need track replay AH-64 Stalls when I pull back to 9 kts and level out the aircraft?

[AngryViper.101]

Hi

I have started to learn the AH-64
However, I recently came across the follow problem.

When I am flying, say 140knts at an altitude of around 800feet, collective set to +- 78%

 

Copilot seems to think I am experiencing a retreating blade stall, is this leading me in the right direction?

next time I will reduce the engine power to 80% and see if that keeps the altitude?

 

The phenomenon you’re experiencing is likely due to a condition known as retreating blade stall¹. This occurs when the helicopter’s forward speed decreases to zero, causing the retreating blade to stall¹.

In forward flight, the advancing blade (the one moving into the wind) generates more lift than the retreating blade (the one moving away from the wind). This is due to the combined speed of the helicopter and the rotational speed of the blade. However, when the helicopter slows down to 0 kts, the retreating blade’s relative wind speed decreases, reducing its lift¹.

At the same time, the angle of attack on the retreating blade increases to compensate for the loss of lift. If the angle of attack exceeds the critical angle, the retreating blade stalls¹. This can cause the helicopter to start falling and shaking, as you’ve experienced.

To recover from a retreating blade stall, you would typically need to reduce power, which decreases the angle of attack on the retreating blade and helps it regain lift¹. It’s important to note that this is a complex aerodynamic phenomenon and can be influenced by various factors, including altitude, temperature, and the helicopter’s weight¹.

[scoobie]

I think you're not making yourself clear. The title says "when I pull back to 9 kts", the post says "when I'm flying 140 kts". Is it 9 or 140 then?
The quotes you pasted below your post are - most of them - just wrong. Retreating blade stall is not when you approach 0 KIAS, but when going very fast.
So at 9 KIAS - no. At 140 KIAS... I don't know (sorry), still haven't got down to Apache properly, but it doesn't sound too fast for the Apache. Check VNE on one of those MPD pages if it happens again (provided that the page on MPD is implemented). If you're above VNE - yes, could be retreating blade stall.
But maybe what you're talking about is this... how do they call it... this "hard pull" manouver to go from fast cruise to a hover as quickly as you can? If so, it may be what they call "settling with power" and you just THINK it is stall. Or maybe you slow down below ETL incidentally having too high vertical velocity (downwards) and just enter VRS?
Hard to say what exactly you're doing.

[Floyd1212]

Yeah, I'm not sure Copilot is doing you any favors with that description.  Try Googling the terms "settling with power" and "vortex ring state" that scoobie mentions above, and read up on those subjects from reputable sources.

Also, don't ever reduce the engine power back from the FLY position (all the way forward).  You can manipulate the collective as needed to fly the helo how you want, but leave the power levers alone.

[AngryViper.101]

okay, i will send a track or next time try and summarise this more clearly ...

[Tom P]

OP Have you done anything prior to learning how to fly the 64? I.e watch BradMicks Flight lessons? Or are you jumping in treating it like a fixed wing and just doing fast control inputs?
How are you going 140kts at 78%? And are you going from 140kts rapidly down to 9kts by pulling back on the stick? Because that would be a bad time.
I attached Brad's youtube playlist in my post. I would suggest watching it, as he was a real life Apache instructor. 

 

[Yurgon]

12 hours ago, AngryViper.101 said:

Copilot seems to think I am experiencing a retreating blade stall, is this leading me in the right direction?

Who or what is "Copilot"? Some fancy language model AI thing?

Because man is that one horribly wrong explanation that you posted there. As was said before, retreating blade stall is a phenomenon that can happen when the helicopter is flying very fast in any direction (realistically that only happens in forward flight, but as far as retreating blade stall is concerned, the helicopter could just as well be flying sideways or backwards).

Just to be absolutely clear:

Quote

The phenomenon you’re experiencing is likely due to a condition known as retreating blade stall. This occurs when the helicopter’s forward speed decreases to zero, causing the retreating blade to stall.

No, just no. This is 100% wrong. Retreating blade stall occurs when the helicopter's speed in any direction is so high that in order to compensate for the advancing blade's lift, the retreating blade must increase its angle of attack beyond the critical angle of attack and, in turns, stalls. As far as I know, the outcome of retreating blade stall would be a very severe rolling tendency plus a very severe pitch-up tendency that can easily get the helicopter out of control and get everyone on board killed. The corrective action when a retreating blade stall is even just suspected is to reduce collective, and then reduce airspeed.

The text you posted includes a link to StackExchange, and it looks like the answers given there are 100% spot-on, so it's even more baffling that anyone, or anything, would refer to that and then write the exact opposite of what happens in a retreating blade stall scenario.

In any case, a video or a track of your attempt would be very welcome, as that allows us to take a look at what's actually happening.

Edited March 15, 2024 by Yurgon

[Floyd1212]

3 hours ago, Yurgon said:

Who or what is "Copilot"? Some fancy language model AI thing?

Yes.

[AngryViper.101]

Thank you for all the advice.

I have since changed my Curvature to 35 + and dead-zone on my stick to 5

This has helped and I have to trim and trim and trim, so still learning that a normal stick jumps to center and on the helo you want to force trim to keep the trim position of the cyclic, this has helped me a lot.

Landing is another thing I must perfect, can do it now, but it takes me several minutes to put the Apache softly and safely on the ground.

Whenever I charge in too fast reducing collective I end up in a horrible situation.

[shagrat]

vor 23 Stunden schrieb AngryViper.101:

Landing is another thing I must perfect, can do it now, but it takes me several minutes to put the Apache softly and safely on the ground.

Whenever I charge in too fast reducing collective I end up in a horrible situation.

That's why you regularly see real world AH-64D approaching a landing deliberately and gradually slowing down, gently transition to a hover in ground effect and carefully putting it down, instead of gung-ho it and risk a crash.

Keep in mind this is a flying tank, not an OH-6 Little Bird.

[Yurgon]

1 hour ago, shagrat said:

instead of gung-ho it and risk a crash

To which this pilot very famously said "Hold my beer!"...

 

[shagrat]

vor 55 Minuten schrieb Yurgon:

To which this pilot very famously said "Hold my beer!"...

 

...and crashed!

I wanted to point out, that you see Apache pilots, usually landing slowly and carefully, as the AH-64D is a tad bit on the heavier side.

Examples:

FARP landing in Afghanistan, Kumar province

 

and a landing on a gras field for an event

 

 

 

Edited March 17, 2024 by shagrat

[krazyj]

and its probably a move he can pull when hes at sea level but in high alt not so much. 

Anyways, to OP I think you need to go through the training missions, they are good and explain things for you. 

and `i  dont know where on earth you found that absolutely horribly wrong description on retreating blade stall, sounds like something one of the influencers on tik tok would come up with. 

Have you flown other helicopters in MSFS,XP or DCS before ? 

[JetCat]

I have noticed this effect too, it kinda feels like the rear area of the main rotor disk stalling, but it is the vortex ring state effect because the helicopter begins to sink rapidly when loosing forward speed and becoming slower than 20 knots or so.

Most of the time I forget to look at the variometer but fully focus on getting it into stable hoover, and it feels like a rear area rotor disk stall yes.

[bradmick]

On 3/17/2024 at 11:33 AM, shagrat said:

...and crashed!

I wanted to point out, that you see Apache pilots, usually landing slowly and carefully, as the AH-64D is a tad bit on the heavier side.

Examples:

FARP landing in Afghanistan, Kumar province

 

and a landing on a gras field for an event

 

 

 

 

Typically when the public is in view, yeah, that's true. But your overall impression would be incorrect. We fly stabilized but fairly quick approaches, they keep you out of the dead man's curve, and provided you've done your pre-landing performance evaluation, you will have the power to arrest the descent. It's not uncommon to hold say, 40 knots and 500fpm for the approach and then do a decel, pull in the power required to arrest the descent and stop solidly IGE. When the publics around, we are extra well behaved, to many eyes and to high profile to be doing anything else.

[BigBorner]

On 3/17/2024 at 4:33 PM, shagrat said:

...and crashed!

I wanted to point out, that you see Apache pilots, usually landing slowly and carefully, as the AH-64D is a tad bit on the heavier side.

Examples:

FARP landing in Afghanistan, Kumar province

 

and a landing on a gras field for an event

 

 

 

 

I dont think the Pilot kissing the Snow wanted to land. I guess he wanted to do this: 

 

[LuseKofte]

On 5/30/2024 at 9:38 PM, JetCat said:

vortex ring state

I read and heard a lot of pilot interviews 

Vortex Ring state is not much mentioned by chopper pilots   
I think this problem is very high in DCS, and might be very correct modeled for all I know. 
I have not read or seen any accidents in real life where this phenomenon has been mentioned. 
However when you fly in a game, one tend to push the envelope to the very end , and I think vortex R has taken more virtual life’s than enemy fire

[bradmick]

1 hour ago, LuseKofte said:

I read and heard a lot of pilot interviews 

Vortex Ring state is not much mentioned by chopper pilots   
I think this problem is very high in DCS, and might be very correct modeled for all I know. 
I have not read or seen any accidents in real life where this phenomenon has been mentioned. 
However when you fly in a game, one tend to push the envelope to the very end , and I think vortex R has taken more virtual life’s than enemy fire

It’s not talked about because it doesn’t happen. VRS in DCS is as far from reality as you can get. The accidents don’t happen because VRS isn’t this omnipresent boogeyman that “just happens” because some magical parameters have been met. 

[shagrat]

vor 3 Stunden schrieb BigBorner:

I dont think the Pilot kissing the Snow wanted to land. I guess he wanted to do this: 

 

I don't think he wanted to land, either. There's a bit of conversation before this post, that's required for context.

Edited June 5, 2024 by shagrat

[Smashy]

On 6/5/2024 at 6:30 AM, bradmick said:

It’s not talked about because it doesn’t happen. VRS in DCS is as far from reality as you can get. The accidents don’t happen because VRS isn’t this omnipresent boogeyman that “just happens” because some magical parameters have been met. 

Any idea if ED is using your feedback to tweak and improve the flight model?

[admiki]

#twoweeks

[Thundersmoke]

OP, it'll take some practice, and definitely defer to Bradmick and other SMEs, but efficient approaches are possible once you get a handle on the flight characteristics.

The general sequence I follow is:

• From cruise speed at low-ish altitude
• Simultaneously decrease collective and pitch up to begin bleeding airspeed
• Manage the collective decrease and pitch up to keep your vertical velocity indicator roughly neutral (you don't want to be climbing or dropping quickly)
• As you get below Effective Translational Lift (ETL) at about 30 knots, you're going to lose a lot of lift.  If you have a haptic seat pad or force feedback, you'll get some buffeting feedback and you'll feel this transition.
• As soon as you feel it or slow below 30 knots, gently pull in more collective to compensate, and begin to lower the nose.  Again, strive to keep the vertical velocity indicator neutral.
• Most times, you'll be wanting to arrive at a hover in ground effect (IGE) at 50' or less.  This will help cushion you.
• As you progress through the different stages, don't forget to be trimming.
• Once trimmed into a hover, you can either slowly set it down manually, or go into hold modes and then slowwwly lower collective from there.

Again, defer to the SME videos and practice, practice, practice.  Your right eyeball should basically be pinned to the VVI to manage your vertical velocity throughout this maneuver, at least until you have the feel and muscle memory down.  As you get better with it, you'll be able to adjust the inputs to modulate altitude in loop with all the rest of the activities.  Just remember, below ETL velocity, you don't want more than -300 ft / minute on the VVI.  There be dragons.

I spent an afternoon on a single player map, taking off from a FARP pad, flying around the airbase a bit, and coming back for a landing.  Over and over and over.  It was well worth the time.

Edited June 9, 2024 by Thundersmoke

[ShuRugal]

On 3/17/2024 at 10:59 AM, Yurgon said:

To which this pilot very famously said "Hold my beer!"...

 

To be fair, this one was specifically an over-torque event.  there wasn't enough power available to pull out of that dive at the height the pilot held it to.  If i recall correctly from when this happened, the pilot and CPG both faced administrative punishment for this one.