Project #5 from EmptyNester - Thrust Duct Support for Hovercraft

The hovercraft calls for a support at 45 degree angles from the platform that the prop mounts to, to the top of the lift duct. The instructions calls for a number of pieces of aluminum bent to appropriate angles to anchor 1/4" plywood to the platform. The edge on the duct would be fiberglassed as the current horizontal support it.

I didn't have the aluminum and it's rather expensive. So I made a support out of 1 1/2" x 3/8" angle and 1/2" conduit.

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I think these serve two purposes. The first is to keep the top of the duct from pulling back on acceleration. The other is to stabilize the duct on turns. There are 4 rudders and a trim wing and the tops connect on the top of the duct. If the top of the duct isn't secured, I think it can deform and hit the prop.

I took the prop off so that when I tacked the conduit - I wouldn't damage it. (I did cover everything, but that we a little big to cover.

how strong is the bottom attachment point of that shroud to the deck? I'd think there would be some pretty strong lateral G forces on something like this. that brace will work great for keeping the fan from leaning back, but because it's attached to one point, it can still pivot around a line drawn between where the brace connects to the deck and where the bottom of the shroud connects to the duct.

The duct itself doesn't have any force on it from the propulsion. The prop is attached to the small platform and that attaches to the deck. (I had an earlier project that braces it to the back of the cockpit. The "anti-decapitation" bars.)

The only two forces on the duct are drag from wind resistance due to forward motion and side to side torque from the rudders.

The duct itself was pretty flexible before it was mounted. About 2 or 3 feet of the bottom of the duct are foamed/glued to the deck and then it's also fiberglassed. The duct still had significant side to side flexibility until the 1/4" plywood was mounted from the platform to the sides of the duct.

The very top still has a little flex and that's what the bars will address. I think it's more of a dimensional stability issue.

Overall, I've been impressed with the strength of the epoxy and fiberglass. But, I can't help but wonder if it won't all fly apart around me first time I get it going real good :)

I take it those pillow block bearings and shaft hold the prop. What absorbs the thrust?

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Originally Posted by parkour

I take it those pillow block bearings and shaft hold the prop. What absorbs the thrust?

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The platform the pillow blocks are on is epoxied and fiberglassed to the deck. It really doesn't seem like it would be strong enough, but these designs have been around forever and are apparently pretty robust.

I guess that one consideration is that when you are on a cushion of air, you have very little friction so that may reduce the chance of failure. They do call for 1/8" aluminium tube to stabilze the platform against the back of the cockpit. That didn't seem like enough for my comfort - so my other project was making supports out of 1 1/2" angle with 1/2" conduit. (Link: http://www.everlastgenerators.com/fo...om-EmptyNester)

The first picture shows it sitting in place before it was attached. The second shows it attached. The third thumbnail was an accident and I couldn't figure out how to delete it from the post.
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Ah, cool. Sure does look like a nice build.