Safety problem with counter rotating blades ?

[Havner]

Looks like it rolled over to the side to me.

 

He rolled to the side cause only left gear got caught.

[Zorrin]

Im not baiting you, Im trying to learn something new here. Seriously, the instructor I had wasnt all there. The class felt cheated out of $2200 a piece so we're trying to get him canned. Im just looking for better information. Like I said, I see what you are talking about. Bad angle from the video, the obvious is still there. If you say that rotor stall wasnt part of it, then Ill take your word from it. Im not going to take the word of someone that spend 6 months in the field after he graduated, just to be an instructor, you know...over someone thats been in the field for more than 6 years.

 

 

That crash was a quick stop gone wrong.

And a fine example of pilot error.

He crashed because he came in too fast and ballsed up his quick stop. At this point the rear landing gear left leg gets caught and tangled up.

He is already well out of position because he ballsed up his approach. And we all know the key to a good landing, is a good approach.

 

So he's now hanging in a kind of limbo. An odd position as he is now starting to pull the power, the fact that half of it was over the water is irrelevant.

 

It crashed because he got the leg stuck and as he tried to escape, he didn't know the leg was stuck, so consequently the application of power did what he expected. Generated more lift.

 

Only because the leg is stuck in the guard rail the rear of it isn't able to lift clear, the blades are still generating the same lift as the frong blades. But because the leg is trapped it is stopping it from lifting.

 

Consequently the front disc is not impeded, hence the front lifts and you are creating asymmetric lift and eventually it rolls because only one leg is stuck.

 

At least that's the prognosis I've made from having seen that video a few times, and for what it's worth also the prognosis of several high-time CPL(H) holders.

[golfsierra2]

Back to topic:

 

Would a rotor concept like that of Kamov effectively prevent blades from colliding ?

[amalahama]

Back to topic:

 

Would a rotor concept like that of Kamov effectively prevent blades from colliding ?

 

Kaman has nothing to do with Kamov, they come from USA in fact.

 

Regards!

[hitman]

That crash was a quick stop gone wrong.

And a fine example of pilot error.

He crashed because he came in too fast and ballsed up his quick stop. At this point the rear landing gear left leg gets caught and tangled up.

He is already well out of position because he ballsed up his approach. And we all know the key to a good landing, is a good approach.

 

So he's now hanging in a kind of limbo. An odd position as he is now starting to pull the power, the fact that half of it was over the water is irrelevant.

 

It crashed because he got the leg stuck and as he tried to escape, he didn't know the leg was stuck, so consequently the application of power did what he expected. Generated more lift.

 

Only because the leg is stuck in the guard rail the rear of it isn't able to lift clear, the blades are still generating the same lift as the frong blades. But because the leg is trapped it is stopping it from lifting.

 

Consequently the front disc is not impeded, hence the front lifts and you are creating asymmetric lift and eventually it rolls because only one leg is stuck.

 

At least that's the prognosis I've made from having seen that video a few times, and for what it's worth also the prognosis of several high-time CPL(H) holders.

Alphaonesix straightened me out on that. My instructor is a real tard. :doh:

[GTengineer]

That accident had NOTHING to do with ground effects. It is very obvious it was a botched landing. After he set it down he tried to correct it and he was stuck while going over.

[hitman]

That accident had NOTHING to do with ground effects. It is very obvious it was a botched landing. After he set it down he tried to correct it and he was stuck while going over.

Ok...like I said, AlphaOneSix set me straight. I understand now.

 

Not to uhmm...hijack the thread again, but how the heck did you overclock your Q6600 that high?? O.o

[RvETito]

Nah, pretty sure it flaps up on 9 o'clock. I have it in my book but here is a quick online reference. This happens because there is a 90 degree phase angle between aero forces and flapping as explained in the bold comment below.

 

 

 

The above graphic shows that the higher angle of attack at the front of the rotor will cause the blade to flap up over the left side of the helicopter. The lower angle of attack over the rear of the rotor will cause the blade to flap down over the right side. The rotor will thus be tilted a little to the right. the sideward tilt of the rotor is increased at low forward speeds when the induced velocities are large, because the inflow not only approaches the rear of the rotor but, additionally, is bent downward. this increases the angle of attack differences.

 

http://www.dynamicflight.com/aerodynamics/flapping/

 

:)

 

I don't know who has written that in dynamicflight.com but it's all wrong, big time, both the picture and the quoted text. Obviously written by someone who has no clue about helicopter rotorblade azimuthal flapping.

 

Lets assume the flight controls (at least cyclic) are in neutral. In hover all blades have the same angle of attack and flapping, that's clear. In case of a forward flight (or any other direction of the velocity vector) and counter clockwise rotor rotation (like in that picture) the advancing blade at 3 o'clock will have the biggest average velocity hence biggest list (depending on V^2) and biggest flap up which decreases the blade AOA. It's called selfcompensation or blade flapping self-damping. Because of the blades inertia (like any other body) the maximum angle of flap is indeed not at 3 o'clock (biggest lift) but phased forward up to 30-45 degrees. That 90' (azimuth 0-180) on that picture is a joke. Similar is what happens on the left side with the retreating blades. At 9 o'clock the blade will have the smallest airflow velocity which will decrease the lift and force the blade to flap down thus increasing it's AOA, hence the retreating blade stall nature. Again, thanks to blades' inertia the lowest point the blade reaches is not at 9 but about 8 o'clock.

 

As a result, in that case the rotor cone in forward flight will be tilted to the left and a bit backward. And that's why ALL helicopters around the world have their rotor (gearbox) axis tilted forward- when in cruise airspeed the rotor lift should not have rear component.

 

As for coaxial counter rotating rotor the picture is all the same for any of the two rotors separately. Two lower rotates counterclockwise (seen from above), the upper clockwise. In forward flight the lower rotor cone tilts to left and back, the upper to the right and back. This makes the gap between the two rotors to decrease at the right side, between 2 and 4 o'clock (helicopter nose is 12).

[CAT_101st]

What you have to consider is that the retreating blade will stall when its at 3 or 9 o'clock so there is no lift at this position. Vice versa on opposite there will be maximum lift.

The upward or downward force will start to move the blade at this position

 

This affect only happens whin travling at the same speed as the rotor. Whin in a hover there is equal lift at all points. think of it this way the blades spin at 200MPH so at a hover you have a blade making lift at 200mph. Now you are moving forward at 100mph you now have the blades on the right side making lift at 300mph and the retreating side at 100mph. it is not till the helo reaches the 200mph mark that the retreating blads have no lift. I will try and find some diragrams and post them.

 

I hope this helps

 

EDIT: Dam it.... beat me to it

[golfsierra2]

Kaman has nothing to do with Kamov, they come from USA in fact.

 

Regards!

 

Thanks, my mistake.

But that does not answer my question. The shown rotor setup, will it prevent the rotor blades from colliding ?

[CAT_101st]

Ok so the KA50 with counter rotating blades can fly faster than a singel rotor helo Or at least be more stable. watching the Sim HQ video 2 I saw the botom blades spinning counter clock wize and top clock wise. Using what we have learnd. The botom blade will have max hight at 8o clock and the top blade will be a slack at same point. So that is the most likly place for the roters to strike eachother.

To anser your question as long as you stay within the operational guids. There will not be a strike. But their can be one if you go out side of the limmits. So NO is the anser.

[CAT_101st]

http://www.youtube.com/watch?v=xyctBKipmCI

 

shows how the roters can cross

[RvETito]

I believe he asked for the Kaman design. No, there's no risk or rotors intersection in the Kaman.

 

The Ka-50 is fast but there are few single rotor choppers that can fly faster. The problem is the high rotormast, it creates big drag which becomes more and more significant as the airspeed increases.

 

Not sure what do you mean by stability. The biggest advantage of the coaxial rotor is at hover- no other design provides such stability and precision. Problem for the coaxial helicopters is the autorotation- then they loose yaw stablity, which can be compensated by the wide range of the flight controls (pedals).

[Feuerfalke]

Ok...like I said, AlphaOneSix set me straight. I understand now.

 

Not to uhmm...hijack the thread again, but how the heck did you overclock your Q6600 that high?? O.o

 

Short answer: Get a good motherboard and fast RAM (1066MHz min!) and a stable PSU. With the Abit IX-38 you can overclock it safely to 4GHz.

[hitman]

I have a good motherboard and fast ram...Ive only been able to get it to 3.2ghz stable (and I think I fried 2 cores on it because its not stable past 2.8ghz anymore).

[arneh]

Interesting that Sikorsky's new X2 design is a co-axial rotor design. They believe it should be able to fly faster than 250 kts, which is by far faster than any helicopter made so far.

 

 

It's also interesting that it reduces rotor RPM at high speed to avoid the advancing blades going supersonic. Apparently it's no concern that the retreating blades will stall.

 

Story about X2's maiden flight a couple of weeks ago.

 

And here is a concept drawing of it as an attack helicotper:

[urze]

Interesting that Sikorsky's new X2 design is a co-axial rotor design. They believe it should be able to fly faster than 250 kts, which is by far faster than any helicopter made so far.

 

http://www.geocities.com/tacticalstudiesgroup/piaseckivtdp.htm

A summary of push rotor Helicoptors - Most of them are not co-axial but very fast.

[Brute]

In case anyone is interested, here's a video of the crash that killed General Vorobyov in Ka-50:

 

http://www.avsimrus.com/files.phtml?action=viewonline&id=15117

 

babelfish translated:

On June 17, 1998 General Vorobyev carried out flight on the exercises of the course of combat training in the complex with the program of the mastery of new aviation equipment on NIR of " In-flight studies of the procedure of the fulfillment of the figures of the complex of [pilotazha]" and from " By the specific routine of the preparation of crew for the execution of demonstration flights on the helicopters KA -50" For the 30th minute of flight at the height of approximately 50 m and the speed is less than 60 km/h in the process of an intensive change in the bank to 116 and an energetic decrease with the large angle of dive occurred the collision of helicopter rotor blades it encountered with the earth, and pilot, without having had time to use recovery facilities, perished as it established the investigated catastrophe commission, the reason for incident became piloting helicopter beyond the limits of the provided by the management of flight operation limitations (they are allowed flights with the angles of bank to 70, the pitch angles to 60 and the angular velocities along all axes to 60 deg/s) in the fateful flight helicopter it dived almost vertically (more than 80). With such pitch angles became possible the cross-communication of system of course vertical along the channel of bank, as a result of which the indication of bank on the instrument IKP -81 spasmodically it changed to 180, which could disorient the pilot, who reflector sharply shifted cyclic-pitch stick this it led to an increase in the rate of descent to 30 m/s and the growth of total angular velocity, which in combination with the small forward velocity of helicopter and the position of right pedal on the support led to the collision of the blades of the carrier [vinta]." (material from the site of airwar.ru)

Edited December 12, 2008 by Brute

[tusler]

Not only do the blades flap but they also have lead and lag and if you have the upper and lower blades with upper drooping, lower flapping up and the lead and lag going wrong yes they could hit each other.

 

In the sim get up a little speed and do some violent:joystick: pitch changes with the cyclic and you will see.