Should the aircraft fly with its gross weight always?

[blueaircraft]

For example, a transatlantic flight from London to New York in a 707 420 INT Conway would render an almost full fuel tank, while PAX and cargo are still high, but not as high. This leaves it close to its gross weight. However, if one were to fly from Johannesburg to Brazzaville in a 707 320 INTJT4A, should the "lack" of fuel in the aircraft's tank be replaced by more PAX and cargo so that the aircraft is close to its gross weight? Or should I leave the payload (not fuel obviously) as is?

Regards
Andrew

[aerofoto - HJG Admin]

Should the aircraft fly with its gross weight always?

Not necessarily .... and not if one flight plans

MGTOW is the "certified weight" that should never be exceeded for any TO or for flight.

We compile our simulations so each load into FS with both 100% fuel and payload (by default) in accordance with tech specs of any aircraft subject. This always results in a nominal overload. The End user is then expected to reduce either fuel, or payload, or both, in accordance with the requirements of their virtual flight/s and to ensure the simulation isn't then overweight

"IN FS" .... I generally first determine the "distance" I want/need to fly.

I then calculate the "fuel" I require in order to fly that distance (without everything suddenly running quiet/shutting down on me before getting there) using the Flying Guide quoted fuel burn rates .... and with around 45 minutes to 1 hour of reserve fuel added over and above the calculated requirement/s.

That fuel requirement translates to "weight" being carried .... and which then dictates what I can load/carry in terms of simulated payload (PAX and cargo/baggage) weight without exceeding the certified MTOW for any simulation.

That's the proper/best way to do it

One may regularly find one can't carry a full payload on much longer flights .... through needing to prioritize fuel requirements in order to reach one's destination.


One should also plan one's fuel requirements so as to not exceed about 20% total fuel remaining (irrespective of payload carried) prior to landing at one's destination airport .... otherwise one will be overweight for landing and which will upset the simulations entire flight profile for the approach to landing.

There are FS programs/utilities one can buy that supposedly calculate fuel requirement/s for any flight, but, I (personally) don't have a lot of faith in them (not that there's anything wrong with them) .... simply because I prefer to flight plan based on the performance data we've compiled(during pre-release testing) for each of our own simulations.


In summary ....


If one wants to prioritize range then one needs to reduce payload.

If one wants to prioritize payload then one needs to reduce fuel .... and which will be at the expense of range.


Also .... after sufficient fuel burn-off following departure one can "progressively" climb to much higher cruising altitudes where fuel burn will further progressively reduce also .... and thereby promoting further range improvement.

That's how I plan all of my virtual flights.

"GOOD PLANNING" is "ESSENTIAL" .... and it also makes FS "MORE FUN" too


Mark C
AKL/NZ

[aerofoto - HJG Admin]

Just coming back to the flight planning aspect of things ....

Fuel and/or payload (or both) can be/need to be adjusted (reduced) in order to safely depart from shorter RWY's.

This often then dictates en-route fuel diversions/transits for longer ranging flights .... and which is quite authentic when/if re-enacting real world operations in FS.

I remember a flight I was on from Niue Island to Auckland (a B732) during 1993. We had a full load of PAX (every seat was occupied .... and to the extent I was in the FD jump seat) and their baggage but no freight. We went out of Niue with a reduced fuel load in order to accommodate its relatively short RWY (prior to it later being extended). We then had to transit to Auckland via Nuku'Alofa/Tonga (about 40 minutes from Niue .... and with a long RWY) in order to load more fuel to continue the flight on to Auckland. As I mentioned above .... this's another way to flight plan, especially from shorter fields, and which can easily, and realistically too, be practiced in FS.

During the late 1950's/early 1960's and before the Intercontinental B707 and DC-8 entered service, Trans-Atlantic B707 (and COMET IV) flights, both ways across the Atlantic, needed to transit through either Gandar, Keflavik, or Shannon (except in favorable conditions) .... because they weren't capable of operating these services direct.

Mark C
AKL/NZ

[avallillo]

Flight at max gross weight is usually something of a rarity, even in long haul operations. My airline did not become a really long range international airline until about midway through my career, and until that point we never got close to the max weight of the 707's, DC-10's and 747's that we operated (we even had certificated our version of the 707-300 for a MTOW of merely 350,000 lb, since landing fees were based upon the max certificated weight, which the FAA would always tailor to the individual preferences of any airline). Not until we started flying to places in the Orient did we come close to max weight; and once the 777's came aboard, they could handle those ranges comfortably. Today, I imagine only the absolute longest flights have to deal with what to offload, and passengers are usually the last thing to go. With an exception I will mention further on.....

On the 767, which I ended my career flying, we did have at least one route out of NY where we could see the full Monty - 408,000lb - on occasion, and this was JFK-EZE. We had to wait at the gate for the load closeout, to ensure that we did not turn a wheel if the weight was above max taxi weight - 409,000 - which would have required a maintenance inspection; not exactly the way to start an 11 hour flight! In cases like these, the payload was restricted, since the fuel to get there was, for all practical purposes, full tanks, and thus cargo was offloaded (or more likely not loaded in the first place), followed by mail and then, only if needed, passengers. Often the res system was programmed to limit seat availability for these flights particularly in seasons that were affected by temperatures and winds. In my experience, we never had to offload anything - they held the stuff that might have to be offloaded and only slung it aboard at the last minute after it was calculated OK to do so.

Interestingly, the only things that were actually weighed before loading were the cargo and, possibly, the mail. Passengers and their luggage were calculated using average weights that have become progressively wishful-thinking as we humans have become Supersized! Those FAA average weights have been twice updated now, since I started flying, adding around 30 or so pounds to each person. Overall, they are fairly accurate, and performance has not been an issue in any passenger incident that I know of....

What is more surprising is that max gross weight operations are an everyday event at the Regionals - those little jets are hard put to get off all but longest runways fully loaded at the higher temperatures of summertime and with the contaminated runway conditions of winter. Non-revving on a Regional is unnerving, since despite what your airline's non rev travel planner shows as seats available, the plane may go out with as many as 10 seats empty due to performance limits.

[aerofoto - HJG Admin]

I enjoyed that read "AVALLILLO"

Interesting account/recollections .... particularly in regard to Regional Carriers and progressive revisions applied to the FAA mandated PAX weight assumptions as people, over the years, have generally become "HEAVIER". If my mind serves me correctly "assumed PAX weight" .... over and above the measured weight of baggage, freight, and fuel on any flight .... became "a factor" (part of the chain) in the case of the MIDWEST AIRLINES/US AIR FLT 5481 accident during 2003 .... although this wasn't the actual cause of the accident given improper adjustments applied to the aircraft during maintenance the evening prior to the flight ....

en.wikipedia.org/wiki/Air_Midwest_Flight_5481

AIR SDAFETY ACCIDENT REPORT
aviation-safety.net/database/record.php?id=20030108-0


Steering a slightly different course here now (only for the sake of general interest and in support of the actual thread topic too). On the subject of "WEIGHT" assignment/s "IN FS" and in order to explain how we/HJG arrive at our stated conclusions in regard to the simulations we offer ....


One of many things Mike and I do when performing extensive pre-release testing during FDE work-ups is we always flight test "at the simulated MGW first and foremost". This then gives us an impression of how any simulation "wants to fly in FS" (key words) and helps us identify what we may need to adjust in order to try'n further perfect simulated flight handling .... "within the limitations of FS" (other key words).

We generally find that once we successfully manipulate MGW performances to our satisfaction .... then .... performances subject to further FUEL & PAYLOAD weight adjustment/s (lower/reduced assignments) within FS are usually equally good .... provided the End User then loads and flies each simulation sensibly (more key words ) . This pre-release flight analysis can take days .... sometimes even weeks or months .... to perfect given it's probably the most difficult and time-consuming aspect of any FS development

As part of our methodology we also adjust the MOI data for each simulation around "officially stated/RW weight specifications" (not talking about manual adjustments within FS here ) fort each aircraft type/series in order to positively influence both handling and feel .... and then other parameters are similarly adjusted too, if necessary, in order to correct or further fine-tune simulated flight behavior. RW Tech-Spec references can vary for the same aircraft types/series operated by different carriers though (particularly in regard to older aircraft types) .... so .... given we can't (sensibly) represent every specification we then apply "an accurate common specification", applicable to each aircraft type/series, in order to arrive at the weight conclusions we finally state and apply to everything we produce/offer.

I've stated this a few times previously .... BUT .... many FS developers tend assign FUEL and PAYLOAD for "a typical flight only" (since that's what most people are accustomed to in FS). However this then denies those End Users whom like to Flight Plan the ability to get the most/very best virtual logistics out of their simulations .... in respect of range and payload primarily. Mike and I generally assign maximum/100% fuel and payload for all the simulations we work up here at HJG (again based on the RW Tech-Specs we source for each aircraft type/series). Applying this methodology generally results in a nominal overload .... but which the End User is then expected to "manually adjust" (using the FS FUEL & PAYLOAD facility) in order to set their flights at/near MGW .... or however they desire to specifically define payload and fuel for the purpose of their intended virtual flights.

We can't ever provide absolute fidelity in regard to virtual flight (it's just not possible to reflect all aspects of real world aviation into FS .... given the limited number of manipulable parameters offered by the host program), but, using our methodology we can, and do, offer "EVERYONE" something "a little more realistic" .... and specifically for the benefit and enjoyment of those whom like/want such

Perhaps needless to say .... since 2000 HJG has always catered for "an entirely different breed" of FS enthusiast.

Mark C
AKL/NZ

[blueaircraft]

Thanks Mark and avallillo! You all confirmed my reasoning on flight planning

[maverick2021]

Jun 25, 2023 20:44:58 GMT blueaircraft said:

Thanks Mark and avallillo! You all confirmed my reasoning on flight planning

I've been reading the topic on fuel burn and PAX zones. I've come with the following formula for calculating fuel for a given flight:

Distance to destination ÷ public range of aircraft = decimal percentage per each fuel tank.

Example: (I'm pulling numbers out of the air here)

MD-11 range = 6725 nm
Distance to destination = 3400 nm

3400 nm ÷ 6725 nm = 0.505 or 50.5% per tank

Next calculate reserve by dividing average ground speed into range.

515 knots ÷ 6725 nm = 0.076 or 7.6% extra in tank.

Summerize: 50.5% + 7.6% = 58.1% in each tank. Add another 7.6% for 2 hour reserve.

This assumes the aircraft has accurate range. If your final answer exceed 100%, reduce each Pax zone by the same amount per zone to maintain CG.

Chesley Hann

[aerofoto - HJG Admin]

I use a different (and I think better/simpler) method of manually fuel planning for any virtual flight. I'll explain as follows ....


At the end of each of our forum based aircraft type manuals is a Flying Guide .... for each aircraft type version we represent.

Within the cruise performance sections of these Flying Guides the FF for each simulation" is quoted (mostly for FL310 only .... but for other altitudes too in the case of some aircraft type simulations we offer). The indicated FF will differ for each aircraft type simulation we offer .... mostly because the engine types, and their known FF rates, each differ. Using the best RW references we can obtain we factor this data into each of the simulations we compile.

PLEASE NOTE: These FF references quoted within each of our forum based Flying Guides are "the actual FF indications" for each simulation at the stated altitude and airspeed/velocity "as recorded by us during pre-release flight testing".

PLEASE NOTE ALSO: Using official TSFC data the indicated fuel flow for each of our simulations is accurate "AT SEA LEVEL ONLY" .... but "IN FS" we generally have to "accept" whatever these indications then become by the time each simulation reaches its virtual cruising altitude (that's the way in which we compile this data for all of our simulations .... whereas other developers undoubtedly use different methodologies). As a consequence of this "acceptance" the recorded FF for each of our simulations, at altitude and for any particular airspeed/velocity, can end up being a little higher, or lower, than should be the case in reality .... and as such actual range may be similarly implicated too and which similarly needs to be "accepted". There's really no such thing as absolute fidelity/total authenticity "IN FS".

The way I fuel plan, and recommend fuel planning be undertaken, and for our simulations at least is as follows ....

1. Note the recorded FF at altitude and for any particular airspeed/velocity for each aircraft type simulation as stated within each of our Flying Guides. This data is mostly quoted in 1,000's of LBS per hour (based on panel FF gauge indications).

2. Multiply the quoted FF indication (per hour) stated within each Flying Guide by the number of hours estimated flying time along any virtual point-to-point route/virtual flight .... this then becomes the basic fuel requirement estimate.

3. Based on the above basic fuel requirement estimate for any virtual point-point-route/virtual flight calculate "an additional 30 minutes more" fuel (based on the combined hourly FF rate of each engine) .... and add this to the above (#2) basic fuel required estimate .... this particular quantity is reserve fuel.

4. Calculate and add "another 10% more" fuel based on the above revised (#3) total for good measure .... and which then becomes the "total fuel loading" for any point-to-point route/virtual flight.


A PARTICULAR EXAMPLE ....


Following any MGW TO and climb to FL310 (a good initial cruising altitude) our MD-83 simulations demonstrate a FF indication of some 3,400 LBS (per hour) at MACH 0.79 .... and which equates to a total of some 6,800 LBS per hour for "both engines combined".

Add 30 minutes reserve or half of the above indicated total again .... and which equates to another 3,400 LBS for a new total of some 10,200 LBS of fuel.

Then add another 10% more fuel on top of the above quantity and which equates to some 1,020 LBS more .... for a new and final fuel loading of some 11,220 LBS in total.

This will be quite sufficient to get anywhere one wants to go within "an hours flying time/range" .... and with a safety reserve of approximately "30 minutes only" .... and with the added assurance one won't be landing overweight upon arrival at one's virtual destination nor running the risk of everything suddenly going "quiet" en route either .... provided adheres to their flight planned performance without any deviation.

Our MD-83's feature a 3-tank configuration .... so .... distribute the above total fuel "evenly" across all 3X tanks .... and which should then result in a loading of some 3,630 LBS of fuel "per tank" (to calculate all of this "quite crudely") in order to avoid fuel imbalance.

For such a short flight and light fuel loading no payload adjustment/s should be necessary.


Again that's how I do it (fuel planning) and what I therefore recommend .... "using our simulations" at least

For flights of significantly longer duration/endurance if ever confronted with a situation where upon fuel planning one's grossly overweight (most large aircraft have a MRW tolerance of around 1,000 LBS higher than their MTOW) .... then one will need to "reduce payload" in order to accommodate the the fuel required to reach one's virtual destination or tech/fuel stop en-route.

Using our customized Flying guide stated information this same methodology can be used for all/any of our simulations .... and works well .... "IF APPLIED CORRECTLY".

The are (apparently) commercial adventure type programs that generate flight plans (including fuel loadings too), but IMHO, its always better to use the FF data we quote within the Flying Guides for each of our simulations as this information is "reliable/accurate" .... simply because this data is what's been been recorded by us during thr pre-release flight testing of each simulation we offer.


Mark C
AKL/NZ

[Mike Monce - HJG]

There's a fairly useful web site available for FS planning: simbrief.com. It's free after registration though they do push the "premium" level but it provides great detail at the free level. Input your departure and destination and aircraft type. Note, not all vintage jetliners are available but I use something that come closest and then adjust accordingly given that the older plane burn more fuel. It will then generate a flight plan based on current weather; this is great for me as I use real weather in all my flights. As to the topic at hand, it will also output block fuel load taking into account upper winds and 1 hour reserve. One issue is that the route is based on the latest AIRAC database which, of course, doesn't' exist in FS9, but just take the general route it generates and again adjust to the nav data in FS9.

Mike