Improved Lift Flow Splitter

Today Adrian and I worked on increasing the effectiveness of the lift fan splitter.

From reading through the design manuals they talk about having the splitter as close to the fan as possible for greatest effectiveness. Some of the lift fan's output is directed into the lift bags, while the rest simply goes into the cavity under the vehicle. The bag has lower flow but higher pressure to maintain the perimeter and keep the air cushion underneath. My splitter was mounted too far down, almost 12 inches below the fan. And with that distance, the bag pressure was allmost equivalent to the rest of the air cushion giving very little force to keep the air underneath.


To make working on this easier we started out by rigging a hoist mechanism to make it easier to lift the hovercraft when in the garage. A few pulleys in the rafters and it worked pretty well. I'd really like to get some better hard points, but until I reinforce the perimeter I"m afraid to use the cleats or the handles too hard. So we attached to the superstructure.

A few notes on the hoisting. I tested the pull using a luggage scale and the front was ~ 55lbs force to hold the front in the air. Two more pulleys at the bottom would be a great help, there was a lot of friction in the system. Since I can relatively easily squat lift the front end. With the pulley system rigged it should be ~4x the force.

To fix the splitter we first installed a wood sheet baffle to traverse the thickness of the hull and keep the bag flow separated from the main lift flow. Then we attached a piece of sheet metal across an equivalent section of the cowling between the lower grill and the fan.  There's over 5" inside the cowling behind the back of the fan.

While we had the cowling out we cleared out half the wires from the lower protective grill. Having verified that there's more than 5" of clearance between the grill and the fan, and it's the output side of the fan, on the undersaide of the vehicle, recessed by 6" from the bottom of the hull, it felt like overkill to have < 1/2" gaps in the grill.  Holding my hand over the grill when testing it did feel like we'd made a noticiable improvement in the airflow.

Also, when we were cleaning up the cut out parts we noticed it was a non-trivial amount of weight too.



Here's a timelapse of the first half of our work. Hoisting and adding the lower baffle.


We took a break to buy the needed sheetmetal. And then returned to work on the cowling.


Here's the video of our final test at the end of the day.




The hovercraft did seem more stable side to side with the improved splitter. And I've learned where to position myself to be in the center, but I think it did better at not dragging the stern when at low speed.

You can't see it in the video but the cowling did rotation slightly when we were testing. Below you can see the picture. Through the whole fan you can see the wooden baffle parallel to the main structure, and the sheet metal splitter just below the fan rotated by ~ 15 degress. The whole cowling actually rotated by that amount. We just need to pin it on the side. It will add one more step for getting it in and out but it will help to keep the air pressure up.

The splitter inside the cowling showing rotation after testing. 

Steering linkage tuning and lift throttle assembly

I've made some more progress this weekend with the help of Adrian.

We had two main tasks for the day. 

First off we had to switch the direction of the steering linkage, and while we were at it we needed to recenter it as well. 

And we replicated Jeff's highly professional linkage on the other side. I'll get some closeups later when there's more light out. I forgot to get them at the time. 

Here's the full timelapse:

For good measure we also tested the linkages.

We started with testing the rudder linkage. The ambient temperature was cooler than I've run the engines before and I was surprised by how easily I flooded the engine before it warmed up. 

You can see that it is approximately centered now. There's a little bit of a question whether it's a wide enough range of motion. If we need more range of motion I can easily add a new pin to the bottom of the rudder with a shorter lever arm. 

The lift engine also flooded when throttled up, but I was able to react and it kept going due to momentum enough for me to lower the throttle.