Post by volkerboehme on Jan 13, 2013 3:51:27 GMT -5
Hi all,
FSAviator adds this link of a modern propliner departure to this discussion:
www.liveleak.com/view?i=5c1_1350976434
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FSAviator has created a very comprehensive document describing this issue. Thanks! See the next post for links to Classic era runway strength ratings.
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The video link I provided to Tom earlier addressed the way Russian attitudes to 'acceptable' airfield and runway surface conditions still differs from perceptions in 'the West'. Like all well designed bush planes, all Antonov monoplanes have high wings to prevent engine, fuel tank, and flap damage when debris is thrown up from runways that would be considered unfit for use outside the former Soviet Union.
A low wing aeroplane such as the Il-14 would either have failed to get airborne from that waterlogged runway, or would probably have suffered significant fuel tank or (asymmetric) flap damage trying, and would have been more likely to crash after unstick, if it ever got airborne. However in the illustrated case the captain underestimated how bad the standing water was. The turbines ingested a lot of mud and small stones, and avionics aerials under the fuselage were ripped off. The take off was successful, but not safe.
Having had some time on my hands over Christmas and New Year, what follows is my attempt to provide a definitive answer to the original question at the top of this thread, and all analogous questions, for the purposes of commercial propliner *flight simulation* origin / destination / alternate flight planning, plus payload and fuel planning. However always remember real life is more complicated than the already quite complex summary below.
As the 2008 Propliner Tutorial explains the Classic era was the era in which international laws replaced national laws, and replaced WW2 Allied nation / Axis nation regulations, for the conduct of commercial aviation. The new international laws now required each part of each commercial airfield to be allocated a dimensionless Load Classification Number (LCN, sometimes called a Pavement Classification Number = PCN) that each captain must compare to the LCN (sometimes called Aircraft Classification Number = ACN) of his or her aeroplane.
Aeroplane LCN / ACN is derived from an equation in international law taking into account Single Wheel maximum Load (SIWL) *at MTOW*, recommended tyre pressure, undercarriage geometry, and other factors, with all three sets of wheels on the ground at 1G. Some aeroplanes have a 'graph' of LCN / ACN versus condition dependent MTOW and the locus I have chosen for inclusion in the tables below is as good a 'starting point to calculate from' as any other. That will become clearer as you read on.
One complication is that the United States refuses to ratify many aspects of international law. Until 2017 when the U.S. intends to comply with the relevant international law, a parallel substitute FAA system of classification is in place for hard runways in that jurisdiction. That hardly matters for our purposes since U.S. certificated aircraft must comply with international law while outside the U.S. and so each has a regulatory ACN, and in practice the U.S. has not (usually) constructed commercial airfields that are below international safety standards, (while demanding the right to do so).
In practice the captain of any commercial aircraft can reduce certificated current LCN / ACN below default aircraft LCN by reducing current (and planned to be current) operating weight sufficiently below MTOW, and even more by reducing tyre pressures until the aircraft LCN / ACN is <= the LCN / PCN of the surface it will be required to move gently across, or stand on. Unfortunately each commercial aircraft has a minimum safe tyre pressure, which is often very close to the default tyre pressure used to calculate the default LCN / ACN.
So that brings us to 'grass' and the LCN of 'grass'. A covering of grass helps to bind the surface and prevent break up, (in lieu of tarmac over concrete). The sub surface is however in principle just 'dirt' of some kind with a thin surface binder that does not provide the bearing strength. The trouble with dirt is that it turns to mud and starts to behave like a viscous fluid when water is added. Tarmac is a waterproof membrane for concrete, but grass is not a waterproof membrane for dirt.
During the Classic era, if a *new* soft airfield was created, or existing soft infrastructure was to be 'upgraded', international law required at least one *new* access route, to at least one *new* runway, and at least some *new* parking, on a soft surface *commercial* airfield to meet a specified LCN when 'dry', and that LCN was 25. However the *touchdown zones* of (only) the relevant *new* or *upgraded* soft commercial runway was required to have additional local excavation and buried 'hard core' = 'aggregate' to 'underpin' the 'soft' runway touchdown zones delivering the necessary increase in LCN to cope with more than 1G impact at touchdown with all the G increased weight spread over only two sets of wheels.
If an airfield owner *chose* to promulgate lower LCN values for lesser *new or existing* runways, that owner was required to also 'strengthen' (only) their touchdown zones pro rata to cope with relevant landing loads. Whatever the cited LCN / PCN of the runway. commercial aircrew only compared their aircraft's default ACN, modified for actual landing weight, to the published PCN of the whole runway. Ensuring that (only) the touchdown zones of runways with an LCN classification were sufficiently strengthened to take landing impact was not an aircrew flight planning problem. However beyond the touch down zones the *new* soft (PCN = 25) runway was unsafe to *land* any aeroplane whose ACN even approached 25. The same applied to all lesser or superior runways. Deep touchdown, beyond the touchdown zone was, and is, likely to damage the runway if ACN even approaches PCN.
Now remember different taxiways have different LCN /PCN, as do different parking areas. MSFS (a well designed AFCAD) always attempts to take different parking area LCN into account, but does not 'usually' differentiate taxiway or runway LCN. However during simulation flight planning we can take into account many things that downloaded files do not include in their code.
In real life aircraft whose LCN / ACN exceeds the LCN / PCN of each area must be denied taxi clearance into each such area and cleared to taxi accordingly by ATC. In the absence of ATC the captain has sole responsibility for ensuring his/her aircraft LCN / ACN, modified for *current* weight, is *currently* below each warranted local pavement LCN / PCN along the taxi route, and at the place of final parking. Local parking area LCN / PCN limits how much fuel and payload can be loaded onto the aeroplane later, prior to departure.
Since grass is not a waterproof membrane for dirt the dry LCN is not sustained once the underlying dirt becomes mud. The owner of the *commercial* airfield was then required to warn pilots by NOTAM whenever a surface that had any promulgated LCN, had become too wet to sustain its dry LCN value. Snow over grass / dirt does not reduce LCN until it thaws. Relevant *new* Classic era primary *gravel* surfaces were also required to have LCN = 25 (compliantly augmented for touchdown), but unlike dirt and grass were less likely to reduce when wet.
Commercial grass / dirt airfield owners were allowed to reduce commercial LCN to a specific value of ZERO, by NOTAM, as an alternative to 'unclassified' = 'commercially unusable'. All Classic era 'small bush planes' and all Classic era 'large air taxis' had LCN / ACN = 0 and if LCN was reduced only to zero they could operate lawfully from 'very muddy' dirt and grass, and some other unusual surfaces, at the sole discretion of the captain.
So the question arises what was the default LCN *at MTOW* of larger classic era propliners. Below I provide many examples. For *flight simulation purposes only* it is reasonable to assume that default LCN / ACN for MTOW reduces pro rata to current weight.
D.H. Heron 1 0 (at 13,500lbs)
S.A. Twin Pioneer 0 (at 14,600lbs)
During the Classic era the above represented the limit of safe commercial operation to and from 'very muddy grass and dirt', or for instance Caribbean, Pacific or Scottish commercial airfields which were just the hard sand on the local beach at low tide, and below the high tide mark, based solely on 'Captain's discretion'.
It is my 'understanding' that all non turbine U.S. aircraft certificated for public transport <= 12,500lbs in the Classic era were granted international LCN / ACN = 0. Outside the U.S. heavier aircraft could qualify if designed to do so. In theory, and maybe in practice, some U.S. certificated aircraft > 12,500lbs could qualify for LCN = 0 when fitted with 'tundra tyres', also known as 'balloon tyres'. Turbine aircraft certificated everywhere and limited to 12,500lbs sometimes had LCN > 0, because the manufacturer had chosen to certificate them for STOL operations landing from steep IFR glideslopes with additional landing impact.
The most important criteria are how many wheels (not legs) carry the weight, how soft the tyres are, and the maximum certificated glideslope for STOL operations by that type of aeroplane, not weight (or size) itself. Pilots frequently failed to flare fully from STOL (=> minus 6 degree) glideslopes and the default LCN = ACN had to allow for that once IFR STOL glideslopes were introduced. The issue is *not* whether the aeroplane will be damaged. *The issue is whether the fragile surface infrastructure will be damaged by the stronger aeroplane*.
Short Skyvan 3 (STOL 12,500lbs)
Douglas C-47A (DC3C) 8 (at 28,000lbs)
Nord 262 8 (STOL 22,700lbs)
Saab Scandia 12
Vickers Viking 12
Martin 2-0-2 14
Martin 4-0-4 14
FK27-100 & 200 14
HP Herald 100 14
Curtiss C-46F 15 (at 47,000lbs)
Bristol 170 Mk.21 15
HP Herald 200 16
Nihon YS-11 16
DHC7-100 and later 16.2 (STOL 44,000lbs)
Bristol 170 Mk.32 17
Avro 748 Srs 1 17
CV-240 19
Airspeed Ambassador 20
Avro 748 Srs2 20
Nord C-160 Transall 20 (at 108,000lbs)
CV-340 21 (at 42,400lbs)
CV-440 22
The many turboprop aircraft 'claimed' as 'DC-3 replacements' in the Classic era of aviation history, all needed to have LCN <=8 so that they could use all types of surface infrastructure that a DC-3C (demilitarised C-47A and similar) could use at 28,000lbs. Although pre war US FARS, and equivalent pre war national regulations had not specified LCN as such, 'wholly unimproved grass / dirt' was the norm even on 'most' major airports, and when dry that 'equated to' the Classic era legal definition of LCN = 8. The DC-3C had not originally been certificated with an ACN either, but its actual ACN 'equated to' ACN = 8 at 28,000lbs. The Nord 262 came closest to achieving the Classic era goal of a DC-3C replacement, but still failed. The post war Classic era of aviation history had higher certification standards and so designing a 'replacement DC-3' actually became impossible.
The LCN that a *new* primary commercial soft surface had to meet when dry in the Classic era was increased far beyond the 'typical' pre war level of only 8, and also far beyond the 'regulation' somewhat underpinned with aggregate allied WW2 soft surfaces that had been infrastructure matched to the C-46 footprint at 47,000lbs, which 'equated to' the later Classic era LCN = 15. Improving a WW2 era soft, (but actually underpinned with hard core in all necessary areas), from LCN = 15, all the way to LCN = 25 (when dry) only required sufficient further investment in excavation and hard core underpinning to achieve.
All the above aircraft can lawfully depart Classic era legislation, *new primary*, commercial grass / dirt / gravel runways at MTOW. However aircraft LCN / ACN well below 25 was still highly desirable through the Classic era of aviation history because it allowed those aeroplanes to operate lawfully into, over and from either Vintage era = 8, or WW2 era infrastructure = 15, infrastructure not yet improved to Classic era LCN = 25 requirements.
**Not all 'soft' runways and taxiways and parking areas are equal**
Each era of aviation history is an identifiable era because it has different legislation and procedures. Which is why the original question has no simple answer.
Even in the Classic era most of every soft *commercial* airfield might have LCN well below 25, and specified as such in its airport diagram, or the relevant national Aeronautical Information Publication (AIP), (modified on a temporary basis by NOTAM as necessary). Whole areas might be unclassified and therefore not fit for commercial use, or might be classified LCN = 0 even when dry. The infrequently used 'cargo ramp', else most of the 'passenger terminal parking' on a soft airfield might be much softer than the new soft Classic era LCN = 25 primary runway, primary taxiway and primary parking.
In the Classic era only a single 'stand' on a soft surface airfield might be LCN = 25. The next 'stand' might be LCN = 15 or even LCN = 8. The 'second' LCN > 15 arrival is soon blocking the only LCN = 25 marked grass or dirt taxiway to the only LCN = 25 grass or dirt stand until the 'first' LCN > 15 propliner is ready to depart, causing significant delays. The same can apply to a busier Classic era soft airfield that has more, but still 'too few' LCN = 25 parking stands.
The issue of using older soft surface partially hardened WW2 era, or wholly unhardened soft surface Vintage era runways, during commercial services in the Classic era also arises and is facilitated by having LCN well below 25. Often only one runway at a 'soft surface' Classic era commercial airfield had LCN = 25. The next best might be only 15 and the worst only 8, or even 0.
The 44,000lbs MTOW DHC 7-100 dates from 1979, well inside the Modern era of aerospace history. Only in the Modern era aircraft manufacturers can apply to have ACN at MTOW tested and certificated to three significant figures (DHC 7-100 series ACN = 16.2). At 44,000lbs a DHC 7-100 series cannot lawfully use *WW2 era* soft surfaces 'underpinned' only to the then 'regulated' LCN = 15 to match the loaded footprint of a heavier WW2 Curtiss C-46 at 47,000lbs.
So let's study a worked example of *flight simulation* commercial fuel and weight planning arising from the intention to operate an aeroplane from a later era, within earlier era infrastructure, or any 'soft infrastructure' whose PCN is lower than aircraft default ACN.
Again certification standards had moved on and *for flight simulation purposes* in order to use unimproved WW2 'soft' infrastructure (PCN = 15) the DHC 7 (ACN = 16.2) must reduce maximum take off weight to;
44000 * 15/16.2 = 40,741 pounds
it must offload
44000 - 40741 = 3,259 pounds of cargo and / or fuel.
to use still unimproved WW2 soft infrastructure.
The DHC7 cannot use 'wholly unhardened' truly soft and unimproved *Vintage era* DC-3C footprint soft surface infrastructure (LCN = 8) for *commercial* services at any weight, but classifying the DHC 7 operator as e.g. 'The British Antarctic Survey' changes the regulations it carries passengers under. As the 2008 Propliner Tutorial explains each era is a different era explicitly because it has different (ever more complex) regulations, compliances and exemptions. The safety requirements became more onerous in each passing era of legislation. Commercial airfields had to improve along with the new commercial aircraft regulations, or continue to limit hosted and visiting *commercial* use to 'large' aeroplanes from the earlier era whose regulations they still met.
However aircraft with LCN / ACN = 16 or 16.2 or 17, or even more, could reduce weight to use standard unimproved 'somewhat underpinned' WW2 era soft infrastructure with LCN / PCN = 15. The question was whether they could make a profit on a commercial service. If the haul was short enough they might, since all the mandatory weight reduction might be fuel not needed and not loaded, and the issue is anyway and always, "How much below MTOW must I depart to ensure that weight will be below Maximum Landing Weight (MLW) at the Initial Approach Fix (IAF) for destination"?
The 44,000lbs and 4 x 1120 shp (TOGA) DHC 7-100 series wasn't a fully successful replacement for the 47,000lbs and 2 x 2000 bhp (TOGA) C46, and of course TWA and EAL would have argued that the 44,900lbs and 2 x 2400 bhp (TOGA) M404 was fully successful much earlier, even though none of the high ACN Convair Liners could be. Of course the Martin Liners had their own problems, (see the Calclassic Convair and Martin Liner mini tutorial).
Bonanza, Wien Alaska, and many other airlines world wide would also have claimed that the 42,000lbs and only 2 x 1835 shp (TOGA) early series F27A from the late 1950s was capable of doing almost anything any of the aircraft above could do.
In the real world it's mostly about how much payload you can load legally alongside minimum compliant fuel for the trip, and that requires more detailed flight simulation fuel and payload planning, taking into account more factors, than all bar the most 'hard core' propliner enthusiasts are ever willing to contemplate. However without making that effort the gap between what a C46, an M404, an early FK27, and a DHC7-100, (from three different eras of aviation history), could each achieve commercially, when operating from unimproved WW2 'soft' surface infrastructure, can never be understood.
Each 'era' of aviation history introduced higher standards of testing for certification of aeroplanes and aviation infrastructure. The criteria used to assess ACN became more demanding, and the regulations concerning PCN to be provided during construction of any *new* or *improved* commercial infrastructure (soft or hard) became more demanding, but pre-existing commercial aeroplanes and pre-existing commercial infrastructure were not required to meet the new higher commercial safety standards. Instead never improved pre-existing aeroplanes and infrastructure were 'eventually' (often many decades later) ordered to be taken out of *commercial* service.
The question, 'How big an aeroplane can use a soft airfield?' is unanswerable without a date that places the question within a specific era of aviation history. The question is all about legislation and jurisdiction, not 'physics'. Legislation changes often. The laws of physics do not. What is 'physically possible' (when delivering a stripped out ancient aeroplane to a museum), and what was 'lawful' in commercial use in different eras of aviation history, are questions with very different answers.
The aircraft listed below cannot *lawfully* operate a *commercial* service to or from even a standard *Classic era primary commercial* soft runway *at MTOW*.
Viscount 700 Srs 29 (at 61,500lbs)
Douglas DC4 & C54 30 (at 73,200lbs)
AT Carvair 31
Breguet Deux Ponts 32 (at 114,000lbs)
Viscount 700D Srs 32
Viscount 800 Srs 32
Canadair C-4 33
A.W. Argosy 200 33 (at 93,000lbs)
Lockheed C-130J 37 (STOL at 155,000lbs on tarmac)
L-049 38
Viscount 810 Srs 39 (at 72,500lbs)
Ilyushin IL-18 42 (at 135,600lbs)
Lockheed C-130J 42 (STOL at 155,000lbs on concrete)
L-749 44
Douglas DC-6 44 (at 97,200lbs)
Douglas DC-6A 49
Douglas DC-6B 50 (at 103,800lbs)
However 'in theory' an individual airfield owner 'might' be able and willing to underpin one 'soft' runway, and one marked soft route to it, and one soft stand, with enough depth of hard core underpinning them all to match LCN = 30 to allow C-54 / DC-4 operation at MTOW, but far more likely aircraft with LCN > 25 were always operating at weights well below MTOW, flying short hauls with light fuel loads, while flying to and from 'new or upgraded primary soft commercial infrastructure' in the Classic era. They may have needed to depart at that low weight to achieve MLW at destination IAF anyway.
The much larger Breguet Provence / Deux Ponts could also operate from a soft Classic era primary commercial runway, with even greater % load reduction than a C-54, yet being much larger could do so with a 'similar' absolute load. I have little doubt that the (114,000lbs MTOW and 135 airline passenger seat) Provence / Deux Ponts was the 'biggest' *commercial* *piston engine* propliner to lawfully fly commercial passenger services from soft runways, but it could not do so at that weight.
114000 * 25 / 32 = 89,063lbs, but a Deux Ponts has an empty equipped weight of 73,040lbs, so its useful load (Crew + fuel + payload) from LCN = 25 infrastructure is around 16,0000 lbs and if the haul is short enough it might make a profit. However the biggest aeroplanes that used underpinned soft infrastructure are not necessarily the ones that can haul the biggest useful load from underpinned soft infrastructure.
The calculation for a DC-4 is instead;
73000 * 25/30 = 60,833lbs, but a DC-4 has an empty equipped weight of 43,200lbs, so its useful load from LCN = 25 infrastructure is around 17,600 lbs and if the haul is short enough it has a much better chance of making a profit.
The CV-340 is not MTOW restricted from LCN = 25 infrastructure and has the following aircraft.cfg data;
[weight_and_balance]
max_gross_weight=47000
empty_weight =30400 ;including oil, catering etc.
So a CV-340 has useful load from LCN = 25 infrastructure = 16,600lbs and over any distance should be able to make a profit.
The poorly designed Airspeed Ambassador is not restricted either;
[weight_and_balance]
max_gross_weight=55000
empty_weight =39500 ;including oil, catering etc.
So the much heavier Ambassador has useful load from LCN = 25 infrastructure = 15,500lbs and over any distance is less able to make a profit.
However we have discovered that aeroplanes which 'appear' to be too heavy, and which 'appear' to have too high LCN / ACN, can in fact use 'standard Classic era primary soft infrastructure' with LCN / PCN = 25 and 'may' actually be able to lift a bigger useful load (at higher cost), than aeroplanes designed with LCN <=25. Most airlines seek to maximise profit. Military organisations instead seek to maximise productivity, and the C-54 remained an important 'underpinned soft' infrastructure airlift asset for many air forces throughout the Classic era. The smaller number of much later Ambassadors were soon scrap.
Freighters like the (93,000lbs MTOW) Armstrong Whitworth Argosy 200 with LCN = 33 could haul significant commercial cargo payloads from LCN = 25 infrastructure too.
93000 * 25/33 = 70,455lbs, but a cargo hauling Argosy (200 series) has an empty equipped weight of 49,000lbs, so its useful load from LCN = 25 infrastructure is around 21,400lbs and if the haul is short enough it should make a profit or be productive enough to provide airlift from such surfaces under contract to the military.
However lifting really large loads from such infrastructure requires a much better designed transport, highly optimised for such infrastructure at huge expense to the relevant taxpayers, like the Nord C-160 Transall with LCN = 20 at MTOW = 108,000lbs allowing a huge useful (legally commercially compliant) load of around 47,000lbs. The Transall was far too expensive to be attractive to airlines, but it exhibited very high military productivity, at very high cost to the relevant taxpayers.
I leave readers to 'go back' and calculate the useful load that a DHC 7 / M404 / FK27A and C46A can each lift from 'regulation' unimproved WW2 soft (but somewhat underpinned) infrastructure with LCN = 15 using Calclassic supplied aircraft.cfgs.
For the DHC 7-100 use;
[WEIGHT_AND_BALANCE]
empty_weight =27820 //fully equipped
max_gross_weight=44000 //max 44100 leaving the ramp
Note that the C46A answer may differ by jurisdiction.
**It is also important to understand that not all hard surfaces are equal**
It is my 'understanding' that most wartime and post war decade 'hard' runways, taxiways and parking, were (by Allied WW2 powers agreement and then international law) LCN = 50. Aircraft that required more could not operate at MTOW from many WW2 'hard' infrastructure airfields, until the runways and taxiways and parking were upgraded, (usually only to LCN = 65), in the mid 1950s. Specific aircraft like the B-29 already needed superior infrastructure to depart at MTOW.
At some point during the Modern era of aerospace history certification procedures changed so that manufacturers could choose to certificate aircraft with a different LCN / ACN for each surface type. See C-130J above. LCN for lighter and older C-130s can 'perhaps' be calculated by reduction from ACN = 37 on all commercial airfield surfaces at 155,000lbs. Concrete is more liable to impact damage than tarmac over concrete and that is acknowledged in the present day certification procedures, but was not taken into account in the Classic era. Certification for STOL impact continues to be relevant.
Remember this answer addresses *international commercial* safety criteria. Real life is more varied and more complicated. Remember too that these criteria relate to the safety of the Concorde that is about to depart next, and whose main wheels will throw the lump of broken concrete, or aircraft debris, through its low wing and will puncture the fuel tanks, venting AVTUR into its afterburners causing it to crash; not the safety of the aeroplane that just departed too heavy and damaged the runway, or suffered partial structural failure during the prior heavy take off, leaving debris on the runway. What is physically possible during military logistics in support of a war zone or realistic military exercise, with significant levels of risk, and what is (un)lawful on a commercial airfield, due to implied risk % to following aircraft, differs.
By the time that the L188 Electra arrived in 1959, most 'busy' commercial and military airfields, outside the Soviet bloc, had one instrument runway, and one taxi route to / from (only) the instrument runway, and some parking upgraded to LCN / ACN = 65 but aircraft with LCN / ACN > 65 were still overweight at MTOW even on most 'busy' commercial, and many military airfields in the early 1960s. There were very few places they could depart at MTOW and the places that were already upgraded beyond LCN = 65, had mostly been upgraded to handle the early B707, not the final dinosaurs of the long haul propliner era. Ensuring that the 230,000lbs Short Belfast could operate at MTOW from existing 'upgraded once in the 1950s' hard runways, now with LCN = 65, was very important to the RAF, but ended up limiting its utility in the Modern era which soon arrived.
L-1049B/C 51 (at 120,000lbs)
Britannia 100 52 (at 155,000lbs)
L-1049G/H 58 (at 140,000lbs)
L-188A and C 59 (at 116,000lbs)
Douglas DC-7 (pax) 60 (at 122,200lbs)
Canadair CL-44D 60 (at 210,000lbs)
Britannia 300 62 (at 185,000lbs)
Douglas DC-7B and BF 63 (at 126,000lbs)
Douglas DC-7F (cargo) 63 (at 126,000lbs)
Boeing 377 65 (at 145,800lbs)
Short Belfast 65 (at 230,000lbs)
L-1649A 70 (at 160,000lbs)
Douglas DC-7C and CF 72 (at 144,750lbs)
Vanguard 952 72 (at 146,500lbs)
The immediately post war Boeing 377 (derived from the B-29) was especially restricted in relation to where it could be tasked to fly, needing very hard runways and taxiways that barely existed in the commercial world, and military grade fuel, in order to operate at MTOW. During the Classic era of aviation history, the issue was not only whether the runway was long enough to take off at MTOW, but also whether it was strong enough. That applied to 'hard' infrastructure, not just 'soft' infrastructure.
Of course the places the high ACN aeroplanes above operated to and from in real life were mostly the very few that had pavement of suitable PCN, but some services would have been weight restricted by inadequate PCN. However as above that might not require larger weight reduction than the need to achieve MLW at destination IAF anyway.
The Soviet Union (and client states) did not ratify international law in the Classic era and did not publish LCN data, but the Lisunov Li-2 would have been 8 or less, and the IL-14 was 'probably' 13 or less. It's problem was its damage prone low wing and flaps. The video I cited makes plain the reality that the issue in the Soviet Union, and Modern era Russia, is not just a few stones or other FOD thrown up by the landing gear while travelling down a runway that has not been swept recently.
The An-10A Ukraina did not repeat that mistake and all lesser only twin engine Antonovs would have been LCN / ACN 15 or under. The piston engine An-14 would have been LCN = 0. The very expensive to develop, and structural failure prone, 126 passenger seat An-10A Ukraina was almost certainly the largest (127,900lbs) aircraft ever *designed* to fly airline passenger schedules from 'underpinned soft field infrastructure' and 'probably' had an LCN below, or equal to, the 108,000lbs Nord C-160 Transall LCN = 20. This allowed the An-10A to lift a useful load of about 56,400lbs from 'soft' infrastructure easily beating even the later Transall. Later Antonovs, from the modern era of aviation history, were designed as freighters, but in atypical, (not necessarily commercial), circumstances have lifted larger (passenger) loads from 'soft' infrastructure. There is little doubt that from the An-8 onwards the Ukraine and Antonov became (and probably still are) the masters of lifting large loads from soft airfield infrastructure.
The very few Soviet *international airports* which accepted foreign airlines in the Classic era would all have had 'just enough' primary infrastructure with PCN = 50 before doing so, but almost certainly no more than PCN = 50 in the Classic era, and 'perhaps' 'Soviet Bloc' hard infrastructure in the Classic era was only PCN = 42.
The Russian Il-18 Moskva, by contrast to the An-10 Ukraina, was designed for international service and for export use only from hard surfaces and complied with international law. It could therefore have a low wing. Nevertheless being Soviet it was designed to have much lower LCN (42) than the earlier Britannia 100 (52) and the contemporary Britannia 300 (62) and throughout the 1960s could depart at MTOW from many more runways in the 'third world', that had never been upgraded from LCN = 50 to LCN = 65, yielding many more export orders. The 135,600lbs IL-18 was the heaviest commercial aircraft designed to operate from hard runway airfields built only to late WW2 Allied nations standards (LCN = 50).
The L1049 / DC7 / L188 / BR10 / BR30 / VC9 (or military B-29) could not use 'normal' hard surface WW2 airfield infrastructure with LCN = 50 *at MTOW*. A 120 passenger seat and 135,600lbs IL-18, or a 94 passenger seat and 101,410lbs Sud Caravelle III *turbojet* could (at MTOW), (see below), but of course so could the 126 passenger seat and 127,900lbs An-10A Ukraina which was reserved solely for high demand Soviet domestic passenger services from 'soft' surface airfields. It did not meet international legal requirements and could not be exported.
During the Classic era of aviation history, often it was LCN that determined what aeroplane could be purchased as a replacement on a given commercial route, in which part of the world, and when, but of course these much larger aeroplanes with LCN at MTOW that is 'too high' may also be able to operate profitably at reduced weight on short hauls where all of the weight offloaded can be fuel.
If you have realistic (not real easy) flight dynamics (a big if) which include realistic MTOW and MLW and MZFW and ready for service empty weight criteria for a given aeroplane, (see 2008 propliner Tutorial), and you know LCN for MTOW you can determine what useful load that aeroplane can lift during a flight simulation sortie from each type of infrastructure, constructed or improved during each era of aviation history. You just have to 'decide' how 'improved' the various parts of the airfield were, beyond their original LCN, by the date you choose to simulate. I have provided the necessary guideline values and worked examples. Runways that were not instrument runways, and the taxiways that served them were often unimproved from time of construction.
For contrast here are some certificated LCN / ACN values at MTOW for early jet transports. They are essential to understanding what happened next.
DH 125 Srs 1(Dominie) 8
FK28 Fellowship 22
BAC 111-200 36
DC9-10 36
BAC 111-400 39
BAC 111-300 41
Sud Caravelle III 47
D.H. Trident 1C 51
Convair CV880-22 53
Sud Caravelle VIR 54
DH Comet 4B 56
B727-100 56
DH Comet 4 57
Boeing 720 60
Vickers VC10 65 (at 312,000lbs)
Boeing 720B 65 (at 234,000lbs)
Vickers Super VC10 72 (at 335,000lbs)
B707-120 76 (at 257,000lbs)
Douglas DC-8 20/30 85 (at 315,000lbs)
C-141A Starlifter 85 (at 384,500lbs)
B707-320B 96 (at 327,000lbs)
Douglas DC8-50 99 (at 315,000lbs)
I believe the 60 passenger seat and 60,000lbs Fokker F.28 Fellowship was the largest *commercial* jetliner ever designed to operate from Classic era commercial soft primary infrastructure. The VC10 was the largest commercial aircraft that could operate from existing world wide major runways that had already been upgraded once from LCN = 50 to LCN = 65 in the mid 1950s, without a further major upgrade to allow B707 / DC8 operation. The VC10 was much heavier than the B720B, Belfast or equivalent USAF turboprop freighters, but could use the same runways, taxiways and stands. However like the Belfast that VC10 capability was soon irrelevant and again had limited other capabilities to the detriment of sales.
The cost to airfield owners, (often in reality municipal and federal taxpayers), of upgrading infrastructure to allow B707/DC8 services was huge, but the profit to the airfield, and commerce within the local / national economy, lost by refusing them was soon greater. The Super VC10 could then be developed to use runways upgraded to take the much lighter earliest B707s, or in a few cases already upgraded to take the very demanding DC-7C and Vanguard. In the 1960s many airfields had hard runways long enough, for the DC7C and VC9, but those runways and surrounding infrastructure often simply weren't strong enough. The CL44 Yukon, the Belfast and Britannia 300 series converted to freighting could haul a full load out of those typical (but not major) 'first world' 1960s airfields with only one runway upgraded only to LCN = 65.
At the end of the Classic era, the very expensive late 1960s Vietnam War period airfield upgrades, to allow MTOW operation of the latest *turbofan* powered jetliners and freighters, with huge tax payer subsidies to fund them, quite suddenly required LCN = 100. That huge LCN quite quickly became the norm for major and even 'typical' civilian and military airfields and LCN largely ceased to be a factor for all lesser and earlier aircraft unless they were still operating to soft surface commercial airfields. By then such airfields were increasingly rare outside the 'Communist Bloc'.
After the B707 and DC8 were designed with no regard to existing pavement capability, imposing huge costs on taxpayers, (who always end up massively subsidising the private sector in aviation), political steps were taken to force future designs to achieve reduced ACN, mostly by having more wheels on each leg, even in the U.S., where in theory ACN was not the explicitly regulated value. However after major reductions in the middle of the Modern era of aerospace history ACN values are creeping up again.
B747-400ER 69 (at 913,000lbs on concrete)
B747-8 75 (at 978,000lbs on concrete)
B777-300ER 85 (at 777,000lbs on concrete)
Nevertheless a fully loaded DC7C or L1649A in 1956 did more damage to airfield infrastructure than a fully loaded B747-400ER is allowed to cause today.
The current ICAO methodology for calculation of current ACN and current PCN is here;
www.faa.gov/documentLibrary/media/Advisory_Circular/150_5335_5B.pdf
It depicts how modern era captains, and airfield owners, use a payware software application to take into account additional real world variables, but its methodology has no practical application to (even modern era) desk top flight simulation which requires a much simpler way to vary only current weight in relation to PCN (deemed to be) available at the date and place being simulated.
Even during modern era simulation there must be no presumption that a B777-300ER can operate at more than (65/85 * 777,000 =) 594,000lbs to, or from, third world infrastructure never improved beyond original construction PCN = 65 in the late Classic era, and the B777-300ER cannot possibly achieve 'Extended Range' starting from that weight when outbound. To the contrary a B747-400ER starting from 860,000lbs pretty much can (with reduced payload). During flight simulation a B747-8 'must' reduce even more to 847,000lbs to use that same late Classic era (never improved) concrete hard runway. The heaviest (or biggest) aircraft often cannot lift (or deliver) the biggest load from / to the available runway, for lots of reasons.
This isn't by any means just a 'grass / dirt / gravel' era and infrastructure issue.
FSAviator (January 2013)
FSAviator adds this link of a modern propliner departure to this discussion:
www.liveleak.com/view?i=5c1_1350976434
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FSAviator has created a very comprehensive document describing this issue. Thanks! See the next post for links to Classic era runway strength ratings.
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The video link I provided to Tom earlier addressed the way Russian attitudes to 'acceptable' airfield and runway surface conditions still differs from perceptions in 'the West'. Like all well designed bush planes, all Antonov monoplanes have high wings to prevent engine, fuel tank, and flap damage when debris is thrown up from runways that would be considered unfit for use outside the former Soviet Union.
A low wing aeroplane such as the Il-14 would either have failed to get airborne from that waterlogged runway, or would probably have suffered significant fuel tank or (asymmetric) flap damage trying, and would have been more likely to crash after unstick, if it ever got airborne. However in the illustrated case the captain underestimated how bad the standing water was. The turbines ingested a lot of mud and small stones, and avionics aerials under the fuselage were ripped off. The take off was successful, but not safe.
Having had some time on my hands over Christmas and New Year, what follows is my attempt to provide a definitive answer to the original question at the top of this thread, and all analogous questions, for the purposes of commercial propliner *flight simulation* origin / destination / alternate flight planning, plus payload and fuel planning. However always remember real life is more complicated than the already quite complex summary below.
As the 2008 Propliner Tutorial explains the Classic era was the era in which international laws replaced national laws, and replaced WW2 Allied nation / Axis nation regulations, for the conduct of commercial aviation. The new international laws now required each part of each commercial airfield to be allocated a dimensionless Load Classification Number (LCN, sometimes called a Pavement Classification Number = PCN) that each captain must compare to the LCN (sometimes called Aircraft Classification Number = ACN) of his or her aeroplane.
Aeroplane LCN / ACN is derived from an equation in international law taking into account Single Wheel maximum Load (SIWL) *at MTOW*, recommended tyre pressure, undercarriage geometry, and other factors, with all three sets of wheels on the ground at 1G. Some aeroplanes have a 'graph' of LCN / ACN versus condition dependent MTOW and the locus I have chosen for inclusion in the tables below is as good a 'starting point to calculate from' as any other. That will become clearer as you read on.
One complication is that the United States refuses to ratify many aspects of international law. Until 2017 when the U.S. intends to comply with the relevant international law, a parallel substitute FAA system of classification is in place for hard runways in that jurisdiction. That hardly matters for our purposes since U.S. certificated aircraft must comply with international law while outside the U.S. and so each has a regulatory ACN, and in practice the U.S. has not (usually) constructed commercial airfields that are below international safety standards, (while demanding the right to do so).
In practice the captain of any commercial aircraft can reduce certificated current LCN / ACN below default aircraft LCN by reducing current (and planned to be current) operating weight sufficiently below MTOW, and even more by reducing tyre pressures until the aircraft LCN / ACN is <= the LCN / PCN of the surface it will be required to move gently across, or stand on. Unfortunately each commercial aircraft has a minimum safe tyre pressure, which is often very close to the default tyre pressure used to calculate the default LCN / ACN.
So that brings us to 'grass' and the LCN of 'grass'. A covering of grass helps to bind the surface and prevent break up, (in lieu of tarmac over concrete). The sub surface is however in principle just 'dirt' of some kind with a thin surface binder that does not provide the bearing strength. The trouble with dirt is that it turns to mud and starts to behave like a viscous fluid when water is added. Tarmac is a waterproof membrane for concrete, but grass is not a waterproof membrane for dirt.
During the Classic era, if a *new* soft airfield was created, or existing soft infrastructure was to be 'upgraded', international law required at least one *new* access route, to at least one *new* runway, and at least some *new* parking, on a soft surface *commercial* airfield to meet a specified LCN when 'dry', and that LCN was 25. However the *touchdown zones* of (only) the relevant *new* or *upgraded* soft commercial runway was required to have additional local excavation and buried 'hard core' = 'aggregate' to 'underpin' the 'soft' runway touchdown zones delivering the necessary increase in LCN to cope with more than 1G impact at touchdown with all the G increased weight spread over only two sets of wheels.
If an airfield owner *chose* to promulgate lower LCN values for lesser *new or existing* runways, that owner was required to also 'strengthen' (only) their touchdown zones pro rata to cope with relevant landing loads. Whatever the cited LCN / PCN of the runway. commercial aircrew only compared their aircraft's default ACN, modified for actual landing weight, to the published PCN of the whole runway. Ensuring that (only) the touchdown zones of runways with an LCN classification were sufficiently strengthened to take landing impact was not an aircrew flight planning problem. However beyond the touch down zones the *new* soft (PCN = 25) runway was unsafe to *land* any aeroplane whose ACN even approached 25. The same applied to all lesser or superior runways. Deep touchdown, beyond the touchdown zone was, and is, likely to damage the runway if ACN even approaches PCN.
Now remember different taxiways have different LCN /PCN, as do different parking areas. MSFS (a well designed AFCAD) always attempts to take different parking area LCN into account, but does not 'usually' differentiate taxiway or runway LCN. However during simulation flight planning we can take into account many things that downloaded files do not include in their code.
In real life aircraft whose LCN / ACN exceeds the LCN / PCN of each area must be denied taxi clearance into each such area and cleared to taxi accordingly by ATC. In the absence of ATC the captain has sole responsibility for ensuring his/her aircraft LCN / ACN, modified for *current* weight, is *currently* below each warranted local pavement LCN / PCN along the taxi route, and at the place of final parking. Local parking area LCN / PCN limits how much fuel and payload can be loaded onto the aeroplane later, prior to departure.
Since grass is not a waterproof membrane for dirt the dry LCN is not sustained once the underlying dirt becomes mud. The owner of the *commercial* airfield was then required to warn pilots by NOTAM whenever a surface that had any promulgated LCN, had become too wet to sustain its dry LCN value. Snow over grass / dirt does not reduce LCN until it thaws. Relevant *new* Classic era primary *gravel* surfaces were also required to have LCN = 25 (compliantly augmented for touchdown), but unlike dirt and grass were less likely to reduce when wet.
Commercial grass / dirt airfield owners were allowed to reduce commercial LCN to a specific value of ZERO, by NOTAM, as an alternative to 'unclassified' = 'commercially unusable'. All Classic era 'small bush planes' and all Classic era 'large air taxis' had LCN / ACN = 0 and if LCN was reduced only to zero they could operate lawfully from 'very muddy' dirt and grass, and some other unusual surfaces, at the sole discretion of the captain.
So the question arises what was the default LCN *at MTOW* of larger classic era propliners. Below I provide many examples. For *flight simulation purposes only* it is reasonable to assume that default LCN / ACN for MTOW reduces pro rata to current weight.
D.H. Heron 1 0 (at 13,500lbs)
S.A. Twin Pioneer 0 (at 14,600lbs)
During the Classic era the above represented the limit of safe commercial operation to and from 'very muddy grass and dirt', or for instance Caribbean, Pacific or Scottish commercial airfields which were just the hard sand on the local beach at low tide, and below the high tide mark, based solely on 'Captain's discretion'.
It is my 'understanding' that all non turbine U.S. aircraft certificated for public transport <= 12,500lbs in the Classic era were granted international LCN / ACN = 0. Outside the U.S. heavier aircraft could qualify if designed to do so. In theory, and maybe in practice, some U.S. certificated aircraft > 12,500lbs could qualify for LCN = 0 when fitted with 'tundra tyres', also known as 'balloon tyres'. Turbine aircraft certificated everywhere and limited to 12,500lbs sometimes had LCN > 0, because the manufacturer had chosen to certificate them for STOL operations landing from steep IFR glideslopes with additional landing impact.
The most important criteria are how many wheels (not legs) carry the weight, how soft the tyres are, and the maximum certificated glideslope for STOL operations by that type of aeroplane, not weight (or size) itself. Pilots frequently failed to flare fully from STOL (=> minus 6 degree) glideslopes and the default LCN = ACN had to allow for that once IFR STOL glideslopes were introduced. The issue is *not* whether the aeroplane will be damaged. *The issue is whether the fragile surface infrastructure will be damaged by the stronger aeroplane*.
Short Skyvan 3 (STOL 12,500lbs)
Douglas C-47A (DC3C) 8 (at 28,000lbs)
Nord 262 8 (STOL 22,700lbs)
Saab Scandia 12
Vickers Viking 12
Martin 2-0-2 14
Martin 4-0-4 14
FK27-100 & 200 14
HP Herald 100 14
Curtiss C-46F 15 (at 47,000lbs)
Bristol 170 Mk.21 15
HP Herald 200 16
Nihon YS-11 16
DHC7-100 and later 16.2 (STOL 44,000lbs)
Bristol 170 Mk.32 17
Avro 748 Srs 1 17
CV-240 19
Airspeed Ambassador 20
Avro 748 Srs2 20
Nord C-160 Transall 20 (at 108,000lbs)
CV-340 21 (at 42,400lbs)
CV-440 22
The many turboprop aircraft 'claimed' as 'DC-3 replacements' in the Classic era of aviation history, all needed to have LCN <=8 so that they could use all types of surface infrastructure that a DC-3C (demilitarised C-47A and similar) could use at 28,000lbs. Although pre war US FARS, and equivalent pre war national regulations had not specified LCN as such, 'wholly unimproved grass / dirt' was the norm even on 'most' major airports, and when dry that 'equated to' the Classic era legal definition of LCN = 8. The DC-3C had not originally been certificated with an ACN either, but its actual ACN 'equated to' ACN = 8 at 28,000lbs. The Nord 262 came closest to achieving the Classic era goal of a DC-3C replacement, but still failed. The post war Classic era of aviation history had higher certification standards and so designing a 'replacement DC-3' actually became impossible.
The LCN that a *new* primary commercial soft surface had to meet when dry in the Classic era was increased far beyond the 'typical' pre war level of only 8, and also far beyond the 'regulation' somewhat underpinned with aggregate allied WW2 soft surfaces that had been infrastructure matched to the C-46 footprint at 47,000lbs, which 'equated to' the later Classic era LCN = 15. Improving a WW2 era soft, (but actually underpinned with hard core in all necessary areas), from LCN = 15, all the way to LCN = 25 (when dry) only required sufficient further investment in excavation and hard core underpinning to achieve.
All the above aircraft can lawfully depart Classic era legislation, *new primary*, commercial grass / dirt / gravel runways at MTOW. However aircraft LCN / ACN well below 25 was still highly desirable through the Classic era of aviation history because it allowed those aeroplanes to operate lawfully into, over and from either Vintage era = 8, or WW2 era infrastructure = 15, infrastructure not yet improved to Classic era LCN = 25 requirements.
**Not all 'soft' runways and taxiways and parking areas are equal**
Each era of aviation history is an identifiable era because it has different legislation and procedures. Which is why the original question has no simple answer.
Even in the Classic era most of every soft *commercial* airfield might have LCN well below 25, and specified as such in its airport diagram, or the relevant national Aeronautical Information Publication (AIP), (modified on a temporary basis by NOTAM as necessary). Whole areas might be unclassified and therefore not fit for commercial use, or might be classified LCN = 0 even when dry. The infrequently used 'cargo ramp', else most of the 'passenger terminal parking' on a soft airfield might be much softer than the new soft Classic era LCN = 25 primary runway, primary taxiway and primary parking.
In the Classic era only a single 'stand' on a soft surface airfield might be LCN = 25. The next 'stand' might be LCN = 15 or even LCN = 8. The 'second' LCN > 15 arrival is soon blocking the only LCN = 25 marked grass or dirt taxiway to the only LCN = 25 grass or dirt stand until the 'first' LCN > 15 propliner is ready to depart, causing significant delays. The same can apply to a busier Classic era soft airfield that has more, but still 'too few' LCN = 25 parking stands.
The issue of using older soft surface partially hardened WW2 era, or wholly unhardened soft surface Vintage era runways, during commercial services in the Classic era also arises and is facilitated by having LCN well below 25. Often only one runway at a 'soft surface' Classic era commercial airfield had LCN = 25. The next best might be only 15 and the worst only 8, or even 0.
The 44,000lbs MTOW DHC 7-100 dates from 1979, well inside the Modern era of aerospace history. Only in the Modern era aircraft manufacturers can apply to have ACN at MTOW tested and certificated to three significant figures (DHC 7-100 series ACN = 16.2). At 44,000lbs a DHC 7-100 series cannot lawfully use *WW2 era* soft surfaces 'underpinned' only to the then 'regulated' LCN = 15 to match the loaded footprint of a heavier WW2 Curtiss C-46 at 47,000lbs.
So let's study a worked example of *flight simulation* commercial fuel and weight planning arising from the intention to operate an aeroplane from a later era, within earlier era infrastructure, or any 'soft infrastructure' whose PCN is lower than aircraft default ACN.
Again certification standards had moved on and *for flight simulation purposes* in order to use unimproved WW2 'soft' infrastructure (PCN = 15) the DHC 7 (ACN = 16.2) must reduce maximum take off weight to;
44000 * 15/16.2 = 40,741 pounds
it must offload
44000 - 40741 = 3,259 pounds of cargo and / or fuel.
to use still unimproved WW2 soft infrastructure.
The DHC7 cannot use 'wholly unhardened' truly soft and unimproved *Vintage era* DC-3C footprint soft surface infrastructure (LCN = 8) for *commercial* services at any weight, but classifying the DHC 7 operator as e.g. 'The British Antarctic Survey' changes the regulations it carries passengers under. As the 2008 Propliner Tutorial explains each era is a different era explicitly because it has different (ever more complex) regulations, compliances and exemptions. The safety requirements became more onerous in each passing era of legislation. Commercial airfields had to improve along with the new commercial aircraft regulations, or continue to limit hosted and visiting *commercial* use to 'large' aeroplanes from the earlier era whose regulations they still met.
However aircraft with LCN / ACN = 16 or 16.2 or 17, or even more, could reduce weight to use standard unimproved 'somewhat underpinned' WW2 era soft infrastructure with LCN / PCN = 15. The question was whether they could make a profit on a commercial service. If the haul was short enough they might, since all the mandatory weight reduction might be fuel not needed and not loaded, and the issue is anyway and always, "How much below MTOW must I depart to ensure that weight will be below Maximum Landing Weight (MLW) at the Initial Approach Fix (IAF) for destination"?
The 44,000lbs and 4 x 1120 shp (TOGA) DHC 7-100 series wasn't a fully successful replacement for the 47,000lbs and 2 x 2000 bhp (TOGA) C46, and of course TWA and EAL would have argued that the 44,900lbs and 2 x 2400 bhp (TOGA) M404 was fully successful much earlier, even though none of the high ACN Convair Liners could be. Of course the Martin Liners had their own problems, (see the Calclassic Convair and Martin Liner mini tutorial).
Bonanza, Wien Alaska, and many other airlines world wide would also have claimed that the 42,000lbs and only 2 x 1835 shp (TOGA) early series F27A from the late 1950s was capable of doing almost anything any of the aircraft above could do.
In the real world it's mostly about how much payload you can load legally alongside minimum compliant fuel for the trip, and that requires more detailed flight simulation fuel and payload planning, taking into account more factors, than all bar the most 'hard core' propliner enthusiasts are ever willing to contemplate. However without making that effort the gap between what a C46, an M404, an early FK27, and a DHC7-100, (from three different eras of aviation history), could each achieve commercially, when operating from unimproved WW2 'soft' surface infrastructure, can never be understood.
Each 'era' of aviation history introduced higher standards of testing for certification of aeroplanes and aviation infrastructure. The criteria used to assess ACN became more demanding, and the regulations concerning PCN to be provided during construction of any *new* or *improved* commercial infrastructure (soft or hard) became more demanding, but pre-existing commercial aeroplanes and pre-existing commercial infrastructure were not required to meet the new higher commercial safety standards. Instead never improved pre-existing aeroplanes and infrastructure were 'eventually' (often many decades later) ordered to be taken out of *commercial* service.
The question, 'How big an aeroplane can use a soft airfield?' is unanswerable without a date that places the question within a specific era of aviation history. The question is all about legislation and jurisdiction, not 'physics'. Legislation changes often. The laws of physics do not. What is 'physically possible' (when delivering a stripped out ancient aeroplane to a museum), and what was 'lawful' in commercial use in different eras of aviation history, are questions with very different answers.
The aircraft listed below cannot *lawfully* operate a *commercial* service to or from even a standard *Classic era primary commercial* soft runway *at MTOW*.
Viscount 700 Srs 29 (at 61,500lbs)
Douglas DC4 & C54 30 (at 73,200lbs)
AT Carvair 31
Breguet Deux Ponts 32 (at 114,000lbs)
Viscount 700D Srs 32
Viscount 800 Srs 32
Canadair C-4 33
A.W. Argosy 200 33 (at 93,000lbs)
Lockheed C-130J 37 (STOL at 155,000lbs on tarmac)
L-049 38
Viscount 810 Srs 39 (at 72,500lbs)
Ilyushin IL-18 42 (at 135,600lbs)
Lockheed C-130J 42 (STOL at 155,000lbs on concrete)
L-749 44
Douglas DC-6 44 (at 97,200lbs)
Douglas DC-6A 49
Douglas DC-6B 50 (at 103,800lbs)
However 'in theory' an individual airfield owner 'might' be able and willing to underpin one 'soft' runway, and one marked soft route to it, and one soft stand, with enough depth of hard core underpinning them all to match LCN = 30 to allow C-54 / DC-4 operation at MTOW, but far more likely aircraft with LCN > 25 were always operating at weights well below MTOW, flying short hauls with light fuel loads, while flying to and from 'new or upgraded primary soft commercial infrastructure' in the Classic era. They may have needed to depart at that low weight to achieve MLW at destination IAF anyway.
The much larger Breguet Provence / Deux Ponts could also operate from a soft Classic era primary commercial runway, with even greater % load reduction than a C-54, yet being much larger could do so with a 'similar' absolute load. I have little doubt that the (114,000lbs MTOW and 135 airline passenger seat) Provence / Deux Ponts was the 'biggest' *commercial* *piston engine* propliner to lawfully fly commercial passenger services from soft runways, but it could not do so at that weight.
114000 * 25 / 32 = 89,063lbs, but a Deux Ponts has an empty equipped weight of 73,040lbs, so its useful load (Crew + fuel + payload) from LCN = 25 infrastructure is around 16,0000 lbs and if the haul is short enough it might make a profit. However the biggest aeroplanes that used underpinned soft infrastructure are not necessarily the ones that can haul the biggest useful load from underpinned soft infrastructure.
The calculation for a DC-4 is instead;
73000 * 25/30 = 60,833lbs, but a DC-4 has an empty equipped weight of 43,200lbs, so its useful load from LCN = 25 infrastructure is around 17,600 lbs and if the haul is short enough it has a much better chance of making a profit.
The CV-340 is not MTOW restricted from LCN = 25 infrastructure and has the following aircraft.cfg data;
[weight_and_balance]
max_gross_weight=47000
empty_weight =30400 ;including oil, catering etc.
So a CV-340 has useful load from LCN = 25 infrastructure = 16,600lbs and over any distance should be able to make a profit.
The poorly designed Airspeed Ambassador is not restricted either;
[weight_and_balance]
max_gross_weight=55000
empty_weight =39500 ;including oil, catering etc.
So the much heavier Ambassador has useful load from LCN = 25 infrastructure = 15,500lbs and over any distance is less able to make a profit.
However we have discovered that aeroplanes which 'appear' to be too heavy, and which 'appear' to have too high LCN / ACN, can in fact use 'standard Classic era primary soft infrastructure' with LCN / PCN = 25 and 'may' actually be able to lift a bigger useful load (at higher cost), than aeroplanes designed with LCN <=25. Most airlines seek to maximise profit. Military organisations instead seek to maximise productivity, and the C-54 remained an important 'underpinned soft' infrastructure airlift asset for many air forces throughout the Classic era. The smaller number of much later Ambassadors were soon scrap.
Freighters like the (93,000lbs MTOW) Armstrong Whitworth Argosy 200 with LCN = 33 could haul significant commercial cargo payloads from LCN = 25 infrastructure too.
93000 * 25/33 = 70,455lbs, but a cargo hauling Argosy (200 series) has an empty equipped weight of 49,000lbs, so its useful load from LCN = 25 infrastructure is around 21,400lbs and if the haul is short enough it should make a profit or be productive enough to provide airlift from such surfaces under contract to the military.
However lifting really large loads from such infrastructure requires a much better designed transport, highly optimised for such infrastructure at huge expense to the relevant taxpayers, like the Nord C-160 Transall with LCN = 20 at MTOW = 108,000lbs allowing a huge useful (legally commercially compliant) load of around 47,000lbs. The Transall was far too expensive to be attractive to airlines, but it exhibited very high military productivity, at very high cost to the relevant taxpayers.
I leave readers to 'go back' and calculate the useful load that a DHC 7 / M404 / FK27A and C46A can each lift from 'regulation' unimproved WW2 soft (but somewhat underpinned) infrastructure with LCN = 15 using Calclassic supplied aircraft.cfgs.
For the DHC 7-100 use;
[WEIGHT_AND_BALANCE]
empty_weight =27820 //fully equipped
max_gross_weight=44000 //max 44100 leaving the ramp
Note that the C46A answer may differ by jurisdiction.
**It is also important to understand that not all hard surfaces are equal**
It is my 'understanding' that most wartime and post war decade 'hard' runways, taxiways and parking, were (by Allied WW2 powers agreement and then international law) LCN = 50. Aircraft that required more could not operate at MTOW from many WW2 'hard' infrastructure airfields, until the runways and taxiways and parking were upgraded, (usually only to LCN = 65), in the mid 1950s. Specific aircraft like the B-29 already needed superior infrastructure to depart at MTOW.
At some point during the Modern era of aerospace history certification procedures changed so that manufacturers could choose to certificate aircraft with a different LCN / ACN for each surface type. See C-130J above. LCN for lighter and older C-130s can 'perhaps' be calculated by reduction from ACN = 37 on all commercial airfield surfaces at 155,000lbs. Concrete is more liable to impact damage than tarmac over concrete and that is acknowledged in the present day certification procedures, but was not taken into account in the Classic era. Certification for STOL impact continues to be relevant.
Remember this answer addresses *international commercial* safety criteria. Real life is more varied and more complicated. Remember too that these criteria relate to the safety of the Concorde that is about to depart next, and whose main wheels will throw the lump of broken concrete, or aircraft debris, through its low wing and will puncture the fuel tanks, venting AVTUR into its afterburners causing it to crash; not the safety of the aeroplane that just departed too heavy and damaged the runway, or suffered partial structural failure during the prior heavy take off, leaving debris on the runway. What is physically possible during military logistics in support of a war zone or realistic military exercise, with significant levels of risk, and what is (un)lawful on a commercial airfield, due to implied risk % to following aircraft, differs.
By the time that the L188 Electra arrived in 1959, most 'busy' commercial and military airfields, outside the Soviet bloc, had one instrument runway, and one taxi route to / from (only) the instrument runway, and some parking upgraded to LCN / ACN = 65 but aircraft with LCN / ACN > 65 were still overweight at MTOW even on most 'busy' commercial, and many military airfields in the early 1960s. There were very few places they could depart at MTOW and the places that were already upgraded beyond LCN = 65, had mostly been upgraded to handle the early B707, not the final dinosaurs of the long haul propliner era. Ensuring that the 230,000lbs Short Belfast could operate at MTOW from existing 'upgraded once in the 1950s' hard runways, now with LCN = 65, was very important to the RAF, but ended up limiting its utility in the Modern era which soon arrived.
L-1049B/C 51 (at 120,000lbs)
Britannia 100 52 (at 155,000lbs)
L-1049G/H 58 (at 140,000lbs)
L-188A and C 59 (at 116,000lbs)
Douglas DC-7 (pax) 60 (at 122,200lbs)
Canadair CL-44D 60 (at 210,000lbs)
Britannia 300 62 (at 185,000lbs)
Douglas DC-7B and BF 63 (at 126,000lbs)
Douglas DC-7F (cargo) 63 (at 126,000lbs)
Boeing 377 65 (at 145,800lbs)
Short Belfast 65 (at 230,000lbs)
L-1649A 70 (at 160,000lbs)
Douglas DC-7C and CF 72 (at 144,750lbs)
Vanguard 952 72 (at 146,500lbs)
The immediately post war Boeing 377 (derived from the B-29) was especially restricted in relation to where it could be tasked to fly, needing very hard runways and taxiways that barely existed in the commercial world, and military grade fuel, in order to operate at MTOW. During the Classic era of aviation history, the issue was not only whether the runway was long enough to take off at MTOW, but also whether it was strong enough. That applied to 'hard' infrastructure, not just 'soft' infrastructure.
Of course the places the high ACN aeroplanes above operated to and from in real life were mostly the very few that had pavement of suitable PCN, but some services would have been weight restricted by inadequate PCN. However as above that might not require larger weight reduction than the need to achieve MLW at destination IAF anyway.
The Soviet Union (and client states) did not ratify international law in the Classic era and did not publish LCN data, but the Lisunov Li-2 would have been 8 or less, and the IL-14 was 'probably' 13 or less. It's problem was its damage prone low wing and flaps. The video I cited makes plain the reality that the issue in the Soviet Union, and Modern era Russia, is not just a few stones or other FOD thrown up by the landing gear while travelling down a runway that has not been swept recently.
The An-10A Ukraina did not repeat that mistake and all lesser only twin engine Antonovs would have been LCN / ACN 15 or under. The piston engine An-14 would have been LCN = 0. The very expensive to develop, and structural failure prone, 126 passenger seat An-10A Ukraina was almost certainly the largest (127,900lbs) aircraft ever *designed* to fly airline passenger schedules from 'underpinned soft field infrastructure' and 'probably' had an LCN below, or equal to, the 108,000lbs Nord C-160 Transall LCN = 20. This allowed the An-10A to lift a useful load of about 56,400lbs from 'soft' infrastructure easily beating even the later Transall. Later Antonovs, from the modern era of aviation history, were designed as freighters, but in atypical, (not necessarily commercial), circumstances have lifted larger (passenger) loads from 'soft' infrastructure. There is little doubt that from the An-8 onwards the Ukraine and Antonov became (and probably still are) the masters of lifting large loads from soft airfield infrastructure.
The very few Soviet *international airports* which accepted foreign airlines in the Classic era would all have had 'just enough' primary infrastructure with PCN = 50 before doing so, but almost certainly no more than PCN = 50 in the Classic era, and 'perhaps' 'Soviet Bloc' hard infrastructure in the Classic era was only PCN = 42.
The Russian Il-18 Moskva, by contrast to the An-10 Ukraina, was designed for international service and for export use only from hard surfaces and complied with international law. It could therefore have a low wing. Nevertheless being Soviet it was designed to have much lower LCN (42) than the earlier Britannia 100 (52) and the contemporary Britannia 300 (62) and throughout the 1960s could depart at MTOW from many more runways in the 'third world', that had never been upgraded from LCN = 50 to LCN = 65, yielding many more export orders. The 135,600lbs IL-18 was the heaviest commercial aircraft designed to operate from hard runway airfields built only to late WW2 Allied nations standards (LCN = 50).
The L1049 / DC7 / L188 / BR10 / BR30 / VC9 (or military B-29) could not use 'normal' hard surface WW2 airfield infrastructure with LCN = 50 *at MTOW*. A 120 passenger seat and 135,600lbs IL-18, or a 94 passenger seat and 101,410lbs Sud Caravelle III *turbojet* could (at MTOW), (see below), but of course so could the 126 passenger seat and 127,900lbs An-10A Ukraina which was reserved solely for high demand Soviet domestic passenger services from 'soft' surface airfields. It did not meet international legal requirements and could not be exported.
During the Classic era of aviation history, often it was LCN that determined what aeroplane could be purchased as a replacement on a given commercial route, in which part of the world, and when, but of course these much larger aeroplanes with LCN at MTOW that is 'too high' may also be able to operate profitably at reduced weight on short hauls where all of the weight offloaded can be fuel.
If you have realistic (not real easy) flight dynamics (a big if) which include realistic MTOW and MLW and MZFW and ready for service empty weight criteria for a given aeroplane, (see 2008 propliner Tutorial), and you know LCN for MTOW you can determine what useful load that aeroplane can lift during a flight simulation sortie from each type of infrastructure, constructed or improved during each era of aviation history. You just have to 'decide' how 'improved' the various parts of the airfield were, beyond their original LCN, by the date you choose to simulate. I have provided the necessary guideline values and worked examples. Runways that were not instrument runways, and the taxiways that served them were often unimproved from time of construction.
For contrast here are some certificated LCN / ACN values at MTOW for early jet transports. They are essential to understanding what happened next.
DH 125 Srs 1(Dominie) 8
FK28 Fellowship 22
BAC 111-200 36
DC9-10 36
BAC 111-400 39
BAC 111-300 41
Sud Caravelle III 47
D.H. Trident 1C 51
Convair CV880-22 53
Sud Caravelle VIR 54
DH Comet 4B 56
B727-100 56
DH Comet 4 57
Boeing 720 60
Vickers VC10 65 (at 312,000lbs)
Boeing 720B 65 (at 234,000lbs)
Vickers Super VC10 72 (at 335,000lbs)
B707-120 76 (at 257,000lbs)
Douglas DC-8 20/30 85 (at 315,000lbs)
C-141A Starlifter 85 (at 384,500lbs)
B707-320B 96 (at 327,000lbs)
Douglas DC8-50 99 (at 315,000lbs)
I believe the 60 passenger seat and 60,000lbs Fokker F.28 Fellowship was the largest *commercial* jetliner ever designed to operate from Classic era commercial soft primary infrastructure. The VC10 was the largest commercial aircraft that could operate from existing world wide major runways that had already been upgraded once from LCN = 50 to LCN = 65 in the mid 1950s, without a further major upgrade to allow B707 / DC8 operation. The VC10 was much heavier than the B720B, Belfast or equivalent USAF turboprop freighters, but could use the same runways, taxiways and stands. However like the Belfast that VC10 capability was soon irrelevant and again had limited other capabilities to the detriment of sales.
The cost to airfield owners, (often in reality municipal and federal taxpayers), of upgrading infrastructure to allow B707/DC8 services was huge, but the profit to the airfield, and commerce within the local / national economy, lost by refusing them was soon greater. The Super VC10 could then be developed to use runways upgraded to take the much lighter earliest B707s, or in a few cases already upgraded to take the very demanding DC-7C and Vanguard. In the 1960s many airfields had hard runways long enough, for the DC7C and VC9, but those runways and surrounding infrastructure often simply weren't strong enough. The CL44 Yukon, the Belfast and Britannia 300 series converted to freighting could haul a full load out of those typical (but not major) 'first world' 1960s airfields with only one runway upgraded only to LCN = 65.
At the end of the Classic era, the very expensive late 1960s Vietnam War period airfield upgrades, to allow MTOW operation of the latest *turbofan* powered jetliners and freighters, with huge tax payer subsidies to fund them, quite suddenly required LCN = 100. That huge LCN quite quickly became the norm for major and even 'typical' civilian and military airfields and LCN largely ceased to be a factor for all lesser and earlier aircraft unless they were still operating to soft surface commercial airfields. By then such airfields were increasingly rare outside the 'Communist Bloc'.
After the B707 and DC8 were designed with no regard to existing pavement capability, imposing huge costs on taxpayers, (who always end up massively subsidising the private sector in aviation), political steps were taken to force future designs to achieve reduced ACN, mostly by having more wheels on each leg, even in the U.S., where in theory ACN was not the explicitly regulated value. However after major reductions in the middle of the Modern era of aerospace history ACN values are creeping up again.
B747-400ER 69 (at 913,000lbs on concrete)
B747-8 75 (at 978,000lbs on concrete)
B777-300ER 85 (at 777,000lbs on concrete)
Nevertheless a fully loaded DC7C or L1649A in 1956 did more damage to airfield infrastructure than a fully loaded B747-400ER is allowed to cause today.
The current ICAO methodology for calculation of current ACN and current PCN is here;
www.faa.gov/documentLibrary/media/Advisory_Circular/150_5335_5B.pdf
It depicts how modern era captains, and airfield owners, use a payware software application to take into account additional real world variables, but its methodology has no practical application to (even modern era) desk top flight simulation which requires a much simpler way to vary only current weight in relation to PCN (deemed to be) available at the date and place being simulated.
Even during modern era simulation there must be no presumption that a B777-300ER can operate at more than (65/85 * 777,000 =) 594,000lbs to, or from, third world infrastructure never improved beyond original construction PCN = 65 in the late Classic era, and the B777-300ER cannot possibly achieve 'Extended Range' starting from that weight when outbound. To the contrary a B747-400ER starting from 860,000lbs pretty much can (with reduced payload). During flight simulation a B747-8 'must' reduce even more to 847,000lbs to use that same late Classic era (never improved) concrete hard runway. The heaviest (or biggest) aircraft often cannot lift (or deliver) the biggest load from / to the available runway, for lots of reasons.
This isn't by any means just a 'grass / dirt / gravel' era and infrastructure issue.
FSAviator (January 2013)