63 CHAPTER 7. THOUGHTS ON TESTING CANARD TYPE AMATEUR-
BUILT AIRCRAFT ‘‘FLY.’’ Jonathan Livingston Seagull SECTION 1. CANARDS
1. OBJECTIVE. To discuss canard flight characteristics.
a. Canard configured aircraft generally fall into 2 categories: the LongEze design (pusher prop, tandem seats) and the Quickie (Q2) design (tractor prop, side by side seats). Canard configured aircraft do not ‘‘stall’’ in the conventional sense. All successful ‘‘loaded canard’’ designs have the angle of incidence (AOI) of the canard set higher than the main (rear) wing.
b. As the airplane’s angle of attack (AOA) increases, the canard should stall first, lowering the AOA of the main (rear) wing. Since the rear wing doesn’t stall, a characteristic ‘‘buck’’ or ‘‘nod’’ takes place. Full aft stick results in the canard alternately stalling and flying while the rear wing never reaches it’s critical AOA and continues to fly. This self-limiting stall characteristic makes a properly designed and built canard aircraft un-spinable. It should be noted, however, that the accident rate for canard designs are approximately the same as conventional designed amateur-built aircraft because of the following:
(1) During take-off, the transition from ground roll to flight can be a more critical procedure in some canards as compared to more conventional designs.
(2) Some canards with combinations of CG and pitch control sensitivity will be more likely to over rotate at lift-off.
(3) Some canards have less visible airframe structure in front of the pilot and in his peripheral vision. Others have more than enough. These differences in design can produce a different reference frame for pilots with many hours of conventional aircraft time and may cause initial errors in pitch attitude, such as the nose too high on takeoff and landings.
(4) In addition, canard aircraft by design have very different take-off characteristics than conventional configured aircraft. Canard aircraft with pusher propellers need a substantially higher rotation speed on take-off.
(5) To rotate a conventional design aircraft, all that is required is enough airspeed to provide sufficient control to attain a positive angle of attack due to the long moment arm from the main gear (the axis of rotation) to the tail, a relatively small amount of lift is required. This lift, generated at a relatively low airspeed, makes it possible to rotate the aircraft into the take-off position slightly below flying speed. Allow the aircraft to accelerate to flying speed and lift off.
(6) In contrast, the canard nose wheel will stay firmly on the ground until an airspeed is reached at which the canard, with full up elevator, can generate enough lift to equal the following:
(i) the load carried by the nose wheel, plus
(ii) the nose down moment caused by the friction of the nose and main gear tires with the surface, and the down-thrust vector provided by the propeller during the take-off roll.
(7) Since the main wing may reach flying speed before the canard, the nose wheel will stay firmly on the runway until take-off speed is reached.
Rotation will then occur, and the aircraft will literally jump off the ground.
(8) Canards with a thrust line above the CG will have appreciable pitch trim change with power. Forward stick motion is required when power is reduced. While this may not be of any consequence to an experienced pilot, it can be a serious surprise to an unwary and inexperienced pilot. This unfamiliar flight characteristic might cause pilot-induced pitch oscillations with disturbing consequences under some conditions (e.g., an aborted take-off).
(9) Due to its unique design, the canard aircraft needs a higher nose up attitude when landing compared to conventional configured aircraft. Many canard pilots are reluctant to raise the nose high on
64 5/24/95AC 90-89A landing due to the limited forward visibility while the nose is up. Consequently, many canard pilots tend to make their approach angle shallow. This shallow angle results in approach speeds quite a few knots faster than what is necessary. For pilots who prefer visibility to shorter runways, it is recommended that canard designed aircraft be tested on runways a minimum of 1,000 feet longer than what would be used for a conventional aircraft of the same horsepower and performance capability.
Longer runways should be used until the pilot becomes more experienced with the landing characteristics of the aircraft.
(10) If the nose is held at a too high an angle on landing, the canard will stall while the main wing is still generating lift. The stalled canard will drop the nose rapidly onto the runway with enough force to damage the nose gear.
(11) Quickie (tractor engine designs) configured canard designs have a limited ability to rotate nose up while on the ground. This tends to increase takeoff speeds because the canard and the main wing angle of attack are limited while the aircraft is on the ground. That is why this design appears to ‘‘levitate’’ off the ground without much apparent pitch change.
(12) Some canard designs are very sensitive to rain or other types of contamination on the leading edge and/or top of the airfoil. Contamination in the form of water droplets, frost, crushed insects, or even poorly applied paint will disturb the laminar flow over the canard and lift is lost. When decreasing lift over drag (L/D) performance, the chances for an accident increase.
2. FLIGHT TEST CONSIDERATIONS.
Technically, a canard type aircraft cannot stall, or at least it will not stall in the normal fashion. A pilot testing the aircraft for stability characteristics should approach such testing with caution in mind.
a. Under certain conditions, usually consisting of aft c.g. problems, the main wing may stall before the canard surface. In this case, extreme pitchup can occur until the canard surface or strakes stall.
The aircraft would then pitch down to a near-level attitude, however the airspeed would be approaching zero and the angle of attack could approach or exceed 45 degrees. This condition (high-alpha), could be so stabilized, with the aircraft in a deep stall, that recovery might not be possible.
b. Testing for pitch stability in a new design or a just-completed aircraft built from a kit or from plans is a requirement the pilot needs to consider prior to carrying passengers. Pitch stability tests are conducted to ensure that the aircraft does not exhibit any dangerous flight characteristics but must be approached and conducted in a logical and sensible manner.
(i) Positive pitch stability is exhibited when the aircraft trimmed for hands off level flight, returns to that state when a control force is applied and released.
(ii) Neutral pitch stability is achieved when the aircraft remains in the pitch attitude attained when a control force is applied.
(iii) Negative pitch stability is demonstrated when the aircraft departs from the pitch attitude attained when a control force is applied and continues to increase in amplitude.
c. The aircraft should be weighed and the c.g.
carefully calculated. At the same time, determine the weight needed and the moment calculated to load the aircraft at the most forward and aft c.g. limits recommended by the designer. Beginning at the most forward c.g., trim the aircraft to a hands off condition and slowly reduce the power, maintaining altitude by increasing pitch attitude. When the stick reaches the full aft position, momentarily release the back pressure followed by full aft stick. The aircraft, in demonstrating positive stability, should return to its original pitch attitude and remain there. The aircraft should display positive stability characteristics.
d. Other tests may be conducted by adjusting the c.g. further aft and observing the tendency of the aircraft. At some point near the aft c.g. limit, you may experience neutral stability, or the point where the aircraft no longer recovers by itself from the upset. Moving further aft in the c.g. range from this point will cause the aircraft to diverge from the trim path in the direction of the upset (neutral stability).
e. Some designers and builders have installed adjustable, moveable ballast containers in the aircraft to allow the c.g. to be adjusted forward or aft during flight. If testing is to be accomplished outside the
65 recommended range, it is advisable to consider the installation of a ballistic recovery system or spin chute system. In addition, the pilot should make a decision about leaving the aircraft if the test becomes untenable.
66 5/24/95AC 90-89A
THIS PAGE INTENTIONALLY LEFT BLANK
67 CHAPTER 8. ULTRALIGHT AIRFRAME INSPECTION ‘‘You can learn 10 things by learning one.’’ Japanese proverb SECTION 1. DIFFERENCES
1. OBJECTIVES. To serve as additional resource for ultralight test pilots and to help the new owner develop a flight test plan for the ultralight.
2. DEFINITION. The term ‘‘Ultralight’’ means a fixed wing vehicle that is powered by a conventional 2 or 4 cycle, gasoline powered engine and is operated under Part 103. It has one seat and does not exceed 254 pounds, excluding floats and safety devices. In addition, the ultralight can be unpowered, in which case the weight is restricted to 155 pounds.
The powered ultralight’s fuel capacity cannot exceed 5 U.S. gallons. The vehicle should not be able to exceed 55 knots calibrated airspeed at full power and level flight and cannot exceed a power-off stall speed of 24 knots calibrated airspeed. The term also includes two place ultralight training aircraft of 496 pounds or less operated under either the EAA or USUA exemption to FAR Part 103.
a. Be aware that both single and dual seat ultralights in this performance class are not restricted only to FAR Part 103 operation. If they qualify, they can be operated under FAR Part 91, if they meet § 21.191(g) amateur-built category or § 21.191(h) operating kit built aircraft in primary category. Only single seat ultralights of less than 254 pounds empty weight, however, can operate legally under FAR Part
103.
b. Many in the general aviation community view amateur-built and ultralights as one and the same design category, therefore all flight testing procedures should be identical. While in many cases this assumption is true, there are several major differences between the two designs.
(1) Most ultralights are assembled from complete kits, unlike amateur-built aircraft of which the major portion (51 percent) of the aircraft and its component parts are manufactured by the builder.
Most of the kit/ultralight manufacturer’s pilot operating handbooks/flight manuals are usually accurate and address the majority of the information covered
68 5/24/95AC 90-89A in the first eight chapters of this AC. The FAA recommends the pilot’s operating handbook always be consulted by the new owner prior to flight.
(2) The changes in ultralight ownership are more frequent than amateur-built and general aviation aircraft ownership. Although the ultralight is ‘‘used,’’ the new owner is usually unfamiliar with the its operating characteristics. A comprehensive flight testing/training program should be a high priority safety consideration of the new owner.
(3) New flying skills should be developed.
Each ultralight pilot/owner should address the effects smaller size, lighter wing-loading, lower weight, and higher drag designs have on low-speed flight.
c. Due to these differences, the FAA recommends that each ‘‘new’’ ultralight owner design a FLIGHT TEST PLAN regardless if the ultralight was bought, used, and/or the ultralight has a Flight Manual supplied by the manufacturer. The ultralight FLIGHT TEST PLAN does not have to be as extensive as the one recommended for amateur-built aircraft but should address all flight conditions and emergencies called out in the ultralight’s flight manual.
d. With these differences in mind, the next three chapters will address problems associated with both NEW and USED ultralight flight testing. Chapter 8 will address pre-test flight inspection, chapter 9 will cover engine and fuel system operation and inspection, and chapter 10 will cover ultralight flight testing.
e. In keeping with that professional approach towards flight testing, it is suggested that a FLIGHT TEST PLAN and other relevant safety recommendations found in the chapters 1 through 7 be adopted by the ultralight owner/operator prior to test flying a new or used ultralight.
SECTION 2. THE TEST PILOT ‘‘There is always a harder way to flight test an aircraft, but that path does not need to be followed. ’’ George Kaseote, FAA Test Pilot
1. GENERAL. Whether the ultralight is brand new or used, it needs to be properly evaluated. A new owner should enlist the services of an experienced ultralight flight instructor who is authorized to give dual instruction under the EAA or the USUA exemption.
a. The instructor should test fly the ultralight only after it has been properly assembled, inspected, engine run-in, and taxi tests have been performed.
It is not recommended that a ‘‘new’’ pilot and a new/used ultralight ‘‘learn’’ to fly together.
b. The test pilot should be experienced and competent. He/she should have made a minimum of 100 solo flights in similar make, model, and type of ultralight and must follow the FLIGHT TEST PLAN exactly. The FLIGHT TEST PLAN should examine the ultralight and its performance capability, beginning with the pre-flight inspection and ending only after the test pilot has explored the ultralight’s published flight envelope as described in the flight manual.
SECTION 3. PRE-FLIGHT AIRFRAME INSPECTION
1. GENERAL.
a. Ultralight owners should remember that the light-weight, thin wall tubing design of an ultralight fuselage/wing structure is particularly susceptible to metal fatigue. When aluminum tubing has been stressed beyond its elastic limit, it takes on a chalky white appearance (corrosion) at the point of highest stress. Warpage and deformation are other signs of high stress points and once discovered, the ultralight should be grounded until the damaged is repaired.
b. The tolerance limit of a tube or fitting can be significantly lowered by over-torquing a bolt. If a bent or damaged support tube or structure is not repaired, the bend or dent will become a crack, and ultimately the crack will become a structural failure.
69 NOTE: If a used ultralight has been purchased, it is highly recommended that the owner perform a detailed acceptance inspection on the aircraft assisted by an experienced individual who is familiar with the make and model aircraft. It is also recommended that all existing hardware (e.g., nuts, bolts, springs) be replaced with new aviation quality hardware.
c. If possible, remove the fabric envelope and check the airframe structure underneath for dents, cracks, and corrosion. Check the top and bottom of the spars for compression (wrinkled metal) damage.
Double check all wings, landing gear, strut, engine, and tail surface attach points for wear, elongated holes, or damage.
d. If any previous repairs are found, check with the manufacturer to see if damage in that area can be repaired and if the repair that was made is airworthy.
2. CHECKLIST. Each ultralight FLIGHT TEST PLAN should include a pre-flight inspection CHECKLIST. The CHECKLIST should include a step-by-step approach to inspection that covers all the manufacturer inspection items as well as the following suggested items starting at the landing gear.
a. Landing Gear. The landing gear is the last part of the light-weight aircraft to leave the earth and the first part to arrive. Since the majority of these aircraft fly from unimproved strips, the stress on the gear is high. The checklist should include inspection items recommended by the manufacturer and inspection for the following:
(1) The condition of the landing gear attach points and alignment of the landing gear and wheels to the longitudinal axis of the fuselage. If the attach points are mis-aligned, the landing gear will not track in a straight line and this will affect take-offs and landings.
(2) Elongated bolt-holes, loose AN hardware, bent tubing, condition and attachment of wheels, wheel bearings, tire inflation, tire condition and brakes.
(3) Brake condition and operation, including chafing of brake lines/cables against the gear struts.
(4) Condition and operation of the steerable nose gear, if applicable.
(5) Condition and attachment of the tail wheel/skid, if applicable.
b. Wing Assembly. The vast majority of ultralight aircraft use a man-made sailcloth material stretched over a tubular frame. This type of fabric is susceptible to ultra-violet radiation from the sun.
If left unprotected, it can become unairworthy in less than 6 months. The checklist should include the following inspection items:
(1) Ensure the sailcloth has not suffered any tears, or abrasion, due to wear or foreign object damage.
(2) Check the sailcloth for obvious ultraviolet (UV) degrading of fabric strength by examining the condition of the fabric on top of the wing.
Compare it to the fabric on the bottom of the wing.
If the top wing fabric shows a significant difference in color (faded), the fabric should be tested for strength with a fabric tester (Maule or Quicksilver) to see if it tests within the manufacturer’s serviceable limits. If no minimum service limits are listed, the fabric should test out at 46 pounds, or 70 percent or more, of its original tensile strength, whichever is greater, to be considered airworthy. If the fabric fails the tests, it must be replaced before further flight.
(3) Flying and landing support cables should be checked for tension, routing, attach points, and condition. Scrutinize the swaged cable ends. It is recommended that a red reference mark (nail polish works fine) be painted on each of the cables abutting the swaged end. If the cable is growing, i.e., a gap forming between the swaged end and the painted referenced mark, there is an impending failure of the swaged terminal. Do not fly the aircraft until the cable is replaced.
(4) Flight control cables should be checked for frayed wires and proper routing. Run a rag over all of the flying and landing wires and control cables (wings and tail). If the cloth snags, this may indicate a frayed wire which demands further inspection. If possible, bend the cable to form a ‘‘U’’ and inspect for internal broken wires. Also, check the cable pulleys for wear and operation. Extreme wear patterns
70 5/24/95AC 90-89A on pulleys indicate misrouting and must be corrected prior to flight.
(5) Check wing leading/trailing edge, wing struts, aileron, flaps, spoiler hinges and attach points for loose rivets, cracks, elongation and wear. Ensure that all hardware (nuts and bolts) are of aviation quality.
(6) Ensure that the bungee, or return springs for wing spoilers (if applicable), are serviceable and will keep the spoiler down flat against the top of the wing when not being deployed.
(7) Check the aircraft’s flight controls rigging every time the aircraft is re-assembled. It is recommended that the cables/rigging for easier assembly be color coded (e.g., red to red, blue to blue).
(8) Check for corrosion on all metal surfaces. Corrosion on aluminum usually appears as a white powder, rough to the touch. On steel parts, corrosion takes the common form of rust. Dissimilar metal corrosion occurs when two different types of metal make surface contact. To obtain additional information on corrosion and treating it, refer to FAA AC 43.9, ‘‘Corrosion Control for Aircraft.’’
(9) Make sure the leading edge of the wing and tail surfaces are clean and free of insects, grass, or mud prior to flight.
c. Fuselage Assembly. The fuselage is the backbone of the light-weight aircraft. All the flight and ground operating stresses encountered by the wings, tail, landing gear, and engine are transferred to the fuselage at the attach points. Exercise extra care when examining these high stress areas because failure of any of these attach points and associated hardware will cause catastrophic structural failure.
(1) Flight controls should be checked for proper operation, travel, and condition of the stops.
There should not be any sharp bends in the flight control cables.
(2) Check engine controls for proper operation; they should be free of bends and properly secured. Ensure that all control cables are securely clamped to the fuselage to prevent the cable from slipping, hence not transferring the desired movement to the engine control.
(3) Check the instrument panel for security and instruments for attachment, proper operation, and range/limit markings.
(4) Inspect for bent or damaged structural tubing. If a tube is bent, it must be properly repaired or replaced. Straightening out a bend will only workharden the tube in the damaged area and hasten the time of failure.
(5) Fiberglass structures should be checked for cracks, delaminations, and holes -- especially on the bottom of the fuselage.
(6) Examine the seat, seat brackets, and seat belt/shoulder harness, attach points, clips/rings, brackets or tangs and other hardware, for security, safety (cotter pins or safety wire), and condition.
(7) Check the shoulder/seat belt harness for condition and proper operation.
(8) Check the ballistic chute hardware and mounting assembly (review information in chapter 1, section 3).
d. Tail Surfaces. The tail, or empennage group, contains two of the ultralight’s three primary control surfaces: the rudder (yaw control) and the elevator (pitch control). In two-axis ultralights, the elevators are the only flight controls on the tail. Special attention must be given to the attach points, hardware, and proper operation for both control systems.
(1) Ensure that the primary controls and trim systems if applicable, have the proper travel, that control cables are properly tensioned, and that all turnbuckles are safetied.
(2) Examine the control hinges and attach points on the elevator and rudder horn for wear, cracking, and elongation of bolt holes, and security of the rudder and elevator stops.
(3) Check the leading and trailing edges of the flight controls for damage.
(4) Check for wear/UV deterioration to the fabric cover.
71 CHAPTER 9. ULTRALIGHT ENGINE/FUEL SYSTEM INSPECTION ‘‘Do not let ego overcome reason.’’ Al Hodges, Ultralight pilot, Homestead, FL (1994) SECTION 1. ENGINE INSPECTION
1. OBJECTIVE. To provide the amateurbuilder/ultralight pilot with a suggested engine and fuel system inspection program in addition to the manufacturer’s check list items.
a. Engine.
(1) Check the engine mount, vibration isolation mounts, and attach points before each flight.
NOTE: If slippage marks are painted across the bolt heads, engine mount, and fuselage at the time the mount bolts are torqued, a break in the paint will give advance warning the mount is coming loose. (Again, red nail polish works adequately.)
(2) Check all hose clamps for tightness.
(3) Check for fuel and oil leaks.
(4) Check air filter for condition and attachment
(5) Ensure that all spark plugs are the correct ones, properly torqued. Check that the ignition wires, caps, and plug cap restraints on inverted engines are secured and safetied. Ensure that the kill switch, if applicable, is within easy reach and works as advertised.
(6) Check that the carburetor and the throttle cable is secured and both operate freely from idle stop to full power stop.
(7) Check carburetor boots for cracks that will suck air and may create a lean mixture, high CHT and EGT, and possible engine failure.
(8) Check the fuel on/off valve, fuel filter, and crossover valve for proper operation and position.
(9) Drain the fuel system of water and sediment.
(10) Ensure that the fuel tank is secured, full, and if applicable, contains the proper mix (ratio) of fuel and oil.
72 5/24/95AC 90-89A
b. Exhaust System.
(1) On most 2 cycle engines, the exhaust system is tuned to the engine in order to have the proper amount of back pressure. Sometimes, due to installation demands, the exhaust system must be modified. If modifications are necessary, contact the engine manufacturer before incorporating any exhaust systems changes.
(2) The exhaust system should be mounted on vibration-damping elements and be safety wired.
The exhaust system ball-joints should not be mounted under a tension load and they should be lubricated with an anti-seize, heat resistant grease to allow the ball joints to move freely. Some exhaust systems use springs to keep pressure (compression) on the ball-joints. If the engine is so equipped, run a piece of safety wire through the spring and secure it to the exhaust system. This would prevent a broken spring from coming loose and hitting the propeller in a pusher configuration or hitting the top of the wing or tail in a tractor design.
(3) Another approach to prevent propeller damage from broken springs is to lay a bead of high temperature silicon length-wise across the spring. If a spring does break during flight, the silicon bead will hold some or all of the broken pieces of spring material in place until the aircraft lands.
c. Fan Cooling.
(1) It is particularly important that installations of fan cooled engines with enclosed cowlings are designed so that the hot cooling air exits the cowl and cannot recirculate back into the cooling fan intake. If there are any doubts, tests should be carried out by measuring the temperature of the air entering the cooling fan.
(2) In most cases, it is unlikely there will be a problem with cooling belt tension on a new engine. On older engines, however, the belt may have bedded down in the V of the pulley causing a significant reduction in belt tension. If corrosion is present on a pulley, the belt wear rate will be rapid. During the visual inspection of the fan cooling belt and pulley, look for evidence of wear and corrosion on the pulleys.
d. Reduction Drive.
(1) A large percentage of engines used on light-weight aircraft are 2 cycle air cooled engines fitted with a rpm reduction drive. The reduction drive is usually a bolt-on unit which drops the high 2 cycle engine rpm down to a propeller RPM that is more efficient.
(2) To check tension on most V belts on the reduction drive, grab the belt and twist. The belt should allow no more than approximately a half a turn.
(3) Ensure that the reduction gear box is filled with oil to the proper level in accordance with the manufacturer’s instructions and drain plug/filter is safetied.
(4) Grasp the propeller (switch off and spark plugs disconnected) approximately half way down each blade. Try first to move the prop in an up and down motion. Pull away from the aircraft and then push in the opposite direction. No appreciable bearing slop should be detected in the reduction gear bearings.
(5) Eccentricity of the driving, or driven, pulley will cause variations of belt tension with rotation, possibly leading to rapid failure of the belt and engine or propeller shaft bearings. Remove the spark plugs and rotate the engine slowly by hand for several turns in small steps (approximately 45 degrees of engine rotation per step). There should be no noticeable change in belt tension at any position. Any noticeable change must be investigated further (e.g., by measuring the run out of the engine pulley and propeller shaft pulley with a dial indicator).
SECTION 2. FUEL SYSTEMS
1. GENERAL. Many problems with lightweight aircraft engines can be directly traced to the type of fuel used. Many states allow automotive fuels to be sold containing 10 percent alcohol without requiring a label stating so. Alcohol can cause serious problems in aircraft engines so first ensure that the fuel source is a reliable one.
a. Test for Alcohol in Automotive Fuel.
Take a thin glass jar, mark it one inch from the bottom of the jar with tape or indelible ink, and fill the jar with water up to that mark. Fill the jar to the top with a sample of the fuel to be tested. There is a clear separation between the water and the fuel.
Put the lid on the jar and shake. Let it settle for about a minute and check. If the ‘‘water’’ line is now above the first mark, the fuel has alcohol in it. Try another source for fuel and do another test.
b. Fuel Primer System. Perform a careful inspection of fuel primer bulbs fitted in suction lines because they deteriorate over time and are a possible source of air leaks, resulting in a lean mixture. Primer bulbs with plastic one-way valves have been known to break loose and completely block the fuel in the fuel line. Positioning the fuel line so the fuel flows upward through the primer bulb will help minimize the possibility of this problem occurring. A permanently fitted fuel pressure gage is recommended because it can check fuel system operation during engine break-in and fuel flow during extreme angles of attack.
c. Filters, Fuel Lines, and Throttles.
(1) Finger screens in fuel tanks should be checked every 10 hours for debris or varnish build up from fuel. Nylon mesh fuel filters are preferred with 2 cycle engines. Paper element filters should be avoided because they may severely and invisibly restrict the fuel flow. This is due to a reaction between water and oil detergents. The fuel filter should be distinctly located, between the fuel pump and the carburetors, to facilitate pre-flight inspection and avoid the possibility of air leaks on the suction side.
(2) Check plastic fuel lines for age hardness, discoloration, and over all condition. Fuel line attach points should be checked before each flight.
Always clamp a fuel line at the inlet and outlet. A slip-on line might slip off in flight. Leave a little slack in the fuel lines to minimize cracking from vibration.
(3) If the 2 cycle engine has two carburetors, make sure the throttles are exactly synchronized. If not, one carburetor will run rich while the other runs lean, causing cylinder overheating and a possibility of the piston seizing or being holed.
d. Causes of High Fuel Consumption
(1) Dirty air filter causes a rich mixture.
(2) Propeller is not matched to the engine.
(3) Carburetor float improperly adjusted.
(4) Fuel pressure set too high.
(5) Wrong carburetor jets installed.
(6) Defective float valve.
(7) Extreme vibration (propeller/engine) that keeps float valve open.
74 5/24/95AC 90-89A