Questions from the Cockpit: The Need for Speed

Kirsten, a private pilot from Georgia, writes: What tricks do air racers use to make your planes go faster?

We’ve got a plane load of tricks for plying the sky at ever greater speeds, but they can be broken down broadly into four categories: Adding power, reducing drag, changing aerodynamics, and reducing weight.

I feel the need…The need for speed! If you do too, here’s how you can up your game:

Option #1: Add more power

The first thing that most people think of when they want to go faster is to simply add more power.

And while that will work, to a degree, more horsepower is not the most efficient option.

In his excellent book The Art of Cross Country Air Racing, Sport Air Racing League Chairman Mike Thompson says, “increasing power is the least effective way to improve speed. The increase in horsepower necessary to increase your speed by 1 mph is amazing, and the closer you get to the wing’s limiting speed, the harder it is to power your way to faster speeds.” 

So don’t get to thinking you can just double your horsepower and double your speed. It doesn’t work like that. Not that there’s anything wrong with more power just for the sheer joy of it, but not only does it take a herd of additional horses to increase airspeed, but each extra horse lightens the wallet while adding to the weight of the plane. And as we’ll see later, weight is an enemy of speed, too.

Option # 2: Reduce drag

Of course, there are two flavors of drag: Parasitic drag and induced drag.

Induced drag is a side effect of lift, and is largely inherent in the design of the plane.

Parasitic drag, on the other hand comes from what Thompson calls “various lumps and bumps on the outside of the aircraft.” 

Smoothing out those various lumps and bumps — or getting rid of them completely — is the essence of most “speed mods.” Some of these mods cost virtually nothing. Others, well…

Starting on the cheap side, a clean plane is a fast plane because parasitic drag can come from dirt, grime, and oil on the belly of the plane — and squashed bug carcasses on the leading edges of the wings and tail. If you don’t think that some crunched up bug bits could make a difference, consider that some completion sailplanes have “bug wiper” devices to keep their wings clean from insect remains in flight. That’s because smashed insect remains on your leading edges act like miniature speed brakes. 

So a good wash job is a great way to free your airplane of parasites. 

The next step above clean is waxed. Wax works on a wing like ice works on a sidewalk. Nuff said. So nothing beats a good wax job — on an airplane that is — and waxing the wings, belly, nose, and tail reduces drag enough to cause a significant increase in speed.

The Comparative Aircraft Flight Efficiency Foundation actually undertook a scientific study of waxing and found it added a whopping 2.8 mph to its Mooney M20E! Just from the reduced drag of increased air flow, thanks to smoother surfaces. 

Of course, parasitic drag also comes from objects and accessories on the airframe, such as antennas. It’s often said the only thing you can put on an airplane that’s worse than a brick is a cylinder, and most antennas are cylinders.

How big a difference could that possibly make? My Race 53 has a “blade” com antenna that has a 250 mph drag force of only 0.85 pounds. Compare that to a standard whip antenna that has a drag force of 2.70 pounds at the same speed!

Of course, Race 53’s wings would shear right off if I somehow managed to go that fast, and the blade is more than double the weight at 20 ounces instead of eight, so it might not be doing me as much good as I’d like to believe. 

Meanwhile, if you don’t mind spending some money — and if you’re in aviation, you probably don’t, or like me, you’ve become de-sensitized to it —there’s no end of fairings that can smooth the flow of air over the body of the plane, reducing drag and adding speed.

The company Laminar Flow Systems, for instance, makes a landing gear, brake, and strut faring system called, kid you not, Fancy Pants, that it claims ups the speed of older Piper Cherokees by a whopping 10 miles per hour, all simply due to reduced drag. That’s a sizable percentage increase in speed, and a guaranteed trophy when racing the guy in a similar plane without Fancy Pants.

Other drag reducers include aileron and flap gap seals, hinge fairings, exhaust pipe “wrap fairings,” wing root fairings, and dorsal fin seals.

Some airplanes can pick up yet more speed by installing re-designed windshields or nose bowls.

A budget version of the fairing family is “gap tape,” commonly used by the sailplane crowd, and also an air racer favorite. It’s used to tape up any cracks or less than perfectly smooth seams that might create even the smallest amount of drag. Taping up the various joints of the cowl to prevent “plume drag” is common place among racers, as is taping the joints of fairings. I used it for a time, but found that when I stripped it off, my paint came with it!

So by simply reducing parasite drag, even without boosting power, we’re flying faster.

Option #3: Play with aerodynamics

Now, while boosting engine power isn’t the most effective way to boost speed, an important component of raw airplane power is the prop that’s lashed to the front of the engine. The pitch of that prop makes a bigger difference than you’d think when it comes to speed, and I speak from experience. After my engine was rebuilt, the same prop gave me crazy-fast cruise speed. Or it did once I could get the damn plane into the air, which took waaaaaaaay too much runway. I had to have the prop re-pitched, sacrificing some of that beautiful speed for the ability to get into the air. 

As with all things aerodynamic, there are always tradeoffs. 

Naturally, a constant speed prop is the best choice, as you can adapt it for changing needs from the comfort of the cockpit. The next best option is a ground adjustable prop, with the fixed-pitch “compromise” props like mine being the last choice in the speed game.

But it’s more than just pitch, as propeller shape matters when it comes to speed, too. For instance, re-equipping a Cessna 182’s stock prop with a three-blade Hartzell Scimitar can add 4 mph.

I added what my family calls Voodoo Propeller Tape (technically a vortelator kit) to my prop that increases RPM by modifying airflow over inefficient areas of the prop, keeping the air attached longer. Think of it as a vortex generator for the prop’s airfoil. 

Aerodynamics. Amazing stuff. Did it up my speed? I think so, but I haven’t raced behind it yet. But she sure leaps off the runway with vigor.

Another aerodynamic trick is to shift the center of gravity (CG) as far aft as possible (within the envelope) to make the plane go faster, which I grant you is counter-intuitive.

Wouldn’t an aft CG make the plane nose-high, turning it into its own speed brake? Well, actually, an aft CG requires a smaller angle of attack to maintain altitude. This is because, quoting author Richie Lengel’s Everything Explained book, there’s “less elevator down force to drag around.”

A lower angle of attack, of course, means less lift is required to get the job done, and with less lift, there’s less induced drag. Less drag, more speed. So if that’s the case, why aren’t all planes built tail-heavy to go fast? Because the tradeoff is reduced stability. 

There’s no such thing as a free lunch in aerodynamics. 

Still, as most races take only as long as a lunch, shifting CG aft for just a little while is worth the reduction in control for some. I know one racer who joked about sneaking out onto the ramp at night and stuffing two one-gallon milk jugs of water in his tail cone. He called it his Creamland Dairy STC. Or maybe it wasn’t a joke. That plane is pretty damn fast.

Of course, for the experimental crowd, they can play with wing shape, wing size, or install winglets to reduce the stubborn induced drag from wing tip vortices — buying ever more speed by toying with the forces and factors that rule flight.

Option #4: Shave weight

The race teams of the tragically discontinued Red Bull Air Race World Championship knew the importance of weight. The Red Bull rules stipulated a minimum weight of just under 1,540 pounds for plane, fuel, and pilot — and most of the teams achieved it.

Why was this important to them? Well, for an acrobatic sport like Red Bull, linear acceleration is one key to victory, as aggressive acrobatic maneuvers bleed off speed, and lighter aircraft can accelerate more rapidly to regain that lost speed than heavier ones can.

Equally important, lighter planes require less lift to stay in the air, and that means they generate less of that nasty induced drag that’s otherwise so hard to get rid of.

The effect of weight on speed is not trivial, for any of us. General Aviation News photographer Lisa F. Bentson got saddled (by me) with the nickname Six-Mile-Per-Hour-Bentson after she rode along with me in Race 53 during the Big Country Airfest race in the 2017 Sport Air Racing League season so she could get some aerial shots. She’s just a little slip of a thing, but her added weight cut my race speed by a whopping six miles per hour.

To minimize weight, SARL pilots strip their planes of everything not absolutely necessary for the race. Baggage, jackets, spare oil, tow bars, and even fuel sumps are heaped in race central before the green flag, while fuel is calculated to the barest minimum (plus legal reserve for all but the baddest boys). All to keep light to fly fast.

Thinking beyond the plane

Over the years, I’ve spent a fair amount of time and money on speed mods for Race 53. I’ve removed canopy cover snaps, yanked venturi tubes, and replaced my strut-based landing light — having my mechanics install lower drag in-wing models. I dumped the “jam jar” rotating beacon in favor of wingtip strobes, switched to low-drag antennas, upgraded my engine, and installed the vortelator kit on the prop. 

And that’s just off the top of my head. I’m sure I’ve done more.

But now I’m in the midst of a mod that will not only be the most cost effective of all, but promises to buy me the most speed — perhaps more speed than all my other mods combined — and it also has to do with reducing induced drag by decreasing weight. But not the weight of the horse in the race, but rather, the weight of the jockey. 

Yes, I’m on a diet. 

So far, I’ve lost 33 pounds, with about 10 more to go to reach my “ideal” weight for my height and frame. It’s slow going as speed mods go, but it has an extra benefit: I knew that air racing was good for my soul and now, I’m discovering, it’s good for my health, too.