correct as-is Flightmodel issues

[JG78_horΛz]

I'm not entirely sure if this is a bug, but I suspect it is based on my experiences with other helicopters in DCS.

1. When flying forward at relatively high speed, if you pull the joystick back just a little too much, the helicopter's nose will uncontrollably pitch up to such an extent that it requires a lot of effort to regain control. Besides that, performing such a maneuver can bring the helicopter to a halt so quickly that it seems very unrealistic to me. To test this, accelerate to full speed, pull the nose up sharply, and a cobra maneuver occurs, causing the aircraft to hover without changing altitude.

2. I often notice that while hovering, even with maximum rudder input, my helicopter is unable to maintain the desired direction. Only when transitioning back to forward flight does it become possible to maintain the direction again.

[admiki]

6 hours ago, JG78_horΛz said:

I'm not entirely sure if this is a bug, but I suspect it is based on my experiences with other helicopters in DCS.

1. When flying forward at relatively high speed, if you pull the joystick back just a little too much, the helicopter's nose will uncontrollably pitch up to such an extent that it requires a lot of effort to regain control. Besides that, performing such a maneuver can bring the helicopter to a halt so quickly that it seems very unrealistic to me. To test this, accelerate to full speed, pull the nose up sharply, and a cobra maneuver occurs, causing the aircraft to hover without changing altitude.

2. I often notice that while hovering, even with maximum rudder input, my helicopter is unable to maintain the desired direction. Only when transitioning back to forward flight does it become possible to maintain the direction again.

Neither is a bug.

#1 You are basically stalling it. @AeriaGloria is better at explaining it.

#2 you are running out of tail rotor power. It is not unknown. You are too heavy for conditions. In real life early Bell 206 helicopters were known to run out of pedal.

[T.Power]

Page 7 tells you all you need to know about Rotors, they are dangerous to fly, human error is the single biggest cause of rotor accidents, VRS is a real issue and there was at least one attempt to ban rotors completely at least in the US, circa 1950 IIRC.  I still run out of pedal flying the Hind for around 10 months, these things want to kill you.

https://www.h-a-c.ca/IHSS_Helicopter_Safety_History_05.pdf

You should try desaturating your joy axis if small movements cause you to stall so easily.

Edited June 15, 2024 by T.Power

[AeriaGloria]

13 hours ago, JG78_horΛz said:

I'm not entirely sure if this is a bug, but I suspect it is based on my experiences with other helicopters in DCS.

1. When flying forward at relatively high speed, if you pull the joystick back just a little too much, the helicopter's nose will uncontrollably pitch up to such an extent that it requires a lot of effort to regain control. Besides that, performing such a maneuver can bring the helicopter to a halt so quickly that it seems very unrealistic to me. To test this, accelerate to full speed, pull the nose up sharply, and a cobra maneuver occurs, causing the aircraft to hover without changing altitude.

2. I often notice that while hovering, even with maximum rudder input, my helicopter is unable to maintain the desired direction. Only when transitioning back to forward flight does it become possible to maintain the direction again.

1. This is a behavior known by the Russians as “Podkhvaht” or “pick up.” It is a blend of two things 

A. Mushing: this is what happens when a helicopter at high speed experiences high enough G load that AOA becomes positive, and up flow of air through the rotor causes it to stall, causing RBS like symptoms as you lose control and thrust 

B. The wing is installed at 19 degree angle. Not coincidentally, the wing also stalls at 19-20 degrees. This means almost any positive AOA will stall the wing. The wing is also quite a distance behind the rotor mast and center of gravity (CG), this means that the lift it creates (up to 25% in cruise) also causes a pitch down moment. It also means that any payload on the wing moves CG back, which increases AOA and thus wing lift. This is one reason that loading weight on the pylons has so little effect on it in cruise.

So when increase G load between 1.4-1.8 G, at some point the Angle of Attack will transition from above your nose to below, your rotor will get up flow and begins to stall and your wing is also stalling. 

The first part of the rotor to stall is the right side, causing a pitch up. The wing being behind the CG/rotor, is causing a lot of pitch down force with its almost 3,000 kg of lift. Now that it’s stalling, suddenly the force pitching the nose down goes away and makes the pitch up worse. 
 

So it’s a cascading intermeshing of issues, that all happen to be caused at around the same time. 
 

There are three ways to recover or prevent this happening! 
 

A. this always happens at a certain G-load, I will post the G chart, a good rule of thumb at medium weights and altitudes is don’t exceed 1.6-1.8 G. If in a level turn, this is around 50-55 degree bank 

B. Decrease collective pitch 1-3 degrees. This will un stall the rotor. You might be surprised how fast it can snap back after just 1-3 degrees less collective. 
 

C. Full stick forward! 
 

Also. If your are nearing the ground, decrease roll angle during recovery. The less your bank angle, the less altitude you lose while this happens 

Also. Manual recommends to increase G to desired load in a turn over the course of 2-3 seconds. This makes a big difference for me 

There is a real G chart for this, but has a huge margin of safety for speed. I usually ignore the speed restrictions, it will always happen at the same G, but the faster you are the more violent it will be. You can get a really good feel for this by doing 50-55 degree angle bank turns. In my experience, weight, altitude, and collective decide what your max G will be

There is dot in the G meter at 1.5 G, it is good reference for minimum G you can sustain at all altitudes below about 2,000m. I made my own color coded picture with yellow/red as danger zones 

Also: the effect of the entire podkhvaht/pick up was made smoother in a patch recently 

 

2. Your second issue, tail authority 

My first suggestion if you you are not overweight or at too high altitude, is watch your Yaw AP. 
 

Your AP can add/subtract anywhere from 18-118% authority, and trim you without your consent. Check if you have an option “Pedal auto move” on. You want to have it off. Turning it off means that if Yaw AP runs out of its 18% authority, it will trim your pedals to use as much authority as it needs. Having it on means that pedals will trim you anytime heading moves more then 7.5 degrees from the heading it’s trying to hold 

I tell most new flyers to keep Yaw AP off. And to only play with it once you are ready to play with the microswitch and all the microswitch options the change the Yaw AP from heading hold to dampening. If you are interested, let me know. I have also written large guides for weapons and autopilot and translated an aerodynamic manual for it. 

Edited June 16, 2024 by AeriaGloria

[admiki]

I am so happy we have AG, so I don't have to type all this c*ap.

[KoN]

I've encountered this violent pitch up at high speeds avoiding trees and ground fire . Thank you for the information very helpful. 

[JG78_horΛz]

Wow, thank you very much for the detailed explanation and the confidence that I can understand it, as this is not physics that you grasp in passing. Regarding your second point, I have to say that I don't use any autopilot at all, so that can't be the factor. What always surprises me is that I can maintain sometimes my first hover position well, and possibly not another one, It seems very random to me..  However, payload could be an issue, as the average DCS pilot naturally has to carry huge amounts of destructive load. For me, it usually comes down to 6 missiles and 2 Stingers. Additionally, I usually only have 50% fuel with me.

[JetCat]

Can this maneuver be done without a complete main rotor overhaul afterwards? Or is the Hind build to withstand such forces?

Edited June 29, 2024 by JetCat

[AeriaGloria]

3 hours ago, JetCat said:

Can this maneuver be done without a complete main rotor overhaul afterwards? Or is the Hind build to withstand such forces?

 

You mean exceeding the G limit and going full into Podkhvaht/pick up /mushing? I would assume some things sensitive are not built for more then 2.7 G. IRL it was said that this behavior sometimes led to tail chopping from the rotor. But the pilot could prevent this as long as they didn’t lower collective too much and pull back 

4 hours ago, JG78_horΛz said:

Wow, thank you very much for the detailed explanation and the confidence that I can understand it, as this is not physics that you grasp in passing. Regarding your second point, I have to say that I don't use any autopilot at all, so that can't be the factor. What always surprises me is that I can maintain sometimes my first hover position well, and possibly not another one, It seems very random to me..  However, payload could be an issue, as the average DCS pilot naturally has to carry huge amounts of destructive load. For me, it usually comes down to 6 missiles and 2 Stingers. Additionally, I usually only have 50% fuel with me.

I see. You manually never turn on AP? If you use auto start it’s on by default. With that fuel and weapons load you are usually under max takeoff weight under 1,000m at all times. 

Move collective slowly, 1-2 degrees per second. Remember your rotor cannot only have VRS, but your tail rotor can VRS if you fly right more then 18 kmh (you can see this on the hover gauge). 

At that weight and below 1,000m alt, it takes around 8-10 degrees of collective to hover. You can also turn off the pedal dampening which uses a hydraulic unit to slow down pedals to a max speed of 3 seconds to reach full deflection from center. So anytime you move axis more then 33% a second it will slow down your input, and you can see this happening with yellow caution light below gyro vertical lights when pedals are moved too fast. You can turn this off with a red guarded switch on lower left instrument panel, beteeen collective gauge and rotor rpm gauge, 

I only ever hit max collective in a hover when out of ground effect or severely over weight. Remember that you don’t gain any thrust between 88-92% rpm. Your governor holds your rotor rpm at 95%, and your tail rotor is tied to this. If your rotor rpm decreases, so does your tail rotor authority, 

I think the more you practice being smooth and getting in and out of ETL and ground effect easily, you will figure out 

I worked on the G load chart I made to make it less conservative and more accurate 

Edited June 29, 2024 by AeriaGloria

[JG78_horΛz]

Thank you for the quick response. I wasn't aware that even the tail rotor is affected by VRS. I can easily imagine that I became too hasty and consequently too impatient for the RPM to normalize. I probably fly the Mi-24 too boldly. I will continue testing and appreciate your thoughts on this topic.

[AeriaGloria]

1 hour ago, JG78_horΛz said:

Thank you for the quick response. I wasn't aware that even the tail rotor is affected by VRS. I can easily imagine that I became too hasty and consequently too impatient for the RPM to normalize. I probably fly the Mi-24 too boldly. I will continue testing and appreciate your thoughts on this topic.

Glad to help. The engine will take 8-9 seconds to accelerate after being in low collective/high rotor rpm. 140 kmh is the speed where the lowest collective will keep you flying. So any speed below that will require an increase in collective. If slowing down for typical landing, I usually start adding power back in around 100 kmh. If you don’t see the shaking for ETL, as long as nose is within +/-7 degrees pitch your hover gauge will come online as soon as you pass 50 kmh ground speed. If you aren’t increasing power for over once you’re below that, it’s probably already too late. 
 

Im sure you’ll get use to the pattern of slow down and pitch up to slow speed, colllective low and using longitudinal cyclic to keep low descent rate. Seeing the high rotor rpm and low engine rpm, then as you add collective you can see that your engines will barely increase power until your rpm slows down to 95% or less. Then once rotor rpm is below 95% the engines will start jumping, and once they hit 90% you don’t need to worry much. 
 

Taking off and landing into the wind is a huge help, sometimes the wind is enough to weathervane you or even VRS the tail if fast enough. 
 

On the autopilots, some like them some don’t. I love it after I learned that you set the attitude hold with trim button. But different strokes for different folks. When you hover btw, your nose will be about 2-5 degrees up, usually 3.5 degrees in no wind and neutral CG. If in doubt, put your nose there. Luckily with its tilted transmission, you don’t ever need to worry about balancing tail rotor thrust like other helicopters. 
 

Doing running landings/takeoff slower and slower is also awesome practice