Flight Dynamics Feedback From Real Helicopter Pilots

[RUBIX]

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.

[nightsta1ker]

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.

[fred64]

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]

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]]

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...

[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.

[RUBIX]

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.

[nightsta1ker]

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.

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. http://youtu.be/MdQ8UN-tLYY

[RUBIX]

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]

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.