When is an aircraft overweight?
No first hand knowledge, but I've been told that when a SR-71 was going on a longer range mission, they took off with less than full fuel, then refueled up to the max fuel carrying capacity before climbing to cruise altitude and the Mach 3 speed.
Ecce Homo! Loquitur...
Quite usual for a military aircraft, whether transport or bomber, to get airborne at maximum weight with a large freight or bomb load and a reduced fuel load and then fill to full from a tanker at the top of climb.
The weight restriction is usually due to runway length and associated engine/climb limitations rather than structural issues.
The weight restriction is usually due to runway length and associated engine/climb limitations rather than structural issues.
A very good friend of mine was a crew chief on B-52s based in Wurdsmith AFB (Oscoda, MI) in the early ‘70s. They carried a big load of real nukes, and, as a SAC asset, were required to be on ready alert (15 min in the air from initial notification)
Apparently, in order to get off the ground, the BUFFs took off with less than 2 hrs fuel (from a 11000ft+ runway) and immediately refueled from the attendant KC-135s that were based across the field and took off intercurrently .
There was no way those eight engines were going to get them off the ground otherwise, and he said that the maximum takeoff weight (which he was responsible for calculating) was “fairly fluid”…
Apparently, in order to get off the ground, the BUFFs took off with less than 2 hrs fuel (from a 11000ft+ runway) and immediately refueled from the attendant KC-135s that were based across the field and took off intercurrently .
There was no way those eight engines were going to get them off the ground otherwise, and he said that the maximum takeoff weight (which he was responsible for calculating) was “fairly fluid”…
Quite usual for a military aircraft, whether transport or bomber, to get airborne at maximum weight with a large freight or bomb load and a reduced fuel load and then fill to full from a tanker at the top of climb.
The weight restriction is usually due to runway length and associated engine/climb limitations rather than structural issues.
The weight restriction is usually due to runway length and associated engine/climb limitations rather than structural issues.
Ecce Homo! Loquitur...
Depends on the runway you are getting airborne from…
At takeoff its maximum weight is 840,000 pounds, including 270,000 pounds of cargo and 332,500 pounds of fuel; after being refueled in flight, C-5s have weighed 920,836 pounds.
I remember reading about a WW2 C47 apparently loaded with PAP (Pierced Aluminium Planking) for airstrip construction that took a very long time to get into the air and climb to its cruising altitude. It turned out at its destination that the freight was actually Pierced Steel Planking! Some error! I forget what the actual weight was but it greatly exceeded the already 'generous' Douglas wartime limit.
I worked in the oil industry for a while. One of my colleagues recounted that in Libya in the 1960s a DC3 was loaded up, mostly freight, for a supply run to his oilfield. It barely got airborne by the end of Tripoli runway, and flew very gently and at very low level round a circuit and landed. It transpired that the load had been calculated in pounds, but the same number measured in kilograms. Half the cargo was unloaded, and they then set off for (and in due course arrived at) their destination.
Last edited by Fitter2; 31st Dec 2023 at 17:14.
In the UK Microlight aircraft are limited to 450kg MAUW, this is both a restriction of the licence conditions of the pilot and also a safety figure for the max loading of the airframe structure. IF the SAME aircraft is certified as a GA aircraft it is allowed to fly at a higher MAUW as the safety margins for a GA aircraft are calculated using a lower factor. Same aircraft, different max weights. Just an observation.........
Rans6..........
Rans6..........
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Somewhat Francophobic, I'd say. The slight weight anomaly (around 800 kg vs a total of around 185,000 kg) was described in the preliminary report, and again in the final report. Rather academic, given its negligible effect on performance and likely inaccuracy, given the use of standard passenger weights. BTW, it's the BEA (Bureau d'Enquêtes et d'analyses pour la sécurité de l'Aviation civile) that conducts investigations - the DGAC (Direction Générale de l'Aviation Civile) is the regulator.
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The slight weight anomaly (around 800 kg vs a total of around 185,000 kg) was described in the preliminary report, and again in the final report.
Concorde experts told me that it was around 5 tonnes minimum!
As TD has said, and certainly flying civvie heavies, this really is an "it depends".
It can be structural ( in fact very often the limiting factor out of places like London and Singapore on Long long haul routes where there's plenty of runway), other places with less generous amounts of tarmac you can end up "capped" by performance...I'm not sure there's a usual reason...
Going back to the OP - in the context of the B-29 - military, wartime, it might be worth thinking about the rules that may or may not have applied to those operations. Applying the modern rules of having to have the performance to allow for an engine failure on takeoff would almost certainly reduce "maximum take-off weight" on the day for many runways. If that wasn't a consideration, wartime and all that, I wonder how many of the B-29s that didn't make it into the air were at or below structural max weight but had an engine go at high speed but before lift off.
It can be structural ( in fact very often the limiting factor out of places like London and Singapore on Long long haul routes where there's plenty of runway), other places with less generous amounts of tarmac you can end up "capped" by performance...I'm not sure there's a usual reason...
Going back to the OP - in the context of the B-29 - military, wartime, it might be worth thinking about the rules that may or may not have applied to those operations. Applying the modern rules of having to have the performance to allow for an engine failure on takeoff would almost certainly reduce "maximum take-off weight" on the day for many runways. If that wasn't a consideration, wartime and all that, I wonder how many of the B-29s that didn't make it into the air were at or below structural max weight but had an engine go at high speed but before lift off.
Last edited by wiggy; 1st Jan 2024 at 00:09.
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I think it was the excellent Serenade to the Big Bird by Birt Stiles where he talks about flying B17s out of England and on one trip, he took off only to feel the aircraft was really sluggish and then started to descend! Quickly he called for wheels down just in time to be able to bounce in and out of a field, back into the climb and wheels up
Turned out it was a deep penetration raid, his ground crew had loaded not just extra but extra extra ammunition for the trip so they were well over gross - and apparenty the ammo was stored "down the back" too
Turned out it was a deep penetration raid, his ground crew had loaded not just extra but extra extra ammunition for the trip so they were well over gross - and apparenty the ammo was stored "down the back" too
The one that says "Yeah, this is the same place the last pilot crashed in!"
The Huey had a weight limit of 9500lb, but for a self-deployment of three aircraft to PNG we had to carry quad tanks with fuel to cross Torres Strait, pilots (2 per) to fly them, spare pilots (to be trained in PNG), crewmen (fly and train), groundies to do turn-arounds and scheduled minor maintenance, and the spare parts and tools to do so.
We needed (and got) permission from Bull5h1t Castle to operate at 10,500lb for the exercise. The hover height was just enough to do cushion-creep takeoffs. By the time we got to any destination airfield (Goroka 6000', Mt Hagen a bit higher) we were down to an acceptable weight.
As an aside to a previous post, our initial training on Hueys always included skidding takeoffs from grass, where even a hover wasn't possible. In Vietnam, PSP was slipperier than grass for such a purpose.
The Huey had a weight limit of 9500lb, but for a self-deployment of three aircraft to PNG we had to carry quad tanks with fuel to cross Torres Strait, pilots (2 per) to fly them, spare pilots (to be trained in PNG), crewmen (fly and train), groundies to do turn-arounds and scheduled minor maintenance, and the spare parts and tools to do so.
We needed (and got) permission from Bull5h1t Castle to operate at 10,500lb for the exercise. The hover height was just enough to do cushion-creep takeoffs. By the time we got to any destination airfield (Goroka 6000', Mt Hagen a bit higher) we were down to an acceptable weight.
As an aside to a previous post, our initial training on Hueys always included skidding takeoffs from grass, where even a hover wasn't possible. In Vietnam, PSP was slipperier than grass for such a purpose.
It’s like anything structural from a cable, to a bridge, to an aircraft, the maximum loading etc permitted is less than actual figure at which point it could fail, to allow an extra safety margin, the aircraft’s MAUW limitations will be similar and set the allow optimum performance for runway lengths, reliability, fatigue , longevity etc, similar will be with engine outputs.
i can give one example of it working the opposite way.
The Beechcraft Baron B-58P was designed with a max all up weight of something like 2800lbs , but in the U.K. the cheaper maintenance programme at the time LAMS had a limit of 2730Ibs.
Therefore Beechcraft introduced the P-58PA ( with an A on the end ) for the U.K. market that had a reduced MAUW of something like 2700lbs, thus being under the requirement for the cheaper service scheme and all that was changed was the MAUW and the badge on the side, plus some paperwork,
i can give one example of it working the opposite way.
The Beechcraft Baron B-58P was designed with a max all up weight of something like 2800lbs , but in the U.K. the cheaper maintenance programme at the time LAMS had a limit of 2730Ibs.
Therefore Beechcraft introduced the P-58PA ( with an A on the end ) for the U.K. market that had a reduced MAUW of something like 2700lbs, thus being under the requirement for the cheaper service scheme and all that was changed was the MAUW and the badge on the side, plus some paperwork,
You may be thinking in Kgs,
The B55 I flew had a max to weight of 5300lbs, the 58P would be around 6200
Evertonian
As a Commercial LoCo bloko, weather was a major factor for us. DC-10's doing MEL/HNL at Midday during Summer... we were counting the kids through the gate & waiting for the right number before loading a pallet on one day that I recall. It was a -30 too!
"Mildly" Eccentric Stardriver
Sue: that was out of Ridgewell I believe. The actual sequence was gear-up to clear the fence, then down to bounce off the field. There is a book, whose title escapes me (possibly Bomber Crew), written by a flight engineer who was on that trip.