Flight Dynamics Feedback From Real Helicopter Pilots

[RUBIX 10]

I am going to try and cover my thoughts on the flight dynamics of the community preview, and give as much constructive criticism as possible. I am looking for this thread to become a common place for real life pilots to give their feedback and discuss with each other about their ideas and ways to improve the flight dynamics.

Here is a small list of things that I have been focusing on to get things started:

1) Torque and pedal control – The torque of the engine on the airframe seems to be reproduced in the simulator very well (maybe a little under simulated if anything), I can feel the forces on the helicopter as I change the collective position. Maybe I can get some feedback from other pilots about the amount of change in the torque from full down collective to full up collective. It will be interesting to get your opinions. As for the pedals, I feel good about having the pedals neutral at ‘light on the skids’ with low gross weight, because the neutral position is really a matter of how the mechanic and pilot want to set up the Push Pull Tubes and Rod Ends (The helicopter I currently fly is near neutral with low gross weight at ‘light on the skids’) (http://www.robinsonheli.com/srvclib/r44sb43a.pdf) This link shows the connection of the Push Pull Tube and Rod End with the Bellcrank...Changing this changes the tail rotor pitch at the neutral pedal position. The pedal authority is very limited however. Full pedal deflection does not represent itself with an out of control spin….especially in the right yaw direction. Hopefully the community could give some advice on how to make this more realistic.

2) Ground Effect – This is one of my favorite parts about the flight dynamics at the moment. The ground effect feels realistic and is represented very well. If I am landing on top of a building, I can feel the helicopter benefit from ground effect after entering a hover above the roof. And when I leave the roof I can feel the ground effect diminish, requiring more power to stay at altitude.

3) Strange roll associated with collective position – I am not sure about the reasoning behind the roll of the helicopter relating to the collective position. As you increase the collective the helicopter rolls right, and as you decrease the collective, the helicopter rolls left. When practicing autorotations in real life, the steps are not: Lower Collective, Right Cyclic, Aft Cyclic, Right Pedal. If someone knows something about this roll or is also curious about it, I would like to know your thoughts.

Edited July 25, 2011 by RUBIX
Edited for length & to add link

[nightsta1ker 10]

Before I make any further comments about this game's development I need to download and try the latest update as I believe significant changes have been made to the flight dynamics. Once I have done this I will post my thoughts under this thread. Unfortunately I don't have time to do this right now, but I will get to it possibly next week. I am overextended, preparing for my CFIH tests, flying a small contract tomorrow, and also have been alpha testing an R22 Beta II for X-Plane. The good news is, I am up to my ears in current flying and sim flying experience and so I will be very sensitive to inaccuracies.

I also plan on describing basic helicopter flight dynamics and principles for the benefit of those that know little of how a helicopter should behave.

More later. And thanks RUBIX! I would also like to encourage other pilots to post their commentary HERE so that we have a central place for pilot feedback.

[FredAirland 14]

I can vouch for nightstalker as an excellent beta tester, he did the test for Helicopter Total Realism MD500 and other models and provided excellent feedback!

(HTR is a free addon for FSX you can find at www.hovercontrol.com)

Fred

[nightsta1ker 10]

I can vouch for nightstalker as an excellent beta tester, he did the test for Helicopter Total Realism MD500 and other models and provided excellent feedback!

(HTR is a free addon for FSX you can find at www.hovercontrol.com)

Fred

Thanks Fred!

[EagleEye-GER- 0]

I can vouch for nightstalker as an excellent beta tester, he did the test for Helicopter Total Realism MD500 and other models and provided excellent feedback!

(HTR is a free addon for FSX you can find at www.hovercontrol.com)

Fred

Ah Fred, more and more helo-heads come to this forum...:ok::)

[nightsta1ker 10]

Just thought I would share: Just got a 90% on my CFI Helicopter Knowledge exam. Now with both knowledge exams out of the way, all I need is a few more hours of test prep before the checkride and I will be a certified helicopter instructor.

[RUBIX 10]

Pertaining to the thread topic, I have a theory about my third point...I hope a dev can comment on this...I believe that they are trying to use the roll associated with collective position as a way to demonstrate Dissymmetry of Lift. This would be an incorrect implementation; Dissymmetry of Lift would result from airspeed and not collective position, and it wouldn't induce a right roll as nightsta1ker says below.

Let me know your thoughts.

On a side note: Congratulations nightsta1ker

Just thought I would share: Just got a 90% on my CFI Helicopter Knowledge exam. Now with both knowledge exams out of the way, all I need is a few more hours of test prep before the checkride and I will be a certified helicopter instructor.

Edited July 26, 2011 by RUBIX

[nightsta1ker 10]

I beleive that right roll in the hover is an attempt at modeling translating tendency, however, it is way too extreme and does not seem to dissipate with forward airspeed as it should.

On Dissymmetry of lift.

As I have mentioned in another thread, dissymmetry of lift is caused by the forward airspeed of the aircraft adding airspeed to the advancing side of the rotor disc and subtracting airspeed from the retreating side of the disc. If nothing were done mechanically to solve this issue then helicopters would be limited to stationary hovering. Lucky for us Juan de la Cierva found the solution: Flapping hinges. Allowing the additional lift from additional airspeed on the advancing side to flap the blade up, and then down on the retreating side. This changes the Angle of Attack of the blade so that the rising advancing blade is creating LESS lift, and the retreating blade is creating MORE lift, despite the significant difference in airspeed. The end result is the lift vector is balanced on both sides of the disc. Ergo: No rolling moment in forward flight. At least, until you get the helicopter up to an airspeed where the flapping hinge can no longer compensate for the difference in airspeed, at which point, you would experience a vibration and oscillations followed by simultaneous roll to the left (on counterclockwise turning rotor systems) and a pitch up of the nose. This is called retreating blade stall, when the retreating blade side has lost so much airspeed due to the forward motion of the helicopter that it can no longer produce lift, and is the limiting factor in helicopter airspeed.

Questions are welcome. Comments will be tolerated as long as they are intelligent in nature. :D

More to come as I have time.

---------- Post added at 02:28 AM ---------- Previous post was at 12:44 AM ----------

OK, so I tested out the latest update. Here are my thoughts.

On the plus side, the obliteration of the null zone did a world of good. Now I can much more easily feel and see the flight characteristics for what they are rather than constantly over correcting my inputs and chasing the stupid thing all over the place.

Now that I can accurately feel the flight dynamics, lets address some issues.

Pedal control is WAAAAAY too light. Small inputs should yield rapid turns.

Though the helicopter will pitch very quickly with input, the actual ground movement is slow to respond. A real helicopter will slide left, right, foreward and back with almost imperceptible pitch changes. The helicopter should be moving over the ground alot more than it is pitching around its axis.

Please decrease the volume and increase the rate of the vibration occuring at ETL. It's a nice touch, but it does not achieve the intent if it doesnt look and feel right. I have said it before, the vibration experienced at ETL is more HEARD than felt, you would be better simulating the PANEL vibrating along with a rattling noise than having the whole helicopter shaking. It just doesn't look or feel right at all.

What on earth is that right rolling tendency in forward flight? As the helicopter moves into ETL an odd thing happens called Transverse Flow Effect, the front part of the rotor is moving into clean air and the the flow into the rotor system is more horizontal than vertical, however, the induced flow at the back of the rotor is increased and the flow is more vertical than horizontal, the result is a difference in angle of attack (and thus, lift) between the front and back of the disk, not entirely unlike what is occurring during dissymmetry of lift in forward flight, though for completely different reasons. Basically, the front part of the disk is in ETL and the back part is not. The effect of this is the vibration I mentioned earlier, as well as a pitch up and slight right roll of the helicopter. The pilot must push through this in order to gain airspeed. Once the ENTIRE rotor system is through ETL this effect goes away, and rather quickly. There should be no right or left rolling tendency in foreward flight unless VNE is exceeded.

Rate of turn in forward flight vs amount of bank angle is way off. A smaller bank should yield a higher turn rate than what is simulated. No pedal input should be necessary to aid in turns in forward flight.

It IS definitely starting to feel like a helicopter, just with some unusual behavior. Good job gentleman and please keep improving! Listen to what the pilots are all saying, I keep reading about the same issues over and over again.

Please watch my youtube videos. I have real helicopter footage as well as some very good helicopter simulator footage, the most recent being the DreamFoil R22 in alpha testing for X-Plane. This thing flies like a real R22. Watch carefully how it behaves compared to the TOH model.

Edited July 26, 2011 by nightsta1ker

[RUBIX 10]

I like what you have to say about dissymmetry of lift nightsta1ker. I think that the roll associated with the collective that I was talking about early is incorrect and should be removed. If someone can explain why it should be in there, let me know.

As for the Translating tendency, that comes from the tail rotor thrust and should induce a right drift, not a right roll. And the drift should be increasingly more prevalent with more left pedal and should decrease with right pedal. With the testing I have done, I feel that this tendency is implemented correctly.

In hover, the game does feel like the helicopter has to pitch and roll a lot in order to get any lateral movement. I think what could be happening is that the main rotor disc and the cabin are too rigidly connected. The main rotor disc should move a little more independently from the cabin and produce the lateral movements without so much cabin pitch or roll.

As for the forward flight and turns, I agree, the roll needed to get a standard turn rate seems excessive. Maybe someone can post a video of a helicopter in a standard turn rate at 70 knots so the devs can get a feel for what it should be.

[nightsta1ker 10]

Translating tendency DOES provide a rolling moment to the right, but only if the center of the tail rotor is lower than the main rotor hub (thats why some of the larger helicopters have the tail rotor on a vertical stabilizer, the reduction in rolling moment due to translating tendency is worth the extra weight in gearboxes and driveshafts). The relationship between the the rolling moment of the tail rotor and the plane of rotation of the main rotor is called roll/couple. I don't know much more about it than that, but it's worth looking into, I can probably find a better explanation in one of my heavier books.

A good example of this is the right roll that occurs in a low G condition in the R22. When the rotor is unloaded in low G, the rolling moment from the tail rotor causes a rapid roll to the right. This is the primary reason why low G is so dangerous for helicopters with a teetering hub: if the pilot corrects for the right roll with left cyclic the unloaded rotor will bump the mast and or strike the tailboom. That little scenario would ruin anyones day.

[RUBIX 10]

I see your point, and how the tail rotor it does create the roll. But are you sure about your description of the direction? Does the tail rotor produce a roll around the main rotor hub? If so, wouldn't a tail rotor in a counterclockwise system produce a left roll if it were below the hub and a right roll if it were above the hub? A good example comes from using your description of the low g situation when the tail rotor is above the main rotor hub with the nose down pitch it creates a right roll. The most important question should be, do the developers need to try and implement this in the flight dynamics?

About the hover characteristics, I have a knew way of describing the dynamics. When the helicopter is in a hover, the center of gravity (CG) of the helicopter will hang directly below the main rotor hub. When you change the cyclic position, the main rotor disc will tilt in the desired direction, but the CG will want to hang directly below the main rotor hub. This creates a thrust in the desired direction without a lot of cabin roll. This description is mainly useful in the dynamics of small inputs during a hover.

Edited July 27, 2011 by RUBIX

[max power 21]

Of course I am no expert, but I have read there can be a rolling tendency caused by the thrust of the tail rotor in relation to the centre of gravity of the aircraft.

[RUBIX 10]

You are right Max Power, the roll created by the tail is translated around the CG. I don't know what I was thinking in my last post.

On to a new topic. I am noticing that there is a lot of downwash created when the main rotor blades are at flat pitch and the helicopter is on the ground. Downwash is created when lift is being produced, this means that dust and grass shouldn't be pushed around while the helicopter is sitting on the ground with full down collective. I also saw another post where someone described downwash exsisting even when the main rotor was destroyed. I hope this can be corrected.

Edited July 27, 2011 by RUBIX

[nightsta1ker 10]

Good catch Max Power, I couldn't have put it better myself.

[ocramweb 0]

Totally agree on the NOTAR state and banking of the preview heli for now.

Other thing:

Have a little fun guys, and set yourselves a Radio trigger with:

vehicle player setHitpointDamage ["HitVRotor",0.85]

to destroy 85% of the tail rotor in flight, and tell me what you think.

[-DirTyDeeDs--Ziggy- 0]

Totally agree on the NOTAR state and banking of the preview heli for now.

Other thing:

Have a little fun guys, and set yourselves a Radio trigger with:

vehicle player setHitpointDamage ["HitVRotor",0.85]

to destroy 85% of the tail rotor in flight, and tell me what you think.

Edited July 29, 2011 by [DirTyDeeDs]-Ziggy-

[RUBIX 10]

That was fun. I enjoyed attempting running landings without a tail rotor. In a hover, the helicopter torque was very noticeable and the right yaw felt correct; although I have not been in that situation myself. I did notice that the tail rotor had some effectiveness in forward flight....even when the damage was set to 1.0. I wonder what that damage rating actually means. If it means that the tail rotor is no longer turning (i.e. a tail rotor gearbox failure) then there should not be any response from pedal input.

[liquidpinky 11]

Totally agree on the NOTAR state and banking of the preview heli for now.

Other thing:

Have a little fun guys, and set yourselves a Radio trigger with:

vehicle player setHitpointDamage ["HitVRotor",0.85]

to destroy 85% of the tail rotor in flight, and tell me what you think.

You could use the script I made up for this to make things easier if you like. ;)

http://forums.bistudio.com/showthread.php?t=121850

[nightsta1ker 10]

Totally agree on the NOTAR state...

What do you mean by this?

[RUBIX 10]

I think he means, No Tail Rotor....Or Damaged Tail Rotor....I don't think he meant to refer to the NOTAR Tail rotor system used on the MD520N or similar.

@ocramweb

NOTAR is a term used by Mcdonnell Douglas Helicopters to describe their anti-torque system http://www.mdhelicopters.com/v2/notar.php

[nightsta1ker 10]

I think he means, No Tail Rotor....Or Damaged Tail Rotor....I don't think he meant to refer to the NOTAR Tail rotor system used on the MD520N or similar.

@ocramweb

NOTAR is a term used by Mcdonnell Douglas Helicopters to describe their anti-torque system http://www.mdhelicopters.com/v2/notar.php

That's what I thought he meant. Peaked my interest. And by the way, Mcdonnell Douglas is no more. Now it's MD Helicopters, which is another entirely different company that bought the rights to the airframe from Boeing who absorbed Mcdonnell Douglas. The company is not doing so hot, aside from the fact that the 500 series and even the 520N are amazing and versatile helicopters, not many are being sold. And the company is losing millions in lawsuits over the 600N which has an abyssimal accident rate. Nearly half of the 600 fleet has either crashed or been grounded since the aircraft's inception.

Edited July 30, 2011 by nightsta1ker

[ocramweb 0]

You could use the script I made up for this to make things easier if you like. ;)

http://forums.bistudio.com/showthread.php?t=121850

Thanks, I made myself, different combination of those just for testing, the heli at first release, but thanks for sharing it with the community...I didn't my bad. You could add a-280 and a +610 on the weight as well so people can feel the difference between an empty heli and a one at max weight, or even over:

I think the weight use on the demo heli is taken from a 530F

Empty Weight=722 kg

Max Takeoff Weight=1610 kg

*set at 1000kg by default in demo (vehicle player setcustomWeightRTD +650)

as well as with and without wind ... (30 setWindforce 10)

That was fun. I enjoyed attempting running landings without a tail rotor. In a hover, the helicopter torque was very noticeable and the right yaw felt correct; although I have not been in that situation myself. I did notice that the tail rotor had some effectiveness in forward flight....even when the damage was set to 1.0. I wonder what that damage rating actually means. If it means that the tail rotor is no longer turning (i.e. a tail rotor gearbox failure) then there should not be any response from pedal input.

If you look closely at the tail with damage set to 1 there is NO tail rotor no more at all ! (visually)

Then during a landing with a tail rotor failure, I will avoid using the anti torque pedals..., and just right turn by using the collective, keeping enough speed not to twirl your head off ;)

What do you mean by this?

And effectively, I meant NOTAR, not to go into the side effect of losing the maneuverability on the heli, but just to emphasis the fact that the preview, make us use the anti torque pedals not far from the way we will need to use them on a notar system, way less than we should with a tail rotor.

(not endorsed on Notar myself, but by the say of those who were...)

Any of you have to induce some pedal correction under 25 torque in no wind condition ingame ? I lift off at 14 empty and 17 at max weight (takistant runway summer time) but I do not need to use the anti torque pedals under 25 or event 30 torque (depending of force and wind direction..) It does not make me feel right at all..

Edited July 30, 2011 by ocramweb

[nightsta1ker 10]

Thanks, I made myself, different combination of those just for testing, the heli at first release, but thanks for sharing it with the community...I didn't my bad. You could add a-280 and a +610 on the weight as well so people can feel the difference between an empty heli and a one at max weight, or even over:

I think the weight use on the demo heli is taken from a 530F

Empty Weight=722 kg

Max Takeoff Weight=1610 kg

*set at 1000kg by default in demo (vehicle player setcustomWeightRTD +650)

as well as with and without wind ... (30 setWindforce 10)

If you look closely at the tail with damage set to 1 there is NO tail rotor no more at all ! (visually)

Then during a landing with a tail rotor failure, I will avoid using the anti torque pedals..., and just right turn by using the collective, keeping enough speed not to twirl your head off ;)

And effectively, I meant NOTAR, not to go into the side effect of losing the maneuverability on the heli, but just to emphasis the fact that the preview, make us use the anti torque pedals not far from the way we will need to use them on a notar system, way less than we should with a tail rotor.

(not endorsed on Notar myself, but by the say of those who were...)

Any of you have to induce some pedal correction under 25 torque in no wind condition ingame ? I lift off at 14 empty and 17 at max weight (takistant runway summer time) but I do not need to use the anti torque pedals under 25 or event 30 torque (depending of force and wind direction..) It does not make me feel right at all..

I've never flown a NOTAR helicopter, so I could be wrong, but I was under the impression that NOTAR helicopters had WEAK pedal control and required MORE pedal input by the pilot. I know about coandă effect, and thus raising collective means less left pedal required and that this is what you meant, but in foreward flight I have heard that the aircraft is not as manueverable due to less pedal effectiveness. A U.S. Border Patrol pilot I knew told me that he was thoroughly worn out after just an hour of flying the MD600N. He hated it and hoped they would replace them. As of now the entired Border Patrol fleed of 600Ns are in storage. I have however heard that the 520Ns are alot better. Glendale PD in SoCal has been operating them for years with no issues and they love them.

Edited July 30, 2011 by nightsta1ker

[ocramweb 0]

that's what I meant .

and good luck for your checkride ;)

[nightsta1ker 10]

that's what I meant .

and good luck for your checkride ;)

Yeah thanks... I'm so close, yet so far away, lol!