The following table gives the effectiveness of the different mountings in terms of the frontal area required per horsepower and the cooling surface, the area being in square inches (Front face area of radiator). Area in wind of type (3) is half the calculated frontal area since one core lies behind the other: Taking the value of the Rome–Turney honeycomb radiator as 60 square feet of cooling surface per horsepower, the frontal area per horsepower will be 0.0169 square feet, assuming that the radiator is approximately 6 inches thick. This amounts to 2.43 square inches of frontal area per horsepower.
Example. Find the approximate frontal area of a Rome-Turney type honeycomb radiator used with a motor giving 100 brake-horsepower. Find Resistance at 50 miles per hour (73 feet per second).
| Class of Mounting | Square Inches Per H.P. | Cooling Surface Per H.P Square Inch |
| Front Type | 4.00 | 117.00 |
| Side Type | 7.20 | 104.00 |
| Overhead Type | 2.70 | 112.00 |
| Over-Engine Type | 5.00 | 121.00 |
Solution. Area = A = 0.0169 HP = 0.0169 x 100 = 1.69 square feet. The honeycomb portion of surface for a square radiator of the above area will measure 16.2" x 16.2". Allowing a 1-inch water passage or frame all around the core, the side of the completed square radiator will measure 16.2" + 1" = 18.2". The diameter of a circular radiator core of the same 1.69 x 144 area will be 17.4 inches, since D = 1.69x144/0.7854. Adding the water passage, the overall diameter becomes 17.4 + 1 + 1 = 19.4 inches. The round honeycomb front radiator used on the 100 horsepower Curtiss Baby Scout measures 20 inches. Hunaker found the resistance of a honeycomb radiator to be R=0.000814 AV², there being 4 honeycomb cells per square inch. A = area of radiator in square feet, and V = velocity in feet per second. Adopting, for example, a speed of 73 feet per second, and an area equivalent to a 19.4-inch diameter circular radiator as above, the total resistance becomes:
R = 0.000814 AV² = 0.000814 x 3.1x (73 x 73) = 13.32 pounds, at 50 M. P. H. where A = 3.1 square feet.
Resistance of Chassis. Disc wheels (Enclosed spokes) have a resistance of about one-half that of open-wire wheels. The N. P. L. and Eiffel have agreed that the resistance of a wheel approximating 26" x 4" has a resistance of 1.7 pounds at 60 miles per hour (Disc type). For any other speed, the wheel resistance will be R = 1.7 V²/3600, where V = speed in miles per hour. We must also take into consideration the axle, chassis struts, wiring, shock absorbers, etc. The itemization of the chassis resistance, as given by the N.P.L. for the B.E.-2 biplane is as follows (60 miles per hour):
| Wheels 2(a)1.75 pounds | 3.5 pounds |
| Axle | 2.0 " |
| Chassis struts and connections | 1.1 " |
| Total chassis resistance(3)60 MPH. | 6.6 pounds |
At any other speed, the resistance for the complete chassis can be given by the formula R = 6.6V²/3600. This allowance will be ample, as the B. E.-2 is an old type and is equipped with skids.
Interplane Resistance. The interplane struts and wires are difficult to estimate by an approximate formula, the only exact way being to figure up each item separately from a preliminary drawing. The resistance varies with the form of the strut or wire section, the length, and the thickness. The fact that some of the struts lie in the propeller slipstream, and some outside of it, makes the calculation doubly difficult. The only recourse that we have at present is to analyze the conditions on the B. E.-2. With struts approximating true streamline form, a great percentage of the total resistance is skin friction, and as before explained, this item varies at a lesser rate than the square of the speed.
