Tuesday, December 29, 2009

787 Wing - A New Twist on Structural Engineering?

(Thanks to Jon Ostrower, at http://www.flightglobal.com/blogs/flightblogger/, for the graphic!)

I was a bit relieved to read comments indicating other folks also thought the 787 wing had an unusual amount of wing deflection during the first flight video.

In particular, the aft view of ZA001's climb-out seemed to indicate an amazing curvature/bending of the wing-

Reuters video of ZA001 First Flight Takeoff
0:18 great T-33 fun- swooping in for chase during takeoff roll
0:37 front view of wing bending
0:53-1:03 amazing (apparent) wing deflection

Now, camera angles can play tricks with our perception (Bonus Prize to those who have already identified a contributing effect- see first post of this new thread).

But discounting that, I did some surfing about to investigate the 787 wing. (Unfortunately, merely on the web, not long boarding as our friend Baron is doing off the coast of Brazil this holiday season- rats! :)

It turns out, Jon Ostrower, who runs the great FlightBlogger website, has been examining this topic for some time- here is his July 30, 2008 article "A Closer Look at 787 Wing Flex" (gulp! guess we're catching up a bit! :). My special thanks to Jon for letting me borrow the graphic above and to link in to his article.

As one of Jon's commenters noted, "One wag joked(?) that the only reason MCboeing put larger windows on the 787 so that the passengers would not get concerned when the lost sight of the wingtip...."

Julius noted the landing gear issues on the first flight of the second flight test article (ZA002), which also sent me surfing- (sounds like the nose gear initially only deployed 75 degrees- the crew did an "emergency" extension (which some say, is not that unusual for first flights or after maintenance) to get it down and locked, but the situation resulted in more video coverage than usual of the landing, which shows some fairly substantial wing flex too- looks like coincident with the ground spoilers deploying- guess those things really do have a big effect on brake effectiveness (among other things, "runway friction coefficient" x "actual weight on wheels") and landing lengths. This also prompted a review of the ZA001 first landing, which shows similar "flapping" during landing. (More correctly, relaxation as the wings unload, but heck, "flapping" sounds more spectacular).

ZA001 First Flight & First Landing (check out last few seconds of video)

ZA002 First Landing

With Jon's blog substantiating our observations, let's investigate this wing flex stuff!

As well commented upon, the 787 is a constructed with composites. I'm no structural engineer, and I'm sure there are many subtle variations, but it seems the terminology of choice is Carbon Fiber Reinforced Polymers, or CFRP.

Trying to find specifications for CFRP was one of the most frustrating experiences I've had on the web- quoted strengths varied widely, and most of the reference material is only available by purchasing trade journal reprints. (Given the wide variance of the open source material, I did not have confidence I would find a definitive answer with the journal articles). There was also some information about reinforcing concrete with CFRP- which while intriguing, I thought not too applicable for our purposes. (It seems CFRP makes a dandy "wrap" for concrete cylinders and beams that make up highway supports- I think after the Northridge earthquake in the Los Angeles area, circa 1994, many of the freeway overpass supports were reinforced with this fabric).

But, with little confidence in any alternative, I resorted to our steadfast reference, Wikipedia, which pointed me to "AS4", which seems to be a representative aerospace CFRP,
Hexcel AS4.

For comparison with conventional, shall we say, "non-disruptive", aluminum construction, I found a variety of sources- it seems like 7075T6 is a good representative material,
Alcoa 7075 fact sheet.

For our study, I used the Hexcel AS4 datasheet "Typical 350ºF Epoxy Composite Properties (at Room Temperature)" values, and the compression values, rather than tension, as bending loads create both conditions, on the "near" and "far" side of the article subject to the bending load. (The compression values used in this study are somewhat lower than the "flexure" strength listed in the AS4 table, so this represents the conservative case- I suspect the flexure values are for tension side of a loaded object, such as when working with prestressed beams, e.g., reinforced concrete and such- any stress engineer types out there?).

From Wikipedia, the above references, and a few other scribbled notes over the pat couple of days, I pieced together this table. (It's in metric units. I confess, rather than demonstrating my enlightenment, it reflects my laziness in not converting to "English" units. Well, make that "American" units, as even the British use the metric system... But since we'll be doing relative comparisons, the unit's won't matter- one less thing for me to goof up! :)

So here's the deal- we'll be using three metrics (so to speak!) of performance:

Young's Modulus, which is "stiffness": the amount of load (force per cross section area) divided by the resultant strain (axial deflection per reference length).

Yield Strength, the load (force per cross section area) that produces permanent deformation in aluminum, or damaged fibers in composites. (Note: this is slightly different than "ultimate" load, which is the "breaking point"- complete failure- but we will assume the airplane is kept out of the damage region).

Density, the mass per volume (perhaps there is a slight difference between "denseness" and "density" ... :)

So, here we go, the Mr. Science overview (these numbers are approximate, and "Your Mileage May Vary", but seemed to be the most typical values I could find):

Material ....... Young's Modulus ...... Yield Strength ...... Density
7075-T6 ........ 69 GigaPascals ....... 430 MegaPascals ..... 2700 Kg/m^3
CFRP (60%) .... 128 GigaPascals ...... 1530 MegaPascals .... 1550 Kg/m^3

Note: the CFRP properties are for "along fiber" loads, not cross-loads, which are markedly lower (more about that later- #1), but for bending, this is appropriate.

A higher value of Young's modulus means a "stiffer" structure- and CFRP is about twice as stiff as aluminum. (So what's up with this goofy-looking 787 wing? Calm down- let's continue! :) At least this "reinforces" our stereotype of "composites being better than aluminum".

A lower density value is also a good thing in general, and CFRP once again demonstrated it lives up to the stereotype expectations of composite's superiority over aluminum- the latter being about twice as "heavy" (dense) as CFRP. (Well, 2700/1550 = 1.74 to be "exact". Hmmm, so far, things are distressingly stereotypical, rather than disruptive!)

A higher yield strength is also a good thing. Again, CFRP follows stereotypical expectations, with a nearly four-fold advantage over aluminum. (Okay, 1530/430 = 3.56 or so, but hey- this is "ball park stuff"! :)

So, all the material properties would seem to be just as we would expect- so why all that wing bending?? Let's consider the primary design criteria for a wing: weight and strength. Does stiffness matter? Uh, well, er, "it ought to". But for now, let's say no (we'll come back to that one also #2!)

Let's look at "strength"- what it takes to keep the wing from "breaking" (Although strictly speaking, we will use yield- the point of permanent deformation- rather than breaking strengths). To handle a given load (bending load, which is converted to axial tension and compression, in the upper and lower wing skins, and upper and lower web caps of the spars), CFRP is about four times (3.56) as strong as aluminum. So, we can use one-quarter (28%) as much, to get the same strength (resistance to yielding or damage). There are two ramifications of this- one is obvious, the other not-so-obvious.

a) Obviously, there's a tremendous weight savings! (Ah, more on THAT later #3). And figure CFRP is about half as dense (0.57), the total weight savings would be about four times two: the composite structure would weight roughly 1/8 of the aluminum wing! (Or a bit less roughly, (1/3.56) x 0.57 = 0.16, or about 1/6; More on this later #4, with some real-world adjustments...).

b) Less obviously (until we saw the videos and Jon's graphic at the top), is: DEFLECTION. Since CFRP is -about- four (3.56) times as strong as aluminum, a wing designer can use one-quarter (28%)as much. But the stiffness is "only" twice (128/69 = 1.82) that of aluminum;

SO, "one-quarter the material" x "twice the stiffness"
(Okay, (1530/430) x (128/69) = 0.52 the stiffness = 1.92 the deflection)

MYSTERY SOLVED ! (Yeah! Well, basically...); Viola!, as one public icon of past exuberantly, and famously, (mis-)proclaimed. (Which icon? I'm not so sure :)

NOW, back to those pesky "later" items mentioned above (#1, 3 & 4; #2 follows later):

#1) "CFRP properties are for "along fiber" loads, not cross-loads, which are markedly lower..."

#3) there's a tremendous weight savings

#4) the composite structure would weight 1/6 of the aluminum wing ...some real-world adjustments

All three of these items can be summarized in one discussion: how much additional material is required to compensate for the anisotropic (directionally dependent) properties of fiber reinforced materials, versus the isotropic (universal in all directions) characteristics of aluminum, and most metals for that matter. (There are some metallic structures, particularly crystalline turbine blades, that are not isotropic, but such exceptions are rare- and expensive).

Wings are subject to complex loads (different than "wing loading", weight/area). Obviously, with the shear, bending, and torsion, the load paths are complex, and this is one area the anisotropic nature of composites can create problems. Consider just how unidirectional composite strength can be: the shear strength of a single-direction layup is only 81 MPa for 90-degree cross load, or a mere 4% of the 0-degree tensile strength os 2205 MPa; and shear strength is only 128 MPa, or 6% of the 0-degree tensile strength. (By comparison, aluminum is equally strong in any axis, and the shear strength of 7075T6 is 331 MPa, or 65 percent of the 503 MPa yield strength in this ASM spec sheet, which is some 20% stronger than the yield strength listed in the Alcoa spec sheet, which did not list shear strength, but to compare "apples to apples", the ratio of shear to tensile strength for 7075 seems to be 65%).

To address complex load paths, CFRP must could be constructed with complex fiber orientation, for maximum strength and minimum weight. This would require individual strands to be oriented in the unique desired directions. A more practical, and less expensive, alternative, is to use CFRP with the familiar 0 degree/90 degree weave orientation. To maintain full strength in either direction (0 and 90 degrees), twice the material is required (the intended 0-degree plies, PLUS plies oriented at 90 degrees). And to handle loads at 45 degrees (as shear strength is weak), plies in both directions must be stronger (read: more- by a factor of the square root 2 = 1.41, or 41%, if my trigonometry is correct). So, potentially, to make a CFRP structure as "isotropic" as aluminum, would require about 2(for 90 degree loads) x 1.41(for 45 degree loads), or about 3 (2.82), times as much material as a "simple" anisotropic structure, and the marvel of a CFRP structure weighing 1/6 that of aluminum now becomes about half (0.47) as heavy. Still an impressive weight savings! And most assuredly, the design engineers will strive to minimize such wasteful excess.

(The ply orientation issue could have other solutions; one might be using 0-60-120 or 0-45-90 degree plies, rather than thicker 0-90 degree plies. The various solutions would result in slightly varying weights, and strengths in off-primary axis directions. It seems I've seen broken composites, and the jagged edge seemed to have fibers pointed in multiple directions- not sure if that is a result of the damage, or the inherent weave pattern of the composite fabric fibers).

Our visual observations of the 787 wing flex, does seem to substantiate this ball-park estimation, of roughly twice the wing flex of an aluminum wing. Regarding CFRP manufacturing and design allowances to handle the anisotropic limitations, Dow Chemical has an interesting article, which states "The key drivers for using CFRP are light weight (50 percent lighter than steel and 30 percent lighter than aluminum)", which would seem to indicate a lot of material is going into making composites act more isotropic (plus, probably some conservative design practices with the still relatively new technology). The Dow claim of only a 30% weight savings over aluminum (rather than our 50%-ish number above) seems to be proven in aviation- there seems to be no real-world weight savings of composite airplane versus aluminum, so far anyway. Perhaps CFRP manufacturing and design allowances to handle the anisotropic limitations (??)

Besides weight, excess material imposes, ah, excess cost. Boy, I thought the mechanical properties of CFRP was hard to find- the cost was even more proprietary and elusive. (Please see accompanying post at the top of this thread).

#2) "Does stiffness matter? Uh, well, er, "it ought to". But for now, let's say no"

One of the advantages of a "flexy" wing is absorbing gust loads and provides a better ride, and improved fatigue life for the rest of the airplane. (With a flexible wing, the overall upward velocity is not changed in response to a sustained updraft, but the rate of upward velocity change is slightly more gradual (and prolonged), so the vertical acceleration is smoother, and forces -and stresses- are lower). This allows components to be made less robust, and lighter.

On the other hand, one of the more alarming presumptions regarding the appearance of unusual/"excess" flex in a wing, regards susceptibility to flutter. And this might be where composites/CFRP shine. The X-29 forward-swept wing program was feasible because of the torsional stiffness of a composite wing. It would seem the 787 is benefiting from this as well, not that it is vulnerable to the inherent wingtip divergence the X-29 had, but still, that flexy wing needs to be resistant to torsion/bending coupling.

Jon's FlightBlogger website has the scoop on this too; some early 777 testbed work for variable camber effects, and his Better Know a Dreamliner - Part Two - ZA002 post yesterday, ("Airplane Two will have the second most hours of the six flight test aircraft and will first participate in the initial airworthiness and flutter clearance, as well as stability and control testing...High speed air testing is also expected to be a significant part of ZA002's aerodynamic check-out along with wing twist that will be measured"). With fly-by-wire controls, and tailored twist characteristics from CFRP construction, this should go smoothly. (Then again, how often have we heard "it's only software" :)

One last (thank goodness!) item to consider is fatigue life. This turned out to be disappointingly proprietary or buried exclusively in subscription trade magazines. The best I could find was Wikipedia CFRP, "Carbon fiber-reinforced polymers (CFRPs) have an almost infinite service lifetime when protected from the sun, but, unlike steel alloys, have no endurance limit when exposed to cyclic loading". So the "flexy" composite wings should not fatigue as aluminum would exposed to such large deflections. (One wonders about fuel and hydraulic lines though, but I suppose these are of a relatively small diameter such that bending will result in a low stress and strain).

Sunday, December 20, 2009

787 First Flight

Congratulations to the Boeing team for the first flight of the 787 Dreamliner.

As well noted by the blog, this occurred on Tuesday, December 15 (2009), About 27 months later than initially forecast.

Boeing has had such a great record for meeting delivery and production schedules, I was curious to review what happened to delay this great day in aviation history. I fear I noted some striking similarities between the 787 and Eclipse 500 programs, at least judging by the press releases. (The most striking perhaps, was the wildly inaccurate press releases themselves, in hindsight).

* "On September 5 (2007) (Boeing) announced a three-month delay, blaming a shortage of fasteners as well as incomplete software"

* "On October 10, 2007, a second three-month delay to the first flight and a six-month delay to first deliveries was announced".

*"On January 16, 2008, Boeing announced a third three-month delay to the first flight of the 787"

* "On April 9, 2008, Boeing officially announced a fourth delay, shifting the maiden flight to the fourth quarter of 2008"

* "November 4, 2008, the company announced another delay, this time caused by the incorrect installation of some of the structurally important fasteners"

* "Boeing confirmed on December 11, 2008, that the first flight would be delayed until the second quarter of 2009."

*"On June 23, 2009, Boeing issued a press release stating that the first flight is postponed..."

It is also interesting to note the EA500 "first flight" was likewise about 27 months late- the deposit locking first flight was August 28, 2002, the "real" first flight was December 31, 2004, 28 months later. It is also telling to note, in both cases, it was near the end of the year (VERY near, in Eclipse's case).


* "On March 28, 2008, in an effort to gain more control over the supply chain, Boeing announced that it plans to buy Vought Aircraft Industries' interest in Global Aeronautica, owner of the South Carolina plant that manufacturers major portions of the 787's fuselage. The purchase will make the assembly plant a 50–50 joint venture between Boeing and Italy's Alenia Aeronautica."

* "In July 2009, Boeing also agreed to purchase Vought's facility in North Charleston, S.C. that makes 787 fuselage sections, for a total cost of $1 billion."


* "The national union representing about 190 Seattle-based FAA engineers this past Tuesday submitted a formal critique to the agency, calling the new policy "an unjustified step backward in safety."

* "The former National Transportation Safety Board (NTSB) chairman who oversaw the TWA 800 investigation, said he's disappointed in the FAA but not surprised."

* "It appears that management has overruled the judgment of the people that have day-to-day responsibility for the safety of aircraft..."


* about 840 firm orders for the 787

* about 840 firm orders for the EA500

More or less, in both cases. The 787 firm backlog was over 900, but there have been some recent cancellations. The EA500 "order"(tm) book was "over 2700", but how many were "real"(tm)? Well, 260 were "delivered"(tm), and Shane reported there were several hundred jilted wantabe owners, and the law suits reported earlier had over 200 plaintiffs.

(Note: I have no doubt the 787 "firm" orders are indeed very real- the 737 "Next Generation" likewise had stupendous firm orders -over 1000- before certification, and they proved to be very real indeed. Plus, Boeing is a publicly traded company- too bad Eclipse was not obligated to adhere to the same transparency standards...).


With the advantage of hindsight, there is ONE singular item which is disturbingly ... convenient, about the entire 787 saga:


So what? With said advantage of hindsight, it seems THAT was just a little bit too...CONTRIVED. (EXACTLY like the December 31, 2004 "first flight" of the EA-500: that sort of thing doesn't coincidentally happen- it was staged).

Which, could make one think perhaps ALL the scheduled events were just a bit too contrived- and that the schedules themselves are contrived.

Using what we've read on our predecesor blogs (EAC and EAC-NG), one can reasonably deduce went wrong at Eclipse- too much focus on meeting scheduled stunts, and not enough focus on real development. Meeting the scheduled milestones, even if so shallowly as to reduce them to being simply contrived stunts, seemed to take precedence over delaying "the show" of scheduled stunts, whether it be first flight, Oshkosh, Sun and Fun, "Certification"(tm), "Delivery"(tm), etc.

With that frame of reference established, one wonders how much the 787 program has suffered from "7/8/7" thinking (artificial/unrealistic milestones/schedules).

Wikipedia 787
FAA to Loosen Fuel Tank Safety Rules...

Sunday, December 13, 2009

First Flight of the Airbus A400M

The Airbus A400M military transport aircraft had it's first flight on Friday, December 11, 2009 (Thanks to Julius for the tip).
As an aviation enthusiast, I consider every first flight an "event" of sorts, and I'm sure the EADS (European Aeronautic Defence & Space, the parent company of Airbus.
The NYTimes has short article, mentioning $30B to go (for 180 aircraft, $166.7M per copy), and 2 to 4 years late, depending on what one reads. (The C-130J is quoted as $48.5M in 1998 dollars- So it's probably more or less, about half what an A400M will cost. The A400M is purportedly faster, and has fly-by-wire flight controls. And, I believe we had some discussion about this technology a while back: COUNTER-rotating propellers, as opposed to countra-rotating propellers- the inboard and outboard props turn in different directions, but there is only one "row" of blades. "Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers[1]. However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 db, and tangentially 10db").

(The Airbus website has a photo of the flight deck towards the bottom).

The aircraft is being built at the CASA facility in Seville, Spain- here's a really nice overview of the CASA facility.

The A400M seems to drop right into the notch between the C-130J and C-17; generally it is touted as a replacement for the C130J, which itself is a fairly recent replacement, of sorts, for the C-130-everything else (mostly H's). While relatively speaking a technical success (eventually), sales have not been overwhelming. The US has been a reluctant customer (the first two customers were the UK and Australia).
The customer list for the A400M is dominated by Germany (60) and France (50), with Spain on tap for 27, and the UK signed up for 25 (same as their original C130J order). Some attribute recent (modest) foreign C-17 sales to delays in the A400M program.
I thought it would be interesting to compare the recent airlift platforms operated by the USA, including the C141 (finally retired in 2006).
The C130J is hard to pin down, I've used "standard" fuel (not including the 18000 lbs in commonly attached external pods, and the -30 length for an extra 15 foot of floor space).
(Ranges and altitudes are important, but have been omitted because they are just too variable, depending on load):

AIRCRAFT________ C-130J-30 __ A400M __ C-141B ___ C-17 ___C-5B
MTOW (LB)________ 164,000 __ 310,852 _ 343,000 _ 585,000 _ 840,000
EMPTY (LB)_________ 75,562 __ 154,000 _ 144,492 _ 282,500 _ 380,000
MAX FUEL (LB)______ 44,240 __ 111,333 __ 153,352 _ 243,134 _ 349,886
MAX CARGO (LB)_____ 44,500 __ 82,000 __ 94,508 _ 170,900 _ 270,000
CARGO (MAX FUEL)___ 44,198 __ 45,519 ___ 45,156 _ 59,365 _ 110,134

Obviously, aerial refueling is an important part of the utility equation when flying at the maximum cargo load with all these airlifters. (Throw on the typical C130 external tanks with over 18,000 lbs of fuel, and it's cargo payload gets cut almost in half too).

A limiting factor in a lot of airlift operations is volume, particularly floor space. The C-130's were stretched in Europe until the C-130J offered the 15 foot stretch from the factory. (Great for hauling cargo, but the extra length was a modest complication in "tactical" (read: short field) operations. The C-141 was stretched (and aerial refueling added) as a result of experience during the airlift to Israel in the 1973 Yom Kippur war. The C-17 has been mentioned as a candidate for a stretch too, although nothing has come of that yet. (Instead, it's the production line that keeps getting stretched out, for the past 3 years or so).

With cargo voume in mind, here's the cargo bay dimensions, with just the flat floor shown for "length" (not the cargo ramp, which is usable to various degrees).

AIRCRAFT_______ C-130J-30 __ A400M __ C-141B __ C-17 ___C-5B
LENGTH (FT)_______ 55 ______ 58.10 ___ 93.3 ____ 88 _____ 121
WIDTH (FT)________ 9.5 _____ 13.12 ____ 10.3 ____ 18 _____ 19
HEIGHT (FT)_______ 9.0 _____ 12.63 ____ 9.1 ____ 12.3 ____ 13.5
463L PALLETS________ 7 _______ 7 _____ 13 _____ 18 _____ 36
FLOOR AREA (SQ FT)_ 522 ______ 763 ____ 961 ___ 1584 ___ 2299

On the other hand, sometimes heavy items DO need to be carried, the M1 Tank being the flashiest bling-bling at most parties. The C-17 can carry one. I suppose if we just put the barrel of an M1 tank on the C17, it would remove the need to transport the actual tank itself. (Which is sort of what the AC-130 does, with the 105 mm howitzer). Or maybe just lower the back ramp and let 'em shoot from there- great fun! (Hey, if you can launch an ICBM from the back, why not?).

More pedestrian uses of airlifters involved the Stryker ground vehicle, which will fit inside a C-130, per design. (At over 22 feet in length, these are reported to be somewhat ponderous to maneuver in parking lots, but get great respect at the exit gate).

It looks as if one wishes to haul their Bradley Fighting Vehicle around, the A400M is a good fit.

(The 463L Pallet is an Air Force cargo standard, outer dimensions 88" x 108" x 10,000 lb capacity. These dimensions don't take full advantage of the A400M's width, so the fact it and the C130J-30 both carry seven is slightly misrepresentative- one of the items I read states the A400M has twice the cargo volume of a C130, but I suspect that refers to the 40 foot floor of the C-130J-10 and all the C130E and H's).

A400M "cutaway" view.
A400M First Flight Video
A400M avionic suite
Main Landing Gear Configuration
Who makes What
(Although I think South Africa has pulled out of the deal- odd, just five weeks before first flight...)

Wednesday, December 9, 2009

A Day That Will Live In Infamy

My apologies for the tardiness of this headline post.

And, for taking "poetic license", in posting a non-aviation headline.

The headline I intended to post will be up on the next thread- delayed as it were, by reflections upon December 7- 1941 in particular. Which was the "trigger event" for the US entry into WW2.

I have thought long and often on this, and I still can't understand why the United States entered WW2 with such enthusiasm. How did we go from such an isolationist stance (or maybe not so isolationist, given the industrial significance of the "lend lease" deal), to such a seemingly non-linear reaction; the horror of over 400,000 combat deaths for the US for the war, in response to over 2,000 deaths at Pearl.

(And one of the later combat deaths involved a special uncle- his specialness becoming known to me only as older relatives relate details to the "younger generation". Which I suppose is why I have pondered the events ultimately precipitating his death with more "critical analysis" this year- certainly something which our blog has excelled at over the past years.

In today's parlance, it would seem a more "limited response" would have been both more appropriate, and less costly for the US.

The only rationale I can surmise, was that it was envisioned to be a short war. Maybe that's the way ALL wars start- it seems Hitler thought so when he invaded Russia (and probably the same goes for Britain and France when they declared war on Germany after Poland was invaded).

(I thought the US did respond with, in retrospect- frankly surprising appropriateness after 9/11- it would seem that moderation would have been considered in 1941. I not disagreeing that the world is better off with the response we had- although decades of Stalinist and Red Chinese rule were arguable no less evil than Nazism and Japanese Imperialism; I'm just perplexed how we swung from mostly isolationist to "total war" in about one day in late 1941).

Rest assured, I do not intend to change the focus of the blog away from aviation. And I don't want to interrupt the ongoing dialog, particularly on two items I'm most interested in, light GA and the 787 (I'm still not sure it will fly this year!, although word is "before Christmas"). But there are a lot of smart people who read and post here- and I would appreciate their reflections upon the why the U.S. entered WW2 with such vigor, rather than participating in a more specific, measured response, as well as their insightful observations on aircraft and the aircraft industry.