Discussion in 'Ford' started by rv6ejguy, Jun 28, 2014.
EGT guages are helpful here......:gig:
I'm not sure why Corvairs come up in a Ford discussion, but the crankshaft issue needs a response. (1) There are new billet crankshafts available. (2) Cranks break when you bend them -- addition of a 5th bearing to take the bending loads imposed by flight maneuvers results in no cranks breaking. There are many of these flying now, from two different vendors.
Maybe you should make a Corvair engine in China. It's well documented and works well when done right, particularly in the 100-120 hp range.
Maybe getting a bit off topic, but unfortunately, there has been at least one crank failure even with a fifth bearing: www.n56ml.com/corvair/break3/
However, there was a modest prop extension and no harmonic balancer and maybe those things in combination with some yanking and banking pushed it too far. The billet crank looks like a good idea.
I do not have Ross' knowledge but I am inclined to agree that an auto engine (and certainly the more modern ones) can operate at high power levels if done correctly--i.e. proper cooling if air-cooled, and managing TV & side loads either by a reduction unit or other measures if direct drive (fifth bearing, minimal length to prop hub, and don't push it with the maneuvers).
I commented on the Corvair crank failures some months ago and questioned the "wisdom" of WW's incredible knowledge base.
1. Not using the factory alloy steel nitrided 140/180 crank was simply foolish. Why would you not use the much better available crank in a DD aircraft application?
2. I never, ever reground cranks in a race engine. Really foolish on a nitrided crank. Every race crank was magnafluxed.
3. Anyone who truly knows anything about performance engine building understands how important fillet radius and finish is.
4. The harmonic balancer is on the engine for a reason or the GM engineers would have put a cheaper pressed steel pulley on the high hp engines, like the pre-'65 engines had. Unless you can instrument and do the same sort of TV studies that GM did, it's a good idea to leave it on.
These dudes learned many things the hard way...
Yeah, nah, they have always had a minimum weight rule and gasoline cars have to add a lot of ballast to meet it.
The LeMans rules at the time were designed to slow gasoline engined cars down for safety and Audi did the sums and realised that it allowed for a virtually unlimited diesel engine powered car to be superior - good on them for taking the advantage but it has taken a few years to redress the imbalance and they still aren't quite there yet.
If they dropped the minimum weights, removed the fuel flow restrictors and freed up fuel tank size restrictions then the diesels would be left for dead.
What are your thoughts on the 4340 billet crank that is being produced?
Do you avoid regrinding simply to preserve the fillet radii, or are there additional reasons? Also, why is it bad to regrind a nitrided crank? Is this because the hardening only affects the outer layer of the journal?
In asking this, I'm not advocating that the HB be abandoned... But, doesn't the presence of a prop change the TV situation, thus requiring more study to ensure the stock HB is doing what we want it to do?
What "Ford" discussion? Oh I see, didn't realise this thread is in the Ford section, but it's not a Ford specific thread anyway. I get to threads through "New Posts".
You confirm my point exactly, thank you, this is no longer a stock Corvair engine but a highly modified and expensive one while I am referring to dead stock Subaru engine that "bolts straight in".
I considered it for about 3 minutes and here's what I came up with: An engine known to break cranks wearing a "Made in China" tag - Oh yeah, surefire market winning strategy there .... :roll:
A 4340 crank, material wise, is about 25% stronger than the factory 5140 140/180 crank. Good move but expensive.
Typically 140/180 cranks have zero wear and ovality because they are so hard , no need to grind them. Yes, the nitrided layer is thin, grind it away and you lose a lot of the reason for nitriding in the first place. You could do it over but why start in the first place? See the first sentence in this paragraph. If you start with a soft and relatively weak 110 crank, you are simply asking for trouble IMO. Many 110 cranks are worn and out of round on the rod journals because they are soft. Why start with a crappy crank and try to re-machine it? Find a mint crank to start with with proper fillet radius.
You are right, most people don't have a clue about TV and refuse to spend any money or time to quantify it with the changes they have made to the engine with new pulleys, extensions, flywheels, propellers etc. TV is insidious many times, just waiting to give you a bad day. You might be lucky, you might not. This is a very big deal on engines with less than 8 cylinders.
I take it that, even with the additional expense, the billet crank from Panther Sport Aircraft would be the way to go for a Corvair, then?
If you are interested in best reliability and your budget can stand it, absolutely. They have addressed both material strength and fillet concerns with these cranks plus they are zero time items. Who knows how many cycles and abuse a 45 year old crank has on it?
If a picture is worth a thousand words, then this video is virtually infinite in its informational value. Well done Ross!
Im not a ford guy but if they came out with a 4 cylinder eco boost engine weighing in around 150 lbs I would have a hard time passing it up. that was great.
Would Titan not fit here...Autoflight gearbox, Honda / Suzuki / BMW / Chevy, Whirlwind Propeller? With many hundreds of hours flown, without incident, in various configurations with the items listed.
I have no info on Autoflight with regards to TV studies. Perhaps you, or someone here, would be able to shed some light.
While the weight is there now, it's 3 cylinders for 1.0, 1.2 and 1.5 liters.
From having been there, Ford had an active ongoing program running instrumented vehicles around the US, Europe, and Asia with customers driving the vehicles. They looked for the most damaging events and how often they occurred compared to less damaging events.
Damage is checked out several ways. For metallic parts you are looking at wear and fatigue, which can be very different events. For non-metallic parts, there is wear and thermal damage. For electronics you have thermal damage and corrosion.
In a lot of ways, cold starts are the worst thing - pistons, bearings, chains, valve gear, starters, and accessories all take it on the chin in -40 F starts. Get an engine capable of running the cold soak test without problems and you have something.
Anyway, they estimate the total fatigue or wear or thermal shock history, and then find the most severe events and then stack up enough of them to give the same total as a 90 percentile driver over 150,000 miles. Sometimes it is short test to demonstrate adequate life, sometimes it takes months. The vehicle durability is 50k miles, and that is about 1200 hours (50 days) on a powertrain dyno or about 15 weeks of driving at the proving grounds. Many groups at Ford and FCA now run double bogies instead of singles, expecting passes too. Why? The customer expectation for vehicle life and reliability keeps going up.
In most aero engines, we have an engine on one end, the prop on the other, and it goes into resonance in the operating range. So, you put a soft spring in the thing to drive that resonance below idle, say 600 rpm. Now you have to go through that resonance at engine start. Cool, but for starting, the engine fires at 90-125 rpm, and then accelerates through the resonance at 600 rpm before getting to an idle speed of 1200 rpm. Well, if your system looks sturdy and heavy but you still have gear issues or if you have trouble getting it to accelerate through 600 rpm, you might go for a clutch in the system. Start disengaged, let it come up above resonance and then engage the clutch, smooth sailing. Except that is a lot of weight. Maybe better isolation device and a beefier set of bearings on the prop shaft is the way to make durability.
Since these are airplanes, where WEIGHT IS THE ENEMY, I would say let's figure out the lowest weight way to be durable. My criteria is these are for sport aircraft. They have to pull g's, do loops and rolls and spins, and be rock reliable. If the clutched PSRU's were the lightest and durable, terrific. If instead a beefier system with no clutch was the lightest while being durable, terrific.
The Bud Warren/Geared Drives clutch is centrifugally operated, comes in as the engine comes up to speed during startup, disengages as the engine spins down. You have no control over it. A manual trans type clutch would allow you to select when to be on or off. Even more weight. Don't know if anyone makes one for their PSRU.
Are the engines factory tested for any industrial use or farm machinery, airboats, or anything like an airplane propeller?
Shift the engagement point above idle and you now have manual control. Clutch would wear faster and generate more heat, so that may be an issue that ends up raising weight.
You make it sound like there is a difference... Look, if you feel better with a Lycoming, go buy a Lycoming.
The testing is primarily done on dynamometers at the automakers and at the airplane engine builders. They run the engines over dutycycles that resemble the worst parts of actual use and that worst part has to still result in a lots of durability - that is they don't break anything, make rated power, pass the emissions tests, and the oil does not show the engine is hurting. And, as I said above, double bogey passes are the norm now, with many programs running triple and quad bogey tests.
Understand that there is also a strong drive to build a lot less engine part numbers for cost reasons. Most of the "car" engines are also "truck" engines somewhere, and the test dutycycles are picked knowing that. The EcoBoost engine featured in the OP's video is also used in the Taurus SHO, and NA versions are also used around the company. The small 3 and 4 cylinder EcoBoosts are used in various Transit vans with much higher frontal area and gross vehicle weights than the Focus sedans, and yes in NA variants. Yes, the dutycycle for the trucks and cars are both used to determine dutycycles for testing. FCA did similar things with their products. These companies may put on different intake and exhaust manifolds for different vehicles, but they only the build them with one set of internals for NA use and one set of internals for turbo use.
Yeah, the automotive base engines are not run 2000 hours at 75% of max automotive power. Folks converting automotive engines for airplanes are not proposing to make 100% of peak automotive power when we use them as airplane engines either. 200-225 hp from EJ257 that are 300 hp in street trim, 300-350 hp from LS3 that make over 400 in street trim. So the new 100% for the airplane is less than it would be in a car, and we get immediate large improvements in durability as a result.
If somebody really wanted to sell them for farm equipment, you would do similar derating. For airboats? Old school V-8's have been used in airboats for generations and they work fine. Yeah, most of the builders use suitable hot rod parts to upgrade SBC and BBC to make high power reliably. These engines were never intended for big powerboats and they have been used that way as reliable long lived boat engines for generations too. The usual donor engines were not high perf to begin with, so suitable cranks, rods, pistons, and valve gear are necessary if they are also running free flowing systems and making big power. Sort of like what you find in a modern high horsepower automotive engine.
The real hard part on all of these is that we are essentially selecting an engine, prop, and PSRU at random and seeing if they run OK together. My standard warning about durability in the face of torsional resonance comes in here, as well as the warning that yaw/pitch rates make the biggest loads on prop shafts. The builder can either design for all of this, then survey their Engine/PSRU/Prop combo for vibe issues or run a few for a long time with some folks running high yaw and pitch rates without problems before I will use one. It does sound like some do pass now.
That is why my big question is always "How many have run, for how long, and at what yaw/pitch rates?" If the guy who builds them warns me away from doing g's and maneuvering, I would skip that product. An airboat box used on big block, big prop applications and doing two second spins will probably be OK with my lighter airplane prop after I check that the engine flywheel and isolator and prop inertia appear to have the right 1st order torsional frequency. And then only after a few someone else's have flown them a while...
To sum up, automotive engines seem to be suitable bases for well engineered and/or well proven airplane engines. But then so do Lycoming's with good fuel and spark management...
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