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Helicopter realism -- or not? Real pilot tests?

Helicopter flying is completely different from flying a fixed-wing aircraft and thus requires different skills.

Re: Helicopter realism -- or not? Real pilot tests?

Postby HHS » Sat Apr 02, 2011 7:53 pm

Well, I'm not the FDM wizard, but I'm interested in and my knowledge about is slowly increasing.

ranger8 wrote in Fri Apr 01, 2011 8:59 pm:HHS,

I did as you suggested with the 22beta files & decreased the weight on the left side. When I flew the cyclic was closer to what it should be, just needs to be a litlle bit farther foward, lateral was good as it was left of center as it should be(if solo).

Thanks, that convinces me at least that the datas I used for the rotor control travel seems to be right.

I did not notice any change in tail rotor authority, when the aircraft was on the ground, I had to be at full right pedal to keep from spinning left,then change to full left pedal as I increased collective to lift up.


Our FDM (FlightDynamicModel =Flight Dynamics Engine or .air in MSFS) has one big issue, and the makes the helis turns around their center. If the CoG and Inertia are set up correct, the heli will not turn on the ground without engines, but soon a little bit Torque is added, it begins- in Idle, independant of the gear settings.
That's one things which you unfortunately noticed. That's the next thing I will try to prevent, but as the heli is really lightweighted and makes it difficult.

Could it be possible that the data that the files were built off of was inverted?(left side should right and vice versa).


Yes, pilot positions and weight settings had been wrong, as the rotor control travel values as well.

or

Could the data be wrong all together?

Well- our flightmodel you can't compare with the one from MSFS. It doesn't use Lookup-Tables, but Blade-Element-Theory. (Yes, like X-Plane!)
So if you feed it with the correct values, you will get the right behavior. Unfortunately there are a lot of values needed, and if one or some more are wrong, it might be that the behavior isn't right anymore at the end.
There aren't all datas wrong. Only few wasn't right, and with that some others needs a small correction to apply with.
Believe me- it is like in Real Life- it is easier to get a fixed-wing fly correct than an helicopter! ;-)

I'll be losing access to our sim for a while, as tonight I am taking it to my business partners house for a couple of weeks for him to work on networking another computer to it and some other things, but I have my pilots operating handbook for the R22 with all specs for each configuration of the R22 models(alpha,beta,betaII).

Would any of that info be of use to you or Groucho?


The Manual can help us for checking the CoG's, and climb rates. Would be great to have all three types in FGFS.

The next step for me is to set the Inertia Tensors, and take a look on the Fuselage configuration....

Thanks for your help, Ranger8!
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Re: Helicopter realism -- or not? Real pilot tests?

Postby ranger8 » Wed May 18, 2011 3:02 pm

Hi HHS,

I tried to reply to you pm, but it wouldn't let me send you a message. I am still very interested in helping any way I can! I will be in Florida until around the 13th of june doing some time in the jet-ranger. I will look at what you got as soon as I get back.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Groucho » Fri May 20, 2011 9:53 am

ranger8 wrote in Wed May 18, 2011 3:02 pm:Hi HHS,

I tried to reply to you pm, but it wouldn't let me send you a message. I am still very interested in helping any way I can! I will be in Florida until around the 13th of june doing some time in the jet-ranger. I will look at what you got as soon as I get back.


HHS has retired from the forums for a while. However he is available via the mailing lists. If in need drop me a note (PM) and I will point you in the appropriate direction.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby sgofferj » Wed Jan 04, 2012 4:51 pm

This thread is a little bit older but I have to comment on it as I think, maybe other beginners might read it too.

My experience with helos includes something like 6 years as a paramedic on rescue helos and something like 35 hours with an instructor before some really bad event blew my budget plans.

Flying a helo in a flight simulator is substantially different from and in my opinion much harder than flying a helo in real life. What was described as "butt feeling" is the most important aspect of that. According to the flight surgeon in the school, in humans, as in most other mammals, the ability to coordinate information from your sense of balance with movements is the most evolved. Otherwise, we would just stumble around. Opposed to that, the eye-hand- / eye-motion-coordination is the least evolved. When flying helos, after quite a short time, a normal person starts to correct unwanted motion of the helo automatically and unconsciously at a stage when the motion is so small that it doesn't even register on the instruments or is clearly visible. You just feel a small movement and instinctively correct to the right direction. Same as you automatically correct the speed and steering input of your car when you feel that it's on the verge of breaking out on slippery ground, long before your eyes see the outside world moving in circles around you.
In a flight simulator, you don't have any kind of input to your sense of balance. And even a 3 axis moving sim cannot fully replicate helo behavior or how it feels (I had the luck of being a few hours in the US Army sims in Illesheim, Germany in the 90's).
That means, in a flightsim you fly plain eye-hand-coordination which means that - speaking in helo terms - all your correctional inputs are already being about half a second late because in the real thing you would have felt the first little signs like half a second ago.

If you are a helo beginner in a fligthsim, you should act like one! In no real life flying school, you sit in the machine, crank the starter and then pull the collective up and start trying to balance what's happening! Besides a ton on theoretical lessons before you even get close to the helo (also a flight instructor tends to love his life!), you usually start very slowly with the instructor showing you something and then you trying to mimic it, while the instructor in the beginning keeps holding the stick also - just in case. As it goes further, he might just give you control over one axis, then 2 and finally all while still being vigilant and keeping his hands at least close to stick and "handbrake".
So, do small steps with your helo. Read about helo physics and theory and practice a lot. Don't just rip the collective upwards and then complain that a flightsim is not realistic if you can't manage the bird.

A word about the R22... Yes, this bird really flies like dry leaf in a storm. I was doing half a year duty in a station at the Baltic Sea which had an R22 as doctor-taxi. My biggest respect for any pilot who can keep this thing stable, especially if the weather is not so nice. At this time, I had something like 20h already in school on a Bell Ranger and our pilot in the station let my try the R22 on the return flight from a mission. It was a beautiful sunny day with almost no wind and nothing and while I already was pretty good with my Ranger, I could hardly keep the R22 flying in a straight line. After 7 minutes I gave it back and told the pilot HOW much more I appreciate his skills now :D. And I had to get a dry shirt in the station :D.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby NumberOneHoverLover » Sun May 05, 2013 10:34 am

I just heard about flightgear yesterday, and I was hopeful, but I can tell you with over 10k hours (5000+ Hours in Robinson R22's and R44's alone), neither of these models fly like the real thing. I can't speak to the other helicopters in flightgear, as I haven't tried them; I was so disappointed with the Robinsons that I just closed flightgear. The real Robinson's are a dream to fly. some people say they are "squirrely", but they are generally sim-only pilots... I know the real Robinsons to be stable platforms and very responsive; flightgear's representation is neither stable, nor responsive (with the exception of the pedals, maybe too much with the pedals...with the collective fully down, you will NOT yaw)

The cyclic input didn't translate well, and ETL was non-existent. The collective was slow and sloppy.

btw, I am a CFII with time in R22 (HP/A/B/B2), R44 (A/R,R2), 206 (JR & LR) , 407, 300, 500C/D/E, AS350, AS355, EC135, A109
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Hooray » Sun May 05, 2013 1:02 pm

Hi & Welcome !

Thanks for taking the time to register and to provide feedback here - that said, it would be more helpful obviously if you could provide specific details, as to how exactly the simulator/aircraft could be improved to feel a little more real.
Please don't send support requests by PM, instead post your questions on the forum so that all users can contribute and benefit
Thanks & all the best,
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Groucho » Mon May 06, 2013 7:34 am

NumberOneHoverLover wrote in Sun May 05, 2013 10:34 am:I just heard about flightgear yesterday, and I was hopeful, but I can tell you with over 10k hours (5000+ Hours in Robinson R22's and R44's alone), neither of these models fly like the real thing. I can't speak to the other helicopters in flightgear, as I haven't tried them; I was so disappointed with the Robinsons that I just closed flightgear. The real Robinson's are a dream to fly. some people say they are "squirrely", but they are generally sim-only pilots... I know the real Robinsons to be stable platforms and very responsive; flightgear's representation is neither stable, nor responsive (with the exception of the pedals, maybe too much with the pedals...with the collective fully down, you will NOT yaw)

The cyclic input didn't translate well, and ETL was non-existent. The collective was slow and sloppy.

btw, I am a CFII with time in R22 (HP/A/B/B2), R44 (A/R,R2), 206 (JR & LR) , 407, 300, 500C/D/E, AS350, AS355, EC135, A109


Thanks for the input which is highly appreciated.

In general experienced real life helicopter pilots find it hard at first to accomodate with the simulated version of their work horses they have become familiar with so they expect a certain behavior which is then missing due to the lack of butt feeling, completely different input devices (with different friction, precision, etc.), limited FOV, etc.
Your findings therefore might be biased by your rich experience in a specific environment, an effect we have encountered very often and which other simulators are as well struggling with.

Regarding the Robinsons- the R44 in FG is indeed not equipped with a realistic flight data model and should therefore not being used to judge for realism.
Luckily I have some real life experience with the R22 (not much, but at least a little bit) and I would not consider it to be a stable platform unless you have various hours of experience with it. I found it extremely responsive and aggressive - an opinion which was backed by the statements of the instructor I had: "If you can fly the R22 then you can fly everything. It will not get worse, just better."
And indeed it is missing a few things in FG- ELT, rotor brake, fuel valve, throttle etc. Not to speak about stall behavior, auto rotation, and more.
(Regarding ELT - the FlightGear R22 has been developed by a team of austrian and german developers. In both countries the obligation for equipping a/c with ELT is not as old as the model is so at the time of development the R22s were not equipped with one. The question is: Would it make sense to have it in a sim? I would say "not really".)

As an open platform FlightGear is able to improve the issues we get based on real life experience and experienced people like yourself are able to deliver the adequate input. So it is appreciated if you would help here.
Thanks in advance.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Johan G » Mon May 06, 2013 10:37 am

NumberOneHoverLover wrote in Sun May 05, 2013 10:34 am:...ETL was non-existent.


Groucho wrote in Mon May 06, 2013 7:34 am:...the obligation for equipping a/c with ELT is not as old as the model is so at the time of development the R22s were not equipped with one. The question is: Would it make sense to have it in a sim? I would say "not really".


ETL as in Effective Translational Lift, not ELT as in Emergency Locator Transmitter. :wink:

Another thing also missing is vortex ring state (maybe related to ETL), which could happen if you descend faster than about 300 fps. An helicopter equivalent of stall if you will (can cause fatal crashes during slow approaches and landings, specially to "tight" places).
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Groucho » Mon May 06, 2013 11:22 am

Johan G wrote in Mon May 06, 2013 10:37 am:
NumberOneHoverLover wrote in Sun May 05, 2013 10:34 am:...ETL was non-existent.


Groucho wrote in Mon May 06, 2013 7:34 am:...the obligation for equipping a/c with ELT is not as old as the model is so at the time of development the R22s were not equipped with one. The question is: Would it make sense to have it in a sim? I would say "not really".


ETL as in Effective Translational Lift, not ELT as in Emergency Locator Transmitter. :wink:


Oops, my fault. I did not read close enough. I had ELT in mind because I remembered ELT being present in the X-Plane R22 which I found remarkable.

Another thing also missing is vortex ring state (maybe related to ETL), which could happen if you descend faster than about 300 fps. An helicopter equivalent of stall if you will (can cause fatal crashes during slow approaches and landings, specially to "tight" places).


Vortex state is not modeled for Yasim according to the FlightGear wiki (http://wiki.flightgear.org/Improving_Helicopter_Realism):

YASim does a pretty good job for helicopter realism in FlightGear. What is implemented is very accurate so far, but there are a few things not yet implemented or fully simulated. Missing features are listed below:
Vortex Ring State Vortex Ring on en wiki
LTE, not fully simulated due to missing Main-rotor vortex: LTE on wiki


I haven´t seen it implemented in the FG helicopters anyway.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Johan G » Mon May 06, 2013 2:10 pm

Groucho wrote in Mon May 06, 2013 11:22 am:I haven´t seen it implemented in the FG helicopters anyway.

mr_no's Mosquito XE have an optional simulation of vortex ring state that can be enabled through a gui menu, but I think that it is unique in that sense.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby NumberOneHoverLover » Tue May 07, 2013 6:38 am

Johan G wrote in Mon May 06, 2013 10:37 am:
NumberOneHoverLover wrote in Sun May 05, 2013 10:34 am:...ETL was non-existent.


Groucho wrote in Mon May 06, 2013 7:34 am:...the obligation for equipping a/c with ELT is not as old as the model is so at the time of development the R22s were not equipped with one. The question is: Would it make sense to have it in a sim? I would say "not really".


ETL as in Effective Translational Lift, not ELT as in Emergency Locator Transmitter. :wink:

Another thing also missing is vortex ring state (maybe related to ETL), which could happen if you descend faster than about 300 fps. An helicopter equivalent of stall if you will (can cause fatal crashes during slow approaches and landings, specially to "tight" places).


Vortex Ring State or "Settling With Power" is caused by high decent rates with "not enough" airspeed to outrun your own disturbed air... Once you're "Settling With power", the more collective you apply, the faster you will sink. In single, and coaxial rotor helicopters, the recovery procedure is to apply forward cyclic.... In tandem-rotor helicopters, recovery is accomplished through lateral cyclic or pedal input.

And yes, I was speaking about Effective Translational Lift. ETL is induced by any horizontal flow of air moving across the main rotor, typically in the 16-18kt range... you get a bump in lift. it's quite noticeable when it happens. When you hit ETL during a normal takeoff, you will have a tendancy to climb, but can apply more forward cyclic to translate that increase in lift to more forward airspeed. if you get a gust of wind at a hover, you'll have to decrease collective to maintain altitude.

Another thing that would be nice to see in the future is "Retreating Blade Stall" (dissymmetry of lift). this is primarily why helicopters have a VNE (Velocity - Never Exceed) imposed.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Thorsten » Tue May 07, 2013 8:03 am

When you hit ETL during a normal takeoff, you will have a tendancy to climb, but can apply more forward cyclic to translate that increase in lift to more forward airspeed. if you get a gust of wind at a hover, you'll have to decrease collective to maintain altitude.


I am not a helicopter expert, I have never flown a helicopter in real life, my knowledge about how to fly helicopters and what I should be seeing comes from two online tutorials, so please treat everything I say accordingly.

One of my current amusements is to fly mountain rescue with the EC-135, but I've also tried the Bo-105 and the EC-130 in the past. I've notices numerous times precisely that behaviour and learned to anticipate it when landing somewhere in the mountain summit regions: As I enter the boundary layer where the strong high altitude winds slow down due to terrain interactions, the airflow across my rotors is reduced and I have to increase collective to maintain my descent rate. Once I get close to the terrain, I have to decrease it again due to the ground effect. I have also observed in the EC-135 that the descent gets very bumpy and accelerates if if descend with little forward velocity fast, and I thought that was the settling with power I found described in my tutorial.

I have no idea if these things work as in reality, but I was impressed that pretty much everything which I had found mentioned in the tutorials translated into some experience in the simulation, and I was rather happy to have gained some basic insights into how helicopter flight works. So I am not sure what to make of your comments.
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Johan G » Tue May 07, 2013 11:10 am

NumberOneHoverLover wrote in Tue May 07, 2013 6:38 am:Once you're "Settling With power", the more collective you apply, the faster you will sink. In single, and coaxial rotor helicopters, the recovery procedure is to apply forward cyclic.... In tandem-rotor helicopters, recovery is accomplished through lateral cyclic or pedal input.

Ah, that explains why it's called "settling with power", I could not really get why. It seems most places I have looked didn't mention what not to do, only what to do (or I have forgotten the part about not adding collective).

NumberOneHoverLover wrote:And yes, I was speaking about Effective Translational Lift. ETL is induced by any horizontal flow of air moving across the main rotor, typically in the 16-18kt range... you get a bump in lift. it's quite noticeable when it happens. When you hit ETL during a normal takeoff, you will have a tendancy to climb, but can apply more forward cyclic to translate that increase in lift to more forward airspeed. if you get a gust of wind at a hover, you'll have to decrease collective to maintain altitude.

Thank you for explaining that. It seemed to me that ETL was an important airspeed, but I never looked into what it was.

NumberOneHoverLover wrote:Another thing that would be nice to see in the future is "Retreating Blade Stall" (dissymmetry of lift). this is primarily why helicopters have a VNE (Velocity - Never Exceed) imposed.

Should not be impossible to implement.

Try out some of the more developed helicopters. From what I have heard (not only in this topic) the Eurocopter EC135 is definitively one of them. And keep the input coming. While nothing happens now, it might trigger an itch and/or will be used later on develop the helicopters a bit further. There's only a few helicopter developers in the FlightGear community as making a really good fixed wing flight dynamics model (FDM) is kind of magic, but making a good helicopter FDM is more like voodoo. :wink:

EDIT: Spelling ELT --> ETL, my turn I guess. :lol:
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Groucho » Tue May 07, 2013 11:47 am

Johan G wrote in Tue May 07, 2013 11:10 am:Should not be impossible to implement.


In fact IIRC the YASIM lib should be able to already support it and I am not sure but it might also support ETL.
Certainty can be gathered from asking on the FlightGear developers mailing list where most experts are hiding at :)
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Re: Helicopter realism -- or not? Real pilot tests?

Postby Groucho » Fri May 10, 2013 1:34 pm

Groucho wrote in Tue May 07, 2013 11:47 am:In fact IIRC the YASIM lib should be able to already support it and I am not sure but it might also support ETL.
Certainty can be gathered from asking on the FlightGear developers mailing list where most experts are hiding at :)


Well, I got an answer from our most proficient helicopter modeler :)

As it comes to helicopter realism the underlying phyiscs are well covered in contrast to simulating aircraft systems.

What this means:

ETL is available in YASIM and can be tested with the Bo105, EC135 and the Mosquito M-XE. Just try it out. It is probably not used in the R22. If it is not observed here this does not mean that FG can not simulate it appropriately. It is simply not included in the model then.

Settling with power (VRS): Is not available in YASIM and therefore not in FlightGear helicopters. The Mosquito M-XE cheats a bit here to have something similar though it is not the correct behavior. What Thorsten notices here is a different behavior which is not the realistic one btw.

Retreating Blade Stall:
Is supported by YASIM but difficult to implement in the helicopters. The only one which definitely has it is the Mosquito M-XE.
Plus it is assumed to have a bug as the helicopter tends to roll on the wrong side then.

If one is looking for the most realistic flight behavior you will have to look at the Bo-105 and the UH-1 of which both have been tested by real life pilots. The UH-1 does not have realistic autorotation.
The EC135 comes close and is based on real data with an appropriate Fenestron behavior.

The challenges in general are:
  • Get your hands on realistic flight data and system model information
  • Have enough time and knowledge to implement it in the helicopter and eventually YASIM

We do not have the perfect helicopter covering all aspects. Some are coming pretty close to the real thing (Bo-105, EC-135, UH-1) - however they are not complete regarding system model and procedures.
Others are pretty good (EC-130, R22, Air Crane) though they could need more work to complete them.
And others are just for fooling around (R44, UH60, Mil24, and most others).

Lots of real good work has been going into the first two categories to make them as good as possible with the available resources and knowledge and kudos to all these spending their time to do so.
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