Too High Ground Friction?

[investdude]

I'm having a problem in FS2004 which seems to only affect HJG aircraft. Often when taking off the aircraft is so slow to accelerate (at a light weight) that it is impossible to get airborne before the end of a very long runway (180 feet ASL). If, after this happens, I try again, I may sometimes be able to get airborne by firewalling the throttles and overboosting the engines and in the air everything seems normal but upon landing the aircraft stops in an incredibly short distance, in like 1/10th of the distance with full auto brake, and this is with no auto brake selected. The HJG 727s have a special taxi function but the throttles advance as far as this function allows and the aircraft remains stationary.

I have found this to happen with HJG 707s and the 737-300 also. It seems like the ground friction becomes too high but how and why is a mystery to me. This has just started happening recently and I have not been able to identify any modification to HJG aircraft or FS2004 that would account for it. Any help with this would be greatly appreciated.

[aerofoto - HJG Admin]

UMMM .... there's "a number" of potential possibilities for this .... SO .... I need to say "A BIT" accordingly

This has just started happening recently

Only just recently .... but .... not before ?

If that's the case then it's unlikely to be the simulation/s.

You may need to look at the calibration of whatever power quadrant/controller device/s you're using .... for starters.

"Ground Friction" is something that can be more evident with some FS scenery than others too .... although there shouldn't be any major or concerning issues when using most default scenery.

The simulations we offer feature varying "weight and engine thrust" configurations, so, performance variation/s are to be expected between types .... both on the ground and airborne too.

I acknowledge ground friction has been noted to be "a very minor issue" with some of our simulations (this has been" discussed here a number of times in the past) .... but .... it certainly "doesn't" apply to some of the simulations you've mentioned and nor does it ever impair their performance/s to the extent you've related either.

Among the simulations offered here we know our B727's and DC-9's are "slightly" affected, but, not to any alarming extent .... and the B737's we offer here each taxi easily and for very little power at all.

"Without" implying what we offer's prefect (and which precisely what I'm "NOT" suggesting) the ground friction we know to be evident is only manifested by "slightly higher" thrust settings needing being applied in order to "initiate/start taxiing", until a decent taxiing speed is achieved, and which through momentum gained can then be easily maintained following thrust reduction and per further modest power adjustment/s, and without any problem/s .... but that's all. "It certainly doesn't" result in TO or any other performance impairment/s like, you say, you're experiencing with the simulations mentioned.

I use all of our simulations in FS2004 too and my response, on this occasion, is based entirely upon past forum feed back and what I've personally noted using each one over the years .... and as recently as just yesterday as a matter of pure coincidence

I wouldn't mind betting the larger part of your problem (if not controller device calibration or scenery related) may be in regard to possibly not having adjusted the weight of each simulation "prior to" departure.

If one refers to our forum based manuals for each simulation an important detail we state is as follows ....

PLEASE NOTE ALSO: By default all HJG supplied simulations load into FS with both "100% fuel and payload" .... resulting in a nominal "overload". This is a perfectly normal result under these circumstances. The end user is therefore expected to manually adjust either fuel or payload, or both, in order to ensure each simulation is set at/near its certified MGW or otherwise in accordance with the requirements for ones anticipated virtual flight.

By default .... maximum fuel and payload is compiled into each of our simulations (based on "a common specification" for each aircraft version .... all of which vary). Unlike other developers .... we never compile a set loading in order to satisfy a particular MGW specification and nor do we ever apply weight to influence performance either. We offer everything in the manner we do simply because doing so then promotes more accurate flight planning. If such flight planning isn't undertaken or is undertaken improperly .... THEN .... one's likely to be confronted with a grossly overweight simulation that'll be performance impaired .... both on the ground and airborne. Therefore one needs to reduce either fuel, or payload, or a combination of both, in accordance with the requirements of one's intended virtual flight.

Again .... I suspect much of your problem/s may possibly be traced to the above.

In regard to the B707's .... following pre-departure weight adjustment/s "maximum power" should always be used for TO .... as stipulated within our supporting manual. In the case of the very earliest among our B707 versions in particular (B707-120 and -138 .... and this also applies the earliest of our C-135's too) "maximum power" and the "water/methanol injection system" must both be employed together in order to boost TO performance during any MGW departure (this was a R/W procedure for these aircraft too) .... or .... one may not reach VR much before the end of even a 12,500+ FT RWY .... and maybe not at all if departing from an equally long but high altitude RWY.

Always bear in mind .... B707's (and DC-8's too) aren't short field capable aircraft under MGW operating conditions .... so .... when selecting any FS airport/RWY .... one also needs to ensure it's "plenty long enough" or one may run out of concrete and become a off-roading candidate .... or worse

Another detail that needs being born-in-mind too is the HJG offered aircraft base packs and panels are specific to each aircraft type version. If these are "incorrectly paired" .... THEN .... either under or over performance/s can result. Therefore always ensure the "correct/recommended" panels are used with the correct/recommended aircraft base packs for each HJG simulation.

The HJG 727s have a special taxi function but the throttles advance as far as this function allows and the aircraft remains stationary

The B727 panels we offer feature such a function (because that's what the original author designed into them), but, we've never recommended it be used .... despite the fact it can't induce any harm either.

My advice is .... don't use it.

Manually apply, and adjust power as required, in order to maintain and/or control ground performance.

At the end of the day though .... and knowing these simulations as intimately as we do .... I don't believe there's any problem that we can, or need to, or are even able to fix .... at least not without risking breaking something else in the process and which is always the greater concern


Mark C
AKL/NZ

[aerofoto - HJG Admin]

Just reiterating what's stated within each of our manuals as follows ....

Power required in order maintain a sensible taxiing speed will vary in accordance with B707/engine type and thrust rating and simulated weight .... as well as natural FS ground friction phenomenon.

PLEASE NOTE: The ground friction phenomenon may be more apparent with some FS scenery than others.

Researching the subject of Ground Friction in FS .... both before and since replying to this posting ....

Community feed back (outside HJG .... and not in relation to HJG products) seems to acknowledge this's an issue affecting both FS2004 and FSX and it's impact can be around 50% greater than should be the case in reality.

Still .... and even in regard to the Ground Friction we acknowledge being evident among "some" of our own simulations .... we've "NEVER" known such too result in performance impairments to the extent, you say, you're experiencing.

Once again it's been noted you mentioned this having occurred "recently" .... therefore suggesting such wasn't the case previously.


Mark C
AKL/NZ

[investdude]

Thanks for your prompt response and very comprehensive answer Tony. I was aware of all the possibilities you mention. I was not aware that scenery could affect ground friction. I did install a scenery upgrade recently and it now appears that this is most likely the cause of the problem. I will uninstall that scenery and see what difference it makes. Thanks for the help.

[aerofoto - HJG Admin]

It's a possibility (especially if your problem/s began after your recent scenery upgrade) .... but I won't go so far as to say it's definitely the sole cause in your case .... because we do acknowledge that some of our simulations require engine power settings "slightly higher" than is realistic (and more-so subject to unchecked weight impositions) in order to commence taxiing, until momentum is gained upon the acquisition of speed, and which then requires thrust reduction in order to maintain a sensible taxiing speed .... albeit for still "slightly higher" than is desirable power indications.

As already mentioned .... this's largely imposed by the natural FS Ground Friction Phenomenon .... and which may be more evident using some scenery than others .... thus similarly affecting some simulations more than others too .... and also suggesting FDE may play a small role in this as well (we can't address the latter though because any attempt to do so now will likely destabilize our current sound packs which are compiled on the basis of certain FDE based elements for authenticity .... and which is the way our audio's made).

FDE-wise .... we can generally offer great ground performance or great inflight performance, but, seldom both .... so .... we focus on delivering great inflight performance/s primarily.

Mark C
AKL/NZ

[dl1011]

in some occasions FS Sceneries can cause that situation depending which ones they are, but they can be fix, ive had issues like that not with HJG, nut with other aircraft like posky with the 757s but was able to get it sorted out, the 727s i have that issues with the overpowering and especially with the MD-80s but i feel i still make the enjoyments with them.

[aerofoto - HJG Admin]

Just "a wee bit more" in regard to this subject of Ground Friction ....

There "IS" an AIR.FILE based modification that could be applied in order to try'n address the low/idle end of thrust curving within any FDE and with potential to reduce the impact of such Friction .... BUT .... there's also a risk associated with doing so.

IN ORDER TO TRY'N PUT THIS AS SIMPLY AND NON-TECHNICALLY AS POSSIBLE ....

"IF" we were to employ such an edit for any of the "minorly affected" simulations we offer (this issue's deemed by us to be "very minor" based on what we've observed and commented over past years), then, as implied yesterday such would also likely impact our sound packs too.

Why ?

Because the compilation of sound packs we offer is based almost entirely upon thrust curving within AIR.FILE's accompanying each simulation .... and which is why our audio tends to function best with simulations we offer and isn't recommended for use with others.

"IF" we edit the FDE based thrust curving .... then .... doing so might resolve this issue somewhat, but, would also then influence (negatively) the low/idle audio within sound packs supported by these FDE's .... the effect of which would likely be manifested per either no audio below the sound packs original idle point and/or certain tones associated with, or slightly above, the original idle point not then working as intended. Such FDE editing would ultimately impose need to recompile and reupload sound pack/s again but short of completely redeveloping any simulation that's simply not going to happen .... for reasons of practicality.

Some might query .... How come the CFM powered B707-700, C-135's, B737's, and DC-8-70's all taxi so easily and for very little power with no evidence of their sound packs being impaired ?

The answer to this is simple and in 2 parts as follows ....

1. The FDE's for these simulations represent "our own" compilation/s of many years standing .... whereas such "doesn't" apply to FDE's associated with simulations we've imported over the years (with the exception of the B737's
we offer and to which we applied our own CFM type thrust curving) and purposely chose to interfere with "as little as possible" .... other than perfecting their flight characteristics or to aid certain panel functionalities.

2. The sound packs for each of these CFM powered simulations were (as implied above) compiled specifically in accordance with this long established thrust curving from the very start.

Only our B727's and DC-9's (possibly our MD-90's/90's too) may demonstrate "much higher than desirable" engine power indications in order to "commence taxiing" .... BUT .... as Ground Friction is somewhat overcome when speed through momentum is gained .... then .... such initially high power settings reduce through less power then needing to be maintained in order to ensure a sensible taxiing speed.

As mentioned earlier within this thread .... (a) We focus our attentions primarily in regard to perfecting flight performance/s .... and (b) There "are" also other influences which can contribute to FS Ground Friction to greater or lesser extent too .... and this's within "a game" that most developers agree Ground Friction is, by default, already overstated anyway.

Hope this helps explain a few things "a little more clearly"

Mark C
AKL/NZ

[Nathan Ford - HJG]

Hi Investdude how are you?

I have just had a quick thought about what’s happening to you. Do you use rudder peddles? If so, do you have the brakes calibrated using FSUIPC? If you do... have you clicked on the “reverse” axis checkbox in FSUIPC? If the reverse axis isn’t enabled the brakes on your rudder peddles will operate in reverse meaning that they are fully on while you are trying to taxi, land etc. 🤭

Cheers,
Nathan

[aerofoto - HJG Admin]

"GOOD" possibility Nathan

Mark C
AKL/NZ

[aerofoto - HJG Admin]

Just recapping in regard to the Ground Friction imposed high engine indications (N1/N2) during taxiing .... because in working up some preview imagery recently as well as some previously announced FDE edits too I made a point of noting these indications almost precisely and which I wanted to relate as follows for the benefit everyone's awareness ....


1. Using the B727's at their simulated MGW these indications will appear around as follows ....

At ground idle ....

N1 = 33%
N2 = 56%
EPR = 1.06

Taxiing .... with a more-or-less sustained speed of 15-20 KTS

N1 = 50%
N2 = 66%
EPR = 1.13


2. Using the DC-9's at their simulated MGW these indications will appear around as follows ....

At ground idle ....

N1 = 33%
N2 = 56%
EPR = 1.06

Taxiing .... with a more-or-less sustained speed of 15-20 KTS

N1 = 50%
N2 = 67%
EPR = 1.17


3. Using the MD-80's at their simulated MGW these indications will appear around as follows ....

At ground idle ....

N1 = 33%
N2 = 55%
EPR = 1.45

Taxiing .... with a more-or-less sustained speed of 15-20 KTS

N1 = 60%
N2 = 70%
EPR = 1.48


The above power observations are based on panels we recommend for use with our simulations.

As already acknowledged within this thread these observations "ARE" appreciably higher than is realistic .... BUT .... apart from imposing need to use greater power settings on the ground it really doesn't detract from the simulation at all .... at least not once speed, through momentum gained, is acquired, so, TO's are quite normal (distance and duration in relation power applied), and climb, cruise, descent, and approach landing are all "more than acceptable" too.

Simulated MGW and engine thrust variations among these simulations will further slightly influence the above observations .... either plus or minus, but, so little this probably doesn't even warrant a mention.

FS FUEL & PAYLOAD adjusted weight for each simulation (not the default MGW configuration) will also result in "minor improvement" too .... fractionally lower engine indications in proportion to weight reduction.

Add-on versus default scenery may further also influence these observations to a greater or lesser extent as well.

Again .... and once airborne (particularly during the high altitude cruise regime) these engine indications are mostly well within the ball park of reality/what they should be for "relatively authentic" performances .... but .... it also needs to understood the artificial FS environment isn't R/W and "the game" does lack any number of parameters that ultimately dictate performance and the actual physics of flying, so, what's realized/practiceable is the best we can currently offer for each of the 2 FS platforms we represent.

Each of the 3 above simulations were HJG "IMPORTS" .... at least that's true in regard to the B727's whilst the DC-9's and MD-80's were "produced for us" as a freeware version of their proprietors originally payware project. The FDE's for each of these are essentially what was supplied to us .... save for edits we've applied in to order correct/adjust the like of aircraft type specifications and to improve their flying characteristics as well promote certain panel/gauge staging as well.

The audio we currently offer (though as already recently advised per "HJG NEWS" 2 of the above simulations are presently having their original audio replaced with far superior data) is totally unimpaired by these higher than desirable ground based engine indications though .... simply because after engine start/spoolup correct audio tones are programmed to playback commencing from the lowest ground idle indications, then increasing up through the scale to maximum power, and similarly back down the scale again to idle .... all based on power adjustment/s and FDE stated thrust curving.

Most of our other simulations (in fact most simulations generally) may demonstrate engine indications resulting in similar ground indications as recorded above .... except those for each of the CFM-56 powered B707-700, C-135 SERIES, B737, and DC-8-70 simulations we offer since each of these benefit from a shared/common FDE element resulting in ground performance that's "almost" unaffected by the FS Ground Friction phenomenon and whilst still promoting superb airborne performance/s too.

Similar information "has been" presented on this forum since around 2010, but, is now presented "HERE" more accurately per the above-presented observations.

As earlier mentioned within this thread .... it's possible to reduce the effect of the Ground Friction phenomenon per FDE manipulation/s, BUT, not without also then imposing complete rewriting of the supporting audio for each affected simulation and which, for the above-mentioned reason, is "quite impractical" (except in regard to complete redevelopment of any simulation) .... and more-so-given this audio already performs correctly if not superbly within FS.

"Performance-wise" and in regard to the simulations offered here remember we tend focus largely upon trying to perfect "flight performance/s" primarily .... because it's within this regime each simulation is actually within its virtual element

Mark C
AKL/NZ

[aerofoto - HJG Admin]

To digress from HJG whilst still focusing on FS and the "Friction Phenomenon".

If one thinks "Ground Friction" in FS is bad/overstated then one should try "Water Friction" ....





















In the case of simulations for most flying boats and amphibians "Water Friction" in FS is "FAR WORSE" .... often requiring "almost maximum power" in order to be able to commence water taxiing

Mark C
AKL/NZ