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. 

Redone handles, new cleats, kill switches, and throttle control.

Thanks to all the help today we knocked a lot of items off the todo list.

It was a great afternoon with Jeff, Derek, Michael, Angel, and Niharika.

I started out the day working on getting the kill switches mounted. I had two proper power boat deadman switches that clip to you to shutdown the engines in case of you falling overboard. However they needed a good mounting housing.

Jeff started out working on attaching the cleats at the corners. We used the 1/4" poplar boards as a backing and the toggle bolts for securing into the plywood. The toggle bolts would go all the way up through the cleat and the board would also be stapled down to distribute the load to the plywood.




As I believe I've mentioned the lift handles were wiggling loose. So Jeff and Derek unscrewed them and pried them from their epoxy. We screwed the handles back in with lock-tite this time. And scuffed them up to try to get the epoxy to secure better.

Meanwhile Michael figured out how to wire in the kill switch for the thrust engine and ran the cable forward to the box I mounted earlier.

After preparing both the new handles and cleats we broke out the epoxy. There were a few complications. Unfortunately the stackup of the spacer board + cleat was too think such that the bolt couldn't reach the toggle bolt. We had to drill out the cleats to get the head of the screws slightly lower.

To test whether the cleat was secured well I pulled upward. Unfortunately this revealed that the port bow plywood was not secure down well at all. And the cleat had been secured down well, but the plywood gave, bending/partially breaking. So we had to mix up an additional batch of epoxy, and both secure the cleat, as well as glue the plywood down. This reinforces the urgency of running reinforcing fiberglass around the perimeter of the body to transfer the loads between the plywood on the surfaces and sides.

Unfortunately that's about when the batteries ran out in the GoPro. After securing everything we added my standard weights of barrels of water. In the beginning of the next clip you can see the buckets have appeared suddenly. The 3 parts of the video are from the 3 batteries used for filming. I'd love to have longer battery life. But at least in the Hero 4 the batteries can be changed quickly, and I have several to swap out.




In the final session we moved onto focusing on the throttle mechanism. Jeff and Michael discovered that they could loosten a nut and make the throttle move much more freely. And Jeff created a throttle mechanism out of an angle brace, 18" of aluminum tube. And most cleverly discovered that 1/4" post electric crimpable connectors can work well to crimp onto throttle cable housing. Experimenting with a few different ratios we successfully made a handle which can easily be moved, gives full range of throttle.

The one problem is that it is mounted at the aft end of the cockpit. We knew this would be a problem before we mounted it, but we wanted to test the mechanism anyway. I just need to find a longer throttle cable with housing. The current one is only 4-5 feet.



The end of the day concluded with testing the throttle and kill switch for the thrust engine. We held off on the lift engine due to all the epoxy around the perimeter. And the buckets balanced on the corner...

We started with testing the kill switches and when we tried the first kill switch it didn't do anything. So I turned it off at the engine and that killed it. After a little puzzling we remembered that the engines required an active connection to kill it instead of interrupting the signal. So it needs both the engine switch and the kill switch in the off position to successfully disable it since they are wired in series. We'll change it in the future to be in parallel such that if either are in off, it will be disabled, and it will require both to be in the on position to run.

The throttle mechanism testing was great. It worked just liked we planned. Which was a surprise due to it being made of ~ $5 in parts, an angle bracket, a bolt, several washers, and a hammered aluminum tube.

Engine mount reinforcements and steering inputs

Today we successfully tried running both the lift engine and the thrust engine simultaneously. Successfully too!

We started with just testing the thrust engine. Bringing it up to full throttle and making sure it was stable with the reinforced engine mounts.

We also tested the rudder action. I am amazed that it seems fully controllable without much load. And in the tests you can definitely feel the difference when adjusting the steering. The steering action is relatively light and seems responsive.

Here's the video of that test:

I actuated the rudders to see if we got good lateral pressure. There was definitely pressure. Hopefully it will be controllable.

And an alternate viewpoint:

The rear was restrained by Michael and Angel, while Christian kept the front from drifting too much. You can see as I try moving the rudder back and forth the craft is trying to move side to side. 

The travel available in the rudder is not symmetric. We calibrated the front such that the stick is centered, however the range of travel available at the stern is not centered so the stick's travel matches it. The mechanism at the back is adjustable with threads so I think I can tune it properly without too much work. Unfortunately though it does require disassembling the rudders to rotate the mounting point along the threads. 

We hovered in and out of the garage successfully as well as repositioning. 

Note getting the kill switches wired in is on the short list.





The hovering is now getting anti-climatic enough that I might consider not filming and editing every moment of it. 

And here's what we did today. 

The main work was to get the tiller mounted in the cockpit and connected to the steering cable. 

Trimming the hinge down to not go too far up the tiller

Is this where you mount a table leg? What side up?

The final tiller solution with the cable mounted on a hinged board and our table leg tiller attached to the hinge.

And the other main work was to reinforce the thrust engine mount. It now has diagonal braces both sideways and forwards. These are bolted into the boards which are glued to the base. So it is much more ridged now. 

Previously if I leaned on it with most of my weight it would visibly deform. Now it does not deform at all. 

Thanks to Michael and Angel for all their help as well as Christian who helped with today's progress and successful testing.  Special thanks to Angel for the in action shots.

And as a final note, I've ordered an important accessory, knee pads...

More bracing for the thrust engine mount and housing

The engine mount worked when we tested it but there were definitely some oscillations which were larger than I'd be happy with overall.

Once turning it off, there are definitely directions in which it will flex when I push hard on it. To take that out I've started adding some bracing.

The first weak point is for and aft support for the fan housing. The top of the fan has a lot of leverage over the small footprint of the housing mount and relies on the plywood to take the load via torsion. To that end I've braced the top of the fan mount forward.

The second weakest direction I identified is lateral movement of the rear of the engine mount. It is currently relying on the plywood bracing at the front of the mount, which is quite rigid, but with 12 inches of leverage the shaking motor can make quite a difference. I secured it with a small diagonal brace, but there's definitely flex in the system. So I'm adding two diagonals which will brace down to the corners of the fan mount, giving direct lateral support just below the engine.

Lastly, the forward thrust of the engine is only taken by the angle brackets making the box for the engine mount. That's going to be the primary loading direction when the engine is running. So I will also run braces forward to transfer the load into the deck via the rear edge of the cockpit.

Here's a timelapse of me securing the fan housing forward and starting to work on the lateral supports. The battery ran out much sooner than I expected.



I used some stainless hinges to secure the top of the fan. I don't need the flexion, but the variable angle bracing is convenient.

The bottom of the braces are through bolts.

The lateral braces, one seen below, pinned but not secured will be through bolted at both ends. I needed to pick up a few longer bolts to properly secure the braces.

Status at the end of the day.

Still todo is also to brace the engine mount forward as well.

More hovering and thrust engine test

Thanks to all the help from Tudor we got in another flight test!

We started out with hovering out of the garage.



Two things were clearly identified from the tests. One is that we have more weight at the back then at the front. Secondly the garage has a defined slope to the left as you enter.

Then we tested the newly mounted thrust engine.



It was great to get the 2nd engine running. We didn't go anywhere since there were several things identified that should be reinforced. And we only had 3 feet of runway ahead of the vehicle.

The engine mount needs a little bit more reinforcement especially torsion around the vertical axis. And unfortunately the screws in one of the newly mounted lifting handles backed out a little bit. They apparently had a little bit of play and were not backed into the epoxy.

And of course the rudder system is not fully functional yet. But it's mostly for a lack of controls now. The whole system at the back should be basically there.

Finally we gently hovered back into the garage.



It's amazing how easily it slides. You can see Tudor's barely pulling on the ropes.

Note about engine manuals

It's been very frustrating finding the appropriate engine manuals.

Briggs and Stratton have nice menus to find your engine based on some part number but that seemed to be focused on integrated designs and I never was able to get the right manual from them.

Eventually I found pdfs of similar models in google searches.

Even then they're not the most useful.

For my future reference it seems that 0.5 quarts for the lift engine and 0.7 quarts for the thrust engine are the appropriate amount of oil.

Thrust engine and rudders

Thanks again to Tudor for all the help.

We started out the day with some additions and reinforcements.

We added a lower rail for mounting the rudders. We added a dashboard panel. And reinforced the engine mount, and glued down a hinge for the steering stick on a backing board.


On our trip to West Marine we were unsuccesful in our search for steering and throttle controls. We did find a steering cable which we picked up. And the other breakthrough we had was finding some clamping oarlocks which make nice bearings for the rudders.



With a brief break for a battery change...

We continued mounting the rudders, including adding posts at the leading edge to tie them together as well as bolting on the end of the steering cable. The combination of the oar locks and some left over T-brackets with some subtle applications of lock washers as spacers of the right radius made the rudders look quite good.

Tudor also rounded off the front of the rudder as well with the sander. We did a tear down and reassembly to clear the airway too.


We ended with a little bit of a cleanup before our next tests...

Thrust engine mounted

With a few more fittings and help from both Christian and Tudor the thrust engine is now mounted and awaiting it's first test tomorrow.

The morning started out with a bit of a setback though. I tried testing our reinforced handles, and the results were a complete failure. Lifting on the handle just tore a handle base plate sized chunk out of the side of the hovercraft.

The results of testing the lift handle.

As a result of this we decided to choose a new handle style, with a larger mounting plate. We found some pull plate handles from commercial doors which seemed to fit the bill and could take advantage of the reinforcement plate we had already installed. (with a little trimming)

After a quick trip for the new handles and some more fittings we replaced the handles and worked toward mounting the engine:




In the video you can see with the screws removed from the rest of the handles, I was able to just pull them off.

After a bit of a break we were able to get the fan and propeller ready to run.



With the fan prepped we focused in on the engine mount.

We significantly improved it by switching to use brackets with a diagnoal piece instead of just the one piece of bent sheet metal.




The oak board for mounting the engine worked way better than I thought. it's quite solid, but still easy to work with.

There were some worries about impingement between the mounting brackets and the through bolts holding the engine mount board to the assembly, because the engine mount needed to be moved to Bthe rear to accomadate the distance to the fan housing. but we were able to get enough spacing to not worry about too little leverage. And really 1 bolt on each side would actually be enough.

The other compromise we found was to add a diagonal brace to the engine mount for lateral stiffness. i had been planning on a full width piece of plywood for the front of the engine mount, but we changed it up to just a diagnoal stringer to allow for increased airflow.

And finally with the engine mounted we mounted the propeller and closed up the fan housing.



At the end you can see us working on filling in the rudder design.

The thrust engine, fan housing and propeller final assembly from the front.

The thrust engine, fan housing and propeller final assembly from the behind

A fun note, this was a 4 gopro battery day. It's great to have easily exchangeable batteries. Otherwise you would have missed a lot of this.

In the course of this day we made a lot of incremental progress and refinements. The fan housing was assembled and disassembled many times. It's frustrating but worth iterating as we see improvements.

It's going to be fun to test the engine tomorrow. We made sure that the collet and propeller mounting is very well secured as we learned is necessary for the lift fan.

Reinforcing lift handles and thrust engine mounting progress

Thanks to Tudor being in town I've been a little bit more active on the project.

We started out by reinforcing the lifting handles as they were making very bad sounds if you started to lift by only one.

We added a poplar plate around the handle to try to distribute the load.

Then we returned to the engine and fan mount. We finished assembling everything and fit checked the fan. After which we glued and screwed down the base parts.

Part 1:



Part 2:



One thing to note is that of the 9 toggle bolts we used 2 failed to twist the toggle correctly. So we had to reverse course and remove the whole assembly to replace the toggles.