Questions from the Cockpit: How do bugs fly?

Brad, a pilot from Nebraska, writes: It’s getting to be that time of year when it seems like I spend more time cleaning the bugs off the leading edges of my Tripacer than I do actually flying it. But it got me wondering: How do the little SOBs fly, anyway? Their wings — from what little left of them I can see — don’t seem to have any camber.

Brad, I feel your pain. After a lovely winter of light post-flight cleaning, I’m once again impressed by how crowded the sky is when it comes to those small flying cousins of ours. But I confess that I hadn’t given bug flight much thought — beyond cursing insects’ lack of collision avoidance skills — until your note arrived.

So I dug into this issue for you, and here’s what I learned: Almost nobody on the planet truly understands insect aerodynamics — and the few who do can’t explain it to the rest of us. So in that regard, insect aerodynamics are absolutely identical to airplane aerodynamics.

Except for the fact that they are, you know, totally different.

Of course, for a long time scientists knew that they didn’t know how insects were able to fly, even though insects clearly could and — based on fossil evidence — had been doing it since very early in the history of life on the planet.

Famously, or perhaps infamously, in 1934, French aeronautical engineer and zoologist Antoine Magnan reportedly “proved” that bumble bees were incapable of flight. In his book Le Vol des Insectes, he wrote, “I applied the laws of air resistance to insects and arrived at the conclusion that their flight is impossible.”

Talk about saying the wrong thing in print. His point was simply that how insects flew remained a mystery to science and that using the understood laws of mechanical flight was in no way helpful. I think it was quite a clever way of making the point, but the poor man has been the butt of party jokes — and the bane of scientists — ever since.

He also never specifically mentioned bumble bees, so who knows where that came from.

Anyway, five decades later, Cambridge-educated biomechanist Charles Ellington “proved” the very same thing for a wide range of insects.

He used high speed photography to study the positioning of insect wings throughout their range of motion in flight, then applied traditional aerodynamic math — including angle of attack, velocity, density of the air, and surface area of the wing — to calculate lift at various times during the wing stroke. Then he added them all up, compared the lift generated to the weight of the insects, and, yep, you guessed it, insects “can’t fly.”

Not even close.

But then he went on to build a new theoretical basis for how they manage it anyway and his work became the genesis of an explosion of research over recent decades.

Now, I’ll be honest: Reading this stuff makes my head hurt. Interestingly, it’s the exact same headache that I get reading about airplane aerodynamics.

And I may have gotten it wrong, but my takeaway is that insects have more in common with helicopter aerodynamics than they do with airplane aerodynamics. And, as we all know that helicopters use black magic to fly, that should put an end to it.

But I know you want more detail than that, so here goes … break out the aspirin…

Insect Aerodynamics

Contrary to what you may expect, insects, in general, don’t flap their wings. Instead, they rotate them in an oval fore-to-aft arc (explaining the helicopter analogy).

Many insects also flip their wings over at the end of each stroke so the wing is angled to generate lift moving both fore and aft. The angle of attack of the wing is crazy high, right at the stall point, which generates a structure of whirling air called a leading edge vortex.

This is apparently much like our wing tip vortices, but these little tornadoes line the entire leading edge of the wing, and their rapid motion creates a flowing Bernoulli-style low pressure above the wing.

In a standard fixed airfoil, this vortex would rapidly separate from the wing, but the moving action of the bug wing keeps the vortex in place.

Additionally, the criss-cross applesauce nature of the wings in motion also engages a property called wake capture, in which the wing recaptures a percentage of the energy of the previous stroke’s vortex. The wing design of some insects, notably mosquitoes, also allows for a similar vortex on the trailing edge of the wing, for double the lift.

The bottom line is that insect wings generate more lift than would be predicted by their structure alone, due to the nature of how they are deployed. I guess you could say that sometimes it’s not the tool, so much as how you use it.

So there you have it. As mysterious, in its way, as the aerodynamics of mechanical flight.

Amazing Feats of Flying

Meanwhile, during my insect aerodynamic research, I discovered some pretty amazing feats of flying and some (tiny) bits of flying trivia that I want to share with you.

Check this out: Insect wings are made up of sclerotin, the same stuff that forms their outer shells. The wings are super thin, so for strength, most have internal ribs, spars, and stringers made of hollow tubes of the same material.

Most insects have four wings, two on each side, so in airplane terms they are bi-wings, although we do have some mono-wing fliers, too. After all, there are more than 1 million distinct species of flying insects.

Some insects have muscles attached to their wings. These are called direct flight insects. Others move their wings by actually changing their body shape. These are called indirect flight insects. The direct fliers tend to have larger wings with a slower beat.

Speaking of beats, insects boast a range from 20 beats per second in dragonflies, to 200 times per second with flies, to 1,000 times per second for midges.

Many insects can control their wings independently of each other for maneuvering flight, but the airmanship of insects is highly variable, ranging from what officials at the Smithsonian Institution call “clumsy” to “acrobatic.”

Some insects can fly backwards, sideways, and even vertically.

And although apparently not common, some can execute true hovers. Many insects have organs called halteres, which are biologic gyros that communicate attitude information to the buzzing critter.

And if it makes you feel any better about your last $100 hamburger run, flight is expensive for bugs, too. An hour of flight uses so much energy that locusts lose 1% of their total body weight.

Maybe that’s why, like some human pilots, some bugs take cross-country trips as gliders, such as aphids, which can catch thermals to reach higher altitude winds, and can then glide for hundreds of miles.

Sorry female flyers, but in many species, only the male insects are capable of flight. However, the Fig Wasp is an exception — only the females fly.

Meanwhile, sadly, some insects only have wings for parts of their life cycles.

Hall of Fame

Now, like human pilots, some insects are record-setters. Here’s a brief look at their Hall of Fame:

• Longest Insect Cross-Country Flight: Painted Lady Butterfly, North Africa to Iceland. That’s 4,000 miles, folks.
• Fastest Speed in Level Flight: Sphinx Moth, 33 mph.
• Greatest Altitude: 20,000 feet, assorted butterflies. I’ve go no clue how they don’t freeze or suffer hypoxia, but it shows us that altitude is not the solution for avoiding bug strikes.
• Largest Formation Flight: African grasshoppers, which can travel in swarms of up to 100 million (((shudder))).
• Largest Flying Insect: The White Witch Moth which, ironically, is black, with a wingspan of more than eight inches.
• Smallest Flying Insect: Fairyflies, which you need a microscope to see, are minute wasps that can be as small as 0.0059 inches long. That’s tip to tail. I couldn’t find a wing span on them. I guess if I flew through a swarm of those, I’d be none the wiser.

But speaking of clearing bugs of the leading edges, nose, prop and spinner, things were worse back in the olden days. In the Paleozoic era, some dragonflies had wing spans over two feet.

Think what a mess that kind of bug strike would be to clean up.