Technical Notes

RECOMMENDED FLIGHT SAFETY ITEMS

	1. MLG Trunnion Mod - Strengthens MLG support structures
	2. MLG Actuator Rear Anchor Mod - Replaces original various unmarked stud/bushing

                    assemblies with appropriate NAS bolt.
	3. Hydraulic Hand Pump Handle Stop - Prevents mechanical interference with aileron controls

                    if  hand pump leaks and raises handle.
	4. Inertia Reel Reinforcement - Better matches inertia reel and shoulder strap load

                    bearing capabilities.
	5. Nitrogen Gear Blow Down System - Assures full landing gear extension with

                    hydraulic and/or electrical failures.
	6. Steel MLG Collars - Replaces aluminum collars having a failure history with steel collars

                    to avoid loss of a MLG wheel assembly.

SUGGESTED MAINTAINABILITY IMPROVEMENTS

	1. Gear Grease Fittings - Adds ability to lubricate soft bushings to minimize wear.
	2. MLG Forward Gas Spring Anchor Bolts - Increases bolt size to fit oversize hole snugly.
	3. Gear Door Hinge Bearings - Replaces soft nose wheel door and  forward MLG door hinge

                    bushings with bearings, reduces friction and wear.
	4. Rear Gear Door Priority Valve Location - Moves valve from down line to up line for better door

                    performance, can use one priority valve in each line if desired.
	5. Accumulator Relocation - Moved to left MLG wheel well for easier checking and servicing.
	6. Canopy Latch Mod - Poli designed; more secure locking mechanism.
	7. Flap Torque Bracket Mod - Strengthens flimsy original mounting.
	8. Flap Actuator Mod - Replaces hidden nut with nut plate to ease actuator removal and

                    replacement.
	9. Aft Fuselage Inspection Panel - Allows access to rudder post mounting and elevator mounting

          assembly.
	10. Elevator Torque Tube Mod - Greatly eases removal of torque tube; an alternative

                      if  #9 is not  installed.
	11. Rear Spar Attach Plate - Original fitting is too short; longer fitting lines up with bolt hole.
	12. Hydraulic Pack Access Door - Adds small hinged door on left side for ease of servicing

                     hydraulic reservoir.
	13. Static Port Inspection Panel - Provides access to static port fittings.
	14. Rudder Pulley Bracket - Design has pulled rivets loose; inspect or strengthen as required.
	15. Main Gear Doors - Sturdier than standard composite doors.
	16. Air/Oil Separator - Reduces oil consumption and oil on belly.
	17. Permanent Oil Filter - Cleanable filter mounts the same as regular disposable filter; includes

                      rare earth magnets to trap any ferrous deposits.
	18. Brake Line Mod - Replaces flex hose with metal line and stainless flex at brakes.
	19. Dual Cowl Flap Actuator Pushrods - Avoids warping cowl flap in high air loads.

OPTIONAL AERODYNAMIC IMPROVEMENTS

	1. Flat Flap Bottom - Recommended by Ed Swearingen.

Here are some key numbers for handy reference in the cockpit. A quick review during your cockpit check before flight can work wonders. It is also suitable for pocketing in an approach plate holder.

SX 300 Speeds - KIAS

TAKEOFF / CLIMB	EMERGENCY
Vr = 90	Descent = 150
Vloff = 100 - 110	Best Glide = 125
Vx = 105	Landing (gear down) = 125
Vy = 125	Landing (field located) = 105
Vcc = 150	Landing (approach) = 90
PATTERN	LIMITS
Downwind = 150 - 120	Flaps (full) = 139
Base = 120 - 110	Landing Gear Extended = 152
Final (flap up) = 100	Landing Gear Alt Extended = 120
Final (flap down) = 95	Landing Gear Blow Down = 105

Angle of Attack (AOA) System

1. Airspeed indicators read the differential pressure between pitot and static pressures. This Angle of Attack (AOA) System uses a conventional 2.25 inch airspeed indicator (with an airspeed range of 40 to 260 mph) mounted on top of the glareshield, to measure the relative differential pressure, i.e., the relative wind angle or AOA, between two vertical locations under the wing.

2. Open the instrument case (voiding the yellow tag), carefully move the lever gear enough to reset the needle’s static position backwards from zero to the 240 mph position and reclose the case.

3. Obtain from a craft store and, for strength, glue an equal length of .018 OD/.05 ID metal tube inside a .25 OD tube (approx measured size). File the ends square. Drill a .25” hole at the bottom rear of the pitot tube behind the heating element and deburr. When inserted into the drilled hole, the tubes should extend out the top about 2 “ and out the bottom about 2 “.

4. With a gentle radius, bend the bottom portion of the tubes forward to about 56 degrees down as shown (the tip should be 1 5/8” below the pitot tube). With JB Weld, secure, build up and blend 1-2” of the base of the tubes into the pitot tube bottom. Sand to a smooth, faired shape.

5. Attach a pitot line at the top of the tubes and run it to the static input port of the AOA indicator. Drill through the canopy defroster duct and run the line out the defroster outlet.

6. Tee off a pitot line from the airspeed indicator pitot connection and similarly run it to the pitot input port of the AOA indicator. Use conventional plastic pitot fittings to connect the lines.

7. Calibrate the system after flying by gently filing the end of the tubes. Increasing the tip’s relative angle downward decreases the air entering, increases the pressure differential and lowers the mph indication at a given airspeed and vice versa. When calibrated, stall should occur at 40-45 mph, 70 mph is about 90 kts on the airspeed indicator, 80 mph is about 100 kts, 150 mph is about 150 kts and 220 mph is about 200 kts. The relative positions, not the numbers, are what is important. You can change the AOA dial face to show degrees or other marks if desired.

8. Because the maximum amount of weight change in the SX 300 from full tanks to empty tanks is a much smaller percentage of gross weight (400/2400=16.67%) than military aircraft whose gross weight can vary 50% or more after dropping weapons and burning fuel, actual airspeeds for the same AOA don’t vary much, but it is a useful crosscheck and, as you slow below 100 kts, the needle is quite sensitive, quickly indicating AOA/speed trends, and is easy to see.

Click on the link below to see the drawing of the Angle of Attack design.

AOA Drawing

SERVICE INFORMATION

STRUTS: Main gear, 125 to 145 psi (2.5" to 3" high). Nose gear, as needed.

TIRES: Main and nose tire, 45 psi.

HYDRAULIC ACCUMULATOR: 650 psi.

GAS SPRINGS: Recommend replacement at each annual inspection.

GEARN GEAR BLOW DOWN SYSTEM: 1700 to 2000 psi.

Hydraulic Accumulator Service:

1. Crack open vent valve (about half open).

2. Attach fill hose (nitrogen bottle) to Schroeder valve; clean valve first by blowing with air

before attaching hose.

3. Loosen valve nut on Hydraulic Accumulator Schroeder valve* (you should hear air flowing

out to the nitrogen bottle. If you do not hear air this means it needs service and is probably

empty, or you don't have the valve open).

4. Open nitrogen fill bottle with regulator set at desired pressure (650 psi).

5. Close valve nut on Hydraulic Accumulator Schroeder valve.

6. Turn off valve on nitrogen fill bottle and bleed off pressure.

7. Remove hose and replace valve cover and check for leaks.

8. Close vent valve.

9. Turn on Master Switch and Hydraulic pump to pressurize system.

A symptom of improperly charged Hydraulic Accumulator is the pump cycling on/off frequently

at end of a cycle. It is a good policy to check the pressure every 25 hrs of operation or when this

symptom occurs.

Servicing The Landing Gear Struts:

1. Place aircraft on jacks and lift with gear fully extended.

2. Wipe struts with hydraulic fluid to clean.

3. Attach nitrogen bottle to Schroeder valve* ; clean valve first by blowing with air before

attaching hose.

4. Slowly increase pressure to 125 - 145 psi on main gear. This valve works only one way.

The pressure you're putting in must be greater than the pressure in the strut to open valve.

If you have too much pressure it can be released by depressing the valve core or by using

a Hartzell Dome tool. Piper p/n 756-771. You can vent the pressure off to the desired psi.

5. After charging, close valve on nitrogen bottle and remove hose.

6. Check for leaks.

7. Replace cap.

Note: The soapy solution kids use for blowing bubbles makes a very good leak detector.

*: The Schroeder valve on the Accumulator is different than the one on the landing

gear. The valve on the Accumulator has a nut that has to be opened (counterclockwise)

after the hose is connected and closed before fill pressure is turned off.

**: The valve on the gear strut has a valve core which allows pressure to enter, but the core

must be depressed to allow air to escape.

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