View Full Version : Number of Fan Blades in 900mm Integrated Design

CrazyKiwi - n/a
16-Feb-09, 05:02 AM
Hi All

Can anybody offer a little help in reccomending the number of fan blades in an integrated design craft with a 900mm duct.

I plan the craft to be 3m by 1.8m approx and of fiberglass construction.

Having made much consideration I have every intention to configure my two robin ec25 engines as a single inline twin (making life difficult maybe but I look forward to the challenge)

The design will be along the lines of the eagle1 and I hope to have a craft with an empty weight of 160kg or under finnished.

Tuned properly I expect my twin ec25 design to achieve 50hp.

Due to availability of fans in New Zealand and cost I plan to use a multiwing 4z fan (900mm as above)

Would people reccomend 5 blade, 9 blade or 6/12 blade fan configuration for such a craft?



Vortex - n/a
16-Feb-09, 10:07 AM
Hi there,

Depends on what you intend to use the craft for...what type of skirt you are going to use......and what type of terrain you will operate the craft over.

If it is perfectly flat and smooth surface you might get away with a 5 bladed fan but...experience has shown that lift and lift pressure is very marginal in 900 duct

You could use 9/9 if you are expecting very rough operating conditions you will get lots of lift flow and pressure however thrust will be reduced.

My favoured option is 6/12, good lift, good thrust. If you do decide you want more lift the going to 8 blades is a very good option, 2nd blade of the pair slightly steeper angle than the first (3-5 deg)

Finally, the 5Z blade is a much better blade and i would use that in preverence to the 4Z


(on the North Sea, still travelling to Denmark....thick fog!!)

tonybroad - n/a
16-Feb-09, 11:17 AM
hi there

i currently use 5/5 in a 920 duct with 50Hp but this is for racing and below 75% throttle lift will suffer

i used to use 6/9 in previous craft and for heavier craft and for my daugters junior craft which ran on reduced power for two years

i've tried 9/9 as well and as keith says stacks of lift but thrust suffers

try 6/9 if that's not enough stick 3 more blades in

i also tried 3/9 - it went like stink flat out and picked up like a rocket but as soon as you backed off the throttle it was dragging it's ar*e on the floor

the 5Z blades are bigger/stiffer/better in my opinion

Sean Atterbury - n/a
16-Feb-09, 02:42 PM
I used 6 in the beginning and later changed to 9. With 9 there was less plough in but also less speed, guess its up to you.

CrazyKiwi - n/a
17-Feb-09, 03:58 AM
Thanks all

I may well go for the 5Z blades instead of the 4Z (Do 4Z even go up to 900?)

I am curious about the 6/9 configuration; Is that 2 blades together then miss a space?

How does 6/9 perform compared to 6/12?

I guess 6/9 is like a 3 blade with a super wide chord blade?

Thanks again


CrazyKiwi - n/a
17-Feb-09, 04:03 AM

Regarding skirt type I plan to use a finger type skirt.

The Craft will hopefully be a high performance cruiser, (If only there were enough hovercraft here to race)



tonybroad - n/a
17-Feb-09, 01:49 PM
i've never compared 6/12 to 6/9 and yes 6/9 is a pair then miss one i doubt there's much in them alhtough the passign frequency will be different so in theory a 6-12 should give you better pressure the only disadvantage i can see is the size of a 12 hub which is bigger then a 9 so less bade for your duct so to speak

keep us all poseted we all like a new build