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.

Thrust Engine Mount Partial Assembly

I started assembling the thrust engine mount today. I didn't get a lot done since I got distracted by other things when I needed to get more screws. But I'm confident between the brackets and some plywood attached to the sides the engine mount will be quite solid.

Here's the time-lapse of what I did today.

 

Thrust engine mount started

I got started on the thrust engine mount. Which is integrated with the fan mount since they need to be closely connected.

I drew up the following sketch to get started.

My sketches

I broke out the buckets as sawhorses again. 

The portable bandsaw blitzed through the wood nicely. Without even effecting the battery level.

My sawing setup

 Here's the results laid out near where they will end up. The T shape is the base. The small square on the left is for the engine and goes above the base of the T.

The rectangle on the floor is for the top of the fan. And the vertical segments are on the left that go next to the fan.

I did not cut the verticals for under the engine as I have not done the stackup analysis to find out how high the engine mount should be for the fan positioning.

The resulting segments layed out near the stern.

I bought some angle brackets at home depot to help with the assembly stages. And I got an oak plank to be the engine mounting block on top of the above structure. 

Better hovering

With the improved engine mount we can hover much better. There's much more airflow and the skirts are kept at a noteably higher pressure. Thanks to Adrian and Michael for their help today.



The flight went very well. It hovered low at idle and made it up to full height at a mid level throttle. With the full power I was easily able to balance the craft. And Adrian reported it was very easy to slide the vehicle around.

Here's a slow motion version. It's great to be able to see the air gap under the skirt. Also watch the fun dust cloud as it gets started running.

A little bit more about the process below. There was some basic assembly to get started. And then we tested the engine while still on the blocks.

The new engine mount at the time of the first test

After the first test we needed to disassemble it again so I removed the extra metal now that the engine had been alligned and bolted down in place.

Metal removed

Trimmed engine mount

Collet with locktite before tightening

 When we ran the first test there was a repeat of the fan blade coming off even with the lock tite.

Scrapes observed on the bottom of the engine.

 We found some scrapes on the bottom of the engine where the fan had actually ridden up the shaft due to the air pressure and was rubbing on the bottom of the engine. I guess it still had enough friction to keep spinning too.

The collet spacing after extreme tightening

So after the fan came off again we remounted the fan, and this time I tightened it as hard as I could. I'm not sure it will dissassemble, but it should at least stay assembled. The collet is down to 2 and a little threads showing vs the original 4 or so when untightened.

We ran it through several tests and it stayed on. Here's a video of the last test where we throttled up to test it at full RPM



Before we got started today we added some handles to the corners for easier moving when off. Here's the timelapse through the first engine test. The battery died during our dissassembly and cutting down the engine mount extra parts.

Here's the view of reassembling the fan and installing it.



The final test on the blocks was interesting as we throttled it up, and in the process we watched the cowling counter rotate from the propeller. I'm not sure exactly the phenominon which caused that. Watch below. The yellow cowling has marks on the sides for alignment.

Skids for the bottom

Today the hovercraft received skids on the bottom as well as reinforcment for the lift fan housing.

The plans call for 1.5"x1.5"x6' skids on the bottom. I instead used the left over 2"x2" stock from the cockpit on the bottom. (Of course And I had 10' lengths so I made two 5' skids, but that seemed really limited for balance. So instead I made another pair, and overlapped them just slightly since the interior space is about 9.5'. Have a look below at the final result.

The skid strips installed

Here's the timelapse of today's work. 

At the beginning we added some reinforcements to the housing around the lift fan to make it even more solid. Now it has plywood in all three directions so it will be much stiffer to any disturbance or vibrations from the engine. 

New Lift Engine Mount

With the help of Michael, we recreated the lift engine mount today.

From the first hover trials the available surface area of the lift fan was significantly limited by the large surface area of the engine mount. A rough estimate is that it was covering 70% of the surface area of the fan, leaving only some small slivers of intake areas open. You can see that all but a 6" chord at the front and back of the fan were open in this post.

For a quick comparison you can see the new mount preassembly on the left with the parts cut away on the right.

The parts of the new mount next to the parts of the old mount.

Here it is on the fan, you can see the front and back has close to double the area, as well as large areas on the sides open as well. The main blocked area is basically under the engine now, and is also  near the center of the blades which is not an efficient area anyway. 

Fit testing the engine mount before gluing.

Here's one last shot of it waiting for the epoxy to harden.

The new engine mount in the clamps waiting for the epoxy to dry.

 The construction technique was to cut down the boards previously used to a 10.5" square around the engine mount. Then aluminum c-channel is fitted side to side and along the sides of the board. That aluminum c-channel is then bolted to 1" steel square tube. The c-channel is epoxyed on the sides of the boards which are sanded down to a press fit.

Looking at the design I think the aluminum c-channel all the way to the edges might be overkill and just more air resistance. I may go back and trim the outside 6" off since the steel should be strong enough on its own.




In this process we had quite a bit of epoxy left over. Michael noticed it was getting hot enough to be either smoking or steaming. In the following video you can see the epoxy puck which had been created by the hardening epoxy still in the bowl. In the first second you can see a little bit of the steam/smoke right by his hand in front of the cabinet. I guess the perimeter is still not yet hardened since it's being cooled by the environment.

It hovers!

In a very momentus event, my hovercraft took it's first flight today! Many thanks to those who were here and gave a hand keeping things under control: Adrian, Ayse, Eric, Jenny, and Wim!

Here are a couple views:

Top corner view:


Lower corner view:


And slow motion side view:

We did start with a fan test and we could see that the bag was successfully inflating.

 It's been a long time getting to this day. It's really awesome to see it all finally come together and hover. It's been a long project and I've gotten distracted many times by many things and pushed this project onto the back burner. But now it's hit a big milestone. There is still lots of work to add the thrust motor as well as better controls. Manually reaching forward and increasing the throttle is not optimal.

There was some excitement in the tests. At the end of the flight the lift fan did fall off of the engine shaft. That was the big bang at the end.

It did validate my design choice to use an enclosed metal duct. Despite the fan coming off while still spinning, there is almost no evidence of it being a problem. After disassembling it there were a few wood shavings in the fan housing, and the end of one blade is a little bit scuffed.

The scuffed fan blade having fallen off the engine shaft.

Wood chips in the bottom of the fan housing upon dissassembly.

The fan blad resting at the bottom of the housing after the first flight.

This reaffirms my concern about the loosening bolt from the previous tests. I'll need to look more into how to make the collet more robust to vibrations. In this case again one of the bolts had again loosened during the testing.

It was interesting that I think it only fell off at the end due to the positive pressure provided by the thrust. I suspect that part way through the test it had loosened enough to start slipping but it was only partially slipping and was held up by the back pressure.


As a side note upgrading the engine mount will definitely be valuable for decreasing vibrations as well as opening up more fan area for through flow. Right now the engine mount is covering most of the fan's surface area. With that more open it should be able to hover higher. It was adequate for this test on very flat ground but I think it will need more in the future.

I'll also take the time to add some more sides to the cockpit near the forward engine to stiffen it up.

The vibrations in the redwood are amazingly large in amplitude. They can be seen clearly in the engine test videos. 

Lift fan running smoothly

So after a little debugging I discovered that there was slight eccentricity between the ducting and engine. I'd checked the blade everywhere, but the problem was with the metal grill where the hub went through it.

So I ended up having to take the whole system apart again. I made a slight mistake in that I mounted the blade slightly higher than before which made inserting the removal bolts much harder.

I also noticed that the grill works better with the radial ribs upward so it fits around the engine mount bolt heads better.

After disassembling I confirmed the impingement was between the collet bolts and the grill.

Top bolt with visible nicks from abraiding with the grill.

The abraided fan grill. The ones at the inner ends are from this incident. The loss of paint at the 3 and 4 inch radius areas are from the original electric fan motor mount.

When disassembling it I noticed that the nicked bolt was actually completely loose. Before going too far I will want to add some lock tight.


At the end of the timelapse you can see that I enlarged the clearance. However the bolt cutters left large sharp stubs that I felt were suboptimal.

So I stopped progress and went to the store to fix that.

The grill after using bolt cutters on it.

You can see my grinding down and cutting off of the stubs, followed by filing them down with hand files.

I reassembled everything. I'm getting much faster at it now. With the larger interior hole it's much easier too. And I made sure to not mount it quite as high up the engine shaft for clearance for future dissassembly.

Once it was all reassembled I then tested the engine again. It ran smoothly and was drawing air in. I think we're on track for trying to hover tomorrow.

Lift fan testing

So once I finished testing the lift engine the next step is to test the lift fan.

Here's a video of the first two test runs of a few second each.


The first one went well and I stopped it conservatively.

The second one developed a loud rattle so I stopped it asap. I'm still debugging where the sound came from in the second run. 

Lift engine testing

So I'm getting close to operational and I wanted to bring up my engine.

I found the serial number on the engine and entered it. But no dice,"Found 0 results matching "120502-0116*"" I followed the video, and found the

Briggs and Stratton manual finder failure.

Despite the fact that I followed their video tutorial on how to find the number and I'm quite sure it's right:

The Briggs and Stratton model number printed on the sheet metal above my muffler

I ended up pulling a PDF off of manualsonline.com it wasn't quite the same model, but it at least gave me the basics. Though it did not tell me what the kill switch was.

It's the little wire coming out the front that you need to ground to kill the spark.

I started by stripping down the lift engine to test it unloaded first.

Then I tested the engine. See the timelapse below. The engine was pleasantly quiet unloaded. The throttle worked fine, however the advise I got from the manual about travelling all the way down on the throttle was incorrect. So I needed to find my aligator clips to short out the coil and stop the spark as I thought the extra little wire was for that.

The one thing about starting the engine that was a little disconcerting was that it was quite smoky obviously burning oil. Since I didn't have the real manual I had no idea how much oil to put in. And I was pretty sure the dipstick wasn't working well without turning things over. After a brief search I found the alligator leads and disabled it.

On inspection though I found this pool of oil below the muffler:

Oil pooled below the muffler after the first run.

Now I think that this is ok. The oil I put in is clear and this is defnitely black. So it's not the oil I put in. Which means that it's oil which was already inside the engine. And several times during the assembly process I had turned the motor completely upside down. So I suspect that I put oil into inappropriate places, such as the muffler. After running the oil on the dipstick looked to be right at the full line so I think that's ok. And by the time that I found the alligator clips the exhaust was much cleaner as well so I think the excess oil has mostly burned off now. The manuals aren't very useful for defining first time bringup procedures. But I'm betting that this also might be expected for the first run due to preservatives added during shipping.

 As a side note, the new "eco safe" jerry cans are terrible. I had almost as much fuel running down my hand as I did going into the fuel tank. I don't really know where it was coming from either. Maybe next time I'll try inverting it and relying on their seal to stop it until its pressed into the tank. But standard pouring just doesn't work. 

Adding baffles around lift duct

I added baffles around the lift fan to block the air from coming right back up next to the duct. This fixes the problem of a round peg in a square hole. I also added a panel on the front to help strengthen the cockpit structure. Below is a timelapse.




You can see the 4 corners glued into place such that the air will not be able to flow back up the corners around the fan duct.

While I was at it I also glued and stapled the small spacer pieces which hold the fan up above the top of the fan housing. 

The engine mount spacer block freshly stapled and glued with the corner baffles also recently installed.

Reinforcement at the front.

I also cut a piece for one of the sides, but I realized it would impinge on my ability to access the engine bolts so some affordances will need to be added before adding it as well as the matching one on the other side.

A close up  of the corner baffle. I ran some extra expoxy along the edge to help protect it from wear since the unsupported plywood felt a little vulnerable.

Lift engine mounted!

The lift engine has been mounted!

The mounted lift engine

It's far from optimal. In particular if I need to do maintenance it will be a big pain as getting inside the housing requires a full disassembly. However it's there and I feel pretty safe with it in place.

I'd also like to decrease the occlusion of the intake. We'll leave that to a 2nd generation however.




One of my worries is about the collet. I hope that it will release when the time comes. The supplied release bolts are black annodized 1/4-20 about 1" long. I removed them as they were just going to be a risk of rattling free.

Fan mount prior to tightening.

The bottom side of the fan with washers added for good measure.

 

 

 

5/16"x3" bolt without washer

 Bolting the engine down went fine except that the 5/16ths washer couldn't fit onto the longer engine mount on the backside so I skipped that. But I did find nyloc nuts for better security.

The other two engine bolts before tightening

The engine in position waiting to be bolted down

Thanks to help from Jenny, getting the engine into place was not too hard. I blocked it up briefly while aligning the protection fan, then clamped it down before drilling the clearance holes manually.

I was able to confirm clearance by spinning the fan using the pull start of the engine.

Before powering up, I need to remember to reinforce the cockpit frame with plywood to avoid parallelagramming. A few pieces of left over plywood will take care of that nicely.

Lift Engine Mount Plate

I've made some more progress toward an engine mount thanks to help from Michael.




In our testing of the stackup you can see it seems to work well enough.

Test stackup of the lift propeller with the lift engine mount

The single board was not wide enough, so we glued two together. The bolts would hold it together, however it is better to hold together independently.

Glueing together the boards with clamps. (First clamp revmovced)

The final mount

A fit check

Prototype Skirt Inflated

Thanks to my helper Jenny today! We successfully inflated the test skirts using

We had to tape together 2 corners. Batten down the perimeter and then make a few tweaks to the starboard hull. (Note it's upside down and pointing into the garage so the starboard side is away from the camera.)

Inflated skirts

Here's the timelapse:



The skirts inflated and could take some weight resting on them with just the shop vac!


Lessons Learned

There were quite a few lessons learned today.

• The port side skirt ended up 2" too short, so the front had to wrap around.

Missed front port corner.

•  
• The front batten port most screw got started cross threaded, and I tried to force it. Unfortunately the weakest point in the system is the wood the tee-nut is threaded into and I ended up with the tee-nut spinning behind the batten. It took some forceful work with vicegrips to get the screw out. And now the threads in the tee-nut are shot, so I think I'll be grinding that section of the batten out and gluing in a replacement segment with a new tee-nut, since the corner is the most critical portion of the batten.

Cross-threaded

Adjusting the starboard side required a little scrunching:

Scrunched skirt under batten from shifting starboard skirt by 2 inches

Also the rear starboard corner does not quite line up correctly. When transferring the template we need to make sure to take this into account.

Corner length miss alignment. The port side was folder over to match.

Next steps:

Landing pads, to protect the skirt when landing.
Lift engine mount. I think I'll test it out of wood for quick fabrication and testing. Then move onto waterjet cut alumninum. I think the wood will be strong enough for initial testing.

Progress on Skirts

A big thanks to my parents who were in town and gave me a hand this weekend.

We made a bunch of progress on the skirts this weekend. Here's the timelapse:




A few details from the process. We are prototyping the skirts using drop cloth plastic picked up at the hardware store since it's cheap and readily available.

Thinking about how to secure the corners we ran into some zippers for tarps which we thought might be useful.

They did end up being useful, however we didn't use the zipper functionality. They turned into good adhesive tape. In the future I think I will do some research to find some good tape to use for joining the skirt elements. Certainly this tape is as strong as the skirt material. And it has a special zipper like anti abrasive rub surface ;-)



We experimentally determined the curves necessary for the joints using masking tape, the plastic and a shop-vac set to blow.

Prototyping with masking tape

The shape of this curve is quite complicated, and we learned the important part is that they line up, as well as the two pieces have the same linear length along the joint.

Two corners secured using zipper reinforced tape.

I also had not worked on the intake for the skirt at the front. So we added a crossmember under the lift fan to be able to catch the air and route it into the skirt.

Adding scoop area for filling the skirt from the lift fan.

We're not sure about the ratio of lift to skirt, but expect that we can adjust it with a baffle if we need more.

With the glue drying we had to stop work on the front skirt section. But once that dries the front skirt segment should be ready to go too.

Once I've verified the plastic skirt works as I like. i plan to cut it apart and measure it to make my templates for the rubberized vinyl version.