Talk:Payload fraction

message: If "payload fraction is calculated by dividing the weight of the payload by the weight of the otherwise empty aircraft when fully fueled" as claimed, then for Ariane 5 (LEO Payload: 16,000 kg;  Total Mass: 746,000 kg), the listed figure of 0.975 is absurd. Do the arithmetic as described, you'll see that payload / (total mass - payload) = 16,000 kg / (746,000 kg - 16,000 kg) = 0.0219. Obviously, a different calculation than was described has been performed here. -- 99.233.186.4 (talk) 18:21, 14 February 2010 (UTC)
replies: text: True, the values listed under "Payload Fraction" are actually [1 - (the described calculation)]. These numbers are in a sense telling us "what fraction of the initial weight is not payload." This should be made more clear in the article. Jtesla16 (talk) 06:05, 9 April 2010 (UTC)

text: It seems to be counting the empty upper stage as payload, which is also questionable.  This same table was copied into the article on mass ratio, where it is even more absurdly incorrect. DonPMitchell (talk) 18:35, 9 August 2010 (UTC)
thread_title: these numbers are absurd

message: Despite referencing aircraft in the opening paragraph, payload fraction does not appear to be at all relevant to aircraft in the same way it is for spacecraft. Rockets and Airliners have very different missions which muddy the water here, the aircraft destination is always variable, unlike the determinate goal of the spacecraft which is always to reach orbit. 
If the mission of our aircraft is to simply get as high as possible, its fuel load could be decreased quite substantially and the payload capacity thusly improved, but it will never reach space. Likewise, if we treat the rocket as an aircraft for a moment, the ratio of payload to fuel could be dramatically increased, if, say, our only goal is to bunny-hop a heavy-lift up to 500 metres. In this scenario, one could potentially load millions of litres of water as a deadweight. 
This is obviously not how the design term is meant to be used, so the article introduces the concept of "useful load fraction"; however, this is quite clearly completely a different definition to payload fraction and it is confusing to conflate them like this. The comparison table needs to have a column for useful load fraction if this term is actually relevant, but even so, the listed payload fraction data for the aircraft seems misleading to the point of being 'incorrect.'
Because, if we eliminate all the nuance of the aircraft mission we are left with just three points of comparison:
* Empty Weight (TARE)
* Maximum Take-Off Weight (MTOW)
* Maximum Fuel Capacity (converted to mass)
A max-fuelled aircraft at its maximum take-off weight, which is the same situation as a rocket on the launchpad.
The payload fraction for this is straight-forward:
\text{Payload }% = \frac{\text{MTOW} - (\text{TARE} + \text{Fuel})}{\text{MTOW}} \times 100
Concorde and the Boeing 747 are comparisons used in this article.
Concorde has a MTOW of 185,070 kg, a 78,700 kg TARE, and its Fuel Capacity is 95,680 kg.
Assuming the Boeing 747-8F, it has a MTOW of 447,690 kg, 197,130 kg TARE, and 180,900 kg  of Fuel Capacity (226,120 L at 800 kg/m3).
With this data, and ignoring the 'max payload' specification of each aircraft for the reason above, we can calculate the payload fraction for Concorde:
\text{Payload }% = \frac{185\,070 - (78\,700 + 95\,680)}{185\,070} \times 100
\text{Payload Fraction} = 5.78%
And for the 787-8F:
\text{Payload }% = \frac{447\,690 - (197\,130 + 180\,900)}{447\,690} \times 100
\text{Payload Fraction} = 15.56%
And this gives us the minimum payload fractions of these aircraft; both far below the "45-55%" or "50%" payload or load fractions suggested in the article. In fact, this type of comparison makes certain rockets more 'efficient' than the aircraft. 
Of course, this is due to the aircraft carrying more fuel than would be necessary to 'reach' space, if it could hypothetically continue its journey into orbit. This brings me back to the main point here: aeroplane and rocket missions are completely different, and comparing the two in this way is... at least, very misleading without further context.
Afiaki (talk) 11:14, 6 September 2022 (UTC)
thread_title: Aircraft are not a useful point-of-comparison to rockets