Cyrus the great wrote:Coaxial helicopters are inherently mechanically more complex, so how much more maintenance heavy is the Ka-50-2 in comparison to the Mi-28? I imagine that it will be on the ground more than the Mi-28. Another disadvantage is that coaxial rotors weigh more as a system and that it doesn't provide adequate yaw control in auto-rotation, however, Kamov claims to have solved the yaw control problem. I'm inclined to believe them.
From that research file from Kamov design bearau itself they have tested the aspect of co-axials in all aspects compared with conventional designs aswell with older Kamov helicopters such as Ka-25/27 to see the difference in capability and limitation.
The overall design of a co-axial rotor layout is quite complex, due the double rotor sheme that has to work properly in the intended, plus overstretched stress limits to assure proper function. The complexity itself is that the design is a hollow structure of the first main rotor (lower) that has to be arranged in a way that a second rotor set can rotate in opposite direction without interference or reducing safety of structural strength or sub systems of the rotor parts. The design is relative solid based on the principle that both rotor sets with the lower being hollow and housing is oriantating to be structural supported by the inner (upper) rotor system and wise versa. That gives both the stability and structural support to work proper in an intented stressful environment, to be able to maneuver without breaking or must bumping.
Anyway, the system is quite complex, but due the complexity of conventional helicopters in the sense of durability and safety issues they have with the tail rotor and most often with the tailrotor shaft which translates via gearboxes the momentum to provide counter torque and the high stress such in effecient design has on several sub parts as shafts, gearboxes and junctions and so on, it provides an uneasy way of maintenance. The number of parts that need to be inspected for proper function within limits is higher then on co-axial designs, despite one block of rotor set and gearboxes along with routine engine checks that recieve and are necessary as major maintenance in comparision with many more parts on conventional designs.
Another thing about maintenance is that co-axial designs have two rotor discs, meaning the weight they lift is half the weight other single main rotor helicopters have to bear. That reduces the stress on the rotor blades and connections which extents the lifespan of such parts and makes maintenance easier. Co-axial designs also reduce stress of the disc load in forward flight, the higher the speed the more benefit you can notice of a co-axial design. In Hovering the Ka-50 for example puts a quite disadvantage on its own design, the lower set of rotors recieves a downwash from the upper blade, which reduces its effeciency to just roughly 10%. This effeciency is increasing with speed of the plattform and at speeds of 230km/h+ the negative downwash effect is almost entirely eleminated and the actual lift and speed increases and is only limited by the air friction and the left downwash on a very low surface of the upper fuselage body and lower blade. In strict theory of co-axial design the helicopter has no speed limits which conventional designs have, due the advancing and retreating blade issue, which creates an inbalance of lift and makes the helicopter tilt at certain speeds, which vary from design and makes the helicopter usually crash fatally.
The Ka-50 for example like advertized
by Kamov can bear
flight worthiness for 14 days without major
maintenance necessity. The Mi-24 does not need maintenance of major level of 3 days, in some cases in Chechnya a few rare examples flew without 5 days of major maintenance, just routine inspections due the bad logistics they had in first war. This are just of course figures under harsh environments, in actual case they inspect and maintenance the machines regularly for safety reasons and to keep the total failure or fatal failure of machines and subparts low to safe costs on spare parts.
As for the part of yaw controls and autorotation. The co-axial design provides better stability in autorotation and does not necessarly have to rely on forward speed to keep itself stable, while in autorotation conventional designs that have lost engine power have a harder time to keep themselfs straight and stable on the way down, which is the key to sustain a high RPM at very low, almost flat angle of attack of the blades while having to keep the machine go forward to not allow it to tilt or to have to much force on main rotor to induce a torque so the helicopter rotates around itself. Kamovs co-axials have an reinforced structure to ensure better and more safety during yaws to the prohibited and limited angles such designs have. The first 4 or 6 helicopters have a slightly different internal concept which, i most probably couldn't differ myself, due the lack of actually being in physical contact with such designs, but they were limited in yaw which also killed Voraboyev test pilot which put it to its limits and tilted the helicopter in a maneuver over its limits which put the rotor discs to close to each other and collidated which ended fatally. The structure was reinforced and today in some videos of aerobatic you can see Ka-50/52 maneuvering very close or even above the limited yaw of 80° it was set for the prototypes. I hope i answered to what you meant by yaw limitations of co-axial designs. They still have them because the rotor design of Kamov is a flexible one to assure high maneuverability for Ka-50/52, meaning the both rotor discs come much closer to each other at Gpulls than S-97 for isntance which has a rigid rotor design which does not have great maneuverability and is trimmed for high speeds rather combat task requirements of maneuverability.
I learned a great deal from the Mi-28 thread, especially from Werewolf's posts. I had no idea that other attack helicopters were so woefully protected. The cockpit glass of other attack helicopters have "transparency armor", which apparently doesn't even protect them from 7.62 rounds, but the cockpit glass of the Mi-28 is armored to withstand 12.7 mm rounds. It's incredibly foolish that other attack helicopters lack this level of protection.
How heavy do you suppose that door is?
It is rather a question of requirements and philosphy countries and armies pursue rather than a dogmatic question. That said there are dogmatics in war and that for aircrafts, the slower they are the higher amount of ground fire they are recieving, from peasant to high military degree, which makes such ground fire more effective then dedicated SAM/MANPADS due the number of available weapons that can be used as anti air and due the rather low distribution of SAM/MANPADS in comparision.
The philosophy of the west (AH-1 and AH-64) were to trying to lift the unrivaled domination of soviet ground forces vs NATO ground forces which have been in quality and quantaty in favor for soviets 4:1, which CIA evaluation says from late 70-80's. The concept was to lift that issue for NATO ground forces by applying CAS/AT operations by air via helicopters use.
The issue still remaint that soviet ground forces are accomanied by dedicated Anti Aircraft plattforms such as SHORAD/MANPAD equipped mechanized and motorized units aswell SPAAG in high numbers. The concept to avoid that was, to avoid the confrontation by itself and the entire layout was attempt to be trimmed in one direction of LOAL/Longbow capability in the later years.
The early years however, they did never address that issue in the design of the helicopter in such a manner as soviets/russians did. Different philosophy, not really my job to judge it, but i would prefer the russian/soviet approach since majority of threats that have downed, damaged and occured on battlefields, old and modern are still projectiles of 7.62 and 12.7mm, increasingly more calibres are used in more intense wars above 12.7mm which are very lethal against any aircraft and even "highly" armored helicopters such as Ka-50 and Mi-28 do not have high survival expectancy once they have entered the effective envelope of such weapons.
I think there is a big misconception going on among many people that hear or read often the advertizement of armored helicopters such as attack helicopters capable of surviving/sustaining 12.7mm and 23mm rounds. That are only cockpit and belly fuselage to center that can do that. The engines are less armored then the cockpit even tho they house a very vital part of the helicopter to assure functionality and therefore survival.
The basic concept of helicopters, i will quickly and in an amateurish way depict to give you just a glance how the armor is distributed and for what reasons.
I use Mi-24 as a sheme of explaining the, usually common approach of armoring attack helicopters, regardless of the design, except one...
In color coded.
Red, offers no protection or in limited amount kevlar layers that are only there to reduce the fragments spreading of HE-F projectiles to reduce the damaged they make to the structural integrity of the entire tail section and tail itself.
Yellow, section is usally sufficient amount of protection that can be often translated to 7,62-12.7mm, however that is the average, not impressive not something you would discard for sure.
Blue is proper protection such as gearbox, engines and an usually simple designed armor plate or cover that protects the tail rotor shaft from penetration from beneath aswell hydraulic and wiring to assure at least low amount of protection to the vital part of the tailsection. The entire tail section can not be armored due the weight limitations and especially that is an aircraft and needs a balanced plattform otherwise it will not fly at all. Therefore almost no attack helicopter offers any protection to the tail section especially after the dark red line where the actual tail begins.
Green is a good amount of protection that usually has several layers to sustain the advertized 23mm projectiles and fragmentation.
Purple, is the section that house more or less the core armor of the section to sustain the most amount of abuse they can recieve, titanium bathtub and steel/titanium plate for seperation of engines,gearbox and steel alloy to protect engines from outside along the usual aluminium alloy skin which is rated and has proven to sustain 12.7mm fire without problems.
Helicopters, can not be armored entirely to sustain 12.7mm let alone 23mm+, that would make them as usefull as a 100+ ton tank, well protected immobile bunker that is object to even infantry with a nice package of explosives.
I can not answer how much the door of the Mi-28 weights but the window is roughly 45mm (or 55mm) thick and roughly 0.8-0.9m² of surface, which makes the BP window weight more than 110-130kg. The door will weight quite some thing, however the door design is 3 layers of armor with quite an amount of air and padded with kevlar to protect wiring from fire of incendiary rounds or contents of warheads.
According to mentions of ukrainian article of bulletproof glass which by design a glass-clad is what is used in military purposed armor transparency the weight of m² at 55mm is around 137kg, so that gives us a rough figure.
Just a relative wild guess but i would think the door weights roughly 180-200kg, could be way off, but i don't have better figures.