turboprop VMO
.
Está servira para distraerle.
Without meaning to be supercilious but what about wind tunnel tests as, presumably, for jets?
Vmo = Maximum indicated airspeed (redline). Above this speed various pieces of airframe may part company or the airframe may be over-stressed. This is also not reflected in many aircraft models.
http://webpages.charter.net/anw/ANW/performance.html
Any further thoughts?
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There was a discussion a few weeks or months ago about the unusual shape of some turboprop Vmo limits. That touched off discussion of some of the possible limiting criteria. One was propellor tip speed approaching local Mcrit.
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Engine limits
I know the Metro VMO (Barber Pole) is 246 KTS at sea level. It is there as an engine limitation. Vd or Maximum dive speed is an airframe limit which is just over 300 KTS.
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kenello I believe that the Jetstream 3x had a UK limit and an international limit due to some difference in the weight of a test bird. As you say the windows where tested with one weight of bird which was accepted by everyone bar the CAA and to keep them happy when the difference was discovered they dropped the Vmo by 10 knts to get a CAA signoff.
The swedish/danish Jetstreams which are operating in the UK have different barber pole settings to the UK reg ones.
The swedish/danish Jetstreams which are operating in the UK have different barber pole settings to the UK reg ones.
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>>The swedish/danish Jetstreams which are operating in the UK have different barber pole settings to the UK reg ones.<<
Likewise with British registered Lockheed TriStars, altho in this case it is Mmo.
UKCAA, M.88
USFAA, M.90
A very slight difference in Vmo as well.
Likewise with British registered Lockheed TriStars, altho in this case it is Mmo.
UKCAA, M.88
USFAA, M.90
A very slight difference in Vmo as well.
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Originally Posted by Mad (Flt) Scientist
There was a discussion a few weeks or months ago about the unusual shape of some turboprop Vmo limits. That touched off discussion of some of the possible limiting criteria. One was propellor tip speed approaching local Mcrit.
Actually it was two months ago. Doesn't time fly ...
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hoss, FAR 25 has the following
Maximum operating limit speed.
The maximum operating limit speed (VMO/MMO airspeed or Mach Number, whichever is critical at a particular altitude) is a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent), unless a higher speed is authorized for flight test or pilot training operations. VMO/MMO must be established so that it is not greater than the design cruising speed VC and so that it is sufficiently below VD/MD or VDF/MDF, to make it highly improbable that the latter speeds will be inadvertently exceeded in operations. The speed margin between VMO/MMO and VD/MD or VDFM/DF may not be less than that determined under §25.335(b) or found necessary during the flight tests conducted under §25.253.
25.253 High-speed characteristics.
(a) Speed increase and recovery characteristics. The following speed increase and recovery characteristics must be met:
(1) Operating conditions and characteristics likely to cause inadvertent speed increases (including upsets in pitch and roll) must be simulated with the airplane trimmed at any likely cruise speed up to VMO/MMO. These conditions and characteristics include gust upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger movement, leveling off from climb, and descent from Mach to airspeed limit altitudes.
(2) Allowing for pilot reaction time after effective inherent or artificial speed warning occurs, it must be shown that the airplane can be recovered to a normal attitude and its speed reduced to VMO/MMO, without–
(i) Exceptional piloting strength or skill;
(ii) Exceeding VD/MD, VDF/MDF, or the structural limitations; and
(iii) Buffeting that would impair the pilot's ability to read the instruments or control the airplane for recovery.
(3) With the airplane trimmed at any speed up to VMO/MMO, there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC, but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached.
(b) Maximum speed for stability characteristics, VFC/MFC. VFC/MFC is the maximum speed at which the requirements of §§25.143(f), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must be met with flaps and landing gear retracted. It may not be less than a speed midway between VMO/MMO and VDF/MDF, except that for altitudes where Mach number is the limiting factor, MFC need not exceed the Mach number at which effective speed warning occurs.
25.335 Design airspeeds.
The selected design airspeeds are equivalent airspeeds (EAS). Estimated values of VS0 and VS1 must be conservative.
(a) Design cruising speed, VC. For VC, the following apply:
(1) The minimum value of VC must be sufficiently greater than VB to provide for inadvertent speed increases likely to occur as a result of severe atmospheric turbulence.
(2) Except as provided in §25.335(d)(2), VC may not be less than VB + 1.32 UREF (with UREF as specified in §25.341(a)(5)(i)). However VC need not exceed the maximum speed in level flight at maximum continuous power for the corresponding altitude.
(3) At altitudes where VD is limited by Mach number, VC may be limited to a selected Mach number.
(b) Design dive speed, VD. VD must be selected so that VC/MC is not greater than 0.8 VD/MD, or so that the minimum speed margin between VC/MC and VD/MD is the greater of the following values:
(1) From an initial condition of stabilized flight at VC/MC, the airplane is upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up at a load factor of 1.5g (0.5g acceleration increment). The speed increase occurring in this maneuver may be calculated if reliable or conservative aerodynamic data is used. Power as specified in §25.175(b)(1)(iv) is assumed until the pullup is initiated, at which time power reduction and the use of pilot controlled drag devices may be assumed;
(2) The minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts, and penetration of jet streams and cold fronts) and for instrument errors and airframe production variations. These factors may be considered on a probability basis. The margin at altitude where MC is limited by compressibility effects must not less than 0.07M unless a lower margin is determined using a rational analysis that includes the effects of any automatic systems. In any case, the margin may not be reduced to less than 0.05M.
All of FAR 25 can be found at http://ecfr.gpoaccess.gov/cgi/t/text...25_main_02.tpl
23.1545 Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds.
(b) The following markings must be made:
(1) For the never-exceed speed VNE, a radial red line.
(2) For the caution range, a yellow arc extending from the red line specified in paragraph (b)(1) of this section to the upper limit of the green arc specified in paragraph (b)(3) of this section.
(3) For the normal operating range, a green arc with the lower limit at VS1 with maximum weight and with landing gear and wing flaps retracted, and the upper limit at the maximum structural cruising speed VNO established under §23.1505(b).
(4) For the flap operating range, a white arc with the lower limit at VS0 at the maximum weight, and the upper limit at the flaps-extended speed VFE established under §23.1511.
(5) For reciprocating multiengine-powered airplanes of 6,000 pounds or less maximum weight, for the speed at which compliance has been shown with §23.69(b) relating to rate of climb at maximum weight and at sea level, a blue radial line.
(6) For reciprocating multiengine-powered airplanes of 6,000 pounds or less maximum weight, for the maximum value of minimum control speed, VMC, (one-engine-inoperative) determined under §23.149(b), a red radial line.
(c) If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range.
(d) Paragraphs (b)(1) through (b)(3) and paragraph (c) of this section do not apply to aircraft for which a maximum operating speed VMO/MMO is established under §23.1505(c). For those aircraft there must either be a maximum allowable airspeed indication showing the variation of VMO/MMO with altitude or compressibility limitations (as appropriate), or a radial red line marking for VMO/MMO must be made at lowest value of VMO/MMO established for any altitude up to the maximum operating altitude for the airplane.
The implication of FAR 23 is that a piston aircraft converted to turbine power without any other mods will have a reduced red line. That is the turbines Vmo will be less than the pistons Vne. Bonanza would be a candidate for this oddity.
Maximum operating limit speed.
The maximum operating limit speed (VMO/MMO airspeed or Mach Number, whichever is critical at a particular altitude) is a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent), unless a higher speed is authorized for flight test or pilot training operations. VMO/MMO must be established so that it is not greater than the design cruising speed VC and so that it is sufficiently below VD/MD or VDF/MDF, to make it highly improbable that the latter speeds will be inadvertently exceeded in operations. The speed margin between VMO/MMO and VD/MD or VDFM/DF may not be less than that determined under §25.335(b) or found necessary during the flight tests conducted under §25.253.
25.253 High-speed characteristics.
(a) Speed increase and recovery characteristics. The following speed increase and recovery characteristics must be met:
(1) Operating conditions and characteristics likely to cause inadvertent speed increases (including upsets in pitch and roll) must be simulated with the airplane trimmed at any likely cruise speed up to VMO/MMO. These conditions and characteristics include gust upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger movement, leveling off from climb, and descent from Mach to airspeed limit altitudes.
(2) Allowing for pilot reaction time after effective inherent or artificial speed warning occurs, it must be shown that the airplane can be recovered to a normal attitude and its speed reduced to VMO/MMO, without–
(i) Exceptional piloting strength or skill;
(ii) Exceeding VD/MD, VDF/MDF, or the structural limitations; and
(iii) Buffeting that would impair the pilot's ability to read the instruments or control the airplane for recovery.
(3) With the airplane trimmed at any speed up to VMO/MMO, there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC, but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached.
(b) Maximum speed for stability characteristics, VFC/MFC. VFC/MFC is the maximum speed at which the requirements of §§25.143(f), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must be met with flaps and landing gear retracted. It may not be less than a speed midway between VMO/MMO and VDF/MDF, except that for altitudes where Mach number is the limiting factor, MFC need not exceed the Mach number at which effective speed warning occurs.
25.335 Design airspeeds.
The selected design airspeeds are equivalent airspeeds (EAS). Estimated values of VS0 and VS1 must be conservative.
(a) Design cruising speed, VC. For VC, the following apply:
(1) The minimum value of VC must be sufficiently greater than VB to provide for inadvertent speed increases likely to occur as a result of severe atmospheric turbulence.
(2) Except as provided in §25.335(d)(2), VC may not be less than VB + 1.32 UREF (with UREF as specified in §25.341(a)(5)(i)). However VC need not exceed the maximum speed in level flight at maximum continuous power for the corresponding altitude.
(3) At altitudes where VD is limited by Mach number, VC may be limited to a selected Mach number.
(b) Design dive speed, VD. VD must be selected so that VC/MC is not greater than 0.8 VD/MD, or so that the minimum speed margin between VC/MC and VD/MD is the greater of the following values:
(1) From an initial condition of stabilized flight at VC/MC, the airplane is upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up at a load factor of 1.5g (0.5g acceleration increment). The speed increase occurring in this maneuver may be calculated if reliable or conservative aerodynamic data is used. Power as specified in §25.175(b)(1)(iv) is assumed until the pullup is initiated, at which time power reduction and the use of pilot controlled drag devices may be assumed;
(2) The minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts, and penetration of jet streams and cold fronts) and for instrument errors and airframe production variations. These factors may be considered on a probability basis. The margin at altitude where MC is limited by compressibility effects must not less than 0.07M unless a lower margin is determined using a rational analysis that includes the effects of any automatic systems. In any case, the margin may not be reduced to less than 0.05M.
All of FAR 25 can be found at http://ecfr.gpoaccess.gov/cgi/t/text...25_main_02.tpl
23.1545 Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds.
(b) The following markings must be made:
(1) For the never-exceed speed VNE, a radial red line.
(2) For the caution range, a yellow arc extending from the red line specified in paragraph (b)(1) of this section to the upper limit of the green arc specified in paragraph (b)(3) of this section.
(3) For the normal operating range, a green arc with the lower limit at VS1 with maximum weight and with landing gear and wing flaps retracted, and the upper limit at the maximum structural cruising speed VNO established under §23.1505(b).
(4) For the flap operating range, a white arc with the lower limit at VS0 at the maximum weight, and the upper limit at the flaps-extended speed VFE established under §23.1511.
(5) For reciprocating multiengine-powered airplanes of 6,000 pounds or less maximum weight, for the speed at which compliance has been shown with §23.69(b) relating to rate of climb at maximum weight and at sea level, a blue radial line.
(6) For reciprocating multiengine-powered airplanes of 6,000 pounds or less maximum weight, for the maximum value of minimum control speed, VMC, (one-engine-inoperative) determined under §23.149(b), a red radial line.
(c) If VNE or VNO vary with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range.
(d) Paragraphs (b)(1) through (b)(3) and paragraph (c) of this section do not apply to aircraft for which a maximum operating speed VMO/MMO is established under §23.1505(c). For those aircraft there must either be a maximum allowable airspeed indication showing the variation of VMO/MMO with altitude or compressibility limitations (as appropriate), or a radial red line marking for VMO/MMO must be made at lowest value of VMO/MMO established for any altitude up to the maximum operating altitude for the airplane.
The implication of FAR 23 is that a piston aircraft converted to turbine power without any other mods will have a reduced red line. That is the turbines Vmo will be less than the pistons Vne. Bonanza would be a candidate for this oddity.
Last edited by Brian Abraham; 2nd Jun 2006 at 09:16.
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Brian is quite correct about those types converted to turbine power, from piston, in the case mentioned, the Beech Bonanza.
Here, Vmo, is placed at the top of the green airspeed arc...IE, there is no yellow speed band on the airspeed indicator.
Thus incicated in the respective STC-modified AFM
Here, Vmo, is placed at the top of the green airspeed arc...IE, there is no yellow speed band on the airspeed indicator.
Thus incicated in the respective STC-modified AFM
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Brian's quite right in the description of how it's derived, but the regs don't give the underlying rationale. I've promised my doctor that I wouldn't get sucked into the discussion on defining limitations but, like fine wine, I just can't resist it, so...sorry.
Designer chappies are tasked with meeting a design specification, that usually includes specific requirements like max speed, g/structural limits, etc. In the interests of self-preservation - particularly in today's litigious society - and under the usual commercial pressures that want to give as little away as possible, he will design to those limits and no more. When built, the prototype will be tested to those limits and no more - done the job, now pay the bill. Depending on the company, the project itself, the certifying regulator and/or the customer, it may or may not be tested further to demonstrate an acceptable margin above that limit that caters for in-service variations and different pilots' ability to respect the limitations. Whatever, the company and/or regulator doesn't want anyone in service going above that limit - proven with a margin or not - so the resulting limitations for service use come out with a plethora of additional limits designed to satisfy the commercial requirement for demonstrating spec compliance while keeping the day-to-day service user away from them. (In civilian aeroplanes this is not usually that much of an intrusion, but it sure as hell is in military aircraft where the difference betwen "Normal Operating" and "Never Exceed" limits often represents a significant reduction in operational capability.) In civilian terms, this difference is represented by Vmo and Vne.
Call me old-fashioned, but I was taught - and have applied as rigorously as I could during my career - that flight testing was there to demonstrate that the full specified flight envelope could be achieved by the average operating pilot within an acceptable margin. So, for example, if the max specified speed was X00 kts then I would expect to demonstrate it to X00 x Ykts, where Y is a factor that is dependant on the pilot's ability to observe and respect the limits. (This factor varies with aircraft characteristics and the limit in question - for example, if the aircraft has no natural stall warning then it is necessary to allow a large margin on any defined pilot-monitored angle of attack limit, because the aircraft provides little cue to help him.) In my experience, this philosophy is not followed by the engineering and commercial specialists - I've tested aeroplanes to their max speed limit and demonstrated that the wings don't fall off, but I've been prevented from testing them further: instead, the in-service limit has been reduced by 10% or so to provide a crude additional margin.
The result: in-service aircraft that are not cleared to their full potential, which (in the military case) crews then take to war and find out empirically what they actually can do - what an amateurish way to work!
OK, I've managed to restrain myself enough to remain polite on the subject, best I now go and lie down in a darkened room and sip camomile tea.
Designer chappies are tasked with meeting a design specification, that usually includes specific requirements like max speed, g/structural limits, etc. In the interests of self-preservation - particularly in today's litigious society - and under the usual commercial pressures that want to give as little away as possible, he will design to those limits and no more. When built, the prototype will be tested to those limits and no more - done the job, now pay the bill. Depending on the company, the project itself, the certifying regulator and/or the customer, it may or may not be tested further to demonstrate an acceptable margin above that limit that caters for in-service variations and different pilots' ability to respect the limitations. Whatever, the company and/or regulator doesn't want anyone in service going above that limit - proven with a margin or not - so the resulting limitations for service use come out with a plethora of additional limits designed to satisfy the commercial requirement for demonstrating spec compliance while keeping the day-to-day service user away from them. (In civilian aeroplanes this is not usually that much of an intrusion, but it sure as hell is in military aircraft where the difference betwen "Normal Operating" and "Never Exceed" limits often represents a significant reduction in operational capability.) In civilian terms, this difference is represented by Vmo and Vne.
Call me old-fashioned, but I was taught - and have applied as rigorously as I could during my career - that flight testing was there to demonstrate that the full specified flight envelope could be achieved by the average operating pilot within an acceptable margin. So, for example, if the max specified speed was X00 kts then I would expect to demonstrate it to X00 x Ykts, where Y is a factor that is dependant on the pilot's ability to observe and respect the limits. (This factor varies with aircraft characteristics and the limit in question - for example, if the aircraft has no natural stall warning then it is necessary to allow a large margin on any defined pilot-monitored angle of attack limit, because the aircraft provides little cue to help him.) In my experience, this philosophy is not followed by the engineering and commercial specialists - I've tested aeroplanes to their max speed limit and demonstrated that the wings don't fall off, but I've been prevented from testing them further: instead, the in-service limit has been reduced by 10% or so to provide a crude additional margin.
The result: in-service aircraft that are not cleared to their full potential, which (in the military case) crews then take to war and find out empirically what they actually can do - what an amateurish way to work!
OK, I've managed to restrain myself enough to remain polite on the subject, best I now go and lie down in a darkened room and sip camomile tea.
