Military Potential Test of the 'Door Hinge' High-Speed Rotor System

The Door Hinge rotor, designated Model 540 by the manufacturer, is a two-bladed, semi-rigid type with a flapping hinge and underslung feathering axis, which incorporates a unique pitch-change bearing arrangement door hinge. All the bearings in the hub assembly are Teflon-lined sleeves therefore, the hub requires no lubrication. The Door Hinge rotor was mounted on a commercial Model 204B Helicopter. The 204 B is similar to the UH-1B except that it has a longer tail boom to accept a 48-foot rotor blade. The test Objectives were to determine whether the Door Hinge High-Speed Rotor System has advantages in speed and vibration level compared to the 44-foot and 48-foot rotor systems presently utilized in the UH-1 series helicopters. The Model 204B Helicopter with the Door Hinge rotors system installed was flown a total of 5 hours and 35 minutes at gross weights of 7500, 8500, and 9500 pounds. A standard production UH-1B was flown once at a gross weight of 8500 pounds for a comparison of vibration levels and autorotational characteristics. Test results showed that the Door Hinge rotor system offered significant advantages in the reduction of vibration at high speeds compared with rotor systems presently used in the UH-1 series helicopters. The approximate 70-percent increase in rotor inertia made autorotation touchdowns less critical to perform, particularly above gross weights of 8000 pounds. Blade slap noise was significantly reduced at high airspeeds and gross weights. Operational suitability was improved by higher speeds, greater maneuverability, and better and autorotative characteristics.