Even Thielert / Continental and Diamond /Austro had to learn the hard way that adapting a (Diesel) car engine to aviation needs is not a simple task. Even the Mooney / Porsche project was a financial train wreck with some unpleasant surprises for the few survivors after Porsche discontinued all support.
Diesels have a couple of real challenges compared to a 6 or 8 cylinder spark engine (I detailed some of these on other threads here and on HBA so won’t rehash the engineering geeky stuff)…..weight for sure, but mostly drive shift and prsu pulse loading and resultant torsion stresses are hurdles.
There’s no perfect solution even with gas engines even though the same issues are not as big an issue. But there’s rarely a perfect solution in aviation with balancing weight, cost, reliability, ECT..
As far as the Porsche engine, Toyota also had a certified V8 engine in late 1990s that wasn’t released, the issue for both wasnt as much reliability or cert costs as reason to discontinue the line ( both already had part 33 certification), but like a NTSB report probable cause, there was more than one reason why both projects fell short. Porsche discontinued support because they payed through the nose to buy back all sold engines and additionally pay for reinstall of original engine types or buy planes back for air frame part out to mitigate loss. This allowed them off the hook to continue support requirement and put the program in the rear view mirror.
Toyota, by the time engine was certified, realized ga was just too small for needed ROI, and the new federal ga revitalization act didnt really mitigate risk as much as thought. Too bad because it would have been a game changer for ga turn around and likely spur on others.
RE marinized car engines….. most inboard engines from most brands are either ford or GM or catapiller or Detroit automotive or truck engines. This allowed marine (relatively without same resources as ga to make stuff from scratch) industry to save on infrastructures to make the things and continue to evolve with latest tech developed by billion dollar manufacturers. The mariniztion was mostly mods for cooling and some coast guard and industry safety standards. Boat engines work far harder than air boat or plane engines due to greater loads of incomprehensible water and drag coefficients. Boat and plane props obviously far different and exert different load factors…initial plane props usually need a customized prop for auto conversions to dial in efficient performance which we did initially using hand carved props for our c172 v8 prototypes ground and flight testing phases…..which allowed us cheaper and easier mods as we could continually plane/sand/cut to dial in design as no commercial prop was available as a starting point. In both aircraft and boat prop design, all reference standard and normal design calculations based on several factors such as speed, weight, power bands, ECT,
Either way, it was the same process for both ….. after this was done we needed to have it mass produced by a certified manufacturer (we were going for a STC to install our engine on multiple legacy certified airframe models and FAA required the prop have its own TC so needed a certified manufacturer to make it …so our design and data was used by sensenich to improve it and to make current production model on the c172 now). In the marinization process, we typically started with a commercially available prop and grinded away blades material to change shape and presses to change pitch and cupping during essentially a trial and error sea trials.
Mrinization allows the marine industry (a significantly smaller sized industry than automotive, as like ga size) to utilize modern tech and mass produced power plants to evolve and have lower cost. If boat engine manufacturers had to make their engines from scratch as aircraft engine makers do, the marine market would look similar to ga in titanically higher costs and old tech. This is why we did the c172 v8 engine conversion using an aluminum car engine.
As some pointed out above, auto conversions got a somewhat deserved bad wrap from the experimental world in the last couple of decades, mostly for amateur designs and junk yard doners with little to no “marinization” for aircraft mission. Personally, I think it’s the path of least resistance to revive recreational ga, others not so much.
As the cost of compliance of the above mentioned FAA inspections and mods for older ga fleet come about, it’s likely such inspections can be made, and required fixes if needed, may be made at far cheaper costs if plane is converted to experimental…..I’m not advocating cheapening out, but these airframes are simple and seems much of the proposed inspection cost is labor which could be done by owners or non part 43 certified entities, especially that of removing parts like sheets to gain access to spar or performing oil and vibration engine analysis on older engines rather than a tear down inspection or rebuilding a normally operating engine….FAA won’t like it but it’s possible if you can make some uniques changes to plane to meet the exhibition criteria. A&Ps are getting scarce and expensive to point that such upkeep could soon become non economical based on plane’s value. Compiled with such costs and that of increasing coat of hanger, insurance and gas, we my need to look outside the box soon.
