Tire exchange
Removal:
1. Jack up aircraft at specified point.
2. Deflate tire completely before removing wheel unit.
3. Do not unscrew the valve insert until the tire pressure has dropped to 0.2 bar.
4. Remove wheel from axle.
5. Loosen wheel bead from the hub shoulder with a rubber or plastic hammer.
6. Undo wheel bolts (with 5 mm hexagon key), remove bolts and washers, split
hub halves.
Mounting:
1. Tires and wheel hubs must be clean and dry.
2. Do not apply excessive force when replacing a wheel.
3. Apply a dehesive agent (or talcum powder) to the hub shoulder.
4. Remove dirt, sand, labels, etc. from the tire.
Apply a moderate amount of talcum powder to reduce friction between tube and tire.
Caution: Too much talcum has the opposite effect.
5. Fill air into tube (placed in the tire) until it is evenly round. Remove nut and washer from valve.
6. Place tire (red mark at valve hole) and tube on the wheel half with the valve hole,
push valve through valve hole.
7. Push other wheel half onto tire, match bolt holes with centering shaft.
8. Insert wheel bolts, washers and any nuts, and tighten to the correct torque (M6: 9 to 10 Nm).
Tighten bolts diagonally.
9. Place a tire in a safety cage when inflating it to mounting pressure for the first time.
If you do not have a safety cage, take great care when inflating the tire.
Inflate the tire to mounting pressure.
The mounting pressure is 10% more than the specified operating pressure.
Check carefully for leaks. Leave to adjust at this pressure for 12 to 24 hours.
Once the tire shows no leaks and is at operating pressure, the wheel unit can
be mounted on the aircraft.
10. Make sure that the wheel unit is mounted perfectly balanced to avoid vibration and excessive wear.
Red Dot:
Larger aircraft tires are marked with a red dot. This is an indication of the lightest spot of the tire. The valve must be placed at this point to eliminate or minimize a balance/vibration problem of the tire.
Notes on inner tubes
Aircraft tubes are made from natural rubber and they are slightly underdimensioned so that it is easier to install them in a new tire.
The layers of an aircraft tire are made of nylon – they therefore tend to become larger with use.
The inner tube also increases in size, adapting to the larger inside diameter of the tire.
If a tube enlarged in this way is later fitted in a new tire, it can happen that it is too big for the inside of the tire, with the result that the tube may crease.
These creases may rub through during operation, causing the tube to loose pressure.
Rubbing through slowly results in slow pressure loss – the pilot is thus warned before a dangerous situation arises.
If the tube tears during a start, the pilot will fail to notice that he is flying with a flat tire.
Taking into consideration all the risks involved with fitting an old tube into a new tire, it is advisable always to fit new inner tubes in new tires.
