THORP T-18 N10TK

OPERATORS MANUAL

Thomas R. Kerns, Builder

7033 Autumn Terrace

Eden Prairie MN 55346

(612) 934-6833 January 13, 2000

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THORP T-18 N10TK

WARNING

This manual is specifically applicable to Kerns/Thorp T-18, S/N 71, N10TK with 135 HP Lycoming O-290 D-2 engine and Cassidy Pacesetter 68X63 propeller. Applicability of this manual to other T-18 aircraft and pilots is not assured due to variations in pilot experience and aptitude, and variations in aircraft configuration, equipment, manufacturing tolerances, and certification (See Section VIII). This manual is provided to others for educational purposes only, to be used as a model for preparing flight manuals for other T-18 Aircraft.

T-18 N10TK utilizes John Thorps original non-folding wing and NACA 63A-412 airfoil, electrical flaps limited to 30 degrees deflection, "standard" short length untapered main landing gear, standard short roll bar, plus pressure cowl, canopy, and wheel fairings. Numerous detail changes have been made for drag reduction on N10TK.

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THORP T-18 N10TK

SUMMARY SPECIFICATIONS

DIMENSIONS

Wing Span 20'- 10"Wing Chord 4'- 2"Wing Aspect Ratio 5.0Length Overall 18'- 11"Height Overall 5'- 1"Wheel Track 5'- 3"Propeller Diameter 68"

AREAS

Wings (gross) 86.0 sq ftAilerons (total) 6.8 sq ftFlaps (total) 6.0 sq ftFin 4.8 sq ftRudder 3.2 sq ftHorizontal Tail 14.2 sq ftVertical Tail Cruise, Sea Level @ 75% 170 mphCruise, 10,000 ft @ 75% 183 mphStall Speed, Flaps Down 60 mphRate Of Climb at Sea Level approx. 1200 fpmTakeoff Roll 900 feetLanding Roll 900 feetRange, 30 Min Reserve 600 statute miles

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THORP T-18 N10TK

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THORP T-18 N10TK

INDEX

PAGE

I OPERATING LIMITATIONS----------------------- 6

II EMERGENCY PROCEDURES---------------------- 11

III NORMAL PROCEDURES---------------------------- 20

IV PERFORMANCE--------------------------------------- 32

V WEIGHT AND BALANCE--------------------------- 35

VI DESCRIPTION----------------------------------------- 37

VII SERVICING REQUIREMENTS--------------------- 43

VIII APPLICABILITY TO OTHER T-18's--------------- 46

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THORP T-18 N10TK

SECTION I

OPERATING LIMITATIONS

INDEX

PAGE

GENERAL----------------------------------------------------------------------7

AIRSPEED LIMITATIONS------------------------------------------------- 7

POWERPLANT LIMITS AND INSTRUMENT MARKINGS--------- 8

WEIGHT AND BALANCE LIMITS--------------------------------------- 9

FLIGHT LOAD FACTORS------------------------------------------------- 9

KINDS OF OPERATION--------------------------------------------------- 10

MANEUVERS---------------------------------------------------------------- 10

REQUIRED PLACARDS--------------------------------------------------- 10

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THORP T-18 N10TK

SECTION I

OPERATING LIMITATIONS-NORMAL AND AEROBATIC

GENERAL

This section lists all powerplant and airframe operating limitations. These limitations are also indicated in the aircraft in the form of placards and instrument color markings.

AIRSPEED LIMITATIONS

NOTELimitations are applicable to both Normal and Aerobatic Category

except where designated as applying to only one category.

AIRSPEEDAIRSPEED DESIGNATION CAS MPH INDICATOR MARKING

Never Exceed (Vne) 210 Red LineCaution Range 165-210 Yellow ArcMaximum Structural Cruise (Vno) 165 End of Green ArcNormal Operating Range 63-165 Green ArcManeuvering Speed (Va) 160 NoneMaximum Flap Extension (Vfe) 110 End of White Arc

NOTE

CAS - Calibrated Airspeed: This is indicated airspeed corrected for position and instrument error.

IAS - Indicated Airspeed assumes zero instrument error.Vne - Maximum safe airspeed which is not to be exceeded at

any time.Vno - Not to be exceeded except in smooth air only and then

with caution.Va - No full or abrupt longitudinal control movements

allowed above this airspeed.

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THORP T-18 N10TKVfe - No operation with flaps extended above this speed.

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THORP T-18 N10TK

POWERPLANT LIMITATIONS AND INSTRUMENT MARKINGS

Engine

Lycoming O-290 D-2 Rated 135 BHP continuous and 140 HP

for 10 minute takeoff290 cubic inches, 7.5:1 Compression ratioRated for 80/87 octane fuel Marvel Schebler MA-3 SPA CarburetorSlick 4370 and 4373 Magnetos

Propeller

Cassidy "Pacesetter 200", 68" diameter by 63" pitch.

Fuel, Minimum Octane Rating, Aviation Grade 80/87

Approved for continuous use--100/130 LLApproved for limited use-- 100/130Approved for limited use--Automotive Unleaded Regular. * See

caution for hot weather operations in fuel system description*Use of fuels with Ethanol is Prohibited.

TachometerNormal Range (Green Arc) 1800-2800 RPMMaximum (Red Line) 2800 RPM

Cylinder Head TemperatureNormal Range (Green Arc) 280-420 Deg. F.Maximum (Red Line) 500 Deg. F.

Oil TemperatureCaution (Yellow Arc) 100-160 Deg. F.Normal Range (Green Arc) 160-220 Deg. F.Maximum (Red Line) 245 Deg. F.

Oil Pressure Normal Range (Green Arc) 65-85 PSIMaximum (Red Line) 100 PSIMinimum at Idle (Red Line) 25 PSI

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THORP T-18 N10TK

WEIGHT AND BALANCE LIMITS

Maximum Gross Weight-- 1640 Lbs Standard Category 1250 Lbs Aerobatic Category

Center of Gravity Range-- Station 61.0 to 71.15

FLIGHT LOAD FACTORS

ACCELEROMETER CATEGORY LOAD FACTOR LIMITS MARKING

Normal Positive 4.6 G Green Arc Negative 2.3 G Green Arc

Aerobatic Positive 6.0 G Red Line Negative 3.0 G Red Line

NOTE

Maximum load factors for Normal Category operations are shown by the ends of the green arc on the accelerometer. Load factors within the yellow arc up to the red radial lines are permitted only in the Aerobatic Category.

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THORP T-18 N10TK

KINDS OF OPERATION

Only VFR Day operations are approved with all required equipment operating as specified in FAR Part 91.

Operation over densely populated areas is prohibited except for purposes of takeoff and landing.

Flight into known icing conditions is prohibited.

Crosswind landings have been demonstrated at 25 KTS.

INVERTED FLIGHT

Flight at negative "G" conditions is to be avoided due to lack of inverted fuel, oil, and battery systems.

REQUIRED PLACARDS

A placard must be in full view of the passengers seat reading:

WARNINGTHIS AIRCRAFT IS AMATEUR BUILT AND MAY NOT

COMPLY WITH FEDERAL AIRWORTHINESS STANDARDS

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THORP T-18 N10TK

SECTION II

EMERGENCY PROCEDURES

INDEX

PAGE

GENERAL---------------------------------------------------------12ENGINE FIRE DURING START------------------------------12ENGINE FIRE IN FLIGHT-------------------------------------13ELECTRICAL FIRE---------------------------------------------13ALTERNATOR/ELECTRICAL FAILURE-------------------14VACCUM SYSTEM FAILURE--------------------------------14ENGINE FAILURE ON TAKEOFF----------------------------14ENGINE AIR RESTART----------------------------------------15PARTIAL POWER LOSS/ROUGH RUNNING--------------16ABNORMAL OIL PRESS/TEMP INDICATIONS-----------16PRECAUTIONARY LANDING APPROACH----------------16FORCED LANDING (COMPLETE POWER FAILURE)---17DITCHING---------------------------------------------------------18SEVERE TURBULENCE----------------------------------------18STALLS-------------------------------------------------------------18EMERGENCY EXIT/BAIL OUT-------------------------------19EMERGENCY DESCENT---------------------------------------19

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THORP T-18 N10TK

SECTION II

EMERGENCY PROCEDURES

GENERAL

This section covers the recommended procedures to follow during emergency and adverse flight conditions. As it is not possible to define every type of emergency that may occur, it is the pilots responsibility to use sound judgment based on experience and knowledge of the aircraft to determine the best course of action. It is mandatory that the pilot familiarize himself with the entire flight manual, particularly this section prior to flight.

NOTEAll airspeeds in this section are indicated airspeeds (IAS)

unless otherwise stated.

WARNINGThese procedures are tailored specifically to T-18 N10TK, S/N 71.

ENGINE FIRE DURING START

If the fire is believed to be confined to intake or exhaust system (result of flooding engine):

(1) Continue cranking engine with starter.(2) Mixture Control--IDLE CUT-OFF(3) Throttle--DO NOT MOVE(4) Inspect aircraft thoroughly for damage and cause prior

to restart.

If fire persists or is not limited to intake or exhaust system:

(1) Mixture Control--IDLE CUTOFF(2) Fuel Shut-off Valve--OFF(3) Electrical and Magneto Switches--OFF(4) Remove fire extinguisher from cockpit floor(5) Exit Aircraft(6) Direct fire extinguisher through the cowling side air

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THORP T-18 N10TKvents.

ENGINE FIRE IN FLIGHT

(1) Mixture Control--IDLE CUT-OFF.(2) Fuel Shut-Off Valve--OFF(3) Electrical and Magneto Switches--OFF(4) Cabin Heat--OFF(5) Canopy Vent--CLOSE (6) Land immediately using "Forced Landing Procedures"

WARNING Do NOT attempt to restart engine.

NOTEThe floor vents may be used for cabin air in the event of an engine

fire. The floor vent intakes are 4 feet outboard from the fuselage,

providing smoke free air.

ELECTRICAL FIRE

An electrical fire is usually indicated by an acrid odor of hot or burning insulation and wisps of smoke.

(1) Electrical Switches--ALL OFF (Leave Magneto Switch ON).(2) Cabin Heater--OFF(3) Air Vents--OPEN only if absolutely necessary for smoke

removal and ventilation.(3) Direct fire extinguisher to the smoke source (the

extinguisher is non-toxic HALON gas).(4) If fire continues, land immediately.

If fire/smoke stops and electrical power is required for the remainder of the flight, pull all circuit breakers out, turn the battery switch on, then turn on the alternator switch and desired circuit breakers and/or switches. Allow a minute between turning on each switch or breaker in order to allow identification and isolation of the faulty circuit(s). Switch off any faulty circuits.

NOTE:N10TK has an avionics / essential buss which may be powered directly from the battery, bypassing the master relay and main buss. To activate the avionics buss independently, turn on the backup radio

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THORP T-18 N10TKswitch and switch off the avionics master switch. Turning on both the avionics master switch and the backup radio switch will power the main buss from the avionics buss.

ALTERNATOR FAILURE

The ammeter displays current flow to and from the battery. Charge rates up to 60 amps will be observed after engine start, with rapid reduction to zero current flow. Indications of discharge will result from alternator failure, and the voltage warning light will glow a steady yellow.

In the event that buss voltage exceeds 15.5 volts the crow-bar overvoltage protection circuit will immediately toggle off the alternator circuit breaker switch, tripping the low voltage warning light which will glow steady yellow. In the event of high buss voltage and a malfunction of the crowbar, the voltage warning light will flash as a warning of excessive voltage.

(1) Alternator Switch--CYCLE to reset the overvoltage relay. If the switch immediately returns to the off position, an overvoltage condition is confirmed and activation of the alternator will not be possible.

(2) If alternator current is not restored, turn OFF all non-essential electrical equipment to conserve battery power and land as soon as practical. Switching on the alternate radio switch then turning off the master switch and avionics master switch will permit operation of the isolated avionics buss without the power drain of the master relay.

VACUUM SYSTEM FAILURE

Excess vacuum may be observed via the vacuum gauge provided. Low vacuum will be indicated by the vacuum gauge and by a steady yellow glow of the low vacuum warning light. Performance of the artificial horizon and directional gyro are suspect if vacuum is outside of the green arc. The turn coordinator is electrically powered and unaffected by vacuum system operation.

ENGINE FAILURE ON TAKE-OFF

If sufficient Runway Remains:

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THORP T-18 N10TK(1) Throttle--CLOSED(2) Land using brakes as required.

If airborne and insufficient runway remains for landing:

(1) Select most favorable landing area straight ahead.(2) If altitude permits, attempt engine restart:

* Carb Heat--FULL HOT* Mixture Control--FULL RICH unless at high altitude.* Fuel Shut-Off Valve--CHECK ON* Magneto Switch--EXPERIMENT WITH LEFT, RIGHT, BOTH.

(3) If Engine restart is not possible, follow forced landing procedures.

WARNING

Maintain flying speed at all times and do not attempt to turn back towards the runway unless sufficient altitude has been achieved.

Altitude required for turnback with no margin is 600 feet. A 50 degree banked turn at 100 MPH is recommended for turnback. Builders

preference is to use a 90 degree turn into the wind followed by a 270 degree turn in the opposite direction to provide runway line-up. Making the 90 degree turn first will minimize maneuvering at very low altitude

near the runway.

ENGINE AIR RESTART

(1) Maintain Airspeed--100 MPH minimum recommended.(2) Carb Heat--FULL HOT(3) Magneto Switch--BOTH (4) Mixture-- FULL RICH or LEANED as required at high

altitude.(5) Fuel Shut-Off Valve--CHECK ON(6) If restart does not occur, change throttle, mixture,

primer, and magneto settings in attempt to restart.(7) Follow "Forced Landing Procedure" if unable to

restart.

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THORP T-18 N10TK

NOTE

The engine starter may be engaged in flight if the engine has stopped windmilling.

PARTIAL POWER LOSS/ROUGH RUNNING

(1) Follow the engine air restart procedures.(2) Land as soon as practical using "Precautionary Landing

Approach" procedures.

Presence of carburetor ice may be indicated by a gradual power loss. Full carburetor heat should be applied for as long as the obstruction persists.

ABNORMAL OIL PRESSURE/TEMPERATURE INDICATIONS

Oil pressure and temperature problems are usually related with one affecting the other.

Before any action is taken, cross check the other engine instruments and control settings for possible clues. Open the oil cooler shutter fully if high oil temperatures are observed.

High oil temperature is generally the result of loss of oil, engine overheating (note CHT and EGT), or a malfunctioning oil cooler by-pass valve. If the situation remains unchecked, oil pressure usually drops resulting in possible engine damage. Power should be reduced while maintaining cruise airspeed. Place mixture in FULL RICH position and land as soon as practical.

Little or no oil pressure is usually caused by a failed pressure regulator valve, failed pump, loss of oil, clogged oil line, high oil temperature, or a defective gauge. A low pressure warning light is provided to alert the pilot to pressure loss when pressure drops below 15 PSI. A landing should be made as soon as practical using minimum RPM changes. Plan a "Precautionary Landing Approach" as engine failure may be imminent.

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THORP T-18 N10TKPRECAUTIONARY LANDING APPROACH

A precautionary landing approach should be used whenever power is still available, but a complete power failure is considered imminent.

Maintain a higher and closer pattern than normal to remain in gliding distance of the intended touch-down point. Recommended technique is to choose a point on the runway beyond which the aircraft could not be safely stopped, and to choose the earliest point at which a safe touchdown can be made (the earliest point may be before the runway threshold if the approach path is clear). Monitoring glide path relative to the two chosen touchdown limits will provide guidance for just how much reserve speed and altitude can be safely carried for the approach in progress.

Recommended setup is:

(1) Airspeed--85 MPH recommended on approach (80 minimum).(2) Throttle--CLOSED when in gliding distance of the runway.(3) Flaps--FULL DOWN when runway is assured.

NOTE

Full cross control slips may be used between 80 and 90 MPH to increase rate of descent.

FORCED LANDING (COMPLETE POWER FAILURE)

(1) Airspeed--Maintain 100 MPH(2) Mixture--IDLE CUT-OFF(3) Fuel Shut-Off Valve--OFF(4) Radio--MAYDAY 121.5 MHZ(5) Transponder--CODE 7700(6) Attempt to position the aircraft 1000 ft. AGL when

downwind and abeam of the intended point of landing.(7) All Electrical Switches--OFF (Except Battery)(8) On Final Approach--Airspeed 85MPH (80 minimum). See

precautionary landing for technique.(9) Canopy Latches--Released(10) Flaps--Full when field is assured.(11) Battery Switch--OFF(12) Touchdown in 3-point or tail low wheel landing.

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THORP T-18 N10TK

NOTE

In the event of a jammed canopy, emergency egress is provided by a canopy breaker tool located on the center console. Remove the retaining pin by pulling on the ring provided, remove the canopy tool and break the plexiglass canopy for exit.

The ELT is located under the pilots seat and may be activated by lifting up on the switch located at the forward end, and may be removed by releasing the retention strap.

Survival gear is stored under the Co-Pilots seat.

ALTERNATE PROCEDURE:

A 360 degree overhead approach is an alternative. The aircraft will loose 1000 feet altitude in one minute with a 360 degree turn flown at 85 MPH, power off, 30 degrees bank. Establish the aircraft at 1100 feet above the intended point of touchdown on runway heading (85MPH and full flap). Roll into a 30 degree bank for 180 degrees of turn. Upon completing 180 degrees of turn, check altitude remaining (more or less than 500 feet?) and position relative to the touchdown zone (abeam or beyond?). Adjust the remaining 180 degrees of turn as required to place the aircraft on the desired touchdown point. In high winds, the turn should be initiated upwind of the intended touchdown zone; posi-tion the aircraft 1000 feet upwind for each 10 MPH of wind.

DITCHING

Should it become necessary to make a forced landing over water, follow "Forced Landing Procedures" in addition to the following:

(1) Land into wind if high winds are evident or parallel to swells with calm winds.

(2) Contact the water with a nose high attitude.(3) DO NOT STALL prior to touchdown.

SEVERE TURBULENCE

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THORP T-18 N10TK

In severe turbulence do not exceed 160 MPH CAS. Maintain a constant nose attitude rather than flying by reference to the altimeter and airspeed indicator.

STALLS

T-18 N10TK has stall strips installed on the inner wing panels which radically alter stall characteristics. These strips should be installed on all T-18's due to the dramatic improvement in stall characteristics with no degradation in aircraft performacnce. Violent maneuvering is required to produce a stall break. N10TK will fly with the stick held full aft under full control power on or off, flaps up or down, at.any C.G. The aircraft shudders from turbulent flow dumping onto the tail from the stall strips, and there will be a tendancy for wing rock right and left but the ailerons and rudder will remain fully functional. Release of back pressure will result in immediate recovery. Aft C.G. stalls are more vigourus and may be result in a stall break if controls are abused.

POWER OFF STALLS

Power off stalls with full flap are gentle, occurring at 60 MPH IAS. Gently lowering the nose slightly below the horizon will provide recovery. Power off stall with no flap occurs at 63 MPH IAS.

POWER ON STALLS

Power on stalls occur at a 45 degree nose high attitude with 57 MPH IAS clean and 52 MPH IAS flaps down. No the aircraft trembles and lowers the nose somewhat if the stick is held full back but no stall break will occur. Vigorus use of rudder in the stall can produce a spin entry.

EMERGENCY BAIL OUT

(1) Throttle--CLOSED(2) Canopy Breaker-- Remove from center console and BREAK

CANOPY.(3) Either; Roll the aircraft inverted, pull your legs back from under

the instrument panel, and push hard forward on the stick to eject from the aircraft, or; Climb out onto the wing and slide down and aft to avoid the horizontal tail.

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THORP T-18 N10TKEMERGENCY DESCENT

The most rapid steady state descent can be made by flying a 2 to 3 "G" spiral at maneuvering speed (159 MPH CAS) or less. Rate of descent increases with "G" and with airspeed. Two "G" stall occurs at 90 MPH IAS, and 3 "G" stall occurs at 110 MPH IAS.

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THORP T-18 N10TK

SECTION III

NORMAL PROCEDURES

INDEX

PAGE

PREFLIGHT INSPECTION----------------------------------------------- 21PRE-START CHECK-------------------------------------------------------25ENGINE START-------------------------------------------------------------25COCKPIT PREFLIGHT---------------------------------------------------- 25ENGINE RUN-UP-----------------------------------------------------------26TAKE-OFF------------------------------------------------------------------- 26CLIMB------------------------------------------------------------------------26LANDING CHECKLIST--------------------------------------------------- 26BALKED LANDING------------------------------------------------------- 26

NORMAL TAKEOFF------------------------------------------------------ 27SHORT/SOFT FIELD TAKEOFF---------------------------------------- 27SHORT FIELD OBSTACLE TAKEOFF-------------------------------- 27ROUGH SURFACE TAKEOFF------------------------------------------ 27

PATTERN ENTRY--------------------------------------------------------- 28NORMAL LANDING------------------------------------------------------ 28THREE POINT LANDING---------------------------------------------- 29WHEEL LANDING------------------------------------------------------ 29

CROSSWIND LANDING------------------------------------------------- 30ROUGH FIELD LANDING----------------------------------------------- 30SHORT FIELD LANDING------------------------------------------------ 30SHORT FIELD OBSTACLE LANDING-------------------------------- 30GUSTY WIND OPERATION--------------------------------------------- 30

ENGINE SHUTDOWN---------------------------------------------------- 31GROUND HANDLING---------------------------------------------------- 31

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THORP T-18 N10TKPRE FLIGHT INSPECTION (Ref. Page 22)1)Remove right side cowl by loosening the 1/4 turn Camlock fasteners then sliding the cowl cheek forward and out. Lay cowl cheek in a protected area with the inner surface down.

Check oil level and secure dipstick. Capacity is 8 quarts, normal fill level is 6 to 7 quarts. Minimum operating level is 2 quarts.

Inspect engine compartment for general condition, security, leaks, etc.

Remove fuel sampler from the upper cheek fairing, drain gas from the gascolator using the aluminum extension tube provided. Check gascolator for leakage and sample for contamination. Hang fuel sampler from the belly vents beside the right main gear for later use. Check for vent obstructions.

Check fuel quantity and secure gas cap.

Check windshield for cleanliness.

Check right main tire for condition and inflation.

Inspect right wheel fairing for security and signs of brake fluid leakage.

(2) Remove tiedown and unscrew tiedown ring from wing.

Check condition and security of right wing, tip, and lights.

Check right aileron for freedom of movement, security of counter-balance weight, security of hinge pins, and freedom of the actuator rod.

Check right flap for security and gently lower to check for 30 degrees freedom of travel.

Inspect canopy and frame for security.

Check right static vent for obstructions, check fin base for security.

(4) Check stabilator and anti-servo tab for security and freedom of movement. Check trim linkage for security.

Check rudder and hinges for security.

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THORP T-18 N10TKCheck tail light and strobe for condition.Check tailwheel and linkage for condition.

DIAGRAM FOR PRE-FLIGHT

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THORP T-18 N10TK(5) Check left side static vent for obstructions.

Check left flap for security and freedom of 30 degrees travel.

(6) Check all four brake pedals for operation.

Power up the main buss and turn on the pitot heat for 20 seconds, note 10 amp discharge on ammeter during pitot heat operation.

Cycle nav lights, strobes, map lights, and panel lights and check for function.

Check fuel quantity indication.

Turn off master switch.

Depress fuel sump valve for 5 seconds to fill the sampler which was previously hung on the tank vent.

Secure co-pilot harness if solo flight is planned.

Remove loose articles and equipment before aerobatic flight.

(7) Check left aileron for freedom of movement, security of trim mechanism, security of counterbalance weight, security of hinge pins, and freedom of actuator rod.

(8) Check condition and security of left wing, tip, and lights.

(9) Check pitot tube for obstructions and for residual heat from the cockpit check.

WARNING:The pitot tube can get hot enough to cause severe burns!

(10) Check left main tire for condition and inflation, fairing for security, check for signs of break fluid leakage.

Visually check engine condition through the left cooling exit.

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THORP T-18 N10TK(11) Check left engine air inlet and carb. air inlet for obstructions.Check landing light for condition.

Check propeller and spinner for condition and security.

(12) Inspect fuel sample, return sample cup and tube to storage compartment and secure.

Install right side cowl by sliding aft and in, secure all Camloc fasteners.

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THORP T-18 N10TKPRE START CHECKSeat Belts and Shoulder HarnessHeadsetsFuel Valve 'ON'Brakes, Test and SetAvionics Master 'OFF'

ENGINE START CO Detector: Press to Test

Oil Cooler Shutter—‘HOT’Mixture--FULL RICHThrottle--CRACKED 1/4 inch openBattery Switch—ONAvionics Master --ONConfirm Warnings: Low Vac, Oil Press, Low Voltage – ONAvionics Master --OFFPrimer--6 Strokes below 30 degrees, 3 strokes below 50 degrees.Stick--FULL AFT Strobes—ONPropeller Area--CLEARIgnition--Turn to 'Start' (Release when engine starts).Oil Pressure--Check for RiseAlternator--'ON', Check for chargingWarm Up—1000 to 1100 RPMAvionics Master –ONVerify warning lights --OFFIntercom--Set Volume, SquelchRadios: as requiredTransponder--'STDBY' and code 1200Turn and Bank—ONNav Lights--ONDefrost and Heat--As Required

COCKPIT PRE-FLIGHT

Flight Controls--Check for free and correct movementElevator Trim--Set to trail with the stick positioned even with the instrument panel bottom.Aileron Trim--Set 20 degrees tab up for solo, neutral with passenger.Instruments—

Altimeter SetD.G. Set

A.H. Set 10 degrees climbOthers: Check

Fuel Valve-- 'ON'Mixture--RICHTransponder--Test & Release to 'ALTITUDE' positionNav. and Strobe Lights--ON

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THORP T-18 N10TK

ENGINE RUN UP

Turn Into Wind, set brakes, stick full aft.Throttle setting--1800 RPMMagnetos--Check (50 RPM max differential between mags, 175 RPM max drop).Carb Heat--Check for 50 RPM drop.Engine Instruments--Within Green Arc.At high density altitude, lean for best power before takeoff.

TAKE OFF

Flaps--As Required (zero to 10 degrees)Canopy--LatchedCarb Heat--ColdOil Pressure--CheckFuel Quantity--CheckThrottle--Full OpenCheck for satisfactory takeoff RPM (2150 +50 static)

CLIMB

Airspeed as Required ( Vx=85 MPH, Vy=105 MPH)Retract flaps at a safe altitudeMixture--Lean as required at altitude

LANDING CHECKLIST

Mixture--RichCarb Heat--Check operation and return to COLDFlaps--As Required (below 110 MPH)

BALKED LANDING

Throttle--Full OpenEstablish Climb at 100 MPHFlaps--RetractTrim--Reset

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THORP T-18 N10TK

TAKEOFF PROCEDURES

NORMAL TAKEOFF

Zero flap is used for normal takeoff. Trim is set by positioning the stick directly below the instrument panel edge and adjusting the trim tab visually to trail.

Directional control is very strong but sensitive. The tail should not be raised abruptly on takeoff; propeller gyroscopic precession generates a strong left turn momnent as the tail rises rapidly. Rudder control response becomes much softer when the tailwheel is lifted off of the runway.

Apply full power with neutral elevator, transition to moderate forward pressure at 20 to 30 MPH to raise the tail to level attitude. Acceleration is noticeably improved in level attitude due to reduced induced drag. Liftoff at 80 to 85 MPH, leveling at 3 to 6 feet AGL until 100 MPH climb speed is attained. On climb out, the nose may be lowered to the horizon at pilots discretion for better forward visibility. Normal cruise climb is 120 to 150 MPH IAS.

SOFT FIELD, NO OBSTACLE TAKEOFF

Partial flap is set by lowering the flaps to match full "down" aileron deflection. Takeoff is initiated with neutral elevator, or with backpressure as required to prevent noseover on a soft surface. The tailwheel is raised 2 or 3 inches above ground as soon as possible and this attitude is held until the aircraft flies off. Accelerate in ground effect to 85 MPH or more for climb-out, retract flaps at a safe altitude.

SHORT FIELD TAKEOFF , FIRM RUNWAY WITH OR WITHOUT OBSTACLE

Partial flap is set by lowering the flaps to match full "down" aileron deflection. Takeoff is initiated with neutral elevator, transitioning to full forward stick at 10 MPH to lift the tail to level for rapid acceleration. Rotate slightly to liftoff at 80 MPH. Climb at 85 MPH Vx, retract flaps after clearing obstacles and attaining a safe altitude.

ROUGH RUNWAY TAKEOFF

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THORP T-18 N10TKThe spring leaf tailwheel produces pitch proposing when rolling at moderate speeds on rough surfaces. Recommended procedure is to set flaps to match full down aileron deflection, use full aft stick until 20 MPH, then use positive forward stick pressure to hold a slightly tail low fuselage attitude as the aircraft continues to accelerate. Liftoff at 75 to 80 MPH and accelerate in ground effect to 85 MPH or more before initiating climb.

If excessive bouncing occurs, avoid pushing the nose down past level attitude due to the danger of a prop strike, or holding the nose too high due to reduced acceleration and the

potential for high bounces at low airspeed. Work to hold a slightly tail low attitude until such time as a bump pushes the aircraft airborne with sufficient flying speed to permit leveling off in ground effect, accelerate to 85 MPH or more prior to climbing.

APPROACH AND LANDING

PATTERN ENTRY

The T-18 is a fast, very low drag aircraft requiring pilot planning to descend to pattern altitude and reduce speed to levels compatible with other traffic.

A downwind speed of 140 MPH at 2200 RPM is recommended when traffic permits, or half flap flight at 100 MPH and 1800 RPM or 85MPH and 1700 RPM if required for spacing. Maximum flap extension speed is 110 MPH.

The aircraft should be trimmed in pitch for all phases of the traffic pattern up to the landing flare.

Recommended procedure is to slow to 100 MPH or less before turning base. Partial or full flap is recommended below 100 MPH to improve over the nose visibility and speed stability as the "backside" of the power curve is approached. Slowing to less than 85 MPH (1.3 Vso) is not recommended until on short final.

NORMAL LANDING

Preferred approach is power off with full flaps at 85 to 90 MPH indi-cated. Decreasing approach speed to 80 MPH is acceptable at light

30

THORP T-18 N10TKweights or with power, but at heavy weight and/or turbulence the power off sink rate at 80 MPH is high enough that lift reserves for the landing flare can become marginal.

The glide path may be steepened as required by side slipping with full rudder at 80 to 90 MPH.

THREE POINT LANDING

In calm air, establish a power off full flap glide at 85 MPH to a point 200 feet short of the touchdown zone (move the aim-point up to the touchdown zone when winds are at 10 MPH or more to allow for wind gradient near the ground). Gently initiate the flare at 40 feet AGL and use a smooth continuously increasing pitch attitude to arrive at runway elevation in 3 point attitude. Flaring too high or too quickly will result in rapid airspeed decay leaving the aircraft dangerously high and slow. Power must be smoothly applied for recovery.

CAUTIONThe relatively high T-18 span loading will result in rapid speed decay if the aircraft is flared high with power off.

Use power to recover from high flare / low speed conditions.

Flaring too low will result in a failure to bleed off speed and excessive float will occur.

Smooth three point touchdowns require learning to achieve 3 point attitude in the bottom of the flare at runway elevation. Flaring at 6 or 8 inches and holding it off will result in a firm arrival when the airplane free falls the last 8 inches onto the stiff main gear.

Three point attitude in N10TK does not produce a full stall landing. Full aft stick will produce a stalled landing with tailwheel contact occurring when the main gear is still 5 or 6 inches AGL, leading to a firm drop. Full aft stick landings are not recommended.

31

THORP T-18 N10TKFlap retraction is recommended immediately after 3-point touchdown to keep the aircraft on the ground when encountering subsequent bumps and gusts on rollout. Directional control on rollout is strong but very quick. Avoid over controlling the rudders. Three point touchdown occurs at 60 MPH IAS and ground rolls of less than 1500 feet can be consistently maintained with light to moderate braking.

WHEEL LANDING

Preferred calm air approach is 90 MPH power off to a point 100 feet short of the landing zone. Flare is initiated at 25 feet AGL smoothly rounding out to zero sink rate at ground contact in the touchdown zone. Touchdown will occur at 70 to 75 MPH depending on the flare used. On ground contact, releasing some of the backpressure used in the flare will keep the main gear firmly on the runway. Subsequent forward pressure will allow level attitude roll out down to 20 or 30 MPH. Tail high pitch stability is excellent and directional control remains strong but sensitive throughout the roll.

CROSSWIND LANDING

Either a three point or wheel landing may be used in crosswinds depending upon pilots preference. Full flap is used in either case to lower the nose on landing approach, and to permit flap retraction to keep the aircraft down following a three point landing. The flight controls are powerful and quick, with demonstrated 25 knot plus crosswind capability in N10TK. For a three-point landing, retract flaps on touchdown. For a wheel lanbing, roll out in a level attitude down to approximately 30 MPH.

ROUGH FIELD LANDING

On excessively rough surfaces, the spring leaf tailwheel induces pitch proposing at moderate to high speeds. Rough field landings should be made with a full flap tail low wheel landing. After contact, raise the tail to a slightly tail low attitude and hold the attitude until speed drops below 20 MPH. Holding the tail up gives pitch control to avoid uncontrolled proposing and bouncing. Attempting three point crosswind landings on rough fields is not recommended. Uncontrolled porposing and bouncing in a three point rollout makes crosswind drift correction difficult.

32

THORP T-18 N10TKSHORT FIELD LANDING, NO OBSTACLE

A relatively flat approach is recommended with partial power, full flap, and 80 MPH. Reduce speed to 75 MPH on approaching the threshold and touchdown either in 3 point or tail low wheel landing attitude. Raising the tail to level attitude immediately after touchdown will maximize braking effectiveness for a short rollout. Minimum ground roll is 800 feet in calm air with heavy braking.

SHORT FIELD LANDING, 50 FOOT OBSTACLE

Maximum performance is obtained with an 80 MPH power off approach, full flaps. Higher speed or power may be needed to hold sink rate in check at heavier weights or in high winds.

GUSTY WIND LANDINGS

High wing loadings and powerful controls make the T-18 relatively insensitive to wind gusts. Approach speeds below 85 MPH are not recommended when gust magnitudes exceed 10 MPH, and approach speeds above 95 MPH are not recommended under any conditions. Use of approach speeds above 95 MPH in strong gusts would jeapordize flap integrity with the 110 MPH flap extension speed (Vfe). Approach above 90 MPH is not recommended under any conditions other than severe wind shear.

33

THORP T-18 N10TK

ENGINE SHUTDOWN

Turn off the Avionics Master before engine shutdown. Run engine up to 1500 RPM for 10 seconds before pulling the mixture control full aft to idle cutoff. After the engine stops, turn off remaining electrical devices, turn off the master switch and magnetos, remove the ignition key to prevent inadvertent activation.

GROUND HANDLING

Aft Movement: Grasp the base of the vertical fin leading edge to pull the aircraft aft.

Forward Movement: Stand beside the fuselage, ahead of the horizontal tail. Place hands on the hip skin to top and/or side skin junctures at fuselage frame locations and / or the comm antenna base to push the aircraft forward.

NOTE

With two persons, movement can be accomplished by each person grasping the wingtips, or by having an assistant push on the propeller

shanks close to the spinner.

34

THORP T-18 N10TK

SECTION IV

PERFORMANCE SUMMARY1550 lbs Gross Weight

All Airspeeds CAS

IAS (MPH)

Power Off Stall, Clean (Vs1)------------------------ 63Power Off Stall, Full Flap (Vso)-------------------- 60Power On Stall, Clean-------------------------------- 57Best Rate of Climb (Vy)---------------------------- 105Best Angle of Climb (Vx)-------------------------- 85Never Exceed Speed (Vne)----------------------- 210Maneuvering Speed (Va)-------------------------- 160Max Flap Extension Speed (Vfe)---------------- 110Best Glide Angle------------------------------------- approx. 100, 11:1 GlideMinimum Rate of Descent------------------------ approx. 85, 900 FPM

AIRSPEED CALIBRATION *

CAS IAS 65 N/A 80 80100 100120 120140 140160 160180 180200

* Airspeed system leak checked and calibrated 6/16/90 over a 5.2 sm speed course from 80 to 180 MPH IAS.

35

THORP T-18 N10TKCRUISE PERFORMANCE

Standard Temperature, Lean Mixture, 135 BHP used as 100% Power Base

% TAS % TASPOWER RPM MPH GPH MPG POWER RPM MPH GPH MPG

SEA LEVEL 2000 FT

50 2060 137 5.6 24.5 50 2100 137 5.624.4

60 2320 154 6.6 23.3 60 2360 154 6.6 23.2 70 2490 165 7.5 21.9 70 2540 166 7.6 21.8

75 2550 170 8.0 21.2 75 2600 171 8.121.2

80 2610 174 8.4 20.6 80 2660 175 8.5 20.6

90 2730 181 9.3 19.4 90 2780 182 9.4 19.4 100 2820 187 10.2 18.4 100 2870 188 10.318.3

114 2910 194 11.3 17.2 107 2910 192 10.817.8

% TAS % TASPOWER RPM MPH GPH MPG POWERRPM MPH GPH MPG

4000 FT 6000 FT

50 2120 137 5.6 24.3 50 2140 137 5.7 24.2 60 2390 154 6.7 23.1 60 2420 155 6.7 23.1 70 2570 167 7.6 21.9 70 2600 168 7.7 21.9 75 2640 172 8.1 21.2 75 2670 174 8.1 21.4 80 2710 176 8.6 20.6 80 2740 179 8.6 20.8 90 2810 183 9.4 19.4 90 2840 186 9.5 19.6 100 2910 189 10.3 18.3 94 2880 188 9.8 19.1

% TAS % TASPOWER RPM MPH GPH MPG POWER RPM MPH GPH MPG

8000 FT 10000 FT

36

THORP T-18 N10TK 50 2160 137 5.7 24.1 50 2180 136 5.7 23.9 60 2440 156 6.7 23.2 60 2450 158 6.7 23.5 70 2620 172 7.7 22.4 70 2650 176 7.7 22.8 75 2700 178 8.2 21.8 75 2730 183 8.2 22.3 80 2780 183 8.7 21.2 80 2810 188 8.7 21.6 86 2830 189 9.2 20.6

Power and fuel flow data are based on Lycoming performance charts for the 0-290-D2, dependent upon Manifold Pressure, RPM, OAT, and Pressure Altitude. Speeds based on speed course calibrated airspeed system.

37

THORP T-18 N10TK

SECTION V

WEIGHT AND BALANCE

EMPTY AIRCRAFTWeight—1004.4 lbsC.G.—63.81 inchesMom.--64091 inch lbs.Datum--55.0 inches is the wing leading edge

Leveling-- The fuselage longitudinal external skin stiffener below the canopy sill is used for longitudinal leveling. The wing center section main spar is used for lateral leveling.

Maximum fuel is 29.5 gallons (177 lbs), 29.25 gallons usable.Maximum oil is 8 quarts (15 lbs)Maximum gross weight is 1640 lbs for "standard" category operation

and 1250 lbs for aerobatic category operations.Center of Gravity limits are 61.0 inches forward and 71.15 inches aft.

WEIGHT AND BALANCE WORKSHEET

WEIGHT STATION MOMENT ITEM LBS INCHES IN-LBS

AIRCRAFT, EMPTY 1004 63.81 64,091

OIL, 8 QTS CAP. 15 28. 420

FUEL, 29.5 GAL CAP. 50.

PILOT 89.

CO-PILOT 89.

UNDER SEAT BAGGAGE 89.

AFT BAGGAGE 107.

38

THORP T-18 N10TKTOTAL

39

THORP T-18 N10TK

SAMPLE, FORWARD CG WEIGHT STATION MOMENT

ITEM LBS INCHES IN-LBS

AIRCRAFT, EMPTY 1004 63.81 64,091

OIL, 8 QTS CAP. 15 28. 420

FUEL, 29.5 GAL CAP. 177 50. 8,850

PILOT 190 89. 16,910

CO-PILOT 0 89. 0

UNDER SEAT BAGGAGE 5 89. 445

AFT BAGGAGE 0 107. 0

TOTAL 1391 65.20 90716

SAMPLE, AFT CG WEIGHT STATION MOMENT

ITEM LBS INCHES IN-LBS

AIRCRAFT, EMPTY 1004 63.81 64,091

OIL, 8 QTS CAP. 15 28. 420

FUEL, 29.5 GAL CAP. 24 50. 1,200

PILOT 190 89. 16,910

CO-PILOT 170 89. 15,130

UNDER SEAT BAGGAGE 5 89. 445

40

THORP T-18 N10TK

AFT BAGGAGE 55 107. 5885

TOTAL 1,463 71.12 104,081

41

THORP T-18 N10TK

SECTION VI

DESCRIPTION

GENERAL DESCRIPTION

T-18 N10TK serial number 71 was manufactured by Tom Kerns, 7033 Autumn Terrace, Eden Prairie Minnesota, 55346. Construction began in January 1972 with first flight occurring in September 1982. All primary structure is built in accordance with John Thorps T-18 plans.

WING

N10TK has a "standard" non-folding three piece T-18 wing with NACA 63A-412 airfoil , top hinged ailerons, and single slotted semi-fowler flaps. Skin thickness on the wing center section has been increased to 0.032" per designers recommendation, and center section wing spar to skin rivets are at 1/2 the original spacing per designers recommendation. Eccentric cams are installed in the outer wing panel aft spar attach fittings to permit adjustment of outer wing panel incidence.

Strobes and nav lights are located in the wing tips and covered with clear lexan lens. Strobe power supplies are inside the wing tips, accessible by removing inspection panels from the wingtip lower sides. VOR antennas are located inside both wingtips.

FLAPS

Flaps are electrically operated with power supplied by a modified Ford power window actuator mechanism. The actuator is mounted on the back of the aft wing spar carry through beam beneath the baggage compartment floor. Infinite selection of flap deflection is available from zero to 30 degrees. Flap position indication is by visual inspection from the cockpit. The protruding flap hinges are enclosed by two piece aluminum fairings for drag reduction.

AILERONS

The standard T-18 top hinged plain ailerons are actuated by push-pull tubes. A counterbalance arm is mounted on the outboard end of each aileron. Roll trim on N10TK is provided by a trim tab located on the left

42

THORP T-18 N10TKaileron. Actuation is by an electric jackscrew assembly on the inboard aileron rib. The roll trim switch is located forward of the roll bar on the pilots side windshield sill. Trim position indication is by visual reference from the cockpit.

EMPENNAGE

N10TK uses the standard T-18 pushrod actuated stabilator with anti-servo tab. Designer recommended modifications incorporated include:Internal doubler in stabilator main spar tube.A portion of lead counter balance weight is located inside the

stabilator outboard leading edges.Anti-servo tab inboard rib to spar juncture is stiffened with .016"

stainless steel straps.

Builders modifications include a vertically oriented electric trim jackscrew assembly positioned on the aftmost fuselage bulkhead. No pitch trim position indicator is provided. Pre-takeoff trim is set by visual reference. Trim actuation if via toggle switches located on top of the control sticks. Trim response rate is set as quick as can be tolerated at cruise speed to permit landing with pitch trim in the event that primary pitch control is lost.

VERTICAL TAIL

Conventional T-18 structure with a strobe light on the fin cap and a nav light in the rudder trailing edge.

LANDING GEAR

N10TK uses a "standard" T-18 main gear which is a stiff welded steel tubular "A" frame bolted to the firewall. N10TK gear legs are the original short untapered configuration providing a relatively stiff ground ride. Tires are 5.00 X 5 Goodyear Flight Custom with Cleveland wheels and brakes. Pilot and co-pilot pedals are provide with brake cylinders with fluid reservoirs and parking brake mechanism integral to the co-pilot brakes. Pilots pedal geometry has been modified to double mechanical advantage relative to the standard T-18 geometry (which is retained on the co-pilot side). The fuel tank support cradles have been modified to provide clearance for fully deflected brake and pedal action. The tail wheel is a conventional six inch Scott steerable tail wheel on a steel leaf spring support.

43

THORP T-18 N10TKINDUCTION SYSTEM

A modified Thorp "Banjo Box" induction system is used on N10TK. Carburetor air enters a ram air snorkel with a proper boundary air bleed, the air passes through an internal diffuser before entering a large automotive air filter (FRAM CA-176PR) at low speed for minimum pressure loss. Turning on carb heat moves a door which blocks off the snorkel intake while opening an intake from the exhaust crossover system upstream of the air filter.

EXHAUST SYSTEM

A crossover exhaust system is used with slip joints in the crossover tubes and ball joints joining to the tailpipes. The tailpipes transition to a rectangular cross section to fit into shallow "ejector stacks" built into the cockpit floor. The ejector stacks reduce drag by providing flush tailpipe exits and thrust augmentation. See Fuselage description.

COCKPIT HEAT

Air is fed from the engine upper plenum to a stainless steel muff on the right hand tailpipe. The muff outlet feeds an airbox which directs hot air either into the cockpit or overboard depending on the heater control position. Cold air may be mixed with the heat air via a cold air inlet valve located on the side wall below the ignition switch, pull for cold air, push off.

COCKPIT VENTS

Fresh air is provided by two adjustable sidewall vents ahead of the main spar, and by an inlet at the back of the canopy. The canopy vent control is located on the forward left corner of the canopy frame.

FUEL SYSTEM

The fuel system is gravity feed. Capacity is 29.5 gallons with all but 1/4 gallon usable. A ram air vent is located on the belly inboard of the right main gear. A back up vent with a one way check valve is located on the fuel filler ring. the back up vent is normally closed but will open with a very small level of fuel tank vacuum (less than .02 PSI). The gas cap is a positive mechanical locking cap with an O-ring seal. The fuel shutoff

44

THORP T-18 N10TKvalve is located on the firewall with a remote shutoff handle centered on the lower edge of the instrument panel.

Shielding, insulation, and forced air ventilation are used to prevent vapor lock in the fuel system; however, heat soaking after engine shutdown can boil fuel in the carburetor bowl if automotive fuel is used and ambient temperatures are above 85 degrees F. This form of vapor lock will prevent engine start until the carburetor has cooled.

BATTERY

A 25 Amp Hour manifold vented battery (Rebat R-25M) is located under the co-pilot seat in a sealed box. The battery vent extends down through the fuselage belly. Desired charging voltage is 13.2 V at 100 F, 13.8 V at 75 F, 14.5 V at 30 F, and 15.0 V at 0 F.ELECTRICAL

A Ford 60 amp alterntor and Ford solid state voltage regulator are installed. A “Crowbar” over voltage circuit is installed to blow the alternator field breaker off line in the event that the buss exceeds 15.5 Volts. A high and low voltage warning circuit provides warning to the pilot.

LANDING LIGHT

A 100 Watt Halogen automotive driving light element and reflector is mounted behind a plexiglass window between the propeller and the carb air intake.

ENGINE ACCESSORIES

The carburetor is a standard Marvel Schebler MA3-SPA with a rubber tipped float needle, metal float assembly, and a power jet main orifice which has been enlarged from 0.0935 inches to 0.0980 inches diameter for proper operation as installed in N10TK.

The starter is a Nissan geared starter in an aluminum adapter bracket.

The alternator is a Ford 60 amp unit with an aftermarket Ford voltage regulator and an aircraft ignition noise suppressor.

The Magnetos are Slicks with impulse coupler on the left magneto only.

45

THORP T-18 N10TKA “wet” Pesco vacuum pump and air / oil separator are installed.

ENGINE PRE-HEAT

Engine preheating is recommended at temperatures below 20 degrees F. A Northwind Zero Start electrical heating element is attached to the oil sump for heating. Plug engine cooling air inlets and outlets with fireproof plugs and plug in the heater for at least 3 hours for pre-heat. Continuous heat use is approved, with steady state cylinder head temperatures of 70 degrees F. above ambient being reached in 4 to 5 hours.

FUSELAGE

The fuselage is basic T-18 with a cut down rear deck for canopy installation. Modifications incorporated include: cut out in rear deck for baggage access, narrow seat backs for in flight baggage access, close tolerance jackscrew and electric motor for pitch trim, Ford power window motor for electric flap operation, designer recommended reinforcements in the wing main spar to fuselage area and in the forward fuselage, and rectangular section ramps cut into the floor skin for flush exhaust ejector stacks with stainless steel and asbestos paper heat shields.

CANOPY

Gee-Bee light green tint canopy with a heavy (3/16") windshield to prevent vibration and bird damage. Tongue and groove joint between the canopy and the roll bar insures alignment of the joint under airloads. Two latches pull the lower forward corners of the canopy forward to seal. The canopy frame has been lowered to within 1/4" of the rear deck to facilitate effective sealing.

COWLING

Modified fiberglass Thorp cowl originally supplied by Ken Knowles. Cooling inlets have been re-contoured to reduce intake area by 40%. Inlet internal flow diffusers have been installed to minimize pressure loss and facilitate sealing to the engine upper plenum. Cooling air exits have been reduced 60% by fairings permanently mounted to the fuselage. Cowling joints are all flush, using riveted and bonded aluminum flanges to make the necessary junctions.

46

THORP T-18 N10TK

COCKPIT CONTROLS

Controls are arranged to permit pattern work without having to let go of the stick or throttle. The control stick grips have an electric pitch trim toggle switch on top, and a radio push to talk (PTT) switch under the thumb. A voice activated intercom (NAT) is permanently installed with panel mounted controls. Intercom Jacks are located behind the pilot and co-pilots outboard shoulders. An additional set of jacks and a PTT switch which go directly to the #1 COMM radio (by-passing the intercom) are located on the left windshield sill for back-up. Electric flaps, Throttle, Mixture, Carb. Heat, and Fuel Shut Off are located on the center sub panel. Throttle and mixture are vernier controls, both of which have return springs on the carburetor arms to move controls to full power and full rich in the event of a control cable failure.

A set of seven panel lights are located under the glare shield lip. The Glare shield extends aft to prevent instrument glare from reflecting in the windshield and to provide suitable location for the panel lights. Map lights with dimmers are located on the cockpit side walls and may be used for back-up in the event of primary panel lighting failure.

All switches in the electrical sub-panel are combination circuit breaker/switches and will move to the "off" position if tripped by an overload

AVIONICS

Installed equipment includes a King KY-97A as number 1 comm, a King KY-197 as number 2 comm, King KN-53 NAV with glide slope receiver, King KI-208 VOR / LOC / ILS indicator, King KMA-24 audio panel with internal marker beacon, Narco AT-150 transponder with Narco AR-850 encoder, and a Northern Air Technologies (NAT) intercom system. Handheld GPS connectors to the left of the pilots seat cushion include a BNC Coax connector from an airframe mounted GPS antenna and a 14volt “cigarett lighter” aux power plug. A one amp circuit breaker on the left windshield frame isolates the aux power plug from the avionics buss. Standard Pilot and Co-pilot headset plugs are located outboard behind crew-members shoulders.

47

THORP T-18 N10TK

SECTION V11

SERVICING REQUIREMENTS

EXTERIOR CARE

N10TK is painted with Sherwin Williams catalyzed arcryllic enamel clearcoat system. The exterior coat is a tough polyurethane clear coat. The paint may be washed with mild soap and waxed with automotive waxes as desired.

WINDSHIELD AND CANOPY CARE

The windshield and canopy are standard Plexiglass arcryllic. Care must be taken to keep the plexiglass clean and unscratched. Flush away grit with water to prevent scratching, then wash with water with mild detergent or commercial plexiglass cleaner.

BRAKE FLUID

The brake fluid reservoirs are integral to the co-pilot master cylinders. Maintain aircraft hydraulic fluid (MIL-H-5605) level at the lines scribed on the exterior of the cylinders.

PROPELLER

Maintain the propeller finish with good quality marine urethane spar varnish with ultraviolet blocking additives. Rebalance the propeller after refinishing. A strip of 3-M clear mending tape is used on the outer 18 inches of the leading edges to provide rain erosion protection. Replace tape on condition (typically 50 hours of use). Propeller bolts should be re-torqued every two to three months to avoid loss of the propeller due lost driving friction when contraction occurs under low humidity conditions. Torque desired is 200 +25 inch lbs.

TIRES

Goodyear flight custom 5.00 X 5 tires and tubes are used. When removing the wheel pants for service, the tires should be lightly greased to facilitate sliding the tight fitting wheel pants off. Rotate the

48

THORP T-18 N10TKaft end of the wheel pant up as high as possible, then lift the pant off of the wheel. A tire pressure of 28 PSI is recommended by Goodyear for these tires at 1500 lbs gross weight. Use of higher tire pressures is not recommended due to loss of shock absorption by the tires.

LANDING LIGHT

The landing light element is a 100 watt Halogen automotive driving light bulb.

BATTERY BOX

The battery box is located under the co-pilots seat. Remove the seat by pulling the two pin retraction cables (at lower front of seat) toward the center of the seat. Lift seat clear, and remove the two phillips head screws from the battery box cover for access. A 25 Amp Hour REBAT R-25M manifold vented battery is installed. Maintain acid level at 1/16" above the plates.

FUEL AND OIL REQUIREMENTS

The engine is rated for 80/87 Octane aviation fuel. Aviation grade 80/87 and 100LL fuels may be used. Addition of TCP lead scavenger is recommended when using 100LL fuel. Automotive regular unleaded gasoline is preferable to 100LL for engine operation. Use caution with automotive fuel in ambient temperatures above 85 degrees. Allowing the engine to heat soak after shut-down with automotive fuel can result in boiling the fuel in the carburetor bowl at temperatures above 85 degrees. The result is vapor lock which will prevent engine restart. If vapor lock occurs, remove the cowls for 15 minutes to allow cooling prior to restart.

Preferred oil for the engine is Shell 15-W-50 Multigrade oil year round. Engine start in cold weather is much quicker and smoother with the multi-grade oil. Oil change is recommended every 25 to 30 hours of operation.

ENGINE COWLING

The side cheeks are removed by loosening the 1/4 turn camlock fasteners. The top cowl may be removed by removing the 8-32 screws along the top of the firewall and the four 3/16 inch bolts which join the upper and lower cowls behind the spinner. The lower cowl may be

49

THORP T-18 N10TKremoved by disconnecting the carb heat bowden cable, disconnecting the landing light power and ground wires, removing the four 3/16" bolts which join the upper and lower cowls behind the spinner, and removing the 8-32 screws along the back edge of the cowl. The cowl will slide straight down, automatically disengaging the carburetor air and carburetor heat ducts.

CARBURETOR AIR FILTER

Replace the carburetor air filter on condition. The filter is removed by removing the lower cowl and unscrewing the carburetor air box cap screws. The filter is an automotive unit, FRAM CA- 176-PL.

50

THORP T-18 N10TKSECTION VIII

CAUTIONS IN COMPARING N10TK TO OTHER T-18'S

T-18 handling and performance varies widely among aircraft due to variations in weight, center of gravity, installed power, and airframe

drag. Some specific differences and cautions in that may be important to other T-18 operators are listed below.

WARNINGThis section is not all inclusive for adapting the N10TK flight manual to other T-18's. The author does not possess sufficient knowledge of all

other T-18's to portray their flight characteristics. Items in Section VIII are the opinions of the author and are offered as a caution to newcomers to the T-18.

CENTER OF GRAVITY AND WEIGHT

N10TK uses a light wooden prop as well as a relatively light engine with few accessories. N10TK cannot be loaded to the design forward C.G. limit of 61.0 inches unless is flown by a 35 lb pilot. T-18's with 180 HP Lycomings, constant speed props, and lots of equipment tend to sit at the other end of the C.G. range with nose heavy tendencies (S-18's with lengthened fuselages may avoid this problem). Flight procedures for T-18's with more forward C.G. may require caution to avoid full power run-up or heavy braking which could result in propeller ground strikes.

The original T-18 design gross weight was 1413 lbs, with a 1250 lbs aerobatic gross weight. N10TK is relatively light and uses a maximum gross weight of 1640 lbs. T-18's with 180 HP Lycomings and deluxe equipment push gross weights up as high as 1800 lbs. These heavier aircraft handle differently from N10TK, resulting in changes in preferred speeds and procedures. Approach and landing speeds may be 8 to 10 MPH higher, and the heavier aircraft must be flown with more attention to avoid developing excessive sink rates at low power and low altitude. Aerobatics in a "heavy" T-18 would not be practical due to the impossibility of getting down to the 1250 lb aerobatic gross weight at which John Thorp designed a +6 and -3 'G' aerobatic structure. I have no idea what the design limits are for folding wing or "S-18" aircraft.

THREE POINT ATTITUDE

51

THORP T-18 N10TKMost T-18's have two inch longer main gear than N10TK. The longer gear makes it possible to get near stalled conditions at three point attitude and significantly softens the ground ride,

STABILATOR STALL

Some T-18's have demonstrated stabilator stall with flaps down and forward C.G.. Stabilator stall in this condition results in a violent nose pitch down or "tuck". Recovery from tuck requires flap retraction, altitude, and fortitude. The tuck tends to occur at the high end of the flap operation speed range and may be preceded by longitudinal oscillation of the control stick and a reversal of stick force VS speed gradient (stick position VS speed gradient remains normal).

John Thorp has recommended limiting flap travel to "two notches" or 30 degrees to reduce tail download and tuck tendencies. Any new T-18 should be tested for tuck tendencies (at safe altitude) with full flap and forward C.G.. Testing should include trimmed and side slipping flight from stall speed up to maximum flap operating speed.

N10TK demonstrated tuck onset symptoms of stick oscillation and reversed stick force gradient when first flown (30 degrees flap and forward C.G.). Subsequent modifications to the wing root fairings cured the symptoms, and N10TK is free of any Tuck tendency.

POWER

N10TK is a relatively low powered T-18, resulting in the desirability to accelerate in ground effect before climbing out. Most T-18's with 160 HP or more are capable of rapidly accelerating to climb speed directly from 3-point attitude without the pause in ground effect.

PROPELLER TYPE

N10TK uses a fixed pitch propeller. T-18's with constant speed propellers will experience remarkably increased drag when the throttle is pulled back at flat pitch (high RPM prop setting). Landing procedures must be modified accordingly.

N10TK lands nicely from a full flap 85 MPH glide with power off. If a constant speed prop were installed, an increased glide speed would be required in a power off approach to prevent excessive sink rates at flat

52

THORP T-18 N10TKpitch. The excellent braking action of a constant speed prop can permit final approach speeds as high as 100 or 110 MPH without producing excessive float (assuming speed is bled off in the flare).

DRAG

N10TK airframe and cooling drag is lower than many T-18's, which is reflected in the performance data. Variations in T-18's can be large (+15 MPH) due to differences in engine installation efficiency, propeller efficiency, and airframe drag (detailing). Large differences in claimed performance also occur due to lack of calibrated instrumentation and/or knowledge of proper flight test and engineering procedures for performance measurement.

AIRFOILS

The original T-18 wing uses a NACA 63A-412 airfoil. Many recent T-18's and nearly all folding wing T-18/S-18 aircraft use the "LDS-1" airfoil which is capable of generating much higher lift coefficients than the original NACA section.

The LDS-1 airfoil would reduce maneuvering speed (Va) used for rough air penetration substantially. If the LDS-1 airfoil lift is similar to the NASA GAW-1, maneuvering speed would be reduced from 159 MPH CAS to roughly 139 MPH CAS.

Landing speed with the LDS-1 may or may not be reduced. Adequate main gear length and/or appropriate wing angle of incidence must be provided to permit three point touchdown with the LDS-1 airfoil if landing speed is to be reduced. If original gear geometry and incidence are retained, the actual three point touchdown speed will not be reduced but the landing approach and initial climb-out could be safely flown at a lower speed due to increased stall margin.

STABILATOR FLUTTER

Buyers of T-18's should be alert for compliance with required horizontal tail modifications. Two T-18's were destroyed in the early 1970's by catastrophic stabilator flutter. Apparently the flutter resulted from tails which were not built in full compliance with John Thorps design, however: John Thorp subsequently developed and flight tested a series of tail modifications to insure that no flutter could occur in a T-18 stabilator.

53

THORP T-18 N10TK

T-18's without the modifications should carry a reduced red line airspeed as specified by John Thorp (around 120 MPH?).

The required modifications include redistribution of the stabilator counterbalance weights placing some of the weight in the stabilator tips, stiffening the tubular main spar with a partial span internal doubler, and stiffening the forward inboard corners of the stabilator anti-servo (trim) tabs with stainless steel strips wrapping around from the end rib to the tab spar. Presence of the weights and stiffeners may be verified by inspection. The tip weights may be either in the form of bullet shaped lead protrusions at the stabilator tips or internal weights in the stabilator leading edge between the tip rib and the next nose rib inboard.

PROPELLER RESONANCE

Caution must be used if a fixed pitch metal propeller is used. Shortening an existing metal prop will change its harmonics leading to possible fatigue problems. Harmonic resonance can result in catastrophic propeller failure without warning to the pilot, with possible (fatal) loss of the engine from the airplane as a result. Sensenich propeller company did some in-flight testing in 1972 of clipped propeller and prop extension combinations on Bob Dials first T-18 (N11BD with a 160 hp Lycoming). The test results, reported in the newsletters, recommend a Sensenich 76 EM6-8-72 propeller with a Thorp 1072 prop extension. The proper model number propeller must be used, at least two T-18 fatalities have occurred from the use of metal props known to be incompatible (Sensenich M74DM propellers are proven to be incompatible). See T-18 Newsletter numbers 35 and 37.

Constant speed props may also be susceptible to harmonic vibration, an engine and propeller combination which has been previously certified should be used. Cutting any metal prop to shorter length without proper testing is dangerous.

Aircraft flying with clipped metal props should have a "sissy strap" installed on the engine. The sissy strap is a length of 1/4" cable woven through the engine cylinders and attached to an appropriate piece of fuselage structure. Propeller failure will break the engine mounts, but is unlikely to break the more elastic cable. Retaining the weight of the

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THORP T-18 N10TKengine on the nose of the airplane retains the ability to make a controlled glide! See T- 18 Newsletter Number 51.

Wooden propellers are also subject to resonant behavior, however: the infinite fatigue life of wood eliminates fatigue failure as an area of concern. The light weight of wood propellers also eliminates the need for a sissy strap. A failed wood propeller would not have sufficient mass imbalance to break the engine mounts.

FUEL CAPS

The fuel cap should NOT be an expanding seal type lacking positive mechanical retention. Many suppliers continue to sell caps which rely on friction of an expanded rubber seal to keep the cap from coming out. All such suppliers should be shot. One T-18 double fatality was attributed to loss of the gas cap and ensuing fire following an otherwise survivable impact. Following the fatal accident, John Walton of Houston tested his own expanding rubber cap. John filled his metal tank 1/3 full with water, tightened the rubber cap as tight as it could be set, and dropped the tank from waist height onto a grassy surface. The gas cap blew out. John correctly concluded that the expanding rubber caps have no place in a fuel tank which shares cabin space with the flight crew! Use a gas cap which has positive mechanical engagement to lock in place. N10TK had a locking arm over the expanding rubber gas cap (reported in the newsletters), which was subsequently replaced with a homemade locking cap.

SEAT DESIGN

Use of a sewn fabric bottom in the seat frame is inadequate to support your precious hide. A hard landing would very effectively pop the stitching out of such a seat bottom, dropping your spine for a hard collision with whatever lies below. Use a steel or stout aluminum seat frame, securely attached to the airframe, with a METAL seat pan (mine is .032" aluminum wrapped around and pop riveted to a welded 3/4" steel tube frame). N10TK also uses three inches of firm "temperfoam" on the seat bottom as an energy absorber (ordinary foam rubber or polyurethane foam will NOT provide protection in an impact, and may increase severity of injuries).

The seat backs in N10TK are steel frame with a canvas web and soft temperfoam cushions. The seat backs are quite narrow (10 inches at the top) to leave a large space between the two seats. The large space permits in flight access to the baggage compartment. The narrow seat

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THORP T-18 N10TKbacks also allow the pilot or co-pilot to place a shoulder behind the other person, easing the space crunch with two broad shouldered people on a cross country flight.

STALL STRIPS

N10TK has small stall strips on the wing centersection leading edge. These strips alter T-18 stall from an abrupt pitch over in which a delayed recovery is impossible to a stall which consists of a prolonged bobbing of the nose with strong buffet. Achieving a stall break requires very abusive flying. The stall strips are like seat belts, NO ONE needs them, and EVERYONE should use them.

COLD WEATHER OPERATION;

Defrosters:Unless you can shovel snow without sweating and fly without breathing, a forced air defroster is necessary for the T-18 in cold climates. Without forced air, keeping the windshield and canopy clear will be require cracking the canopy open while taxiing, and wiping the canopy beside you should you exhale while facing the Plexiglas. I have two defroster slots in my glare shield about 5 inches long and 1/4 inch wide. Four small (2 inch) 12 volt muffin fans supplying forced air to the slots resulting in a flow aft from the base of the windshield and along the sides of the canopy. I have not found it necessary to supply heated air to the fans, I just draw air from behind the panel. Warmth flowing up from the cockpit heater is adequate. Two small muffin fans would probably be adequate.

Heater:My heater air source is a 2 inch SCAT tube from the back of the engine baffles. This feeds a homemade tailpipe muff similar in size to the unit sold by Richard Vangrunsen for the RV series, followed by a homemade stainless steel air valve on my firewall forward of the co-pilots left foot. The air valve is designed to keep air flowing through the heat muff even with the heat turned off to prevent overheating the muff and tailpipe. This set-up provides very warm air at flow rates that make my pant legs ripple. An adjacent and independent cold air valve bringing air from the engine plenum is used to regulate temperature. I open both valves as fully as possible to flood the cockpit, assuring relatively uniform temperature anywhere in the cockpit. Temperature is regulated by closing down either the cold or hot air inlet as required.

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THORP T-18 N10TKAir taken from within the cowling upper plenum is at maximum static pressure, having reached near zero velocity (full dynamic pressure recovery). I installed a contoured scoop within the left engine cooling inlet in an attempt to recover air pressure as a cold air source to mix with the heater. It works, but is not nearly as powerful as the simple 2 inch SCAT tube off the aft baffle. Simple works....

Electric engine pre-heaters are essential. I use mine when the airplane will sit at temperatures below 20 degrees F or so. The Tannis heaters are great but very expensive, I use an inexpensive Westwind Zero start system from Wag Aero. If I plug my cowl inlets and exits, and let the heater run for two to three hours, the oil sump will be over 100 degrees and the cylinders will be pleasantly warm to the touch. A blanket over the cowl helps when temps drop to zero and below. Pre-heating permits easy starts with no priming and no undue engine wear.

Oil coolers must be closed down in cold weather. I completely cover the inlet surface of mine with aluminum tape for the winter. I can operate with the cooler completely covered up to about 65 degrees OAT without exceeding 220 degrees oil temp.

I restrict my engine cooling air inlets when OAT on the ground drops below 10 or 15 degrees. Fancy inlet plugs would be nice, but I just use a couple of strips of duct tape to close down the inlets by one full width of tape. This maintains cylinder and oil temperatures in sub-zero conditions, permitting deadstick landings without dropping CHT below 200 degrees. The tape strips and engine pre-heating will do a lot for protecting engine life!

FRESH AIR:Most T-18’s use a fresh air inlet on the aft end of the canopy skirt. The pressure differential is large at that location, yielding a powerful inflow of air which washes forward and over the pilots shoulders. I have experimented with a series of doors to control and enhance the airflow. An open inlet with no door, 6 inches wide and 1.8 inches fore and aft provides substantial flow. Adding inward opening doors with forward or aft edge hinges will restrict flow quite a bit, with the aft hinged door being least restrictive. I tried external slats and turning vanes to direct more air down into the slot with little success. My current installation which provides a very powerful inflow is an aft hinged door which opens outward, creating a scoop for air. Yes, I am sure it is draggy when deployed, but the cool air is well worth it! I have a curved deflector mounted on the inner surface of the door at the hinge to deflect the airflow forward and to counterbalance the door air loads.

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THORP T-18 N10TKI also have inlets in the leading edge of my center section similar to Cessna inlets but located at the outboard end of the centersection to stay clear of engine fumes. In the event of a smoking engine (I had one when an oil pressure switch disintegrated) these vents can be left open to provide clear air to the cockpit. My inlets pressurize the entire leading edge of the centersection allowing air to enter the cockpit via We-Mac vents in the fuselage sides adjacent to the wing. Flow rate is very low compared to the canopy vent, and I would not recommend them in this configuration, but the potential can be improved. I flew a Mustang II which used small NACA ducts just forward of the main spar underneath the wing. This is a high pressure high flow rate area, and the result was a REALLY impressive ventilator. Use of the lower surface NACA duct should improve flow, and a bit of ductwork directing the air to panel mounted vents which can be directed toward your face as in the Mustang II provides very effective use of the air available.

FLAP ACTUATOR TUBE SEALS

There are three T-18’s here at Flying Cloud Airport, each with a different type of air seal to close off the flap actuator slot. Without a seal, the slot produces a tremendous draft making winter flight an ordeal. My T-18, N10TK, uses sheets of 1/16” Phoenelic with a one inch hole riding on each flap actuator tube and held against the inner side of the fuselage skin by .025” sheet metal guides. The Phoenelic is cut to butt against the rear spar mounting bulkhead when the flaps are up while extending aft far enough to close out the flap slot. The slider rides on the top edge of the lower fuselage longeron as the flaps move aft (with flaps down, the seals do not close out the forward end of the flap slot). The seals work well and are trouble free but could be a chore to retrofit to a fully assembled airplane.

Dave Fox, N444DD, worked at adding seals similar to mine but decided there had to be an easier way, and created aluminum boxes covering the flap actuator arms and attached to the inside of the fuselage side skins. The aft ends of the boxes are open to the rear along the cable run. Sewn fabric cones seal from the open aft end of the boxes to the flap cables. This works great and may be easier to put into an assembled existing airframe than my sliding seals.

Darshan Karkey, N4MY, looked at our efforts and concluded that there must be a still simpler approach. Darshan cut a 0.9” hole in a sheet of rubber gasket material, slid it over the one inch flap actuator tube so that it is on the outside of the fuselage, and super glued the rubber to the actuator tube. Darshan trimmed the forward end to clear the rear spar with flaps up, and trimmed the aft end to just cover the slot. The

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THORP T-18 N10TKrubber just slides against the side of the fuselage, and air loads hold the rubber against the fuselage side, sealing off the slot when flaps are up.

‘Sorta reminds me of the story of the three little pigs, except that the guy with the straw house wins hands down in this version!

The other essential to a comfortable winter cockpit is to seal the canopy. I built my canopy frame to have just 1/4” clearance from the deck which provides an effective seal with the standard T-18 bulb seal. Latch design can influence the seal against the rollbar. If a single latch is used at the top center of the canopy, very little force will be available to pull the canopy forward into the rollbar seals. Pulling from the center can flex the canopy frame which slips forward relative to the canopy Plexiglas, limiting useable pressure. I used two latches, one on each side a five inches up from the canopy to more evenly pull the canopy forward. When sealing the canopy, keep in mind that the airloads will try to pull air OUT of the cockpit. Air loads will cause the sides of the canopy to flex outward and up slightly at the seat back frame, and will provide significant lift to distort the aft end of the canopy, raising it up off of the deck. I have hold-down pins on the aft end of the canopy frame which engage the canopy rails when the canopy is closed. The hold-downs prevent airloads from lifting the back and creating a gap. Many variations on the canopy aft hold-downs can be seen by walking the T-18 line at Oshkosh. Most use pins on the canopy frame aft cross bar which slip in under the back edge of the canopy rail when the canopy is closed, and some have pins which engage between the canopy side frame and a fitting on the deck. A couple of T-18’s use pins at the seat back frame as well as the aft end of the canopy to control canopy lift. Even a small leak will make a tremendous amount of noise while compromising cockpit heat control.

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