With the new propeller I also purchased a new throttle linkage. So I needed to find the best way to hook it up. So to get the best look at the possible throttle mechanisms I ended up tearing down the engine. Now you can see the governor and throttle linkages clearly.
The twist throttle linkage
Top view of the engine with gas tank and air filter removed
The air filters for reference
The engine with the gas tank and air filter removed, and screws on the ground
The end results of my research was to identify that the best place to attach the throttle is actually on the exterior handle.
My final solution
The bare end
A little bit of electrical tape for grip
Three zip ties to hold axially
Another view of the zip ties, also showing the zip tie with the screw attachment point.
After using pliers to tighten the zip ties
The zip ties trimmed
The zip tie mount installed on the front of the engine
Demonstrating the mechanism
With the friction released the external handle does not hold position. And removing my other throttle mechanism we're now able to control the throttle with a twist of the wrist.
It's a little bit more sensitive than I'd like, but being able to change throttle quickly will be nice. And I suspect that most control will be bang bang style anyway. Right now there's not much spring return, but I believe that once the governor spins up the return spring will be tighter and pull it back. Since at stop the governor is leaving the throttle wide open the throttle linkage only tensions at the very end.
Next up I need to get a handle bar to mount the throttle onto. I'm not sure if it should be on the tiller stick or not. A single joystick control would be nice, but possibly confusing/ergonomically challenging if it requires continuous torque.
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.
The hovercraft is surprisingly dirty after just a few minutes flying around a "clear" parking lot.
Dirt collected under the thrust engine
More collected on the side
Another view of the dirt at the rear
There's even dirt in the center of the fan. Clearly there's a lack of airflow there...
After cleaning off as much dirt as possible I set to work to improve the hover performance.
I took two approaches. First I started by clearing out more of the grill wires. It made a large difference for the thrust fan. And since the lift fan is actually well protected, I cleared out 3 of 4 on the bottom, and 2 of 3 on the top except for the outer ring where I did 3 in a row where I expect the highest speed.
In addition there was a gap between my metal diverter plate and the board that is attached to the skirt attachment leaving about a 3/4" gap across the whole width. And with the wires removed I could now relatively stretch some Duct tape across the gap. I think this might be my first correct use of Duct tape ever!!
Sealing the diverter with duct tape front view
Duct tape rear view
And reassembled
The propeller is much mor eexposed. i plan to build up a higher housing around the lift engine to keep me and other things farther away from the lift engine to avoid any problems with foreign object entries. I'm even thinking of a shroud/hood that will scoop forward air and also dampen the noise hopefully.
