View Full Version : Blade angle after a long time away...

erbus - n/a
12-Jul-08, 08:24 PM
....well finally back after about a year & half.

Had major problems getting a new manifold + exhaust made (company went bust and had real problems getting my template back).

I'm just rebuilding the craft again but this time i've increased the blade count to 9 instead of the original 6.

its about a 950mm duct driven by a cuyuna 440 and the question is:

whats a good ballpark figure for the blade angle?

As usual any advice most welcome, thanks

hover t - n/a
14-Jul-08, 06:18 PM
Hi Dave

I would say you will have to back the blades of a bit from the setting you were using last time.You will probably find the hover will lift better with 9 blades fitted but the top speed will be down a tad as the blades will have to run at a lesser pitch because of the fan load on engine.


erbus - n/a
15-Jul-08, 04:30 PM
thanks trev,

i cannot remember the old setting (should have noted on strip down!)as it took me long enough to get there...hence the reason for asking for a ballpark figure.

I thought it would be a lesser angle but was hoping for a rough start point so i can match the blades to power output.

hoping to get the craft back on the water in a couple of weeks time.

Have now repaired the lower hull with a new layer of fibreglass (more wieght) and beefed up the tow/tie point which were very flimsy before, also got a lovely home brewed s/s silencer and manifold (more wieght) at long last...

hover t - n/a
15-Jul-08, 04:58 PM
Dave I would try 40 deg to start off with thats 31mm from the center of the hub to the bottom leading edge of the blade and see how it goes. Its just a case of trial and error until you get it set up properly,I use a joiners set square to set up my fan which has 16 blades, it makes things easier and I know that all blades are set to the same pitch.


Paul Fitz - n/a
15-Jul-08, 06:24 PM
What is the engine power and fan speed, or alternatively, the ratio used and the speed at which maximum engine power is produced?

erbus - n/a
17-Jul-08, 09:32 PM

will give the 40 deg a try and start from there - many thanks


the cuyuna 440 produces about 48 bhp at about 7000rpm if i remember as to fan speed i have never been able to ident the gearbox so ratio is unknown....

thanks for all the help, hopefully after the usual trial and error I'll get there..



Paul Fitz - n/a
18-Jul-08, 07:40 PM
40 degrees will be far too much pitch.

Assuming 9 x 5Z blades fitted in a 9 blade hub.

For 45-46 Hp fan absorption.

fan rpm - degrees

2600 - 37.5

2800 - 32

3000 - 31.5

3200 - 29

Ballpark figures http://hovercraft.org.uk/images/icons/smiley_icons/icon_surprised.gif)

As 6 blades were fitted before, I suggest you start at 30 degrees.

see PMed file for adjustment dimensions.



erbus - n/a
24-Sep-08, 09:54 PM
Thanks again for all the info, 40 was too much of a load 37 seems a lot better before i got fed up of all the hub bolts numerous times today....

hoping to get the old beast out this weekend after almost 18 months dry.

...will try and get some photos as it would be nice to get some more history on it (ghl dragonfly circa 1980)