Posting in Architecture
New research suggests a bird-shaped airplane -- with angled wings and a fatter body -- would make the modern plane more fuel efficient.
New research suggests that a bird-shaped airplane -- with angled wings and a fatter body -- would make the modern plane more fuel efficient. I spoke recently with Geoffrey Spedding, an engineer at the University of Southern California, about this discovery -- and how it could change the way we fly.
How did you discover that a bird-shaped design would make planes more efficient?
To start at the beginning, Joachim Huyssen [of North-West University] in South Africa was wondering about efficient aerodynamic designs and whether the current dominant configuration is the best available. There are several features of that design that are aerodynamically not convenient and not optimal. The best possible [design] from an aerodynamic point of view is a wing by itself. You would think then the best possible airplane would be a flying wing, and, in fact, flying wings have been made. But the difficulty is two-fold:
- You have to make the wing so big to pack people and cargo in that you end up wasting a lot of space. The waste of space causes aerodynamic drag, the airplane is more heavy than it should be. Your optimal design turns out to be not optimal after all.
- All existing airplanes have this tail plane in back. The purpose of the tail plane is to provide pitch stability. The nose goes up or the nose goes down -- you control that with the tail plane. This comparatively little tail plane sits at the end of a long body on the conventional plane. The purpose of the long body is to carry the tail plane and put it a long way [from the plane's center of gravity], so it has a large effect. But that's a really inefficient way to do business. All the time you're dragging this tail plane through the air, its only purpose is to make sure you don't pitch up or down. It doesn't otherwise do any good and it forces you to have a long, cigar-shaped body, which is not the best shape a body can be.
[Huyssen] thought: Suppose we could pitch up or pitch down using just the wings. He probably did sneak a look at birds -- seeing that they obviously did it. You have to have some forward and backward motion available. That's why he came across this design. If you look at the wing from above, it sweeps forward and then it sweeps back. If you do that and you can control those sweep angles, then that is sufficient to provide stability. You don't need a tail plane -- and you don't need a long body. You can pick the most aerodynamically-efficient body, which is surprisingly a lot fatter than these cigar-shaped things we have now.
It turns out that you can put a stubby little tail on the back of that body and control the flow of air over the body. It acts like part of the wing. Remember, we were saying that the best possible shape is just a wing by itself. We did these comparisons: What does the flow behind the wing look like? What happens when you put a body on that? Plus a tail? You can restore the air flow to just about what it was without the body. It's as if there's no body there, it's just the wing. That has to be more efficient.
We worked together for a year in South Africa thinking about this and developing ways to explain it. But these ideas had never been tested until this summer. [Huyssen] came over to USC and we tested a model he made in a wind tunnel. We made measurements that showed this was indeed the case. That's what we got so excited about.
Did you find out how much more fuel efficient it would be to design a plane like this?
No. To be honest, we can't. Not yet. We have high hopes. I think unless we demonstrate at least 10 to 20 percent, then it's probably not worth it [as far as] the extra costs involved, the redesign. It's going to have to be very clearly worthwhile in order to tempt people to do this.
What would it mean to redesign planes to look like this?
Designing aircraft is a very complicated balancing of many different constraints and requirements. We've thought of as many of the aerodynamic ones as we can. That includes the aerodynamic efficiency and where the control services go and how stable the plane is. This is basically an aerodynamic efficiency argument. If it does work on those grounds, then it's worth taking a look at these things. I think we've demonstrated that it does work on aerodynamic grounds alone. On the aerodynamic side, you win many times over. The wings can now be shorter and lighter. The body can be lighter because it's more volume-efficient.
Would this redesigned plane have any limitations compared with planes today?
Nothing in this argument depends on the size of the plane. According to us, the jumbo jet should look like this and so should the small, single person plane.
Talk more about the test you did over the summer.
We took a simple, straight wing and we put it in the wind tunnel. We can measure aerodynamic forces very accurately and we can measure the flow characteristics very well. That's why Huyssen came all the way over here from South Africa to put his model in our wind tunnel. We conducted a series of comparisons. The first was the wing just sitting in the wind tunnel by itself. We measured the flow field behind the wing, verifying that it looked as we thought it should. Then we added a body to that wing and it messed up the flow field just like we thought it would. The exciting part was when we added a tail to the back of that body. It cleaned up the flow remarkably, so the flow behind the wing-tail-body combination looked just like the flow behind the wing alone. That was the key test we hadn't done before and that showed the basic idea worked.
What are the next steps for this project?
I'm going to go back to the lab and do more tests with different angles between the components, different tail shapes to fill out the table of results. At the same time, we're publishing a paper on this result. Then, I want to find some funding from a commercial airline or NASA or somebody like that. I'm going to work with a professor of architecture here who is interested in new interior designs which are now possible because the shell is a different shape.
Image, top: Bird plane rendering / RJ Huyssen
Image, bottom: Geoffrey Spedding
Dec 8, 2010
To the Administrator You are right. It is hard to compare the costs of building an airplane today as affordably as we could 50 years ago. It is much more expensive today! Think about what it would cost to build a Model T Ford today. Compare the costs of a C-130 built in the 1960's to one built today, even after correcting for inflation. Since every airplane today is built without a lot of curves, their costs are already low and hard to beat. I get your hypothesis that composites will be cheaper, but where is your evidence - the V-22? the Boeing Dreamliner?
Those long, slender wings remind me of the common observation that an ant can carry 6 times its weight on those skinny legs. But if you scale an ant up 1000 times, the ant's volume and mass increase by a factor of a billion, while the cross-sectional area of its legs (hence their strength) increase by only a million. So the ant that seemed so strong when it was tiny is utterly crushed by its own weight when expanded. Seagulls and raptors are beautiful and must be very efficient as they seem to glide effortlessly, but that doesn't guarantee that the design works when expanded to a size to carry significant cargo or passengers.
@pbevilaqua You are talking about a technology older than 5 decades. No comparison to today's capabilities. Also, cost is high only initially. When every plane is built with lots of curves, cost will get as low as it is today for the inefficient shapes. This happens always when there is progress. Your "very slightly higher drag" is NOT so slightly. Actually, the next generation of aircraft and the revised aerodynamics will allow a near double performance.
Birds have an energy surplus. An efficient airplane will do better than a bird. Specifically, a wing designed this way will only show superior aerodynamic efficiency at lower speeds than we would like, and structural efficiency (weight- power/mile) will be lower.
If being all wing was the most efficient way to fly, then birds would look very different from what the look like today. The creature most "all winglike" I can think of falls under the category of Rays (Manta, Sting (not the singer), etc.). Interestingly enough, if you study how birds fly (slow motion X-ray films of birds flying in a wind tunnel), you will see that they actually swim (butterfly stroke) through the air. Although I doubt that any practical application of flapping wings (bird-like or ray-like) will be applied to commercial aircraft, mainly because there is no 'practical' application, perhaps we should be studying rays and fluid dynamics. Come to think of it, the B2 does look like a Manta ray, rather than a fat, short bird. Please don't through the Manta ray into a wind tunnel. They hate that. You can however use the same technique (slow-mo-X-Ray film) of a ray in a sleuce (like an "Endless Pool"), using water instead of air.
Just hope thet (the Planes) dont swoop down and steal my pizza slice while I'm walking on the beach!
The good thing is that you could name the airlines after the birds the plane is modeled after. Welcome to: Gooney Bird Airlines -Bumpy on landing but we get you there Wild Pigeon - We who where you don't want us to Starling Airlines - We swarm every airport with flights Seagull Airlines - We Scavenge the low end passengers! Pelican Airlines - To and From Florida Only!
Everything old is new again. Take a look at the Lockheed Constellation. It was designed by aerodynamicists using the principles you are rediscovering. Trouble was, the birdlike fuselage was too expensive to manufacture. A simple cylinder with every cross section the same is much cheaper to make and those cost savings more than compensate for the very slightly higher drag. Similarly, the Spitfire used an aerodynamically optimum elliptic wing planform that was too expensive to manufacture. All airplanes today use a cheaper tapered planform that has very slightly higher drag. As you said, "Designing aircraft is a very complicated balancing of many different constraints and requirements."
The lessons learned and the advances in flight controls incorporated in the the B-2 Bomber would be a big step in using this design in the future.