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rv7charlie

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Oops; mistyped the earlier message about fuel use of rotaries vs Lycs; obviously I intended to say that rotaries burn (slightly) more fuel. I've flown a couple of 'loose formation' cross countries in my 160 hp Lyc -4 with Tracy Crook's Renesis powered -4. Both times he burned ~10% more than me, but I was running E-free premium car gas and he was burning 87 octane E-gas, which at the time was at least a dollar/gallon cheaper than my E-free premium, which was almost a dollar/gallon cheaper than avgas. The only reason I brought rotaries into the discussion was to answer the question about automotive conversions being able to run lean of peak.

Toobuilder, you apparently have the misfortune of living in CA (at least when it comes to gas prices). There's still a pretty big delta between mogas & avgas where I live. Even E-free premium (which carries a significant price penalty) is still ~50 cents/gallon cheaper than avgas. Of course, it also doesn't foul plugs, and the oil and the engine interior stays cleaner, longer.

Question: If your 540 has low enough compression to run 87 mogas, do you believe that it can attain .38 BSFC at 75% power? (Not 40% power at 16K feet, but actual 75% power at typical 7k-9k feet altitude.)

I'm still waiting for those Lyc dyno charts showing .38 BSFC @ 75% power. I see lots of internet reports of miraculous in-flight BSFC numbers, but I haven't yet seen *any* that specified *all critical flight parameters* of the flight(s) where the numbers were supposedly calculated. *Maybe* it's do-able when dialed back to sub-40% power.

dwalker's mention of marine engines is a good example; as he said, marine engines come very close to aviation engines in duty cycle.
 

Toobuilder

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I have the dyno sheets from Lycon and it does list a BSFC number, but I also do not believe the claimed output. It is significantly overstated in my opinion, and that means the BSFC number is invalid. That said, and to Charlies point above, there are enough RV's flying around that pretty soon one RV-6 with a Lyc is flying with another RV-6 with a (insert auto conversion here), and the guys are doing a 100 mile breakfast run. In every account that I have read or heard of, the auto engine burns the same or more than the lyc. Same speed, same air - similar fuel burn. I have NEVER seen a documented case where the auto conversion does 20% beter on fuel burn in a head to head test.

Of course it makes sense, doesnt it? It takes X power to go Y speed... That X power takes a certain amount of gasoline to produce, and it does not care what name is stamped on the valve cover. Example: everyone knows the 540 burns more gas than the 360, right? Well, if I fly my Rocket with my RV buddies and I slow down to match their cruise speed, guess what - I have the same 8 GPH they do. The extra weight and cylinders I'm dragging along just dont make much difference.
 

rv7charlie

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The rotary is an 'outlier' in that it typically does burn 5-10% more (87 octane E-mogas) fuel than a typical Lyc (on avgas) at the same power levels. Having said that, I have a friend who flys a Renesis powered RV7A, and he says that when he flies with a neighbor's Lyc 180 RV (8, iirc), they burn the same fuel quantity. Now, this is obviously what you just read on the interwebs. But he's about as ego-free as anyone I've ever met, and rarely participates in internet forums; even the rotary list. I think he's up to around a thousand hrs on his junkyard engine so far.

Now, I suspect that Toobuilder's above post contains a lot of answers about relative fuel efficiency, kinda hiding in plain sight.

Lycs are 'mature' tech, in mature airframes which are optimized for Lycs.

Alt engines *very* rarely have anything close to an optimized cooling system. That alone muddies the true BSFC number if you're using the a/c as the dyno, since almost all alt engines are shoehorned into airframes optimized for Lycs (which means that the Lyc starts out with a much closer to optimized system, and is typically much easier to fully optimize *in the airframe* than almost any alt engine.

Alt engines are *very frequently* installed by builders who, to be blunt, don't know what they don't know. There are obvious exceptions to that, but... And I say that knowing that there's likely a lot of stuff I don't know yet. ;-) Not only will the a/c likely be cooling challenged, actual engine tune is also often sub-optimal.

Last (for the moment), the Lyc, even at '75%' is operating at a very small fraction of its potential output, because of the incredibly low rpm. Most alt engines, on the other hand, typically operate at a much higher percentage of their potential output. (Ross hinted at this earlier). This *should* give them significantly *poorer* BSFC numbers than the Lyc. If they 'break even' in real world BSFC vs an electronically controlled Lyc, I'd call it impressive. I won't be surprised at all if, with a properly set up airframe and controller, they easily surpass a Lyc, configured as Lyc typically sells the engine (mags & carb/injection). You can make the Lyc quite efficient, but it's not really, in the traditional sense, a Lyc any more, after making the required changes. Just ask the FAA if you don't believe it.

That claimed 20% number is interesting. As a point of reference, what fuel burn improvement do we typically hear for the relatively new electronic engine controllers on Lycs, vs the original carb/mags version? I often hear 1.5-2 GPH bandied about. If we're talking about a 150-180 HP Lyc and the 180 according to Lyc's numbers burns just north of 10 GPH at 75% power, that looks a lot like 20% spread to me. Now, if the alt engine seller (who's engine has electronic control) claims a 20% improvement over a Lyc that's still an actual Lyc, is that any less reasonable?
 

Toobuilder

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Well, Ross has essentially developed a zero drag cooling system for his Subie installataion, and I'm sure he's had the opportunity to fly with another SDS Lyc powered RV-6 head to head. Would be interesting to hear what the same airplane, the same engine mangement system, but radically different engine architecture looks like from a fuel burn perspective.

It all really boils down to real world numbers, not BSFC numbers on a dyno. Head to head is what counts. Anyone want to fly an Alt engine RV against my Rocket on a 200 NM cross country and compare fuel burn, I'm down.
 

AdrianS

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I like the vagueness and "seems like". It IS hard to provide hard numbers to compare the rotary efficiency vs the Lyc because being honest, there is a serious lack of consistency between builds. MY build will very likely result in a configuration that compared with a Lyc of equal performance will burn at least a 1/3rd less fuel. Now, if you compare that motor against a smaller lyc and ignore all performance numbers, I am sure the lyc might perform the same or better. The biggest issue I have when people say its a "thirsty engine" is they are comparing say an 0-235that pushes the plane 170knts vs a rotary conversion that pushes the same type airframe around at 200knts, assuming similar cruise settings. If the Lyc has a CS or other in flight adjustable prop, the difference grows again. .
As noted before, you can SAY, all you want, that a choked down Lyc pushing along at 30% throttle will sip fuel, but that is not a valid comparison.

Now lets turn to the 4V/VVI etc. things that seem not important for flight engines.
4V technology can provide more power at higher RPM, which might be helpful if you are using a PSRU, but 4 or 5v per cylinder technology is mostly good to build power all throughout the range and NOT make a peaky high RPM motor. The person building the engine will need to understand which camshafts and valve sizing to use, but it is a fallacy, and a bad one, to dismiss multi-valve engines from flight engines.

VVTL (Variable Valve Timing and Lift) technology is absolutely the future of airplane engines if they want to increase power and efficiency. This again is not a high RPM technology, rather, it allows for a much broader powerband across its usable range. Yes, early versions were used to have a high-lift and duration cam profile which allowed for good power down low with a noticable "VTEC KICKED IN YO" kick in the pants at higher RPM, but modern and better programmed versions these days are amazing in operation.

VLI (Variable Length Intake) technology again provides a very broad powerband. When working with the Mazda Renesis we did a bunch of testing with the variable runner and valve arrangements- removing them, opening them earlier or later etc.- and honestly just leaving it alone with some minor tweaking provided the best powerband we could ask for. The same was true in the 996/997 Porsche and pretty much everything else.

Yes, these give high power are redline, but the most important thing they do is to broaden the powercurve so that the usable power is available early and carries throughout. In a flight engine this means that you can have your available cruise power- where your spending most of your time- at a lower rpm, with lower fuel use and higher efficiency than ever before.

ALL of the things that make auto engines better for cars make them better for flight. And you only have to look at the current marine engines and thier tech to figure that out. Once all two-stroke, the market is being dominated by 4-cycle, multivalve, VLI/VVTL engines that are not only more powerful, but more reliable and quieter on the water. The use of turbo and supercharging is changing the game yet again, with 400hp class engines available in outboards that are the size and weight factor of the old 250/300hp class engines. And these engines run in basically two positions- WOT and idle, for most of thier lives.



While I tend to enjoy watching circular arguments ebb and flow, this is one where
VVT is used to broaden the power / torque band, which is useful for cars.
An aero engine is always operating at 75% or more of max revs - so why would it need a broad power band?

Ditto multi-valves. They are used to
a) Reduce the inertia of each valve, allowing higher RPM operation.
b) Provide a larger inlet / exhaust area, to promote gas flow at high RPM.

If you're operating at below about 6000 RPM, a 2-valve head can easily provide sufficient flow.

How many large capacity v8's have more than 2 valves / cyl?

How does an LS motor provide the power it does with a two valve head and no OHC?

I love my screaming 1.6 litre, with its 20 valve head, VVT, and 8500 rpm redline - but it's not an aero engine.
 

rv6ejguy

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A well designed 4 valve engine suffers nothing at low rpm compared to 2 valves however geared auto engines don't operate at "low" rpm when fitted to aircraft, most run in the 4000-5500 rpm range (cruise/ TO). The new Adept aero engines are geared and 4 valve and have excellent (better than Lycoming) BSFC figures if we take their dyno data they supplied to me at face value. I did a video comparison on these compared to a variety of aero engines, both SI and CI.

At 2400-2700 rpm, 4 valves doesn't do much for you though except add weight. 2 valves and pushrods work fine down here and even have a bit lower valve train frictional losses.

Outside of Chev and Dodge V8s, most other brands use 4 valve heads these days. Much as I like LS engines, the specific output of them is easily exceeded by a plethora of 4 valve V8s from other manufacturers.
 

Bigshu

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and some operators get 4000+ hours out of a 2000-hour TBO engine; operators like pipeline patrollers and fish spotters.
If they are operating commercially, are they still part 91 operators? If not, they should be sticking to the TBO from the manufacturer, right?
 

Toobuilder

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If they are operating commercially, are they still part 91 operators? If not, they should be sticking to the TBO from the manufacturer, right?
Operators can petition for an exemption from MFG TBO if they have the data to back it up.
 

Dan Thomas

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Operators can petition for an exemption from MFG TBO if they have the data to back it up.
We have a similar but different thing in Canada. Private operators aren't held to hard TBOs. Commercial operators can put their engines on an on-condition program that starts at or before about 3/4 of the way to TBO, and requires tracking of several parameters such as oil consumption, compression, filter debris, static power, oil analysis, and so on. At TBO the cylinders are removed from one side of the case and the internal stuff is inspected. It's all right here:
Airworthiness Notice - B041, Edition 4 - 31 March 2005

I did some calculations of the time (labor costs) and other requirements as compared to just replacing it at the TBO (+10% as per our MSA) and found that there was little advantage to it (for us) especially considering that the core value (to Lycoming) drops as you pass TBO plus a certain percentage (can't remember what it was).

That was in flight training, where the engines are run hard almost every day, little chance for corrosion to set in but those engines do get some abuse. In pipeline/powerline patrol or fish spotting, the engines are run at cruise all day long, with none of the frequent start/stop/heating cooling cycles, ham-handed throttle and mixture control movement, and the like. I wouldn't want to run a jump plane or glider tug engine on condition. Those get hot and then real cold.
 

pfarber

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lol still arguing over the design of two completely different motors with two completely different missions and which one is right-er

The question is can a car motor work in an airplane? Yes, yes it can. The fact that a car motor uses VVT or an ECU is tangental to the question. They work. They work great. Are they as highly tuned for a low rpm/light weight miaaion of a GA motor? No, that was never their mission (ok, Corvair, we see you in the corner).

The first airplane ever was powered with a car motor.

But the pinnical of propeller driven aircraft would be WWII and the massive V12s of the worlds best fighters had PSRU's (aka were geared motors) because they spun 12-13ft props.

Everything being discussed has already been done. PSRU's work. EFI/ECUs work. Car motors in aircraft work.

What we really should be talking about his how to make car motors BETTER at being airplane motors. Because as we all know, they work fine in cars and airplanes.

What's funny is that airplane motors in cars fare much worse that car motors in airplanes.
 

Dan Thomas

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No. It was a purposed-designed engine for the Flyer.


BJC
Yup. The car engines of the day were heavy and of very low power. If the Wrights hadn't had their machinist build that engine, they'd have been several years later flying powered for the first time.

I wonder what the TBO of that engine might have been? Five or ten hours, maybe?
 

pfarber

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No. It was a purposed-designed engine for the Flyer.


BJC
And ICE is an ICE. The copied BMW for the material and other current designs of the time. They tweaked it a bit, but it was basically a car motor.

"
The Brothers' first airplane was coming together nicely by 1903 -- all but the engine. Their scientific work with gliders, with their wind tunnel, and with airfoils had put them far ahead of other would-be airplane makers. But they needed an engine that weighed less than 180 pounds and delivered at least 8 HP. The automobile makers who answered their letters said they couldn't be bothered with custom-built engines. So the Wrights finally went to Charlie Taylor and said, "Let's build our own engine."


They settled on a four cylinder in-line design -- like turn-of-the-century car engines, but with an aluminum-alloy block.....

"
 
Last edited:

Dan Thomas

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And ICE is an ICE. The copied BMW for the material and other current designs of the time. They tweaked it a bit, but it was basically a car motor.

They settled on a four cylinder in-line design -- like turn-of-the-century car engines, but with an aluminum-alloy block.....
And it had serious shortcomings, as would be expected of a primitive engine asked to produce high power.

From 1903 Wright Engine

we read:

The 1903 engine mounted in the Wright Flyer during restoration. As the engine heated up, the firing chambers on the left side of the engine nearest the pilot would glow red hot.

It produced as much as 16 HP but that would fall to 12 HP as it heated up. I can't imagine that the aluminum crankcase would last too long with red-hot cylinders in it. Iron begins to glow in daylight at around 1100°F, above the melting points of most aluminum alloys. Aluminum has lost its strength long before it reaches its melting point. As the article above says, those engines didn't last long at all.
 

pfarber

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Mad props for machining a motor from scratch, but they I still believe they simply copied what they knew as 'best available art' and simply omitted what they didn't need for weight. They had little idea of air cooling the motor.

From what I could find, the first successful air cooled aircraft motor was the 1909 Gnome N-9 at a whopping 165hp.... just 6 years after Kitty Hawk!
 

TFF

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Almost every car in 1903 had one off engines. There were not many on the road anywhere. The architecture of the Wright engine is not like car engines of the day. It was the best for that day. Not best today. Langley’s engine ended up under water. Mercedes first airplane engine ended up under water. Everyone went after it like a government would and a couple of homebuilders went the other direction and did it.

Technology was moving fast like computers today and because of that, Europe did exactly what Japan did in the 50’S and China does now, disregarded IP and went whole hog and passed US, because flying here was to be sued by the Wrights. One of the few inventions where IP was not defendable, even if their case was wing, because the government needed it.

A Gnome is an industrial work of art that only a big company could make. Definitely not build in a barn. It’s also not an engine to not have a perfected way to fly behind either.

About five years ago there was a Wright engine for sale on Barnstormers. One of the few left in private hands. That would have been a prize. I know someone with a Gnome in his hangar. So cool.
 
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