This´s a fairly complex query .... both technically and historically .... and one which probably requires an appropriately complex technical and historical response.
I´ll try´n cover everything within a single reply, but, which won´t/can´t be short
It´s wrong to make direct comparisons between the F/F of any of our DC-8´s and B707´s and despite the fact both aircraft were powered (and are simulated to be powered) by the the same engine types/marques .... and then not to expect the F/F observations of both to vary.
On a test rig the F/F of each engine type/marque would be observed to be "at specific rates" in conjunction with specific power settings .... etc.
But .... put these same engines on the wings of 2 entirely different aircraft types .... like the B707 and DC-8 .... and these F/F observations are going to become quite (if not dramatically) different .... "basically" for reason of their different aerofoil/wing designs and the weight of each aircraft type too. The wing of both the B707 and DC-8 underwent a number of modifications in order to improve its aerodynamic efficiency/lessen drag following their entry to service and throughout the early developmental marketing and production period of both aircraft types .... "prior to" the B707-320B/C and DC-8-50 at least.
Both the B707 and DC-8 originally suffered drag related problems with neither aircraft type meeting their projected airspeed and range/performance garuntees .... due to drag.
Both the B707 and DC-8 wing also varied in regard to that of the DC-8 having slightly less wing sweep than the B707 and being slightly slower but also a bit more stable too (especially in rough air) as a result .... whereas the B707 wing had slightly more sweep than that of the DC-8 and was slightly faster although early versions (again "prior to" the -320B/C) were also limited in respect of be able to operate into some airports during certain meteorological conditions.
Either way .... both became even better/"superb" aircraft as they evolved, but, the B707 was always slightly superior to the DC-8 in respect of its performance and economy as a PAX carrying aircraft .... although the DC-8 became much more versatile, and to some extent more valuable later (primarily as a freighter), due it´s stretch-ability.
In regard to your FS observations the following "has to" be appreciated .... if not merely taken into consideration ....
Our B707 FDE´s are now the "oldest" we offer and have not been updated since 2006/7 .... but .... are scheduled to be revised during 2019 since time´s not available for us to do so this year given what we plan to release before the end of the year.
In comparison .... our DC-8 FDE´s were all updated and re-released (with Benoit´s new and far superior soundpacks) during early 2015. As part of that DC-8 FDE upgrade we sought to focus on airspeed performance in particular .... among W&B data and many other technical revisions too. The cruise airspeed aspect of performance for each DC-8 simulation was primarily achieved by addressing certain drag parameters .... particlarly among the DC-8-10 through 50 series .... simply because it´s in this respect (R/W changes apploed to the aircrafts wing tips, chord, as well as a 1 degree cruise flap modification too as the DC-8 evolved) that early versions these aircraft, through drag reduction, began to near their projected airspeed/range performance guarantees. In flying our DC-8-10/11 series note how they´re airspeed restricted .... but .... and then note how this gradually improves from the DC-8-12 and -20 .... and through both the -30 and -40 series too .... despite the simulated weight increases for each type. The airspeed/altitude performances for each of these DC-8 simulations are now almost spot-on .... "IF THEYÉ FLOWN PROPERLY TO START WITH .... at least as recommended per PP5 (the last page/section) of our following linked forum based/online manual for these simulations ....
DC-8 INSTALLATION & HANDLING NOTES/MANUALtonymadgehjg.proboards.com/thread/8019/hjg-panel-installation-handling-notesAgain .... the performance of each of our DC-8 versions "IS" different .... as they should be .... aided by the recent FDE revisions and our recommendend procedures for each of these simulations.
In regard to F/F observations ....
As I recall .... the currently stated FFS values for each DC-8 engine type/marque (and these do differ among most DC-8 versions ... as Mike has already emphasized) came straight from the same engine type/marque stated FFS values for our B707´s .... and which though older data are still close to reality. I wouldn´t recommend further editing the FFS values for any of our B707´s and DC-8 for the following reasons ....
The variations that may be observed in the F/F indications between our B707´s and DC-8´s are entirely due to the recent drag parameters we´ve "had to" impose in order to ensure authentic airspeed performances for each of our Dc-8´s within the high altitude cruise regime .... and which will llkely see their F/F indications being somewhat higher than those for comparative B707 versions. What I´nm trying to say here is .... the FFS values for each our B707´s aren fairly inaccurate too, but, any defficienies evident in their fuel burn (these simulations will probably be under burning and slightluy over performing too) will be due to their not yet having been subjected to the same sort drag influences recently applied to our DC-8´s. 12 years is a long time in FDE terms .... and as the newer DC-8 FDE´s should indicate .... we´ve learned a lot during this time and which still needs to be applied to our B707´s .... and wwhich will be so in due course.
ALSO ....
It must always be born-in-mind that our F/F indications (all of which are based on R/W data for each engine type/marque) are as accurate as we can possibly make them "AT SEA LEVEL" (this is, or should be, an FS standard .... an FFS value needs to be accurately set then actual F/F and the peformance of each simulation then manipulated per drag parameters only .... one "is not" encouraged adjust the stated FFS values) .... but .... due to the various limitations/idiosycracies of the FS program otself (the way in which it´s compiled to perform), and regardless of what we do to try´n improve matters too, we "have to" accept whatever these F/F indications become by the time each simulation reaches cruising altitude. Despte our F/F indications being accurate at sea level .... these simulations may still be seen to be either under or over burning fuel at cruising at altitude and the range of any simulation similarly then being somewhat less or greater than it should be in reality.
Additionally .... although our flying guides might recommend a particular loading and airspeed/MACH velocity at cruising altitude too, this doesn´t mean one should fly these simulations that specific airspeed/MACH velocicity. In fact one can often save a considerable amount of fuel by slightly reducing airspeed/MACH velocity during cruise .... and possibly extend range. Each of our simulations also loads into FS with 100% fuel and payload .... with the end user then being expected to manually adjust this data so each simulation is set within its stated MGW limitations for each aicraft type. Adjusting/reducing payload (only) will typically promote the carriage of more fuel .... and therefore extende range quite considerably .... "if done properly"
As freeware and payware FS developers .... what we all provide (as it loads into FS by default and without any adjustments) can, at best, only offer relatively authentic altitude/airspeed performance .... or .... relatively authentic F/F indictions, but, not both together .... and "THAT´S THE WAY FS WORKS"
I trust this satisfactorily explains/covers the technical side of what we do, and are able to deliver, given certain limitations imposed by FS itself
BOEING had a considerable head start over DOUGLAS during the early to mid 1950´s through development of its jet powered B367-80 .... which evolved into a the KC-135 .... and later the B707. When the US government called for tenders for a jet powered aerial refuelling aircraft for the USAF, BOEING already had a candidate in the form of its B367-80 whereas DOUGLAS "did not" .... and upon loosing this tender, and later realising what BOEING was moving toward (in regard to the civil B707), it was suddenly "forced to" meet the BOEING challenge, though it could ill-afford to do so, but, had to do so if it were to remain competitive within the world civil aviation market.
It´s often been said that DOUGLAS, and its DC-8, played catch up with the B707 throughout the production of both aircraft types, but, which is a fallacy given that it was DOUGLAS´s airline experience, and it´s DC-8, which actually influencerd the B707 design .... ultimately in BOEING´s favour. Both parties were also concerned, at this time, in regard to their rival GENERAL DYNAMICS/CONVAIR plans to develop both the high performance CV-880 and CV-990 and its potential impact upon/intrusion into their perceived future civil world markets too.
BOEING´s development of the B707 was greatly assisted by its government grant/subsidy to develop the KC-135. DOUGLAS lacked this major cost off-setting advantage though .... and not only had to fund developent of the DC-8 itstelf, but, also had to build an entirely new aircraft manufacturing plant and then relocate from Santa Monica, to Long Beach, especially for DC-8 production. From the start of their marketing campaigns the DC-8 .... through DOUGLAS´s not benefitting from similar government development subsidies as had advantaged BOEING .... was more expensive than the B707 .... which costwise was more favourable to any number of operators then contemplating transitioning into the jet age.
Whilst DOUGLAS was certainly far more experienced than BOEING in regard to civil aircraft development .... BOEING learned "very quickly" .... and won valuable B707 contracts due to DOUGLAS´s relucatance (financial inabilty) to tailor its DC-8 to specific customer requirements until much later, but, which BOEING keenly set out to do, and could more easily achieve, from the very start of its B707 marketing program (especially in regard to both the QANTAS and BRANIFF contracts for special performance capable B707 versions). By the time DOUGLAS eventually realised how its marketing policy/strategy was actually restricting the success of DC-8 marketing in favour of the B707 .... and began to offer DC-8 versions of various performance capabilities .... BOEING was already planning to expand its civil flightline to include the B720, B727, and B737 (and much later the B747 versus the DC-10 and L-1011 also), and in doing so was able to offer "a family" of aircraft types to satisfy airline requirements in respect of long, medium, and short range applications .... effectively enabling airlines to operate BOEING specific fleets to meet their service/route requirements .... as well as being able to offer more favourable aircraft purchasing terms than DOUGLAS could .... until much later on and following DOUGLAS´s DC-9 development, merger with McDONNELL, and development of its SUPER DC-8 series. By this time though BOEING had a firm foothold within the world civil aviation market (GENERAL DYMNAMIS/CONVAIR had been more-or-less knocked out .... suffereing king hits imposed by BOEING´s B720 and its own inexperience too) and the sales of B707´s began to exceed those of DC-8´s (many DOUGLAS operators remained loyal to DOUGLAS though) .... all of which was largely aided by BOEING´s more advantageous financial position, more successful marketing strategy, from the very start of this Jet Race.
Despite the advantages of one aircraft type over the other, the competition which prevailed between BOEING and DOUGLAS/McDONNELL-DOUGLAS saw the B707 and DC-8 both become "superb" aircraft in their own individual and differant ways. Despite the fact that BOEING sold 50% more B707´s than DOUGLAS sold DC-8´s its actually debateable as to whether or not either aircraft made any/much money for their respective developers due to constant modifications that were applied to both designs throughout their production and in order to try´n seek the ultimate edge/advantage .... but which also pushed the development break even points for both aircraft types much further down the line and into the future. At the end of the day though .... the DC-8, due to its versatility, has remained in civil service far longer than the B707 .... with at least 5 airframes still operational/serviceable around the world today whereas no B707´s remain in commercial airline service.
Given this background it can "possibly" be said that events leading to the demise of DOUGLAS/McDONNELL-DOUGLAS (the companies merger with McDONNELL during the early 60´s .... then its eventual acquisition by BOEING during the early 1990´s) were probably set in motion during the early to mid 1950´s .... due to it/DOUGLAS not only being forced to move into jetliner development before it might have otherwise have been willingly to do so, but also, having to had finance its entire jetliner program itself and which it was less easily able to achieve without assistance in the form of a merger or government development subsidies.
It´s been speculated that DOUGLAS might have outsold the B707 had it offered (been able to offer) the SUPER DC-8 series sooner (due to limitations in regard to further developmet of the B707 design), but, it was unable to do so, or launch its DC-9 either, without the merging with McDONNELL. And by the mid to late 1960´s jetliner development and marketing was already changing direction .... in favour of wide-body jet transports .... in the form BOEING´s B747 .... and which was then rivalled by not only McDONNELL-DOUGLAS´s DC-10 and the LOCKHEED´s L-1011 TRISTAR .... but also by the AIRBUS A300B too .... all lf which created even greater challenges, and risks, for each of these civil aircraft manufacturers.
Mark C
BOG/CO
