Improvement of Wheel Brake on Sailplanes
The question often arises here and in discussion forums, how the wheel brake performance on sailplanes can be improved.
Almost all new sailplanes are equipped with drum or disk brakes by the German manufacturer Tost. Here sometimes exotic modifications are proposed. For example, how the braking power can be increased by changes in the lever mechanism. As manufacturer we can only caution in the strongest terms against making changes in the brake mechanism. The brake is a safety related mechanism and cannot simply be changed.
This brings us to the question what causes insufficient braking, and what can be done about it.
As far as DG sailplanes are concerned, the following three items arise:
- Insufficient brake effectiveness of drum brakes can almost always be traced to lack of servicing. I am sure you are aware that every new steel cable will stretch slightly when first used. This lengthens the cable slightly in the first few months after delivery, and the original setting of the brake is changed. If you pull the dive brake lever you should not feel a hard stop, but with a pull of at least 20 daN (approximately applying 20 kg of power) you should feel the elasticity of the steel cable. If you come to the dive brake stop before this you cannot achieve proper brake application.
- The following refers to reduced braking action in older aircraft which is often due to accumulation of brake dust on the brake pads. The only thing to be done is to disassemble the brake drum and clean it with compressed air.
- Often the apparent insufficient braking power is imagined by the pilot. Damp or wet grass has considerably less friction than dry asphalt. The wheel could be locked and the brake functioning properly. In this situation a car would swerve immediately. But an airplane is steered by the rudder, and the pilot might not notice that the wheel is locked.
- There are situations where maximum braking power is required, for instance when landing out into a short field. If you require such braking power that the sailplane gets on it's nose, even if it means that the fuselage bottom is scratched, then you should order a disk brake as special equipment. But that should only be done in an emergency, because today's high performance sailplanes no longer have skids and are likely to damage their fuselage in extreme braking. But it's still better than hitting a fence or another airplane.
Disc brakes don't require as much maintenance because they don't have a Bowden cable that can become crimped or dirty from brake pad dus
Conclusion:
Do not under any circumstances, "modify" the brake mechanism.
Do not oil the brake, as some customers have done.
If you think the brake is not operating properly check to see if the cables are adjusted according to the service manual.
Disk brakes achieve better brake performance, which is important in emergency situations.
- friedel weber - 