Even the pros put their blades together

Another fun example of why it's good to have flexing aerofoils:

What we see there is wingflutter, can happen when you overspeed and is really really BAD to encounter (Hell of a ride tho :P ). But the point being - if those wings had been stiff that guy would have been using his parachute at the end of that video. :P

On 1) Varies. I'm not sure what the most common material in military aviation is, but I'd bet on composites.

 

On number two, fatigue changes a lot of things in aircraft, most importantly what kinds of forces they can withstand. I'm not a materials engineer either. But to make one thing clear: all aerofoils flex. And more than several inches - at cruise a Boeing 787 has it's wingtips a full 10 feet higher than when stationary. If wings did not flex, they would crack, because the flexing of an aerofoil spreads the stresses throughout the entire structure, rather than all stresses being taken out at a single weakpoint as would be the case in a stiff construction. I am not sure how much the blades of a helo like the Ka-50 flex, but as you could see in the video I linked that was how they flexed while in the air. That was not a stationary test. (I think it's a Cobra.)

 

As a side-note, this principle is also used in construction of tall buildings - they are made to flex with the wind, since that is a much better alternative than having them fall down in a dramatic fasion the first time there's any kind of wind on them. (Or, for that matter, an earthquake.)´

 

The theory of this is pretty simple to observe: take a piece of spaghetti with one end in each hand, and bend it. It breaks. Take an identical straw of spaghetti and boil it for a few minutes and repeat the experiment. It no longer breaks. Get the right material and you can make a rotorblade or wing that has sufficient stiffness to maintain the same shape and lift throughout the flight envelope but still flex enough so as to dissipate forces throughout the structure.

 

EDIT

And on calculating... Well, what kind of computation power do you want to bring along in the helicopter? Show me a computer strong enough to make all those calculations, with the detail of the flexing, fatigue and all other such factors, that will fit in a helicopter. And then figure out a way to make it do those calculations properly and with confidence enough to let you set the limits close enough that you won't badly handicap your pilot.

 

I mean, seriously, the Soviet Union, Russia and several other countries have operated coaxials for a LONG time and you'd think that if what you are asking for was feasible and practical they'd jump on it? So unless you know of a way to calculate this properly, in real time, with sufficient precision, I'm not sure you should be happy with a "shouldn't be THAT bad". If that is the case, design such a system yourself and become a multi-millionaire. ;)

I believe you are getting fatigue and bending confused. Fatigue changes the AMOUNT that materials bend, it is not a description of material bending itself, though bending of material causes it. Fatigue is the material slowly changing its stiffness and structural integrity over time due to repeatedly being bent, forming micro-cracks or just breaking molecular bonds.

The amount that a material will bend is very easy to calculate. Simplyfying the problem (not because it is hard, but because I don't want to waste the time on it), rotor bending is SIMILAR to a spring, which is governed by Hooke's Law F= -kx (force = -k times displacement).

So, your point about difficulty in calculating rotor disk position is only valid if you're talking about actual FATIGUE, which would slowly change the "k" in Hooke's Law. I wouldn't think it would be a factor, but it's a GREAT POINT- how much DOES fatigue figure into rotor disk position. I would assume not much, but you should challenge your assumptions just to make sure. I don't THINK I would want to ride in a helicopter that fatigue had caused the spring constant k to change so much that the rotors were bending like 10 centimeters from where they would have bent if brand new, but hey, what do I know. k is easy to determine, and so long as k hasn't changed significantly because the rotors are about to literally crack and fall off, you know EVERYTHING you need to calculate the position of the rotor disc.

Again, I am not a materials engineer, I am an electrical engineer, so I have no claim to knowing with absolute certainty that materials fatigue would not have an significant impact. No doubt it would have an impact, but I would think, again, that you would want to replace your rotors long before the amount of bending significantly deviated from the amount of bending in a brand new set of rotors. From my knowledge of electrical engineering, I can tell you that you are VASTLY underestimating modern computing capabilities. Yes, I know your computer runs Vista slowly, but that's because Vista is !@## EVEN IF the calculation took so long that you couldn't do it real time, you could always use a handy little thing called a "lookup table" where the position of the rotor disk for like, 50 million different flight conditions is already calculated and stored in memory. "Show me a computer that can do this and fit inside a chopper"- it's called an iPhone, and not only can I fit it inside a chopper, I can fit it inside my pocket.

So basically, I see no reason why this can't done. And no, I wouldn't be a "millionaire" if I did this, this is a pretty common kind of problem. The first kind of problem like this was probably the F-16, unstable in one axis. The F-16 uses a computer to constantly calculate how to keep the aircraft pointed straight, and if those computers fail, then the aircraft goes out of control. In 1979 Lockheed Skunkworks made the F-117, UNSTABLE IN THREE AXES, fly. The computer in the F-117 had to constantly manipulate the control surfaces just to keep the aircraft from tumbling out of control, let alone translate the pilot's movement of the stick to make the aircraft maneuver. Your pitot tubes ice over in that thing, and you'd better get out in a hurry! So, I'd say that our computing power has come a long way in 30 years. Calculating the positions of the rotor disc, and overriding any pilot actions that would cause it to collide with something, like the PNVS/TADS, refueling boom, or even ANOTHER rotor disc, should be an easy problem for modern computers to handle.

I think you are right about at least one thing though though- they just depend on the pilots not being stupid rather than waste the time and effort putting such a system on the chopper. Even though it seems to me a very solvable problem, it would still take millions of dollars of development, testing, and integration that can be saved by just depending on the pilots to do their jobs correctly.

At the end of the day, i think if Kamov intended to produce the KA50 with some sort of effective flight governor their budget would have been dramatically increased if not blown out. And for what really, a good pilot knows the limitations of his/her aircraft. How many KA50's have crashed due to rotors colliding while flying within safe flight parameters specified by Kamov?

It's great we have computers that can do 50 million calculations a second but sometimes it's best just to use the good old brain, where you can have a solution with 4 calculations. ;)

Oh I very much don't agree, flying sober I've only had a blade clash once and that was being under fire and panic. I've probably flown 150hrs sober or so.

No problem at all to keep it within safe limits I thinks.

 

I'd imagine that you'd get a boom strike with a normal helicopter in the situations you get blade clash in the Ka-50(?)

No I stand by "NUTS!". While I don't have numbers to back up why coventional designs are better and have zero inclination to research it, it seems that a simple analysis suffices: No other major manufacturer is building coaxial rotorcraft. Why? We all know the advantages. So why aren't the other guys going with the best design? Well they are and coaxial it isn't. An attack helicopter is a flying tank. It doesn't need to be fast. It just needs to be a safe and stable launch platform. If helicopters really were zooming over the battlfield trying to gain "air superiority" over one another then the Ka50/52 might be the machine to have. But that's a cartoonish view of the role of combat helicopters. Don't get me wrong. I too love the virtual version on my desktop and yes I can reliably fly it with no harm done to my virtual body. But by real body doesn't even want to be within 2 clicks of the thing when it's airborne. And since Russia was smart enough to say, mostly, "NYET!", the world--Russian and Turkish pilots in particular--is safer.

No I stand by "NUTS!". While I don't have numbers to back up why coventional designs are better and have zero inclination to research it, it seems that a simple analysis suffices: No other major manufacturer is building coaxial rotorcraft. Why? We all know the advantages. So why aren't the other guys going with the best design? Well they are and coaxial it isn't. An attack helicopter is a flying tank. It doesn't need to be fast. It just needs to be a safe and stable launch platform. If helicopters really were zooming over the battlfield trying to gain "air superiority" over one another then the Ka50/52 might be the machine to have. But that's a cartoonish view of the role of combat helicopters. Don't get me wrong. I too love the virtual version on my desktop and yes I can reliably fly it with no harm done to my virtual body. But by real body doesn't even want to be within 2 clicks of the thing when it's airborne. And since Russia was smart enough to say, mostly, "NYET!", the world--Russian and Turkish pilots in particular--is safer.

Heh.. Where did all this about "air-superiority-gaining-Ka-50/52's-zooming-over-the-battlefield-cartoonish" come from!? :huh:

My argument was purely about the fact I don't think the design is "nuts", most people (real pilots and us virtual pilots) have no problem not getting blade-strikes (when flying sober).

That leads me to believe that those that do have that problem would be getting boom strikes in conventional helicopters instead (we'll see when the Apache comes out :D ).

If one makes sure those red and yellow push lights don't blink and beep - there's no problem (just as with any other helicopter).

Besides

Ethereal,

You've objected to my use of the words "shouldn't be too hard" or it's an "easy problem for computers to handle". You are right to object there, as I am being somewhat vague. When I say, "it shouldn't be that hard" what I mean is that I feel this kind of problem should certainly be one that can be solved and implemented by engineers. It would still be hard in that it might be intellectually challenging to the individual people working on it, it might require a bit of computer programming, and would take millions of dollars to solve it and implement it on all the choppers you wanted to put it on, but the chances of failure to solve the problem should be very low.

What has also not even been considered is a sensing system that, rather than calculating, simply senses the position of the rotors. Such a system, if you used, like, ultrasonic ranging, could simply tell the computer where the rotors are, vastly narrowing down the complexities of calculating where the rotors will go next if the maneuver the pilot is commanding takes place. In fact, all that might have to be done is if the rotors come within a couple centimeters of some part of the aircraft, opposite collective is applied to keep them from striking. Ultrasonics might be superior to like a little radar or laser range finder as it would not emit in the EM spectrum, ultrasound attenuates very fast in air anyway, and no real sensors to detect that kind of thing are used on the battlefield, so you're not going to making yourself more detectable with such a system. I donno if ultrasound would be fast enough though. You might HAVE to go to lasers. If you used a laser, you could probably make it very hard to detect by using a wavelength that is heavily attenuated by CO2 or H2O, and using one that has a wide beam divergence.

So, many solutions exist to the problem of keeping the blades from striking something or, in the Ka-50s case, each other. Again, I think that maybe the reason something like this hasn't been implemented on modern choppers is that such a system might cost more than it would save, especially 15, 20 or more years ago when "modern" choppers were being designed, and technology to implement something like this would have been more expensive.

Yet, sometimes even expert pilots make mistakes, or, as someone pointed out, you accidentally kick the cyclic and it chops off the TADS/PNVS. Those choppers and IR cameras are expensive, and yet technology like computers, laser range finding, or ultrasonic imaging keeps getting cheaper. I wouldn't be surprised if some sort of self-rotor strike avoidance might be included in future generations of choppers.

Ultrasonic sensing for something that's almost supersonic?

Anyway, note that while auto-hold and other interesting FBW systems do exist for helicopters, they won't prevent those helis from cutting themselves up, just as they won't prevent a pilot from flying his place into the ground at mach 1.

While I don't have numbers to back up why coventional designs are better and have zero inclination to research it' date=' it seems that a simple analysis suffices: No other major manufacturer is building coaxial rotorcraft.[/quote']

 

Sikorsky.

 

But as for which design is safer or better, thing is it depends on what you need. The Soviet navy liked coaxials for one very obvious reason: they take less space aboard ship. This is less of an issue on land, which might go some distance to explain why they haven't been adopted as much in land forces.

 

But if you want to make a judgement call on the safety of them, you would need to include the Ka-25 and it's derivatives in the dataset. Though you have said you aren't inclined to research it but rather just stick with your opinion.

 

I don't know whether conventionals or co-axials have a better or worse safety record. But it's not a simple thing to judge. Coaxials may suffer the risk of intersecting rotorblades, but they also reduce the risks from RVS, retreating blade stall and completely eliminate the issue of problems with tailrotors. I have heard that they are less proficient at auto-rotation though, but that's just a vague memory from a thread which I believe mentioned that the tail rudder was there to help control the Ka-50 during autorotation.

 

Another point in safety for the Ka-50 specifically though is that it has a zero/zero ejection seat. What do you do in an Apache or Cobra if your tailrotor is shot to pieces? You hope the impact won't be too bad... (And while the Apache at least does have pretty good odds of keeping the crew alive in a crash due to it's safety systems and normally low altitude, I'd still prefer the option of just leaving the aircraft. :P )

 

And since Russia was smart enough to say' date=' mostly, "NYET!", the world--Russian and Turkish pilots in particular--is safer.[/quote']

 

The key word is "mostly". :P The russian navy has used coaxials for a LONG time. Indeed, Kamov coaxials have been operational since the early 50's. If memory serves the first coaxial observation choppers were built in the late 40's but it wasn't until the 50's that they were operational in numbers - just like most helicopters. The coaxials have as long a history as conventionals.

 

That leads me to believe that those that do have that problem would be getting boom strikes in conventional helicopters instead (we'll see when the Apache comes out ).

 

Or just get their tailrotor shot away. I have had my entire tail section blown clean off in DCS and still flown home. I want to see people do that with a conventional helicopter. ;)

 

Yet' date=' sometimes even expert pilots make mistakes[/quote']

 

Yeah, which goes for all helicopter designs. My point is that for me as a pilot to trust a limiter or other system, I want it to have margins built in. And in the case of the proposed system, even if feasible to construct, those margins would impair my ability to use the aircraft's full potential in combat. Which could cost both my life and the lives of those I'm sent to support.

 

10 years down the line I have absolutely no doubt that computer capabilities will be sufficient to do the calculations - but that is then. And the question would still remain of whether it's possible to do it with sufficiently slim margins so as not to impair the pilot while still allowing the system to be trustworthy.

 

I am not as sure of that, and would much rather just trust my training. This is not something like an unstable aircraft design needing computer help to be stable enough for the pilot to control it at all. Co-axials can be safely operated and have been safely operated even long before there even was the damping channels we have on the Ka-50.

 

This whole discussion seems based on people grossly overestimating one danger of the design and seriously underestimating the dangers of the conventional helicopters.

 

I, myself, would much rather fly an aircraft where I know I can lose a major chunk of the airframe and still be in control of the aircraft rather than one where a single hit in my hind quarters might mean all I can do is turn religious very very fast. :P

Ultrasonic sensing for something that's almost supersonic?

Well, since I would assume you would be measuring the rotors from below them, the nearly supersonic velocity of the rotors is perpendicular to the incoming ultrasound wave, so it shouldn't make a difference if you're just ranging. Though you might get some interesting effects, you'd still see the pulse bounce back. But, even ultrasound still travels at only 343m/s, and less at altitude, so you'd likely just want to go with a lidar/ladar/radar.

... yeah. Not to mention self-noise, the pressure wave being dragged from the rotor, the pressure wave FROM the rotor, and all kinds of other fun things that would likely make it useless. Please don't make stuff up like that - lidar anda radar tends to have minimum distances as well, and what you're suggesting is reactive which is simply not good enough.

Further, how is the computer to know that cutting the boom off is a fair trade for avoiding some form of collision? Even the F-16's FBW allows you to over-control just a bit before it dampens - ie there's some lag in what it does.

... yeah. Not to mention self-noise, the pressure wave being dragged from the rotor, the pressure wave FROM the rotor, and all kinds of other fun things that would likely make it useless. Please don't make stuff up like that - lidar anda radar tends to have minimum distances as well, and what you're suggesting is reactive which is simply not good enough.

Thanks GGTharos for informing me that all the classes I have taken, papers I have read, conferences I have attended, and hardware I have tested is make believe. I had no idea! It all seemed so real at the time.

Really, truely, you have no right to speak on things you haven't the slightest clue about.

But, since you already know it all, I'm not going to waste any more time with this.

.. you mean like devices I've used in the field? I'm aware there are sensors that can do the measurement if you want, but I bring to question their usefulness in this task.

Really, truely, you have no right to speak on things you haven't the slightest clue about.

Hey Pot, meet Kettle.

1) What are the blades made of?

2) I HIGHLY doubt that fatigue is going to be an issue, but I am not a materials engineer, so I can't say for sure. I'd think that any material that would change by more than several inches would a) badly in need of replacing and b) not something you'd want to make a rotor out of anyway. But again, I can't say for sure, because that would be something outside my area.

 

As far as the system for calculating rotor disk position, it shouldn't be THAT bad. Hell, we made the F-117 fly and that was in the late 70s.

No matter what material you use the blades will flex in flight. First couple times I went up in a commercial airliner I was freaked by how much the wings swayed up and down just while rolling on the ground. In flight it was smooth. But heli blades are constantly changing angles over the course of a single revolution and I dont think it would be possible elliminate flexing. Even if you did, it would likely cause excessive stress on the main shaft because something has to give or it would just break apart from the violent forces being placed on it.

If computers are so good these days why bother having pilots? ;)

The airforce is moving to unmanned fighter aircraft. They are in development.

No, they are in what might be at a stage of 'proof of concept' ... definitely quite far from development.

No matter what material you use the blades will flex in flight. First couple times I went up in a commercial airliner I was freaked by how much the wings swayed up and down just while rolling on the ground. In flight it was smooth. But heli blades are constantly changing angles over the course of a single revolution and I dont think it would be possible elliminate flexing. Even if you did, it would likely cause excessive stress on the main shaft because something has to give or it would just break apart from the violent forces being placed on it.

I'm talking about fatigue, not flexing. Fatigue would cause flexing to slowly increase over time, which would be very bad.

Hey Pot, meet Kettle.

Oh no doubt, I've been guilty of this. But in THIS particular case- I'd trust an actual engineer over someone who's not in the matter of what is technically possible or not.

For example, all the objections raised are easily solved. Rotor pressure wave- use a high-pass (or maybe a band-pass) filter. We're talking about ULTRASOUND here. All those other effects are low frequency. The talk of "You can't measure because there's so much noise around!" is ridicuously technically naive. Filters and signal processing correlation routines easily can pick out signals out of VERY noisy environments- just look at your radio. With antenna and filter design, you pick ONE specific frequency out of a myriad of frequencies all simultaneously transmitting.

GGTharos argues that because he has never used a system that would measure at close enough distances or fast enough, then such a system can't exist. That's like me saying because I never used a telescope that could see galaxies 9 billion light years away, the Hubble Space Telescope doesn't exist.

The fact is, you can use faster electronics and shorter pulse times, and if you STILL have a minimum distance problem, you can simply move your sensors further away. Upward facing lidar systems on the stub-wings/pylons, anyone?

So, to top it all off, he insults me by saying that I am "making things up". Please....

Speed2 beat me to it regarding a simplistic rotor-clearance measurement based limiter. As for "combat needs" that's what an override switch is for. What's one more switch in the Ka-50 series cockpit? You could even have different levels of clearances: High clearance for transit, low clearance for combat, and off for combat damage or extreme cases.

I wonder if some sort of physical anti-interference solution also exists potentially, some sort of ramp or whatnot at partial blade radius to make rotor collision non-catastrophic. P.S. It's also 6000 near misses per minute... remember counter-rotating ;P

Ultrasonic or some sort of EM-based system is just a minor quibble over the correct engineering means. The ability to sense those distances on short time scales is extremely "in the bag" as modern engineering goes.

So then, can someone say why hasn't such a thing been put into use on real life aircraft? AFAIK, in any case.

Because everything hasn't been invented yet and Ru aeronautical engineering is soooo concerned with pilot safety.

Because everything hasn't been invented yet and Ru aeronautical engineering is soooo concerned with pilot safety.

You are correct :D As far as i know the Ka50 and KA52 are the only two combat heli's with ejection seats. :P

Yeah 26, I actually snorted beer when I saw that.

We are discussing the only attack helicopters in the world (though I haven't checked the Rooivalk nor the new Iranian light attack helo) that are equipped with an avenue for the pilot to safely exit the aircraft, and people are regurgitating old prejudices about alleged soviet lack of concern for their pilots.

Just because Stalin didn't give a crap about the lives of his infantrymen doesn't mean that 1980's soviet commanders and leaders thought their pilots lives to be of no consequence.

Instead, ask NATO helo designers why they don't care enough about their pilot safety to install an escape method. ;)

(Though the answer is likely doctrine-based, where the Apache f.ex. already has relatively good crew survivability due to normally low altitude and speed combined with a solid cockpit design.)

Instead, ask NATO helo designers why they don't care enough about their pilot safety to install an escape method. ;)

 

(Though the answer is likely doctrine-based, where the Apache f.ex. already has relatively good crew survivability due to normally low altitude and speed combined with a solid cockpit design.)

That's pretty easy, the trade off is cost and weight. Combined with the attitude, in general, that if the you and the aircraft are in good enough shape to eject, you're in good enough shape to autorotate.

Aye, and if you are not in an envelope where you can autorotate you are most likely so low-and-slow that your cockpit, seat, belts and airbags will suffice for crew protection? As an example, the odds of catching a 64 hovering at 500 meters AGL are pretty low, but if you catch one (and down it) while it was hovering at 20 meters AGL the crew are better helped by the cockpit design than an ejection seat?