**Chapter One**

**Your Airplane's
Parasite Drag**

As an airplane owner and pilot, perhaps you'd like to understand more about your airplane's parasite drag. What it does, what it is, what it means, and especially what it's costing you. All this drag that not only slows up your airplane, but also requires the expenditure of power, and thus fuel, and therefore your money, to overcome it. As you pay for your airplane's drag, you might as well know what it is you are paying for. Therefore, our purpose is to look into the causes and effects of your airplane's parasite drag, and give you a better understanding of what your airplane's parasite aerodynamic drag may be costing you.

**The
Gross Equivalent Drag Area**

**Why We Use the Gross Equivalent Drag Area. **For
our purpose, there is a difficulty with the often-used formula
for the so-called "Equivalent Flat Plate (Drag) Area (EFPA
or EFPDA). When using the EFPA formula to get reliable figures
for comparing two or more piston-engine propeller-driven
airplanes, we need accurate figures for the propeller efficiency.
However,

**Chapter Three**

**Wing Profile
Drag - Some Causes**

**The Wing Drag.**
While your airplane's wing creates the lift that makes your
airplane fly, it also causes a good bit of fuel-consuming
parasite profile drag. This wing's profile drag makes up a large
portion of your airplane's total drag. It diminishes your
airplane’s most important advantage: its cruise speed.

**Chapter Four **

**Wing Drag - The
Cost **

**Our Four Example Airplanes. **In the various
sections on the parasite drag of your airplane's main assemblies,
we will base our drag calculations on four types of manufacturer's
General Aviation light airplanes:

1. A 2400-pound four-seat airplane.

It is powered by a 160-HP engine and a fixed-pitch propeller; n = 0.75.

**Chapter Five**

**Fuselage Drag -
Some Causes**

**Airplane Drag**. The total drag of your
airplane's fuselage assembly depends mostly on the turbulent drag
of its parts and on their mutual interference. That is where
their form or pressure-drag comes in. In this case, form-drag is
due mainly to the disturbance or wake created by the fuselage. as
a whole. Important factors are its main cross-sectional area and
longitudinal fairing lines.

**Chapter Six**

**Fuselage Drag -
the Cost**

**Compared to the wing drag,** the fuselage drag
is a lot harder to pin down with any accuracy.

When looking at the parked airplanes at the Wittman Field at Oshkosh you will see the most extreme variety of shapes and sections, surface finishes, protrusions and protuberances on the fuselages of these mostly older airplanes.

**Chapter Seven**

**Landing Gear
Drag - Some Causes**

**The Conventional Landing Gear**. The
conventional fixed non-streamlined tricycle landing gear,
protruding into the air-stream as it does, creates a lot of
parasite drag. As this parasite drag makes up a surprisingly
large of part of your airplane's total drag, it greatly
influences its performance and cost.

**Chapter Eight**

**Landing-Gear
Drag - the Cost**

**Fixed Landing Gear Drag. **The fixed landing
gear creates up to approximately 30 to 40 percent of the total
airplane drag. For a design study, for landing gear without
fairings, the percentage of total airplane drag was assumed to be
38 percent. For the faired gear it was 14 percent. One author
gave a Cdo of 0.022 for the Cardinal RG (based on wing area S and
at zero-lift coefficient) and 0.033 for the basic Cardinal.

**Chapter Nine**

**Engine Drag -
Some Causes**

**Cooling and Cowling Drag. **The purpose of your
airplane's cooling system is to carry off the heat developed by
the engine with the minimum possible loss in engine power. while
maintaining the required engine temperature under all flight
conditions. Transferring the engine's heat to the cooling-air (even
if through a radiator on a liquid-cooled engine) always requires
a portion of the engine's horsepower. There are many reasons for
this power loss. For

**Chapter Ten**

**Engine Drag ****---**** the Cost**

**Cowling- and Nacelle Shape.** Your airplane's
engine cowling(s) and nacelle(s) are far from the low-drag forms
we like to see on our light airplanes. Even the best shapes of
engine-cowling and -nacelles make up a large part of the total
airplane drag. Putting in bigger engines to increase flying speed
only makes things worse. As an airplane's engine's total engine-instal

**Chapter Eleven**

**Tail Drag - Some
Causes**

**The Practical Causes**. While our interest is
strictly in the practical causes, and the cost of the tail-drag
in your aviation-gas dollars, the drag of the tail-surfaces
depend on various important aerodynamic and design factors. For
example, a big engine needs big tail surfaces. So do twins.

**Chapter Twelve**

**Tail Drag - The
Cost.**

**Tail Drag Cost for the Four Airplanes.** Here
is some NACA data, based on tail surface area outside the
fuselage, with no tail-lift provided. Profile drag per square
foot, at 100 mph, in plan-view or side-view, including
interference drag, at 100 mph, is roughly

**Chapter Thirteen**

**Maneuvering Drag**

**Control Surfaces**. A good percentage of your
airplane's total drag comes from the deflection of the control
surfaces during cruise flight. When you deflect the control
surfaces from their neutral position, they cause a definite
addition to the total airplane drag.

**Chapter Fourteen**

**Trim Drag -
Causes and Cost**

**Many General Aviation light airplanes** come
with pitch, roll, or yaw trim control in the form of trim tabs at
the control-surface trailing edge. Each use of trim-control
causes trim drag. We'll look at this in some detail below.

**Chapter Fifteen**

**Slip-stream
Effects and Drag**

**Your Airplane's Slipstream. **Your airplane's
propeller-slipstream consists of the accelerated mass of air
thrust backward by the propeller. It is roughly the size of a
cylinder of the same diameter as the propeller. This accelerated
speed of the slipstream gives your airplane the thrust required
for its forward flight. The slipstream is an air mass with a
higher velocity than the

**Chapter Sixteen**

**Interference
Drag **

**Causes and Cost**

**Interference Drag - Causes**. In the airflow
around or over an airplane part, the combination of an increasing
pressure and the inward curvature causes a turbulent boundary
layer. To keep the airflow interference low, the boundary-layer
flow around each part must match closely. The aerodynamic
pressure-distributions and boundary-layers of two shapes
intersecting or placed

**Chapter
Seventeen**

**Flying-time
Savings **

**from Drag
Reduction **

**Time-savings for 1 to 1000 hours of cruise flight.**

Just to show you how we get the figures for Tables No. 3, 4, and 5, we work out the time-savings made possible by drag reduction. As before, from 95% drag down to 50% drag in steps

**Chapter Eighteen**

**Savings in Fuel
Costs**

**Through Drag
Reduction**

**Money saved on Fuel expenses.** In this Chapter
we work out the savings in fuel-costs we get from drag reduction
on light airplanes. This time we will also use the factors we get
from calculating the third root of D2/D1. We have a good,
practical reason for this. With its drag

**The
Effect of Your Airplane's Parasite Drag Reduction in Straight and
Level Flight.**

**Parasite drag reduction** gives
benefits at both ends and at the middle of a flight. However,
while the take-off and the landing phases take only a relatively
short period of the flight time, the cruise-flight section may go
on for from two to five hours. Thus any drag-reduction benefit

**The Effect of
Drag Reduction**

Part** 2**

**Speed
Increase with Drag Decrease.**

**Keeping the Same Engine. **Next
we first take a look at how the maximum performance of our 160 HP
2400-pound airplane increases when we reduce the drag in the same
way but keep the same engine. Like when the owner decides to have
some mod shop do something about

**The Effect of
Drag Reduction **

**Part 3**

**Increase
in Horsepower Required for same increase in V**_{max.}** **

**Next we look** at by how
much we will have to increase the engine's horsepower rating to
get up to the same 26% speed increase. Here again we use the same
formula, with the V_{max.} multiplied by the third root
of the relation between the higher HP over the original hp. This
time we increase the horsepower in steps of ten hp, up to double
(100 % extra) the original hp. The resulting figures in Table 1-3
clearly show that increasing your airplane's speed by putting in
more horsepower is the least efficient way.

To get the same 26% speed-increase we get from a 50% drag decrease you would have to put in 100% more horsepower. Short of adding another engine, that is only valuable as a pencil and paper-exercise. Which, of course, is what we are doing here.

Suppose you put double the engine power in your airplane.

**Chapter 20**

**Drag Reduction **

**Climbing Out
Faster**

While most information on climb-out mentions the effect of increased horsepower available, decreasing an airplane's drag will also increase its rate of climb.

**Chapter Twenty-one**

**Drag Reduction -
Gliding Farther**

**Parasite Drag:
Your Enemy**

Note No. 1. Countless articles and books are available on what to do when the prop stops and you find yourself flying an overweight glider. Therefore, there is no need for me to go into that here. My purpose here is strictly to show the effect of drag decrease on a number of hypothetical airplanes, with the also hypothetical propellers are all stopped.

Note No. 2. The tables in this Chapter are based on computer calculations, and include induced drag. For preliminary calculations, flying speeds in 1.0 mph speed increments were used from stall speed to maximum speed. Final calculations for Rate of Sink and L/D-ratios are based on speed increments of 0.10 mph.

**Your gliding airplane**
descends through the air because energy is being consumed by the
drag forces acting on it. This energy can only be provided by
your airplane