January - present, 2010

2010-02-04

• Continued work on the 4-Place PAV Prototype.
  • Continued with the wiring.
  • Completed the baffling & installed 2 cooling fans.
  • Completed a new tilting mast and test fixture. We began to test the mast, and had a slight failure of a shear web bond at a vertical lift of 6810 lbs and a side load of 1054 lbs at the top of the 55" long mast. We have repaired the bond, and plan to continue testing this week.
  • Installed a fire suppression system.
  • Installed the gascolator and fuel pump.
  • Performed a 'dummy' layup of the new rotor tip design. We discovered a few aspects of the design that could be improved, and will start a new 'dummy' layup this week. Pending a successful 'dummy' layup, we will start construction on a 16' diameter test blade, followed by full size blades for the 45' diameter rotor.
  • Continued testing the second test spar. The spar had previously been cycled 10,000 times going from 45,000 to 262,500 lbs. For the next test, we increased the load to 360,000 lbs. After several seconds at that load, the spar failed. The failure appears to have started at a dogleg in the unis that were supported with circumferential windings. We have started design on a fourth spar to eliminate the uni dogleg and let the titanium plates carry the load direction change. Note this is exactly the same load at which the first spar failed, however at that time we thought that failure occurred because of a circumferential windings failure. (Note the failure of the second spar occured after a third test spar had already been built - see below.)
  • Laid up a third spar to test. In contrast to the previous design, fillets were included in the mold itself, so that no extra pieces were required for the circumferential windings. Additionally, the titanium pieces in the spar were prepared for bonding by sanding, without any chemical treatment (the two previous spars had been chemically treated). This spar failed after 8,838 cycles going from 45,000 to 262,500 lbs. It appears that the lack of chemical surface treatment caused to the failure.
    
    For reference, these spar proof test loads are based on 160,000 lbs of centrifugal force from the rotor at 400 rpm (the max jump takeoff rpm).
    

2010-01-05

• We completed the second milestone under our contract with AAI, performing a critical design review for the 4-Place PAV Prototype. The review was a bit unconventional, considering that we've already begun construction of the aircraft, but it brought AAI up to speed on the design, and it was good for us to hear critiques from new people.
• Please excuse the lack of an update for December. We were tied up with a few very important projects.
• Continued work on the 4-Place PAV Prototype.
  • Continued with the wiring, including voltage regulators and the nav/comm antennas.
  • Continued work on the baffling system.
  • Completed a new tilting mast and performed a proof test. The mast failed in the steel fitting at the pivot point at a load of 34,300 lbs (this is still a good safety factor, but short of our intended proof test load). Upon inspection, the failure was due to a weld that didn't achieve full penetration. We have begun work on a new mast and redesigned the tooling to ensure a full penetration weld. We've also redesigned the mast test fixture so the mast can be tested in every possible load configuration.
  • Completed modifying the tip of the rotor blade mold. The new shape makes the transition more gradual from the constant chord section to the increased chord at the tip. We also laid up molds for a short 15' diameter blade to do a proof test of the rotor tip. This test blade will match the real blade in the tip, but will be a continuous structure from one side to the other in the inboard region. The blade will be spun at a high rpm that will produce a centrifugal force from the tungsten weight 3 times higher than possible from the actual 45' dia rotor at its maximum overspeed rpm of 400.
  • Laid up a second spar to test. In contrast to the previous spar, this spar was laid up mostly in a single operation, rather than in two halves that were bonded together. Additionally, resin/carbon inserts were installed to provide a radius for wrapping the circumferential windings.
    
    Multiple tests have been completed on this spar. In the first, load was applied in 25,000 lb increments up to 275,000 lbs, taking measurements from several strain gauges at each load. For the second test, the spar was cycled 10,000 times from no load to 238,000 lbs. The third test was a repeat of the first, to verify that the strain measurements were the same (i.e. no damage occured during the fatigue test). After the first test, and after 1,000, 5,000, and 10,000 cycles in the second test, ultrasonic inspections were performed to ensure that no delaminations had occured. We have shipped the spar to an outside company, where more involved fatigue testing will be conducted, followed by a test to failure.
    
    We have begun construction of a 3rd test spar. Fillets were added to the mold itself, so that no extra pieces will be required for the circumferential windings. This spar will also have a skin of 1 ply of 0-90, eliminating the need for the spiral windings that ran the length of the two previous spars.
    
    For reference, these spar proof test loads are based on 160k lbs of centrifugal force from the rotor at 400 rpm (the max jump takeoff rpm).
     
  • Completed proof testing of the new fixed horizontal stabilizer. For the first test, a symmetric load of 2200 lbs was applied. For the second test, a 200 lb load was applied at the outboard tip.
  • Completed proof testing of the engine support - 9 g's static down load and 960 ft lbs (436 hp at 2400 rpm).
  
  
  

  Engine Support Torque Test Setup Spar with Instrumentation New Tilting Mast Horizontal Stabilizer Symmetric Proof Test