I put everything back together with help from Michael today. I think we're almost ready for another field test!
We added one enhancement for the lift fan. A little bit of rubber padding between the engine mount and the safety grill. I hope that this will avoid any rattling between the two. And it should also take out some of the vibrations.
Rubber padding installed
Close up of the rubber padding during the installation process
Our simple design is reusing some used RC car tires. They're cut and splayed open. And then zip tied to the engine mount.
One thing we noticed and were surprised about was the amount of rust that's accumulated on the engine mount. There's nothing structural, but it was more than we were expecting since the craft has always been in the garage.
One other thing that we had to do was to bang out the small indent where the lift fan cowling was slightly dented from its past life with wheels mounted there.
We also tested again with the sound meter. Even with the padding the lift fan is still at similar levels. Mid to high 90s db at idle and almost 105db throttled up.
Here's me trying out the new mount with the fan and exploring the envelope of CG which is now much larger.
We tested out the thrust fan too. Again the engine noise is basically all the noise and it ranges from the mid 90s up to just over 110db at full throttle. It also appears to be the majority of the noise coming from the engine. Of course the
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.
Since I was having trouble with the lift fan propeller and I've tested it more than the thrust fan I decided to do the same operation for the thrust fan just in case.
Dissassembling it there were no major signs of wear from spinning like the lift fan which had shavings everwhere and clear galling and grooves. There is a little bit of wear.
The thrust fan shaft after
The collet freshly removed
Since I used the end cap in the middle of the lift engine hub I needed to make another one.
Here's the end result, not pretty, but effective enough.
The hub assembled with longer bolts extra washers and locknuts.
The final assembly from slightly behind.
The hub before assembly with the keys installed.
The keys and bolt in a fit check.
And here's the evidence that the fan stayed on. For at least 5 minutes....
While running this test I was watching closely for wear and tear and any malfunction. And I noticed that the grill protecting the fanwas flexing quite a bit when I throttled up. So I setup the camera in a different vantage point. Sorry it's a little bouncy since the tripod is now on the hovercraft. But you can see the grill flex when I throttle up best by watching how much of the engine shaft you can see.
TODO lift
I also did some continued testing of the lift fan. I found two more points of failure. Since i've dissassembled and reassembled the lift fan so many times, two of the screws holding the grill down wiggled out of place. it was kind of exciting to watch one of them start bouncing across the grill and then disappear between the wires never to be seen again. One more reason I'm glad that I have the metal housing. And there's the thick piece of wood between me and the lift fan too.
I filmed the lift engine tests but unfortunately the gopro had operator error and so I have two unexciting pictures for each test. One before the test, and one after the test. During this test I was excited to realized that the tilting of the hovercraft does effectively allow me to move it side to side by releasing air out from the side of the skirt. By leaning I could choose to loosen or tension the docking lines on either side of the vehicle.
The other interesting result of the lift engine test was the below grill failure. As far as I can tell this wire was vibrated free from its housing. It does not appear to have had a traumatic experience from cutting and just sprung itself loose from a weakness in the weld under the high vibration environment of the lift engine.
The one piece of wire that has proven to be not well attached. You can also see the hold where the sheet metal screw has self vacated.
The whole loose strand, and both screw holes which were vacated.
I am going to be looking for ways to decrease the vibrations of the lift engine. Mounting it on the two horizontal bars is generally strong enough but leads to a lot of resonances which I think are making everything harder to keep in place. And also makes things louder and less comfortable on the craft.
After all my trouble with the collet slipping I have upgraded the fan mounting technique.
I ordered some shaft keys since both the shaft and collet are keyed. And I also ordered some 3/8-24 bolts to thread into the end of the engine shaft. And I modified the outside mounting plate with a center hole to allow it to bolt to the end of the engine shaft.
The blot ane key fit checking
The key fit in nicely. Though surprisingly the woodruff key I ordered was the wrong size. I didn't expect that it and the may key would be different width. The main keyway was 3/16" but the woodruff key slots on the back were clearly 1/8". But the collet was also 3/16" so that works better.
The 1-1/4" was the right length to fit in.
Key fit check
The face plate modified with a center hole for the shaft end blot.
Fully Assembled hub, with the new plate visible between the hub and the propeller assemble.
An external view of the assembly
I identified that the grill housing is going to be vibrating against the engine mount, but listening to the running sounds I think it's a minimal amount of the noise of the system.
And finally the moment we've been waiting for. The test!!
It worked quite well. I hovered much higher than I can really remember except for a brief moment in one of the recent tests as I got the hub super tight. Which suggests to me that it was never really not slipping previously.
This is great! I'm looking forward to more tests soon!
I took it all apart, and found out why I got such a different sound.
Damage to the lock nuts
With the slightly shorter collet mounting meant that the locknuts holding the fan to the housing impacted the screen housing before the mounting bolts impacted the bottom of the engine.
The nuts before fully removed.
Doing some research I've found that the B&S engine shaft appears to have 2 woodruff keys slots as well as a standard keyway. And the end of the shaft is tapped with 3/8-24 and is about 1.3" deep.
I will use the end cap plate, to hold the assembly to the end.
End cap plate, which will need to be drilled out in the middle.
And I've ordered keys to go into the keyways and stainless bolts to secure the plate to the bottom of the shaft. The plate will keep it from riding up, and the bolt will keep it from dropping down. And the keys will keep it from spinning.
With the new collet installed I then moved onto testing the engine. Since I was on my own you'll see that I rigged up some eyes in the walls of the garage and secured the hovercraft from moving significantly laterally.
Here's my first flight.
Everything went relatively well but there's some ominous rattling near the end. It's easier to notice now that I listen to the recordings. But what do you do after a successful test? Try again...
Yeah, not so good. It was clearly not doing things properly since it didn't even start hovering. And by then it had been loosened so of course it fell off again. But it's nicely contained in the housing.
So I took it all apart again. Measured that it hadn't worn more than a few thousands off the bushing, and put it back together again. This time I put more than the recommended 95 inch pounds, but not excessively. But then I ran a very short test:
It hovered well, but I took it apart anyway and there was an extra quarter turn I was able to get out of the tightening bolts. So I tested again.
This time I throttled up a bit and everything seemed ok. But I took it all apart and was able to tighten each bolt a quarter turn again. So one more check.
Things sounded better, and the bolts did not have freedom when I took it apart. So I decided to try again.
Everything sounded good and it was hovering very high. I've had some balance issues so I tried adding some weight at the front to feel the balance. It was riding super high and super stable when I throttled up. However as I throttled down to feel it settle, the propeller started hitting the underside of the engine as it had slide up the shaft during the testing. That's what made the horrible noise at the end.
So I'm a little frustrated now...
I think that there's some work to be done. Leveraging the keyway seems like a good idea. And also using the end of the shaft, and the end bolt would make sense. This is the mounting technique for most lawn mower blades.
So after waiting several weeks for Univeral Hovercraft to send me a replacement collet I was excited to get it mounted up again and get hovering again.
Some new parts
When dissassembling I found a lot of metal filings.
The removed propeller with worn collet and filing visible in the old housing.. Also note the shorn off bolt.
And based on those metal filings I thought I'd check the size of the collet new vs old.
New collet lower edge measurement
Old collet lower edge measurement
There's an exciting ~15 thousands of an inch extra clearance which
New collet top side measurement
Old collet top side measurement
And the wear was almost as much on the other side of the collet too.
For reference I also measured the shaft. And it's pretty close to the expected size still.
Shaft size near the end
Shaft size where there appear to be the most wear
So I moved onto reassembling the lift fan. Taking note of the bushing instructions.
Collet bushing instructions
I did notice some differences in dimentions of the bushing mounting blocks, but the critical dimension where the bushing rides appeared to be the same.
New and old bushing housings side by side
New and old bushing housings side by side.
I put everything back together. And I installed the collet to the shaft before installing the propeller so I could see and access it better. Everything looks good.
Reassembled collet end view
Reassembled collet side view
The bolts were all secured with lock-tite.
A close up trying to show the lock tite
I added the propeller on last before reinstalling.
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.
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.
