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Why are PSRUs so hard to design?

Everwild

Well Known Member
I've been reading through a lot of alternative engine threads and it would appear that there are auto based engines that check most of the boxes for aircraft. The LS3 in particular seems to have legs. The weak link seems to be reliable PSRUs.

Why hasn't anyone been able to crack the code on reliably transferring 300hp to the prop without blowing up the PSRU gears or prop?

Seems there's a fair sized market with the RV-10s, scaled mustangs, and a number of certified craft that might benefit from a 280-325hp proven auto conversion that was made up of a package of custom and off the shelf parts, run on mo-gas etc?
 
I’m not an engineer, but I think a large issue is the fact that internal combustion engines are not really ‘smooth’. A high speed camera will show the prop accelerating a bit on the power stroke, with the blade tip lagging slightly behind. As the power ends, the tip ‘whips’ back into position and may even overshoot a bit. One reason props are so expensive. Gear trains have the same problem. The teeth are alternately being driven against each other harder, then slightly relaxed, then a hard push again. This can cause all sorts of fatigue issues. Cars tend to have large, heavy flywheels on the engine side of the gearbox, along with a torque converter which allows some slip prior to the gear box. And the tires have good traction with the road preventing any high frequency whipping on that side of the gearbox. I think turbines have fewer gearbox issues, because they are inherently ‘smooth’ (continuous, not pulsed).
 
Rotax has done a good job with theirs.

Is it that a proper engineering and resources to be allocated to it?
 
It's not hard to design a reliable gearbox if you hire the right ME and vibe engineer and do proper TV and durability testing. Gonna cost some money however. Most small gearbox designs to date have been done by folks not versed or experienced in these things.

I'd argue that the Rotax gearboxes are not great designs as they never dealt with the serious TV issue present at low rpm. They simply raised the idle speed to 1400+ to move them out of this range. It works but is hardly an elegant solution as there is a lot of residual thrust for landing.

The LS engines are too heavy for any of the current RV designs. I'd be looking at some of the more modern 2 to 2.4L turbo 4 cylinders if you want to be weight competitive with a 540. A bunch of these are rated at 300-400hp and could be de-rated to 275ish for takeoff and 200 in cruise.

For 360/390 replacement, perhaps the new 1.6L 3 cylinder Toyota G16E engine would be a good choice, 268hp stock, de-rated to 200ish hp.
 
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Varying degrees of influence.

Like a lot of things, designing/applying a design only for a narrow set of conditions isn't too hard. A design for all possible conditions gets complex. One of the issues in very short summary, gearing design is greatly simplified if only driven in one direction. Gear lash is easily designed around in that condition. Pull the throttle for a decent and let the prop drive the box creates a whole new set of issues. Sure there are design mitigations but they all cost money and add weight.

Even the PRSUs designed for aviation use tend to have issues; early GTSIO contis come to mind IIRC.

If there were real money to be made, someone would do it right for EAB application.
 
I think folks tend to forget that there have been way more geared aero engines produced than direct drive ones. Almost every engine produced in the WW2 era was geared and faced much more severe operating conditions compared to droning along in cruise as most GA aircraft engines do.

Almost 1 million aircraft produced 1939-1945 worldwide, many of those multi engine- plus spares.
 
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Just real engineering, not for amateurs.

It's not hard to design a reliable gearbox if you hire the right ME and vibe engineer and do proper TV and durability testing. Gonna cost some money however. Most small gearbox designs to date have been done by folks not versed or experienced in these things.

I'd argue that the Rotax gearboxes are not great designs as they never dealt with the serious TV issue present at low rpm. They simply raised the idle speed to 1400+ to move them out of this range. It works but is hardly an elegant solution as there is a lot of residual thrust for landing.

The LS engines are too heavy for any of the current RV designs. I'd be looking at some of the more modern 2 to 2.4L turbo 4 cylinders if you want to be weight competitive with a 540. A bunch of these are rated at 300-400hp and could be de-rated to 275ish for takeoff and 200 in cruise.

For 360/390 replacement, perhaps the new 1.6L 3 cylinder Toyota G16E engine would be a good choice, 268hp stock, de-rated to 200ish hp.

This !!!!

Gear drives are no more complicated than any other core detail of an engine. The first paragraph says it all. You have to have the right expertise in engine torsional vibration and gear designs.
 
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I gained sympathy for these complications in the middle of a discussion with a Detroit OEM engine-design engineer when he started talking about 7th order vibration modes. "Seven?" I asked, and, ticking off his fingers, he listed them in order.

I was still baffled but now experiencing a headache.

Never brought it up again as I recall.

FWIW
 
TV is well understood by vibe engineers as are the methods to mitigate it. Almost every car today uses fluid/ spring damped flywheel couplings.

Most amateurs have little or no knowledge of this most critical aspect. TLAR engineering isn't the best way to approach this though some have had moderate success using this method. In my view, a successful PSRU design has to demonstrate it can go to the same TBO as the engine it's attached to.

The gearbox design itself is probably secondary to to high amplitude TV mitigation in the success of a PSRU. Eliminate or severely curtail TV and you reduce a lot of the stresses on the whole package allowing the design of a lighter, more durable gearbox.
 
The three most common types of PSRUs are: v-belt, toothed-belt, and gear type. I'm fundamentally opposed to having a "rubber band" drive my propeller. For the reasons why, have a look at some top fuel dragster slow motion shots of the supercharger drive belt. These transmit about 1500 hp from memory and they live a hard life, not only having to deal with torsional vibration from the engine to the supercharger, but also transmitted back from the supercharger to the engine. In addition to the torsional vibration causing longitudinal stretching pulses, belts also exhibit flapping between the pulleys and various frequencies.

For gear type PSRUs, previous respondents have mentioned proper design by mechanical engineers (sizing the gear teeth) and torsional vibration engineers (tuning/detuning the various vibration modes). To this I would add: the PSRU must be a light as possible commensurate with reliably transmitting the power. This light weight means smaller margins for mechanical strength.

For each different propeller (blade type and number) the PSRU must be designed/analyzed for strength and torsional vibration, and then must be tested to verify the design. In addition, the PSRU itself can create vibration modes in both the propeller and engine.

If you read the history of piston engines up to the end of their development (WW II) these engines were tested to destruction to uncover the weak areas, including the gear reduction. Very expensive. Very time consuming.
 
For each different propeller (blade type and number) the PSRU must be designed/analyzed for strength and torsional vibration, and then must be tested to verify the design. In addition, the PSRU itself can create vibration modes in both the propeller and engine.

I think one needs to design the PSRU for a specific engine and prop combination otherwise the investment in testing time and money would sink the project trying to make some sort of "universal" PSRU. This subject doesn't work that way.

I have flown behind a PSRU for 20 years and some 460 hours. It's never let me down and never been apart internally in that time but it leaves a bit to be desired and has shown some minor issues like oil seeps (bolt heads and threads not sealed), damper wear (replaced rubber bushings for $60 at 260 hours) and TV at lower RPMs (much reduced by doubling flywheel MMOI). So I have a few hours tinkering with it.

Another friend flying the same gearbox has had more numerous and serious issues, requiring multiple journeys into the gearbox. Warning signs allowed inspection and rectification before failure and it's never let him down in flight. He has 2 more cylinders, 70 more hp and a much higher prop MMOI so our experiences are somewhat different, though he's had similar seeping and TV issues.

I agree, good design by people experienced in this field followed by lots of rig and flight testing to validate is required if you want a reliable, refined and durable package and as you rightly point out, all 3 components must be tested together. They are all affected and intertwined.

Tracy Crook's PSRU design for Wankels seemed to work out well on the second iteration driving lightweight props but he is a savvy engineer who understands TV and came up with a simple and workable solution, proven over many hundreds of flight hours. I don't consider his design TLAR but rather very clever and economical. A tribute to his abilities. He proved PSRUs don't NEED to be expensive.
 
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Anyone ever experiment with a magnetic gearbox? Stumbled on the concept and wonder if it has a practical application in aircraft.

https://www.youtube.com/watch?v=MP5ah6tEi04
https://www.youtube.com/watch?v=EAELukfr2oY

No free lunch ever but seems to solve a number of problems. Guessing it's not very magnetometer friendly:) But they must be addressing that with electric motor driven aircraft.

Sure looks like a great way to do this to me. Another fun video showing a very simple implementation: https://www.youtube.com/watch?v=eaMD_9kOlTA

Magnet PSRU 3d printed.png
 
Drivetrain engineering and torsional vibration are both old sciences. The engineering world knew practically everything necessary for a reliable PSRU by 1950 or so, and today we have tools those engineers could not have imagined.

Here in EAB, we remain victims of our own ignorance. Somebody slaps something together, and everyone congratulates him on his "willingness to experiment" when in truth experimentation is largely inappropriate. It's a design engineering task...the application of known principles...but dare question the experimenter and one might think you've offered to bomb the EAA museum.
 
Dan is right from a commercial perspective. This is a job for people trained in this field if you are going to be selling PSRUs to others.

For the guy doing a one off for himself I say power to you, go out and experiment, enjoy the designing and building experience but be fully aware of what can go wrong. Best to learn all you can about TV before you start.
 
This is the Adept V6 with a spur gear reduction drive. It incorporates a cush drive in the upper sprocket. I like the journal element bearings instead of roller/ ball types as these solve many problems I've seen with other drives.

Looks to be pretty light compared to typical bolt-on drives like my Marcotte which is 47 pounds.

adept.jpg
 
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Engine Development

I've been reading through a lot of alternative engine threads and it would appear that there are auto based engines that check most of the boxes for aircraft. The LS3 in particular seems to have legs. The weak link seems to be reliable PSRUs.

Why hasn't anyone been able to crack the code on reliably transferring 300hp to the prop without blowing up the PSRU gears or prop?

Seems there's a fair sized market with the RV-10s, scaled mustangs, and a number of certified craft that might benefit from a 280-325hp proven auto conversion that was made up of a package of custom and off the shelf parts, run on mo-gas etc?

Here is a great article on the development of the Pratt & Whitney R2800:

No Short Days

While this is focused primarily on the crankshaft design and testing, it provides some excellent insight into the level of effort it takes to develop an aircraft engine/PSRU combination and resolving vibration and resonant frequency issues.

Skylor
 
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DB601 PSRUs

This is the Adept V6 with a spur gear reduction drive. It incorporates a cush drive in the upper sprocket. I like the journal element bearings instead of roller/ ball types as these solve many problems I've seen with other drives.

Looks to be pretty light compared to typical bolt-on drives like my Marcotte which is 47 pounds.

View attachment 32629

While in Germany it was fun to visit the Mercdes-Benz museum in Stuttgart since they had so many cool engines that were opened up to see the construction detail. Being a rotary in a/c guy, seeing how they engineered the internal PSRU looked to be both simple and lightweight!
 

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I think folks tend to forget that there have been way more geared aero engines produced than direct drive ones. Almost every engine produced in the WW2 era was geared and faced much more severe operating conditions compared to droning along in cruise as most GA aircraft engines do.

Very few of them were realistically expected to run for more than 100 hours or so before they were shot to pieces. Even if the airframe survived they'd pop another engine off the production line before putting it back into service.

They weren't exactly designed for endurance.

- mark
 
Massive 18+ cylinder engines run smoother than a 4 cylinder. More cylinders firing away. I'm no expert, but it seems like they'd be easier on a gear box (and propeller).
 
Very few of them were realistically expected to run for more than 100 hours or so before they were shot to pieces. Even if the airframe survived they'd pop another engine off the production line before putting it back into service.

They weren't exactly designed for endurance.

- mark

The same designs were used for civil aviation post war, almost every radial is geared, the Merlin evolved for civil and military transport in the form of the Northstar etc. Worked fine for thousands of hours.
 
Massive 18+ cylinder engines run smoother than a 4 cylinder. More cylinders firing away. I'm no expert, but it seems like they'd be easier on a gear box (and propeller).

It can be more challenging on a four cylinder where there are torque reversals than a V12 for instance but they still had to deal with TV, not just at the prop gearbox but also at the supercharger drive and other accessories. These were very complex engines with multi speed and stage superchargers, multiple magnetos etc.

If you read about the development of the big radials, it was very time consuming to understand and fix all the vibrational problems on these despite lots of cylinders.

Fortunately today, all this is well understood. Plenty of math and computer simulation available which would be big time savers over what was available in the 1940s.
 
except

Massive 18+ cylinder engines run smoother than a 4 cylinder. More cylinders firing away. I'm no expert, but it seems like they'd be easier on a gear box (and propeller).

Except the crankshaft does not go around in a circle, but a funny ellipse for all but one cylinder. This was all done with slide rules and testing, no fancy computers.
 
It's the crankshaft . . . .

Massive 18+ cylinder engines run smoother than a 4 cylinder. More cylinders firing away. I'm no expert, but it seems like they'd be easier on a gear box (and propeller).

It might seem that way, but the longer crankshafts are the challenge for torsional vibration, on stationary engines they can be much heavier to add the required stiffness. They are much more "active" than one would think.

Engine Design Factoid: Small and large engines share one key parameter - piston speeds. They relative to the expected life and performance of the engine. Our continuous power Lycoming is basically the same as continuous power diesels of the design era.
 
It may be instructive to look at the Thielert/Continental and Austro diesel gearboxes as the closest products to what we may want from the certified world. They (now) both have dual mass flywheels and are not lifed to TBO (except for low power Austros). They are used in many training aircraft so must be reasonably robust, but both solutions are heavy. The Thielert offering initially had a very short life but is now at 1200hrs.
If you have the time/money to design a sensible gearbox and the money/facilities to build & test the design it is clearly possible. But will there be a return on that investment?
 
Which Engine Platform Then?

Seems the small market and lack of EAB consensus on alternative engine platform(s) keeps the Lycosaurus going as the ubiquitous choice.

If there was critical mass consensus on <200hp, and <300hp engine platforms, then guys like Ross would probably invest in the R&D to develop well engineered, robust and reliable redundant EFII and a PSRU's.

@Ross if you could pick ANY auto engine, which platforms would you choose to build upon for the 150-200hp, and 250-300hp ranges?

Seems the auto industry push is toward very high compression, direct + port injected, turbo engines to squeeze the most out of every liter. Like the new 4 cylinder Mercedes M139 which makes 416HP out of the box.

I would imagine these high compression engines would make torsional vibration an even more significant challenge as the power pulses are going to be much higher than they are in our current aircraft engines.

After a little research Toyota, Mercedes and Subaru seem to be building 4 cylinder engines that are beefy enough for tuners and racers.
 
If there was critical mass consensus on <200hp, and <300hp engine platforms, then guys like Ross would probably invest in the R&D to develop well engineered, robust and reliable redundant EFII and a PSRU's.

@Ross if you could pick ANY auto engine, which platforms would you choose to build upon for the 150-200hp, and 250-300hp ranges?

After a little research Toyota, Mercedes and Subaru seem to be building 4 cylinder engines that are beefy enough for tuners and racers.

I toyed with the idea of designing a flat 6 geared engine about 10 years ago, around 4L displacement, pushrod, 2 valves per cylinder using as many OTS components as possible- pistons, rockers, rods, pushrods, cylinders etc. Would have had air cooled, nikasil coated, aluminum cylinders and liquid cooled heads.

We have the local capability to machine the cases and heads from billet. In the end, I was too busy with the EFI business to start a huge project like this though I was and am very interested.

If I had to start exploring automotive engines, for 4 cylinder Lyc replacements, I'd begin with the Toyota G-16E. For 6 cylinder replacement I'd investigate the 2-2.4 turbo engines that most OEMs produce today. Pick the one with the best service history and current availability of parts.
 
If I had to start exploring automotive engines, for 4 cylinder Lyc replacements, I'd begin with the Toyota G-16E. For 6 cylinder replacement I'd investigate the 2-2.4 turbo engines that most OEMs produce today. Pick the one with the best service history and current availability of parts.

Main problem that I'd see with most of the state-of-the-art engines is that they are running relatively high compression ratios, often are direct injected and need a lot of computing power (and knock sensors) to keep in check.

How well do knock sensors perform in combination with a prop? I don't know.

Ideally, one would like to retain the stock ECU, as all of the complexity of tuning that engine has been done by the manufacturer already. However with the ECU checking a zillion CANbus inputs from gearbox, aircon unit, windows regulators, dashboard, key fob and what have you, threatening you with a limp-home mode that might be safe in a car environment, but potentially lethal during takeoff, this is most likely not a very healthy path to follow. As we've learned around the turn of this century when trying to trick OEM Subaru ECUs into submission.

Aftermarket ECUs are of course available, however these seem not the easiest engines to tune. Ross, you're obviously very knowledgeable in this field. How do you see this?

In the meantime, even though it may not be the most sophisticated engine out there, I am still very happy with my Subaru, and am working on a turbocharged one on my RV3...
 
I'm no fan of DI, even in new cars as they frequently come back to haunt you with higher maintenance costs down the road. Wonderful when they are working, not so great when the injectors or HP pumps fail or your valves carbon up.

Aeromomentum removes the DI hardware on their Hyundai based engines and replaces with port type. Will have to see how that works for them in the long term.

The OEM ECUs of today are not aviation friendly for all the reasons you point out.

The Subaru EJ engines are a pretty old design now but soldier on. Their strengths and weaknesses are well known and they're mostly well supported with lots of aftermarket parts available too. I still have customers fitting them to new builds.
 
I'm no fan of DI, even in new cars as they frequently come back to haunt you with higher maintenance costs down the road. Wonderful when they are working, not so great when the injectors or HP pumps fail or your valves carbon up.

Aeromomentum removes the DI hardware on their Hyundai based engines and replaces with port type. Will have to see how that works for them in the long term.

The OEM ECUs of today are not aviation friendly for all the reasons you point out.

The Subaru EJ engines are a pretty old design now but soldier on. Their strengths and weaknesses are well known and they're mostly well supported with lots of aftermarket parts available too. I still have customers fitting them to new builds.

I fully agree with you. No fan of DI either (and especially in combination with the engine being forced to swallow its own crankcase fumes, and the valves no longer being cleaned by port injected fuel)

Didn't think one could go from DI to port type injection without also loweing the compression ratio. Interesting.... Or one simply needs to up the octane rating of the fuel? Could be.

In my view, the Subaru is not really the remarkable engine it is sometimes made out to be. 160 hp from 2.5 liter displacement is rather lame. And it isn't particularly lightweight either. But like you said - they seem to work on aircraft.

So I'm sticking to them for now... :)
 
Didn't think one could go from DI to port type injection without also loweing the compression ratio. Interesting.... Or one simply needs to up the octane rating of the fuel? Could be.

In my view, the Subaru is not really the remarkable engine it is sometimes made out to be. 160 hp from 2.5 liter displacement is rather lame. And it isn't particularly lightweight either. But like you said - they seem to work on aircraft.

So I'm sticking to them for now... :)

My 20 year old BMWs have 11 to 1 CR with port injection, run fine on 89 octane fuel at this elevation (4000 MSL). My bike is 12.8 to 1. Runs on 87 octane, also port injection. Quite doable by limiting timing at high MAP. Once MAP drops with altitude at WOT, you can start re-advancing timing. High CR is good for aircraft as MAP is lower up high.

Yes, the EJ is unremarkable, just being opposed makes it the right shape to go where a Lyconental usually resides. Pretty light in my view. My long block is about 210 pounds.
 
It's amazing, isn't it? And with fancy computers today, you'd think we'd be able to perfect those designs even further.

When you look back in time to when auto manufacturers began to rely more on computer simulations than physical testing it was not too surprising that they made some pretty severe mistakes. Like Mercedes and the A class which rolled over during the "elk test" because of a suspension design that simply had too little physical testing before it was launched (overconfidence in the computer simulation). Just shortly after that came the new generation E class engine which was supposed to set new records for fuel efficiency.... No it was worse than the engine it was supposed to replace. They had to cancel the new engine and go back to the older one until they got their problems worked out...

The point is that the people who create the "Tech" whether it be software, computer models or new computer hardware itself, they set expectations by over hyping and over promising what their stuff can do. No-one dare question the hype at a working level, because your company just made a potentially multi million $ investment to buy it and it was said that it was going to cut the development cycle from perhaps 5 iterations to maybe 2, with the corresponding reduction in physical prototypes, manpower and development time. When the new tech fails to deliver, usually the budget is already exhausted, the development time is up and the people needed to correct the situation not available because they were laid off right after buying the new Tech solution.
 
The point is that the people who create the "Tech" whether it be software, computer models or new computer hardware itself, they set expectations by over hyping and over promising what their stuff can do. No-one dare question the hype at a working level, because your company just made a potentially multi million $ investment to buy it and it was said that it was going to cut the development cycle from perhaps 5 iterations to maybe 2, with the corresponding reduction in physical prototypes, manpower and development time. When the new tech fails to deliver, usually the budget is already exhausted, the development time is up and the people needed to correct the situation not available because they were laid off right after buying the new Tech solution.

Sounds like an airplane maker headquartered in the western US. They are still re-learning this lesson I hear.
 
While many engineers of today think that computer simulation is a substitute for testing and validation, it isn't. Simulation is a tool to help you get close. Only by building something and testing it do you prove the design is sound.

I know several instances of hyped lightweight parts which were designed on CAD with FEA, which started breaking soon after market introduction. On one of them, I could tell just from looking at it that it was scary. Some folks blindly believe what the computer spits out. Garbage in= garbage out applies here.

If you estimate loads without actual load data, every calculation down the line may be compromised. FEA is only as accurate as the basic data being fed into it. Resonant vibration adds another significant dimension to many types of parts, especially those attached to engines.
 
I'm no fan of DI, even in new cars as they frequently come back to haunt you with higher maintenance costs down the road. Wonderful when they are working, not so great when the injectors or HP pumps fail or your valves carbon up.

Aeromomentum removes the DI hardware on their Hyundai based engines and replaces with port type. Will have to see how that works for them in the long term.......

Sorry for the drift. Would it be correct to assume you are limiting this reservation to gasoline engines (lubricity issues and subsequent parts life problems)?

Because of the uber high pressures required, I'm doubting I'll ever see a DI engine I'd want to fly behind regardless of fuel type. Safety/redundancy would dictate a back-up fuel pump. The weight and electrical load would be substantial, e.g. 3-4 HP or so. Unless there's a clean sheet design with two mechanical pumps, PI makes even more sense then for this application. We can dream at least.
 
This thread has drifted pretty far from the the OP for sure. I've contributed to that as well.:eek:

Multiple auto OEMs have had multiple issues with GDI hardware in the long (or even short) term. Single HP pump dependency is one good reason to question their use in aircraft but on the electronics side, control is much more complex than PI so the user will have many obstacles to tackle. Few people on this forum would either consider using a DI automotive engine with PSRU or have the resources and knowledge to make it work anyway.

The benefits of DI for aircraft applications seem questionable given the lower MAP at altitude where the likelihood of detonation is much reduced.
 
Viking

Viking is using the Honda on some of their engine PSRU combos and dumping the crankcase fumes overboard. I'm still trying to decipher if they are reliable.
 
My 20 year old BMWs have 11 to 1 CR with port injection, run fine on 89 octane fuel at this elevation (4000 MSL). My bike is 12.8 to 1. Runs on 87 octane, also port injection. Quite doable by limiting timing at high MAP. Once MAP drops with altitude at WOT, you can start re-advancing timing. High CR is good for aircraft as MAP is lower up high.

Yes, the EJ is unremarkable, just being opposed makes it the right shape to go where a Lyconental usually resides. Pretty light in my view. My long block is about 210 pounds.

Where is the like button when you need one ;)
 
We got to see the failure of one of the 130hp DI engines recently. Supposedly the oil level had been a little low, oil pressure dropped, oil squirters couldnt cool the pistons adequately, one cylinder started detonating and in seconds had blown out part of the headgasket. Coolant system got pressurized by combustion gas, dumping all the coolant overboard. Engine then overheated. Apparently the whole chain only took a few minutes.

So, what this does tell me is that the Viking system must not have working knock sensors or the ability to respond to them. I know the 150 engine that I have has knock sensors and it is recommended to replace them with a different type that is not resonant and then their use has to be programmed on a dyno. If one backs off the timing in response to knock sensors, this failure either would not have happened or else it might have taken much longer to progress giving the pilot adequate time to respond to a dropping oil pressure situation.

Here is the video https://youtu.be/19qpxutW_m4

Jan, for all the things he has done in the past seems to be going to pretty long lengths to protect his products reputation and helping customers stay in the air. Bear in mind the core engine is $1000-$1300.

Viking is using the Honda on some of their engine PSRU combos and dumping the crankcase fumes overboard. I'm still trying to decipher if they are reliable.
 
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Because of the uber high pressures required, I'm doubting I'll ever see a DI engine I'd want to fly behind regardless of fuel type. Safety/redundancy would dictate a back-up fuel pump. The weight and electrical load would be substantial, e.g. 3-4 HP or so. Unless there's a clean sheet design with two mechanical pumps, PI makes even more sense then for this application. We can dream at least.

Careful with those requirements. Every turboprop I've flown is direct injection (injectors in the combustion liner). We're talking 800psi+ and over 100gph on the PT-67D at takeoff. There is also only one high pressure fuel pump. Yes they do fail, everything eventually will. A coworker of mine had a high pressure fuel pump chew it's self to bits. But of the last 200,000 engine hours my company has flown, it's only happened once. I'll take those odds. It's also not a flimsy diaphragm pump that Lycoming uses.
 
David, do you understand the difference in complexity between a passive nozzle that is continuously fed fuel from a high pressure pump (I will come back to that characterization later) and where fuel flow is determined by the operating pressure from the pump and a vehicle common rail system where pressures are 2000+ bar or 30 000 psi and where the injectors are actuated open and close under those pressures at frequencies of 40hz. and are expected to do that with absolute precision for 2000+ hours or 288 million operating cycles ? The systems are in no way comparable at all.

So once again, do you think that a pump operating at 800 psi is comparable to one delivering 30 000psi (or more) ? Especially if one builds a multi stage pump, there are many ways to get to long lasting 800 psi pumps. If you take the Bosch VE rotary injection pump from the mid 90s, they were developing pressures over 3000 psi using a cam driven piston and have a history of lasting over 300 000 miles on the Cummins 5.9 engine. Because of having a single piston and needing to feed 6 cylinders at 3200rpm, this particular pump was being actuated at 160hz. at 6000hrs one would be looking at 3.5 billion actuations and they were a very reliable injection pump - more or less a benchmark for the entire industry and what made the modern direct injection diesel engine possible.

The later family of P series injection pumps had 1 plunger and cam for each cylinder and could support even higher pressures and higher RPM operation and they were basically the last of the pre-common rail systems out there. But much larger, heavier and needing more power to drive, thus not what I would consider optimum for an aviation application.

Careful with those requirements. Every turboprop I've flown is direct injection (injectors in the combustion liner). We're talking 800psi+ and over 100gph on the PT-67D at takeoff. There is also only one high pressure fuel pump. Yes they do fail, everything eventually will. A coworker of mine had a high pressure fuel pump chew it's self to bits. But of the last 200,000 engine hours my company has flown, it's only happened once. I'll take those odds. It's also not a flimsy diaphragm pump that Lycoming uses.
 
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