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,
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 airplanes most important advantage: its cruise speed.
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.
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.
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.
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.
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.
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
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
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.
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
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.
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.
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
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
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
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 Drag-Reduction
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
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
Increase in Horsepower Required for same increase in Vmax.
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 Vmax. 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.
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.
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