UltraProps.com

Suggested Propeller and Engine Combinations for Original Ultra-Prop

(Other prop/engine combinations not specifically listed may be extrapolated from this proven list)

Generic Engine HP Reduction Prop Diameter* Pitch**
  R503 DC 52 2.58:1 104 59" 15 or 16
  R503 SC 48 2.58:1 104 59" 14 or 15
(best) R447 40 2.58:1 104 59" 13 or 14
  R477 40 2.58:1 104 59" 16
(best) R377 35 2.58:1 103 59" 13 or 14
  R377 35 2.58:1 104 59" 11
  R277 28 2.58:1 103 59" 10 or 11


Airboats Engine HP Reduction Prop Diameter Pitch
  Honda/B&S 13 direct drive 103 36" 13
  Honda/B&S 20 direct drive 103 42" 15 or 16
  Honda/B&S 20 direct drive 104 42" 14


Generic Engine HP Reduction*** Prop Diameter Pitch
  Hirth F33 28 2.5:1 103 59" 10 or 11
  Hirth F33 28 2.5:1 103 52" 17 or 18
  Hirth F33 28 2.5:1 102 59" 13 or 14
  Hirth F33 28 2.5:1 102 55" 17 or 18
  MZ 34 27-32 2.34:1 103 57" 10 or 11
  MZ 34 27-32 2.34:1 103 52" 15 or 16
  MZ 34 27-32 2.34:1 103 49" 17 or 18
  MZ 34 27-32 2.34:1 102 59" 10 or 11
  MZ 34 27-32 2.34:1 102 57" 13 or 14
  MZ 34 27-32 2.34:1 102 52" 17 or 18

*Increase pitch by one degree for every one inch decrease in diameter.
**A change in pitch of one degree is worth about 200-300 change in engine RPM. Increasing pitch will decrease RPM. Decreasing pitch will increase RPM.
***Other lower reduction ratios are available
.

NOTE:  If a loud "buzzing" noise is noted at high RPM with high-pitch blocks, it is because the tips are stalling. Do not operate the propeller in this range. Either a lower pitch or smaller dia. prop must be used.

Tests have shown that at and below 52-in. dia., no blade tip stalling will occur with 18-degree pitch blocks below the rated 3100 RPM.

Between 52" dia. and the full 59" dia., the approximate tip stalling RPM or onset of buzzing is shown in the table below for various pitches.

Diameter

18 deg pitch

16 deg pitch

14 deg pitch

59"

1900 RPM 2400 RPM 2700 RPM

58"

2050 2450 2700

57"

2100 2700 3100

56"

2250 3100 ---

55"

2400 --- ---

54"

2550 --- ---

53"

2800 --- ---

52"

3100 --- ---


This information is provided courtesy of Competition Aircraft Inc.
Copyright 2017

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