Tuesday, February 2, 2010

What I Learned in School This Week...

Well, I must confess, I'm not quite as studious as Thomas Edison, shown to the right, in this dated photograph (of a likewise rather dated Mr. Edison). But after the cookies and milk run out, I do pay some attention in class (Airframe and Powerplant).

One of the interesting activities was a field trip to a local repair shop, where there was a demonstration of working with composites, especially repairing them after some ham-fisted damage is done. (The instructor stared at me a lot during this demonstration, for some reason or other). It turns out that, much to my surprise, that composites are really pretty darned easy to repair. The basic technique is to-
1) Identify the area of damage
2) Remove damaged material
3) Glue new stuff in
That all sounds simple, and when performed by someone familiar with the methods, it really IS simple.

A little tap hammer is used to acoustically listen for delaminations and damage, although there are acoustic "scanners" which can do the same thing with ultrasound.
Then material is sanded down until the delamination is removed.
If a honeycomb core is used, even it can be cut out and "plugged" with a honeycomb insert (and lots of glue/resin).

Layers of Carbon Fiber fabric are then laid over the damage, in orientation described dictated by the specific location (and load path at that location) as described in a repair manual. Plies are alternated 0-90 and 45-135 degrees, up to 4 plies thick, and then resin is worked into the fabric and heat cured. Another set of up to 4 plies is laid, and cured. Etc, until the desired strength is obtained.
Lightning strike fiber (copper mesh, or some such) is then laid over the repair- some sort of smoothing jel for a nice finish is applied, and it's cured and painted. Typically a repair takes one to two shifts, I was told. Neat!

One thing we were cautioned about regarded working with the materials. The resins of course, are rather nasty. But fragments/filliments of the carbon fiber itself are pretty bad news too: the work bench was actually a vacuum table, to capture the dust. Wikipedia has a nice article about Carbon Fibers ("Carbon fibers are the closest to asbestos in a number of properties...").

Although discovered in the good ole US of A, it seems our plucky British friends were early adopters of this rather, um, "disruptive" technology:

"The high potential strength of carbon fiber was realized in 1963 in a process developed at the Royal Aircraft Establishment at Farnborough, Hampshire.. The process was patented by the Ministry of Defence and then licensed by the NRDC to three British companies: Rolls-Royce, already making carbon fiber, Morganite and Courtaulds.. They were able to establish industrial carbon fiber production facilities within a few years, and Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine.

"Even then, though, there was public concern over the ability of British industry to make the best of this breakthrough. In 1969 a House of Commons select committee inquiry into carbon fiber prophetically asked: "How then is the nation to reap the maximum benefit without it becoming yet another British invention to be exploited more successfully overseas?" Ultimately, this concern was justified. One by one the licensees pulled out of carbon-fiber manufacture. Rolls-Royce's interest was in state-of-the-art aero-engine applications. Its own production process was to enable it to be leader in the use of carbon-fiber reinforced plastics. In-house production would typically cease once reliable commercial sources became available.

"Unfortunately, Rolls-Royce pushed the state-of-the-art too far, too quickly, in using carbon fiber in the engine's compressor blades, which proved vulnerable to damage from bird impact. What seemed a great British technological triumph in 1968 quickly became a disaster as Rolls-Royce's ambitious schedule for the RB-211 was endangered. Indeed, Rolls-Royce's problems became so great that the company was eventually nationalized by Edward Heath's Conservative government in 1971 and the carbon-fiber production plant sold off to form Bristol Composites."


Now it doesn't quite date back to Edison's time (February 11, 1847 – October 18, 1931), but some keen eared folks (unfortunately, Mr. Edison was rather deaf) will recall that the RB211 was destined for the Lockheed L1011.

"Because Lockheed was itself in a vulnerable position, the government required that the US government guarantee the bank loans that Lockheed needed to complete the L-1011 project. Despite some opposition, the US government provided these guarantees. In May 1971, a new company called "Rolls-Royce (1971) Ltd." acquired the assets of Rolls-Royce from the Receiver, and shortly afterwards signed a new contract with Lockheed. This revised agreement cancelled penalties for late delivery, and increased the price of each engine by £110,000".

"A major differentiator between the L-1011 and the DC-10 was Lockheed's selection of the Rolls-Royce RB211 engine for the L-1011. As originally designed, the RB211 turbofan was an advanced three-spool design with a carbon fibre fan, which would have better efficiency and power-to-weight than any competing design. This would make the L-1011 more efficient, a major selling point.

"American Airlines opted for the Douglas DC-10, although it had shown considerable interest in the L-1011. American's intent in doing so was to convince Douglas to lower its price for the DC-10, which it did. Without the support of American, the TriStar was launched on orders from TWA and Eastern Air Lines. Although the TriStar's design schedule closely followed that of its competitor, Douglas beat Lockheed to market by a year due to delays in power plant development. In February 1971, after massive development costs associated with the RB211, Rolls-Royce went into receivership. This halted L-1011 final assembly and Lockheed investigated the possibility of a US engine supplier, one option presented would have been the potential outsource of the RB-211 production to Orenda, but by then it was considered too late to change engine suppliers to either General Electric, or Pratt & Whitney.

"The British government agreed to approve a large state subsidy to restart Rolls-Royce operations on condition the U.S. government guarantee the bank loans Lockheed needed to complete the L-1011 project...


"Kenneth Keith, the new chairman who had been appointed to rescue the company (RR), persuaded Stanley Hooker to come out of retirement and return to Rolls. As technical director he led a team of other retirees to fix the remaining problems on the RB211-22. The engine was finally certified on 14 April 1972,[11] about a year later than originally planned, and the first TriStar entered service with Eastern Air Lines on 26 April 1972. Hooker was knighted for his role in 1974."
It is interesting to note that the original Eclipse engine (the Williams EJ-22) was also a three-spool design. Disruptive engine technology is a real pain!

Speaking of that...the name Orenda made MY ears perk up (although this late at night, that's about all). Fellow GA propeller heads (as opposed to turbofan fans), will perhaps recall one of the pseudo urban legands of late, the Orenda V8.

"The Orenda OE600 is a 600 hp-class liquid-cooled 8-cylinder V-block aircraft engine intended to re-introduce piston power to aircraft normally powered by the famous Pratt & Whitney Canada PT6 turboprot. The piston engine offers much better fuel economy, which Orenda Aerospace felt would be attractive for older aircraft whose engines were reaching the end of their lifespan. However, changes in Orenda's business in the post- 9/11 time frame led to the project being canceled.

"Unfortunately, the events of 9/11 required Orenda to re-focus entirely on their military projects, and the OE600 project was canceled. The design was later purchased by a group of investors who intend to sell the engine under the Texas Recip brand, but it is unclear if this project is continuing. On August 29, 2006 the president of Texas Recip, Paul Thorpe was sentenced to 3 years and five months for defrauding investors, telling them the money was being invested in the engine project, or other investments, when it was actually being used to pay off investors in a previous scheme.

"More recently the project has been picked up by TRACE Engines of Midland, Texas. Yorkton Aircraft is handling Canadian installations in agricultural aircraft."


While current VLJ Engines are Candian (PWC-61X), Orenda is also Canadian.

It seems the disruptive engine game can lead to knighthood, a Collier trophy, or a jail sentence- (overall, I'd say Eclipse should be pleased with the Collier! :)

Sunday, January 24, 2010

Reading and Writing...Volts and Bits

I was impressed with the mechanically-oriented Airframe and Powerplant classes, as discussed last week. While browsing the school's bookstore, I was also impressed with the texts for the avionics program. (I had originally thought they were included in the A&P program, but it is a separate track. (Many student's continue with it after the A&P I'm told).

I hadn't encountered anyone with the certification, but the The National Center for Aerospace & Transportation Technologies, NCATT (http://www.ncatt.org/about.php) (formerly called the National Center for Aircraft Technician Training), offers professional accreditation. (I don't think it's part of the FAA processes, yet anyway). The local school issues a graduation certificate, and then one can continue with the optional NCATT certificate.

Interestingly, it would seem both the A&P and avionics certification are increasingly helpful in a number of industries, as employers seek qualified candidates. The wind energy business was in particular pointed out, both for the A&P mechanical applications, and the electronic control and power distribution aspects.

The following syllabus is the one followed by my local institution, in the past it has been a four-term program, and the fifth term is an option for those pursuing the national certification.





Session 1 (15 weeks)13 credit hrs
Technical Mathematics3
Basic Electricity and Electronics3
Basic Electricity and Electronics Lab4
Introduction to Avionics3


Session 2 (15 weeks)7 credit hrs
Avionics Systems & Troubleshooting2
Avionics Systems & Troubleshooting Lab2
Basic Communication Electronics3


Session 3 (15 weeks)8 credit hrs
Wiring and Cannon Plug Lab2
Aircraft Electrical, Comm & Nav 13
Aircraft Electrical, Comm & Nav 1 Lab3


Session 4 (15 weeks)10 credit hrs
Aircraft Electrical, Comm & Nav 23
Aircraft Electrical, Comm & Nav 2 Lab3
Basic Communications Electronics Lab4


Session 5 (15 weeks)11 credit hrs
Principles of Avionics3
Certification Preparation for NCATT 13
Certification Preparation for NCATT 23
Global Professional Standards2



The reading list for do-it-yourselfers (and study-it-yourselfers):

Basic Mathematics for Electricity and Electronics ($219)

Grob's Basic Electronics: Fundamentals of DC and AC Circuits ($151)

Grob's Basic Electronics: Experiments Manual ($80)

Grob's Basic Electronics: Problems Manual ($77)

Avionics Training- Systems, Installation and Troubleshooting ($69)

Avionics Databuses ($127)

Introduction to Airborne Radar ($159)

Basic Communication Electronics ($69)

Aircraft Wiring and Electrical Installations ($27)

Automatic Flight Control ($117)

Avionics Troubleshooting and Repair ($46.50)

Avionics Systems: Operation and Maintenance ($25.50)

Aircraft Instruments and Integrated Systems ($120)

Avionics Test Equipment Handbook ($86.50)

Aircraft Electricity and Electronics ($106)

Some of these are a bit dated- going back to the mid 1990's (ahem). I suppose a large percentage of general aviation aircraft are even older, so maybe not such a big deal. Good reference material anyway. (The "Grob's Basic Electronics: Fundamentals of DC and AC Circuits" in particular looked like a handy starting point aspiring students and DIY-ers to become familiar with).

Things change- the textbooks, as well as the test equipment. Seems like all the Oscopes I see anymore are the digital LCD ones. (And just after I figured out how to set the clock on my VCR, along comes DVDs... "Just when you figure out the answers, they change the questions".

I've *almost* overcome that digital trepidation because of the multi-color traces available with Tektronix "Digital Phosphor Oscilloscope" (DPO) - and probably a lot of other manufacturers. Interestingly, Hewlett Packard is no longer among those competitors, having ditched the test measurment business with a controversial spin off (Agilent). No shortage of controversy at HP, for sure. Here's a link to some of the "real" stuff though.

As typical, Wikipedia has a nice article on Oscilloscopes. Scroll down a bit, and you'll come across the "Digital Storage" section, and note:
"The first Digital Storage Oscilloscope (DSO) was invented by Walter LeCroy (who founded the LeCroy Corporation, based in New York, USA) after producing high-speed digitizers for the research center CERN in Switzerland. LeCroy remains one of the three largest manufacturers of oscilloscopes in the world."
Intereseting- I though of CERN (allowing my crude translation of things backwards- Center of European Research into Nuclear Stuff- I guess they left the "S" off) as a recently developed organization, but it dates back to 1954. Lot's of publicity about the Large Hadron Collider.

I would suspect a certificate in Avionics might be a good resume item for these other high tech industries- wind farms today, fusion reactors tomorrow! (Unfortunately, fusion energy seems about as far off as the flying car...).

Of course, there have been a variety of approaches to the flying car thing. But let's hope that regardless of the industry they enter, our friends with avionics certificates can get their career's off the ground!

(Or at least into high gear- not reverse! :)

Monday, January 18, 2010

Read'n, Writin', and... Riveting ??

A funny thing happened on the way to the airport near where I lived, about, oh, 20 years ago or so. I stopped by a hangar the local junior college had, which was offering Airframe and Powerplant classes. The time requirement was substantial- can't remember the specifics, but it was 18 months, something like 4 hours per night, 5 nights per week, AND all day Saturday. Yikes! Sounded like great fun, but too much time.

Fast forward 20 years or so. And over the holidays, a funny thing happened on the way to a different airport...

This time, I looked a bit deeper into the programs. I'm sure there are a lot of great programs around the country (and world- although I confess to being ill informed about programs in other countries (and am just becoming somewhat literate about those in the USA).

I thought other folks might enjoy what I've discerned as the requirements- or at least what seems to be the typical requirements at a community-college level program. (There are "professional" programs at for-profit schools, Spartan being one of the leaders, I believe. And a number of 4-year programs, Parks College being the one I am most familiar with. But there seems to be more 2-year programs, some offering the training/certificate for only the A&P license, although most offer an associates degree with only a few more classes required).

As I understand it, there are three parts of an "Airframe and Powerplant" license (certificate, actually, although all the other unknowing non-A&Ps like me seem to universally refer to it as a license); the "General" (math, physics, blueprints, FAA regs, etc), the "Airframe", and the "Powerplant". One can obtain and Airframe, or a Powerplant, or an Airframe and Powerplant certificate.

The requirements for the certificate can be met with either work experience or academic training. The work experience is 18 months for either the Airframe or Powerplant, or 30 months for both. The academic training option is the General plus Airframe, or General plus Powerplant, or all three for the full "A&P". These are the requirements to be eligible to take the FAA written tests, after which one takes an oral exam, and a "practical" (hands-on) exam which is administered by a DME (Designated Mechanic Examiner).

I would think military experience would be one way to meet the experience requirements, and probably a number of jobs at an airframe manufacturer or "mod shop". (One challenge might be over-specialization though- perhaps some readers can shed light on this avenue).

The academic route consists of 1900 hours of supervision and instruction. Not including breaks. That's a pretty fair amount of time. (The "General" portion is 400 hours, "Airframe" is 750 hours, and "Powerplant' is 750 hours). For a four-year program, with two 16-week semesters, that's 3 hours per day x 5 days per week x 16 weeks x 2 semesters per year x 4 years. Make that 3.5 hours per day or so, to include breaks. Or, for a two-year community college, that's 7 hours per day or so, including breaks. Or shorter days, but more of them, if one includes Saturdays and the summer terms.

Where I live, the program is offered during the day, and during the night, as a five term program, with three 15-week terms per year- one "General", two "Airframe", and two "Powerplant" terms. The day class meets 7AM - 3 PM, Monday through Thursday; the night class meets 4 PM - 10 PM, Monday through Friday, with appropriate breaks to make it 25 hours of classroom and "lab" time per week. Any absences must be made up, down to the minute, so it's a pretty demanding schedule.

Here's the list of classes, in the normal order they are taken, at the community college (A&P(with associates degree)/vo-tech (old terminology, I suppose; the A&P certificate only).



Session 1 (15 weeks)23 credit hrs
Technical Mathematics2
Physics & Aerodynamics2
Basic Electricity4
Aircraft Drawings1
Maintenance Publications, Forms & Records2
Mechanic Privledges & Limitations1
Ground Operation & Service2
Weight & Balance2
Materials & Processes4
Fluid Lines & Fittings1
Cleaning & Corrosion1
General Review & Test1


Session 2 (15 weeks)23 credit hrs
Wood Structures1
Aircraft Coverings (Fabrics)2
Aircraft Finishes2
Sheet Metal & Non-metallic Structures8
Aircraft Welding2
Assembly & Rigging4
Aircraft Fuel Systems2
Hydraulic & Pneumatic Systems2


Session 3 (15 weeks)25 credit hrs
Aircraft Landing Gear Systems4
Position & Warning Systems1
Aircraft Electrical Systems6
Fire Protection Systems1
Aircraft Instrument Systems1
Ice & Rain Control Systems1
Cabin Atmosphere & Control2
Communication & Navigation2
Airframe Inspection3
Airframe Review & Test4


Session 4 (15 weeks)26 credit hrs
Reciprocating Engines11
Turbine Engines9
Engine Fuel Systems1
Auxillary Power Units1
Propellers4


Session 5 (15 weeks)24 credit hrs
Engine Instrument Systems1
Engine Fire Protection Systems1
Engine Electrical Systems2
Ignition & Starting Systems3
Engine Lubrication Systems3
Engine Cooling Systems 1
Fuel Metering Systems4
Induction & Airflow Systems1
Engine Exhaust & Reversers2
Engine Inspection2
Powerplant Review & Test4


Optional Courses to complete A.S. Degree18 credit hrs
English (Communications)3
Humanitities Elective3
Social Science Elective3
General Elective 13
General Elective 23
Computer Science3




So what if you don't have time for the classes- but If you're like me, the topics sound really interesting? Home study won't do much to geting a A&P certificate, but flipping pages at the community college bookstore was interesting. Here's a reading list, which seems to compose (I think:) the entire booklist of one typical A&P curriculum. I've listed the prices at the JuCo (yeah, that's another oldie term) bookstore. Sometimes on-line is cheaper, sometimes, a little higher. In general, I like to support the brick and mortar stores.

FAR/AMT 2010: Federal Aviation Regulations for Aviation Maintenance Technicians ($25)

Ac 43.13 - 1b/2b Acceptable Methods, Techniques, and Practices of Aircraft Inspection and Repair ($25)

The Aviation Dictionary for Pilots and Aviation Maintenance Technicians ($21)

Aviation Mechanic Handbook ($15)


Aircraft Electricity and Electronics
($110)

Aircraft: Basic Science with Student Study Guide ($62)

Aircraft: Powerplants with Student Study Guide ($110)

ASA General Test Guide 2010 ($14)

ASA Powerplant Test Guide 2010 ($14)

ASA Airframe Test Guide 2010 ($14)

Aircraft Gas Turbine Engine Technology ($107)

Airframe & Powerplant Mechanics Powerplant Handbook ($20)

Airframe & Powerplant Mechanics Airframe Handbook ($20)

Aviation Maintenance Handbook - General ($40)

Aircraft Maintenance and Repair with Study Guide ($110)

The whole books tab comes up to about $700 or so. Tuition at most CC's is around $100 per credit hour, which comes out to about $3000 per "term" for my local A&P school. Multiply by five terms, throw in tools for $2K and FAA exams, the total for an A&P license is probably $18K or so. I'd guess it's around double that for a private for-profit school.

The investment in time is equally expensive, especially if one is working full time: figure 70-80 hour weeks between work and school- sometimes in five days. Lot's of folks have two full time jobs (boy, do I have a lot of respect anyone doing that, or this!). Generally, loans are available to help with the financial burden. The time constraints are less easily ameliorated. Does the A&P certificate "pay off"? I would think so, over time. And it opens doors to opportunites that might otherwise be unavailable. Even at one's present job, it might be the differentiator when layoffs come, or a promotion comes along.

Plus, it looks like a heck of a lot of fun!

Best wishes to all who might be interested in an A&P program- perhaps some are currently enrolled in one. (I know several of our fellow bloggers are already A7P certificate holders).

Wikipedia article on Aircraft Maintenance Technician (AMT) Certification.

Find an A&P school near you. (Something like 170 or so to chose from in the USA).

Tuesday, January 12, 2010

Composite Aircraft Part 2 (Biz Jets and such)


Well, after our expose' last week on the ratio of empty weight to maximum takeoff weight, I am sure to have established my credentials as a half-wit amongst our learned stress engineer friends.

But why leave things only half done? Ignoring the advice of one of my favorite Presidents ("Don't get caught"... -oops, that was Tricky Dicky...but I imagine that's pretty much what they all say),

"Better to remain silent and be thought a fool than to speak out and remove all doubt. "

(Well, I think Abe Lincoln would not be accused of trying to not-get-caught. Although he was accused of just about everything else- politics was probably even uglier then than now, although it seemed some common sense and civility was briefly evident during the 1950's through 1980. Oh well, accidents happen).

Anyway, here we go with a review of business jets (or let's say, business aircraft- as I've included a few turboprops. All twins though, (well, or triples, or quadruples, in a few cases. And, a few Single Engine Jet's...Make that ALL the SEJs :). I deliberately did not include pistons, just to try to try to keep the scope narrowed. I'm sure I also missed a number of great foreign (and probably domestic) aircraft which would well qualify for inclusion- go ahead and mention your favorites, and I'll put them in the tables.

I believe it was Julius who mentioned the Beech Premier as being a notable exception to the laundry list of "failed" composite programs. And inconvenient truth, as it were, to my thesis that composite aircraft (commercial anyway) are:

1) Heavier than their aluminum counterparts
2) Cause cancer and baldness and explode all the time

(Okay, just kidding about that last one:)

My discomfort with a "disruptive" outliar- oops, not talking about former Eclipse stuff- some would insist that the correct terminology in that case would be out-right liar; however in this case: Outlier (interesting read, btw) variance of the Premier program, into the realm of commercially successful composite airplanes, did prompt me to compile a short list of what I had considered "failed" composite airframe programs, versus their nearest successful aluminum competitors. The results were modestly surprising, and challenged a few perceptions I have held about some of these programs. (These are the numbers I found on the web, ymmv, etc.; please post a correction if you see anything too far off, but I believe these numbers use the same methodology, allowing reasonably accurate comparisons).


ManufacturerModelEmpty WtMTOWRatio
AdamA-700555093500.594
CessnaMustang555086450.642
BeechPremier I8430125000.674
CessnaCJ2+8000125000.640
GrobSPn7889138890.568
CessnaCJ38720138700.629
BeechStarship10120149000.679
CessnaBravo8750148000.591
Hawker400023100395000.585
BombardierCL30023300388500.600



Adam A-700 versus the Cessna Mustang. I had always thought the Adam looked like a porky little critter, and would surely be a heavy pig compared to the Mustang. But weight ratio wise, no- the Adam was quite respectable (the Mustang isn't too bad either). I suspect the aerodynamics of the A-700 weren't quite as good though. But, the composite Adam failed, the aluminum Mustang succeeded. Not saying it was the airplane's fault- just a data point. This round- Commercial success: Composites 0, Aluminum 1; Technical success: Composites 1, Aluminum 0.

The ,Beech Premier I (a Premier II is in development) versus the CJ2+ was also a bit of a surprise- I figured that since the Premier was successful, it would have a great advantage over the Cessna- but no, the Premier has a "heavier" ratio than the Cessna (which was also a commercial success). This round- Commercial success: Composites 0.5, Aluminum 0.5 (tie); Technical success: Composites 1, Aluminum 0.

The Grob SPn was one of my favorite development programs. Although it was still early in it's development program, with the likelihood of weight gain as certification changes dictated. But it failed commercially. Or rather, the company did. But again, it's a data point. This round- Commercial success: Composites 0, Aluminum 1; Technical success: Composites 1, Aluminum 0.

I think everyone (including me!) wants to root for the Beech Starship. But it was a financial disaster- only 50-ish were built, and all were bought back to be destroyed. (Well, most of them brought back anyway- a few still in circulation: I saw one fly by a few months ago). And it was heavy. This round- Commercial success: Composites 0, Aluminum 1; Technical success: Composites 0, Aluminum 1.

The last comparison is the Hawker Horizon/4000 versus the Bombardier Bd-100/Challenger 300. (The names of both airplanes changed over the past few years, as indicated). These two airplanes are about as close as it gets to direct competitors- they even had their first flights just 3 days apart. The Horizon is another airplane that has been a financial disaster, with a long development program, and low deliveries to date; the aluminum CL-300 has been a great commercial success. But, the Horizon is slightly better weight ratio than the CL-300, so I'll give it the technical nod. This round- Commercial success: Composites 0, Aluminum 1; Technical success: Composites 1, Aluminum 0.

So, "what's the score" for this five-pair comparison?
Commercial success: Composites 0.5, Aluminum 4.5
Technical success: Composites 4, Aluminum 1.

(I biased the technical success in favor of composites- as long as it was not deficient compared to the aluminum competitor).

To me, the surprise was not that the composite airplanes are so well represented in the financial failure category- which is mostly what I have observed. Rather, the surprise was that they indeed really ARE a bit lighter than their aluminum competitors. I guess I had attributed their financial failure to having a poor weight ratio, but it seems that is not the case.

So if the weight ratios are superior, why the financial failures? I would say, one big contributor, is the cost associated with development of a composite airframe. (Of course, it has been a difficult time economically, for all manufacturers, aluminum OR composite- but still, there seems to be some correlation apparent).

Further observations of the commercial ramifications of composite airframe development:
The A380 was 2 years late...
The 787 is over 2 years late...
Grob who was designing the composites for the Lear 85 (as well as their own SPn) went bankrupt.

I'm not saying there is a direct link between commercial fiasco and composites, but it seems the Premier is the only exception to that hypothesis so far. (Yes, there are lots of orders for the 787, so it may eventually break even. And over the course of years, be profitable. But I think it would have been more profitable, more sooner (er, something like that), if it would have been built of aluminum. (And yes, most of these airplanes are largely aluminum. But I still say there is a correlation between using composites and financial success- or lack thereof).

SO- if that was fun, how about comparing ALL the biz jets (and some select turbo props) ??

I strove to use comparable weights (empty without crew). In general, it seems differences in the empty weight:MTOW of 0.02 are where it gets "out of the noise", and 0.05 seemed to be especially relevant.

Another surprise- while the "sturdy" Kingair line dominates the bottom of the empty:mtow ratio table- but it's interesting to note what's at the second-to-last position. (Hint: Hondajet. And rather dramatically so. (We'll be discussing the Hondajet in a future "headline" thread). Almost as surprising, the Bombardier/Canadair Challenger-series came in at the top- in spite of having the appearance of being rather short and, well, dumpy. (Beauty is in the eye of the beholder though- no offense intended. And it has a great weight ratio!)

So, how did "our favorite VLJ" do? The Eclipse EA-500 scored a very respectable 0.597. Given the rumored weight gain, and deviation from the optimal configuration (rumored to be 40% or so)- that competitive number is all the more impressive. (Congratulations to the structural design team!)

ManufacturerModelEmpty WtMTOWRatio
BombardierCL-60421620482000.449
BombardierCL-301-3R20485451000.454
BombardierCL-600.late18450401250.460
BombardierCL-601-3A19950431000.463
LockheedJetStar I18450389400.474
GulfstreamG-IV35500736000.482
DassaultFalcon 7X34072700000.487
Lear236151124990.492
DassaultFalcon 900EX23875483000.494
DassaultFalcon 900B22611455000.497
BombardierGlobal Express48800960000.508
Lear25D7640150000.509
GulfstreamG-V46200905000.510
DassaultFalcon 5020170388000.520
Lear247064135000.523
CessnaCitation III11670220000.530
DassaultFalcon 50EX21700407800.532
CessnaCitation SII8060151000.534
GulfstreamG-200 (Galaxy)19200354500.542
LockheedJetStar II24178445000.543
GulfstreamG-III38000697000.545
Lear35A10120183000.553
Hawker100017200310000.555
Saberliner4011250201720.558
GulfstreamG-II36544655000.558
CessnaCitation I6631118500.560
DiamondD-Jet287051100.562
IAIWestwind II13250235000.564
Hawker850XP15800280000.564
BombardierCL-600.early22825404000.565
PiperPiperJet410072500.566
IAIWestwind II11750207000.568
GrobSPn7889138890.568
Hawker900XP16020281200.570
DassaultFalcon 20018290320000.572
Saberliner75A13200230000.574
DassaultFalcon 1010760187400.574
CessnaCitation Ultra9395163000.576
DassaultFalcon 10011145193000.577
GulfstreamG-15015100261000.579
DassaultFalcon 200020735358000.579
DassaultFalcon 2016600286600.579
SwearingenSJ30-27700132000.583
GulfstreamG-100 (Astra)14400246500.584
Hawker400023100395000.585
Hawker75015800269500.586
Lear6013850235000.589
CessnaBravo8750148000.591
CessnaCitationjet6160104000.592
AdamA-700555093500.594
CessnaCitation X21700364000.596
EclipseEA-500355059500.597
Aero Commander690A6126102500.598
Lear55C12858215000.598
CessnaSovereign18150303000.599
BombardierCL30023300388500.600
GulfstreamG-25023750396000.600
BeechB-1007092118000.601
Lear31A10253170000.603
EmbraerLegacy 60030000496040.605
CessnaCJ410260169500.605
CessnaCitation X22100361000.612
Lear6014502235000.617
BeechB-2007755125000.620
BeechKingAir 3509326150000.622
GulfstreamG-I21900351000.624
CessnaEncore+10540168300.626
CessnaCJ38720138700.629
Lear8521100335000.630
CessnaXLS+12760202000.632
CessnaCJ1+ (source1)6765107000.632
CirrusSF50380060000.633
CessnaCitation XLS+12800202000.634
EmbraerPhenom 30011450180200.635
Lear4513744215000.639
CessnaCJ2+8000125000.640
Lear40XR13461210000.641
CessnaMustang555086450.642
SwearingenMerlin IIB6452100000.645
Hawker40010550163000.647
PiaggioAvanti II7500115500.649
Aero Commander10007289112000.651
SwearingenMerlin IIC8150125000.652
MitsubishiMu-27570115750.654
CessnaCJ1+7025107000.657
EmbraerPhenom 1006932104720.662
BeechPremier II9120137000.666
BeechPremier I8430125000.674
BeechB-200GT8520125900.677
BeechStarship10120149000.679
HondaHondajet625692000.680
BeechC-90GTi7000101000.693




Monday, January 4, 2010

Time to "Scale Back" our Expectations for Composites?

Happy New Years greetings to all!

Although as we start a new decade, I recall some of the year 2K hubbub- which leaves me mindful of the debate over exactly when a new century starts, and presumably, how to designate decades...BTW, the Royal Observatory also says Jan 1, 2001- but what the heck, we have other things to worry about, so I'll stick with Jan 01, 2010. (Now about Tiger Woods...).

I have to admit some satisfaction with our last thread, in examining why the 787 wings appeared to flex so much (incorrect aspect ratio in some videos resulted in an exaggerated depiction of the radius of curvature), and why they really DO flex so much (higher yield strength x4 aluminum, so only 1/4 as much as used; so despite the fact it is x2 as stiff, structures deflect twice as much (1/4 x 2), roughly (very!) speaking.

What I have less satisfaction with, whether composite airplanes are (or are not) lighter than aluminum airplanes. Which, of course, as an aviation "critic", and "enthusiast", prompted a simple comparison of the 787's nearest stablemates in the Boeing barn, the 767 on the smaller side, and the 777 on the larger side. I have always considered structural efficiency to be measured by empty weight to maximum weight, given other factors being about the same:

* Commercial service (not ruggedized for military operations)
* Pressurized (significant structural stresses involved)
* Jet powered (Similar systems)
* Operating environment (all more or less 35K feet and Mach 0.8-ish)

I had three expectations:

1) A "scaling" effect, that the larger (At least, higher MTOW) an airplane was, the "better" it's structural efficiency would be (empty/MTWO)
2) Newer aircraft would benefit from CAD analysis and be tailored for ultimate structural efficiency, and have superior empty/MTOW ratios
3) Composite airplanes (well, as Baron pointed out, -partially composite) would have better ratios than all aluminum airplanes.

The first expectation was reasonably well met, but the other two pointed to decidedly "disruptive" conclusions! (Now, there is probably a reason for this, but dang if I know what it is...)

Of course, this led to that, and after looking at the 787's nearest family members, I remembered what I have been told about the Boeing 757- that a) it was designed during the energy crunch of the 1970's, and as such, was designed to be unusually light, an as such, included some unusually expensive structural innovations, such as extra lightening holes, etc- whether or not this is true, I'm not sure, but when the 757 was discontinued in favor of the latest and longest versions of the 737, I wondered how much of the purported manufacturing expense savings of going to a "one (737) family" product came from commonality, and how much came from the 757 design itself. So I included the 737 lineup to compare to the 757 versions.

And the 757 was designed to replace the 727, so I looked at it too. Okay, that's a pretty old jet, so how about the other icon-ic (thank you very much!) jet of that era, the 707? How about the extreme of the Boeing product line, the 747, and if that "heavy", how about it's contemporaries, the DC-10 (and MD-11 derivative) and L-1011. How about the other Douglas jets, the DC-9 (and MD-xx derivatives). Not to offend our European friends, how about the Airbus lineup?

And neither would I want to offend our Canadian nor Brazilian friends, especially if the smaller DC-9/MD-95 and 737's are mentioned, the Bombardier CRJ-series and Embraer ERJ-series were included. And then other (original) "regional jet" aircraft were considered- the Fokker 70 and 100, the Dornier 328Jet.

And what the heck, if I looked at DC-9's, why not DC-8's? And how about it's contemporary, the Consolidated Vultee/General Dynamics/Convair series. And if I'm going back to the older jet airliners, why not go ALL the way back, to the Comet?

If considering "unusual" (rare in the US, nowadays, anyway) airliners such as the Convairs, how about the Russian Ilyushins? At this point, I decided just to include every main-stream (even if non-USA) jetliner that I could think (and find in Wikipedia or Airliners.net): the French SUD Caravelle, the British Vickers VC-10 (I've actually seen these in military guise); the Russian Tupolev and Yakovlev, and the British "regional-ish" jet the BAC-111.

And for fun, I included the British/French Concorde and Russian Tu-144 SST's, and the Russian Antonov STOL jet transport. (The STOL outcome was expected, the SST was not).

Anyway, that's the train of thought that led to this compilation.

The weights are pounds, and the the "empty" weight is "operating empty", if I could find it (but the differences usually weren't too great). The radio is Empty/MTOW.

Aviation enthusiasts will recognize the names of these- but just in case we no longer recognize the airplane, Airliners.net/Aircraft-data has a listing of most of these, and there are also generally Wikipedia entries available.

Here's the initial comparison I was curious about, regarding the 767-787-777 comparison:



ManufacturerAirlinerEmptyMTOWRatio
Boeing777-2003070005450000.563
Boeing777-200ER3150006560000.480
Boeing777-200LR3260007660000.426
Boeing777-F3260007660000.426
Boeing777-3003536006600000.536
Boeing777-300ER3669407750000.473
Boeing787-32230003750000.595
Boeing787-82420005025000.482
Boeing787-92540005470000.464
Boeing767-2001766503150000.561
Boeing767-200ER1816103950000.460
Boeing767-3001897503500000.542
Boeing767-300ER1984404120000.482
Boeing767-300F1900004120000.461
Boeing767-400ER2290004500000.509





That was a tasty appetizer, but here's the "main course". The "Top 10" contained some surprises to me- half of them are freighters. (I thought the floor reinforcements, cargo handling equipment, and beef up around the large cargo door cutouts might "outweigh" weight savings obtained from the removal of passenger accommodations and accouterments- but it looks like that is not the case: the "stripped down" freighters are a bit lighter).

The other five "Top 10" finishers included some real surprises too:

The venerable DC-8, grand-daddy of more modern jet "freight dogs", is still showing the kids how it's done. (Well, it did really well in our comparison anyway). First flight of the original DC-8 was on May 30, 1958.

The Concorde SST was certainly not one I would have expected near the top. The rival Tupolev Tu-144 SST did well also, at 0.472 (versus 0.425). The Concorde first flew on March 2, 1969; the Tu-144 first flew on December 31, 1968.

The Boeing 777-200LR was in the top 10 also (as was the 777-Freighter, largely based on the -200LR). I expected the 777 to do well in this comparison- and this is even better than I expected. The first flight of the original 777 was on June 12, 1994.

The Russian Ilyushin IL-62 was a bit of a surprise- firstly, it is Russian, and I think of the stereotype of "rugged" (read: heavy) construction methods. Apparently, this is not (always, anyway) the case- it matched the Airbus A380-800 freighter. It features the funky twin-pod aft-mounted engines (total of 4), similar to the Vickers VC-10 Super of that era, which did well itself (0.468 versus .428). The Ilyushin original version flew in September 1963, the Vickers original version flew on June 29, 1962.

And, the upcoming A350 rounds out this list- although it is still a "paper airplane" (or "paperless airplane", as it is designed with CATIA). And it still hasn't been rolled across a scale- first flight is scheduled for 2012.






ManufacturerAirlinerEmptyMTOWRatio
DouglasMD-11F-HW2485676305000.394
DouglasMD-11F2485676100000.407
DouglasDC-8-63CF1463003550000.412
DouglasDC-8-621419033350000.424
Aerospatiale-BACConcorde SST1735004080000.425
Boeing777-F3260007660000.426
Boeing777-200LR3260007660000.426
AirbusA380-800F55600013000000.428
IlyushinIL-621530003575860.428
AirbusA350-900 (est.)2550755910000.432
DouglasDC-8-321340003100000.432
IlyushinIL-62M1573603637600.433
Boeing707-320B1464003336000.439
DouglasDC-8-631537493500000.439
Boeing747-400ER4069009100000.447
Boeing747-4003932638750000.449
DouglasMD-11C-HW2839756305000.450
DouglasMD-11-HW2839756305000.450
AirbusA310-300F1629003616000.450
LockheedL-1011-5002327495100000.456
DouglasMD-11CF-HW2882966305000.457
DouglasDC-8-611488973250000.458
AirbusA340-500 HGW3850008400000.458
AirbusA340-2002800006100000.459
AirbusA340-5003770008200000.460
Boeing767-200ER1816103950000.460
Boeing747-200B3830008330000.460
Boeing767-300F1900004120000.461
DouglasMD-11CF2882966250000.461
DouglasMD-11ER2911206305000.462
Boeing747-200SP3250007000000.464
Boeing787-92540005470000.464
Boeing707-0201031452220000.465
DouglasDC-10-302661915720000.465
DeHavilandComet-4754001620000.465
DouglasMD-11C2839756100000.466
Boeing737-200HW606001295000.468
VickersVC-10 Super1568283350000.468
DouglasDC-8-731665003550000.469
AirbusA340-3002870006100000.470
AirbusA330-200F2400005100000.471
VickersVC-101469803120000.471
DouglasMD-112839756025000.471
Boeing747-3003928008330000.472
TupolevTu-144 SST1874003970000.472
DouglasDC-9-30571901210000.473
Convair9901205602550000.473
Boeing777-300ER3669407750000.473
Boeing707-1201225332570000.477
Boeing727-2001000002095000.477
AirbusA340-600 HGW4010008400000.477
Boeing777-200ER3150006560000.480
Boeing787-82420005025000.482
Boeing767-300ER1984404120000.482
AirbusA300-600F1807003751000.482
SUDSE210-III490001014000.483
TupolevTu-154959001984150.483
AirbusA340-6003920008100000.484
DouglasDC-9-40586701210000.485
Boeing747-8i4729009750000.485
IlyushinIL-962678605511600.486
DouglasDC-10-402702135550000.487
Convair880940001930000.487
Boeing747-1003580007350000.487
Boeing737-400730401497100.488
IlyushinIL-96M2918875952380.490
Boeing737-700ER841001710000.492
LockheedL-1011-2002316004660000.497
Boeing757-200-PW1275202550000.500
DouglasMD-87-JT8D-217C-ER748801495000.501
Boeing757-200-RR1278102550000.501
AirbusA310-3001833003616000.507
AirbusA380-80061000012000000.508
SUDSE210-12650001278000.509
Boeing767-400ER2290004500000.509
AirbusA310-200F1596003123420.511
DouglasDC-9-50618801210000.511
SUDSE210-10588001146000.513
Boeing737-500688501332100.517
AirbusA330-2002640005100000.518
SUDSE210-VI-N548001058000.518
AirbusA321-2001070002060000.519
DouglasMD-81-JT8D-217A778881495000.521
Boeing757-300-PW1421102725000.522
DouglasMD-88-JT8D-219779761495000.522
LockheedL-1011-12245794300000.522
BAC111-500545821045000.522
Boeing757-300-RR1424002725000.523
Boeing737-800911081742000.523
DouglasMD-87-JT8D-217C732741400000.523
Boeing737-300HW724901385000.523
Boeing737-200606001155000.525
Boeing737-900ER984951877000.525
SUDSE210-VIR580001102000.526
DouglasDC-10-152401714550000.528
AirbusA300-600R2004003785000.529
CanadairCRJ-200F-LR28212530000.532
TupolevTu-204-2201300702441550.533
DouglasMD-90-55919001725000.533
FokkerF-100-Tay650541001010000.536
Boeing777-3003536006600000.536
AirbusA330-3002740005100000.537
EmbraerERJ-190-IGW619051141980.542
Boeing767-3001897503500000.542
AirbusA319-100900001660000.542
AirbusA300B41981323649800.543
Boeing737-900945801742000.543
Boeing737-700841001545000.544
Yakovlevyak-40D20725379200.547
Boeing737-600800311455000.550
DouglasDC-9-1049900907000.550
EmbraerERJ-145LR26470480000.551
AntonovAn-72 STOL42000760600.552
IlyushinIL-86-late2535314585600.553
AirbusA320-200940001700000.553
TupolevTu-154M1219152204600.553
CanadairCRJ-200F-ER28212510000.553
SUDSE210-11R634001146000.553
EmbraerERJ-195-IGW638671152780.554
DouglasMD-81-JT8D-209778881400000.556
CanadairCRJ-1000ER51100918000.557
EmbraerERJ-14025900465000.557
EmbraerERJ-190LR619051108910.558
DouglasDC-10-102401714300000.559
CanadairCRJ-900LR47250845000.559
Boeing767-2001766503150000.561
EmbraerERJ-170LR48082855160.562
EmbraerERJ-135ER23554418880.562
Boeing777-2003070005450000.563
BAC111-40049857885000.563
DouglasMD-90-30880001560000.564
AirbusA310-2001763123123420.564
IlyushinIL-86-early2590434585600.565
FokkerF-100-Tay62053740950000.566
EmbraerERJ-145ER25722454150.566
CanadairCRJ-100051100900000.568
EmbraerERJ-170LR46605820110.568
EmbraerERJ-195LR638671119710.570
EmbraerERJ-135LR25176440920.571
CanadairCRJ-200LR30292530000.572
Boeing737-100618641082180.572
CanadairCRJ-900ER47250825000.573
CanadairCRJ-700LR43200750000.576
AirbusA318-100870001500000.580
EmbraerERJ-17548082826720.582
Boeing737-300724901245000.582
DouglasMD-95 (717-200) HGW707901210000.585
CanadairCRJ-90047250805000.587
EmbraerERJ-17046605793430.587
BAC111-20046404790000.587
YakovlevYak-4020725352750.588
EmbraerERJ-190619051053570.588
Boeing727-1001000001690000.592
EmbraerERJ-195638671075620.594
CanadairCRJ-1000EL51100859680.594
Boeing787-32230003750000.595
CanadairCRJ-70043200725000.596
Dornier328JET_HGW20710345240.600
YakovlevYak-42D760921267650.600
YakovlevYak-42760581256600.605
Dornier328JET20600335100.615
CanadairCRJ-10029180474500.615
TupolevTu-2041285302085500.616
FokkerF-7049985810000.617
TupolevTu-13460627981050.618
TupolevTu-334-100D757851199750.632
DouglasMD-95 (717-200)698301101000.634
TupolevTu-334-100662501016300.652
BAE146-20073415930350.789




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"
= TWICE THE DEFLECTION
(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).

SCHEDULE SLIPS
* "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).

SUPPLY CHAIN PROBLEMS FROM OUTSOURCING

* "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."

CONTROVERSIAL FAA MANAGEMENT INVOLVEMENT

* "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..."

STUPENDOUS BACKLOGS BEFORE IT EVER FLEW

* 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...).

ONE THING STANDS OUT...

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

THE ROLL OUT WAS ON 7/8/7

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...