flipdewaf
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Creating the Next VLA

Wed Jul 12, 2017 2:59 pm

I started this thread because myself and Matt6461 were taking the A380 plus thread miles off topic I think. I have put my reply from that thread on here to keep the discussion going and not derail everyone else.



Matt6461 wrote:
I was gonna say, "Odd model," but I see that it's indirectly estimated using fuse H, W, L.

Kind of I guess.
Theory says as it gets bigger it gets heavier (makes sense if you use wet area or not).

Matt6461 wrote:
I'd say the A35K is the only representative example. It's far lighter than 77W for about equal payload/range. The 787/A330 comparison is confounded by comparing an 11hr plane to a 16hr plane (and .82M to .85M).

Good point although my estimator comes out with lower weight than the actual suggesting that CFRP makes things heavier...

Matt6461 wrote:
Every time OEW's have significantly upgraded MTOW, they've had to strengthen fuselage as well.

I'm not sure that's the case, nothing substantial anyway (notwithstanding the A340NG)

Matt6461 wrote:
That 660 pax thing is an important revision.
What I found is that when comparing the empty weights to the OWE numbers the difference between them was modeled very closely by using the max squashed in pax number for the estimation.

I have added all the data to the model but just one area I'm not sure on, the engine weight you mention of 33000lb, is that total? each? if each how many (looks like two big ones?)

Matt6461 wrote:
And much thanks for taking the time on this. If you're ever in Chicago I owe you a beer.
No Probs, Im sat in the office trying to work out how to best build a model for waste treatment systems at the same time. My company does have some sites near chicago so if I'm ever around I'll shout you out.

Fred
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SCAT15F
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Re: Creating the Next VLA

Wed Jul 12, 2017 10:33 pm

BWB or HWB twin open rotor or triple ultra-fan.

Turbofan BPR's are getting so large that cowl drag and sheer size/weight could potentially make one 100k lbs thrust engine less efficient than 2 45-50k engines.

Turbofans are trying so hard to be open rotor... NASA research through the ATP program proved that open rotor will maintain an efficiency advantage over any turbofan at speeds up to mach .9. 'Nuff said.
 
speedbird52
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Re: Creating the Next VLA

Thu Jul 13, 2017 5:47 am

I don't think there ever will be another VLA.
"I have control" Three Words That Could Have Saved Lives.
 
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Matt6461
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Re: Creating the Next VLA

Thu Jul 13, 2017 9:44 am

Good idea to break off the thread.

flipdewaf wrote:
I have added all the data to the model but just one area I'm not sure on, the engine weight you mention of 33000lb, is that total? each? if each how many (looks like two big ones?)


That's total. Two engines, ~90k thrust, 5.5lb/lb-T.
 
flipdewaf
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Re: Creating the Next VLA

Thu Jul 13, 2017 1:10 pm

Matt6461 wrote:
Good idea to break off the thread.

flipdewaf wrote:
I have added all the data to the model but just one area I'm not sure on, the engine weight you mention of 33000lb, is that total? each? if each how many (looks like two big ones?)


That's total. Two engines, ~90k thrust, 5.5lb/lb-T.

Some basic Data
MZFW - 280t
MTOW - 381.8t
OWE - 202.9t

1 engine drag at 92ms^-1 (180kts) at 0 ft ISA conditions is ~122klb thrust. (with gear) 110klb without (my aero section is still a WIP which I think over eggs the lift independent drag somewhat but gives a figure of 36klb required for A321 @80ms^-1 (160kts) so seems in the right ballpark.

If I beef up the engines required to 130klb for the required performance and adjusted the engine dimensions by the same factor over 90klb.

OWE goes up to 207t and the drag rises a little bit but MTOW didn't change so the only drag increase in really from the nacelle wetted area.

Fred
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Matt6461
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Re: Creating the Next VLA

Thu Jul 13, 2017 2:43 pm

I didn't realize you're working a drag model as well. What was the result of the fuselage model with the additional info?
 
flipdewaf
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Re: Creating the Next VLA

Thu Jul 13, 2017 3:14 pm

Matt6461 wrote:
I didn't realize you're working a drag model as well. What was the result of the fuselage model with the additional info?

37t, it seems a much lower root chord pushes you further into the bending dominated regime than the A380 and so the difference isn't all that great (still about 1.5t)

the drag model is still very much a work in progress but seems to give reasonable numbers. Using some basic VBA I can get it to run through a multitude of weights and speeds and will give me the best height and Speed to give me a maximum UL/D for any weight I choose. The heights seem a bit high at the moment and it doesn't seem to matter what I choose it seems to want to make everything fly at 236ms^-1.

Fred
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flipdewaf
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Re: Creating the Next VLA

Thu Jul 13, 2017 3:20 pm

Just modeled it with a big wing 700m^2 (7530sqft) and the weight went up to 210t and the drag at 92MS^-1 reduced to 92klb...

Fred
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Matt6461
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Re: Creating the Next VLA

Thu Jul 13, 2017 4:17 pm

flipdewaf wrote:
Just modeled it with a big wing 700m^2 (7530sqft) and the weight went up to 210t and the drag at 92MS^-1 reduced to 92klb...

Fred


What span for the big wing?

I'm assuming 210t is OEW?

So your model says A380's fuse weighs 38.5t? Does that seem a bit low?
 
flipdewaf
Topic Author
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Re: Creating the Next VLA

Thu Jul 13, 2017 7:51 pm

Matt6461 wrote:
What span for the big wing?

79.8m
Matt6461 wrote:
I'm assuming 210t is OEW?

yup
Matt6461 wrote:
So your model says A380's fuse weighs 38.5t?
it was either high 38s or low 39s and your dimensions gave just under 37.5 I think ( computer is in the bag and I'm on tablet trying not to get muddled with my chemical oxygen demand figures in my head from another model.
Matt6461 wrote:
Does that seem a bit low?
not really, I believe the A321 was about 10.5 so feels right. It's the wings that add the beef on these big birds, like 80t for the A380, add 4 engines at 9t wet and your well on your way to 200t+ owe.

Fred
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