sunrisevalley
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787 Under Carriage Changes For More TOW

Tue Jul 10, 2012 11:43 pm

The 787 is said to be limited by the present under carriage to a TOW of ~254t. An analysis of the structure by Lissys puts the weight of the present undercarriage at ~8.6t or ~ 3.8% of MTOW. In the absence of such things as ACAP documents we don't know what the pavement loadings are and by inference the tire loadings. I would assume that the existing "hardware" could be strengthened with a modest increase in weight . My question is what is possible with the tires? Presently there appears to be plenty of daylight /space between the main strut and the tire for additional width. I would assume that with a wider cross section tire the present pavement loading could be held but could the tire be redesigned to carry more weight?
Any thoughts?
 
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Stitch
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RE: 787 Under Carriage Changes For More TOW

Wed Jul 11, 2012 1:07 am

GE has been mumbling about raising the thrust of the GEnx1B from 75,000lbs to 78,000lbs for the 787-10, so I wonder if Boeing thinks there is some MTOW growth still left in the undercarriage.
 
CM
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RE: 787 Under Carriage Changes For More TOW

Wed Jul 11, 2012 1:31 am

Quoting sunrisevalley (Thread starter):
I would assume that with a wider cross section tire the present pavement loading could be held but could the tire be redesigned to carry more weight?

The 787-9 gear is already modified relative to the 787-8 in order to reduce pavement loading. It has larger tires on wider spacing, which necessitated raising the pressure deck 9" in the 787-9 in order to accommodate the larger gear into the wheel well. It is very unlikely Boeing made this change without getting every bit of TOW capability from the gear, considering they knew they would be moving straight from the 787-9 into the 787-10. Any added TOW (relative to the 787-9) would likely mean a major redesign of the wheel wells and a very difficult re-integration of the 787's center section. I do not believe Boeing is even remotely considering taking this on.
 
sunrisevalley
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RE: 787 Under Carriage Changes For More TOW

Wed Jul 11, 2012 11:52 pm

Quoting CM (Reply 2):
I do not believe Boeing is even remotely considering taking this on.

Thanks CM. So at this time it is very unlikely that the 787-10 will have any meaningful increase in TOW vis a vis the 789.

Quoting Stitch (Reply 1):
GE has been mumbling about raising the thrust of the GEnx1B from 75,000lbs to 78,000lbs for the 787-10

If the ~251t MTOW is held is there need for more power than about 74k pounds? Basically all that is happening is a swap of fuel for payload. Apparently RR are offering more optional power also. I assume this is via a "plug" if needed,. But the 3% or so lower fuel burn will be attractive.
 
ferpe
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RE: 787 Under Carriage Changes For More TOW

Thu Jul 12, 2012 1:06 pm

Quoting sunrisevalley (Reply 3):
If the ~251t MTOW is held is there need for more power than about 74k pounds? Basically all that is happening is a swap of fuel for payload. Apparently RR are offering more optional power also. I assume this is via a "plug" if needed,. But the 3% or so lower fuel burn will be attractive.

I have been having the same thougths as well, there might be an explanation to some of it: The longer body of the 787-10 will have an effect on the start (and therefore one engine out case which is the dimensioning part for max take-off power), it will increase the wetted are and it will increase the part of the fuselage flying with a high AOA when rotating and up until V2. Thus the drag will increase compared to 789 and that one engine would need to be stronger to maintain the same take-off performance. It might also be that B want to improve that TO performance for the 787-10, my analysis in the wings thread shows the 789 to be pretty weak in this respect even with 74klbf.
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imiakhtar
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RE: 787 Under Carriage Changes For More TOW

Thu Jul 12, 2012 1:36 pm

Quoting sunrisevalley (Reply 3):
Apparently RR are offering more optional power also. I assume this is via a "plug" if needed,. But the 3% or so lower fuel burn will be attractive.

RR was noted as saying at Farnborough that the 787-10 was likely to require around 76k and as such they were readying an engine for 78k.
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