10

Engines should be a type that has been certificated by the Ci-

plane performance, weight and balance, and the propeller

vil Aeronautics Administration. Civil Aeronautics Administration engine specifications, which are available to the public, specify the power, speed and other limitations which apply to each engine model. The engine should be mounted in such a manner

clearances must also be considered. In the case of propellers with metal blades, the vibration characteristics of the engine-propeller combination are also of primary importance.

that it will operate properly under all normal conditions and

so that excessive vibration is not transmitted through the mounting to the airplane structure. Most engines have provisions for the use of vibration isolating rubber bushings.

Thepowerplant installation includes primarily that portion of the aircraft which furnishes the motive power. This includes among other items, the engine, engine cowling, firewall, propeller, fuel system, oil system; cooling system, exhaust system; the related accessories, controls and instruments and the attachment of these items to the structure of the aircraft. The installation usually consists of all parts forward of the firewall as well as the supply and control

systems to the rear of the firewall. For instance, fuel tanks and traps supporting the tanks as well as cockpit controls for operating the engine are included. Airworthiness Evaluation - To evaluate the airworthiness of a powerplant installation in an aircraft, consideration should be given to the design and construction details, the operating characteristics, and features incorporated to permit maintaining the continued airworthiness of the installation. The objective is to achieve satisfactory powerplant operation under the atmospheric conditions, altitudes, and maneuvers to be encountered in ground and flight operation.

Propellers used in civil aircraft should be types that have been certificated by the Civil Aeronautics Administration. The propeller specifications issued by the Civil Aeronautics Administration list the propeller ratings in terms of horsepower and revolutions per minute. They also list, in a few instances, the maximum cylinder bore of the engine on which the propeller is eligible for use. The engine ratings and bore must not exceed the values for which the propeller is approved. Specifications for constant-speed propellers and most controllable propellers also list approved accessories such as governors, etc. Although a propeller may be satisfactory for use insofar as the propeller and engine ratings

and bore are concerned, the air-

Propeller Vibration - To determine that the vibration characteristics of the propeller are satisfactory in any given installation, the blade-vibration stress must be measured during operation. Past experience has indicated that this procedure is necessary with all propellers except wood types. In some cases it is possible to determine the effect of changes, or slightly new combinations, by ground tests or comparisons with previous data, but in most cases flight tests for this purpose are necessary. The propeller manufacturers have the stress-measuring equipment necessary to accomplish these tests. Fatigue due to vibration is the most frequent cause of propeller failures. Vibration impulses can be caused by various irregularities of airflow, but these are usually important only for very large diameter propellers of approximately 13 feet and over. Engine power impulses, however, are the main cause of propeller vibration. Vibration, if continued at the natural frequency of the propeller, may cause pro-

11 peller failure after a few hours.

Metal propellers must therefore never be used without ascertaining from the Civil Aeronautics Administration whether the vibration characteristics of the

engine - propeller combination are approved. Each engine has a critical range of operation for

each type

of

propeller with

which it is combined. If this range is in normal, engine-operating range, a placard is required to caution the pilot

against operating in the dangerous range and the tachometer should be marked with a red arc in this range. Propeller Pitch Limitations -

and

Speed

In the case of fixed-pitch and ground-adjustable-pitch propellers, the following information is determined at the time the

airplane is type certificated, and

is included in the airplane specification: Static r.p.m.'s at maximumpermissible throttle setting, (Not less than . . . . . .r.p.m.) (Not more than . . . . . .r.p.m.) Propeller diameter, (Not less than . . . . . .inches.)

(Not more than . . . . . .inches.) These data serve to insure compliance with minimum performance requirements, particularly takeoff and first minute climb, and will also assure against the possibility of overspeeding during takeoff or in a power-off dive. Normally, propellers made of wood will require a different range of static

r.p.m.'s limits than metal propellers. Propeller Replacements - Generally, fixed-pitch or ground-adjustable-pitch propellers which fall within these limits should provide satisfactory performance. In replacing propellers or

altering the pitch so that the static r.p.m.'s and diameter limits are no longer complied with, the airplane should be put through the following simple

flight tests to assure that safety has not been sacrificed:

(a) Takeoff with full throttle or the maximum-allowablemanifold pressure and climb at the best-rate-of-climb speed. If

the best rate-of-climb speed is not known, it may be estimated

as a speed one-third of the way

between the power-off stalling

speed and the maximum levelflight speed. The engine r.p.m.

should not

exceed the

rated

r.p.m. during this test.

(b) With the throttle closed dive the airplane at 110 per-

cent of the maximum level-flight speed. The engine r.p.m. should not exceed 110 percent of the maximum continuous rated engine speed in this test. (c) Climb the airplane at full throttle or the maximum allowable manifold pressure at maximum gross weight and at the speed mentioned in item (a) above. Likewise, in the case of controllable and constant-speed propellers, the aircraft specification will list the propeller di-

ameter and the settings at which the blade stops should be set in order to assure conformance

with minimum performance requirements. The diameter and

stop limits are given for each specific controllable and constant-speed propeller which has been approved for use on the airplane.

If these settings are

changed, the suitability of the new settings should be checked

in the same manner as described above for fixed-pitch propellers.

Df course, in selecting propellers, c a r e f u l consideration should be given to the provision af adequate clearance between ;he propeller and the ground and

between the propeller and airplane structure. Propeller Clearances - For land planes with tail wheel type landing gear, the minimum satisfactory clearance between the

propeller and ground is generally considered to be 9 inches with the airplane in a horizon-

tal position and the landing gear

deflected under the most forward center of gravity position with the maximum gross weight of the airplane for takeoff.

In addition to this, consideration should be given to how much this clearance will be decreased with smaller angular displacements of the engine nose below the horizontal position together with the smoothness and surface conditions of the runways from which operation is anticipated. The minimum clearance between the propeller and the engine, engine cowling, and other parts of the airplane is dependent upon the relative movement present and the effect it produces upon the vibration characteristics of the propeller. With the most adverse relative movement of the parts, the propeller should clear the engine parts and cowling by at least ¥4 inch, and other portions of the airplane by at least 1 inch.

14 rear lead-through (the compression tube that the spars attach to). The tank has an eight ounce displacement brass float on an arm brought down through the front upper left corner of the tank. This provides a shaft for

the attachment of an indicator

pointer for a fuel gauge directly readable from the cabin. The wing-tip floats are made in the same way as the hull. They will be supported by three struts. One "V" strut will be attached to the lift strut, and one lateral strut will attach to

a modified jury strut on the

Owen S. Billman 0n one of my first pleasurebusiness trips in my "Little

Pink Cloud" early last spring, I flew into the Tri-Cities Airport

at Endicott, New York.

After

looking over my little ship, the airport operator told m e . . . .

"There's another of you "Experimental" fellows building a l i t t l e amphibian somewhere hereabouts. . . . name of Fryklund." Well, it didn't take me long to trace him down. His name is Robert Fryklund of 3627 Lott Street in Johnson City, New York, a project engineer in manufacturing research with International Business Machines at Endicott, New

York. He learned to fly a few years

ago, but was singularly impress-

ed by the lack of utility of the average lightplane for sportsmen-flyers. He's one of the

many who loves hunting, fishing, swimming and picnicing in

addition to flying.

In this part

of the country, there are countless places to use a seaplane or

amphibian, but there are few

front lift strut. such airplanes available within the financial reach of the aver-

age pilot. As a result, he decided to design and build a weekend knockabout for sportsmenflyers. His airplane is a two-

place, high wing tractor amphibian, with a retractable tricycle landing gear, and built solely for utility. It will have a moderate cruising speed, a low landing speed, and will feature economical operation. The pertinent data is as follows Wing span . . . . . . . . . . 35' 6" Length . . . . . . . . . . . . . . . . 24' Wing area . . . . . . . . 180 sq. ft. Gross weight . . . . . . 1300 lbs. Empty weight . . . . . . 830 lbs. Useful load . . . . . . . . 470 lbs. Engine . . Continental A-80-9 @ 80 hp., & starter Fuel capacity . . . . . . . 16 gal. Power loading . . 16.3 Ibs./hp. Wing loading . . 7.3 Ibs./sq.ft. Chord . . . . . . . . . . . . . . . . 63" Beam of hull . . . . . . . . . . 48" Baggage allowance . . . 40 lbs. Bob decided to use the wings from a standard Taylorcraft BC-12, in order to keep produc-

tion time to a minimum, and due to its having a so-called "zero moment" wing. He has reinforced the drag bracing by installing 4000 lb. test wire to take up the drag of the wing floats. He is using the standard Taylorcraft elevators and rudder, but has built his own stabilizers. The fin is integral with the fuselage. The hull is made of Fibre-glas cloth, and was made in a developable sheet metal mold of flat pieces, reinforced by an external wooden framework, into which was applied polyester resin and glass cloth, using a paint roller and paint brush. The sheet metal used in the mold was 26 gauge galvanized iron. The hull was designed by

making use of information found in NACA reports listed at the

end of this article.

His hull

features a pointed step similar to the NACA Model 35 hull. A parabolic downward inflection of planing surfaces was made in an attempt to more evenly distribute planing pressures on the bottom of the hull.

This also is expected to reduce the drag of the hull while planing in the water.

In forming the hull, three plies of glass cloth were used

for the faces of the sandwich

over a half-inch thick honeycomb (a phenolic impregnated

paper), making a wall thickness

of %" over the forebody and

the bottom only of the afterbody ell Racer are as follows: Weight empty 310 pounds, gross weight

with 150 pound pilot and 2V 2

gallons of fuel 475 pounds. Wing area 76 square feet. Fuel capacity 8 gallons maximum. In the 1932 Edition of the Fly-

ing and Glider Manual there was published a how-to-build article by Orville Hickman on

an airplane called the Powell P. H. Racer. These plans were

The struts for

the floats are made from material taken from the rear lift

based on the original Powell

Racer but included a steel tube

fuselage and tail surfaces and

other changes. It is not known if any airplane of this modified

design was ever built.

of the hull. The sidewalls and turtledeck were made of three plies of glass cloth without the

honeycomb. The turtledeck is removable in one unit for easy

access to the inside of the fuselage. It is fastened to the hull

by a stepped lap joint involving

thirty-two threaded inserts.

The 16 gallon gasoline tank is removable with four bolts,

and occupies all the space aft

of the engine cowling over the roof of the cabin, back to the

strut of a "Cub". Fifty-two retaining bolts hold

the hull to the airframe. These are grouped in clusters about the landing gear attachment

points, lift strut points, nose wheel saddle, and stabilizer strut attachment points. All bolts are in shear as far as stress from hull weight or water impact is concerned. The retractable tricycle gear uses 16" main wheels and a 12"

nose wheel, all employing modified Aeronca oleo-spring struts.

The main wheels are made of four inside halves of Aeronca wheels. The nosewheel was the tail wheel of a Cessna UC-78. It retracts into a free-flooding,

self-bailing well with clam-shell

doors. All wheels retract by means of a hand crank and winch. There is a mechanical