How fast would you like to cruise?

[Graviman]

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... :ok:

[ShyTorque]

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).

[Graviman]

ShyTorque, 240ktas would give you a nice round 4 NM/min. :p

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?

[ShyTorque]

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.

[darrenphughes]

MACH 50..........more, I need more!!!:E

[GeorgeMandes]

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

[before landing check list]

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.

[ShyTorque]

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

The rules say IAS. For the hair splitters, its actually FL100, which would in practice be the same as 10,000 feet, but here we are, a direct quote from CAP393:

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.

[Brilliant Stuff]

Offshore I used 85% which gave 125-130kts depending on the aircraft.AS365N

In the current job we pull 9.5FLI and get 128kts. EC135T2

[Graviman]

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:
http://hometown.aol.co.uk/martingarrish/images/s76_x2.gif

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?

[ShyTorque]

:E 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.

[before landing check list]

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.

[Graviman]

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. :ok:

Gravidude - Hehehe. :cool:

[ShyTorque]

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.

I hope it does stick. I always thought the X wing was a plumber's worst nightmare and the ABC concept was potentially more sound as it essentially develops the existing technology a little further. :ok:

Hurry up though, I retire in the next decade. ;)

[Dave_Jackson]

Posted by Graviman;
"several things have happened since the development of S69 ABC."
Would this [350 kt cruise] helicopter be one of them? (http://www.unicopter.com/1281.html) :rolleyes:

[ShyTorque]

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...... :oh:

[Graviman]

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.

[ShyTorque]

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". :rolleyes:

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.

[Old Skool]

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

[Dave_Jackson]

Graviman;
"Any good engineer will tell you that the key to efficient VTOL is low disk loading" IMHO, any rotorcraft engineer will tell you that a key to efficient HOVER is low disk loading.


"i would say there are three contenders for high speed commercial VTOL."IMHO, any good innovator will tell you that the key to efficient conceptualization is lateral thinking (http://en.wikipedia.org/wiki/lateral_thinking).
For example, Lateral Symmetry (http://www.unicopter.com/Lateral_Symmetry.html) http://www.UniCopter.com/RollLaugh_2.gif

Dave

[relyon]

There are many locales where the local geography comes into play. Pittsburgh International Airport (KPIT) serves the Pittsburgh, PA area. The airport hub is 16+ miles west of the city center because there's neither sufficient level land near the city nor adequate approach paths even if there was.

Once the outdoor tables and chairs start tumbling ...
Point made. Many large helicopters already do this. I rode on an Mi-8-MTV in Finland and distinctly remember it blowing and swaying 50+ foot birch trees on takeoff and landing.

Bob

[Graviman]

Some interesting comments about machine size and heliport location, Relyon and ShyTorque. All go to give a good overview of the constraints sorrounding any new helicopter design.

I'm actually slightly suprised by this thread, since i expected lots of pilots to come forwards offering examples where their operations are compromised by a conventional helicopter lack of speed. :confused:

Perhaps i should reword the initial question to:

What operations would benefit from an increase in cruise speed.

Once a typical role has been established then perhaps i can more fairly ask what cruise speed should be achieved. :ok:

[Dave_Jackson]

What operations would benefit from an increase in cruise speed.Military operations.


This ain't VTOL but it is; speed, coaxial and no airports. :)

440 mph in 1934 with floats
http://www.unicopter.com/Temporary/Float_Plane.jpg

[Bitmonx]

I guess some Pilots that are getting paid by the hour just like myself, don't want to go too fast......but after a long day in a very uncomfortable 206, many would wish they had a cruise speed of 250 kts.

[relyon]

At first glance, I thought most if not all operations would benefit from an increase in cruise speed. Thinking about it some more, I see numurous instances where cruise speed matters little, if at all. Then there are those in between.

Offshore operations, EMS, tours, and the like could definitely benefit from a higher cruise speed depending on the distance between points. A long range crew change or rescue operation could make use of higher speeds but at some distance it becomes less critical. In cases where surface operations prevail, cruise speed matters far less. Operations such as fire fighting, logging, utility line maintenance, ski area maintenance, agricultural drying and spraying, heli-skiing, skydiving, and the like spend a lot of time in a reasonably local area and the higher cuise speed capability just wouldn't be used. For military operations, enroute time and getting in and out quickly is important but so is loiterability for things like ground attack or reconnaissance.

Bob

[ShyTorque]

I agree, which is why, in my opinion, the tilt rotor will have limited success; it is a specialised "niche" aircraft with limited appeal to the majority of present helicopter users.

[before landing check list]

Hey Bit, I started life at 90kts and thought it was fast. Then I evolved into Hawks and 150 was way cool. Then the Cessna C550 at 350TAS and I thought I was in the big leagues. Eventually I "stepped up" to the DC9 and Lear35's at 500+ kts and thought I was on top of the world. Now I realize it really does not matter because when you go faster, you go further. You will still be in the air 2 hours or so. I "evolved" again to the 61 at 120kts and I am loving life

[before landing check list]

Shy, you are right about the niche market. I think Spec Ops is that niche.

[Graviman]

Hmmm, some good food for thought being posted on this thread, all. :ok:

So it's fair to comment that the most important aspect to high speed helicopter design is it's range. If the mission is long range VTO to VL, then this also implies that pilot comfort is more important than on a conventional helicopter. What flight time would most pilots consider reasonable? Should our hypothetical high speed helicopter be nipping at the heels of turboprop range?

My preference for this thread is to consider civil mission requirements only. This is because military requirements will not be so driven by operational cost, so the chosen configuration may not reflect this. Naturally, all comments are still welcome.

[ShyTorque]

What flight time would most pilots consider reasonable?

Depends how strong the coffee was.....

[VfrpilotPB/2]

Gazelle 75% seems a good target!

Peter R-B

[birrddog]

Graviman,

As a private user (&pilot) of Helicopters, there are two factors I have to evaluate when chartering (or as the case may be looking to purchase) fixed wing or helicopter.

These can be broken down into two categories.
1) a) Short flights, where the time/convenience value makes sense to save 1-2 hr on a 2-4 hr journey (avoiding a car service to/from a nearby airfield)
1) b) Landing facilities available (short runways, no runway, etc.)

2) Longer flights, where limited in range/load/cost per seat mile offered by helicopters.

I like helicopters, and as such pay for the convenience and the experience (as budget allows). I also get to land in some interesting places, but these days not many places a car/airport is more than 45min-1hr away from an airport.

Where I see value is a helicopter that can give me the benefits of 1 (a & b), but can compete against small to medium fixed wing in 2.

This way, one can look at "just buying a helicopter" for a wider variety of civilian missions, and hopefully have the machines that cost less to operate per flight hour.

[relyon]

Offshore crew changes to platforms, rigs, or ships is a reasonable example civilian mission, particulary those deeper out, say 60+ NM. There's no fixed wing aircraft that can do it and for VTOL aircraft the faster the better. It might seem like tiltrotors or tandems (fore/aft or lateral, interleaved or not) helicopters might work great because of their speed, but they don't because of the physical size constraints when they reach the destination.

Presently most if not all offshore LZs are basically confined pinnacles with lots to run into. Even in cases where there is sufficient space, operations usually dictate a preference for multiple aircraft on the helideck, so space is still at a premium. A given weight aircraft needs to have as small of a footprint as possible. For the offshore mission I think single main rotor, coaxial, or intermeshing designs literally fit best.

In numerous discussions here on PPRuNe and elsewhere I've noted a trend towards aerodynamic purity and efficiency above all else from a design perspective. I agree those are great goals to aim toward and are high on my list when I think think of how best to do something. But the real mission limitations that exist also must be considered and often need to come first.

Oh yeah, more comfortable seats would be great. I spent many hours driving my wife's 1999 Plymouth Grand Voyager and found those to be the most comfortable vehicle seats I've sat in. I don't think they weighed [much] more than those in a BH206 or BH407 but they were immensely more comfortable, especially on long (2+ hour) drives.

Bob

[Graviman]

Been away for a couple of days, but...

ShyTorque, i have always maintained that the purpose of civilisation is for the production of coffee! In fact, after the Egyptions built pyramids and such, the engine was invented for the purpose of mining and transporting coffee. ;)

Birrddog, you make some good comments there. Definately agreed that the only way a high speed helicopter can be commercially viable is to keep costs comparable to a conventional helicopter. This means low disk loading and minimisation of mechanical complexity. Would i be fair in commenting that doubling the speed of a helicopter might allow a machine approaching twice the hourly costs? My reasoning is halving the flight time, although in practice there would be other variables to consider.

Relyon, offshore is one of the applications i was thinking of. In fact anything which required VTOL, but benefitted from speed. I'm really searching for as many potential applications as possible for consideration.

I accept that aerodynamic purity should not interfere with the function of the machine. Limited landing area is definately a consideration, and is the main reason that coaxial seems the most practical to me. Do you think that requiring say 4 blades per rotor would cause difficulties? A civilian machine could not commercially stow/fold the rotors away after each flight.

[Shawn Coyle]

Cruising speed in the order of 200-220 knots and a range of 300-400 miles (with IFR reserves, a whole other subject) would open a whole range of missions for helicopters - trips would be sub 2 hour time, and as long as there were suitable IFR infrastructure, (such as zero-zero approaches that would guarantee arrival), things would become completely different.
But just cruising speed improvements won't sell the concepts.
Some possible missions include a lot more corporate operations (Europe and NE US especially); just-in-time parts delivery for expensive industries; EMS to specialized facilities; plus some others we've probably not thought of but where time is critical and it currently can't be done with existing equipment.

[relyon]

Four bladed rotors, or for that matter anything greater than two bladed rotors, can be made to work in confined destinations. Obviously, if the machine can get in and out safely with rotors turning it can be parked there as well, but the need to park multiple helicopters can get interesting to say the least. I've both seen and come up with some very inventive ways to park AS350s, BH407s, and the like in fairly tight quarters, and that's without the ability to perform ground handling moves or even the wheels to do it with. The coaxial rotor crossing azimuth will be critical in some cases and a 45/135/225/315 arrangement (assuming a four bladed non-folding system) might work best from a parking perspective. Castoring wheels for ground use with the blades stopped might work too.

Bob

[Ascend Charlie]

Double the speed won't just double the costs of operation.

A simplistic look at it is that 2 x the speed = 4 x the drag = 8 x the power required (power is proportional to the cube of the speed)

Do you use smaller engines running at their (most efficient) max to get to top speed, but have nothing left over for OEI? Or bigger engines to provide some spare capacity but which are hopelessly inefficient at loiter speeds?

In my previous life, the main trip was from airport/heliport to private house 130nm away, no aids at the house end. In the S76 it took 1 hour doors close to doors open, and a cruise at 140-145kt. Upping the cruise to 200 or 250 would be a huge bonus to the boredom factor, but the last 15 miles was often a careful VFR sneak up a cloud-topped valley, or at the other end was a 5-minute loiter while the helicopter-unfriendly ATC tried to fit us into the control zone while still dealing with a jet 20 miles away.:*

[Graviman]

Shawn, what else is required to convice operators about high speed helicopters?

Relyon, would some kind of synch release mech help with ground handling (along with your castors)? This could be a manual release, requiring tie-down, which would clunk back into position as soon as the rotors turned. Alternately a motor trimmed crossover adjustment - but that sounds complicated...

Ascend Charlie, it's a strange fact about fixed wing that if the minimum drag point in increased in airspeed the drag value remains constant. This requires increasing the wing loading (ie a smaller wing), so perhaps you are right since we want our hypothetical helicopter to have low disk loading for good autorotational characteristics. Clearly OEI would significantly affect airspeed, but the trick would be for it to not impact the range.

[topendtorque]

to private house 130nm away, no aids at the house end. In the S76 it took 1 hour doors close to doors open

That is surprising. I had heard that there was a nice light hanging on a post right by "the house", that the "old fella" could see from miles away??????, and it was :mad: if you didn't.


or at the other end was a 5-minute loiter while the helicopter-unfriendly ATC tried to fit us into the control zone while still dealing with a jet 20 miles away.:*


This is not at all surprising, I often wondered why the Sydney controllers were so dangblasted obstinate. Luckily for me I only ventured there at very irregular intervals.
I always came away with a taste of wonder at how a lowly helicopter that was beetling along at fifteen hundred feet could possibly interfere with a jet that was at least 10,000 ft vertical and twenty miles away. absolute c***heads I reckon, an insult to have to fly near them..

[Shawn Coyle]

What will it take to convince operators about high speed helicopters?
Having a few of them around will produce competition, which will sharpen up everyone.
If Eurocopter hadn't come out with the AS350 series, would Bell have produced the Bell 407? Give the customer some choice, and watch the results.

[relyon]

Interesting you should mention a sych release as I was thinking of the same sort of mechanism but didn't put it in my reply. Such a release could be very usable as often it's not that folding blades are strictly necessary but the ability to move them is if they can't be folded. One can get quite a fair number of machines in a fairly small space when combined with castoring wheels. The ability to attach a [portable electric] ground dolly to one or more wheels or having motors in the wheels (though that would add weight) might make such dense parking a one or two person operation.

Bob

[Graviman]

Thanks for the response to this thread guys. :ok:

Shawn, i agree that if you build a better mousetrap the world will beat a path to your door.
Relyon, that is a good practical perspective.

So the hypothetical high speed helicopter should aim for 300-400 miles (with IFR capability), not compromise it's ability to land (and be parked) in tight places. The outlay cost could be marginally higher than a conventional helicopter, and operational cost (per hour) could increase proportionately with speed. Also the payload capacity should not suffer unduly, by allowing some overall weight increase, but we only really need consider up to 250Kts.

Hmmm, difficult spec. Perhaps i should concentrate more on what size of payload would benefit the high speed. The unstated assumption is that the machine should ferry passengers, but would point-to-point cargo be a better approach? Should the machine be sized to suit EMS and SAR requirements?

Does anyone have any thoughts about the size of machine which should be first targeted?

[Shawn Coyle]

I guess a question that should be asked is - does it need to be a helicopter? There were lots of interesting concepts tried in the 50's and 60's that withered on the vine because the technology wasn't ready. Which of those should we re-visit?

[Graviman]

That's a fair question, Shawn. I imagine that rotodyne will be a favourite, although tip jets would not meet emissions or noise regulations in place now. Are you considering more autogyros or STOL fixed wing? In fairness to Nick, we should not overlook the potential of tiltrotor for STOL, despite it's high disk loading for VTOL.

Perhaps another question should be: how much more would i willing to pay to minimise my runway length?

[Bladestrike]

I'm thinking about a million miles per hour.

The take off and landings are the fun part.

I recall flying in the bush how much I hated ferry flights, but get me on some job with a take-off/landing, or at least a cycle (slinging/bucketing) every five to ten minutes, I'd be happier than a pig in ...well...you know....

...and here I am flying 200 mile legs offshore.......