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Sagebrush posted:What's the tradeoff? Just shorter maintenance intervals? The standard 2,000-hour overhaul for a GA piston engine works out to like 90,000 miles in a car engine; certainly that's shorter interval than anyone would use for their car but also I bet the 2,000 hours is highly conservative. This gets into the subject of 200 threads on the HBA forum. There's a few funny things going on. More than a few... so lets start at the begning. Airplane engines are: Operated at full throttle most of the time. (Though not full manifold pressure..) Operated at 70-100% of maximum rpm most of the time. Turn a reasonable rpm for directly driving a propellor. Are built on 1940's technology and materials. Are usually air cooled. Have have antiquated cam and port profiles. Have antiquated combustion and piston designs. Have little ability to self regulate their cooling. Are very, very large leading to bearing compromises. Have large pistons, leading to ring compromises. Burn significant amounts of oil. Leak oil. Are very carefully maintained. Are built to the tune of hundreds of examples a year. Auto engines are: Operated at high manifold vacuums most of the time. Operated at 5-20% continuous power output most of the time. Turn rpm that are completely incompatible with efficient propeller design. Are built on modern technology. Are water cooled. Have modern port and cam profiles. Have modern fast burn cylinder head designs. Have very good temperature control. Are generally quite small, allowing for stiffer rotating assemblies, and smaller bearings. Have small pistons, and have good piston ring control. Generally don't burn any oil. Generally don't leak, anything. Are poorly maintained. Are built to the tune of 100,000's per year. Engine weight gets into a funny place. Some auto engines are very competitive for aero engines for a given horsepower level. The big difference you'll see between say... that camry versus lycoming comparison is that the camry engine is going to get 20-30% better fuel economy. Though, that's not a really good comparison. In the case of that cigar plane that never flew... American aluminum v8's are lighter than the equivalant Aero engine. And can withstand much more horsepower. If you have a gearbox, for a given 450lb powerplant, you could be seeing two, or three times the horsepower, and be able to do it for usefully long periods of time. Generally speaking, aero engines are very flimsy affairs. They use an engine construction method that hasn't been used in the automobile world since the 1930's. That, combined with the very large crankshaft and then even larger conrods, leads to a quite heavy engine. You could probally knock 1/3 of the weight off an O-360 if you started over again today. Between modern thinwall casting methods, siamesed cylinders and cylinder heads, and modern bearing design choices, you'd easily knock 6" of length, and 3" of width off the engine. This is the big difference between an O-200 and the Corvair that people seem to like to put in homebuilt airplanes. it's amazing that "the better engine" is still 1960's tech. PT6A posted:My hunch would be that turboprops are superior to piston engines for anything beyond the smallest applications, so they've largely replaced them, but turbofans are only superior to turboprops for specific mission profiles, which is why the two exist side by side. Jet engines are generally superior, as long as you're operating at near maximum power output. As soon as you start spending a lot of time at part throttle, piston engines are much, much better. The biggest factor that we can easily control for in and engines BSFC is compression ratio. Turbines have really bad compression ratios unless they're operating at their maximum output. Turboprops are just jets with "low airspeed speed adapters" on them. Hah. There are also some really troubling scaling issues with turbines, while "in theory" you could build a turbine with any given power output, as you scale turbines down, the bleed air around the edges of blades, rotors, bearings, and cooling spaces start to matter more and more. It also starts becoming a bigger and bigger issue handling the boundary layer restrictions, and cooling of parts. Even on something like a J79, many cooling passages are smaller than your pinky! If fuel economy, or the need to throttle are on the menu, pistons are superior. If you just want to get up, and get there fast, turboprops win.
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Mar 20, 2018 16:24
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Crap, that just reminded me, I have an O-235 cam in my desk - I should see if there's any lobes that are in good enough condition to measure on my work's cam checker.
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Mar 20, 2018 17:05
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Turbines can be throttled near instantly in automotive applications at the sacrifice of even more fuel economy  . The second iteration of the Howmet TX ran it's engine at full power the whole time and just dumped the excess turbine gasses, bypassing the power turbine, in low/partial throttle conditions like braking and cornering. Since the engine just ran full power the whole time and diverted power to the wheels as needed, the vehicle had full torque from dead stop and instant throttle response.
um excuse me fucked around with this message at 17:34 on Mar 20, 2018 |
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Mar 20, 2018 17:29
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That propeller looks like it came out of an air conditioner condenser unit.
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Mar 20, 2018 19:15
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Bad Angus! Bad!
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um excuse me posted:Turbines can be throttled near instantly in automotive applications at the sacrifice of even more fuel economy Turboprops aren't all that far form that.
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Mar 20, 2018 20:02
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This may be a long term AutoX strategy for me, since fuel consumption is virtually inconsequential. I just need to find a PW200 for cheap.
um excuse me fucked around with this message at 20:12 on Mar 20, 2018 |
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Mar 20, 2018 20:09
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um excuse me posted:Turbines can be throttled near instantly in automotive applications at the sacrifice of even more fuel economy That's neat. After I read your first sentence I said "uhhhh no, it's the opposite" until I finished the rest of the post.
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Mar 20, 2018 20:22
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Nerobro posted:Turboprops aren't all that far form that. Depends. Garretts are like what you say. They're single spool, so the entire thing runs at the prop RPM so if you're already in flight, it's ready for an immediate power application and the prop will go to coarse to accept it. [Edit for clarity: of course the prop RPM is way lower due to gear ratio, I mean that they're geared together and always running at the same percentage of max RPM.] The more common PT6 family has the core running separately from the prop, so if the power lever is at idle, the core will be at low RPM too, even if the prop is at full RPM; and will therefore suffer from spool up lag. vessbot fucked around with this message at 21:24 on Mar 20, 2018 |
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Mar 20, 2018 20:28
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I'll be interested to see if the design needs of hybrid vehicle engines have better overlap with piston aircraft design goals. Spinning a generator in the peak efficiency band all the time seems a lot more in line. There's an unseen renaissance in internal combustion tech in the last 10 years that nobody cares about because cars aren't cool anymore, but stuff like FCA's MultiAir system and Nissan's upcoming variable compression crankshaft are loving amazing. We really don't appreciate how crazy it is for mundane 4-cyl passenger sedans to be pushing 300HP.
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Mar 20, 2018 21:10
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shame on an IGA posted:I'll be interested to see if the design needs of hybrid vehicle engines have better overlap with piston aircraft design goals. Spinning a generator in the peak efficiency band all the time seems a lot more in line. The 4 cylinder mustang outputs 310 hp. The old v8 5.0 was what, 220hp?
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Mar 20, 2018 21:19
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hobbesmaster posted:The 4 cylinder mustang outputs 310 hp. The old v8 5.0 was what, 220hp? The Honda S2000 got almost 250 horsepower out of a naturally-aspirated 2-liter 4 cylinder. And that wasn't even an insanely expensive car. Current turbo-boosted cars routinely get well north of 150 horsepower/liter. There's a freaking Volvo wagon that gets 180. It's ridiculous.
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Mar 20, 2018 21:26
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shame on an IGA posted:I'll be interested to see if the design needs of hybrid vehicle engines have better overlap with piston aircraft design goals. Spinning a generator in the peak efficiency band all the time seems a lot more in line. Converting the output of a piston engine to electrical energy, then back into rotational energy at the propeller will always be less efficient than just directly driving the propeller from the piston engine. What would work better, however, is like an integrated starter/motor-generator working in combination with a piston engine. Size the piston engine that its maximum output is just a bit more than the aircraft needs to cruise, then have the electric motor provide supplemental power for takeoff, climb and whatnot, which is usually limited to 15-20 minutes per flight. Additionally, use the windmilling propeller to generate power on descent to charge the battery/whatever is used.
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Mar 20, 2018 22:07
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vessbot posted:The more common PT6 family has the core running separately from the prop, so if the power lever is at idle, the core will be at low RPM too, even if the prop is at full RPM; and will therefore suffer from spool up lag. The PT6 (and other free turbine designs) allows more core speed variability. But the difference between flight idle, and full power is still not a big jump. Ground idle is another thing entirely...
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Mar 20, 2018 22:22
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shame on an IGA posted:We really don't appreciate how crazy it is for mundane 4-cyl passenger sedans to be pushing 300HP. I do, because I remember when the V8 mustang made 215 hp in the late '90s.
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Mar 20, 2018 23:11
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Nebakenezzer posted:I do, because I remember when the V8 mustang made 215 hp in the late '90s. And not the 150hp v8 out of the grand marquis? *shivers*
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Mar 20, 2018 23:19
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Nerobro posted:And not the 150hp v8 out of the grand marquis? *shivers* Chevy’s 307 smallblock put out as little as 115.
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Mar 20, 2018 23:25
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shame on an IGA posted:We really don't appreciate how crazy it is for mundane 4-cyl passenger sedans to be pushing 300HP. While it wouldn't be quite apples to apples, it would be interesting to see how long a 300 hp car motor could run at 80% power before something broke. Either actually running back and forth across the salt flats or mounted on a bench with fans blowing equivalent speed for cooling.
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Mar 20, 2018 23:28
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Nerobro posted:Generally speaking, aero engines are very flimsy affairs. They use an engine construction method that hasn't been used in the automobile world since the 1930's. That, combined with the very large crankshaft and then even larger conrods, leads to a quite heavy engine. You could probally knock 1/3 of the weight off an O-360 if you started over again today. Between modern thinwall casting methods, siamesed cylinders and cylinder heads, and modern bearing design choices, you'd easily knock 6" of length, and 3" of width off the engine. This is the big difference between an O-200 and the Corvair that people seem to like to put in homebuilt airplanes. it's amazing that "the better engine" is still 1960's tech. Yeah but monobloc engines look boring. e: So pretty:  https://oldmachinepress.com/2014/01/12/nordberg-stationary-radial-engine/ Platystemon fucked around with this message at 23:37 on Mar 20, 2018 |
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Mar 20, 2018 23:35
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hobbesmaster posted:The 4 cylinder mustang outputs 310 hp. The old v8 5.0 was what, 220hp? The 1986 SVO Mustang was a 2.3L turbo outputting 200hp and 240lb-ft, not shabby for that era, albeit a limited production vehicle. Looks like they were predicting the Mustang of 30 years later. No idea how the reliability of those is though!
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Mar 21, 2018 00:04
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Ola posted:While it wouldn't be quite apples to apples, it would be interesting to see how long a 300 hp car motor could run at 80% power before something broke. Either actually running back and forth across the salt flats or mounted on a bench with fans blowing equivalent speed for cooling. If my 24 Hours of Lemons experience is any indication, maybe two hours at at time.
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Mar 21, 2018 01:59
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Platystemon posted:Yeah but monobloc engines look boring. "This engine displaced 29,556 cu in (484.3 L) and produced around 2,000 hp (1,500 kW)." Okay, so those anemic 1970s V8s are starting to look pretty good now.
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Mar 21, 2018 02:20
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Phanatic posted:"This engine displaced 29,556 cu in (484.3 L) and produced around 2,000 hp (1,500 kW)." yeah but they made that at 400 RPM. If they could turn fast enough to spin a propeller you're talking about 10,000 horsepower. At auto engine speeds 20-25,000.
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Mar 21, 2018 02:51
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Sagebrush posted:yeah but they made that at 400 RPM. gently caress, that's 26k ft-lbs of torque at 400 rpm. That's pretty drat impressive.
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Mar 21, 2018 04:20
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charliemonster42 posted:gently caress, that's 26k ft-lbs of torque at 400 rpm. That's pretty drat impressive. That whole article is wonderful. quote:In 1956, a 12-cylinder Nordberg radial engine was put into service at the municipal power plant in Winterset, Iowa. This engine is still in service as of 2016. In 1957, three 11-cylinder Nordberg radials were installed in the South Florida Water Management District Pump Station S-9, just west of Southwest Ranches, Florida. Each of these engines powered a pump with a 143,625 gpm (543,679 L/m) capacity. These Nordberg radials were retired in 1989 because of the scarcity of spare parts. One of the engines is currently on display at John Stretch Park in Lake Harbor, Florida. Nine 12-cylinder engines were installed in the Wastewater Treatment Plant at Deer Island (Boston), Massachusetts in 1968. Over five years, each engine had averaged 22,315 hours of operation. This equates to the engines running 12.25 hours a day, every day, for five years.
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Mar 21, 2018 04:31
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The Lycoming O-360 is practically a large displacement ancient VW beetle/van motor that costs a loving grip to rebuild. loving FAA can go spin its collective rear end in a top hat on a rusty spike. A turbocharged Subaru engine with conversion and a prop gear box does fine.
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Mar 21, 2018 05:20
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Yeah, no offense, but I really don't trust a Subaru motor like I would a Lycoming or air cooled VW.
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Mar 21, 2018 12:13
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CommieGIR posted:Yeah, no offense, but I really don't trust a Subaru motor like I would a Lycoming or air cooled VW. evil_bunnY fucked around with this message at 13:57 on Mar 21, 2018 |
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Mar 21, 2018 12:32
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The more modern Rotax and Jabiru piston engines aren't shining beacons of reliability either, I think any single engine piston flight is inherently a bit sketchy regardless of manufacturer. We are having our O360 overhauled right now, it made it over 2000 hours but had all 4 cylinders replaced at various times. Cost with new cylinders is just over $24k plus the labor to remove and reinstall it.
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Mar 21, 2018 13:49
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sanchez posted:The more modern Rotax and Jabiru piston engines aren't shining beacons of reliability either, I think any single engine piston flight is inherently a bit sketchy regardless of manufacturer. A lot of the sketchiness of air cooled piston engines in aircraft is because we still let the seat-monkey control fueling, and have no real way to evenly cool the engine. (Or prevent it from cooling too rapidly, for that matter.) You can’t expect modern engine reliability from an engine with cooling, fuel, and spark control from the 1920s.
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Mar 21, 2018 14:00
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We'd have much better engines in small aircraft if it weren't so costly to certify something modern to replace these ancient and yet absurdly expensive to overhaul designs. Yeah, I know that lots of FAA regulations are written because people died. I have to wonder how many engine related incidents could have been avoided if pilots didn't have to gently caress with the mixture or worry about managing engine temperature or getting ice in the carb etc etc. poo poo, we should be pushing to get lead out of aviation fuels, but there are too many ancient engines flying around that would munch valves without it.
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Mar 21, 2018 14:21
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EightBit posted:We'd have much better engines in small aircraft if it weren't so costly to certify something modern to replace these ancient and yet absurdly expensive to overhaul designs. The new Part 23 rules just took effect recently (end of 2017, I think,) but I’m not aware of any aircraft or engine that has been certified through the new process, yet. There is a significant push to dispense with 100LL, but as you mentioned, a minority of the GA fleet can’t run on anything else, and that minority of the fleet burns the majority of the fuel used every year. It’s a difficult problem.
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Mar 21, 2018 14:29
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the complete lack of technical advancement in aviation piston engines in the last 50+ years is beyond frustrating
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Mar 21, 2018 15:08
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MrYenko posted:There is a significant push to dispense with 100LL, but as you mentioned, a minority of the GA fleet can’t run on anything else, and that minority of the fleet burns the majority of the fuel used every year. It’s a difficult problem. Correct me if I'm wrong, but isn't the main problem isn't that these engines need some amount of lead for whatever reason, but rather that no one's been able to formulate 100-octane fuel that has the appropriate physical characteristics for aviation use while also being economical to produce? Another problem is that, although there are piston engines that run on Jet A now, they aren't attractive to training fleets because you have to convert the entire fleet at once or buy a new fuel tank. EightBit posted:I have to wonder how many engine related incidents could have been avoided if pilots didn't have to gently caress with the mixture or worry about managing engine temperature or getting ice in the carb etc etc. We have fuel-injected engines now that avoid the issue of carb icing, and I can't imagine a circumstance where one wouldn't have to worry somewhat about engine temperature. Short of liquid-cooling systems, which are heavy as gently caress, you're always going to have to be somewhat mindful of how power, temperature and airflow are interacting to cool your engine. PT6A fucked around with this message at 15:19 on Mar 21, 2018 |
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Mar 21, 2018 15:15
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e.pilot posted:the complete lack of technical advancement in aviation piston engines in the last 50+ years is beyond frustrating Are we at least pushing incentives for advancement, i.e. taxing the hell out of leaded fuel and thus covering the externalities of its continued use?
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Mar 21, 2018 15:25
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Potato Salad posted:Are we at least pushing incentives for advancement, i.e. taxing the hell out of leaded fuel and thus covering the externalities of its continued use? Of course not.
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Mar 21, 2018 15:30
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evil_bunnY posted:I've never looked at suby motors but aircooled VW are not something I'd want turning the screw on any aircraft I'm on. https://en.wikipedia.org/wiki/Volkswagen_air-cooled_engine#Aircraft VW aircooled motors have been well proven as aircraft engines. Here's a Cessna 172 with a 180HP Turbodiesel https://www.youtube.com/watch?v=aY6DOG5pjW0 CommieGIR fucked around with this message at 15:33 on Mar 21, 2018 |
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Mar 21, 2018 15:31
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CommieGIR posted:Yeah, no offense, but I really don't trust a Subaru motor like I would a Lycoming or air cooled VW. Most of them don't burn oil right off the factory line!
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Mar 21, 2018 15:42
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Ola posted:While it wouldn't be quite apples to apples, it would be interesting to see how long a 300 hp car motor could run at 80% power before something broke. Either actually running back and forth across the salt flats or mounted on a bench with fans blowing equivalent speed for cooling. A lot of commercial generators use engines from the automotive world. I think these would be a good example of what sort of power output you can reliably get from one of these engines under a continuous load. Generac for example will sell you a 5.4L 2V Ford Modular motor, rated for 230-260 HP peak in the trucks it shipped in, driving a 50kW generator while running on natural gas or propane. It's producing 80 HP at 1800 RPM when operating at rated power.
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Mar 21, 2018 16:33
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Speaking of differences between aviation engines and car engines, does anyone know why maintenance intervals and break-in periods for automotive engines are given in distances instead of hours? Presumably highway miles are way easier on all a car's systems than the equivalent distance driven in the city. Is it just because cars don't have the equivalent of a Hobbs meter?
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Mar 21, 2018 16:56
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PT6A posted:Speaking of differences between aviation engines and car engines, does anyone know why maintenance intervals and break-in periods for automotive engines are given in distances instead of hours? Presumably highway miles are way easier on all a car's systems than the equivalent distance driven in the city. Is it just because cars don't have the equivalent of a Hobbs meter? Vehicles that I know of which spend most of their lives idling (airport ground equipment) do have Hobbs/hour meters installed, but they're being maintained a lot differently than a road car.
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Mar 21, 2018 17:02
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