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Is the Flight Model As accurate as it Should?


Riemann

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Hi,

the FM model seems to be realistic but there are some flaws according to me.

(Note: in real life i'm a licensed helicopter pilot but had no experience with huey)

 

The first one i noticed is that the inherent instability in hover is too pronounced.

The causes could be:

1) cyclic control is too autoritative

or

2) the helicopter mass distribution (CoG or inertia or both) is not accurate

 

What do you think about?

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1) cyclic control is too autoritative

 

 

If you mean the cyclic has too much authority, I agree. I fly helos IRL as well, just not Hueys. A buddy of mine has in the past, though, and always mentions how stable they are. The cyclic control would be fine, if the teetering motion didn't happen when static. In my experience with semi-rigid helicopters, the teetering motion gradually gets worse with over-controlling. This one moves 5-8 degrees on the artificial horizon without touching the cyclic at a hover.

 

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I've got 12 hours on the Huey. It's very easy to fly in real life, very intuitive, as opposed to flying in DCS. I don't know if this is because of the lack of good controls, peripheral view and the seat of the pants feeling, or if it's because of the flight model.

Other than that, I think the flight model is very very good.

 

Sometimes though, I think the Huey is TOO susceptible to settling with power.

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G'day guys,

 

I have around 1250 hours on the H model and was also a Maintenance Test Pilot for much of that time.

 

The 'amount' of instability is quite accurate (for something which can't be measured :) ), however the main problem at the moment (which you and several others have mentioned) is that the instability is mostly in the pitch axis, when it should be mostly in the 'drift' axis.

 

The aircraft feels as though the centre of lift and the centre of mass are at the same point and the aircraft is balancing on a basketball, trying to tip/fall over constantly.

 

Instead it should feel as if the centre of mass (fuselage) is hanging below the centre of lift (rotor) and the aircraft should feel like a pendulum, trying to drift and wander constantly, but not tip (as much).

 

Some of the FM changes made during develepment increased the stability in the hover greatly, however the agility was also greatly reduced, sometimes to the extent that the angle of bank wouldn't exceed 80-90 degrees at full cyclic deflection. The current beta implementation is the best compromise so far.

 

To summarise, I feel the FM is very good, certainly the best I've experienced in a sim, but still has room to improve. I'm encouraged that the dev team have been very receptive to testers and users and will continue to improve the experience.

 

Keep pushing issues/problems/improvements as you have been and things can only get even better! :)

 

Cheers,

 

- Bear

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...I think the Huey is TOO susceptible to settling with power.

 

I definitely agree with you there. :)

 

I've some crazy/stupid things in H models and never been close to vortex ring.

 

It's much better than it was... and we'll keep pushing for improvement.

 

Cheers,

 

- Bear

Pacifism is a shifty doctrine under which a man accepts the benefits of the social group without being willing to pay - and claims a halo for his dishonesty.

 

- Robert A. Heinlein

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When you transition out of the ETL the rotor "bite" seems too severe. even with smooth control inputs you hit a "brick wall" where you have to apply near full rudder deflection. When decelerating at a gentle rate you have to make large collective adjustments, not just when coming out of ETL but when well out of it. Seems like the angle of attack of the rotors isn't steady.

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the centre of lift and the centre of mass are at the same point and the aircraft is balancing on a basketball, trying to tip/fall over constantly.

 

I don't know, the bird is so unstable at times that one feels as if the CoM resided somewhere _above_ the lift center as currently modelled. But then I really don't know what I'm talking about, having only flown a Cessna a couple of times IRL! So disregard - just ruminating guys and gals ;)

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When you transition out of the ETL the rotor "bite" seems too severe. even with smooth control inputs you hit a "brick wall" where you have to apply near full rudder deflection. When decelerating at a gentle rate you have to make large collective adjustments, not just when coming out of ETL but when well out of it. Seems like the angle of attack of the rotors isn't steady.

 

bullseye that is why I can't seem to land! :joystick:

 

It should be just like the KA50 when I'm landing. :pilotfly:

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bullseye that is why I can't seem to land! :joystick:

 

It should be just like the KA50 when I'm landing. :pilotfly:

 

Maybe with all the AP channels off. I did some reading on coaxial rotor flight dynamics and it eliminates some bad tendencies of traditional single rotor design and reduces some. The vortex ring is one of the things it reduces, aside from the jumpy collective and the brick wall transition from ETL i'm not having any serious issues with the FM. Having said that I expect the shark to fly differently than the Huey (not accounting for the AP assistance). As they say the FM is a WIP so i'm just posting some of my thoughts on the matter. I'm not a Huey pilot so i'm far from an expert.

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I've got 12 hours on the Huey. Sometimes though, I think the Huey is TOO susceptible to settling with power.

Regarding the settling with power / vrs discussion, I also concur. It seems too easy to get into vrs and when it occurs it happens rather quickly and abruptly, making it extremely dangerous and not at all forgiving. The only time I've crashed in the campaign is from falling into vrs during approach. It may just be that my approach procedure is not ideal but I find myself a little high when approaching a point to land and therefore have to finish the approach very slow during the descent to avoid overshooting the landing site. The aircraft becomes very unsettled in this state and I try to avoid descent rates greater than 500-1000 fpm. Difficult to maintain visual reference at the higher heights above the ground and I tend to go in and out of translational lift requiring large changes in collective inputs to maintain the safe rates of descent. Very difficult and as soon as I momentarily exceed 1000 fpm the aircraft quickly enters vrs and exceeds 2500 fpm. At that point I push forward on the stick to attempt to exit the condition with no room to recover and therefore crash at high sink rate.

 

I don't recall this being a huge deal on the Huey and have always heard the Huey being a forgiving and stable platform.

 

On another note, I'm curious if the developers modeled the bell flybar mechanical stability system. It should function as a pitch and roll damper. I find that the aircraft is quite unstable in hover and during the takeoff and climb out, questioning if the stabilizing functionality of the flybar has been modeled or if it has, whether its effect needs to be with greater authority. Can some Huey pilots weigh in regarding this discussion?

 

Finally one little thing I found that did not seem correct. With the rotor stopped and the rotor blades aligned in the fore-aft position it seem that when you put in fore-aft cyclic input the teetering head tilts forward and aft. This does not seem correct because if you follow the pitch links up to the flybar from the swashplate and down to rotor blade pitch horns there's no moment arm that would permit that movement to occur. Assuming the 90 degree phasing there should be no cyclic pitch input from the swashplate or movement of the teetering head when the blades are in the fore-aft clocked position.

 

The head should be free to teeter as well. Even when the rotor is not turning. This is why the blades are tied down when the helicopter is parked, to avoid the wind blowing the rotor to teeter back and forth. During high winds some crew are instructed to hold the tip of the blade during engine start to prevent the rotor from teetering wildly at the initial rotor turn.

 

1024px-Bell_UH-1D_SAR_%28Ltg_63%29.jpg

 

You can see how in this picture the rotor is tied down. If not tied down and if there are winds, it may teeter around back and forth like a seesaw, hence why they tend to be tied down.

 

Other than that I wanted to congratulate the development team on an amazing product. By far the best conventional heli sim out there. Very well done guys. Autorotations are a joy to fly.


Edited by Buznee
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VRS is currently overmodelled, but it's being improved.

 

Don't know whether the stab bar is specifically modelled in code, but I doubt it.

 

Of note, the stab bar doesn't 'prevent' main rotor flapping or disturbance due to external influences, but will return the rotor to its original control position, thereby providing an 'analogue' SAS.

 

I'm not sure when, but at some stage some form of 'droop stop' type of mechanism became available, which would hold the blades level when parked. I don't know much about them as Australia never had them fitted.

 

I haven't looked at the control response while shut down, but I'll look at it today and submit the bug.

 

Cheers,

 

- Bear

Pacifism is a shifty doctrine under which a man accepts the benefits of the social group without being willing to pay - and claims a halo for his dishonesty.

 

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Thanks for the replies guys. I did confirm the bug regarding the rotor head movement when the rotor is stationary and moving the cyclic. This should not happen. If you go in the sim with rotor stationary and move the cyclic, look carefully at the pitch links (pushrods) between the stabilizer bar and the main rotor horn you will see that it changes length (Stretches) in order for the main rotor head to tilt. Since the rotor is set to tilt in the sim with cyclic movement and the stabilizer bar is not moving, therefore the pushrods have to change length for that work. In reality the pushrods should not change length therefore constraining the rotor head from moving unless the stabilizer bar itself also tilts. I believe in the real helicopter if the pilot moves the cyclic when the rotor is stationary only the blades change angle but the rotor is not constrained to tilt or teeter from cyclic control input.

 

You can see in this UH-1N start up video, the stabilizer bar is actually free to tilt and starts in a tilted angle until the rotor begins to turn and straighten the stabilizer bar out.

 

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  • ED Team

...

On another note, I'm curious if the developers modeled the bell flybar mechanical stability system.

Stabilizer bar is modelled in our sim, and now we have significantly improved it model. Huey is now more stable. For users it will be accessible with nearest update

 

...

The head should be free to teeter as well. Even when the rotor is not turning.

Of course! we know about it! We want to make the animation of the blades honest, but we can not yet do it!:)

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Stabilizer bar is modelled in our sim, and now we have significantly improved it model. Huey is now more stable. For users it will be accessible with nearest update

 

 

Of course! we know about it! We want to make the animation of the blades honest, but we can not yet do it!:)

 

 

Sounds really good :thumbup::thumbup:

 

 

What about flares ? :D

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Stabilizer bar is modelled in our sim, and now we have significantly improved it model. Huey is now more stable. For users it will be accessible with nearest update :)

 

Hooray! Cheers :)

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I haven't seen it yet, but since we're on the subject of the rotors, is there a rotor brake? I haven't found it in the cockpit, so I've been using the collective to slow the rotors down. If there is a brake for the rotors, it would be good so I could stop them inline with the fuselage.

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  • ED Team
I haven't seen it yet, but since we're on the subject of the rotors, is there a rotor brake? I haven't found it in the cockpit, so I've been using the collective to slow the rotors down. If there is a brake for the rotors, it would be good so I could stop them inline with the fuselage.

Not "rotor brake". See att.

2087318967_STABILIZERBAR.thumb.jpg.db883e6fc3d58a769bde44d36817c728.jpg

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Hog_driver111th meant the hydraulic rotor brake:

 

Rotor%20Brake%20Hydraulic%20System%2011-4.jpg

 

Could be useful, but not essential.

 

[edit]That one above is of course the newer one, mostly seen on civilian 205A-1s. The Kiwis, are using the older style on their UH-1H:

 

rnzaf-bell-uh-1h-iroquois_picm122-12291.jpg

 

Now the question is how seriously are we approaching to the idea of using that helicopter on ships in DCS ?


Edited by Sundowner.pl

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Hog_driver111th meant the hydraulic rotor brake:

Oh!..:)Sorry! first did not understand))

 

...

Now the question is how seriously are we approaching to the idea of using that helicopter on ships in DCS ?

strange question. In the DCS can already be used on aircraft carriers Huey. If that's what you mean. If not - you need more detail to clarify the essence

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I know we can land on ships, I've done that already - still there are some problems with it - as the helicopter is sliding on the deck side to side, and creeping forward. But that's DCS problem, not Huey.

 

Now what I meant is how deep into over-water operation do you want to go, because landing on a ship is one thing, but start-up, shut down, and flying without visibility of the shore is a different matter - for that there are few systems that are needed:

 

1. Rotor brake - to slow down the rotor quickly. As the deck is pitching and rolling there is a danger of hitting something with slow moving blades.

 

2. Radio altimeter.

 

3. Navigation system - since all we can see is water, we need something to navigate other than a compass and stopwatch. There are few options here:

- LORAN

- INS

- GPS

- Doppler

Any of the above needs a different kind of equipment that is not yet in the DCS: Huey, be that a different radio set, HSI, or a new panel.

 

Now If this would be my project, and a decision would be made to "go offshore", I would put in an HSI (ID-2103/A), and a Doppler navigation system (AN/ASN-128 ). It's least amount of codding and modeling work, and can work independently from the DCS core engine. Yet giving pilots all the tools needed to navigate over water.

 

So the question is: do you want us to fly away from the shore? ;)


Edited by Sundowner.pl

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