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Old 03-01-2010, 02:03 AM   #31 (permalink)
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Quote:
Originally Posted by Clev View Post
Still 23 mpg at 124 mph is about the same as my Saturn gets at 83 mph. Not too terrible for the speed. :-)
Another advantage is that depending on your route, you can cut a lot of miles off. I used to fly a lot from Reno to central Idaho (north of Sun Valley. In a car it's maybe 500-600 miles and an all-day drive. In the Cherokee, it's about 400 miles and 3:20 flying time.

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Old 03-02-2010, 05:36 AM   #32 (permalink)
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Very intersting thread, as much as I lurk, I wonder how I never found it.

the engine is a huge part of what the efficiency is. I did not find specs for the orignal posted plane, but did find it started off with a volkswagen conversion.

I also found an ea82, unrelated, seems a much older story,subaru engine (1781cc) a man did the same flight, west coast to east extremely low fuel consumption- over 200mph. I wondered what the liquid cooled did for homogeny, it is not quibble about carburators, even p51s had a perfect can of whoopass with it upside down and 400 mph.

The 3 main boxer won't be beat in any category of efficient.

I have learned my own little sube on earth exceeds the norm to the point of mythical at 92mph...

given the weight of the plane and modern materials, I wonder if a boxer 2 cyl could get going that fast. one person, superlight.
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Old 03-02-2010, 11:19 AM   #33 (permalink)
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The biggest limiting factor with GA aircraft is the old engines they use. The PA31 we use (Piper Navajo) has two LT540's. That's 540ci (8.8L!!!) turbo and they make 350hp. We're talking like worse than the average american V8 there! The turbos keep the power up as you climb.

Most piston AC engines were designed in the 1950's-1960's. They're simple air cooled 2v pushrod engines. Usually really low compression and commonly carburated because of the cost of certifying an EFI system.

The heads are about as good as you grandfather's 3.5hp briggs & straton lawn mower engine and they use huge quantities of fuel to keep the engine cool. The cylinder balance is horrible (they run per cylinder EGT) and they run 2 sparkplugs per cylinder.

They do not meet modern standards of efficiency or power output but nobody can afford to design,build and certify a modern replacement. I'm not sure about home-built or experimental, but the AC I'm familliar with have a TBO on the engines so every X hours you need to remove and rebuild them. Goodbye $75,000.

Since they have mixture adjustment and EGT/CHT probes there are a number of manufacturers who have approved an enleanment cycle during cruise to drop fuel consumption.

I think it would be nice if they could update the engines with a modern 4 valve OHC engine that is EFI and could run on non lead fuel. AFAIK you can't even buy unleaded at the pumps. 100LL is the best we can get.

Best thing I've seen so far is a turbo diesel conversion for some cessnas done down in texas I think. About $120k and it burns 1/3 less fuel and you fuel it on JET-A.

Sorry, but aircraft are not the pinnacle of efficiency.
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Old 03-02-2010, 02:04 PM   #34 (permalink)
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Quote:
Originally Posted by hackish View Post
The biggest limiting factor with GA aircraft is the old engines they use. The PA31 we use (Piper Navajo) has two LT540's. That's 540ci (8.8L!!!) turbo and they make 350hp. We're talking like worse than the average american V8 there! The turbos keep the power up as you climb.
Google says that the PA31 gets about 1,016 miles on 182 gallons of gas, or 5.6 mpg. I don't know of many cars that can get that kind of mileage at 211 kts. Do you measure your mpg, and does it go down even further at lower speeds?

Heck, even a fully loaded 737-700 gets 2,759 miles on 6,965 gallons. Southwest crams 137 passengers into that space, so that's about 54 passenger miles per gallon. A fully-loaded Suburban will beat that, but not at 400+ mph.
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Old 03-02-2010, 02:10 PM   #35 (permalink)
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Quote:
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Sorry, but aircraft are not the pinnacle of efficiency.
Not trying to be difficult but...
Compared to a car?? The average fuel mileage in the US is around 20 MPG. Small airplanes are pretty close to that if not over. If you add passenger load they are much better than the average car with only one person in it.

Even the new Dreamliner A380 when loaded with passengers on a long haul is about 45 mpg/person.


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Old 03-02-2010, 03:44 PM   #36 (permalink)
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Another aspect is that one mile of road will take you exactly one mile. One mile of runway on the other hand can take you much farther. A small GA aircraft has a recommended time between overhauls of about 2000 hours. If the engine is still making power and passes annual inspections and the aircraft is not used for commercial purposes the overhaul is not necessary. for the 150-200 hp engines overhaul is more on the lines of 10-30000$ Many older, low hp engines run very well on auto gas.
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Old 03-02-2010, 04:33 PM   #37 (permalink)
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FYI, One of the original designers of the Q1 (Gene Sheehan) is currently signed up to compete with an electric powered version of the Quickie in the NASA sponsored Green Flight Challenge. $1.5 million dollar prize! The contest is a flight efficiency competition for aircraft that can average at least 100 mph on a 200-mile flight while achieving greater than 200 passenger miles per gallon.

CAFE Foundation

Looks like fun.
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Old 03-02-2010, 06:04 PM   #38 (permalink)
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Don't bag on current aero engines!

Quote:
Originally Posted by hackish View Post
The heads are about as good as you grandfather's 3.5hp briggs & straton lawn mower engine and they use huge quantities of fuel to keep the engine cool. The cylinder balance is horrible (they run per cylinder EGT) and they run 2 sparkplugs per cylinder.

They do not meet modern standards of efficiency or power output but nobody can afford to design,build and certify a modern replacement. I'm not sure about home-built or experimental, but the AC I'm familliar with have a TBO on the engines so every X hours you need to remove and rebuild them. Goodbye $75,000.

Since they have mixture adjustment and EGT/CHT probes there are a number of manufacturers who have approved an enleanment cycle during cruise to drop fuel consumption.

I think it would be nice if they could update the engines with a modern 4 valve OHC engine that is EFI and could run on non lead fuel. AFAIK you can't even buy unleaded at the pumps. 100LL is the best we can get.

Best thing I've seen so far is a turbo diesel conversion for some cessnas done down in texas I think. About $120k and it burns 1/3 less fuel and you fuel it on JET-A.

Sorry, but aircraft are not the pinnacle of efficiency.
I've done some thinking on aero engines. Air-cooled direct drive aero engines represent a set of compromises that IMHO turned out better than we should expect. Light weight, compact, long service life, and very reliable. The all-up weight for an IO-520 is around 600 lbs. If you tried to build a "modern" water-cooled engine that is rated for 285 HP continuous, all-day every day with a 1800 hr TBO, you'd need some kind of overbuilt, supercharged V-6 or V-8 that would weigh at least as much, if not more.

Fuel efficiency in air-cooled opposed direct drive engines can be quite good, too. (GAMI has demonstrated BSFCs of less than .038 lbs/hp/hr, which approaches current diesels. This is with carefully calibrated mechanical fuel injection and magneto ignition.

I agree that modern fuel injection and ignition control could improve aero engines, and with redundant systems (like magneto ignition), reliability would be comparable. Cost would probably be similar.

I'm less convinced with things like overhead cams and multiple valves per cylinder. Direct-drive engines will never turn faster than about 2700 RPM due to prop limitations. At low RPM, two valves breathe better than four. You only need four when you want to rev fast, because the individual valves are much lighter and won't float. Same argument for pushrods -- they work fine at 2700 RPM, and a pushrod motor is much lighter and more compact than an overhead cam (see Chevrolet LS motor for support for this argument).

Adding a gearbox between the crankshaft and the propeller may be a better proposition today than it was years ago. They add to purchase cost, maintenance cost, and usually reduce TBO (see Continental TSIO-520 vs GTSIO-520, O-300 vs GO-300, etc), but with current manufacturing, maybe the cost difference can be reduced. I don't know enough about this one to comment. I do know that Bombardier was testing the waters for introducing a full-size engine (larger than their Rotax line) that would be a geared V-6, but they canceled it.

No-lead is coming. Engine manufacturers (and aftermarket folks like GAMI) are working on retrofittable electronic ignition that will allow almost all current engines (with the likely exception of the fire-breathing TIO-540s in your PA-31) to run on unleaded.

As for aero diesels, most of them produce less power and weigh much more than the O-320 or O-360 they're replacing. And then there's that $100K plus firewall-forward price. The Deltahawk Diesel looks interesting, but it's not certified yet.

So to cut a rambling post short, don't be down on current aero engines. Yes, there's room for improvement, but they work amazingly well for 50-year-old tech!
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Old 03-02-2010, 11:57 PM   #39 (permalink)
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The average fuel mileage in the US is around 20 MPG. Small airplanes are pretty close to that if not over.
That also depends on the airplane. Remember that almost all non-homebuilt light airplanes are '50s or '60s designs, so it's maybe fair to compare their mpg to say a '59 Chevy. If you look at some of the homebuilts, you can find (as in the original post) much better mpg.

Quote:
If you add passenger load they are much better than the average car with only one person in it.
But the average light plane also has only one person in it :-)
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Old 03-03-2010, 12:02 AM   #40 (permalink)
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can you pulse and glide an airplane?
at least once.

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