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H.S.C.T. Weight Question  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (7 years 5 months 2 weeks 3 days 20 hours ago) and read 1673 times:

The Concorde-B didn't weigh much more than the regular Concorde, but with the modified engines it could fly at the same speeds over like 5,000 nm. Why was the HSCT to weigh as much as 738,000 lbs, it's range isn't really all tha much different than the Concorde-B: especially considering the HSCT didn't need a droopable nose and the extra fuel to carry the added weight?

Even the old 1960 SST designs such as Lockheed's L-2000-7A, with drooping noses and continuous afterburning for cruise still managed to weigh in at 540,000 to 590,000 lbs. The B-2707-300 with a tailplane, droops, and flaps weighed in at 635,000 lbs with virtually the same capacity. The HSCT however, without the need of a drooping nose and the extra fuel to carry it, the absense of afterburners, a lower, more efficient cruise-speed an improved L/D-ratio, composites and SPF/DF-Bonding should even with it's increased passenger capacity over the B-2707-300 theoretically weigh a lot less than 738,000 lbs.

Why was the NASA/McDonnell Douglas/Boeing HSCT design so heavy?

Andrea Kent

[Edited 2007-05-07 06:01:19]

6 replies: All unread, jump to last
 
User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 1, posted (7 years 5 months 2 weeks 3 days 19 hours ago) and read 1662 times:

Quoting Blackbird (Thread starter):
The Concorde-B didn't weigh much more than the regular Concorde, but with the modified engines it could fly at the same speeds over like 5,000 nm.

All range numbers I've seen for Concorde B are much more modest, in the vicinity of 4,500 statue miles, which is significantly less than the HSCT's goal of 5,000 nautical miles. Like the production Concorde, Concorde B would have cruised at or below Mach 2.04, while the HSCT was aiming for Mach 2.4. Many of the improvements that were proposed for Concorde B ended up on the "A" models, such as thinned intake lips and extended control surface trailing edges, so some of the range improvements that were envisioned for B were actually realized.

The HSCT's payload was three times greater than even Concorde B's and would have obviously required a bigger and stronger structure. There would probably be little improvement on the propulsion front; if anything, a higher bypass ratio will result in an SFC penalty at supersonic speeds vs. the straight turbojet. Turbofan engines and complex variable geometry silencing systems are much heavier than the Olympus. All these factors would reverse part of the weight savings attributable to new materials.

Quoting Blackbird (Thread starter):
Even the old 1960 SST designs such as Lockheed's L-2000-7A, with drooping noses and continuous afterburning for cruise still managed to weigh in at 540,000 to 590,000 lbs.

The L-2000-7 had a lower payload and less range than envisioned for the HSCT. Given Boeing's experience with the B2707, I would guess that Lockheed's MTOW estimate for the L-2000 also would have proven optimistic in reality.

Quoting Blackbird (Thread starter):
The B-2707-300 with a tailplane, droops, and flaps weighed in at 635,000 lbs with virtually the same capacity.

This figure is for the prototype, which would have been a lighter aircraft with had much lower payload capacity than the production article. In late 1968, by the time the -300 was formally submitted to the FAA, the production model was at 750,000 lbs. MTOW and could carry a 49,000 lb. payload over 3,610 nm on an ISA day. By early 1971, Boeing and GE admitted that the GE4 could not meet sideline noise requirements in its present state. A mass flow increase from 650 lb/sec to 815 lb/sec would have been needed to achieve sideline targets. This would have taken the -300's gross takeoff weight up by another 40-50,000 lbs. to preserve range. (By this point, the afterburner had been deleted from the production GE4.)

This is all rather ironic, given that Boeing thought the structural factors that plagued the variable-sweep wing could have been fixed had the FAA allowed the 2707-200's takeoff weight to rise from the contractually stipulated 675,000 lbs. to around 750,000 lbs. The FAA refused and Boeing could not get the weight down without unacceptable compromises in payload and range. Therefore, Boeing had to perform radical surgery and scrapped the swing wing in favor of the double-delta. This was designed to preserve the swing wing's climb performance in order to meet the increasingly important low-speed noise requirements. The result was a very large and modestly swept outer delta that proved far less efficient throughout the speed range. Despite a decrease in both range and payload, the -300 ended up at 750,000 lbs. anyway and was going higher by the time the plug was pulled.


I think the primary answer is that designers in the 1960s were simply too optimistic in their gross weight estimates. Concorde started out in the 320,000 lb. range and ended up at 408,000 lbs. with comparatively small gains in mission payload and range versus the original spec. The deterioration of the 2707's payload-to-weight ratio over time is painfully clear. With more knowledge about the structural challenges of complex wing planforms and long, thin fuselages and better tools at their disposal, designers today are probably a lot more realistic in their modeling.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 2, posted (7 years 5 months 2 weeks 3 days 9 hours ago) and read 1625 times:

From what I remember the -200 went up to 750,000 lbs and go the plug pulled. Boeing then went to a double-delta with a tailed-design. The -300 was smaller featuring a tailed double-delta and was lighter to the best of my knowledge.

It may not have weighed 635,000 lbs, but it sounds unlikely that it would have weighed 750,000 lbs. And even then, we have composites and SPF/DB, and all sorts of ways of lightening weight. Especially if the design didn't have an afterburner, and was slower than BOEING's design which (2707-300) was capable of Mach 2.7, the HSCT can do Mach 2.4, which requires less fuel-burn and was the most efficient speed chosen.

Andrea Kent


User currently offlineB2707SST From United States of America, joined Apr 2003, 1369 posts, RR: 59
Reply 3, posted (7 years 5 months 2 weeks 2 days 22 hours ago) and read 1580 times:

Quoting Blackbird (Reply 2):
The -300 was smaller featuring a tailed double-delta and was lighter to the best of my knowledge. It may not have weighed 635,000 lbs, but it sounds unlikely that it would have weighed 750,000 lbs

This apparently was the intention, but the production -300 quickly reached 750,000 lbs. by October 1968, less than six months after Boeing abandoned the -200 (Aviation Week & Space Technology, Oct. 28, 1968). The -300 prototype MTOW was set at 635,000 lbs. The Dec. 9, 1968 issue of Aviation Week & Space Technology has a relatively detailed and very interesting piece on the -300 including the following chart:

Big version: Width: 477 Height: 771 File size: 134kb


Among other developements, reference mission payload fell from 280 pax on the 2707-100 (detailed specs on the -200 are hard to find, due to its short life and constant state of flux) to 234 pax on the -300, reference mission range fell from 3,819 nm to 3,610 nm, supersonic L/D fell from 8.5 to 7.1, subsonic L/D fell from 15.5 to 13.8, and OEW fell "50-60,000 lbs." to 290,000 lbs. Takeoff field length increased by almost a mile, from 6,300 feet to 10,800 feet. Landing field length increased from 6,300 feet to 7,800 feet. Wing sweep decreased from 72 degrees to 50.5 degrees.


AW&ST's March 15, 1971 issue details the further 40-50,000 lb. weight gain due to the required GE4 airflow growth. This is unambiguously in addition to the production model's 750,000 lb. MTOW.

Quoting Blackbird (Reply 2):
It may not have weighed 635,000 lbs, but it sounds unlikely that it would have weighed 750,000 lbs. And even then, we have composites and SPF/DB, and all sorts of ways of lightening weight.

But as I said above, how much of that extra weight do you have to add back to support heavier engines, heavier silencers, a larger payload, more fuel (SFC will not fall all that much), and a larger airframe to carry it all? Based on where the -300 was at cancellation, I would be quite impressed with an HSCT that could carry a true 300-pax payload (not 250) over 5,000 nm (not 3,600 nm) under Stage 3 or 4 standards (not in flagrant violation of every modern noise rule) with a MTOW of 740,000 lbs. Unfortunately, even this seems beyond the current state of the art.

--B2707SST



Keynes is dead and we are living in his long run.
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 4, posted (7 years 5 months 1 week 2 days 21 hours ago) and read 1505 times:

Quoting Blackbird (Thread starter):
The Concorde-B didn't weigh much more than the regular Concorde, but with the modified engines it could fly at the same speeds over like 5,000 nm. Why was the HSCT to weigh as much as 738,000 lbs, it's range isn't really all tha much different than the Concorde-B: especially considering the HSCT didn't need a droopable nose and the extra fuel to carry the added weight?

Range isn't a function of overall mass. It is primarily a function of the ratio of fuel mass to total mass and the specific fuel consumption. Heavier planes need more thrust to get them going, hence they use more fuel, hence more fuel is carried. They don't somehow go farther unless they're using the same engines as a lighter plane, but they may not make it off the ground by then.

This may help:http://pr.erau.edu/~gallyt/ae302/Performance-Part5.pdf
Quoting Blackbird (Thread starter):
Why was the NASA/McDonnell Douglas/Boeing HSCT design so heavy?

Because compared to Concorde, they were giant, in the 280-330 foot length category. As I mentioned with the square-cube approximation, if Concorde were scaled up 50% longer, the wing area would approach the est. 7500ft.sq. wing of HCST and the weight would approach a million pounds. But SST's designs (thesedays atleast) are intended to use a predominately composite structure as oppsed to Concorde's aluminum, which shaves off about 200,000 lbs.

More than likely, if a modern effort was to develop an SST, they may be forced to follow the arbitrary 80x80 meter box. Size would bring down the weight considerably, however, so would the other specs like capacity and range -- generally...  

[Edited 2007-05-15 05:30:33]


The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 5 months 1 week 2 days 6 hours ago) and read 1478 times:

If I recall, you could park an HSCT type plane at an angle, which would keep it in the 80 x 80 meter box

Andrea


User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 6, posted (7 years 5 months 1 week 2 days 3 hours ago) and read 1469 times:

Quoting Blackbird (Reply 5):
If I recall, you could park an HSCT type plane at an angle, which would keep it in the 80 x 80 meter box

Yes, at a 45-degree angle of the 80m box would be a 113-meter diagonal; and as much as people think taxiing would be a problem, only during turns, span is usually between 1/2 and 1/3 the length. Most planes have a huge distance from the main undercarriage to the tail (when I say tail I mean tail cone of the fuselage), HSCT type have just as much from the nose to the nose gear. A camera system would be useful and likely installed.

I wonder how Concorde pilots were trained for the 40 or so foot distance from the nosewheel to the pilots cabin...

Still, even at 80 meters of length and fuselage width of say 4 meters (6 seat abreast at 18 inch with 20inch aisle), 300 pax is possible at 36inch pitch.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
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