Tonight I tested the oil pump – it worked so well that the pressure blew off one of the plastic tubes I was using for testing and sneezed oil over everything. After I cleaned up the mess I connected it into the system and did another test run. The extra resistance of the oil passing through the turbo bearings caused the pump to stall out on the first attempt. The pump was originally designed to move air, so it’s not surprising that oil was too much of a load. To remedy this I made a new crankshaft for the pump on the lathe with as short of a ‘throw’ for the piston as possible. With the shorter throw, the pump is moving less oil per rev which reduces the load and prevented the motor stall. After this change it successfully ran continuously and held an average pressure in the system of about 75PSI, right about where it needs to be. To keep things simple I don’t have a bypass or pressure regulator in the system; because of this the pressure gauge flutters with each pump stroke but this doesn’t hurt functionality.
The motor draws about 5A, at 12V this is ‘only’ 60Watts and is about the same or even a bit less than when it was an inflator pump. Since it will now be running for longer time periods though I need to keep an eye on the motor temperature. I also need to protect the plastic gear from the (eventual) heat of the combustor above. To address both of these problems I’ll likely make a heat shield for this area as well as add a cooling fan.
This weekend I resumed work on the jet engine project. When I last left off I had just completed the frame and mounted the turbocharger/combustor. I had also fabricated an oil tank out of an old propane tank and mounted it under the turbo, but had hit a bit of a wall with what to do for an oil pump. There are electric oil pumps available, but basically all of them would be overkill for this application. Also, since this is a hobby I’d much rather put in the time to make something custom vs paying for parts. Turbocharger jet engines have been done by many others, my approach with this is to see how compact and well packaged I can make one – that doesn’t happen by bolting together a bunch of off-the-shelf parts.
I had considered using the bus’s old oil pump, but this created more problems than it solved (connection of inlet/output pipes would be a challenge as would driving it and selecting a motor). Today after a taking a fresh look at it I realized that an old 12V tire inflator pump that I had could be adapted to work. The plastic casing had broken, but the ‘guts’ were all metal and should hold up to oil pump duty. The only problem was that the cylinder head of the pump had no way of connecting an inlet pipe – being designed for air, it just drew in air from a small hole. To fix this, I made a new cylinder head on the lathe with one large hole in the center. A tee fitting screws into the head and I’ll put a check valve on each side. This larger single-hole head should also help compensate for the increased load of pumping oil, much thicker than air. Once I start running oil through it I may have to make some tweaks to avoid overload (lower voltage, thin oil, etc) but this at least gives a path forward for experimentation.
I also shortened the oil tank to make more room underneath for other support systems and made a threaded port on the lathe to weld into the tank to connect the oil pump. The welds aren’t the greatest looking, but are leak-free and that’s what matters – they should clean up OK after some grinding. For now the whole project is in fabrication mode, but once everything is in place and working I’ll go back and do body/paint work on all the parts to make it look nice too.
Last night and today we replaced the top on the Beetle. It was in ‘OK’ shape but was showing its age and the back window had begun separating/leaking, requiring roof replacement. Complexity level for this ranks right up there with an engine rebuild or debugging bad assembly code. The biggest challenge is that all the miscellaneous springs, ropes, and bungees involved don’t have the usual ‘this clearly bolts there’ pattern – instead it’s a spider web of cords that have to be routed just right, and their appearance changes greatly depending on how far up/down the roof is. With the help of lots of reference images though it all went back together correctly. Fortunately for modern tops like this there’s enough repeatably between cars that the tops come pre-cut with all the right seams/edges pre-made; there’s no trimming or other ‘upholstery’ type work that would be required on an older car.
It’s been a busy summer with a number of miscellaneous trips. To keep with the recent aviation theme, I’ll share the photo below that I took on a recent commercial flight of an Antonov 124 – a large russian transport plane that you definitely don’t see everyday. It’s the smaller version of the world’s largest airplane, the AN-225 Mriya.
This weekend we headed south to a small airport with an on-field BBQ restaurant. It’s an hour and a half drive, but only 20min by air.
The pictures of the light sport plane landing give a good representation of the between-the-trees approach. This is not uncommon at small airports; it’s a bit intimidating at first but is not a problem if you stay on center-line and are ready to make a go-around if something doesn’t look right.
After another flight I was signed off to fly the Archer and we took it out this weekend for a scenic/practice flight. It was a nice, relatively clear, day and Christina got lots of pictures.
(and for anyone that notices – I’m not flying a plane with no tail number, that would be very bad. I just edit it out of the photos the same as I do with license plates or any other identifying info)
We drove down to the coast this weekend for an aviation conference. It was very rainy but the worst of it passed by mid-morning. We went to a number of great classes and learned a lot. There were several military helicopters and an Osprey that were there and open to free tours. Christina got a lot of pictures.
Today I started making a speedometer calibrator to compensate for the somewhat smaller tires on the bus vs original. I’ll use parts from an old speedometer cable to attach the calibrator to the speedometer, so I ‘only’ need to make two pulleys that differ in diameter by a percentage to the current speedometer error (Reads ~6-7MPH faster than actual) and a base plate with bushings for the pulleys to mount to. There’s very little load, so I’ll just use a big o-ring as the drive belt.
After a busy winter and uncooperative weather I’m finally back to doing some flying; first the usual Cessna 172 a few weeks ago and then this weekend a new type: Piper Archer. The Archer is roughly the same size but ‘low wing’ rather than ‘high wing’ like the 172; other than that and cruising a bit faster (~145mph vs ~135mph) it basically works the same way. After another hour or so of adjusting to the differences I should be cleared to go solo with it.
This weekend during a test drive of added soundproofing, the front left started getting noisy and shortly later there was a pop and a slight swerve. I safely got it to a parking lot, but the front wheel bearings were metal-on-metal at that point, and the wheel had shifted outwards so it wasn’t possible to drive any further.
With the wheel shifted out I didn’t want to risk further damage when loading on a tow truck, so Christina came to pick me up and we returned with a trunk full of tools and spare bearing from home to replace the bearing on-the-spot. This would have been a ~30min job except that the spindle nut and inner race of the outer bearing had lightly welded themselves to the spindle. I returned with a dremel (and inverter to power it) – the spindle nut was removed, but removing the bearing race was not possible. I found a big metal spacer that served the purpose of keeping the wheel retained on the spindle, though it did not work as a bearing and wasn’t driveable more than a few hundred feet.
With the spacer in place it was safely towed back. The next morning with better light and bigger tools I was able to get the bearing race off of the spindle. The bearing was even available locally and I got it all back together quickly. Special attention was paid to the bearing end-play, this was set to the correct spec with a dial indicator and the bearing thoroughly greased. This was then repeated on the other side.
The front wheel bearings were perhaps the only area that I had not yet gone through since getting the bus; so the failure isn’t necessarily surprising. Both sides had minimal grease and light rust pitting which, along with the bus’s new faster speeds, contributed to the overheating and failure.