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From the Hooper UAV paper linked above:
....in a four-cycle engine all of the oil passes at some time into the high temperature region adjacent to the piston compression rings and is then returned to the crankcase...In stepped piston engines, however, this hot zone is lubricated by a simply metered small quantity of oil, on a total-loss basis. Andrew, you there buddy? Upper rings are total loss lubrication? If so, how is it metered and supplied? |
I would suspect this is done the same as in the high pressure compression world, which is my day job. We use small high pressure pumps that inject metered quantities (typically on the order of drops per minute, low single digit pints per day, running continuously) into the ring-wiped area via small bleeder holes in the cylinder wall, or occasionally through the piston itself on a few types.
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The Hooper paper mentions 1:200 ratio for oil metering. Looks like a quart of oil per 50 gallons of fuel.
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After reading about the Hooper engine design and seeing the test results I find nothing stunningly advantageous over modern 4 stroke engines. Power to weight ratios are similar at similar rpms and specific output is also similar, perhaps 10% better for the Hooper in both cases.
The oil stays clean but you have to add more and change less. Parts count is less and that should mean it may be less expensive to manufacture in the same quantities. The big disadvantage is that the BSFC figures are not very good, especially when operating on heavy fuels. Might be ok for a UAV, not so good for civilian users paying their own fuel bills. It's an interesting concept. Will be interesting to see the test figures on Andrew's E-330 engine. |
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In summary, cruising at 16,500' using 90% of rated power for a fuel flow lower than a gas engine will provide a substantial increase in cruise performance and range and cost savings vs a Lycosaurus. |
Update with additional details
The most common question is asking about the production and testing status. Andy has completed fabrication of all production spec parts and started assembly of the first batch of engines last week. They began doing non-powered testing and found a common leak in a cylinder wall near a cooling port. After they dove into the issue, it was determined a manufacturing chamfer was causing the leak so an adjustment had to be made to the cylinder castings. Those were recast this week and should be back for assembly and testing by the end of the month. That was the only issue (other minor ones had already been solved) during final assembly, so it’s going smooth. Andy was a bit surprised and quite happy that he wasn’t seeing any other defects at this point like he expected. He is still on schedule for testing and initial delivery to an OEM in February and I’m aiming for my engine in April – May as scheduled.
Testing will begin in earnest once the assembly is complete and he’s got a lot of time scheduled for dyno and bench work. He has designed and manufactured all components in accordance with ASTM standards and will be conducting testing IAW their criteria as well. This is similar to what Rotax uses and I’ll be posting the criteria on my build log once I get that page built. He will be conducting additional proprietary and endurance testing as well. The engine mount design has been finalized and analyzed for the RV-10. It uses a truss mount system with reinforcing tubing to attach the upper mounts while the truss supports the forward portion of the engine via the bed mount adapters. The trusses are currently being reviewed for ease of manufacturing as well as ability to locate accessories on the truss, eliminating the need for firewall mounting for most of the associated pumps and electrical components. The mount retains all stock bolt locations on the firewall and the nose gear strut attach points. Overall, his analysis sees a stiffness increase of 30% over the stock Van’s mount, although I cannot attest to actual details of that statement since I’m not a mechanical engineer. ![]() ![]() Andy’s goal is to offer a complete power unit to customers. This would mean the engine, engine mount, dual ECUs, ignition, sensors and harness, oil pump and filter, coolant pump, alternator (see below), and exhaust (turbo if desired at extra cost) would all be included in the purchase price. The builder would need to provide fuel pumps (see note below), coolant radiator, oil cooler, and any required cowling modifications (details coming soon on that). This is pretty different than the Lycoming packages out there now, as builders often have to piece meal the power unit together with exactly what they want. His goal is a seamless installation and complete package all designed to work together to be reliable, efficient, and powerful. I’m hoping all that is true since I’ll be the first to test it out! I’m also working hard with some help from others to sort the details out and make it successful. At this time, we are projecting using an engine master switch in the cockpit to power an engine bus consisting of all pumps, ECUs, and ignition. While some may desire a switch for each ECU and ignition, a failure of either would be indicated in the cockpit via CAN bus and a fault light (similar to your car’s check engine light). Either ECU can run the entire engine. I’m still asking about ignition coils. With the engine master, it will be possible to apply master switch power to the aircraft and not have ECUs, pumps, etc. run unnecessarily. It also allows for the master switch to be turned off in flight in the event of electrical component failure and still have power to the engine (assuming the fault isn’t in the engine bus wiring!), helping to minimize the impact of electrical faults. The alternators will be available in 40, 60, 100, and 120 amp versions. The generators that are modeled on the attached picture (on the front side of the accessory gear box just under the case, the bottom most cylinder is the starter motor) are an extremely lightweight 40 amp model that will not be included in the base package price. He left those on the drawing to illustrate the option, as some markets may want the light weight and not need high amperage output. The traditional looking alternators are spline driven and mount to the rear of the accessory gear box. One alternator of the customer’s choice of rating will be included and a second alternator will be an option. I have asked about possibly using a third on the front mounts with the B&C vacuum pad mount being the model of choice. I ask about the third because I will be using one alternator on a 24 volt system to power my AC, including the compressor, eliminating a belt driven engine mount compressor. Andy is working really hard and has every intention of keeping to the projected price of the engine. We talked for a while about the need to be competitive in the market and he understands that. He realizes that even if the engine is a game changer, no one is going to buy it for $100k compared to a Lycoming. He is aiming for accurate manufacturing, reduced parts counts, and efficiency of the design with shared parts of the V12 to keep costs under control. He is also looking to include an incredible warranty with the engine for builders. I can’t go into the details, but let’s just say that Andy will personally and professionally stand behind each engine. More details will be coming soon, and if it all works out, the warranty will be a game changer. Projected maintenance is going to be vastly different than a traditional Lycoming. With the oil not coming into contact with the combustion side of the piston, the oil is not exposed to extreme temperatures and its only purpose is to splash the connecting rods/pins and lubricate the main journal bearings. Therefore, oil changes will be few and far between. He has performed over 400 hours on one engine without needing to change the oil. This is due to the additives lasting longer with reduced heat. It will also reduce the size of the oil cooler needed. TBO conversations are ongoing and will depend on testing results. Andy does want to minimize the need for builders/users to tear the engine down. Quite frankly, he stated he doesn’t want people “dicking around” with his engine, he wants them flying it. Finally, Andy and AC-Aero will be exhibiting the new V4 Hawk at Oshkosh this year in the EAA Innovation tent! I’m sure he will get quite a bit of attention there and we all hope he has some great testing data to share with others. I aim to have mine installed and possibly test run by that time so I’ll be able to share some photos as well. I’m not sure if I’ll be at OSH or what dates I’d be up there as I just got a new role as Executive Officer for my C-17 wing here, so will be busy. Anyway, lots of information. I hope it answers some questions and generates others. We’ll have another call in a few weeks then go quiet for a while so Andy can focus on testing and delivery. Feel free to drop me a message if you’d like. Thanks! |
I'll ask Andy about the lubrication for the upper rings. I'm not sure of the details on that myself, but it's a great question to ask.
Testing will give us more specific details about power / torque curves as well as fuel burn, so I can't quote any exact numbers on that. Based on testing, the engine is expected to produce more power at less fuel flow than a Lycoming, however, that hasn't been proven with test numbers yet. |
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The Hooper engine has dreadful BSFC- especially on Jet A. |
Yes
Yes, people keep confusing this Combined Cycle engine with a Diesel compression ignition engine...it is not.
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In the engine world, this holy grail of a multi fuel capable engine has been around for a long time, particularly for military applications. The only way it is really viable (so far), is when you look at the cost of the whole gasoline infrastructure for the Navy for example. It yields a cost of over $400/gal at point of use. If the recip was as reliable as a turbine (PT6), then it's (hopefully) lower cost would provide some advantages. We should discuss off line some times. |
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