The AH-64 Apache Thread

[Nightmare515]

hi Nightmare, i have some question:

what's going to happen with the rotor blades when the pilot do a high G (too high) maneuver ? is it posible to overstress the airframe or mainly the rotor blades ?

and what's going to happen at overspeeding the chopper ? loosing lift on the left side or damaging/breaking the rotorhub or blades ? how the overspeeding starts ? shaking the blades and the airframe or starts to lose the control of the helo ?

how the tailplane works ? will it help to pull up the nose at high speed ? i mean will it work like an elevator on a conventional airplane ? - (iv never seen the trailing edge of the tailplane in higher position)

thank you for you answers

 

When you look at the videos of the helicopters doing barrel rolls and other high G maneuvers pay attention to the rotor system. You will notice the blades are "coning". The blades are getting stressed almost to the limit and theoretically they can literally rip off of the rotor hub if they cone too much. It's mainly the rotor system that will be stressed.

 

When the helicopter goes past its max speed, called Vne (Velocity Never Exceed) we run into what is called Retreating Blade Stall. The rotor blades can flap up and down to equalize the lift throughout the rotor disk. At some point the blades on the left side simply cannot flap enough to equalize the lift of the right side so the system will stall.

 

A physics phenomena known as Gyroscopic Precession means that in regards to a rotating disk any input made on the disk will actually be applied 45 degrees after the input is made. Sort of like when you take a bike tire and spin it on your hand and try to tilt it to the right you notice it actually tilts forward. So whenever the helicopter rotor system stalls the right side (which has more lift) produces that lift but that lift is applied 45 degrees later so it lifts the front of the rotor system up. So when you exceed the helicopters max airspeed it causes the aircraft to pitch up and roll left.

 

When getting into retreating blade stall the best thing to do is to slow down immediately so that the rotor system can equalize its lift again. This phenomena is the reason why helicopters are limited so such slow airspeeds when compared to fixed wing aircraft.

 

Shaking may be experienced when entering retreating blade stall but it usually happens so fast that there is often very little notice. I'm not sure if any helicopter can actually exceed their Vne while cruising at max power in level flight. I'm sure if there was a massive tail wind they probably could. The only way for the AH-64 to exceed its Vne under normal conditions would be in a dive.

 

BTW those 2.2G limits are arbitrary. The 64 can pull maneuvers higher than that its more of a "don't do this all the time you might break something eventually" limit.

Hope this helps!

Edited May 29, 2014 by Nightmare515

[hypersonik]

 

When the helicopter goes past its max speed, called Vne (Velocity Never Exceed) we run into what is called Retreating Blade Stall. The rotor blades can flap up and down to equalize the lift throughout the rotor disk. At some point the blades on the left side simply cannot flap enough to equalize the lift of the right side so the system will stall.

 

A physics phenomena known as Gyroscopic Precession means that in regards to a rotating disk any input made on the disk will actually be applied 45 degrees after the input is made. Sort of like when you take a bike tire and spin it on your hand and try to tilt it to the right you notice it actually tilts forward. So whenever the helicopter rotor system stalls the right side (which has more lift) produces that lift but that lift is applied 45 degrees later so it lifts the front of the rotor system up. So when you exceed the helicopters max airspeed it causes the aircraft to pitch up and roll left.

 

When getting into retreating blade stall the best thing to do is to slow down immediately so that the rotor system can equalize its lift again. This phenomena is the reason why helicopters are limited so such slow airspeeds when compared to fixed wing aircraft.

 

 

 

Interesting, I wonder if this also happens on the KA-50 due to its rotor Set up .

 

if anyone Pulls it off let us know. :)

[Flagrum]

Interesting, I wonder if this also happens on the KA-50 due to its rotor Set up .

 

if anyone Pulls it off let us know. :)

The effects of retreating blade stall are not so pronounced. The two rotors rotate in opposite directions and thus the effect for the upper and the lower rotor cancel eachother almost out. The effect is noticable as the upper rotor generates more lift than the lower and thus suffers more from retreating blade effect - but it is not as violently as in the Apache (at least, not as violently as it sounds here :o).

 

An other factor in the Ka-50 is the dissymetry of lift that causes the side with the forward moving blades generate more lift and thus the blades bend upwards - up to the point the lower rotor disc intersects with the upper. With as fatal results as you can imagine. :o) This is the more relevant factor for co-axial helos in regards to Vne.

Edited May 29, 2014 by Flagrum

[hypersonik]

The effects of retreating blade stall are not so pronounced. The two rotors rotate in opposite directions and thus the effect for the upper and the lower rotor cancel eachother almost out. The effect is noticable as the upper rotor generates more lift than the lower and thus suffers more from retreating blade effect - but it is not as violently as in the Apache (at least, not as violently as it sounds here :o).

 

An other factor in the Ka-50 is the dissymetry of lift that causes the side with the forward moving blades generate more lift and thus the blades bend upwards - up to the point the lower rotor disc intersects with the upper. With as fatal results as you can imagine. :o) This is the more relevant factor for co-axial helos in regards to Vne.

 

ty +1

[Nightmare515]

Just a correction to what I said about Gyroscopic precesion. The action happens 90 degrees after the input is made not 45 degrees. I was halfway busy multitasking when I wrote that and wasn't paying attention.

[Nightmare515]

The effects of retreating blade stall are not so pronounced. The two rotors rotate in opposite directions and thus the effect for the upper and the lower rotor cancel eachother almost out. The effect is noticable as the upper rotor generates more lift than the lower and thus suffers more from retreating blade effect - but it is not as violently as in the Apache (at least, not as violently as it sounds here :o).

 

An other factor in the Ka-50 is the dissymetry of lift that causes the side with the forward moving blades generate more lift and thus the blades bend upwards - up to the point the lower rotor disc intersects with the upper. With as fatal results as you can imagine. :o) This is the more relevant factor for co-axial helos in regards to Vne.

 

So would the Vne limiting factor of the KA-50 be due to the limited amount of blade flapping that can occur to compensate for disymmetry of lift because of the close proximity of the blades to one another?

 

Since the rotor disks spin opposite each other then retreating blade stall should still occur simultaneously on both disks but on opposite sides of each disk right?

 

So they cancel each other out like you said. Why does the upper rotor disk generate more lift than the lower? Shouldn't they produce equal lift on opposite sides of the disk?

[ENO]

Wonder if it has something to do with different pressure between the blades? Be interested in knowing how the bottom blade handles the down wash from the upper one... what that does to pressures in terms of speed of air over the blades from the bottom to the top.

 

I'm spitballing but it must have something to do with it?

Edited May 30, 2014 by ENO

[Flagrum]

So would the Vne limiting factor of the KA-50 be due to the limited amount of blade flapping that can occur to compensate for disymmetry of lift because of the close proximity of the blades to one another?

 

Since the rotor disks spin opposite each other then retreating blade stall should still occur simultaneously on both disks but on opposite sides of each disk right?

 

So they cancel each other out like you said. Why does the upper rotor disk generate more lift than the lower? Shouldn't they produce equal lift on opposite sides of the disk?

Yes, while the forward spinning side of the rotor disc bends upwards, the other side remains horizontal (no coning due to retr. blade stall). So while the right side of the lower rotor disc bends up, the right side of the upper remains horizontal.

 

Regarding lift produced by the upper and lower rotor: as far as I understood it, the downwash of the upper rotor reduces the performance of the lower one.

[Nightmare515]

Yes, while the forward spinning side of the rotor disc bends upwards, the other side remains horizontal (no coning due to retr. blade stall). So while the right side of the lower rotor disc bends up, the right side of the upper remains horizontal.

 

Regarding lift produced by the upper and lower rotor: as far as I understood it, the downwash of the upper rotor reduces the performance of the lower one.

 

Very interesting. thank you.

[Sceptre]

When paying DCS: Huey, you can rip the rotor blades right out of the mast if you pull too many Gs.

[FoxHoundELite]

https://www.facebook.com/photo.php?v=741990752519230

 

men that's brilliant and so professional

[hypersonik]

lol :thumbup: It gets the job done and spirits high.

[FoxHoundELite]

yeah XD

[NRG-Vampire]

https://www.facebook.com/photo.php?v=741990752519230

 

men that's brilliant and so professional

 

yeah, cool apache porn :rotflmao:

 

 

So when you exceed the helicopters max airspeed it causes the aircraft to pitch up and roll left.

 

great and thank you for the detailed explanation, but if the VNE cause a pitch up then will the rotorcraft automatically slow down and come out from the retreating blade stall ?

so reaching VNE will not cause a deadly event, mainly if the pilot react well ?

 

in many videos we can see that the tailplane/stabilizator is horizontal at a high speed flight and in diagonal position when the chopper is hovering, so is the tailplane always "go after" the AOA and the rotor downwash keeping the helo more stable in the air or is the tailplane able to "steer" as well ?

thank you :thumbup:

Edited May 30, 2014 by NRG-Vampire

[Nightmare515]

yeah, cool apache porn :rotflmao:

 

 

 

 

great and thank you for the detailed explanation, but if the VNE cause a pitch up then will the rotorcraft automatically slow down and come out from the retreating blade stall ?

so reaching VNE will not cause a deadly event, mainly if the pilot react well ?

 

in many videos we can see that the tailplane/stabilizator is horizontal at a high speed flight and in diagonal position when the chopper is hovering, so is the tailplane always "go after" the AOA and the rotor downwash keeping the helo more stable in the air or is the tailplane able to "steer" as well ?

thank you :thumbup:

 

The problem is that the helicopter pitches and rolls left almost instantaneously. So yes it will slow down technically but you will also likely be in an extreme left dive if not inverted. The lift produced by the right side is so great that without the left side being able to compensate it has the force to flip the aircraft over.

 

We are taught to slow down the second you even think you are encountering retreating blade stall. Usually by the time it actually happens it is too late to do anything about it. I don't personally know of anyone who has recovered the aircraft from it once it has pitched up and rolled left. I have heard plenty of stories of people who have unfortunately died from it. Since the only real way to get into it is to be in a pretty steep dive you must think of the flight profile at the time. The aircraft is already in a steep dive now imagine being in a steep dive then getting flipped upside down then trying to flip right side up and pull up at those high airspeeds without destroying the aircraft. Helos aren't nearly as maneuverable as jets in that aspect.

 

I think you may be thinking that the pitch up and roll happens slowly, however, it does not. It happens almost as fast as a fighter jet doing a barrel roll.

 

The stabilator (tailplane) in the 64 adjusts itself automatically according to the aircraft speed. We can manually control it as well if we need to do so for certain situations. You are correct that in level flight it tends to be horizontal while at a hover it is tilted at an angle. It's not used for steering it's used to help with climbs and dives.

[Nightmare515]

https://www.facebook.com/photo.php?v=741990752519230

 

men that's brilliant and so professional

 

haha thats hilarious. If only we had hidden cameras with us everywhere overseas I'm pretty sure the general public would honestly believe we had lost our minds.

 

I can't count the number of times I have walked into the tent and seen the most outrageous of things and simply shook my head and walked out lol.

 

Like they say, war is 99% boring and 1% sheer terror. Gotta do something to keep from being bored lol.

[CobaltDragon]

Nightmare515, do you use this name on the Bohemia Interactive forums? I think I have seen u there too :)

[Nightmare515]

Nightmare515, do you use this name on the Bohemia Interactive forums? I think I have seen u there too :)

 

No I'm not a part of those forums.

 

Internet is getting more and more crowded, I've used this same name for over 15 years and that's the first time I've heard of anyone else with it lol.

[Nightmare515]

So once again the weather has decided to come in and I didn't get to fly today :/

 

I flew around last night practicing flying at night without the use of my HMD (the symbology in your eye). Its amazing how much we rely on that thing and how weird it feels to fly without it in your eye. I almost forgot that I knew how to fly a helicopter without all of the fancy gadgets. Interesting to say the least...

[topol-m]

Seeing how there are people in here who know the apache in details, I'll take the opportunity and ask some questions:

So I've found this data about the TADS: TV (127x mag), Thermal Imaging (36x mag), Direct view optics (18x mag). Does the MTADS have an improved magnification level? These are just numbers but how would they translate in a real life situation? Say we have near perfect conditions (flat surface, no camo used, no fog, etc.)

1. At what distance can you spot a tank-sized vehicle?

2. At what distance can you tell it's an abrams and not a challenger II for instance?

[Nightmare515]

Seeing how there are people in here who know the apache in details, I'll take the opportunity and ask some questions:

So I've found this data about the TADS: TV (127x mag), Thermal Imaging (36x mag), Direct view optics (18x mag). Does the MTADS have an improved magnification level? These are just numbers but how would they translate in a real life situation? Say we have near perfect conditions (flat surface, no camo used, no fog, etc.)

1. At what distance can you spot a tank-sized vehicle?

2. At what distance can you tell it's an abrams and not a challenger II for instance?

 

I don't remember the exact resolution numbers for the MTADS I believe it's something like the equivalent of a 900p HDTV. It's very clear the images you see on youtube from gun cams and whatnot don't really do it justice.

 

As far as spotting a tank I can't really give you a precise distance to where you'd be able to identify it. I've seen objects with great clarity at 3000m. I've only shot at training targets but I am sure you'd be able to positively ID a vehicle at that distance and probably from even greater distances.

 

With the zoom capabilities of the MTADS you can literally see people's facial expressions from great distances. Again can't give you precise numbers as I wasn't really paying attention I was just casually looking around.

 

Ill try to pay attention to the actual ranges the next time Im scanning around for things while flying and see if I can get some better numbers and estimates for you.

[topol-m]

@Nightmare515

Thanks, appreciate it! It's awesome to have a real apache pilot posting on these forums!

[Nightmare515]

@Nightmare515

Thanks, appreciate it! It's awesome to have a real apache pilot posting on these forums!

 

Thanks!

 

I flew tonight and did some more scanning around. I was able to clearly ID what type of cars were driving down the road at about 3500m. Part of this is because I "know" what an F-150 looks like so my brain sort of puts the pieces together but I could still easily tell it was a full sized pickup. We are trained to do the same thing with military vehicles.

 

We go through quite a bit of vehicle identification training to ensure we know what various types of vehicles look like both friend and foe. Due to the training we are able to figure out what things are even if the picture isn't crystal clear. I have an edge in that aspect because I was a tanker before this and we had to do the same things in that field.

 

I can say this. In the Abrams I could identify targets at 4000m under the FLIR. The Apache MTADS is a much better FLIR system than whats in the Abrams so I'm sure I could ID things from much farther. I was trying to look around and find more stuff but its late Friday night and there was literally like 1 car on the road my entire flight. Everyone had already made it to their respected parties or other beer drinking spots by the time we got in the air lol.

 

Hope this helps.

[topol-m]

It surely does, thanks for the info. If you're able to identify targets at such distance (pretty impressive btw) with the abrams no doubt the apache would top that. Also am I right to assume that given the higher magnification the TV imaging has it would be possible to identify targets at much longer distances daytime compared to using FLIR night time?

[Nightmare515]

It surely does, thanks for the info. If you're able to identify targets at such distance (pretty impressive btw) with the abrams no doubt the apache would top that. Also am I right to assume that given the higher magnification the TV imaging has it would be possible to identify targets at much longer distances daytime compared to using FLIR night time?

 

In theory yes and no.

 

In reality most people use the FLIR both day and night. Images tend to look "weird" when you start zooming in too much. Kind of like taking a set a nice binoculars and looking at license plates down the road. Yes you can see them but it doesn't look the same as if you were standing right behind the car looking at it with your naked eye.

 

FLIR is just easier, things glow and stick out. In the Abrams the only time I ever used the day sight was to try and verify what I was looking at in case I couldnt quite tell in the FLIR.

 

The next time you are on an airplane and coming in for landing just take a moment and look out of the window and look around outside. Now try to imagine finding a person or a vehicle out there among all of that other stuff with a pair of binoculars. It would be very hard, but if everything man made started glowing then it would be easier.