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iChris

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iChris last won the day on April 27 2020

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  1. That’s correct… Most U.S. manufacturers will turn the tail rotor clockwise when viewed from the helicopter's left side, taking advantage of the tip vortices coming off the main rotor. When the tail rotor turns in the same direction as the primary rotor vortices, it reduces the relative airspeed of the tail blades, and the available thrust is limited. When the tail rotor turns against the central rotor vortex, the performance increases because of the square-law connection between thrust and increased relative airspeed. Two notable helicopters turn their tail rotor in the so-called wrong direction. They are the MD500 and Robinson R22. However, they both share another less conventional concept, for their time, NACA 63-415 asymmetrical tail rotor blades. More common were symmetrical tail rotor blades like those on the Bell UH-1, AH-1, 204/205/206, 212, 412, and Hughes 269/TH-55. Frank Robinson left Bell Helicopter in 1959 and joined the Aircraft Division for Hughes Tool Company, assigned to the U.S. Army's OH-6 Light Observation Helicopter and other Hughes 500 projects. Frank had already established himself as an authority on tail rotor design. Frank found the NACA 63-415 asymmetrical tail rotor blades exhibited noteworthy improvement in performance over the symmetrical blades. Frank brought some of those design characteristics and gave birth to Robinson Helicopters (1973) and the R22. Frank reduced gearing in the tail rotor gearbox to save weight at the aft end of the tail boom. Consequently, due to the engine's reversed position (Front end facing aft), the driveshaft from the engine to tail rotor ended up turning the tail rotor in the wrong direction. Furthermore, asymmetrical tail rotor blades came with an inherent consequence, an undesirable twist or pitching moment. Frank countered the effect with a built-in coning angle designed into the tail rotor. The overall compromises ended up cutting weight, and light helicopters like the OH-6 and R22 still provide better than adequate tail rotor performance. MD Helicopters seem satisfied, sticking with the wrong-direction design on their current MD500E/F series. Incidentally, the R44 and R66 tail rotors turn the right way.
  2. Pressure is equal to force over the area in which the force is applied. The calculation that you’re referring to would only give the theoretical capacity or capability of the pump. You’ll need more configuration or design specifications for an exact pressure value. Begin by taking a look at the pump’s data plate. You need the pump’s horsepower and or torque specification along with what you have. Hydraulic Pump Calculations_1 Hydraulic Pump Calculations_2 Example taking the pump below: Horsepower = ( Q_Flow rate_GPM x P_Pressure_PSI) ) / (1714 x Eff ) hp = (Q x P)/(1714 x Eff) or P = (hp x 1714 x Eff) / Q or P = (torque_inch_pounds x rpm) / ( Q x 36.77) (less 10 -20% for efficiency) The Horsepower required to produce 2 GPM @ 1000PSI at 80% efficiency estimates as: hp = (2 x 1000) / (1714 x .80) = 1.46hp
  3. Numerous factors define the final tail-rotor design, like rotor diameter, tip-speed, blade area, number of blades, blade twist, fin surface area, the direction of rotation, Pusher or Tractor, etc. The least unfavorable compromise is the designer's primary task. Most conventional tail-rotors are Pushers mounted on the left side. Induced velocity below the tail-rotor is higher than above it; therefore, it reduces net thrust if the tail-rotor is blowing toward the fin. The exceptions to the Pusher are the Sikorsky UH-60 and Bell, 212, 214, 412. Also, the Bell UH-1, 204, and 205 were initially Pushers, and some were recently converted to Tractors. In 1954 Bell designed the XH-40, the prototype of the UH-1, AH-1, and subsequent first production Bell 204 and Bell 205 were all Pushers. Sikorsky designers chose to tilt the UH-60 tail-rotor shaft so that part of its thrust could help counter CG issues by lifting the helicopter's rear end. The Tractor configuration was chosen to provide clearance with the fin without using a longer driveshaft. Bell chose the wrong direction of rotation when in 1954, it designed the XH-40, the prototype of the UH-1 series. Bell's solution 15 years later was to flip the tail-rotor installation from the left side of the fin to the right, using the same hardware. To Bell's good fortune, the tail-rotor blades had no twist, allowing for the change.
  4. Bell’s technical description of their 429’s tail rotor follows: “Four blades stacked system, 65” diameter, with low tip speed, scissor arrangement, composite T/R blades with swept blade tips.” High blade tip speeds account for significant noise. Noise control can be accomplished by reducing rotor blade tip speed and increasing the number of rotor blades—studies done by members of Airbus, Sikorsky, and US Army referenced below. The simplest way to permit flapping is to use a teetering hinge on two-bladed tail rotors. There are simply two teetering rotors spaced a short distance apart on those four-blade tail rotors. Bell stayed with what works. Their time-tested teetering two-blade tail rotor with delta-three. Two teetering rotors making up the Hughes/MD 500 four-blade quiet rotor and the AH-64 Apache tail rotor are not at right angles primarily because the scissors configuration simplifies the control linkage arrangement, and there is also some evidence the design is quieter. Note the similarities of three manufactures Hughes/McDonald Douglas, Bell, and Sikorsky. Similarities between the old and the new tail rotor hubs, H269A/AH-64, Bell206/Bell429, and S58/UH60 below: https://apps.dtic.mil/dtic/tr/fulltext/u2/775391.pdf pg. 115 https://www.icao.int/environmental-protection/Documents/EnvironmentalReports/2016/ENVReport2016_pg42-45.pdf
  5. You asked, "anyone heard of a tail rotor consuming > 15% power?" absolutely. Flight envelopes account for more than that. The numbers are a result of a specific design. There are no metrics other than that from a specific design. Roughly, the tail rotor consumes up to about 10% of the total power for the helicopter. However, allowances of up to 20% may be made for design purposes to ensure sufficient maneuvering and transient capabilities. We can also look at it as a percentage of the total main rotor power. The power required by the tail rotor typically varies between 3% and 5% of the main rotor power in routine flight and up to 20% of the main rotor power at the extremes of the flight envelope. In addition to the yaw function, the flight envelope's extremes require adequate tail power for sideways flight. It is not apparent why anyone would want to fly sideways, but there are plenty of examples. Film cameras are often mounted in the main cabin and only have a clear view of the side. Flying the machine sideways allows the camera to shoot forwards. Flying sideways allows an attack helicopter pilot to dodge fire while keeping his rockets aimed at the target. Pilots regularly fly sideways as a matter of course, because this is what happens when hovering in a side wind. You're flying sideways at the same speed as the wind but in the opposite direction. In the case of a clockwise-from-the-top helicopter, the wind coming from the right side is undesirable as it increases the tail rotor inflow, and so requires more power. The worst-case will then be where the pilot wishes to make a maximum speed yaw-left in a strong wind from the right side. The tail rotor now has to overcome main rotor torque, boom drag due to the side wind. The FAA/military test tail rotor performance under those conditions. The primary criteria to generate enough thrust to balance main-rotor torque in full-power climb with a right-cross-wind with at least a 10% margin left over for directional control.
  6. The text you quoted states that "cruise-charts are not drag-charts, it can be noted the lowest point of a drag chart does not necessarily match the lowest point of the power required curve in a cruise chart." As in Eric Hunt's post above, D = P/V. Were P = rotor power (induced, profile) + the rest of the helicopter (parasitic, tail rotor). Eric already answered your question as to why. It's in the math, rearranging the equation D x V = P. It's a helicopter, not just D = P. You have to account for the V and the other power requirements. We're dealing with the total power required supporting more than just the drag of the helicopter. The issue is forward flight (cruising flight) performance. Another power drain is that the turbine engine is more efficient at high power than at low power because of the fuel-flow needed to keep the gas generator spinning, regardless of the power output. Fuel-flow is the center of interest. Remember, fuel-flow is proportional to power; that's why fuel-flow versus airspeed curves mimic the power-required curves. Power is proportional to Fuel-flow. To maximize endurance, we want to maximize the amount of time that we can stay in the air. Since the fuel flow is proportional to the power-required, fuel flows lowest when the power-required is a minimum. The speed corresponding to the bottom of the power-required curve is the speed for maximum endurance. To maximize the range, we want to get the maximum distance for each pound of fuel burned. Therefore, the maximum range airspeed occurs where a line from the origin is tangent to the power required curve or fuel-flow versus airspeed curve below.
  7. Refer to the specific series noncommercial/military flight manual. Maybe informational status only indication. Example Army OH-6A manual section below, even though calibration is also 35 pounds:
  8. In FAA’s eyes a "small rotorcraft:" 14 CFR Part 1.1 defines a small aircraft as an aircraft of 12,500 lbs. or less maximum certificated take-off weight. Therefore, any rotorcraft, could be considered small by the Part 1.1 definition (aircraft) if the rotorcraft/helicopter is less than 12,500 lbs. Part 1.1 Aircraft means a device that is used or intended to be used for flight in the air. Part 1.1 Small aircraft means aircraft of 12,500 pounds or less, maximum certificated takeoff weight. § 29.811 (f) Each emergency exit, and its means of opening, must be marked on the outside of the rotorcraft. In addition, the following apply: (1) There must be a 2-inch colored band outlining each passenger emergency exit, except small rotorcraft with a maximum weight of 12,500 pounds or less may have a 2-inch colored band outlining each exit release lever or device of passenger emergency exits which are normally used doors.
  9. Your speakers are not polarity sensitive so bands 2 & 4 (speaker wires) on the u174 may be reversed wired without a problem. The same for the mic bands 1 & 3 (mic). In most cases the mic is not polarity sensitive. However, with an older mic or special purpose designs, you may have to swap the mic wires around. Once you identify your mic wires, any reverse polarity won’t hurt the mic, it just won’t work, just swap it. Your PTT switch above is yellow/black wiring between your radio and the u94. It could be one or two wires. The one wire setup eliminates the extra wire run by using the shield ground at the u94, see photo below. What you have is a momentarily "on" switch that grounds the radio's PTT circuit to key the mic. If you’re going to eliminate the switch, you don’t need the yellow wire. If not, the yellow wire should go to one of the two terminals on the switch and the other switch terminal should have a connection to the black (GND) wire. On one of the four terminals on the u94 receptacle, you may find a black and white wire soldered to the same terminal. There’re using the black (GND) wire as the speaker return wire Isolate-Detect- Correct, the old troubleshooting adage.
  10. From your post, I assume you’re trying to replace the u-94 jack with a u-174 plug or trying to make an adapter cable with a u-174 at each end so as not, destroy the u-94 jack. With the documentation at the link below, you should be able the back-track the wiring. Open up the u-94 jack and plug in the u-174 plug. From there, you can back-track the known wiring form the u-174 back to the correct connections on the u-94 side. You can also see how the David Clark H10-76 u-174-plug wiring matches up with the u-94. It’s not as hard as it may seem, the system effectively (on the headset end) only uses four (4) wires, two (2) wires to the mic, two (2) wires for the speaker or earpiece. The only reason you have six (6), is they parallel-off two additional wires from the base pair of speaker wires to a second speaker or earpiece. There may be a seventh wire, often used as a shield ground. Upstream of the u-94, you normally have six (6) wires. Again, two wires for the speaker/earpieces and two for the mic. The remaining two wires for the Press-To-Talk (PTT). PTT wires are often blue/yellow, mic- red/white, speaker-white/black or white/green. The normally always wires are, red-mic and white or black speaker. Color codes may differ between manufacturers, so don't expect a color-color solution. However, plug and terminal designations are constant. See link: Wiring Document U94/U174 Your u-94 is probably pretty close to one of these below: u-94 color/function Red- Microphone High White- Microphone Low Green- Speaker High Black- Speaker Low Yellow - PTT High Blue- PTT Low
  11. It appears your memory hasn't failed you. At least that was the way it was before Airbus. Maybe the qualified flight instructor requirement part came in later manuals.
  12. The ability of the compressor to pump air is a function of RPM. At low RPMs, the compressor does not have the same ability to pump air as it does at higher RPMs. To keep the blade angle of attack and air velocity within desired limits and prevent compressor stall, it is necessary to "unload" the compressor in some manner. In other words, the compressor needs to see less restriction to the flow of air through the use of a compressor bleed air system. CLICK PHOTO TO ENLARGE
  13. You don’t need to rebuild the R22/R44 helicopter or overhaul its engine. However, regardless of the certificate, the aircraft has to be airworthy. It is well-established that an aircraft is deemed 'airworthy' only when it conforms to its type certificate (if and as that certificate has been modified by supplemental type certificates and by Airworthiness Directives), and is in condition for safe operation. Experimental won’t get you pass that. It's a documented practice in line with FAR 43.15c and Appendix D to Part 43. If the aircraft is not used for compensation or hire it could be operated part 91 under the annual inspection only requirements of 91.409a. In that case (with respect to the engine) there would be no required engine overhaul. You could continue on each year as long as the engine passes the annual inspection requirements in Appendix D to Part 43. That’s your on-condition operation. Also, as long as the owner complies with chapter 3 page 3.9 or page 3.10 in the R22 maintenance manual, the aircraft and engine can be maintained under FAR 91.409a, 43.15c, and Appendix D to Part 43 in an airworthy condition. To fully understand you may need to read the posts below and the supporting documentation. R22 Airworthiness past 2200hrs/12yrs R44 12-Year Inspection Required for Part 91? Legal Interpretation MacMillan Apr 22, 2011 FAA Order 8620.2B - Applicability and Enforcement of Manufacturer’s Data
  14. NTSB Updates on Kobe Bryant Accident A ground camera captured an image of the helicopter entering the clouds. Radar/ADS-B data indicate the aircraft was climbing southwesterly along a course aligned with Highway 101 just east of the Las Virgenes exit, between Las Virgenes and Lost Hills Road. The helicopter reached an altitude of 2,300 feet msl, approximately 1,500 feet above the highway, but below the surrounding terrain when it began a left turn. Eight seconds later, the aircraft began descending as the left turn continued. The descent rate increased to over 4,000 feet per minute while the ground speed reached 160 knots. The last ADS-B target was received at 1,200 feet msl approximately 400 feet southwest of the accident site. A still photo obtained from a security camera located in a road maintenance yard adjacent to Mureau Road and Highway 101 showed the helicopter proceeding westward along the highway and disappearing into the clouds. Mureau runs just to the north of Highway 101. The Board as yet does not know why the pilot entered the clouds. NWS photo looking east from a hill near the crash indicates the tops of the clouds near the site were about 2,400 msl. Full text: NTSB Updates on Kobe Bryant Accident By Rob Mark
  15. The quote was Aviation accidents.... Job-related mortality of wildlife workers in the United States, 1937-2000 “Abstract Wildlife biologists face a variety of job-related hazards that are unique to this profession, most of them involving the remote areas where work is performed and the unusual techniques used to study or manage wildlife. Information on biologists and others killed while conducting wildlife research or management was obtained from state and federal natural resources agencies, solicitations on wildlife-based internet discussion groups, and published obituaries. Ninety-one (91) job-related deaths were documented from 1937 to 2000. Aviation accidents, drowning, car and truck accidents, and murder were the most common causes of death. Thirty-nine (39) aviation accidents accounted for 66% of deaths, with aerodynamic stalls and power-line collisions being the most significant causes of accidents for which information was available. These safety threats should be taken into consideration during the design and planning of future research and management projects.” REF: https://www.jstor.org/stable/3784446?seq=1 Some communities have enacted zoning laws, building codes, fire regulations, etc. that can affect establishment of helicopter landings in residential neighborhoods. They’ve developed codes or ordinances regulating environmental issues such as noise and air pollution. A few localities have enacted specific rules governing the establishment of a heliport. Therefore, contact officials or agencies representing the local zoning board, the fire, police, or sheriff's department, City Council, and the Mayor’s office. Get with your neighbors, kill it at the local level, and the FAA will not approve it in opposition to local laws. Also: http://stophelipad.org/home.shtml
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