Cargo-Experimental (C-X) program designs

overscan (PaulMM)

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Patent drawings of the Boeing CX
 

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boxkite

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The Swiss "Interavia" magazine 8/1981 published an artist's impression of Lockheed's C-X proposal (the later C-17). Four engines PW2037 had to be installed. No further details. What was the model number? Which other competitors lost against the McDonnel Douglas design? Any recommended articles or books regarding the topic?

SOURCE: Interavia 8/1981 (page 749)

[Moved to existing thread - MODERATOR]
 

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overscan (PaulMM)

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Boeing, Douglas, Lockheed CX. Nice scans via Defense Visual Information Center website (http://www.dodmedia.osd.mil)
 

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LowObservable

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overscan said:
...Douglas CX

Ewwwww! Can't you put up a DISTURBING IMAGE warning? ;D

Although you can see why MacDAC won. Just thinking about the loadpaths between the horizontal tail and the center-to-rear fuselage splice gives me a headache.
 

hesham

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Hi,

and from Flightglobal,and notice Boeing design had a winglets.

http://www.flightglobal.com/pdfarchive/view/1981/1981%20-%202231.html
 

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Triton

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Model of Lockheed C-X concept circa 1980.

Source: Norton, Bill STOL Progenitors: The Technology Path to a Large STOL Aircraft and the C-17 American Institute of Aeronautics and Astronautics, Inc. 2002
 

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yasotay

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Triton said:
From DefenseImagery.mil, an artist's concept of the Air Force's proposed C-17 transport aircraft, formerly known as the C-X transport aircraft. Date Shot: 9/22/1981

Source: http://www.defenseimagery.mil/imagery.html#a=search&s=artist%27s%20concept&guid=0cd29e374e4c7600ca4d37437a83a8bb1cc2c203

Ah yes the "Snooker" painting that the Air Force used to pursuade the Army that they would use the C-17 to land mounted combat forces in unprepared areas. So the Army invested, because it would be able to land without needing very predictable runways.
 

Stargazer2006

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Triton said:
Model of Lockheed C-X concept circa 1980.

Source: Norton, Bill STOL Progenitors: The Technology Path to a Large STOL Aircraft and the C-17 American Institute of Aeronautics and Astronautics, Inc. 2002

Different times, different marketing strategies. Try to go selling an Airbus A400M or a Lockheed C-27 with a girl holding a model nowadays... would look downright silly, right?
 

Triton

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Stargazer2006 said:
Triton said:
Model of Lockheed C-X concept circa 1980.

Source: Norton, Bill STOL Progenitors: The Technology Path to a Large STOL Aircraft and the C-17 American Institute of Aeronautics and Astronautics, Inc. 2002

Different times, different marketing strategies. Try to go selling an Airbus A400M or a Lockheed C-27 with a girl holding a model nowadays... would look downright silly, right?

Different times indeed. In the "Unbuilt 747s" topic, I posted a photograph of a girl surrounded by models of unbuilt Boeing 747 design concepts. I believe that if a company were to do this today, people would be offended and outraged.
 

Skybolt

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Yes, but use Sacha Baron Cohen attired as Bruno (with the umlaut) and you'll istantly be "provocative" and "modern"....
 

yasotay

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Skybolt said:
Yes, but use Sacha Baron Cohen attired as Bruno (with the umlaut) and you'll istantly be "provocative" and "modern"....

Not what I wanted to think about today...
 

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Here's the three candicates in a group photo...
 

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Triton

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Triton said:
Model of Lockheed C-X concept circa 1980.

Source: Norton, Bill STOL Progenitors: The Technology Path to a Large STOL Aircraft and the C-17 American Institute of Aeronautics and Astronautics, Inc. 2002

Hmmm, looks like Bill Norton was mistaken and this is an AMST concept.

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Two Boeing in-house models show size comparison between AMST (YC-14) and C-X (C-17) proposals. Fuselage diameter is larger on C-X, to meet USAF requirements.
 

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Pioneer

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I've been looking for more info on this three-engine Boeing CX design for years!
Thanks for sharing Circl-5
Keep it coming! As their must be more info on this interesting design!

Regards
Pioneer
 

Triton

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I wonder if the Boeing C-X proposal would have been named Stratofreighter II?

Andreas Parsch has this to say about the "missing" C-16 designation:

C-16

The C-16 designation was never officially assigned to any aircraft. However, it was tentatively reserved no less than four times before it was finally cancelled for good. The first reservation, dated 27 November 1973, was for "YC-16" for an unidentified Boeing aircraft, but this reservation is marked as "not used". On 13 March 1975, the designation C-16A was reserved for the deHavilland DHC-6. However, this aircraft was eventually designated as UV-18A, and C-16 remained unused. On 17 December 1975, C-16 was again put "on hold" for the Air Force. This third reservation was officially cancelled on 30 April 1981, shortly after the fourth and final reservation for C-16 was made on 13 April 1981. The latter was for the "C-X" aircraft (which eventually became the C-17A Globemaster). A formal request for allocation of an MDS designation, forwarded on 3 September 1981 by the USAF Nomenclature Office to HQ USAF for approval, says:

1. The attached letter requesting a Model Series Designator for the C-X Aircraft is forwarded for consideration and approval.

2. We do not recommend assignment of C-17 as requested in subject letter.

3. This office recommends assignment of C-16A to this Aircraft as "16" is the next available number in the Cargo Aircraft category. C-16 has been on reservation for this aircraft since April and skipping this number is in conflict with AFR 82-1, paragraph 3g.

However, only one day later this letter was cancelled and replaced by the following:

1. Disregard ASD/ENESS letter, 3 Sep 1981, same subject.

2. The attached letter requesting a Model Series Designator for the C-X Aircraft is forwarded for consideration and approval.

3. We concur with assignment of C-17 as requested in the attached letter.

4. The designation "C-16" will have to be marked in the DoD master list of aircraft designations as "Not Used".

There was obviously a reason to skip C-16, but unfortunately it was not written down. It is reported, however, that the design number 16 was skipped because of "concerns over confusing the plane with the F-16 during the stress of high combat radio traffic".

Interestingly, when Boeing worked in the 1978/80 time frame on a four-engined YC-14 derivative for the C-X competition, some drawings were labeled with "C-16". However, this was simply a Boeing in-house label reflecting the anticipated designation of the C-X, and not related to any officially reserved C-16 designation.

There are two reports which associate the C-16A designation with other aircraft. In light of the above documentation, these reports are either wrong, or refer to unofficial and/or classified use of a previously unused designation. The first report says that C-16A was planned to be used for a Cessna 208 Caravan intended for use by the U.S. Army (but eventually not accepted) in missions against leftist rebels in El Salvador and Nicaragua. Another unconfirmed report states that the designation C-16 is allocated to Boeing 737s in CRAF (Civil Reserve Air Fleet) used by AFSOC (Air Force Special Operations Command).

Source:
http://www.designation-systems.net/usmilav/missing-mds.html
 

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More photos of the Boeing C-X factory proposal model. The C-X competition was won by the McDonnell Douglas C-17. Today, these two designs would not compete, because the government allowed both companies to merge. Mergers are good for shareholders and CEOs, but often bad for everyone else.
 

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circle-5

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Triton said:
Thank you, circle5. Is this model from the Boeing Archives?
No, this is from my model collection. Three of these were built at the Boeing model shop in early 1981: two are in the Boeing archives (one silver, one camo) and this one.

The landing gear detail is quite interesting -- will post later.
 

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Thanks from me as well Circle-5
Do we know what this Model designation this Boeing 3-engine derivitive of their YC-14 is??
Would love to see the actual specifications for this!!
But I think I've already denoted this :)

Regards
Pioneer
 

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Pioneer said:
Do we know what this Model designation this Boeing 3-engine derivitive of their YC-14 is??

Boeing Model 1050 / C-16 (Between the McDonnell Douglas YC-15 and C-17 transports)

Not sure this airplane would qualify as a "derivative" of the YC-14. Both AMST finalists served as proof-of-concept vehicles for the much-larger C-X designs, but there was very little airframe commonality, if any.
 

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Boeing C-X (Model 1050) main landing gear detail on factory proposal model:

No.07: Gear up -- paratrooper jump door blocked by fairing extension in normal position.
No.08: Gear up -- jump door cleared by hinged-up fairing extension, which doubles as slipstream shield for rapid troop deployment.
No.09: Gear down -- jump door blocked again.
 

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Maveric

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Great circle-5, fantastic projects. Thanks for sharing. Do you have some data (powerplant and others).

Thanks
 

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circle-5 said:
Boeing C-X (Model 1050) main landing gear detail on factory proposal model:

No.07: Gear up -- paratrooper jump door blocked by fairing extension in normal position.
No.08: Gear up -- jump door cleared by hinged-up fairing extension, which doubles as slipstream shield for rapid troop deployment.
No.09: Gear down -- jump door blocked again.
Thanks for sharing!!Although I have to admit its a very technical solution / arrangement RegardsPioneer
 

Jemiba

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Pioneer said:
Although I have to admit its a very technical solution / arrangement RegardsPioneer

Indeed ! That leads to the question, why the jump door wasn't just moved 1.5 m aft ?
 

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Jemiba said:
Pioneer said:
Although I have to admit its a very technical solution / arrangement RegardsPioneer

Indeed ! That leads to the question, why the jump door wasn't just moved 1.5 m aft ?

1.5 m aft is the hinged, drive-up loading ramp (see outline on model) with its hydraulic actuators and pressurization seals. Lots of heavy structural elements in that area, which would not allow a door. That's my opinion -- I could be wrong.
 

aim9xray

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No, I think you are correct.

The basic problem (as I humbly see it) with the Boeing design is caused by the basic lack of scalability of the powerplant. While MDC could change engines to uprate thrust (20k JT8D to 37k pounds thrust PW2037) as they enlarged their YC-15 to the C-17, Boeing had no larger engines from which to pick and had to add the third CF6-50 in a clunky tri-motor configuration to increase power.

Putting the engine in the tail also caused the other engines to be cantilevered even further forward of the wing to maintain the CG range...not good for weight.

I don't think that this overly complicated fairing/door arrangement could have scored well in comparison to the MDC example either...
 

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Jos Heyman said:
Does anybody have basic dimensions for the Boeing design?

If somebody has access to old issues of Aviation Week, from between (approximately) November 1980 and August 1981, there should be some articles describing all C-X designs, including both Lockheed proposals, with specs.
 

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I have fragments of design documentation for the Lockheed C-X proposal (the model L-610). Looking through it again for the first time in over 25 years, it tells a fantastic story. I'll put some time into cleaning up some of the woeful old photocopies and start a series of posts over the next few weeks.

As a teaser, the graceful L-610 had nearly the same overall dimensions (span, length, and height) as the lumbering and oafish C-17, but a takeoff gross weight about two-thirds that of the C-17. The cargo box cross section was only 6 inches more narrow, and actually a tad taller on the centerline than that of the C-17, but to allow a significantly smaller fuselage diameter the L-610 cargo box that featured clipped upper corners (it wasn't square'ish). Less weight (hence less wing area), but the same span gave the L-610 a wing with a significantly higher aspect ratio (major driver for higher L/D) than the C-17. Many people still remember that the C-17 turned out not only heavier than proposed, but also way more draggy. It fell far short of initial key payload-range requirements until the Air Force reduced those requirements (at least twice during the C-17 development!).

So, how did Lockheed propose such a lighter airlifter for the same C-X RFP that gave us the tubby C-17? The C-X RFP did not specify a max cargo weight requirement. Instead, it allowed the bidders to propose the lowest cost design solution that they believed was optimally sized to allow movement of a given Army mechanical unit, over a required range, and into a specified airfield that had a fixed sized tarmac for cargo unloading (by the way that ramp space restriction severely restricted span). The resulting proposals essentially required three L-610 for every two C-17. The cost estimates then boiled down to relative airframe/engine costs (would buying a third more jets that would each be cheaper be less expensive), maintenance costs, fuel costs (the more aerodynamic jet burning less fuel), aircrews, etc. It's easy to see that it was a complicated competition for the Air Force to compare designs and ultimately score and rank bids.
 

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'lumbering and oafish' - isn't that a prerequisite for a stractical transport aircraft?

Interesting points, I look forward to more info on the L-610.

Chris
 

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First installment on details of the Lockheed L-610 C-X proposal, submitted in January 1981.

First, a humble-pie correction to my post of 3 July 2020. The L-610 was not two-thirds the weight of the C-17. From an OWE standpoint, more like three-quarters, and maybe 80% of the design weight. Those pesky facts popped up when I was compiling the statistics for the attached graphic.

The attached pdf is a fairly unique illustration for a proposal document of that period. It is a cutaway illustration (like those famous Flight International works of art). The computer-aided design packages of the late 1970s into the early 1980s were extremely primitive by today's standards. This cutaway was a hand-drawn illustration likely based on some lofting drawings, but meticulously crafted line by line. I apologize for the resolution. It comes from an ancient photocopy of what was probably a blue-line print of the original drawing.

I am next working on a three-view general arrangement drawing, and then some comparisons of the cargo box dimensions (spoiler alert: the L-610 with its 17.5.-foot wide and 12.8-foot tall cargo cross section was very close to the C-17's 18.0-foot wide and 12.3*-foot tall cargo box cross section). *height under the wig box carry-through, aft of the wing the height rises to 13.5 ft
 

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Pioneer

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First installment on details of the Lockheed L-610 C-X proposal, submitted in January 1981.

First, a humble-pie correction to my post of 3 July 2020. The L-610 was not two-thirds the weight of the C-17. From an OWE standpoint, more like three-quarters, and maybe 80% of the design weight. Those pesky facts popped up when I was compiling the statistics for the attached graphic.

The attached pdf is a fairly unique illustration for a proposal document of that period. It is a cutaway illustration (like those famous Flight International works of art). The computer-aided design packages of the late 1970s into the early 1980s were extremely primitive by today's standards. This cutaway was a hand-drawn illustration likely based on some lofting drawings, but meticulously crafted line by line. I apologize for the resolution. It comes from an ancient photocopy of what was probably a blue-line print of the original drawing.

I am next working on a three-view general arrangement drawing, and then some comparisons of the cargo box dimensions (spoiler alert: the L-610 with its 17.5.-foot wide and 12.8-foot tall cargo cross section was very close to the C-17's 18.0-foot wide and 12.3*-foot tall cargo box cross section). *height under the wig box carry-through, aft of the wing the height rises to 13.5 ft
Nice find Hank58 and thanks for sharing with the forum.


Regards
Pioneer
 

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So the C-17 got the same illness as the early Short Belfast (also known as Belslow, ROTFL, british humor how I love you).

There has a lot of heated debate about the F-35 showing how wrong can a combat aircraft development go. But transport aircraft doesn't seem immune to development troubles, too (cough, Belfast, cough, C-5, A400M, C-17).
 

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Another installment on details of the Lockheed L-610 C-X proposal, submitted in January 1981.

As promised, I completed my clean-up of the three-view general arrangement of the L-610 (see the first of the three attached PDFs). Several features of the selected design approach are readily apparent.

First, unlike the AMST requirement to deliver cargo to a semi-prepared austere 2000-foot airfield, the C-X RFP specified an austere 3000-foot airfield. Lockheed did a number of trade studies looking at a range of high-lift systems from the upper-surface blowing (USB) demonstrated by Boeing with the YC-14, to externally blown flaps (EBF) featured on the McDonnell Douglas YC-15, to simple full-span slats and slotted fowler flaps used by the C-5A. Those studies showed that for airfields less than about 2500 feet powered lift, USB or EBF, was required although even then military cargo transports were takeoff limited (acceleration critical) more than landing distance limited (approach speed critical). The C-X 3000-foot field could be achieved with the much simpler slats and slotted fowler flaps.

A bonus stemmed from that high-lift system choice. By avoiding powered lift systems, the takeoff and landing configurations' pitch-trim requirements from the tail and elevator were much reduced. Not having that tail-power requirement allowed Lockheed to size the tail for reduced static stability. That size reduction in-turn saved weight and drag.

The second PDF is the three-view general arrangement of the C-17 as a reminder. Also, since the C-17 stubbornly retained the EBF high-lift system not warranted by the relaxed 3000-foot airfield requirement (but possibly needed by the jet's higher wing loading); take a gander at that huge tail-elevator combination. It's almost a tandem wing configuration, and that's no compliment!

The third PDF is a planform and side-view comparison of the elegant L-610 and the C-17. The aerodynamicists among you can discern the graceful higher aspect-ratio wing of the L-610 and the diminutive empennage surfaces from the move to relaxed static stability. Plus, the wing looks like it is on the fuselage in the right place longitudinally, unlike the distinctively forward-mounted wing of the C-17. I'll have some fuselage cross sections soon, to more clearly show the L-610's slimmer lines.

I just have a few more illustrations I want to finish for a future post showing the cargo box comparisons between the L-610 and the C-17. Then I want to wrap this series up with some comments and speculations on why the aesthetics-challenged C-17 won out. Grudgingly, I think there are some good reasons.
 

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