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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. |
Tim, you are putting experiment back into experimental aviation and test flight back into phase I and phase II. More power to you.
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Tim,
Thanks for the detailed update. A really good warranty and complete installation package will help people make a switch from traditional engines if the performance and durability/ reliability is there I think. |
Check out the Facebook RV-10 page for some pictures while I try to figure out my malfunctioning build log website.
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No worries, the diesel moniker was confusing to me as well initially. HFSI (Heavy Fuel Spark Ignition) might be a be a way to avoid confusion.
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Finally got the pictures loaded. More to come but I?m tired of inter web dealings for tonight!
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http://www.marineenginedigest.com/sp...-outboards.htm |
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I'll pass the feedback on about his name.
Just to clear it up, the engine is not a traditional diesel engine. It is a heavy fuel, spark ignighted engine. Moving on, I'll post an update on the fuel system as we've worked out the details on the architecture. I finally got my build log website back up to host the pictures. |
Perhaps Andrew will introduce CI versions later?
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I don't think so, or at least anytime in the near future. He's got enough on his plate getting these out and in production for some time to come. Never know though.
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Ya'll are not crazy. It was originally marketed as the "Higgs Diesel".
https://www.facebook.com/AdvancedCom...1078573388897/ |
We have finalized the fuel and cooling system layout which is pretty unique and pretty exciting. We really had to work at this to incorporate fuel as a coolant as Andy had envisioned. A comprimise was made to add a larger heat exchanger instead of only using the wings and tanks as heat exchangers, as there are times where the amount of fuel in the tanks just wouldn't provide enough heat dissapation needed.
![]() ![]() So following our super scientific Power Point, the fuel will come from the selected wing tank through a filter in the wing root to the duplex fuel valve. Airflow Performance boost pumps plumbed in parrellel will push the fuel forward of the firewall into a 1.5-2 gallon non-vented header tank and pressurize the tank and lines to 51 psi. Located on the header tank will be a pressure sensor, coolant outlet and return fittings, and injector rail outlet fitting. The pressurized tank will allow the entire fuel rail to be pressurized at the required 51 psi controlled by a pressure relief valve located after the rail. The relief port will return to the selected tank via the duplex fuel valve. The ECU will control the fuel boost pumps which will have internal overpressure protection as well. In the event of a pump failure, the ECU will automatically turn on the secondary pump and provide annunciation to the cockpit. From the header tank will also be a coolant circuit. Airflow performance pumps will be variable speed and controlled by the ECU depending on engine temperature. The primary pump, plumbed in series with the secondary pump, will not have flow throug capability to assist in keeping the engine temperature optimum. The secondary pump will have flow through capability and will be activated by the ECU if the temperature rises beyond limits and/or the primary pump fails. After the engine cooling jacket, a thermostat will direct fuel either to return to the header tank or to a heat exchanger (radiator) to dissapate excess heat. Once challenge that this solution takes care of is a requirement to heat the fuel prior to the injector rail to a minimum of 130 degrees F. This provides better combustion in the cylinders, keeping in mind that the Jet A combusts via spark, not compression. We did not want to have an inline, power zapping, electric heater for the fuel. While the engine will start and run fine on cold fuel, the optimum performance will be gained once the fuel is warm. Testing will determine if we will need to add an inline heater for cold weather ops prior to take off, but no heater will be needed in flight. Our next area of focus is on the details of the electrical system/controls/ECU. We're planning a call with Andy early next week to get a production update and discuss the cockpit controls needed as well as ECU interface with avionics. |
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Also, Is there any concern that that radiator cannot give up enough heat in ground ops? What happens during the OSH departure parade, where you are idling for 30 minutes at a dead stop in 100* ambients? To make the worst case worse, assume you started the engine already heat soaked. Don't know the boiling point for jet A, but being a multi fuel engine, this seems to be an issue running on gas, even at 50 PSI. Maybe an electric fan? Disregard the second paragraph. I see that the pressure relief is on the fuel rail, eliminating that heat issue. Larry |
You say the primary coolant pump does not have flow-through capability - so if it fails how does the in-series secondary coolant pump continue to cool the engine?
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Now we're talkin' something different.
Minor note...probably want good filtration between the header and fuel rail, given the circulation through block castings, |
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Larry |
PWM on brush type DC motors could be a bad idea. Others have noted a serious reduction in pump life and some pumps plain don't like it and don't respond well at low duty cycles. Better test that thoroughly on the bench before getting married to the idea in the airframe.
Complicated system, lots of places for something to go wrong. If you want to warm the fuel, a simple tubing loop in the coolant would do the trick. You won't be able to sink much heat into the fuel for long at high power with that small header tank capacity. |
Has one of these engines ever flown with this cooling system? Is it also for 100LL, autogas etc.?
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From an earlier post, I understood that a full scale prototype of this engine is yet to run on a stand, let alone fly. So, this is a good oportunity for feedback on the design concept.
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I regret that I didn't directly address with him the idea of trying to 'smooth' the PWM into variable DC to drive the gerotor pumps, but I did ask about using a true 'analog' variable DC voltage to drive them. He said that it would have no detrimental effect. He did not say, but I suspect, that using a variable DC voltage to control pressure using a gerotor in a dynamic environment would be frustrating, because you'd lose the full torque at variable rpm that's available with PWM. |
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We will have the option to do a fan on the heat exchanger for ground ops. I plan to incorporate that into the cooling plenum design for the heat exchanger. The fan can be run by the ECUs just like in a car. |
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We looked at a liquid to liquid heat exchanger for warming the fuel, but the most increase you can get is about 40F, not enough to get to the 130F. We're trying to avoid electric heaters since they pull so much power which could impact operations with a limited electrical system capability. |
The engine has not flown at all yet, I may be the first in a manned flying machine. There will be plenty of testing before I give it a go, though.
These are all good points, and yes, this is the time to get feedback into the design process! Thanks for the points brought up here, it's a big help. There is some inherent complication but we are trying to keep it simple at the same time. If you want to see complicated, take a look at any of our Technical Orders for the C-17. Your mind will be fried with how many things can (and usually do) break! We'd like to avoid that. |
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Should be able to get a lot more than 40F rise with oil or coolant to fuel HX. Commonly done on older GA turbine stuff. |
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Tim,
I played with this idea (fuel as coolant) quite a bit during my early building phase when it was looking like the Deltahawk might actually happen and I was drinking the Koolaid. You're right in that you'll need an air-to-fuel exchanger for at least part of the time, but you may be surprised how much heat you can dump in the wing if you'll take a couple things into consideration. I was looking at a low-pressure header tank, with the pressurized fuel pumps pulling out of the header tank to the engine. The fuel/coolant in the header tank was only going to be about 10 psi and the flow rate was fairly high, displacing a lot of it through the header tank (which would have a coolant loop through the engine) back to the wing tank through a duplex valve, and with the return line going all the way to the far outboard bay of the wing tank. This forced the returned hot fuel to flow through the tank all the way back to the inlet and wet the entire tank surface to the fuel temp, providing a pretty decent heat sink, even with low fuel levels. You'll still need some additional air cooling though - but it's reduced. Your design is using the fuel pumps themselves to produce the flow through the header - you might want to put the fuel pumps AFTER the header, and use high-flow low-pressure boost pumps to move more fuel through that header and back to the tanks for thermal transfer. |
You can sink a fair amount of heat into the full load of fuel on an RV but not a 2 gallon header tank with no recirculation to the mains.
Figure around 50-60,000 watts are being dissipated into the coolant at cruise power on a 300hp engine. |
Ross, I believe they are brushed pumps. I'll have to check my notes from Don, as I can't remember off the top of my head.
Greg, so we are right there with you on some aspects. That was how we originally thought we'd dissapate the engine heat but to Ross' point, when you get down to 5-6 gallons of fuel left in a tank (which is a reality with an hour reserve fuel left on board), you run out of surface area in the tank to bleed the heat. Then it becomes a question of how to decide where the fuel goes based on heat, wing first then up through the system then to HX first or to small HX then to wing, etc. What we are afraid of is getting to a low tank level and running out of options to get rid of the heat. So we played with the idea of a lift pump and then a boost pump from the header tank. That's still on the table as option B. I haven't gotten a 100% confirmation the cooling jacket of the engine will withstand 51 psi, so the pressurized header tank may or may not work. Our thought behind it was eliminating complexity with a need for four fuel pumps (two lift, two boost). But yes, we have a design setup with two lift pumps to the header tank, then using boost pumps for the fuel rail and cirulation pumps for the cooling cirtuit. Ross, do you have any pics or designs for a HX? I'm only finding some diesel truck stuff at this point before trying to roll my own as a test. |
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