This page is posted here since on some www. pages were
misleading information for Props and Fans - it is a safety issue and
please don't use the next best fan / prop on any engine without
being familiar with your resulting Tip speed.
I want to mention as well that "Gougeon Brothers" with the help
of NASA have done multiple studies on wood composite for wind turbines
! If a composite part is correct build it has better physical
properties than most plastics / metal's.
As well as the physical properties of plastics is changing with temp. (
+ / - = more flex / brittle ) and if not correct protected
against UV will lose their strength. There is a lot more in a prop than
just plain plastic is better than wood !!!!!
The following part is from "Construction Requirements
for Cruising Hovercraft" of the HCGB
Please use the info for your safety and perhaps get
their book!
A number of proprietary axial and centrifugal fans are
available and suitable for use on light Hovercraft. The use of these
fans is to be limited to a combination of rotational speed and diameter
giving blade tip speed of less than that shown in the Table
below.
| Type |
Maximum Tip Speed
m/sec |
Maximum Tip Speed
ft/sec |
| Multiwing Type 2,3,6 |
137
|
450
|
| London Fan Co ("Breeza") small hub |
137
|
450
|
| Turflo ("Trfoil") |
137
|
450
|
| Multiwing Type Z |
168
|
550
|
| Multiwing Type 2,3 (Glass filled Nylon blade) |
168 |
550
|
| Centrifugal Fans |
185
|
280
|
Tip speeds in excess of 137 m/sec are likely to produce
noise levels in excess of 78 dBA at 15m distance. A maximum design tip
speed of 122 m/sec is recommended to be used for this reason where
practical. On the next Table you find the fan speed in RPM for the
limiting tip speeds - 122 m/sec is recommended - 137 m/sec design
maximum - 168 m/sec is the absolute limit for Multiwing Z and Nylon
blade fans.
| Tip Speed |
122m/sec |
137m/sec |
168m/sec |
| Diameter (m) |
RPM |
RPM |
RPM |
| 0.50 |
4660 |
5233 |
6417 |
| 0.60 |
3833 |
4360 |
5348 |
| 0.65 |
3585 |
4025 |
4936 |
| 0.70 |
3329 |
3738 |
4584 |
| 0.75 |
3107 |
3489 |
4278 |
| 0.80 |
2913 |
3271 |
4011 |
| 0.85 |
2741 |
3078 |
3775 |
| 0.90 |
2589 |
2907 |
356 |
| 0.95 |
2453 |
2754 |
3377 |
| 1.00 |
2330 |
2616 |
3208 |
| 1.10 |
2118 |
2379 |
2917 |
| 1.20 |
1942 |
2180 |
2674 |
| 1.30 |
1792 |
2013 |
2468 |
| 1.40 |
1664 |
1869 |
2292 |
| 1.50 |
1553 |
1744 |
2139 |
|
