January - November, 2009

2009-11-02

• We are creating two new spinoff companies - one for manufacturing which will initially build kit aircraft and military UAVs, and one for development and prototyping (more info). This is an opportunity to be involved with slowed rotor compound aircraft. If interested, please visit our Employment Opportunities page.
• Continued work on the 4-Place PAV Prototype.
  • Continued with the wiring. Wiring for most major systems is now complete.
  • Continued work on the baffling system.
  • Continued work on the new tilting mast. Ribs and other internal components have been completed and installed. The two halves must still be bonded together.
  • Began 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.
  • Completed laying up a short section of the rotor skin, machined the skins as necessary, and began a proof test. We decided to test the skin independently of the spar, so that the strength of each can be determined. On one end of the skin is the pin joint that is laid up exactly as we plan to attach the skin to the spar. To pull on the skin, we need another pin joint, but because of constraints of the test fixture, we couldn't build up that joint in the same manner. We laid up as much titanium inside the mold as we could, machined away what was required to fit in the test fixture, and then added doubler material to the outside of the skin after the primary cure. After 4097 cycles at 240,000 lbs, this doubler delaminated from the skins. Fortunately, the reduced titanium inside the skins was still able to carry the load. We've re-attached the doubler in a modified manner that should reduce its stress concentration factor, and have resumed the test. Once we reach 10,000 cycles, we plan to slowly increase the load to 360,000 lbs and perform 1,000 cycles at that load. If the skins pass those 1,000 cycles, we will slowly increase the load until the part fails or we reach the limit of our test fixture.
    
    For reference, these proof test loads are based on 160k lbs of centrifugal force from the rotor at 400 rpm (the max jump takeoff rpm). 240k lbs is a 1.5x safety factor under the cyclic loading, and 360k lbs is a 2.25x safety factor for static loading.
     
  • Bonded together the two halves of the new spar, machined as required, and performed the proof test. We had the same plan for the spar proof test as that described above for the skins. On our first attempt at loading the spar, we delaminated the spar along the centerline at 200,000 lbs. This was due to the angle of the unidirectional carbon in the region where the thickness increases in the transition from the spar caps to the titanium lug. The spar was repaired and circumferential windings added in the appropriate location to address this problem.
    
    After the repair, we resumed testing of the spar. We successfully completed 10,000 cycles at 240,000 lbs. As we began slowly increasing the load for the next phase of testing, we heard some popping at 300,000 lbs and paused. At first, the popping stopped immediately after we paused, but after several seconds of silence, the spar failed. On inspection, it appears that the failure was in the circumferential windings where the two spar caps come together (not the circumferential windings that were added as described above).
    
    We do have plans to improve the spar design, and we do plan to build and test another spar. But to put the achieved load into perspective, as mentioned above, the load on the spar will be around 160k lbs at 400 rpm. We would have to spin the rotor at 550 rpm to put 300k lbs of load on the spar. To look at it another way, if we only spin the rotor to 365 rpm, we'll only have 133k lbs of load on the rotor, which will let us operate with the same 2.25x safety factor that was our original target.
     
  • Completed modifying the spar mold. The spar for the test described above was laid up in two halves and bonded together. The new mole will allow the spar to be laid up and cured in one operation.
  
  
  

  Modifying Plug for New Blade Tip Left Half of Tilting Mast Upper Skin for Proof Test Installing Spar for Proof Test

2009-10-06

• We are creating two new spinoff companies - one for manufacturing which will initially build kit aircraft and military UAVs, and one for development and prototyping (more info). This is an opportunity to be involved with slowed rotor compound aircraft. If interested, please visit our Employment Opportunites page.
• Continued work on the 4-Place PAV Prototype.
  • Continued with the wiring. The instrument panel is now installed in the aircraft.
  • Continued work on the baffling system.
  • Built the two skins of the new tilting mast. Internal components must still be made before bonding the two skins together.
  • Bonded together the two halves of the new spar. This particular spar will be tested to failure in the test fixture.
  • Began laying up a short section of the rotor skin to use in the spar proof test.
  
  
  

  Laying Up Blade Skin Sections for Proof Test Tilting Mast Skins Engine Compartment (note upper rear baffling)

2009-09-14

• We apologize for the delayed update. There was a pressing engineering project that kept our webmaster busy.
• We are creating two new spinoff companies - one for manufacturing which will initially build kit aircraft and military UAVs, and one for development and prototyping. This is an opportunity to be involved with slowed rotor compound aircraft. If interested, please visit our Employment Opportunites page.
• Continued work on the 4-Place PAV Prototype.
  • Continued with the wiring. The instrument panel and hydraulic system wiring have been completed and are awaiting a functional test.
  • Began work on the baffling system.
  • Installed soundproofing on the firewall.
  • Comleted the new mold for the new tilting mast.
  • Built the mold for the new spar design & laid up the two halves of the spar. These two halves will be bonded together to complete the spar.
    
    Compared to the previous design where the spar was bonded directly to the blade skins, this new design uses a pinned attachment. We have been working with some outside companies on this new design, and their help has been invaluable in performing finite element analysis on the spar - a capability that we didn't have previously. The current design is now slightly different than that described in a previous update. We had originally intended for the unidirectional carbon to wrap around the pin, but based on finite element analysis, this approach wasn't feasible given the limited overall thickness of our blade at the joint location. Instead, the spar will be constructed similar to the skins, incorporating titanium plates into the carbon laminate structure. The titanium is needed because it is much better able to handle concentrated loads than the carbon. We had originally intended to use stainless steel for these plates, but titanium more closely matches the stiffness of carbon, which allows the load to be transferred better with lower stress concentrations. We have performed several coupon tests with this construction method to verify its load handling capability.
     
  • Built a fixture to test the new spar design. We tested the fixture itself to a load of 521,000 lbs before it began to yield. This is 3.3x higher than the tension that will actually be on the spar at the highest operational prerotation speed (400 rpm - 160,000 lbs), and 2.6x higher than the tension during the overspeed proof test in the test pit (450 rpm - 200,000 lbs). The test plan with this fixture is to perform 10,000 cycles at 240,000 lbs on the spar (1.5 times the max operational prerotation load), dropping to zero load between each cycle, and then perform 1000 cycles at 300,000 lbs, 400,000 lbs, and 500,000 lbs, or until the spar fails. If the spar survives all 13,000 cycles, we will take it to the 521,000 lb maximum of the fixture. However, we expect the spar to fail before reaching 500,000 lbs.
  
  
  

  Laying Up Spar in Mold Cured Spar Halves Test Fixture End with Hydraulic Cylinder Test Fixture End with Fixed Support New Tilting Mast Mold Engine Compartment Instrument Panel Wiring

2009-08-04

• The 47th Annual Popular Rotorcraft Association Convention Fly-in is being held in Mentone, Indiana, from August 4th through the 8th. Carter is sponsoring a Time to Climb contest at the event, which will take place on Thursday.
• We took the 4-Place PAV Prototype to this year's EAA AirVenture in Oshkosh, Wisconsin. The aircraft was unveiled on Sunday, July 26th, and was on static display through the following Saturday in the EAA Welcome Center. Company president, Jay Carter, gave a forum, titled Carter's SR/C Technology and PAV Update, on Saturday, August 1st. For more information and photos from the event, take a look at our Oshkosh 2009 page.
• Continued installing many of the mechanical components, including elements of the hydraulic and pneumatic systems and controls.
• Completed the new fixed horizontal stabilizer outboard vertical stabilizers, including attaching bonding the outboard vertical stabilizers to the horizontal stabilizer, and all pre-finish and painting.
• Completed installation of the landing gear fairings onto the center wing section, including pre-finish and painting.
• Continued work with test specimens to determine the best methods for constructing the new rotor, which will now use a removable pin to connect the spar to the blade skins.
• Completed modification of the tilting mast plug for a new tilting mast.
• Continued wiring for various electrical components in the aircraft.
  
  

  4-Place PAV Horizontal Stabilizer 4-Place PAV with Canopy Open Instrument Panel Engine Compartment Modified Tilting Mast Plug Carter Display at Oshkosh more OSH photos

2009-07-06

• We are taking the 4-Place PAV Prototype to this year's EAA AirVenture in Oshkosh, Wisconsin. The aircraft will be unveiled on Sunday, July 26th, and will be on static display through the following Saturday in the EAA Welcome Center (located along the main road, Celebration Way, close to AeroShell Square). Company president, Jay Carter, will be giving a forum, titled Carter's SR/C Technology and PAV Update, at 11:30 am on Saturday, August 1st in Pavilion 11, the REMOS Aircraft Pavilion (more info).
• Continued installing many of the mechanical components, including elements of the hydraulic and pneumatic systems, position sensors, and servos.
• Completed the final bond of the new fixed horizontal stabilizer and installed it on the aircraft. Completed final bond of the new moveable elevator. The outboard vertical stabilizer still need to be bonded to the horizontal stabilizer, and prefinish and painting must still be completed for all parts of the assembly.
• Completed construction of the landing gear fairings and began installation on the center wing section.
• Continued work with test specimens to determine the best methods for constructing the new rotor, which will now use a removable pin to connect the spar to the blade skins.
• Began construction of the new tilting mast.
• Installed the EFIS units, radios, and various other avionics in the panel. These systems are now functional. Began wiring for other electrical components in the aircraft.
  
  

  Fixed Hor. Stab. Installed on Aircraft Landing Gear Fairings on Wing Center Section One Side of New Tilting Mast Instrument Panel

2009-06-01

• Continued installing many of the mechanical components in the 4-Place PAV Prototype, including elements of the hydraulic and pneumatic systems, position sensors, and servos.
• Continued construction of the new fixed horizontal stabilizer and moveable elevator, to replace the existing stabilator. We completed the tooling for internal components and made the parts.
• Began construction of the landing gear fairings.
• Continued work with test specimens to determine the best methods for constructing the new rotor, which will now use a removeable pin to connect the spar to the blade skins.
• Repaired the rotor test stand.
  
  
  

  Horizontal Stabilizer Parts Landing Gear Fairing

2009-05-04

• Continued installing many of the mechanical components in the 4-Place PAV Prototype, including the engine, tilting mast cylinder, throttle cables, elements of the hydraulic and pneumatic systems, position sensors, and servos.
• Continued construction of the new fixed horizontal stabilizer and moveable elevator, to replace the existing stabilator. We laid up the skins, and are currently working on the tooling for internal components.
• While proof testing the rotor, the rotor failed at 390 rpm, 10 rpm lower than our intended maximum proof. We filmed the test with a high speed camera at 600 frames per second, so we were able to see very clearly that the failure occurred somewhere in the bond between the spar and the skins - the spar pulled out of the skin fully intact, which would only be possible if that bond failed. Examination of the debris afterward indicated that the failure was interlaminar shear just below the surface of the spar. Following the failure, several engineers from outside Carter visited our facility, including an engineer who specializes in composite analysis. They helped confirm the cause of failure.
  
  There were several contributing factors, but the main one was the stress concentration in the region where the spar first attaches to the skins. The average bond stress over the spar surface was very low - on the order of 200 psi. However, in the region where the spar first attaches to the skins, the stress was much higher. This was exacerbated by a small void between the spar and the upper skin due to resin shrinking which occurred during the cure cycle. These stress concentrations are hard to determine without a composite finite element analysis program, which we did not have. The visiting engineer who specializes in analysis did have the appropriate tools, and was able to quantify these concentrated stress levels.
  
  Another contributing factor was that the rotor was built with a pre-preg layup, as opposed to a wet layup like all of our previous rotors. The pre-preg spar was stiffer than previous wet layup spars, increasing the stress concentration noted above. Additionally, the nature of the pre-preg layup produces shear planes between the plies that are not present when rovings (twisted strands) are laid down individually. The prepreg increased the likelihood of a spar interlaminar shear failure.
  
  Once there was a local failure where the spar first attached to the skins, this failure propagated down the length of the spar in a 'zipper' type failure, and the skins separated from the spar.
  
  It should be noted that this method of bonding the spar to the skins had been used successfully on all prior rotor blades, and in Jay Carter's previous experience in the wind turbine industry. Not a single wind turbine ever had this type of failure, with some of them still in operation after 25 years of continuous service.
  
  After brainstorming with the outside engineers, a better method of attaching the spars to the skins was devised. The attachment will be done with a removable pin. Since stainless steel is better able to handle the concentrated pin load than carbon, the skins at the pin attach point will have many sheets of stainless steel laminated between the uni layers. By incorporating the sheets into the layup, there will be plenty of bond area to transfer the load to the carbon. For the spar, the fibers will wrap around the pin, so there won't be the same reliance on a bond. We are currently laying up test specimens to verify the loads that can be achieved in this type of joint.
  
  
  

  Components Installed in Engine Bay Horizontal Stabilizer Skins

2009-04-06

• Company president, Jay Carter, will give a presentation at this year's Sun 'n Fun Fly-In in Lakeland, Florida. The forum will be Saturday, April 25th, at 9:00 am in Tent 3.
• Installed the AC condensor and numerous components of the hydraulic & pneumatic systems for our 4-Place PAV Prototype. Completed many miscellaneous fit & finish tasks.
• Built new exhaust headers for the Lycoming IO-540 engine, to better fit our installation.
• We have contracted with a company to do the interior finish of the PAV. They have provided us with a sample of the seat upholstery (pictured below). The final finish will be a tan interior.
• Began construction of a new fixed horizontal stabilizer, to replace the existing stabilator. The fixed design is substantially lighter. Depending on schedule, this new stabilizer may be installed on the aircraft prior to the first round of flight testing.
• Continued testing the rotor for the PAV prototype. We have had the support of a large aerospace company for this testing, and with that support, we've had access to inspection equipment we didn't have before. An ultrasonic test was performed on the rotor, and a large region of delamination was detected on one blade. This delamination was most likely caused several months previously during construction. The blade was accidentally dropped around 3 ft onto the concrete floor. We didn't detect any damage through a visual inspection, and didn't have the means to do an ultrasonic inspection at the time. After discovering the delamination, we completely removed the lower skin of the damaged blade, and then built and installed a new lower skin. We have reached 380 rpm thus far, and expect to complete testing this week.
  
  As stated in previous updates, we plan to proof the rotor to 400 rpm during this phase of testing, which would allow us to run to 350 rpm for the first phase of flight testing. We have contracted a university and an aerospace company to perform structural analyses that are more detailed than we can achieve with our tools. With the results of those analyses, we will build a second rotor. Once we have at least two rotors, we will proof test one to 450 rpm, which would allow operation to 400 rpm and provide for very dramatic jump takeoff performance.
  
  

  Rotor Being Repaired Components Installed on Firewall Upholstered Seat Sample New Exhaust Headers

2009-03-02

• Completed pre-finish of the fuselage, center wing section and horizontal stabilizer and painted them.
• Installed the Heating Ventilation & AC blower housing, heater and AC cores, air direction flap and sealing baffles.
• Fabricated and installed the front canopy balance / snubbing cylinder.
• Installed the rotor for our new 4-Place PAV prototype on the test stand. Completed the dynamic balancing and began testing. We are working with a major aerospace company on these tests. Accelerometers have been mounted on the mast to measure accelerations. We have done numerous tests to determine natural frequencies of the mast and the test stand itself. So far, we have run the rotor to 300 rpm, and everything appears to be going well. We plan to proof the rotor to 400 rpm during this phase of testing, which would allow us to run to 350 rpm for the first phase of flight testing. We have contracted a university and an aerospace company to perform structural analyses that are more detailed than we can achieve with our tools. We hope to have the results of those analyses back before the first phase of flight testing is completed. If those results confirm our analysis, we will proof the rotor to 450 rpm before the second phase of flight testing.
  
  We have had two minor setbacks during this testing. First, the main driveshaft broke. We believe that it was combination of fatigue and shock loads from years of testing props to failure and the previous rotor blade proof failure. The driveshaft was replaced. Then, the driveshaft that connects the prerotator pulley to the prerotator gearbox failed. We did not analysis the stress concentration correctly and it saw a high oscillating stress which caused a fatigue failure. The shaft has been redesigned and is being fabricated.
  
  

  Painted Fuselage Rotor on Test Stand

2009-02-02

• Completed the prefinish and painting of the new 45' rotor for the new prototype, the 4-Place Personal Air Vehicle. Installed pitch and flapping sensors in the rotor.
• Designed & built a new bracket to support the gearbox & tilting mast control cylinder.
• Performed a proof test of the fore/aft loads to be carried by the new bonded bracket that attaches the tilting mast to the fuselage. However, a new design was developed to modify the gearbox bracket described above to carry those loads through a strut running to the prop thrust beam. The new design will be completed this month, and we will have to test it to the same proof load as the bracket was tested to.
• Built spring loaded hydraulic strut that will assist the pilot in opening & closing the canopy.
• Test fit the instrument panel in the aircraft.
• Completed pre-finish of the fuselage and horizontal stabilizer. These parts still need to be painted.
  
  

  Completed Rotor Proof Test of Fore/Aft Load at New Mast Attachment

2009-01-05

• Completed all shear webs & ribs for both blades for the new rotor.
• Bonded both blades together and to the spar.
• As described in a previous update, we've built a new bracket to hold the tilting mast which uses variable spring rate elastomerics. We've installed the bracket, and completed the proof test for the lift force. Each bracket was loaded to 22,500 lbs, which is still 12% more than the bracket would see under the extreme worst case of a full lateral rotor tilt at max pitch and max overspeed rpm. To get the same load on each bracket with the stick centered would require 45,000 lbs of lift. A few changes were made to the strongback in order to perform the proof test - under normal operation in flight, the load would be distributed over the entire aircraft. However, to perform the proof test, the load was reacted at the landing gear attachment only, causing secondary bending and load concentrations that the aircaft would normally never see.
• Completed the prop drive and aircraft prerotator hardware, including the new gearbox.
• Finished a modification to the engine support as a result of relocating the prop pitch governor.
• Received the completed instrument panel. Greg Richter of Blue Mountain Avionics has been handling the electronics for this aircraft. The panel includes two EFIS Two units, customized to perform functions specific to the PAV, as well as one EFIS Lite for a backup. Greg has also completed control circuit boards to control & monitor rotor pitch, rotor rpm and aircraft pitch.
  
  

  Preparing Rotor for Pre-Bond Fuse w/ Mods for New Mast Attachment Completed Instrument Panel