“Van Nuys Tower, experimental November Two Mike Uniform, Sepulveda Pass at 3,000, request transit along the 405, going to Whiteman with Golf.”
Traffic on the 405 is heavy. Below me thousands of cars are creeping through the pass between the Los Angeles basin and San Fernando Valley. I’ve been following the Malibu coastline eastward at 3,500 under a shelf of KLAX Class B and above the patches of urban desert left by last year’s wildfires. The Getty Center—a sprawling hilltop museum that generously provides a landmark even to pilots indifferent to art—has now slid beneath my left wing, and I’m dropping down to 2,900 to pass under Burbank’s Class C.
Now comes the fun part.
“November Two Mike Uniform,” Van Nuys comes back. “Remain east of the 405 below 1,700.”
If you’re not already a subscriber, what are you waiting for? Subscribe today to get the issue as soon as it is released in either Print or Digital formats.
I throttle back, pop the air brake, and push the nose over. Little more than half a minute later I’m level at 1,600.
The exhilarating nosedive is made possible by a panel of foam-cored, carbon-fiber sandwich, 44 inches by 8, that swings out of the belly like a door opening. The big bluff board roughly doubles the airplane’s drag.
Air brakes are among those things—the onward march of modernity relies on them—that you don’t see the need for until you get them, and then you can’t imagine doing without them. Like many pilots, I first made their acquaintance when I began flying sailplanes. Absent an engine, the only way to control the approach slope is with drag. In airplanes with engines, however, there seemed not to be such a pressing need. The propeller itself, backdriving an idling engine, adds some drag. You can dirty up some more with flaps and possibly gear. Then there is always the special friend of taildragger pilots—the forward slip. It was simply a matter of piloting skill not to arrive too high.
- READ MORE: Why We Fly, Indeed: There’s Always Something New Out of Africa
- READ MORE: Where to Put It: Is Stabilizer Position Wisdom or Whim?
Still, every once in a while you’d want to get down extra quickly or in a short distance. ATC may want an expedited descent, or you may be flying on top and suddenly see your destination 10,000 feet below you. For those moments, you need an air brake.
An air brake serves two purposes: It enables you to decelerate rapidly without gaining altitude, and it allows you to descend rapidly without over-cooling your engine. When air brakes first came into use, they were all about descending. The invention of dive-bombing, during the inter-war period, had created a need for drag.
The idea of dive-bombing was to be able to aim bombs more precisely by minimizing the hard-to-predict horizontal component of their trajectory. The precision of dive-bombing was especially important in naval warfare, because if your bomb missed the ship, it missed everything. On land you could at least hope that an errant bomb would produce some collateral damage. The German Junkers Ju 87 “Stuka” could dive almost vertically, making it very accurate but also difficult to recover. Some models were equipped with an apparatus intended to get them safely out of a dive even if the pilot passed out from G forces along the way.
The Stuka, draggy to start with, had long, narrow spoilers that swung out of the bottom of the wing. Another famous dive bomber, the Douglas SBD Dauntless, which had a starring role in the Battle of Midway, used hinged, perforated spoilers, also below the wing.
As World War II went on and the Allies gained air superiority, dive-bombing eventually gave way to other ground attack methods. But the arrival of jet fighters gave new life to air brakes. Lacking propellers, jets did not have the built-in braking available from an idling engine, and both their clean design and residual thrust of their throttled-back engines made them hard to slow down.
I’ve used the terms “air brake” and “spoiler” interchangeably, because, although not all air brakes are spoilers, all spoilers are air brakes. The job of a spoiler, especially an upper-surface one, is often described as “dumping lift,” but, unless spoilers are being used for roll control or after landing, that is a misnomer. Except during brief periods when the angle of attack is changing, lift is always the same as weight, and so the extended spoilers you see outside your airliner’s window are not changing the total lift, although they are changing its distribution across the span. Their purpose is to add drag, making the airplane descend faster to keep up its airspeed.
Air brakes have taken many forms. A 1949 report by the National Advisory Committee on Aeronautics, NASA’s precursor, painstakingly itemized 32 different types of air brakes and locations on the airplane, with effectiveness data on each. Some types—the Swiss-cheese fences of the Dauntless, for instance—have since gone out of fashion, and others, like tail cones and ailerons that split and spread out—have appeared to take their place.
An air brake should have certain desirable characteristics. If manual, it should be easy to deploy and retract. It should not tend to pop out of its own accord. In case of failure to retract, it should not keep the airplane from climbing. It should produce no drag when retracted, and little noise and vibration when deployed. It should not change the airplane’s trim. It should increase the rate of descent by a worthwhile amount, like 1,000 fpm or more. It should be usable up to VNE, and preferably beyond.
My own air brakes have been a mixed bag. The ones in the first Melmoth (1973-82) were aluminum honeycomb boards that rotated out of a spanwise slot in each wing. They were hydraulically actuated, and, because I neglected to include a restrictor to slow the flow of hydraulic fluid, they jumped out almost instantly, producing a disconcerting, if fleeting, impression of free fall. I could have fixed that fault, but Melmoth was run over and destroyed by an errant Cessna before I got around to it.
My second effort is a bit better. It’s much bigger, and it can be extended gradually. On the negative side, it produces, at higher speeds, a chaotic sashaying motion that is due to something called a Kármán vortex street. This is not an address in Budapest but a series of eddies that break loose at irregular intervals from alternating sides of the brake. The effect, for passengers, is akin to driving on a poorly maintained dirt road with underinflated tires.
This description does not make the air brake sound like a very desirable thing, but really it is. I use it on every flight, and it’s an integral part of the landing checklist.
At least one company, Precise Flight, produces wing-mounted air brakes as retrofits to a number of general aviation types. I have never flown an airplane equipped with them, but I assume they are better behaved than mine. Still, air brakes are like your own children—well behaved or not, you can’t help but love them.
This column first appeared in the March Issue 968 of the FLYING print edition.