Archive of Weekly Updates
July - September, 2004
2004-09-27
- Worked on the new scimitar propeller. Salvaged the main spar from the previous prop. Laid up the skins for one blade. Made all internal parts except for one leading edge spar.
- Received and began checking out new sensors to use in the aircraft as part of the Army contract. These sensors include a yaw/pitch/roll sensor, and a very accurate airspeed/altitude/vertical speed sensor.
- There was an article featuring the Carter heliplane concept in this month's issue of Sea Power. A reprint has been posted on this site: Sea Power article
- Carter is looking to hire an electronics technician/engineer. If you are interested, take a look at the job description.
2004-09-22
- We apologize for this weekly update being late. The webmaster was busy with a very important engineering project, and did not have time to work on the weekly update until today.
- Tested the propeller. Corrected several problems with sensors on the test stand. The 11.8:1 compression ratio for the engine works well, with the engine running about 100ºF cooler than its limit.
- On Thursday, we noticed a crack in one of the blades, which appeared to be a buckling failure. We modified the design of the prop to increase the column stability of the structure in that area, and performed a detailed stress analysis/review of our previous analysis, to ensure that there was nothing that we were missing in our analysis (the project that tied up the webmaster). We have begun work on the new propeller. Since there are not many changes and most of the tooling is already completed, this new prop should be finished within 2 to 3 weeks.
- Carter is looking to hire an electronics technician/engineer. If you are interested, take a look at the job description.
2004-09-13
- Finished the scimitar propeller and mounted it on the test stand.
- Modified the engine on the test stand. Before the prop failure in August, the engine was running at a 12.5:1 compression ratio. It worked so well at the higher compression ratio, that when we rebuilt the engine, we increased it to 13.0:1. Unfortunately, this was a little too high and caused knocking, so we swapped head gaskets to reduce the compression ratio to 11.8.
- UPDATE 2004-09-15 Carter is looking to hire an electronics technician/engineer. If you are interested, take a look at the job description.
2004-09-06
- Bonded both blades of the scimitar propeller.
Scimitar Propeller
(both blades laid up)
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- Began work on a test rig to test a new landing gear design. The new landing gear is being designed for a 4000 lb. aircraft to handle a 30 ft/s impact, or for a 6000 lb. aircraft to handle a 20 ft/s impact. The test rig will be able to simulate up to a 30 ft/s impact with varying loads.
- Continued measuring rotor structural properties for the Army contract.
- Completed a modified fire detection system in the aircraft.
2004-08-30
- Completed the tooling for the modified spar for the scimitar propeller, and completed the actual spar. Completed all internal components for the propeller.
- Fabricated a new drive shaft and prop pitch push-pull shaft to replace those damaged in the prop failure.
- Completed test fixture for Army contract and began measuring rotor structural properties.
- Photos:
New Prop Spar
(with circumferential
winding jig still
attached)
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Test Fixture: Laser
Projection Surface
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Rotor: Note the
mirrors for reflecting
the lasers
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- Since the hub drag has been such a large percentage of the total drag of most helicopters and one reason why many people do not believe the Carter SR/C can achieve efficiencies approaching or exceeding some fixed wing aircraft, Georgia Tech has performed a study/analysis of why the Carter hub design and spinner can have such a low drag. Their hub and pylon drag estimate for the 2 bladed Carter Heliplane-150 (150 ft dia) was 4.83 sq ft. Based on their analysis and the drag coefficients used, this should be a conservative estimate and is still less drag than the 6.54 sq ft of drag Carter has used in all of its Heliplane performance calculations. Their analysis will be posted to this website shortly.
UPDATE 2004-08-31 The analysis has been added to this site: Hub Drag Analysis
2004-08-23
- Laid up the skins and internal shear webs for the new scimitar propeller.
- Continued work on the tooling for the modified spar for the scimitar propeller.
- Began work on a test fixture to measure rotor structural properties as part of our Army contract.
2004-08-16
- Continued work on the modified scimitar prop spar. The plug has been completed, and work is being done on the mold.
- Installed and calibrated strain gauges in the rotor head to measure rotor lift.
- Georgia Tech had previously performed an independent performance analysis of the slowed rotor concept, comparing it to other types of aircraft. The analysis showed that a slowed-rotor aircraft has the potential for the highest efficiency at cruise of any aircraft other than a jet, much better than other VTOL aircraft. Just recently, Georgia Tech prepared a more detailed summary of that analysis. Carter has received a copy of that analysis, and posted it on this website: Georgia Tech Aircraft Comparison
2004-08-09
- The prop failed during testing on Monday. The failure occurred at 5000 rpm on the engine (2222 prop rpm) while we were obtaining performance data. We had misdiagnosed the crack that appeared in testing the previous week, and applied the wrong fix, which actually masked the problem from further detection. There was a local high stress in the bond between the spar and the blade, and when it failed locally, it created a zipper-like effect, failing the whole bond and allowing the blade to pull off of the spar. We have modified the spar to correct this high stress area, and should have the propeller rebuilt within 4 weeks.
- Despite the structural setbacks, the propeller is very promising. Even with the mis-applied structural modifications, the propeller only weighed 40 lbs, very light for a propeller able to efficiently absorb 600 HP. When it is rebuilt with the modified spar and with proper structural modifications, it should only weigh 34 lbs. At full throttle, it produced 1900 lbs of static thrust at 391 HP and 2222 rpm (5000 engine rpm), for a figure of merit of 0.826. At part throttle, it produced 1203 lbs of static thrust at 1778 rpm and 180 HP, for a figure of merit of 0.904. These measured values were within 1% and 8%, respectively, of our predictions, with the actual values being slightly higher than our predictions. This indicates that our projected cruise performance of 91% efficiency at 250 mph and 92% efficiency at 300 mph should be accurate, as well.
- When the propeller failed, it caused some damage to the test stand and engine. Because the drive shaft had been made stronger, the prop support failed instead of the drive shaft, though the drive shaft still bent. The sudden jerk from this broke some of the engine bosses, bolts, and support brackets. We have already built up our spare engine to be ready to put into the test stand once the test stand is repaired. The damaged engine is currently being inspected for any internal damage.
- Carter put a significant effort into computer maintenance this week, which we will mention here as a public service. Adware and spyware had become a significant problem on our computers, even though all of us had been running freely available anti-adware/spyware programs. So, here are a few recommendations based on our efforts:
1. Install good anti-virus software. This should be your #1 priority.
2. Install a good anti-spyware/adware program. One of our co-webmasters compared several freeware and commercial programs, and found that Pest Patrol was by far the most effective- it would find programs that others didn't, but never the other way around.
3. Periodically ensure that your computer is staying up to date with critical Windows updates by actually visiting Microsoft's Windows Update Page. On all of our computers, the malware programs had deactivated the automatic Windows Update feature.
4. Do not run P2P programs (KaZaA, Grokster, iMesh, etc.) unless you are looking for trouble. The computers in our office that were worst off had been used to run P2P programs, even though freeware anti-adware/spyware programs had been run on those computers almost daily.
2004-08-02
- Continued testing the new scimitar propeller. We still have not tried to optimize pitch vs. rpm to give the most possible thrust, but the thrust we have been getting so far is still very good, the highest being 1903 lbs @ 393 HP and 2222 RPM (5000 rpm engine).
- On Thursday, after 2 minutes of run time at 5300 rpm engine, we discovered a small compression crack in both blades near where the spar attaches to the blade. Because the propeller was designed to absorb 600 HP, to achieve our desired tip speed of Mach 1 for proof testing with only a 400 HP engine, we had to greatly reduce the pitch of the propeller. Because of the twist in the propeller, this caused the outboard sections to be at nearly flat pitch, while the inboard sections were still at a positive pitch. With the inboard sections producing most of the thrust, there was a significant bending moment that the propeller was not designed for. We have added more carbon to reinforce the propeller in the area where the cracks occurred.
- Added an oil cooler to the propeller test stand, to help reduce oil temperatures at high power.
- Completed and installed the new prop spinner bracket.
2004-07-26
- Even though most of the crew will be staying in Wichita Falls to work on the aircraft, Carter will have the Monarch, a single place autogyro with the Carter extreme energy absorbing landing gear, at this year's EAA Airventure in Oshkosh, WI. It should fly some every day. Look for us at Aero Shell square. Also, company president, Jay Carter, will be giving a presentation titled, "Carter Aviation Technologies - Progress, Updates and Future Plans" on Sunday, August 1st at 10 US TOOLS Pavilion. More info: Airventure Website
- Worked out several bugs in the data telemetry system on the propeller test stand.
- Relocated the oxygen sensors on the test stand engine. They had been too close to the exhuast outlet, which at low power settings allowed fresh air to reach the oxygen sensors and give a false lean reading, which in turn caused the engine to run much too rich.
- Reinforced the propeller pitch arm with additional carbon in the area where we believe the failure occurred on the previous prop.
- Ran the propeller on the test stand. There was a slight imbalance which had to be corrected. We will continue testing the propeller this week.
- Began work on the new prop spinner bracket. Modified the spinner to interface with the new bracket.
2004-07-19
- Ran the spinner for the scimitar prop on the test stand. It appeared that there was a natural frequency at 1100 rpm, which caused a slight resonance at that rpm and at its second harmonic of 2200 rpm. We are redesigning the spinner bracket to increase its stiffness so that the natural frequency will be at a higher rpm than that at which we operate the propeller.
- Completed and balanced the new scimitar propeller.
Scimitar Prop on
Balancing Fixture
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- Completed all modifications to the electronics and data collection system of the propeller test stand.
- Modified the prop pitch control cylinder on the test stand by adding a spacer to the cylinder, so that the cylinder will now bottom out before the prop pitch bracket comes into contact with the prop spar.
- Began work to replace the tail camera on the aircraft. The new camera will have a higher shutter speed, which will reduce motion blur in the video. A small video screen will be mounted in the cockpit, so that the pilots will be able to monitor the camera in flight. We also plan to broadcast the video to our test flight control, so that control will also be able to monitor the camera in flight.
2004-07-12
- Completed the main spar of the new scimitar propeller, including laying up the root block and wrapping the circumferential windings.
- Bonded one blade of the scimitar propeller.
- Completed repairs and reassembly of the propeller test stand.
2004-07-05
- Began construction of the new scimitar propeller. We went back to our original resin system without the high temperature additive. We laid up a new main spar, leading & trailing edge spars, skins, shear webs and ribs.
- Made up a spin balance fixture and balanced the new scimitar propeller spinner.
- Welded up the drive shaft for the propeller test stand.
- Relocated numerous electronics in the aircraft to accommodate the new, larger gas tank.
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