New lift fan!

Today was exciting. I swapped out the lift fan from the Universal Hovercraft kit with a Hascon Wing Fan cut to size 24.5" that I ordered from Slipstream Hover. The size was picked to give 1/4" of clearance on on the 25" interior space I measured and talked with the representative about optimal size to select.

Unpacking the new lift fan

The new fan is a 5 bladed fan. With a cast hub with mounting points for each blade, and a machined collet flange. Each blade is molded plastic cut to length.

I also have a new twist throttle control from them to try out.

The two propellers. Old foreground new background.

When I removed the old fan, it just slid off once I released the shaft end bolt. Clearly the collet was not clamping correctly. 

The new lift fan fit check on the engine shaft

Installing the fan was easy. The collet was nicely layed out that I could easily put the bolts in from the bottom. So I could use a ratcheting socket and tighten it easily and evenly. The shaft is a little worn these days and it tightened further than optimal, but the collet has a full cut instead of just the lower part of the flange which gives it more travel. And after testing the collet appears to be holding successfully. I put the end nut onto the shaft as well which will keep the propeller from sliding off the end of the shaft, but it does not have a plate that prevents the fan from riding up the shaft.


The hub is much more compact and the overall blade is a little bit lighter. But the most important thing is that the blade is noteably more balanced. Looking down when spinning the old fan by hand, the plywood circle could be seen oscillating with at least a 1/4" asymmetry. Which meant that it vibrated the whole system quite a bit.

Here's my first test of the new fan. I spun it up to idle speeds briefly and then inspected it before trying to throttle it up.


A few interesting notes are that with the new fan, it actually was effectively hovering even at idle.

Here's me trying out hovering and moving my weight around on top of the hovercraft with the new fan throttled up.


For reference I filmed a similar segment earlier with the old fan. You can see more vibrations, as well as notice that the vehicle does not lift off even at idle. I was previously worried about the vibrations and was considering more reinforcements for the lift engine mount but I don't think that's necessary anymore.





Noise level: 

I thought that the new fan might be quieter, but apparently not. I think that most of the noise is actually from the engine. I tested both the new and old fan, and idle and full throttle. And I found that it was about the same.

95 db at idle lift only UH fan

105 db at full hover throttle, lift only UH fan.

Here's my testing again with the Hascon fan. My phone was giving me trouble turning on the camera. But the readings were not significantly different than the priors so I didn't bother figuring out why the camera wasn't starting properly. You can see that these measurements were taken between 1 and 2 meters away from the noise.


So although I probably don't need to reinforce the engine mount. A housing to contain the engine noise and protect the fan, as well as provide ram air pressure.


One other note is that the new hub is notably smaller which means that the engine fan is now actually about 2" higher. I was previously considering making the baffle take up more of the lift fan area, however despite the larger gap between the diverter and the fan blades, we're still getting much better performance. Until it's the limiting factor I'll probably drop the priority of refactoring that for now.

One new piece of technology I've deployed now is some tamper marker paint to see if things are vibrating loose.

Tamper paint as first applied

Tamper paint after being run before fully dried

 Above you can see that I didn't quite wait long enough for it to dry. But it's showing that the nuts are not moving.

Additional dot on the shaft to detect upward movement.

As mentioned above the end shaft bolt only keeps the hub from coming off the end of the shaft, so I added this dot of marker paint to show if the hub rides up the shaft at any point.