Ground handling physics of PMDG planes

[Christopher Low 5,352]

I know that there was some criticism of the updated ground handling physics when PMDG released the 737NGXu, but I am curious to know what the real world airliner pilots think about this. I use the previous version 737NGX, a version of the 777 that is too old to be updated, and the latest version of the 747-400 in P3Dv4. That being the case, I have the old ground physics in the 737 and 777, and the new physics in the 747. Of course, I do not have any experience with the real planes, so I am not able to say which is more accurate. However, my opinion is that the ground physics of the 777 feel more realistic than the 747. When I turn the 777 on the ground, I feel a bit of resistance....and this is what I would expect from a large airliner with a triple gear main undercarriage. Those two sets of six fixed position tyres should offer quite a bit of resistance to a turn. On the other hand, the updated 747 feels very light through turns, without any great feel of resistance at all from the four sets of four fixed position tyres.

Maybe I am missing something here? I would be curious to know what the real world airliner pilots (particularly former 747-400 pilots) think of the new PMDG ground handling physics.

Edited January 18, 2022 by Christopher Low

[SimeonWilbury 220]

Not a pilot here, but the 747 does have body-gear steering on two of the main gear bogies to help with tight turns on the ground, so they aren't all fixed position per-se. On the -400 I believe it is active below 16kn GS (at least that's what I remember from the manual). So that helps it a bit better at low speeds. You'll notice in the PMDG 744 that if you go beyond 16kn GS the aircraft turns more slowly and it becomes very difficult to make any tight turns.

I haven't tried the 777 but have tried both versions of the 737, all I can really say about the 737 is it's my least favourite aircraft in regards to ground-handling but that was the case even with the older, less realistic steering.

Edited January 18, 2022 by SimeonWilbury

[Bob Scott 7,719]

The MLG tires on both acft aren't all on fixed axles.  The fuselage-mounted body gear (two inner and aftmost) MLG trucks on the 747-400 are hydraulically steerable up to 13 deg left/right, and the 777's two MLG rear axles are also steerable, so turning dynamics are explainably likely to be a bit different between the two acft.

[kand 205]

This is very difficult to compare as ultimately all simobjects use the same physics, and SIM1.dll has the sliding coefficient of tarmac/concrete set to a low level which results in skidding. Unless PMDG are controlling the FDE externally the only variables can relate to weight and turning radius of the nosewheel, perhaps the damping moment of the suspension also affects the turn? 

I am fortunate to have around 20hrs on the BA 777 level D sim, slow speed turns were easy but at high weights anything over 10kts could result in side force. One of the most riskiest manoeuvres BA undertook was a 180 turn on the runway at one of the narrow Carribean airports. We demoed this and with differential thrust and braking you can just make the turn but you have to stop with the nose at 45d to the runway and overhanging the grass. Starting from a stand into that turn was very difficult to get right. From the flight deck it feels like you are moving backwards! 

p3d ground handling is primitive although with the introduction of sloped runways in v5 I imagine there are some changes to contact points. From a physics perspective sim1.dll is the culprit with the ridiculous rolling/sliding/braking friction coefficients. FDE designers have to compensate for the rolling which throws all the thrust values out which in turn breaks the fuel consumption at low levels of thrust, this is why every time a new version of p3d is released, out comes my hex editor! 

Interestingly MSFS has tried to sort this out, but that is even worse sometimes with the wheels gripping the runway at high speed like they were magnetised to the surface! 

[jon b 2,047]

2 hours ago, SimeonWilbury said:

On the -400 I believe it is active below 16kn GS (at least that's what I remember from the manual).

Yes that’s right, it activates decelerating through 15 kts and deactivates accelerating through 20 kts, the body gear turns only after 20 degree of nose wheel steering is used.

The 747 is nice and smooth in the taxi and has exceptional  damping on the nose wheel suspension.

I use a cat3 design nose wheel tiller on the sim, I’ve not noticed anything jump out at me as being bad with the latest PMDG 747 taxi behaviour. But I’ve not taxied it too much, I tend to start engines running on the runway and go !

[F737MAX 5,584]

17 minutes ago, jon b said:

[...] I’ve not taxied it too much, I tend to start engines running on the runway and go !

😱

You mean to say that a professional aviator doesn't spend 30+ mins at the gate, starting up from cold and dark, aligning the IRUs, uploading your nav, payload and weather data into the FMC, and requesting an IFR clearance from VATSIM, while having GSX deliver fuel, food, baggage and self-loading freight?
Shocked! Shocked, I tell you... 😄

[Patco Lch 1,465]

How about braking action on a contaminated runway?

[jon b 2,047]

@F737NG

flight simulation is all about fantasy of one sorts or another, and the fantasy for me is just turning up and blasting off without all the associated BS that seems to go with flying nowadays ! 😀

[LRBS 947]

3 hours ago, F737NG said:

😱

You mean to say that a professional aviator doesn't spend 30+ mins at the gate, starting up from cold and dark, aligning the IRUs, uploading your nav, payload and weather data into the FMC, and requesting an IFR clearance from VATSIM, while having GSX deliver fuel, food, baggage and self-loading freight?
Shocked! Shocked, I tell you... 😄

@F737NG, I guess there is a misunderstanding here re @jon b. First, regarding real-life taxing the 747 he is 100% correct, smooth operation all across. Also, there are some discrepancies with the PMDG taxing at low gross weights. But as RSR said "only 1%" or qualified people in type will notice. 

I fully understand Jon's choice to start the engines after a short preflight and go versus requesting and waiting for VATSIM for clearance or "GSX deliver fuel, food, baggage, and self-loading freight?". We do that in real life and some of us are quite tired of it and just prefer to avoid that nonsense.

Yes, for a PC pilot it is as much as close to reality as possible.

No need to be "Shocked" about choices.

[jon b 2,047]

2 minutes ago, Vlad Tepes3 said:

@F737NG, I guess there is a misunderstanding here re @jon b

 

2 minutes ago, Vlad Tepes3 said:

No need to be "Shocked" about choices

I can detect F737NG’s distinctive  British sarcastic humour in his post, which probably doesn’t come across well written down on the internet and read by those not native to these shores 😀 I don’t think for one moment he is actually shocked, at my severe lack of professionalism  😉😄

[jon b 2,047]

9 minutes ago, Vlad Tepes3 said:

We do that in real life and some of us are quite tired of it and just prefer to avoid that nonsense.

👍😀 yes !

[F737MAX 5,584]

49 minutes ago, Vlad Tepes3 said:

No need to be "Shocked" about choices.

As @jonb already pointed out, I'm just as 'shocked' as Capt. Renault is in this clip... 😉

https://tenor.com/view/casablanca-humphrey-bogart-claude-rains-rick-blaine-captain-renault-gif-15943064

(I'm not shocked in the slightest).

In my opinion, Flight Simming can be done as professionally or as casually as anyone wants.
Whether it's someone trying to land and stop a 747 at min. fuel at Saba after doing a barrel roll on approach or replicating a full-blown, IFR-cleared transatlantic flight with frequent position reporting, ending with a diversion at destination due to RVR falling below minima.

A lot of us here are not aviation pros, so we tend to like replicating real-world ops as much as possible. That's why we often get threads like this one here, asking about the realism level of what we are using to replicate flying.

[Patco Lch 1,465]

1 hour ago, jon b said:

 

I can detect F737NG’s distinctive  British sarcastic humour in his post, which probably doesn’t come across well written down on the internet and read by those not native to these shores 😀 I don’t think for one moment he is actually shocked, at my severe lack of professionalism  😉😄

I used to watch the Bennie Hill show back in the day, so I am an aficionado of British humor.😂 

[C2615 319]

9 hours ago, Vlad Tepes3 said:

No need to be "Shocked" about choices.

👀 I was shocked even then, he went to bought the $300+ tiller anyway

[IanHarrison 522]

11 hours ago, jon b said:

@F737NG

flight simulation is all about fantasy of one sorts or another, and the fantasy for me is just turning up and blasting off without all the associated BS that seems to go with flying nowadays ! 😀

You sound like my son, who flies the PMDG 744 upside down and does slam dunk landings on impossible airfields.

I take all the time needed to load everything.

(I suppose when you are retired and live on your own, then you need to fill the time).