Getting 45 MPG at 207 MPH .... can you pulse and glide an airplane?
 

Autopia has an interesting piece about an airborne fuel economy competition won by this funky looking plane getting 45 MPG at 207 MPH:

http://www.wired.com/images_blogs/au.../speedy091.jpg

Source: Getting 45 MPG at 207 MPH | Autopia | Wired.com

Now the article says:

I know there are a few pilots around here. What I wonder is whether that quote about P&G is true. I would think that you could pulse & glide an airplane, pulse = gain altitude; glide = well, gliding.

And theoretically you should be able to pin an airplane's engine's load pretty much indefinitely at exactly the right BSFC point for max pulse efficiency, no?

Full article: Getting 45 MPG at 207 MPH | Autopia | Wired.com

Yes, if you had a plane that was essentially a powered glider. Bart Rutan's Voyager that made its nonstop around-the-world flight was exactly that, and traveled about 25,000 miles on about 8300 lbs of fuel. At 6 lbs/gal, that's only 20 mpg, but they were hauling over 9000 lbs. of weight on a plane that only weighed 939 lbs empty.

I think it may be what happens when you put wings on a mustang perhaps?

Pretty much. The large variation in automobile operation and lack of suitable gearing relative to displacement is the only reason a car has to pee and gee in order to optimize engine efficiency.

It would not surprise me if you could max your cruise distance simply by adjust your rate of climb so you were at bsfc peak, then coast back down at VBG
(feathered prop would be nice).

Wish I knew the specs (CDA, etc etc).

FYI wikipedia entry: Rutan VariEze - Wikipedia, the free encyclopedia

puts it at 35mpg at 181 mph in "stock" form.

There are several dozen variations of this plane including one done with really long wings that is close to a glider in performance. Most build them with a hotrod motor cause they will close in on 300 mph if done right..... and even plane people can never go fast enough...

Lol
Dave

That's essentially how all commercial scheduled flights operate. They accelerate (pulse) to 30,000 ft cruising altitude where the air is thin and resistance is low. Then they semi-glide back down.

From my experience in smaller propeller planes, they do operate at best BSFC all the time after takeoff is completed.

You made the key point right there.

There's no need for "pulse" as we think of it in automotive terms cuz cruise loads a/c engines accordingly for the duration.

That is another reason why you generally can't just pluck an automotive engine out of a car and stick it into an aircraft. The duty cycles are waaay different, with the auto engine loafing along most of it's life with brief periods of higher load, and the a/c engine working pretty hard most of it's life, with brief periods of even higher load. That's why we ought not laugh too hard at an a/c engine that uses, say, 330 cubic inches to put out 100 hp. It's not because the engineers were dense.

There are motorized gliders that I suppose could be considered "pulse-and-glider(ers). They aren't in it for the fe though. They are mostly for recreation- not seriously trying to get from a to b- and the motor gets the tow plane out of the equation and allows for more thermals-hunting per mission anyway.

Airplanes can choose their speed and altitude, so they can adjust their situation to their best BFSC map and get great mileage, if they are designed for that purpose and can climb high enough.

Much of this same technology can be used in cars, as long as you disconnect the engine from the wheels. While the airplane can use altitude to store energy, cars can use hills for the same purpose, but with cars you have to be lucky enough to find the right hill.

The motor gliders are superb examples of P&G in airplanes, especially if they can find a thermal, which is similar to a draft in a car.

I have thought about a hydraulic power boost for takeoff in an airplane, so the engine size could be reduced,

We used to catch Mallards in a jon boat with a crab net. If you chased them, they would take off and land a few hundred yards away. After 3 or 4 chases they were too exhausted to get off the water and they would go underwater, and we would scoop they up with the crab net.

The point is they used so much more energy taking off than it took to maintain flight it was easy to take them alive.

I believe the same applies to vehicles, and the practice of having giant engines to allow acceleration. Short term energy high capacity energy storage for the seldom encountered surges of power necessary to drive, would allow much smaller engines to do the job. If steep grades were an issue the some form of pressurized induction would allow speed to be maintained on steep grades.

regards
Mech

Except that their glides are interrupted by ATC commands to level off at intermediate altitudes. Some of the technologies associated with NextGen ATC will allow airliners to literally glide with engines at idle from upwards of 30,000 feet to landing.

Jesse: I'd read about this (changes in ATC to permit more efficient commercial "glides").

Thanks for the answers, everyone. I'm continually amazed at the collective knowledge here.

as far as drag in an aircraft goes there is two types. Induced and parasitic.

Induced is created when the wing is at a high angle of attack as airspeed increases this drag drops.

Parasitic is created by the fusulage and all the protrusions. It increases as the airspeed increases.

Both are on a curve. There will be an airspeed where the combination of the two are at its lowest.

Combine that with an engine that operates it's BSFC at that airspeed and Pulse and glide will not be nessisary.

The other thing you could do if the engine's bsfc rpm pulls the aircraft past it's lowest drag speed is climb. The thinner air makes the engine produce less power, the thrust is reduced due to lower pressure on the prop (or stream of jet exaust). There is less parasitic drag and the wing creates less lift.

The thinner air also means the indicated airspeed is lower (the aircraft "feels" less air moving over it) while the true airspeed goes up (actual speed the plane is moving through the air)

So what airliners are doing is one big "pulse" to get to an altitude that allows the plane to cover ground very quickly while flying in low drag. The fuel burned in the climb is almost always more than what was saved during the decent. But the fuel consumption is so low at altitude that it quickly makes up for the fuel used in climb and then some.

a continental O-300 (opposed 300 ci) makes 145 a GO-300 (geared opposed) is good for 175hp the standard o300 has a TBO of 1800 hours at 2500rpm the GO300 gets 1200 hours at 3200 rpm I think.

lycoming gets 150 hp out of a O-320 and an O-360 is good for 180-200hp

these engines are making RATED (not peak) HP at 2500rpm

the 100hp engines are about 200-235 cubic inches.

Air cooling limits the specific outputs as well, and keeping the revs down saves the weight and losses of a gear reduction for the prop. I think the aero engines sound better, too.

Thanx for looking up the numbers; I didn't. I just recall that output/cid is low compared to other engines.

As far as the sound goes, I don't particularly enjoy listening to them. :mad:

Well lookey here, a pointy nose.

http://www.wired.com/images_blogs/au.../speedy091.jpg

That's the shape of the landing gear mount, in a situation where it works OK.

so, if doubling your speed takes 4 times the power, roughly speaking, and power is proportional to fuel consumption, again roughly speaking, then with the right engine combo, you should be able to cruise @ 90mpg at 103mph and 180mpg at 52mph?

Would narrow wheels and direct drive, instead of wings and a propeller help or hurt mpg?

Narrow wheels instead of wings will prevent flight! LOL

Doubling the speed takes 8 times the power. Power is proportional to the cube of the speed, not the square.

Well, except for the fact that IIRC the stall speed's about 65 mph :-)

Some of the mpg improvement probably comes from cruising at higher altitudes* - around 12,000 ft or up to 18,000 with oxygen - where the air is much thinner, so drag is less. I don't know how induced drag from lift would compare to tire drag, but the low frontal area is about the same as the VW 1L car.

* And that's boring. Flying's more fun when you come back with bits of sagebrush in the gear :-)

What do you mean? Why would the nose be pointed for the landing gear?

as you increase your speed you are reducing induced drag, but you can get going fast enough that induced drag is a very small portion of your total drag.

There are situations where you can increase speed and reduce power.
Like near stall, when there is not much air moving over the aircraft, so the parasitic drag is very low but you are dragging the wing through the air with the bottom facing the apparent wind.

http://upload.wikimedia.org/wikipedia/en/1/12/Drag.jpg

We need to get this man a dead horse and something to beat it with.

another efficient homebuilt plane
Dragonfly FAQ - Dave Morris
http://www.air-and-space.com/2005081...flight%20l.jpg

Oh, that's a big one. The root of this line of development was the Quickie Q1, a single place design with the front wheels on the canard wingtips. It originally flew on 22 HP. Quickie Files
The Windrose motor glider is probably more the way to go if one wants to do gliding, though. Many sailplanes could easily carry a small motor - many of the best ones carry ballast. The records are over 1,000 Miles on Zero gallons, but you don't get to choose the route on those flights. There is a proposal to tether two sailplanes together, to work as kites on the differential in wind speed with altitude. That would give more options, but usually mostly downwind, like a square-rigged ship.

I think that was what I was thinking of. I remember thinking I like that design and if I ever had space, time and money I'd build one of those or a culp special (I like the culp's classic look)

Dragonfly numbers...
 

That's 48 mpg at cruise! Sweet

A friend of mine has a Piper Cherokee (840 statue mile range on 36 gallons, which I take to be about 23 mpg at a cruise speed of 124 mph.) Because it's carbureted, there's a lot of fiddling with the mixture to get it to run properly at various temperatures and altitudes. I would imagine that it would be a little more efficient (and a lot cleaner) if it were fuel injected.

Still 23 mpg at 124 mph is about the same as my Saturn gets at 83 mph. Not too terrible for the speed. :-)

You can pulse and glide this one. It's a G109B motor glider. Not near as fast but once you get up you can feather the propeller and ride the air currents until you need to fire the engine up again. They're comfortable and quite fun to fly.

http://de.academic.ru/pictures/dewik...glider_arp.jpg

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.

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.

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.

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.

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.


Just saying...

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.

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.

Don't bag on current aero engines!
 

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!

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.

But the average light plane also has only one person in it :-)

can you pulse and glide an airplane?
at least once.