hauger said:
First, I know nothing of fling-wing aerodynamics,
No comment required.
hauger said:
but where my thoughts went with the whole rotor shape change was to allow faster rotor speeds to increase the max GWT of a machine. I don't know if if works this way or not, if increased rotor speed allows for greater lift capability.
"Rotor shape change" would have little to do with rotor speeds.
Rotors are larger and have more mass than propellers - some amount of weight is necessary in order to preserve rotor RPM in the final stages of an autorotation aside from the natural mass - hence any additional speed generates more stress on the rotor system. Better balance is also required as things speed up.
There are other ways to influence lift: aerofoil shape, blade length and chord, blade pitch, number of blades etcetera.
Rotor blades are wings. Aside from the obvious fact that they rotate in order to generate lift rather than move along with all other parts of the airframe on a seized-wing aircraft, every point along the blade is moving through the air at a different speed, and corresponding points along other blades are often, but not always, moving through the air at different speeds. This is why one can see variations in pitch, or a twist, along a blade's length.
The Griffon's blades are described by Bell as "sculpted", as the aerofoil and chord vary along the length as well as the pitch. This is achievable as the blades are moulded synthetics rather than metal.
As the disc is tilted in order to split the more-or-less vertical lift vector of a hovering helicopter into vertical and horizontal (thrust) vectors, the airflow through the rotor changes significantly from something equivalent to a propeller's (straight through, but in our case downwards) into an angled and then largely sideways flow.
This is extremely simplified, of course. I know enough to operate the things; designing them is well outside of my lane.
Lift is increased by increasing the pitch of the blades collectively. This increases drag on the blades, and slows them down. Constant rotor RPM is maintained by working the engine(s) harder. At some point, the engine(s) run out of additional steam and any further increase in pitch causes rotor RPM to droop. Yes, more powerful engines could be installed, but there is always a trade-off - expense, weight, size, increased fuel consumption etcetera.
Higher ambient air temperature causes engines (and other dynamic components) to run significantly hotter, and temperature limits may be reached before power limits. It also makes the air less dense, degrading rotor performance.
Higher operating altitudes also degrade performance, and KAF is about 3000 feet above sea level.
hauger said:
I gotta go with the thought that if this was beneficial, someone would have incorporated it by now.
Yes. This is pretty much why I don't make design suggestions on Nuclear Reactors.ca.
hauger said:
I do disagree with the above quote though for in theater ops.
Based upon what experience? Add "operations" to your opening statement.
hauger said:
Helo speed can be highly beneficial depending on the employment of the asset.
Not much. Helicopters travel relatively short distances in tactical operations, and increasing speed will, at best, only shave a couple of minutes off of flight times over those distances. Most missions in our present theatre would be less than 50-60 km from KAF, which at 100 knots is less than twenty minutes.
While boosting theoretical max speeds may look nice on the shiney brochures, they are largely irrelevant when flying around with doors open and things hanging off of the sides or bottom, like guns, missiles, and slung loads.
You could do a Tim Allen and make a Leopard capable of doing 150 km/hr if you wanted to waste enough money and burn enough fuel, but why? Even if there was some small and occasional benefit to getting to places quicker by road, it's not moving any quicker cross-country without disrupting the internal organs of the crew and tactical movement is just not feasible.
hauger said:
As an air defense platform (aka: attack helo),
Attack hels are
not "air defence platforms". They are attack hels. They make things on the
ground blow up, burn, and bleed.
hauger said:
speed can be highly beneficial.
If it was, you'd still have to solve the other limiting factors previously mentioned, and even if that was achievable with current technology, it would most likely impose other limitations elsewhere. Like every single other military machine, helicopters have their strengths and weaknesses. They complement other vehicles and aircraft, which in turn complement them. Each machine has been optimized for its intended role.
hauger said:
A properly armed attack helo capable of speeds between 250 and 300 KIAS at various altitudes are very effective at providing low level harassment of tactical transport ops as well as providing the same ops with useful and beneficial attack coverage.
Are you refering to enemy or friendly ops, or both, and rotary- or seized-wing transport ops (the implication of your terminology would indicate the latter to me)?
This is not the role of AHs, and "harassment" of aircraft is not a useful activity compared to shooting them down.
Friendly transport aircraft would be escorted/protected by fighters, and enemy ones would be attacked by fighters and ground-based air defence systems. They exist for that purpose, among others.
AHs would be busy with the roles for which they are designed. To apply them to other jobs would require more of them anyway, so why not simply use something actually designed for the job?
Higher speeds add nothing to shooting ground targets, anymore than running around a target helps shooting at it with a rifle.
hauger said:
This is a capability Canada doesn't have,
CF18.
hauger said:
Apparently there's some issue with escort roles for our Griffon v. the Chinook due to speed.
As pointed out by Strike,
no AH can keep up to a Chinook. None were ever designed for that role, as there was never any requirement until now. So the big fat helicopter goes a little slower, and it takes four or five minutes longer to get where it's going. In the overall scheme of things, that's not usually a big deal.
In less permissive environments, for which all battlefield helicopters have been designed, helicopters operate at low level around 100 knots or less as it's damned difficult to follow contours, dodge wires, trees, and cows, and navigate at any higher speed at an altitude that gives cover and concealment. Chinook, doctrinally, would fly from Corps areas to Division or Brigade areas and no further forward, so lower altitudes are not required and higher speeds are feasible. Its tactical limit was a minimum altitude of fifty feet. AH escort would have been extremely rare, just as truck convoys would not be provided with AFV escorts, as it was not necessary. There was no more tactical movement for Chinook than there was for HLVW.
Kiowa's tactical limits were "skids clear of ground and one-half rotor diameter from vertical obstacles". Speed was adjusted to match the necessary altitude. When I was using every little fold in the ground or shrubbery for concealment, I'd be just creeping along. At four feet, I'd be up to 40 to 60 knots tops. Griffon's (and Twin Huey's) minimum altitude is fifteen feet above obstacles and one-half rotor diameter, although we now have lower limits (four feet) at drastically reduced speeds (essentially taxiing) for certain missions. Griffon lacks the visibility and agility of Kiowa, hence lower is not a good idea. Speeds of 90 to 100 knots are certainly suitable for 15 to 50 feet above obstacles, which generally allows sufficient concealment for airmobile ops.
Faster just makes one go higher, which makes one more vulnerable.
Permissive environments allow other methods of operation (such as staying above effective small arms range), wherein, as we have seen, the characteristics of different helicopters may not be "ideal".
Any helicopter designed specifically for current ops may well be less than ideal for more traditional roles, and we could find ourselves back in that type of environment at any point in the future. We have bought a fair amount of ground equipment specifically for our current theatre that may be less than fully useful in the future also. Nothing does everything for everyone everywhere every time. That's life.
