Incorrect Weight Calculations

Hi, I’m loving the new look SimBrief! I have a custom DA62 airframe saved and found that the planner is not using the passenger weights I set (85kg), or the 25 kg baggage for each passenger.

Plus, I was wondering if the “Estimated” ZFW and TOW allowed for a slight over variation on the limit set in the saved airframe.
Passenger count of 5, with baggage, should weigh 550 kg. The planner has set 5 passengers with a total payload of 448 kg.

Additionally, estimated ZFW is 1830 kg + block fuel 139 kg = 1969 kg estimated TOW. The planner says the estimated TOW is 1960 kg. It’s omitting the additional 9 kg.

It’s not a huge deal, but when you have kids and trying to squeeze a quick fly in on the weekend :sweat_smile:

Nope, ZFW + block fuel is equal ramp weight, not takeoff weight. Takeoff weight is ramp weight - taxi fuel.

Your briefing will indicate “PAYLOAD/CARGO LIMITED BY MTOW”, although it’s not very intuitive since the passenger count is unaffected (IIRC real dispatch software does the same, except dispatchers are then smart enough to recompute the flight w/fewer passengers and/or adjust other parameters until this is no longer a factor).

@SimBrief in the new version, these weight limit remarks have been made less obvious, I would say? One could argue there’s no point in fixing it since apparently 90% of users have no clue what it means (and the rest who do can find them), but still, maybe something could be done to improve it a little? Perhaps they should be right below/above the loadsheet (currently separated by the flight route) and, when present, possibly highlighted in bold or something?

Also, recomputing passenger numbers is probably rather complex, but when payload is limited, just passing through the requested passenger count can be really pointless (easily half of the requested amount in some cases)? Even if somewhat unrealistic, perhaps the passenger count could be dashed instead to somehow convey that it’s not actually applicable anymore?



@RVTLordZod BTW, your airframe has a MZFW of 2200 kg and an OEW of 1720 kg, so the maximum payload is 480 kg anyway; you’ll never fit five 110-kg “passenger + luggage” units in it.

That’s actually realistic; small general aviation aircraft can rarely carry a full load of adult passengers with 25 kg of luggage each anyway (nor is there enough physical room in the DA62 for 125 kg of “typical” luggage, either).

It might be more realistic and practical to set up passengers without luggage by default, and add luggage via the freight text input field instead (which, as an added bonus, has single-kg precision since the redesign, as opposed to the old design where you had a rather coarse 100kg precision – rather unsuitable for small aircraft) :slight_smile:



Hey Tim, thanks for the reply.
I forgot to mention that the example with 5 passengers had all the weights/loads set to “Auto”. I completely understand the “PAYLOAD/CARGO LIMITED BY MTOW” message, but I find it interesting that the tool would put in a full compliment of passengers if it is going to exceed the MTOW when set to assign the number automatically.
I re-generated a flight that has weights/loads set to auto, and also setup the airframe so passengers have no cargo… the tool went straight to 6 passengers, which is over the 480 kg payload limit.

I understand what you are saying about the number of passengers and cargo numbers being unrealistict, but like I said, when you’re trying to squeeze in a quick flight in a simulator, it would be handy to be able to leave everything on auto and generate a quick flight that has accurate weight numbers, instead of maxing out the passengers and going over the payload. I’m happy to work-around the issue, but thought the devs might like to know how the tool is behaving.

As for the block fuel, your explaination makes sense and I can see how it gets added up in the briefing:

Hi, thanks for the feedback.

Currently this behavior is intentional, in the sense that SimBrief will increase the passenger count right up to the MTOW/MZFW. Even if the last passenger’s weight cannot be completely fit into the aircraft.

In other words, as long as the 6th passenger can be partially fit into the allowable payload, that passenger will be included in the count. If that passenger were not included (i.e. the load gets restricted to 5 “whole” passengers), your ZFW would have been arbitrarily limited to something like 2,145 kg.

The reasons for this are that SimBrief is not a load planner, nor was it originally designed with GA aircraft in mind. In an airline environment, the flight plan is generated hours before departure, while the weight and balance is done much later. With this in mind, from a fuel planning perspective, it’s better to over-estimate the payload and ultimately depart lighter, than the other way around.

Another thing worth mentioning is that by default, SimBrief always includes the weight of the pilot in the aircraft’s empty weight. So when it plans 6 passengers, it actually means there are 7 people on board. So if your aircraft has only 6 seats, I recommend either setting the max passengers to 5 in your custom airframe, or alternatively, keep it at 6 but subtract the pilot’s weight from the airframe’s OEW (which will result in more payload space).

I guess that none of this really answers your question of how to make everything “just work” in auto mode. Another option is of course to simply set a lower max passenger count in the airframe settings. For example, setting it to 4 will prevent the system from planning a heavier load than this, which should eliminate this issue for the most part.

Good catch, I think I’ll add payload restriction alerts to the top of the Flight Briefing page so they are more visible. Maybe in the next update.

Best regards,

Ah, I see. I now understand the relationship, and distinction, between a flight plan and load plan. Thank you for the explaination, and even suggesting a work around by modifying the max number of passengers.

FWIW, the DA62 comes in 5-seat or 7-seat configurations, so that’s indeed 1 pilot and 4 or 6 passenger seats, as opposed to 4/6 total seats. Although you’ll never fit 7 american adults in there :smiley:

Another thing to keep in mind is, for such small airframes, depending on conditions, even a single passenger can significantly affect aircraft performance, so regardless of the chosen solution (include pilot in OEW or don’t include it and make it a passenger), it’s a good idea to try and match the weights used by the addon you’ll be flying and its payload manager as closely as possible.

It should also be noted that the default simBrief DA62 profile has 1570 kg as the default empty weight; other addons I’ve seen use e.g 1590 kg (Aerobask) and the DA62 AFM refers to the individual aircraft’s “Mass And Balance Report” but does list an example “empty mass” of 1600 kg (and also describes empty mass as “The mass of the airplane including unusable fuel, all operating fluids and the maximum quantity of oil”).

This suggests two things: (1) in this particular case, the simBrief profile does not actually include the pilot in the aircraft’s empty weight and (2) yours does, but also, depending on whether you consider the empty weight without pilot to be 1570, 1590 or 1600 kg, your pilot weights between 120 and 150 kg :slight_smile:

Of course, going back to the my initial comment, if the addon you’re using actually weighs 1720 kg with the pilot included, then there’s not much you can do except live with the slightly limited useful load that comes with the addon you’ll be flying.



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