View Full Version : Propeller vs fan

Arny - n/a
21-Sep-07, 10:39 PM
I know next to nothing about hovercraft but being a pilot of some 30 years a know a little about propellers and I am surprised that the main method of propulsion on light hovercraft is the ducted fan.

Why are there not more propeller driven craft?

hectorshouse46 - n/a
22-Sep-07, 06:23 AM
May be it's cultural. I have a prop driven craft. Our river Tay outing had three props and one duct craft. I think both are good. Trevors Osprey (duct)is awsome...although he keeps blowing my seats away when we're setting up to leave http://hovercraft.org.uk/images/icons/smiley_icons/icon_surprised.gif) My father was an aircraft engineer boefore retiring. I spent most of my childhod around small aircraft and props (not too close obviously). Visited Buxford recently, prop technology was so advanced on those later WW2 aircraft. Anyway back to the thread.

I think there may be more props appearing on hovercraft over time. My three bladed Ultraprop has proved itself to me in more ways than one. I destroyed my new, that's NEW power washer lance by inadvertently (spelling) sticking it in to the moving prop when washing of the dreaded sea salt. It diced the lance like a carrot. 90% of the bits rattled around inside the cage. Amazingly whilst I wouldn't use the blades again the damage to them was so slight that I'm beginning to wonder what they're made of. Mental note 1) remember your new power washer lance is longer than the old one. 2)Don't talk yo your sister and brother in law whilst washing the back end of your hovercraft....there that should save me some cash later !!!!! My point is some folks in the UK have have concerns over prop gaurding and containment. But has been said before these are aviation quality props running well below max rpm.

I know that should more props appear the shared knowledge will spread resulting in more efficient, quiet and clever set ups.

Best Regards

Steve H

GavinParson - n/a
22-Sep-07, 07:11 AM
There are three main reasons.

In the formative years of amateur hovercraft building, small to medium size propellors were hard to find and reasonably expensive. Plastic bladed air conditioning fans were cheap and the blades easily replaceable so they became the first choice for light hovercraft.

Secondly, because props are usually bigger than fans the thrustline is higher and can add to plough-in problems in smaller craft.

Thirdly, a craft with a big prop and cage won't fit into a standard UK garage. Many craft owners need to stow their craft in a garage so a fan driven craft becomes the only option.

Nowadays since the growth of the ultralight/ microlight industry, a wider range of props has become available with many such as the Ivoprop or Ultraprop being used for hovercraft.

In the US props have always been more prevalent. Builders usually had more space to build and store their craft and there is more of a culture of carving your own prop or getting one from airboat builders or from guys like Bob Windt.

Over the years there have been conflicting claims over which is more efficient/ quieter. For my money, a prop is better for a large crusing craft. Keith Oakleys tests seem to suggest that props are not necessarily quieter than fans (in his experience anyway) but the sound is of a set of frequencies more acceptable than a screaming fan. I'm glad to see that the research continues and craft may become even quieter.