How fast would you like to cruise?
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How fast would you like to cruise?
Helifolks,
I've started this thread since i feel it is time Rotorheads began the debate about how fast future helos should be expected to fly. This is not official market research, but i would like to understand how much of a constraint cruise speed really is. What i would like to understand is:
1. What is the machine operation?
2. What cruise speed is normally used?
3. If there was no constraint how fast would the machine be cruised?
At the moment i am assuming there is no payload or range penalty paid for the increased performance. This is because total drag tends to stay the same at higher speeds (for fixed wing, ignoring compressibility), so that a more powerful engine has a higher fuel burn but for less time.
Thanks in advance...
I've started this thread since i feel it is time Rotorheads began the debate about how fast future helos should be expected to fly. This is not official market research, but i would like to understand how much of a constraint cruise speed really is. What i would like to understand is:
1. What is the machine operation?
2. What cruise speed is normally used?
3. If there was no constraint how fast would the machine be cruised?
At the moment i am assuming there is no payload or range penalty paid for the increased performance. This is because total drag tends to stay the same at higher speeds (for fixed wing, ignoring compressibility), so that a more powerful engine has a higher fuel burn but for less time.
Thanks in advance...
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In UK the rules say 250 kts max and with the introduction of mode S transponders, it is now being enforced!
My type cruises at 155-160 kts. That's a good speed but strong winds can still add a chunk of time to a long leg.
200 kts would be nice (but helicopter pilots like easy maths in nm/min so 210 would be better).
My type cruises at 155-160 kts. That's a good speed but strong winds can still add a chunk of time to a long leg.
200 kts would be nice (but helicopter pilots like easy maths in nm/min so 210 would be better).
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ShyTorque, 240ktas would give you a nice round 4 NM/min. 
Interesting answer, which i assume applies to any UK based service - be it EMS or transport. Does this mode S transponders limit apply only in UK, and if so is that only over land? Some of the North Sea drivers must wish machine cruise speeds higher?
Am i right in assuming that the real limitation is more the machine range? So cruise speed increase only really benefits a machine capable of long range/endurance?
Interesting answer, which i assume applies to any UK based service - be it EMS or transport. Does this mode S transponders limit apply only in UK, and if so is that only over land? Some of the North Sea drivers must wish machine cruise speeds higher?
Am i right in assuming that the real limitation is more the machine range? So cruise speed increase only really benefits a machine capable of long range/endurance?
Last edited by Graviman; 28th Mar 2008 at 16:59.
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250 kts is the Air Navigation Order (legal) limit for all UK uncontrolled airspace below 10,000 feet, except for military traffic.
I was trying to be realistic with the desired airspeed.
I was trying to be realistic with the desired airspeed.
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It has been my experience in helicopters that anything much more then 70% in straight and level flight is just wasting fuel. Not much bang the buck. Climbing is another matter. The 61 will cruise about 120KIAS with Carson Blades.
Last edited by before landing check list; 28th Mar 2008 at 10:30.
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As long as we are joshing this around, seems like we are interchanging indicated and true. 250 KIAS at 10,000 feet at standard temperature is about 291 KTAS. George
Speed limitations
21.—(1) Subject to paragraph (2), an aircraft shall not fly below flight level 100 at a speed
which, according to its air speed indicator, is more than 250 knots.
(2) Paragraph (1) shall not apply to—
(a) flights in Class A airspace;
(b) VFR flights or IFR flights in Class B airspace;
(c) IFR flights in Class C airspace;
(d) VFR flights in Class C airspace or VFR flights or IFR flights in Class D airspace when
authorised by the appropriate air traffic control unit;
(e) an aircraft taking part in an exhibition of flying for which a permission is required by
article 80(1) of the Order, if the flight is made in accordance with the terms of the
permission granted to the organiser of the exhibition of flying and in accordance with the
conditions of the display authorisation granted to the pilot under article 80(6)(a) of the
Order;
30 March 2007
CAP 393 Air Navigation: The Order and the Regulations
Section 2 Page 11
(f) the flight of an aircraft flying in accordance with the A Conditions or the B Conditions; or
(g) an aircraft flying in accordance with a written permission granted by the CAA authorising
the aircraft to exceed the speed limit in paragraph (1).
(3) The CAA may grant a permission for the purpose of paragraph (2)(g) subject to such
conditions as it thinks fit and either generally or in respect of any aircraft or class of aircraft.
21.—(1) Subject to paragraph (2), an aircraft shall not fly below flight level 100 at a speed
which, according to its air speed indicator, is more than 250 knots.
(2) Paragraph (1) shall not apply to—
(a) flights in Class A airspace;
(b) VFR flights or IFR flights in Class B airspace;
(c) IFR flights in Class C airspace;
(d) VFR flights in Class C airspace or VFR flights or IFR flights in Class D airspace when
authorised by the appropriate air traffic control unit;
(e) an aircraft taking part in an exhibition of flying for which a permission is required by
article 80(1) of the Order, if the flight is made in accordance with the terms of the
permission granted to the organiser of the exhibition of flying and in accordance with the
conditions of the display authorisation granted to the pilot under article 80(6)(a) of the
Order;
30 March 2007
CAP 393 Air Navigation: The Order and the Regulations
Section 2 Page 11
(f) the flight of an aircraft flying in accordance with the A Conditions or the B Conditions; or
(g) an aircraft flying in accordance with a written permission granted by the CAA authorising
the aircraft to exceed the speed limit in paragraph (1).
(3) The CAA may grant a permission for the purpose of paragraph (2)(g) subject to such
conditions as it thinks fit and either generally or in respect of any aircraft or class of aircraft.
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Already some interesting comments...
ShyTorque, your input has already been extremely helpful. I took your 210ktas practical requirement quite seriously.
The world will soon be a place where helicopters have the technical capability for cruise at >250kts. Ok this is only one small experimental machine (X2), but if succesful then the technology will potentially be rolled out across all helicopter types. Since the demand will drive the development, i'm trying to assess the demand.
One example of our near future hypothetical helicopter:
GeorgeMandes, 291ktas for 250ktas at 10'000ft is an interesting thought. Using ShyTorques preference for simple navigation, that implies that perhaps 270ktas is a practical design target. I suspect the manufacturer of our hypothetical near future helicopter would chose 240ktas as a good compromise between simple navigation, CAP393, and technical constraints.
[Edit: correction to my initial misunderstanding that % refers to TQ and not Vne - thanks BLCL]
BLCL, how does 70% torque compare to minimum level cruise at Vy torque required for say S61? If our hypothetical helicopter could improve the rotor efficiency losses above current 70% TQ (in the same way that laminar flow aerofoils improved fixed wing speed penetration) would this tempt you to set a higher cruise speed?
Brilliant stuff, is 85% TQ constrained by fuel consumption like BLCL's 70%? If you had the designers ear for a near future replacement for your AS365N or EC135T2 then would you be tempted to ask for a higher cruise speed capability than 125-130kts? What would be your constraint on top speed for offshore usage?
The world will soon be a place where helicopters have the technical capability for cruise at >250kts. Ok this is only one small experimental machine (X2), but if succesful then the technology will potentially be rolled out across all helicopter types. Since the demand will drive the development, i'm trying to assess the demand.
One example of our near future hypothetical helicopter:
GeorgeMandes, 291ktas for 250ktas at 10'000ft is an interesting thought. Using ShyTorques preference for simple navigation, that implies that perhaps 270ktas is a practical design target. I suspect the manufacturer of our hypothetical near future helicopter would chose 240ktas as a good compromise between simple navigation, CAP393, and technical constraints.
[Edit: correction to my initial misunderstanding that % refers to TQ and not Vne - thanks BLCL]
BLCL, how does 70% torque compare to minimum level cruise at Vy torque required for say S61? If our hypothetical helicopter could improve the rotor efficiency losses above current 70% TQ (in the same way that laminar flow aerofoils improved fixed wing speed penetration) would this tempt you to set a higher cruise speed?
Brilliant stuff, is 85% TQ constrained by fuel consumption like BLCL's 70%? If you had the designers ear for a near future replacement for your AS365N or EC135T2 then would you be tempted to ask for a higher cruise speed capability than 125-130kts? What would be your constraint on top speed for offshore usage?
Last edited by Graviman; 29th Mar 2008 at 10:35.
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Sorry, that comment about 210 kts instead of 200 kts was actually made slightly tongue in cheek. Although mental maths is made easier by a convenient nm/minute figure for pre-planning a trip, once in flight these days the FMS or Garmin 530 does most of the caculation work. 
Strange thing is, I've heard these questions asked before, about twenty five years ago and more. Sikorsky and others spent huge amounts of time and money on the ABC / X-wing concepts then it all went out of fashion and they gave up.
Last edited by ShyTorque; 28th Mar 2008 at 22:52.
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Gravidude, 70% does not give you "VNE", I was just saying in the 14 different airframes I have flown, a rule of thumb I have found that much above 70TQ gives you high fuel flow without a whole lot of airspeed increase. Of course if you were climbing I may pull more.
Last edited by before landing check list; 29th Mar 2008 at 13:16.
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Svenestron, naturally for us engineers the objective is to push machine performance as high as we are technically able. The problem usually comes down to the fact that performance increase also increases the cost. This then comes down to market expectation/requirement. My initial intention for this thread is to generate some kind of unofficial metric for this, so that helicopter developers can target theirs plans accordingly.
ShyTorque, several things have happened since the development of S69 ABC.
1. CAE analysis techniques have come on in leaps, allowing greater confidence in a new design while still on the "drawing board".
2. Fly by wire and GPS have become common place, so that the right control technology for the job can be selected.
3. The internet allows manufacturers direct access to pilot and customer feedback.
My intention is to use this forum as a means to provide unofficial feedback on market requirements. This makes the design teams job easier when they are trying to justify a new project to the board. Ultimately it is up to us to drive the market requirement, to make sure ABC sticks this time.
BLCL, right 70% torque. Sorry this is where my inexperience shows me up. I'll go back and ammend that last post.
Gravidude - Hehehe.
ShyTorque, several things have happened since the development of S69 ABC.
1. CAE analysis techniques have come on in leaps, allowing greater confidence in a new design while still on the "drawing board".
2. Fly by wire and GPS have become common place, so that the right control technology for the job can be selected.
3. The internet allows manufacturers direct access to pilot and customer feedback.
My intention is to use this forum as a means to provide unofficial feedback on market requirements. This makes the design teams job easier when they are trying to justify a new project to the board. Ultimately it is up to us to drive the market requirement, to make sure ABC sticks this time.
BLCL, right 70% torque. Sorry this is where my inexperience shows me up. I'll go back and ammend that last post.
Gravidude - Hehehe.
Last edited by Graviman; 29th Mar 2008 at 11:02.
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My intention is to use this forum as a means to provide unofficial feedback on market requirements. This makes the design teams job easier when they are trying to justify a new project to the board. Ultimately it is up to us to drive the market requirement, to make sure ABC sticks this time.
Hurry up though, I retire in the next decade.
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Posted by Graviman;
"several things have happened since the development of S69 ABC."
"several things have happened since the development of S69 ABC."
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I never been able to see the logic in huge helicopters. Once the downdraught gets to a certain size, it becomes a huge problem, more so for civilian aircraft.
They need exponentially more space to operate in and out from. To minimise the downwash problem, when in the vicinity of other aircraft or ground equipment, they need wheels so they can ground taxy. Because of the weight, the wheels need a hard surface. You really need an airport.
Once you need an airport to safely operate the aircraft, it's game over for rotary......
They need exponentially more space to operate in and out from. To minimise the downwash problem, when in the vicinity of other aircraft or ground equipment, they need wheels so they can ground taxy. Because of the weight, the wheels need a hard surface. You really need an airport.
Once you need an airport to safely operate the aircraft, it's game over for rotary......
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Dave, i would say there are three contenders for high speed commercial VTOL:
1. Compound Helicopters (Which the Reverse Velocity Rotorcraft ended up as)
2. Tiltrotors
3. ABC Helicopters.
Any good engineer will tell you that the key to efficient VTOL is low disk loading - which means as large a disk diameter as practical, thus a compact rotor layout. When you take into account the down thrust associated with wings, this only leaves the ABC as the best contender IMHO. The complexity of that coaxial rotor is just the price you have to pay for the increase in performance.
ShyTorque, that's an interesting point about larger helicopters needing all of the infrastructure of an airport anyway. What size from your experience means that fixed wing is the best option? I'm guessing S92 is about as large as a high speed commercial passenger helicopter would get to. For ABC there are rotor system mass advantages with size, since you need 6 or 8 blades in total anyway.
1. Compound Helicopters (Which the Reverse Velocity Rotorcraft ended up as)
2. Tiltrotors
3. ABC Helicopters.
Any good engineer will tell you that the key to efficient VTOL is low disk loading - which means as large a disk diameter as practical, thus a compact rotor layout. When you take into account the down thrust associated with wings, this only leaves the ABC as the best contender IMHO. The complexity of that coaxial rotor is just the price you have to pay for the increase in performance.
ShyTorque, that's an interesting point about larger helicopters needing all of the infrastructure of an airport anyway. What size from your experience means that fixed wing is the best option? I'm guessing S92 is about as large as a high speed commercial passenger helicopter would get to. For ABC there are rotor system mass advantages with size, since you need 6 or 8 blades in total anyway.
Last edited by Graviman; 31st Mar 2008 at 11:39.
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Once the outdoor tables and chairs start tumbling and the owners of the cars in the adjacent car park justifiably start complaining about debris being thrown about in the downwash, you know you have reached a practical size limit. You then need to think about a nearby field rather than a helipad, so the usefulness of the machine becomes more limited, less convenient.
Once you include a car ride of more than fifteen mimutes or so at either end of a short air journey, people are sometimes less willing to go by helicopter and begin to think: "Fields, taxyways, runways, car journeys? May as well go fixed wing".
Certainly, as far as many of the UK's helipads and infrastructure are concerned, the S-92 is about as big as it would be sensible to go.
Once you include a car ride of more than fifteen mimutes or so at either end of a short air journey, people are sometimes less willing to go by helicopter and begin to think: "Fields, taxyways, runways, car journeys? May as well go fixed wing".
Certainly, as far as many of the UK's helipads and infrastructure are concerned, the S-92 is about as big as it would be sensible to go.
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I have it on good authority that above 150kts a certain appendage shrinks, i don't know if this is proportional to the speed as a 'sliding scale' as it were. AND if the wind changes it will stay that way...or would it shrink with altitude.
If it's a 'sliding scale' i may be Vne limited...as it were
If it's a 'sliding scale' i may be Vne limited...as it were
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Graviman;
IMHO, any rotorcraft engineer will tell you that a key to efficient HOVER is low disk loading.
IMHO, any good innovator will tell you that the key to efficient conceptualization is lateral thinking.
For example, Lateral Symmetry
Dave
"Any good engineer will tell you that the key to efficient VTOL is low disk loading"
"i would say there are three contenders for high speed commercial VTOL."
For example, Lateral Symmetry
Dave