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Boeing Vs. Airbus Wing Design Philosophies  
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Posted (2 years 5 months 1 week 23 hours ago) and read 28688 times:

In the A350 prototype thread no 1 post 236:

A350 Prototypes Production Thread Part 1 (by ferpe Oct 26 2011 in Civil Aviation)

I compared the A350 wing with the 787. They have many similarities and smaller differences but one difference that seemed large was the wingloading, Airbus going for a larger wing with more wetted area and Boeing preferring a smaller wing with lower weight and accepting a higher wingloading    .


I then decided I ultimately wanted to understand the consequences of it all. As only the 787-8 and not the 350 was available as PianoX model (excellent preliminary design tool with a free of charge demo copy here www.lissys.demon.co.uk/PianoX.html ) I started to implement a simple model my-selves.

Reading the Piano manual before was of great value and I have continuously been able to verify my results with the PianoX 788, 767 and 346 models that are provided for free (using the Output : Detailed flight profile and Point performance ), a big thanks to Dimitri Simos for making this really well designed tool available to us enthusiasts    and for having the complete Piano 5 guide on the web.


Dimitri also helped me to solve the biggest problem I had, things just did not jive even though I had implemented everything that made sense from http://adg.stanford.edu/aa241/AircraftDesign.html , the Aircraft design course written by R Shevell of Douglas fame.


   This part of the Piano manual is more true then one thinks:

http://www.lissys.demon.co.uk/pug/c03.html#s05


  ..........................WE ARE COMPARING APPLES AND ORANGES.............................  


The wingareas we are throwing around do not have the same definition, the one for 788 (325m2) is Trapezoidal, the 443m2 for the A350 is Airbus and even PianoX mixes definitions e.g. using Boeing Wimpress for the 767, Airbus for 346 and Trapezodial for 788    . Here the definition of the areas (from the Piano 5 guide):



And here how they pan out for some of the types we discuss all the time (I now measure them   Sad

m2............................................Trapezoidal.......Airbus........Boeing/Wimpress........Exposed
787-8, 9, 10.....................................325..............370...................360......................301
A350-8, 9, 10...................................400..............443..............................................362
777-200--300ER...............................428..............454..............................................372
767............................................................................................283...........................
330....................................................................362...................................................


Here the wingloadings (MTOW/Wingarea) I skipped Wimpress as I only have one value and it is more complicated to measure. Haven't measured the ACAP drawings of the 330 and 767 yet:

m2............................................Trapezoidal.......Airbus.........Exposed
787-8..............................................701..............616...............757
787-9..............................................772..............678...............833
350-8..............................................648..............585...............715
350-9..............................................670..............605...............740
350-10............................................745..............673...............819
777-300ER......................................821..............774...............945
777-8X............................................682..............630...............784
777-9X............................................731..............689...............840
330....................................................................649


So if we take e.g. the Airbus column (might be practical as Airbus publicizes these values, IIRC Boeing does not) we can see that the 788 and 359 as the two new main models have similar wingloadings!!!    .

And the next bigger models using the same wing (787-9 vs 350-10, (35J has a 4% larger wing but the reference area stays the same) has the same wingloading as well    , so all this talk about differences in their wing design philosophies re wingloading is    .


This conclusion came when I already had my model working and tracking PianoX within a couple of % so I am happy anyway because I now have a tool to check a lot of things, but more of that in another post    .

[Edited 2012-04-16 13:59:26]


Non French in France
81 replies: All unread, showing first 25:
 
User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 1, posted (2 years 5 months 6 days 22 hours ago) and read 28425 times:
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A very interesting subject.
IMO, difficult to differentiate between the twp designs in clean conditions. They are both high-aspect ratio with variable -geometry camber, high aeroelasticity wings.
The big difference is - and has always been - in the low speed, wing high lift devices :
- the Airbus uninterrupted trailing edge flaps generates more lift and less drag than the separated inner / outerr flaps plus an engine gate, high and low speed ailerons (the aspect ration of the uninterrupted flap configutration is a lot higher ).
-On the other hand, Boeing's leading edge device configuration seems to bez able to generate more lift...
So where is the comparison, I'm curious.
I personally don't have any info on the complexity of the mechanical designs.



Contrail designer
User currently offlinedlednicer From United States of America, joined May 2005, 544 posts, RR: 6
Reply 2, posted (2 years 5 months 6 days 19 hours ago) and read 28359 times:
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DATABASE EDITOR

Quoting Pihero (Reply 1):
I personally don't have any info on the complexity of the mechanical designs.

You might be interested in these documents:
High-Lift Systems on Commercial Subsonic Airliners
Mechanical Design of High Lift Systems for High Aspect Ratio Swept Wings

Quoting ferpe (Thread starter):
using Boeing Wimpress for the 767

Funny enough, a couple of years ago I mentioned to Jack Wimpress (the guy its named after) that Boeing uses the "Wimpress area" to define the area of wing planforms and he expressed surprise - he wasn't aware that there was any such thing.


User currently offlinemandala499 From Indonesia, joined Aug 2001, 6869 posts, RR: 75
Reply 3, posted (2 years 5 months 6 days 14 hours ago) and read 28272 times:

Ferpe,
Fascinating ! And we haven't gone into the Krueger vs Slats and VGs vs clean wing debate which would explain:

Quoting Pihero (Reply 1):
The big difference is - and has always been - in the low speed, wing high lift devices :
- the Airbus uninterrupted trailing edge flaps generates more lift and less drag than the separated inner / outerr flaps plus an engine gate, high and low speed ailerons (the aspect ration of the uninterrupted flap configutration is a lot higher ).
-On the other hand, Boeing's leading edge device configuration seems to bez able to generate more lift...

  

Now, are patents driving these choices?

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 4, posted (2 years 5 months 6 days 7 hours ago) and read 28166 times:

Quoting dlednicer (Reply 2):
Funny enough, a couple of years ago I mentioned to Jack Wimpress (the guy its named after) that Boeing uses the "Wimpress area" to define the area of wing planforms and he expressed surprise

Before we dig into the differences can anyone (OldAeroboy?) explain why Boeing uses such a intricate scheme to define a reference area, it kind of factors down the body covered area of the Yehudi (why) and not the wing proper (why not if the if you factor the yehudi?)



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 5, posted (2 years 5 months 3 days 15 hours ago) and read 27790 times:

The mystery Wimpress seems to stay with us for a while, then we can cut into the meatier stuff  Wow! . To start things right of the bat I have copied a region of the little excel model I have fiddled with the last month or so after this B vs A apples-oranges wing mystery triggered me  :



What we see here is a snapshot of a spec range flight with the "maxPaxnoCargo 3" class load. The fuel is burned to Cl 0.5 for the 788 (83% which is about average fuel load for the spec mission for these frames which are close to 50% OEW/MTOW) and then all the rest of the frames are compared at this average fuel load. I have only included the FL where Cl is 0.5 for a 83% load (350), the other FL shows the same picture at the Cl 0.5 weights. Cl 0.5 is a typical design point for this class of frames.

Our figure of merit is as before L/D (yellow) and we can see that the new wing for the 777X is the class leader (based on the little data we have, span and 10% larger wingarea then 77W) and that the 350 comes next closely followed by the 788 and jumbo is 77W as is should be (this is clearly not the FL for the 77W, it is at Cl 0.6 and clearly close to buffeting, the 77W should be at FL 330 or even 310 but I kept it here for comparison. I have not added compressibility drag accordingly, to make sense of the 77W range vs model range I had to add some 10 promille comp. drag (compared to below 5 for the rest) which seems to about the design point for the 77W wing). Total drag is highlighted in lbf and the lift = weight (kg) at FL350.

As can be seen the 99% Breguet prediction is pretty close (I have adjusted the climb and reserve fuels to closer to actual then Shevells proposed values) so the model seems to work  . Here we can see that Albaugs statement of 8000nm design point for 777X is sandbagging   , seems to be good for 8500nm  .

So given that all the data is there for the clean wings lets now speculate why this is so (and what are the culprits of my model as per Shevell in the OP)  .

[Edited 2012-04-20 21:55:32]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 6, posted (2 years 5 months 3 days 15 hours ago) and read 27759 times:

Just to avoid confusion, the 777-8XL is not the XL, it is the X, the normal -1000N competitor which I took the 65m wing for so they are in the same gate class, the predicted OEWs for the 777X does not come into play other then in the range prediction, not in the L/D. Those can seem high but are realistic, the new engines + wing will come in at about the same as 77W (10% more area and heavier engines due to higher PR) and the fuselage will add length which negates the 5% gain Al-Li parts will give (there other weights like MLW, MZFW is just put there and not very realistic, they don't influence the model, e.g. the 8X MZFW should be higher and so on, I will clean this up ).

The aspect ratio does include the effect of RWT (85% of physical length included in the AR) and winglets (45%) as per the other thread here at Tech/Ops.

[Edited 2012-04-20 23:07:17]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 7, posted (2 years 5 months 2 days 22 hours ago) and read 27531 times:

I guess it is not so easy to start commenting on some calculations I have made when you only see a lot of results and have no idea what is behind them. As I had a lot of fun developing the model (very gradually I might say   ) here a little how to and some tips for those who want to have a go for themselves:


- the Shevell course is very good but his notation in the formulas can be a bit cryptic, I found that looking up the same thing in Wikipedia e.g for Induced drag helped a lot. Toorenbeek is a bit much to read for what it gives but it can give some good rule of thumb values for e.g. wing load distribution factor in landing config (0.7).


- One only needs to implement a model for drag really, as cruise lift = weight so once you have drag your have L/D, add TSFC to that and you have the Shevell range formula which is Breguet. Breguet works fine if one is careful with the inputs, the rule of thumb weights he proposes are surprsingly usefull, I got better reserve values from my payload-range chart exercises (where Zeke gave me some tips) but there is less then 5% difference.


- TSFC is tricky though as the engine guys don't like to give it out. PianoX is very good here as Simos knows TSFC in and out (his first Piano was made for RR Derby to model their engines flight behavior). TSFC varies with altitude more then the drag below 36000 feet after which the temp remains constant and TSFC calms down. Therefore using the right average TSFC is important in the Breguet equation. Use PianoX in Point performance mode (with weight to give same thrust for different altitudes) to get a table like this:

..................................788...........767
Cruise TSFC FL390...0,5304.....0,5918
Cruise TSFC FL370...0,5320.....0,5905
Cruise TSFC FL350...0,5375.....0,5977
Cruise TSFC FL330...0,5472.....0,6122
Cruise TSFC FL310...0,5581,,,,,0,6253

Other engines behave similarly e.g. I have reduced these values with 2% to get the 350 table and with 4% to get the 777X table (RR say you gain 1% TSFC per year in engine development typically).


- Once one have the Cl for e.g. the 77W one sees that it has to start it's cruise at FL310 vs 350 for e.g. the 788 or 350, therefore one needs to take a lower average TSFC for 77W, this is more important then the diff in drag or L/D for FL 330-350.


- Tip re Excel, use named cells and areas all the time, it makes things much easier, here the Breguet formula in this way:

=0,99*(Cruise_speed_TAS_kt/Cruise_TSFC_FL370)*L_D_cruise_370*LN(Wi_spec_range/Wf_spec_range)

This is the formula in each cell for the range rown with the typical frame data in the colums. If all the values are in the column with these labels to the left excel will automatically pick the right values. Constants like density for FL370 I have in named cells. The ,99 is for the inefficiency of the step cruise climb.

- some of the parasitic drag stuff one can short-cut in the first go, control surface and nacelle base drag is negligible (nacelle drag not), for the upsweep drag I have measured 0,0006 on the 350 and use that until further for all frames. The nacelles have the same typical length as the wings MAC and about 10% of the area so I just added this to the wing parasitic drag calculation. (4 holers need double dose of course  )

- for induced drag I use 0.9 for the span efficiency factor, it is a good starting point.

- I have put compressibility drag at 0.0005 for all frames except those with very high wingloading (77L, 77W) where I have it at around 0.0010

Much more to say but later... 

[Edited 2012-04-21 15:30:53]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 8, posted (2 years 4 months 3 weeks 6 days 11 hours ago) and read 27046 times:

So later was quite a bit later    .

Based on initial results I have expanded the model in several areas. I expected to find that frame efficiency improved with increasing FL to an optimum where also L/D was highest and then tapered of. I found the aerodynamic optimum to be rather weak and that the true reason for frames seeking highest possible FL is a mix of aero and engine TSFC reasons. So I modeled in TSFC variantion as well and seeked a better figure of merit then just L/D. Breguet theory sais I can pick the range factor/constant (speed/TSFC * L/D) but even more meaningful is Specific Air Range (SAR) i.e. the Range factor divided by the cruise weight. This gives the nm covered per kg fuel burned at that FL which is a more interesting number then Range factor.

As can be seen from the improved model the optimum FL based on SAR differs from best L/D (all at average cruise weight of 83% of MTOW) for e.g. 788, 358, 359, 777-8X, 332 and 333:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Aircraftrangemodel788-330.jpg


So based on this model lets focus first of finishing the analysis/discussion of the B vs. A wings in cruise condition (easiest), then go to landing and finally to the most difficult, the start (at least I find it so  ). I will refrain from how the numbers are calculated here and rather make a "DIY Frame analysis tool" thread otherwise I wander of into "amateur analyst wonderland" and we never come to the differences  .

As can be seen the new generation of high aspect ratio CFRP wings creates the basis for efficient frames (777-8X vs 77W for instance, starts at FL 350 instead of 310 (line 106 states initial and mid cruise FL, initial cruise is best SAR at 97% weight with Cl below 0.55), cruises at FL390 instead of 350 at mid cruise weight and there covers 0,075 nm/kg fuel instead of 0,062 ).

Also look at the 358 vs 789, they haul 270 vs. 280 Pax but the 358 who has a shorter fuselage with a lower wetted area (line 34) has the same SAR as the 789 despite 2% more efficient engines. Clearly the wing is a bit to large for this frame which can also be seen that the Dp is clearly higher the Di (line 127, 128) whereas the 789 has them close together (theoretical frame optimum is when they are equal but that is when one assumes constant TSFC. At FL370 and over TSFC is almost constant and there this rule applies).

One can also see that the 350-1000 wing is a bit stretched, initial cruise lands at FL330 (SAR 0.075) for MTOW flights which is below the more SAR optimal 350-370 FL. So with a clean sheet design the 350-1000 would probably have increased span or larger winglets in addition to it's 4% TE extension (primarily serving Landing and TO performance).

So what is the differences in the cruise wings between A and B? I would say smaller then within their own ranges i.e. 787, 350 and 777, in cruise config the 787 and 350 generation wings are pretty similar at least at this analysis depth (non CFD preliminary sizing theory), next level would involve supercritical wing design knowledge and I don't think the framers let us in on that  Wow! .

But there is a surprising level of behind the scenes things one can reveal with this simple model when trying to fit the model range with the OEM spec range, there one sees for instance that A counts on the 350 having a rather smooth surface whereas B has learned that the 787 really is not that major improvement  Wow! (or I have the OEW or TSFCs a bit wrong  Wow!  ) .

On a more general sense a good first analysis of a wing/frame combo is checking the wingload and spanload (MTOW/effective span, I will add it to my table). They give a good hint on initial and subsequent cruise FLs in order to get those touchy engines to breathe their preferred species of air  Wow!   .

[Edited 2012-04-27 03:09:39]


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User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 9, posted (2 years 4 months 3 weeks 5 days 7 hours ago) and read 26741 times:

Anyone in the know who can comment on the method I have used to compare the frames and their wings? Rather straight forward or?


Non French in France
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 10, posted (2 years 4 months 3 weeks 4 days 18 hours ago) and read 26601 times:

Hi Ferpe. I'm just dropping you a note to encourage you to keep adding to this thread. I know it seems like you are talking to yourself, but I (and I am sure others) am finding the topic really interesting; I just haven't hand anything of value to contribute... yet.

User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 11, posted (2 years 4 months 3 weeks 4 days 12 hours ago) and read 26529 times:

Thanks CM    . I could see that there where readers of the thread but not sure if it was of value to anyone, so feel motivated to take it to the meaty bits (after finishing of the cruise part below )   .


As Pihero so rightly stated:

"IMO, difficult to differentiate between the twp designs in clean conditions. They are both high-aspect ratio with variable -geometry camber, high aeroelasticity wings.
The big difference is - and has always been - in the low speed, wing high lift devices : "

we can see just that, it seems the wings are pretty similar in clean wing conditions:


SURPRISED
This is not quite what I expected when I started building the tool but the wingaera discovery kind of gave a hunch they could be more similar then thought and the deeper poking with the excel seems to confirm that. I was pretty sure the drag and L/D values would give some clear insights into e.g. the somewhat large size of the 358 wing and I expected that to be contrasted with a bit to small 789 wing. Both things were confirmed, the 358 has more parasitic drag then induced drag at optimum cruise level and the 789 has these at the theoretical optimum (see graph) but the wingloading causes it to start the cruise at the less then optimal FL330, something it shares with it's stretch cousin, the 350-1000.

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Totaldragcurve.jpg



THEORETICAL OPTIMAL FL
Classical theory, which does not cater for transonic effects, says you can increase the lift until optimal Cl (given in Roskam as an optimal seeking L/D formula) which is somewhere around 0.65 or even more and thus a wing with smallest possible wing area and broadest span is the best choice for cruise. But that is ignoring transonic effects, a smaller wingarea forces a larger pressure differential and the ensuing lower pressure on the wing overside means higher local air speed = more supersonic area = compressive drag rises fast. PianoX seems to stay away from that by the rule of keeping the Cl below 0.55 and I have adopted his hint  being pretty blind when it comes to transonic effects.



BREGUET RANGE
One thing that has really surprised me was the power of the range calculation. I have learned that the Breguet range equation was kind of the "cheaty" way of calculating range (assuming all things constant except fuel=weight burn of) however it seems even Piano uses it but in a more clever way. As Shevell, Roskam etc states, if things do not remain constant (TSFC, TAS as a function of M below 36kft ) or you are forced to fly at constant FL (Breguet assumes you can always slowly cruise climb to keep Cl and therefore L/D constant) you just hack the flight into many Breguets each having it's new set of constant values and its start and stop weights. Hack it fine enough and you come close to reality, IMO this is what Piano does. I use the excel to find the average flight values instead and does only one Breguet with these, seems to be good enough to see what is interesting, the frames that fall out of the raster    .



RASTER FALLING   
This is a signal to try and understand what is not plain vanilla with the frame. Can be wrong assumptions on OEW (=how much fuel to burn) or TSFC (wrong MPG) but can also mean the framer assumes a very good roughness constant (350?) i.e. smooth skin due to e.g. CFRP construction. The 788 lost some 500nm between first ACAP and flight tests, 300 of those one can see came from weight but 200nm come from something else. The model suggest a parasitic drag increase. Now why wouldn't it be faulty TSFC or OEW?

TSFC
All 787 use the same engines so if I have the TSFC to low all should be better in range then the model, they are not, the 789 and 7810 are under. But the 789 and 7810 have laminar flow tails so I allocated a 30% friction drag reduction on the laminar flow tails and that seemed to be somewhere right, it made all the 787s fit the range model with std roughness factor. Given that 787 have two more air condition inlets I then reasoned; all in all they probably are comparable in the roughness factor to say the 777 as this factor includes all effects of skin roughness, intakes,outlets etc and intakes/outlets are draggy items and before things like frames etc are cocured that skin is only marginally saved from fasteners/rivets. The 787 range seem to fit the model with std roughness (which is probably a bit worse then B though 2005) and a 30% improvement of friction factor for the 789, 7810 VTP, HTP.

OEW
The latest ACAP OEW was 111.5t for a 224 seat 788, I compare with 250 seats as there is an official range figure there (7650nm). Add the 1.5t for the seat diff and we have 113t official OEW. Until there is more plausible evidence I can't place this figure and the model seems to support that, first at my 116t the range fits. If I put in the 113t we see 8000nm    something B would love to have seen in the NAMS testing   .


  
So range fitting gives good food for though and signals one to go hunting for reasons, perhaps one finds something    .



LANDING CASE   
After much ado on to the landing case. I am not on top what requirements the final approach has, kind of heard below 150kt but what other criteria would there be?

[Edited 2012-04-29 00:47:18]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 12, posted (2 years 4 months 3 weeks 3 days 9 hours ago) and read 26290 times:

The textbooks covers landing distance etc (here the Shevell course http://adg.stanford.edu/aa241/AircraftDesign.html ) but I will not venture into that, it is to complicated and beyond the scope of this thread, I will only look at the approach speed and what lift coefficient the wings would have to produce to fly these approach speeds safely.

According to the Schevell course FAR 25.125. states:

(2) A stabilized approach, with a calibrated airspeed of not less than
1.3 VS, must be maintained down to the 50 foot height.


So given that I have read that A and B wanted the 350-1000 and 77W to have an approach speed lower then 150kt I will use 150/1.33 = 113kt as the dimensioning speed for the landing case. At the MLW the discussed wings then need to produce the Cl in the table:



I have not included the drag data as this is only available with any accuracy via wind tunnel test even today according to the textbooks and A and B. Further, drag (as far as I know) is not necessarily avoided in landing config, you want a rather draggy config to have reasonable power on so that your power reduction at flare creates a positive deceleration and defined touchdown. Also having the engines at higher revs is desirable for the go around case, the time to TOGA config will be reduced. Once you go to that TOGA config (which should be similar to start config) you are interested in good L/D again and therefore low drag as margin for the engine out case, more on that in the start post.

Given the lower interest for maximum L/D the drawback of the B principle with a flaperon between the inboard and outboard flaps will be less critical, it will affect the spanload diagram somewhat and hence agument the induced drag but not on a scale where it will be a problem IMO. The start case is touchier as will be seen.


The required Vstall lift coefficients allow the modern wings to use simpler drooped hing flap mechanisms as discussed in the A350 thread, the highest Cl is for the 789/7810 to produce at 2.60. We know from Dynamicsguy that requires higher deployment angels and therefore reinforced flaps but the simple drooped principle is still OK.

The 77W need more Cl and did not have the advantage of spoilers that could droop and control the flap-wing slot, therefore a complexer Fowler arrangement was needed. One can also see that the -8X and -9X could live with drooped flaps for landing, it might be another discussion for the start engine out case given the rather low TOpower/MTOW ratio   for those frames.

[Edited 2012-04-30 04:29:03]


Non French in France
User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 13, posted (2 years 4 months 3 weeks 3 days 8 hours ago) and read 26267 times:
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Hello, Ferpe !
Fascinating study and thanks for putting so much time into it.
A few remarks, though :
1/- The basis for Airbus performance speeds is the Vs1g for all FBW airplanes. The concept is being taken slowly by Boeing into consideration, but AFAIK, the FAR 1.3 Vs is still current

2/6 The values of Clapp - don't think of anything but the lift coeff in approach (!!!) seem awfully high, especially for the 777 for which we have the data from the NASA study we've referred to already and which stands at Clapp = 1.5.
I do not believe one second that, considering the less than optimum solution (exhaust gate and mutiple ailerons), modern airplanes haven't improved on that.
I would admit, though to that value for a clean config at opt AoA.

I buy the champ if wrong.

Cheers !



Contrail designer
User currently offlineferpe From France, joined Nov 2010, 2804 posts, RR: 59
Reply 14, posted (2 years 4 months 3 weeks 3 days 5 hours ago) and read 26197 times:

Quoting Pihero (Reply 13):
The values of Clapp - don't think of anything but the lift coeff in approach (!!!) seem awfully high, especially for the 777 for which we have the data from the NASA study we've referred to already and which stands at Clapp = 1.5.

2) You were right, what I had in the table wrongly labeled was Clmax @ Vs where the frames have to show in flight tests (I presume) that they don't stall until 115kt in landing config. Here a better table with both Cl @ 150kt and @ 115kt. Airbus or Trapezodial at the end of the line stands for Airbus or Trapezodial measurement rules for the wingarea, I use this as PianoX use Airbus for Airbus planes and Wimpress for Boeing planes and that any other info most likely can be in Trapezodial like the NASA one you mentioned. Wimpress is only some 3% less then Airbus so I use the one where we have more data which is Airbus. By using the right reference area one can compare the Cl values (with Piano and other sources):



I have not seen the NASA study you referred to, can you give the link?


1) Could you explain the Airbus performance speeds a bit more? What does Vs 1g mean?

[Edited 2012-04-30 08:32:40]


Non French in France
User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 15, posted (2 years 4 months 3 weeks 3 days 4 hours ago) and read 26182 times:
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Quoting ferpe (Reply 14):

I have not seen the NASA study you referred to, can you give the link?

here it is :Rudolph study on hi lift dev

Quoting ferpe (Reply 14):
Could you explain the Airbus performance speeds a bit more? What does Vs 1g mean?

try this link :
getting to grips with aircraft performance
click on the screen icon to open the document.

on page 35, 36,; you have the definition and the application to approach speeds on page 113.



Contrail designer
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3526 posts, RR: 66
Reply 16, posted (2 years 4 months 3 weeks 3 days 4 hours ago) and read 26176 times:

Quoting Pihero (Reply 13):
A few remarks, though :
1/- The basis for Airbus performance speeds is the Vs1g for all FBW airplanes. The concept is being taken slowly by Boeing into consideration, but AFAIK, the FAR 1.3 Vs is still current

The last Boeing airplane to use 1.3 Vs for approach speed was the 737CFM Classic in the mid-1980's.

All subsequent models have used Vs1g and the 1.23 factor for Vapp.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 17, posted (2 years 4 months 3 weeks 3 days 3 hours ago) and read 26135 times:
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Quoting OldAeroGuy (Reply 16):

The last Boeing airplane to use 1.3 Vs for approach speed was the 737CFM Classic in the mid-1980's.
All subsequent models have used Vs1g and the 1.23 factor for Vapp.

I'd really like to see the proof of your statement as in 2000 I taught a course on aircraft performance in which FARs were still related to the Vsr = Vclmax / sqrt N where N is always and thedefinition was left to the manufacturer.
Reading the FARs is a bit confusing as the old notions do not seem forgotten as notations as Vs still abound.

But maybe I need to update my library.



Contrail designer
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 18, posted (2 years 4 months 3 weeks 3 days 2 hours ago) and read 26127 times:

Quoting Pihero (Reply 17):
I'd really like to see the proof of your statement

Just one example: Page 7 of the 777-200/300 TCDS under the Cert Basis - Equivalent Safety Findings section

Quote:"14 CFR 25. (several sections) Use of 1g Speed Instead of Minimum Speed in the Stall as a Basis for Compliance. (All 14 CFR 25 Sections, except structural, dealing with stall speeds/related factors for turbojet airplanes)."

You can find the TCDS here:
http://rgl.faa.gov/Regulatory_and_Gu...02e6/$FILE/T00001SE%20Rev%2029.pdf


User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 19, posted (2 years 4 months 3 weeks 3 days 2 hours ago) and read 26120 times:
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The date is Sep 2005


Contrail designer
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 20, posted (2 years 4 months 3 weeks 3 days 2 hours ago) and read 26114 times:

Quoting Pihero (Reply 19):
The date is Sep 2005

Not sure I am following you, Pihero. Are you saying you believe the equivalent safety finding for 777 stall speed was granted in September 2005?


User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 21, posted (2 years 4 months 3 weeks 3 days ago) and read 26059 times:
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Don't know. Is it the original TCDS ?
On the same subject, comes to my mind the fact that , for Airbus and JAR, the Vs1g concept was for FBW aircraft only... When submitted to the FAA, it was accepted in the US with a proviso that Vs1g = ;94 Vs in order to keep some sort of continuity in perf determination ( so that 1.23 Vs1g = 1.3 Vs).
Therefore, when I did my course - and I clearly remember referencing on FAR and JAR books - the certification on US planes was on old Vs, although I confess the T7 did not entert the discussion. The 737, yes, but to which point , or type rather.
Tom, please enlighten me !



Contrail designer
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 22, posted (2 years 4 months 3 weeks 3 days ago) and read 26047 times:

Quoting Pihero (Reply 21):
Don't know. Is it the original TCDS ?

Unless otherwise noted in the TCDS, items under the Cert Basis section are deviations from the Cert Basis Amendment Level used for certification of the type. When an Equivalent Safety finding or Special Condition has been granted subsequent to Type Cert, it will always note the date. In the case of the Equivalent Safety Finding for the 777 to use 1g speed instead of minimum speed in the stall as a basis for compliance, no date is noted. This means the Equivalent Safety Finding was granted with the original TCDS, dated April 19, 1995.


User currently offlinePihero From France, joined Jan 2005, 4450 posts, RR: 76
Reply 23, posted (2 years 4 months 3 weeks 2 days 23 hours ago) and read 26022 times:
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Quoting CM (Reply 22):
In the case of the Equivalent Safety Finding for the 777 to use 1g speed instead of minimum speed in the stall as a basis for compliance, no date is noted. This means the Equivalent Safety Finding was granted with the original TCDS, dated April 19, 1995.

OK. But for some reason, in the yeart 2000 and for AI in 2002 (date of their "get to grip with Aircraft Performance ", the FAR document was still : FAR 25.103 Stalling speed :
(a) VS is the calibrated stalling speed, or the minimum steady flight speed, in knots, at
which the airplane is controllable, with Zero thrust at the stalling speed, or […] with
engines idling”.
FAR 25 doesn’t make any reference to the 1-g stall speed requirement.
Nevertheless, Airbus fly-by-wire aircraft have been approved by the FAA, under
special conditions and similarly to JAA approval, with VS1g as the reference stall
speed.

On the basis of that FAR in 2000, I have assuimed that Vs1g is something very new ( thought about the 787 cert, and not before.
I guess I may owe you guys a beer.



Contrail designer
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 24, posted (2 years 4 months 3 weeks 2 days 22 hours ago) and read 25999 times:

Using 1g speed instead of minimum speed in the stall as a basis for compliance is just one example of a larger trend by both OEMs; they are increasingly willing to deviate from the published regulations (whether it be via special conditions, equivalent safety findings, or other mechanisms) if it will help them to eliminate unnecessary margin in their designs.

Something which most people don't think about is the fact that airplane designs and OEM's understanding of performance are way out ahead of the regulators. The FARs lag the state-of-the-art in the industry by a considerable measure and an aircraft designed precisely to the letter of the FARs would accept many needless limitations. The OEMs make an effort to educate the regulators and to help them on a path for meaningful reform of the regulations, but it is an unduly bureaucratic process, meaning it is tedious, deliberate and very slow.

The lack of technical depth in the regulators is a risk to the OEMs in the sense there is always a chance it will end up limiting the product. It is not uncommon for a lack of understanding on the part of the cert agency to result in artificial limitations or other kinds of unwarranted conservatisms being imposed an airplane. This lack of expertise within the regulators combined with increasing aircraft complexity is the reason delegated authority is so important to the OEMs. Often the OEMs are the only ones who truly understand their design.


25 OldAeroGuy : Don't have access to the 737NG TCDS where I am right now, but I did play a key role in the 737NG Part 25 Aerodynamic Certification. Remember that it
26 Pihero : Respect where it's due. And thanks for the infos this site badly needs So I understand better the liberty the FAA gives the "applicant" for - in this
27 ferpe : If I take 150kt approach speed and divide with 1.3 or 1.23/0.94 I get the same result, 115kt. I understand that Vs1g is a better definition as Vs can
28 Pihero : That's what they were aiming for, for "continuity"'s sake. Yep ! All protections come from that - for once - accurate determination of "stall speed".
29 Post contains links and images ferpe : The NASA Rudolp study of high lift devices is quite interesting, here the essential diagram where he compares the then prevailing aircraft in approach
30 Post contains links and images ferpe : And so to the trickiest part of the analysis (framers! we need your windtunnel data ) but also perhaps the most interesting, cause here the difference
31 Post contains links and images ferpe : For clarity the start flap setting in the tables are at equivalent Cl increase of about 1, this is a main flap element deployment angle for a hinged f
32 Post contains images ferpe : Some more tidbits on start and landing; WHY NO KRÜGERS ANY MORE? In the Airbus vs Boeing thread Mandala499 and me tried to understand why A did not u
33 OldAeroGuy : I think you're using the wrong wing definition for the -8X. From what I've read, it will have the same wing as the -9X. This would make sense from a
34 OldAeroGuy : The Wimpress area factors the non-trapezoidal parts of the wing area as projected into the body as a function of the exposed span of the non-trapezoi
35 Post contains links and images ferpe : This has been my conclusion as well, no point in doing 2 wings for 2 models, especially if the 71m wingspan gate problem is solved by folding the rak
36 Post contains images ferpe : I have gradually come to understand that, initially I wondered why not use only he exposed area but then saw this interesting picture in a 787 presen
37 Post contains links OldAeroGuy : This is only true for the initial part of the takeoff roll where the engine jet plume is free to expand as there is no freestream velocity to contain
38 ferpe : OK, this then explains a lot, thanks for pointing it out. It seemed rather wasteful of B as I had it described (it might be that Dynmicsguy gave this
39 OldAeroGuy : Remember, the Wimpress area convention was developed during the 1950's when these beautiful CFD graphics weren't available. It did a reasonable job o
40 Post contains links and images ferpe : Exactly what I thought, thanks this means I can stop my logical hunt , makes sense. Re the flaperon function, here a nice video from the 787: http://
41 Post contains links OldAeroGuy : http://www.youtube.com/watch?v=Q0_juw3lOo0&feature=related This video is an even better illustration of 777 flaperon takeoff movement. At first th
42 Post contains links and images ferpe : After finishing the start phase I found this picture in the van Dam paper: and also the formula for the climb gradient after clearing the 35ft obstacl
43 Post contains links and images ferpe : After the last post I wanted to summarize the thread and include also the typical climb performance in the final table. Before that I went through all
44 WingedMigrator : Any chance you could make an educated guess about the performance of a hypothetical A380-900 ? Maybe give it a stretch to 85 m, MTOW around 600 t, sam
45 Post contains images mffoda : And if you thought flying a 80m A/C was a problem... What do you adding 5 meters will do?
46 Post contains images astuteman : Make some notable customers very happy, and also ensure that we will continue see that when Boeing aircraft start to encroach on these sorts of dimen
47 OldAeroGuy : Great work and even if there are a few areas of uncertainty, it's interesting to make a few observations. 1) At 525 pax, the A388 has the worst fuel b
48 OldAeroGuy : I suspect the greatest peeps will come from the airports where 85m long airplanes are expected to operate. Few gates at the world's major airports ar
49 747classic : GE is already prepared for this scenario and will certify the GEnx-1B PIP2 with a raised T/O rating of 78.000 lbs. Although Boeing hasn’t asked for
50 Post contains images astuteman : On those criteria, I wonder if an alternative wingtip solution would also be considered..... couple of points... Firstly, the A380 also has WAY the l
51 OldAeroGuy : OK, let's try to adjust for these numbers. Assume we increase the passenger count by 20%. .20*525 = 105 But the additional passengers will increase z
52 Post contains links and images ferpe : Thanks for those comments, I am also puzzled by the results for the A380. I found a slight misfit, I had the OEW at the ACAP 270t, I now have put in
53 Post contains links and images ferpe : Some more comments: - please read the average fuel flow at line 243, the one at FL370 is a momentary FF at 83% weight which is mid cruise weight. As t
54 OldAeroGuy : I don't understand how increasing OEW decreases fuel burn per pax. Ferpe's model shows a fuel flow of 11,680 kg/hr, in line with your observations.
55 Post contains images ferpe : My bad, it is the other way around as would be natural (270t gives 0.0515 and 276t gives 0.0521). I have another model where I count backwards from t
56 sunrisevalley : I have been wondering about various fuel burn claims and took a look at a still air comparison between what QF might expect with one of the A380 vari
57 astuteman : In reality, both of those figures are light. The R/P chart Airbus use implies an OEW of 282 tonnes (assuming the 569t variant). In real life it's dry
58 Post contains links and images ferpe : As I stated this is a momentary value at mid cruise weight, the average value is at the bottom. The FF varies from 15.5t at start of cruise down to 1
59 WingedMigrator : Hi Ferpe, thanks for all that additional data. Having tinkered with my own Breguet spreadsheet over the years, I have a basic concern with your final
60 Post contains images ferpe : You are correct, at this stage I have verified the drag and TSFC variation model (the OEMs spec range at spec Pax+Bags is a good check) more then act
61 astuteman : That seems like a big spread. It might be worth seeking some corroboration from some of the more informed members able to point to actual figures.. R
62 parapente : I think we will see some clever feather winglets on the 389 I feel this is very likley.When the present wings were designed they were designed to the
63 Post contains images ferpe : Corroboration with PianoX: Loading plane: Airbus A380-800 (569t, 270t OEW, 525 Pax)....Done. DETAILED FLIGHT PROFILE {design range & standard pay
64 ferpe : If Airbus can add 1m effective span each side it will increase the range with 200nm and put the fuel burned per nm and m2 at 0.0458
65 Post contains links and images ferpe : I have corrected this faulty formula, at the same time I took the time to look over and improve other items I need for a more general comparison over
66 WingedMigrator : Curious about the A389 numbers... should V2 not be higher than the A388, given the same wing?
67 Post contains images ferpe : No, the formula is dependent on available thrust when one engine has fallen away, the TWB thrust of 3*88klbf vs 3*72klbf for the T900 gives the diffe
68 Post contains links and images ferpe : Over the time since I started this thread it has been referenced many times by me and others as it contains a good rundown on how one can analyse a ci
69 Post contains links and images ferpe : On Leehman.net I posted this in a discussion around the possibility of a A350-1100. There was the usual dicussion where different values of wingloadin
70 Pihero : ...expressed more often as 2.4% climb gradient for a twin, 2.7 % for a tri and 3.0 % for a quad. AFAIK, the *screen height* is still at 35 ft Thanks
71 Post contains links and images ferpe : I did some further checking with some FCOMs, Clmu of 2.0 is to optimistic, we shall rather have 1.7 as a good start value. I have remade the table wit
72 Post contains images 817Dreamliiner : Two questions: 1) How is the wing area for the 787 370m2? A google search shows it at 325m2, which figure is correct? If using the 325m2 figure, I ge
73 ferpe : Look in the opening post (OP) of this thread, there you have it all. The 325m2 is the value that the original PianoX analysis put on the 787 wing. A
74 Post contains images 817Dreamliiner : Thanks for answering my questions. I understand it a lot better now.
75 Post contains links and images ferpe : I gave some 777 values in a General Aviation forum which was debating the 777X and the existing models, after my posting -200Er and LR numbers Poncho
76 Astuteman : What makes me laugh about your analysis here Ferpe, is the huge amount of scepticism that met the original A350-1000's performance specifications.. I
77 KarelXWB : According to zeke (if I remember it correctly), the improved 308t A350-1000 will be able to do everything the CX 777-300ER can, but with a 20% lower
78 Aviaponcho : My best guess for A350-1000 is 131t MWE ... put in a 350PAX Interior and I got 150t BOW and 155t DOW... (working on 2006 slides from airbus vs 777 and
79 Post contains images Stitch : He also noted that the A350-1000 is about 8 tons lighter than a 777-300ER in four classes (160t vs. 168t) with effectively identical passenger seatin
80 zeke : About 40t lighter at takeoff.
81 Post contains images Stitch : With a 43t lower MTOW, that's not surprising. Seriously, it does show the benefits of the lower fuel burn - less fuel needing to be tanked.
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