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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old January 31st, 2018, 09:27   #31
1.9ZOOK
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When it comes to an airplane engine,I think I'd rather have high RPM horsepower over
torque any day.
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Old January 31st, 2018, 15:49   #32
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Quote:
Originally Posted by 1.9ZOOK View Post
When it comes to an airplane engine,I think I'd rather have high RPM horsepower over
torque any day.
Not really....My Lycoming has a redline of 2700rpm! Mind you it's 320cu in with a 5 inch bore. Don't think I've ever seen a torque rating for it anywhere, but it makes 160hp.
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Old February 2nd, 2018, 06:22   #33
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Quote:
Originally Posted by Powder Hound View Post
I really love the 'near certification' or 'very near certification' language used to describe new engine projects in general aviation. Apparently, from looking at the wreckage of chapter 13, chapter 11, and completely dead companies that were very near certification, this terminology is a clear display of the 90-10-90 rule. That is, the design, engineering, manufacturing of prototypes, acceptance, starting of a test program, getting the FAA to promise to work on it, getting the work done, going through any number of test, re-engineer, re-manufacture, test again scenarios, and getting to that 'very near certification' point will take at least 90% of your funds, provided you have a budget measured in cubic $$. Getting past that last 10% hurdle will take the other 90% of your funds (meaning: at least 80% more than you'll ever raise).
Seriously, the herculean effort of trying to get a new engine certified these days explains very well why we aren't seeing any new engines making it to the certificated airplane engine market.
And the fun part is this: even if you manage to get an engine certificated, you still need to get a certificate for each and every airplane model you want to install it into. So if you want to install it into an airplane, and want to change anything about that engine compartment, you'll need to certify it yet again.
I think the GA market is going to evolve into foreign manufactured airframes and experimentals, with the latter taking the largest portion. And companies like Deltahawk, well, there aren't really companies, there's only Deltahawk. The only reason they've survived this far is with sales to the military who don't really need FAA certification to fly a drone. They have expended all the resources of several well-heeled investors, and the only reason they've survived is by selling the company to someone else (the Ruud family if my memory serves). Yes, they have made some very small fortunes, by starting with very large fortunes.
But that is the way it is with airplanes.
I want to build one, someday. But I'll probably be forced to content myself with rebuilding a Corvair engine (which compare very favorably with the similar offerings from lycosaur engines), and if I want to really jazz it up figure out how to do a blown direct injected 2 stroke with liquid cooling. A wankel will be fun to work on in the spare time, if I can figure out how to do a reduction drive that doesn't weigh more than a substantial boat anchor like the Ross unit does.
Or maybe I'll just rescue TDIs, turn them into trucklets, and go feral pig hunting to feed the family.
Cheers!
PH
Yes, what you say is quite true. However, fortunately there ARE a few genuine companies who are actually capable both technically and financially to crack the FAA nut. SMA is the government of France, so they certainly can finance their certification projects, but more to the point, they are the ONLY one thus far to figure out that genav engines are far simpler when direct drive and only make sense when compression ignition. The 305/230 SHOULD have been installed in every airframe that needs that power and can manage the weight, but EADS/Socata/SMA/Renault was and is not very good at understanging the business climate in North America. When they say their 460 is nearing certification, I mean European, with FAA to follow. They have some exceptionally smart features (full mechanical backup, direct drive, air cooling, conventional layout) and there is no question they will get to where they have announced, not sure exactly when.

Austro was a fantastic example of Diamond starting from scratch and getting auto based diesels into certified production in a very short time. Proves it CAN be done. EPS is another good example - clean sheet of paper, have met and exceeded EVERY design goal from the onset, properly financed, not a lot of really deep pockets, but well on the road. I expect to see them selling their engines in 2018 strictly into the certified market (initially all retrofit).

Note how many clean sheet spark ignition designs have been certified recently...I count NONE (the last IIRC was Orenda - also BTW automobile based). If you are going to have a piston engine that makes any sense, it will be a legacy design with some updates (ignition and eventually injection) or it will be a diesel.

What kills things these days are three major factors: #1 is the massive fleet of existing airplanes vs. the shrinking ranks of licensed pilots. We won't have a significant market for new airframes in the certified range for many years or decades. #2 is the ridiculous price of almost everything. The Soloy STC for SMA is a good example. I can remember a time when Joe Lunchbucket could easily afford to slip into the Mom and Pop flight school and order up a shiny new 172 (although I never did figure out WHY one would do that!!!) on a single income and mortgage. Since we discovered real estate with no limits, the vast majority of families in larger urban areas have two people working flat out to pay for "location, location, location", plus our addiction to more "stuff" dramaticaly shrinking the pool of discretionary spending money for airplanes. Finally, #3 is the really big one: lawyers. When Cessna suspended production of light singles in the '80s, more than half of the cost of an airplane was insurance premiums! With an army of ambulance chasers looking to pounce on the weakest member of the herd, airframe and engine manufacturers are simply not smart to be doing business inside of the US borders.

Your comments on gear drives significant. IMHO anyone using a 4 cylinder engine and trying to use a gear drive is nuts. The nature of cyclical variation in torque of such an engine dictates that it be huge and have a phenomenally good drive coupling/damping. Even with the right number of cylinders (i.e. 5 or more for a 4 cycle, 3 or more for two cycle) remember that Lycoming and Continental both had certified, gear reduction 6 bangers back in the day. They are long out of production and overhaul costs are eye watering.

We can only hope that the re-write of FAR 23 will make the climate for aviation business better here than it has been for some time. But without addressing the legal liability lottery, not only aviation but a LOT of other manufacturing jobs and businesses will continue to be sourced offshore.

BUT: I predict that EVERY new genav engine for the foreseeable future will indeed be a diesel. The advantages are just far, far too great to continue wasting time trying to use a truly idiotic fuel and technology to fly higher, further and faster.
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Old February 2nd, 2018, 06:33   #34
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Quote:
Originally Posted by 1.9ZOOK View Post
When it comes to an airplane engine,I think I'd rather have high RPM horsepower over torque any day.
Horsepower is simply an expression of the amount of torque multiplied by RPM to produce power. The shape of the torque curve determines the shape of the power curve, but the limit on RPM is propeller efficiency. The larger the prop diameter, the more efficient it is. The limit on prop RPM becomes the speed of sound. As the tips go into the transonic region, the noise made and efficiency of the system becomes a BIG problem, thus the 6' props out there will all stop at 2700 or less RPM. Gasoline engines (and little automobile diesels) need to turn up a fair bit more RPM to make enough power to get the power/weight ratio needed to drag an airplane off of the ground. Problem is: those gear drives are exceedingly difficult to make reliable and economically viable. Thus, direct drive, and those PRM ranges (2500ish for 200ish HP engines) are duck soup for diesels to run sufficiently high boost to get the torque curve fat enough to make the required power at that speed - without having to be a monstrous displacement.
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Old February 4th, 2018, 11:46   #35
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Well said. Another big plus on the side of compression ignition is the promised demise of 100LL. Hard to fly an airplane that only allows that fuel if that fuel is not available. I think that's the only reason you can still get 100LL anywhere.

I like the idea of a turbocharged direct injected 2 stroke because to me it is probably the easiest way to get a reasonable amount of power (180-200hp range). I've seen people poo-pooing this claiming that 2 strokes are dirty, smoky, inefficient. That those people are sadly uninformed as to the current state of affairs is funny, since the comments came from member(s) of this forum who should know better than to regurgitate old obsolete information.

I think liquid cooling will be the best way to solve the cooling problem due to the waste heat generated by this scheme in the space that heat is generated. If I was able to do this with a converted Corvair, I just don't think the air cooling fins on the OEM cylinders and head are sufficient. And there might be a bonus weight differential since the structure required for the cylinder head on a valveless liquid cooled head (the blown 2 stroke is ported) is much smaller and lighter than any air cooled 4 stroke head.

But, my idea may never see the light of day. As always, massive funds that I don't have are required.

Oh, well. OTOH, a regular 100hp converted Corvair can easily run the smaller Zenith STOL air frames. Fun!

Cheers!

PH
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Old February 7th, 2018, 18:32   #36
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Power Hound; here is your 2 stroke supercharged (100HP) turbo compounded (125HP), light and liquid cooled - just not your regular grandfather`s Oldsmobile block.

http://www.geminidiesel.aero/aviation

Should be VERY close to release to the homebuilt market.
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Old February 7th, 2018, 18:40   #37
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That design was used in naval ships.
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Old February 7th, 2018, 19:33   #38
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Also used in British delivery vans for many years and the Chieftain tank both main and its smaller generator engine. The opposed piston seems like a great way to do 2 stroke and having driven a chieftain I'll say that they sound really cool. On the other hand there have been a lot of issues over the years with the details like most engines find. Two cranks with a connecting shaft/reduction create some reliability issues. The need for a blower to feed the air in is also a problem. There is no fail safe if the blower or its drive fail.

Some have said that reduction drives are no big deal and point out the engines used from pre WWII and later. The Merlin, Alison and others of that type-V12, High HP etc all used a reduction drive to keep their huge props in a more efficient speed range while allowing the engine to run at a higher rpm for better efficiency and power. They did work pretty well but if you look into the manuals and specs you find that the redrives had to be overhauled at riduculously short periods. The Merlin wasn't meant to run for 2000 hrs like our ancient tech lycoming/continental flats. A couple hundred hours on a Merlin was an exception rather than a rule. Part of this was the power output demanded from the displacement and part was the redrive.

Radials also used reduction gearing to keep prop speeds down. They normally used planetary gear type reductions so each gear and tooth had reduced loading along with spreading the load on the main gear symmetrically. Still something to consider when looking at running little engines fast with redrives vs direct drive slowpokes.

I love the diesels and would really like to fly one someday. My last Lycoming made 2000+ hours and was still flying well. 160HP O-320. I'd really like to see the torquey diesel with the much better efficiency drop the fuel requirements.

Frank
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Old February 12th, 2018, 07:51   #39
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Frank: Blower drives without backup are no different from prop re-drives that also have no backup - except the blower drives are a LOT less loaded and succeptible to harmonics (prop blades make great tuning forks). The Gemini you will note is essentially a 3 cylinder two cycle - that means overlapping torsional inputs, thus the cranks and drive gears can be considerably lighter than those in a 4 cycle 4 cyl - as that configuration suffers a complete torque reversal every 180 degrees making for a VERY heavy crank and HUGE potential to incite very large harmonics. BTW: this is why the prop reduction drive for a 27 litre Merlin is not much bigger than that for a 1.7 litre Thielert.

Oh...I should have added regarding the Gemini engines and backup: the 100HP engine is positive displacement pump (roots I imagine) but the 125HP is turbo compounded - to the extent that one supercharger could be considered and/or configured as backup to failure of the other.
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Old February 13th, 2018, 18:41   #40
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The reason they do it that way is to have the supercharger to provide positive boost at very low (read: starting) rpm, then at normal cruising speeds, the turbocharger takes over and allows an efficiency increase.

The Gemini engines sounds good, but I doubt I'll be able to afford it. For some reason, engine companies for aviation want $20k and up, probably a $25k floor by the time I'd be ready for one, and that even for the non-certified market.
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Old February 14th, 2018, 05:51   #41
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Let me tell you a little bit about the Corvair: The engine was originally designed to use the Reynolds 390 aluminum system to make the barrels (same stuff as the CanAm big blocks and the Vega) but the technology wasn't production ready, so they went cast iron. The intent was to compete with Continental 0-200!

Personally< I vastly prefer reduction drives for automotive engines - not just because of the power density, but because of crank loads (propellers need a LOT of torsional and radial as well as a bit of axial load capacity that automotive cranks and cases can't provide).

I had hoped the old Ross drive would do the job, but it seems it is a bit light in the gear department. There are other similar drives (used on rotaries with great success) but have not seen on corvairs. I have built literally hundreds of engines and drives (was once an airboat manufacturer) and to make even a simple timing belt or HTD drive, the weight can get out of hand. Even direct drive VWs, I used a separate torsional damper with a short prop shaft on BIG Timken taper rollers.

http://www.n56ml.com/corvair/donors.html

direct drive build: http://www.hainesengineering.com/rha...ft/corvair.htm

direct drive guru: https://flycorvair.net/2014/02/02/co...ines-for-sale/
forget trying to do a poor boy conversion, use the right stuff, pay the price (no where near Rotax or C85 numbers)

and I can endorse that arrangement due to this:m m https://flywithspa.com/corvair-5th-bearing/
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