777 ground friction changes in P3D v4?

[threexgreen 3,135]

Just now, Budbud said:

I'm still missing the Lua dynamic friction for the T7 in P3D v4 as I used it in FSX but without it it feels the same in both sims FSX and P3D.

Is the dynamic friction feature not yet included in FSUIPC5?

[Budbud 227]

Hi,

Yes it is but I understood from Pete Dawson's post here that it is doesn't work in P3D v4 so I didn't even try it.

http://forum.simflight.com/topic/83542-p3dv4-ground-friction/?do=findComment&comment=505020

Maybe I'm wrong and it's worth testing it. I'm beta testing another software for now so I don't have much time to perform tests for myself.

 

[threexgreen 3,135]

2 hours ago, Budbud said:

Hi,

Yes it is but I understood from Pete Dawson's post here that it is doesn't work in P3D v4 so I didn't even try it.

http://forum.simflight.com/topic/83542-p3dv4-ground-friction/?do=findComment&comment=505020

Maybe I'm wrong and it's worth testing it. I'm beta testing another software for now so I don't have much time to perform tests for myself.

 

I just hope there won't be friction issues with the NGX when it's avialable...

[downscc 1,327]

Any issues you have with "friction" or more accurately rolling resistance with the B77L in P3Dv4 is due to your configuration.  I just checked, out of curiosity, and with a 728.8 klb GW she easily breaks away with as little as 28%N1 and 27%N1 will get you to 10-15 kts and continue to accelerate for as long as you have pavement, which in my short test was 19 kts at the 8000 ft marker at KLAX.  This doesn't seem like an "issue."

[01A045 9]

6 hours ago, downscc said:

Any issues you have with "friction" or more accurately rolling resistance with the B77L in P3Dv4 is due to your configuration.  I just checked, out of curiosity, and with a 728.8 klb GW she easily breaks away with as little as 28%N1 and 27%N1 will get you to 10-15 kts and continue to accelerate for as long as you have pavement, which in my short test was 19 kts at the 8000 ft marker at KLAX.  This doesn't seem like an "issue."

The thing is, I can achieve the same result with only 25% or 26% of N1 in previous versions. And with the LUA enable, same thing can be done with even 24% N1. 

[Driverab330 74]

On 6/15/2017 at 2:47 PM, hawx2k said:

Good morning,

I just flew the 777 for the first time in P3D v4 and noticed a significantly increased ground friction (in FlyTampa Dubai). Without (constant) significant thrust (N1 >28%) the plane would stop taxiing after a short while (within 10-15 seconds). I'm not sure if I have done something wrong or if this is an intentional change (I'm not flying a T7 in real life, so couldn't tell :D).

Thanks for any insight.

Jan

 

Just a bit of sharing of what the real airplane feels like.

Taxiing the real 773ER (772LR would be similar and probably worse if light) would be like driving a car with conventional automatic transmission with a torque converter, anything below 300tons the airplane will break away at idle thrust albeit very slowly.

Then after the airplane gets up to about 5-6kts it will accelerate a bit faster with idle thrust when taxiing on a completely flat taxiways. And you will need to use the brake to control your speed. Otherwise it will keep accelerating. 

The normal practice when taxiing on a long straight taxiway is to let the airplane accelerate to ~30kts then applies the brakes smoothly to slow down around 15kts and then let it accelerate again. Repeat the same process units you reach the runway holding point or the ramp/apron area. 

Usually it is normal for guys to push the thrust up to about 28%-30% N1 to get it rolling initially especially when a 90deg turn is required shortly after, because the airplane slows very quickly in turn so it is normal to keep the thrust at around 25% N1 to prevent the speed from decreasing when in a turn. Even on an upslope taxiway at MTOW, 35% -38% N1 of break away thrust is all you need. 

anything below 250tons on the 773ER the airplane would be accelerate even if one engine running only (we shut down one normally after landing to save fuel nowadays after a cooling period of 3 min when workload and airport facility permits) 

To be very honest even in the Level D simulator which the pilots use for their training and check, the ground fiction model is never correct, because  it is hard thing to model.

And this is one of the reason why simulator landing is not "quite real" as well, and there are companies which provide an "add on" algorithm to level D which aims to fine tune it. 

Even the landing distance performance on the PMDG 777 was not correct either, and basically what you get when you use Autobrake 2 in P3D/FSX at Groundspeed of ~150-155kts will roughly give you a Autobrake 4 stopping distance in real life which is about ~1900m-2000m (6200-6400ft). May be it is my own problem but it is completely fine to me, I did not use any FSUIPC software, the only thing aircraft add on is pmdg 777 on my computer. 

other than that, the overall simulation experience is quite good.

Hopefully you can fine tune your fiction and bring the thrust down a bit in order to maintain your Taxi speed. 

Have a good weekend gents. 

 

 

[anden145 2,284]

I haven't really noticed any issues with the 777 but one thing I don't understand... When reading through this thread, there seems to be an unwillingness of helping to identify the underlying problem and more of a confrontational attitude of those experiencing it, in order to promote an agenda which goes to discredit the support given from PMDG and the product.

Oh, well... Gents, how about trying the following:

1. Disconnect ALL hardware from your computer. And I do mean ALL. Everything till you end up with having a keyboard and mouse connected.
2. Duplicate Kyle's scenario found here.
3. Let us know what results you get.

Start with the most basic setup and work your way from there. Default airport. Everything disconnected etc. If there's no problems when doing this, we can eliminate that the 777 is to blame. If not - well, then maybe we could be one step closer to identifying it... 

[hawx2k 6]

Thanks Anders.

I'll just ignore the insinuation and assume that the fact that you seem to ignore all my previous posts that attempted to replicate what Kyle had suggested is a mere oversight and get to the point:

- re-ran the test as I already did per:

- this time indeed with an empty plane and short fuel (in my initial test I had admittedly full fuel and standard payload which of course should naturally increase friction) and default airport (P3D default Eglin AFB, RW19)

1. as before I disconnected all hardware except mouse and keyboard: set N1 to approx. 30%; the plane accelerated faster than in my initial test which is normal because the plane is lighter (got to about 40kts by half the runway), then reduced to thrust idle; plane decelerated moderately but noticeably to about 20 kts within 10 seconds and would come to a standstill after about 20 seconds.

2. re-connected all external hardware (HOTAS joystick and throttle, Saitek pedals) and re-ran the above test: the exact same result. There is no difference.

This pretty much replicates what Kyle @scandinavian13 had found (as I had already stated in my previous post) and rules out any external hardware mis-calibration or other issues with the hardware setup. So I think we are at jeopardy of agreeing violently that we get the same results in our tests (albeit Kyle didn't test the deceleration part), but we seem to disagree on the conclusion: is this the correct behavior and had it changed to previous 777 versions? 

@Driverab330 seems to suggest it is not the real thing:

I for sure can't tell since I'm not a RL pilot.

The only thing I can say is that I remain committed to resolving the issue (if it is one) and hope PMDG support can do the same (as I am used to it does) and we can leave the somewhat controversial attitudes behind us and stick to the facts.

Thanks,

Jan

 

[pete_auau 1,154]

Going  to add my 2  cents  in this  topic, users  expect   the  sim to behave   as per  the  rw  aircraft its not  going  to happen you will always  have  different  variables  in play   so  as  Driverab330  has  stated  in his  post above  said  the  overhaul  simulation is  good

[Mephic 129]

Ignoring all pointless accusations, I've disconnected the Saitek Yoke, rudder pedals and both of my Throttle sets and repeated Kyle's test adding also decceleration part where the actual problem is and result is exactly the same, plane stops itself much quicker than in v3, with or without hardware connected.

Since LM changed their ground friction model between v3 and v4 I believe some adjustments had to be made, but obviously I might be wrong as I'm not developing this aircraft. 

[ZKOKQ 984]

Having the same issue. Does not roll like it did before. At idle thrust, it slows to a stop. Turning on a taxiway should not require 28 to 30% thrust to keep the old girl turning. Hardware removed....still the same. I'm with Tomasz on this.

[Driverab330 74]

In short, the thrust requires to keep the real airplane moving in a straight line on a flat taxiway even at MTOW is idle thrust. you would definitely need some thrust to break away from standing still at MTOW and during a turn, but that's it. 

As you can see in this video at time 16:15, the FO was PF, they were turning in to a Parking Bay in TaiPei  (RCTP), his hand was not even on the thrust lever and the N1 were showing 21.5% which is idle thrust all the way until they stopped. 

Also you can see from some of the shot on the upper EICAS showing after landing the thrust was at 21.5% most of the time. 

This is quite a good flight deck video.

Anyways, I am sure PMDG knows about this issue now, they are probably looking into it at the moment. Hopefully there will be a slight improvement in the near future, but this is definitely not deal breaker. 

 

 

 

[ZKOKQ 984]

3 minutes ago, Driverab330 said:

In short, the thrust requires to keep the real airplane moving in a straight line on a flat taxiway even at MTOW is idle thrust. you would definitely need some thrust to break away from standing still at MTOW and during a turn, but that's it. 

Thanks. If only the current version of the 772 would do that. But it's not. Thrust is applied all the way to pre take off.  I use to be able to turn, and tight turns with marginal thrust, and of course the P3D / FSX  taxiways and runwys are flat, no slopes. So comparing real world is not adressing the issue. But thank you anyway.

[JRBarrett 3,044]

52 minutes ago, Mephic said:

Ignoring all pointless accusations, I've disconnected the Saitek Yoke, rudder pedals and both of my Throttle sets and repeated Kyle's test adding also decceleration part where the actual problem is and result is exactly the same, plane stops itself much quicker than in v3, with or without hardware connected.

Since LM changed their ground friction model between v3 and v4 I believe some adjustments had to be made, but obviously I might be wrong as I'm not developing this aircraft. 

This is exactly what I am experiencing, and it "stands out" because it is noticeably different than V3 prior to the unified V3/V4 installer. 

It's NOT so much the breakaway thrust as the deceleration. With my brake axis completely disconnected in the 777-200F, with a payload of 75,000 pounds, and a fuel load of 50,000 pounds, if I accelerate to a taxi speed of 15 knots then close the power levers to idle, the aircraft comes to a complete stop in less than 20 seconds. That seems excessive.

This may be a change in ground friction in P3DV4, which would be beyond PMDG's control - but I believe V3 users are seeing the problem too, and did not have the issue in the previous V3 version of the 777.

[hawx2k 6]

3 minutes ago, JRBarrett said:

This may be a change in ground friction in P3DV4, which would be beyond PMDG's control - but I believe V3 users are seeing the problem too, and did not have the issue in the previous V3 version of the 777.

Affirm: it is the same in v3 now. Tested both with the new installer.