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rv6ejguy

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To date, there are quite a few mandated component replacement parts on most of the aero diesels out there before TBO/TBR, turbos, injectors, sensors, alternators, prechambers on the WAM here etc. This cuts into any fuel saving costs plus with the high purchase price, no net savings were realized over 2000 hours on a Lyc 360 according to a cost analysis done by TAC a couple years back.

Until the price comes down on aero diesels to the same level as the SI competition, they will save no money in the course of their lives in North America. In other parts of the world with high avgas prices, it's a different story.
 

PMD

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I've pointed to real world examples of SI torque and hp being much higher than CI at the same boost pressure but you continue to believe it's not true. I'll put this out there like I have for the last decade on forums- show me just one example of a diesel of the same displacement and same boost pressure putting out more torque and hp and I'll believe it. Nobody has yet.
Sorry I missed responding to this post. I have been on a remote Northern jobsite doing long hours so just quick glances at computer. I can't honestly say I have ever compared MAP to torque at comparable RPM for SI vs. CI engines, but it is very common for CI engines to be able to run very high MAP for extended times - as even the best knock sensors of SI engines run into detonation limits before CI runs into its limit (usually piston crown temp). Not sure if I mentioned restarts, but it is HPCR that allows modern CI to start at extremely low temps (equivalent to worst of altitude) and in over a half century of running diesels in the Arctic I have never had one flame out due to ingested air temp.
 
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PMD

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Joined
Apr 11, 2015
Messages
498
Location
Martensville SK
To date, there are quite a few mandated component replacement parts on most of the aero diesels out there before TBO/TBR, turbos, injectors, sensors, alternators, prechambers on the WAM here etc. This cuts into any fuel saving costs plus with the high purchase price, no net savings were realized over 2000 hours on a Lyc 360 according to a cost analysis done by TAC a couple years back.

Until the price comes down on aero diesels to the same level as the SI competition, they will save no money in the course of their lives in North America. In other parts of the world with high avgas prices, it's a different story.
All very true. It will take some time for first of all some new and more cost effective designs to hit the market (as I will continue to point out - 2 cycles most likely) and as they gain experience the component costs and service lives will get down to current SI levels. The Thilert gearbox TBR history being a typical example that is not exactly coming anywhere near decent service life - but look at the success of Rotax and getting PSRU life/cost under control
 

rv6ejguy

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Sorry I missed responding to this post. I have been on a remote Northern jobsite doing long hours so just quick glances at computer. I can't honestly say I have ever compared MAP to torque at comparable RPM for SI vs. CI engines, but it is very common for CI engines to be able to run very high MAP for extended times - as even the best knock sensors of SI engines run into detonation limits before CI runs into its limit (usually piston crown temp). Not sure if I mentioned restarts, but it is HPCR that allows modern CI to start at extremely low temps (equivalent to worst of altitude) and in over a half century of running diesels in the Arctic I have never had one flame out due to ingested air temp.
The thing is, CI engines HAVE to run much higher MAP to make the same HP as SI turbo engines. Detonation isn't an issue these days with DI on SI engines. We have plenty of SI production engines making over 110hp/L on 87 octane, 150-250HP/L on 91, some at 320HP/L on E85. By comparison, I am not aware of any production CI engines producing over 132hp/L.

I am not sure how a diesel would restart at altitudes above 18,000 feet where the effective compression ratio would be half of that at SL- so 16 to 1 would effectively be 8 to 1 up there. Lose the turbo and you'll have an immediate flame out.

The Thielert had a crappy PSRU design originally. PSRUs are very reliable if designed correctly however. There have been more geared aero engines built than direct drive ones if we count all the WW2 inline and radial engines.

Small 2 stroke CI engines haven't shown to be any more efficient to date than legacy SI aero engines running LOP, they just have a better power to weight ratios than their 4 stroke CI cousins and that is certainly important in aircraft. Witness the WAM here- no better cruise BSFC figures than an old Lyc 235 but it is quite light.
 
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tspear

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Similar stories from 0-320s that are used constantly. 3,000 hrs at car speeds = >150k miles = <300k at average flight training speeds. Not bad, but diesels should be able to go far beyond that - thus why the abject failure of putting Thielert engines/gearboxes into trainers (or anything else). IMHO, the whole Thielert experience was the aviation equivalent of the 5.7 GM damage to the automotive diesel world. VW fixed that in cars (then destroyed it all on their own) so we are just waiting for an aviation VW to show up with a decent diesel (expect 2 cycle).
Thielert was embezzlement. That is what took the company down. Yes the tech had teething problems, but what sank it was the millions stolen.

There are plenty of Thielert based engines that have run past TBR, the MPP version of the DA-42 has engines which have gone over two times past TBO before being sent in. From a Diamond web Q&A presentation, Diamond and AE staff stated the the engines which have come back for overhaul have had no noticeable wear on the case, or core components for engines used in the DA-42, either the NG platform or the MPP. They did express concerns about the accessories, which are "aviation" parts actually. The car parts seem to be doing better.

Tim
 

tspear

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Feb 12, 2014
Messages
987
Location
Outside Boston
To date, there are quite a few mandated component replacement parts on most of the aero diesels out there before TBO/TBR, turbos, injectors, sensors, alternators, prechambers on the WAM here etc. This cuts into any fuel saving costs plus with the high purchase price, no net savings were realized over 2000 hours on a Lyc 360 according to a cost analysis done by TAC a couple years back.

Until the price comes down on aero diesels to the same level as the SI competition, they will save no money in the course of their lives in North America. In other parts of the world with high avgas prices, it's a different story.
I have crunched the numbers comparing the DA-42 and the SR22 many times. TCO is pretty close to a wash in the states for the engines/prop. The SR22 and the DA-42 both work out to be roughly $200 an hour airplanes for engines/props OpEx plus reserve. The SR22 wins though because the CapEx is much lower if you are willing to accept no FIKI. When you start getting into FIKI, the CapEx difference declines.

Tim
 

lelievre12

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Jul 15, 2020
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The thing is, CI engines HAVE to run much higher MAP to make the same HP as SI turbo engines. Detonation isn't an issue these days with DI on SI engines. We have plenty of SI production engines making over 110hp/L on 87 octane, 150-250HP/L on 91, some at 320HP/L on E85. By comparison, I am
The thing is, CI engines HAVE to run much higher MAP to make the same HP as SI turbo engines. Detonation isn't an issue these days with DI on SI engines. We have plenty of SI production engines making over 110hp/L on 87 octane, 150-250HP/L on 91, some at 320HP/L on E85. By comparison, I am not aware of any production CI engines producing over 132hp/L.

- Yes is true on cars. Zero detonation issues these days. However in planes running 100LL many 'modern engines' in planes don't monitor Lambda due to lead fouling of the o2 sensors. They leave them out. The ECU's therefore run 'open loop' where you hope that the programmer accounted for the myriad of operating conditions to retain FAA mandated detonation margins. You also pray that the default mapping upon a sensor fail is equally generous with fuel. Great if you have a good programmer, not so good if your experimental was garage built in Minnesota and you now fly in Vegas. Or if your converted car engine is purchased from folks whom really don't know what they are doing.

I am not sure how a diesel would restart at altitudes above 18,000 feet where the effective compression ratio would be half of that at SL- so 16 to 1 would effectively be 8 to 1 up there. Lose the turbo and you'll have an immediate flame out.

- Its actually pretty hard to start a Diesel with less than ~12:1 unless your glow plugs are good. Flameouts of CI at altitude should definitely be avoided. I've never tried it with my Thielert, however if the engine could be freewheeled on the prop (steep) dive there may be enough mass flow to spool up the turbo and increase combustion pressure. Not sure.

The Thielert had a crappy PSRU design originally. PSRUs are very reliable if designed correctly however. There have been more geared aero engines built than direct drive ones if we count all the WW2 inline and radial engines.

- CI PSRU design was cursed with the much stronger harmonics of CI engines. Early Thielert managed the torque pulses by retaining a clutch plate that was designed to slip at the RPM ranges where harmonics were a problem. Here is a pic of mine.

1623507773698.png


The PSRUs rarely failed in early engines so was not 'crappy' per se. However the clutch plates sure failed. Oil contamination, wrong friction material etc etc. They would burn out and lose drive. These days those problems are in the past as all CI makers use modern dual mass flywheels which eliminate the harmonics. However they are a lot heavier........

Small 2 stroke CI engines haven't shown to be any more efficient to date than legacy SI aero engines running LOP, they just have a better power to weight ratios than their 4 stroke CI cousins and that is certainly important in aircraft. Witness the WAM here- no better cruise BSFC figures than an old Lyc 235 but it is quite light.

- Actually some 2 cycle engines are getting pretty **** good. The weight advantage coupled with good full power BSFC easily beats many turbo lycosaurs which run low CR and much higher ROP BSFC at rated power to avoid detonation. As one crappy example my TSIO520 are runs >35GPH at takeoff power. Thats 0.67 lb/hp/hr. Bombardier E-TEC easily beats that all day long. Most dyno tests I have seen of the E-Tec are in the 0.58lb/hp/hr range at rated power. And that's a 170HP engine you can lift with one hand.

 
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Andy_RR

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Sep 29, 2009
Messages
308
Location
Melbourne, Australia
Mark Wilksch tells me that despite the relatively poor BSFC of the IDI WAM120 they would routinely plan about 20%-25% less fuel burn on their demonstration Thorpe T211 compared to a typical O-200 example. Despite not being invovled in the current WAM operation - which is sadly a husk of its former self - Mark is endeavouring to support WAM flyers via this Facebook page, Mark also flies his own RV-9A with a WAM120 installed.
 
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lelievre12

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Jul 15, 2020
Messages
137
The WAM spec BSFC is .49/lb/hp at full power. My TSIO Clunkinental is 0.67/lb/hp.

The WAM spec cruise BSFC is 0.43/lb/hp and my Clunkinental is the same when LOP.

2 stroke WAM beats Clunkinental particularly with the better full power BSFC in not requiring excess ROP fuel to avoid detonation/high CHT.

Clunkinental can be tuned for better full power economy but the trade off is higher EGT/CHT and resultant mid time top overhauls.
 
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