflux velocity approx.. 3 fold the stall speed of the aircraft where the stall speed in mph is estimated as 4 x the square root of the wing loading in oz./sq.ft. For example, a glider with a wing loading of 9 oz/sq.ft. will have a stall speed of approx.. 12 mph and a power train with a calculated efflux of approx.. 36 mph.

3. Motor current

In flight, the motor current will reduce to approx.. 75% of the static value. For Speed 400 motors, the maximum permitted continuous current is 9 amps i.e. 12 amps static.

Peter Harries.

 

(Editor's note: The above information is potentially very valuable to electric enthusiasts and is not readily available elsewhere. All results have been obtained by actual bench tests. I am hoping to persuade Peter to provide further data for other motors/gearboxes in a future edition of the newsletter.)

To Silentflight index