Category Archives: Aerospace & Defence

Theoretical exam for PPL(A) under Part FCL in France

Certificat d'aptitude.

Certificat d’aptitude.

Today I received the letter informing me that I had passed the épreuve spécifique of the exam for obtaining the PPL(A) under Part FCL.

It was the second attempt I took for this part. I got 68 multiple-choice questions right out of 72; the minimum required to pass being 54 (75%), whereas in the previous attempt I had gotten right 51, short of 3. Sure, this time I studied a bit more and practiced more with tests. However, I wanted to share in this post, as a tip, what I understand it was the key difference: Chez Gigli.

For the first exams I took, back in November I based my study in the manual edited by Cepadues and a book including 700 exam questions with the explanations of the correct responses. This worked relatively well. However, the version of the book I had dated from before Part FCL was introduced (replacing JAR FCL) and thus the topics are organized in 5 exams (vs. the current two).

PPL exam questions book by Cepadues.

PPL exam questions book by Cepadues.

For the second attempt I bought a 1-month access to Chez Gigli as my instructor had recommended years ago and my friend Rapha had mentioned, too. The cost of the book from Cepadues is ~25€, whereas the 1-month access to Chez Gigli costs 20€, for longer time more, though there are discounts (life-long access being 90€).

However, the way Chez Gigli is organized is terrific. You can record your previous results, focus on and review the questions you got wrong, practice only among questions you never saw before, focus on actual exam questions, last year questions, etc. You can see the progress of your scores per topic. Your tests are timed. Explanations of the correct answers are very good and there is a forum per each question so students can ask doubts or further clarifications. It is way more powerful than a book. And you notice it as long as you get to see all the questions, focus on your mistakes and correct them. You get in a matter of days from scores of 70% to 95-100%.

Scores' dashboard in Chez Gigli website.

Scores’ dashboard in Chez Gigli website.

While I was doing the last exam I felt way more comfortable. In most of the questions I didn’t even need to think. Just in a few of them I had some doubts between a couple of answers. I completed the exam way faster than needed, more relaxed and the result, 94.4%, was a success, as the practice had gone. Thus, if you are in France preparing to get your PPL, do not give it a thought: sign for a subscription to the website.

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Learning Curves: Boeing 787 case (from Dec 2012 to Dec 2014)

Last year, I wrote in a couple of posts an introduction to the concept of the learning curve and provided a the case of the Boeing 787 in 2013 (based on figures disclosed by Boeing CFO, Greg Smith). In the first of those posts, I discussed that:

Boeing does not disclose outright what is the actual learning curve it is achieving in its program. Nevertheless, in its investor relations conferences it provides information here and there of cost savings achieved, etc. This can be interpreted as derived from learning curve effects, and would permit to build a model, even if based on scarce information.

This year again, let me quote again one of those excerpts from Boeing executives in order to update the exercise:

“On the 787-8, we’ve seen a decline in unit cost of approximately 30% over the last 175 deliveries and on 787-9, we’ve seen declines of 20% since the first delivery. Based on this progress, our production schedule and planned productivity investments, we continue to expect the 787 to be cash positive during 2015 and we still anticipate deferred production to decline shortly after we’ve achieved the 12 per month production rate in 2016. No change to these fundamental milestones.” Greg Smith, Boeing EVP – CFO at Q4 2014 Earnings Conference

As I mentioned last year, to the avid reader, and knowledgeable and savvy analyst, this paragraph is enough to deduce an actual learning curve achieved by the 787 for each aircraft model, provided that information reported by Boeing CFO, Greg Smith, was accurate.

Through the end of 2014, Boeing had delivered 212 787-8 and 10 787-9. The 787-9 were all delivered in 2014. The 212 787-8 were delivered as follows:

  • 2011: 3 aircraft.
  • 2012: 44 a/c.
  • 2013: 63 a/c.
  • 2014: 102 a/c.

Greg Smith is mentioning a cost reduction of 30% over the last 175 deliveries. As he was talking at the 2014 earnings call, we can safely assume that the figures were put up for him using deliveries and costs only through the end 2014 (and not counting info from January 2015 deliveries). That means that the cost improvements are measured theoretically from the aircraft 37th through the 212th (175). You can extract a report from Boeing website of the complete 787 deliveries here. I did it. Analysing it you see that between the beginning of December 2012 and the end of December 2014 176 787-8 were delivered (1).

Thus, the exercise to find out what learning curve Boeing achieved during that time span is as simple as to see what learning curve yields an “approximately 30% unit cost improvement” from the unit 36th (2) to the unit 212th. The beauty is that we do not even need to know the initial unit cost to perform the calculation, as the relative improvements in terms of percentages are independent of the starting point. All the information has indeed been provided by Boeing.

As I did in the blog post of the last year, in this first graph below I just plotted some generic learning curves, from 95% to 75%. This form of representation provides a good view of how learning is intense at the beginning of the production process and it stabilizes later on. It also shows well how learning is more intense and cost reductions are bigger for a 75% curve than for a 95% curve.

Generic learning curves.

Generic learning curves.

However, in the previous curves it is difficult to distinguish the 36th and the 212th units which are needed for the calculation. Thus, I plotted the same curves in a log scale for the numbers of units produced in the graphic below:

Boeing 787 learning curve over 176 units through Dec 2014 calculation, delta unit cost between 36th & 212th units.

Boeing 787 learning curve over 176 units through Dec 2014 calculation, delta unit cost between 36th & 212th units.

In this second graphic I added the information of what relative cost reduction is achieved between the 36th and the 212th units for each of the curves (3).

To make sure that readers are not lost, let’s take the 87% curve (in red). Following that curve, the unit cost of the 36th unit produced is a 48.7% of the 1st unit cost, whereas the unit cost for the 212th unit produced is a 34.1% of the 1st unit cost. The difference is then 48.7% – 34.1% = 14.6%, which represents a 30.0% cost reduction from the 36th unit cost. If you follow the same calculation for each of the curves, you will obtain the following unit cost improvements between 36th and 212th units:

  • 95% curve: -12.3% unit cost improvement
  • 90% curve: -23.6% unit cost improvement
  • 87% curve: -30.0% unit cost improvement
  • 85% curve: -34.0% unit cost improvement
  • 80% curve: -43.5% unit cost improvement
  • 75% curve: -52.1% unit cost improvement

Thus, from the information provided by Boeing of units delivered and unit cost improvement (“approximately 30%″, Greg Smith) we can deduce that from December 2012 through December 2014 the average learning curve that the 787 program has achieved is about 87%. Thus, in line with aerospace average indicated by NASA (85%), or in line with the reported 84% achieved in the 777. Though a bit lower than that calculated for 2013 (see here last year’s post). We can interpret that mismatch as either as a minimum error inherent of these estimates (85% vs. 87%) or that indeed the rate of improvement has somehow slowed down in 2014 in comparison to 2013.

Had Boeing been able to achieve effectively a 85% curve in the last 175 deliveries, bear no doubt that the message from Greg Smith would have been along the lines of an approximate 35% cost reduction (being the mathematical result 34%), instead of the reported 30%.

All these numbers refer to the 787-8. Now, remember that Boeing CFO also indicated that “on 787-9, we’ve seen declines of 20% since the first delivery”. 

Here, the calculation that needs to be done is the same. 787-9 deliveries started in 2014. If we assume that Greg’s comment referred only to 2014 deliveries (not 2015 ones), then the calculation must be made on 10 787-9 delivered between June and December 2014.  Here the learning curve obtained is a 93.5% ~87-88% (5) (6).

—

(1) I guess Greg Smith rounded to 175, but his “decline in unit cost of approximately 30% over the last 175 deliveries” refers to actually some fixed internal monthly reports and is based on 176 deliveries (not 175). (4)

(2) Taking into account the note (1), I will use 176 aircraft and deliveries from the 36th aircraft through the 212th.

(3) Bear in mind what a relative cost reduction is in contrast to the fact of relative costs represented in the vertical axis as percentages of the initial cost (100%).

(4) The taking of 175 instead of 176 aircraft practically does not change the result. For the same 87% curve the calculated cost reduction in one case is 30% and in the other 29.6%.

(5) This is in line with the slow down of the learning curve for the 787-8 comparing 2013 result with the result along the time span December 2012-December 2014.

(6) I initially calculated 93.5% as a result of a 20% cost reduction between the 1st and 10th units produced. However, as Matt B pointed, the first 3 787-9 have not been delivered (though they are units produced from which there was a learning effect). When you calculate what is the result for a 20% cost reduction between units 4th and 13th (the first 10 delivered), you get a curve between 87-88%, more or less the same one than for 787-8. Thus, it seems than at the beginning of the 787-8 production they went along a 85% curve that has slowed to a 87% for both models.

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XB-36 tires

Two years ago, in 2013, I visited the Pima Air and Space Museum near Tucson, Arizona. One of the airplanes that really catches your attention in it is the bomber Convair B-36 Peacemaker, with its 10 engines: six turnin’ and four burnin’ (I wrote a post about it here).

Ten engines: "six turnin' and four burnin' ".

Ten engines: “six turnin’ and four burnin’ “.

When I wrote that post, I received the following comment from a reader, Ian C.

If you are ever back on this side of the pond, the National Museum of the Air Force has an XB-36 tire. It is just ridiculously large.

Last year, in 2014, we travelled again to the USA and this time we visited the National Museum of the Air Force (1) in Dayton, Ohio.

Let me close the loop by showing you this famous tire accompanied by some facts about it.

XB-36 tire

From the Wikipedia:

The XB-36 featured a single-wheel main landing gear whose tires were the largest ever manufactured up to that time, 9 feet 2 inches (2.79 m) tall, 3 feet (91 cm) wide, and weighing 1,320 pounds (600 kg), with enough rubber for 60 automobile tires. These tires placed so much pressure on runways, the XB-36 was restricted to the Fort Worth airfield adjacent to the plant of manufacture, and to a mere two USAF bases beyond that. At the suggestion of General Henry H. Arnold, the single-wheel gear was soon replaced by a four-wheel bogie. At one point, a tank-like tracked landing gear was also tried on the XB-36, but proved heavy and noisy and was quickly abandoned. (2)

—

(1) See here the post my brother Jaime wrote about our visit to it.

(2) This is not the post to do so, but it triggers the need to write one day about the California Bearing Ratio, doesn’t it?

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Dayton Aviation Heritage

It is well-known that the first ever flight (1) was made by Orville Wright on December 17, 1903, over 120 feet during 12 seconds at a field in Kitty Hawk, North Carolina. It is less known that Orville was born in Dayton, Ohio (August 19, 1871), and that it was in Dayton where the Wright brothers had their different businesses, where they studied the physics of flight, made several tests, and prepared for the few weeks a year they would spend in the windier Kitty Hawk.

That makes Dayton deserve an Aviation Heritage National Historical Park and a visit from truly yours (and family), in a regular pilgrimage to aviation sites.

The Historical Park is composed by different buildings and sites at different locations in and around Dayton, among them:

  • The Wright Cycle Company and visitor center. The company is located at the original place, however the interior has been renovated and now shows replicas of what could be expected to be found in such a shop. The visitor centre is a museum dedicated to the Wright brothers (their family, their careers, other businesses they had) and the principles of flight and to the understanding of the Dayton at the time (a rather ingenious place measured by the different patents and business the flourished there those days). In the centre you may watch as well a 37′ documentary about the Wright Brothers (2).

  • The Wright Brothers Aviation Center, at the Carillon Historical Park, hosts an original 1905 Wright Flyer III that Orville himself helped to restore.
  • The Huffman Prairie Flying Field and interpretive center. These are located in an open-to-the-public area of the Wright-Patterson Air Force Base (3). The interpretive center houses some displays and the same documentary that at the visitor center. In front of it there is the Wright Memorial, in Wright Brothers Hill. A few kilometres from it there is the Huffman Prairie. There the brothers made hundreds of tests. They began using it in 1904 to make their initial airplane a practical invention. It is there where they trained the first pilots (the first ever flying training school). There you will see both a replica of the hangar they used at the time and of the catapult they used for the take-offs.

Before visiting the prairie go by the interpretive center to make sure it is open. You may also get a ranger to give you some tour. The same goes for the Cycle company, which you will need to ask a ranger at the visitor center to open it for you. All these places can be visited for free, though you will be more than delighted to contribute to their preservation.

I leave here some of the pictures we took.

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(1) In a heavier than air powered and controlled airplane.

(2) The documentary, Wright Brothers: On Great White Wings, is narrated by Martin Sheen and produced by Finley Holiday Films, which produces documentaries for several national heritage parks. It can be found here (20$).

(3) This Air Force Base hosts the National Museum of the US Air Force, pay a visit to the great account of our visit in my brother’s blog.

Note: Bear no doubt that some pilgrimage will bring me some day to Kitty Hawk…

 

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My forecast of Boeing Commercial Airplanes 2014 revenues

In the previous years I have been estimating the discounts Boeing applies to its list prices of commercial aircraft. You can see here the result of last year estimate (based on 2013 figures). The results I arrived at are that Boeing has been increasing its discounts in the recent years, and that in 2013 they topped ~47%.

Boeing Average Discount Evolution, 2013.

Boeing Average Discount Evolution, 2013.

With this post I wanted to take a step ahead and put the model to the test by using it for forecasting what will be Boeing Commercial Airplanes revenues for the year 2014.

As of today, January 15th, these have not been announced yet. In Boeing’s investor relations website you can see that the 2014 earnings conference call will take place on January 28th.

How will I reach to my forecast?

  1. See here Boeing (net) orders for the year 2014: 1,432 aircraft among all models.
  2. See here Boeing deliveries in the year 2014: 723 aircraft among all models.
  3. See here Boeing 2014 list prices.
  4. See in the above curve the average discount I will use: 47% (unchanged from past year, this is a hypothesis that will be put to test with how accurate the forecast turns out).
  5. See here [PDF, 841KB] Q3 2014 earnings press release. I use it to see how were faring in 2014 Boeing Commercial Airplanes services, deducing it from the reported Sales of Services, Boeing Capital and Global Services & Support. Up to end September 2014, the services figures were declining in comparison to 2013 figures. I will assume the global figure to follow the same proportional decline; arriving at ~589m$ for Boeing Commercial Airplanes services (remember, this figure will not be actually explicitly reported).

With all these ingredients… my forecast is: 60.2bn$ (1).

In the 2014 Q3 report you can see Boeing’s own guidance for year-end figures:

Boeing's 2014 Financial Outlook at Q3 2014 earnings press release.

Boeing’s 2014 Financial Outlook at Q3 2014 earnings press release.

Some comments:

First, you can see that my forecast (60.2bn$) is a bit more optimistic than Boeing’s own outlook 3 months ago, 57.5-59.5bn$ (2).

Second, in the 2014 Q3 release, you can see the revenues up to end September (below). In them, you can see that up to then, revenues of Boeing Commercial Airplanes had increased 13% in relation to 2013 (12.66% to be more precise). My forecast is a bit more optimistic here as well: at year end the increase in revenues will be +13.6%.

Boeing Commercial Airplanes revenues Q3 2014.

Boeing Commercial Airplanes revenues Q3 2014.

Final comment: if Boeing managed in 2014 to command better prices on delivered aircraft, the figure will be even higher. If the figure is lower than the 60.2, and in line with their forecast, it’ll mean that the market is forcing Boeing to apply ever higher discounts to their published list prices.

I am now looking forward to January 28th and Boeing’s earnings call!

++++++++

Update on February 11th:

As announced, Boeing published on January 28th its full 2014 results [PDF, 838KB]. Which were the Boeing Commercial Airplanes revenues?

Boeing Commercial Airplanes revenues full 2014.

Boeing Commercial Airplanes revenues full 2014.

That is 59.99bn$, or 206m$ short of my detailed forecast of 60.196bn$. This means that I missed with my forecast by a 0.3%, not bad. Even better taking into account that the main discrepancy have been the lower level of services under the commercial airplanes unit.

The result, as my intuition went was above the upper limit of the bracket Boeing gave as guidance for the full year in the 2014 Q3 report, 57.5-59.5bn$ (see note (2)).

—

(1) To be more precise the forecast from the model is 60,196m$.

(2) If my forecast turns out correct some may be tempted to say that this is the usual trick played by CFOs: to present better figures than expected.

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Swiftair MD-83 EC-LTV, BEA interim report

Some weeks ago I read the first interim report from the “Bureau d’Enquêtes et d’Analyses” (BEA) on the accident suffered by the Swiftair MD-83 matriculated EC-LTV on July 24th in Mali (find the report here, PDF 5.2MB). The last 1’30” of that flight must have been scary.

Take a look at the records of altitude, attitude, bank angle:

EC-LTV parametres

MD-83 EC-LTV parameters (2014, Mali).

Probably you are familiar with this other graphic that has appeared in the press:

EC-LTV trajectory worked out by BEA from FDR.

EC-LTV trajectory worked out by BEA from FDR.

Today, at lunch while on a training course, I had the chance to discuss about the accident with the course instructor (a retired former Airbus senior vice president in customer services) who pointed me at a similar accident undergone by a MD-82 HK-4374X in Venezuela in August 2005.

I went to the BEA website to check for the report of that other accident (here, PDF 20MB, in Spanish). While the investigation of the EC-LTV will most probably reach to the conclusions of the root causes of the accident, the are many similarities between the cases:

  • Hot weather conditions (ISA+10 or above, that is temperatures not below -30 degrees at FL31),
  • proximity of thunderstorms,
  • use of anti ice (inducing a penalty measured in about 3,000ft penalty for available engine thrust),
  • autopilot engaged in “Speed on Thrust” mode in “Altitude Hold” (making the aircraft pitch upwards when losing speed due to the lack of available power at FL310 due to hot weather and use of anti ice),
  • engine EPR close to maximum values for both engines (followed by a oscillations when the airplane starts to lose speed),
  • …
HK-4374X parametres.

MD-82 HK-4374X parameters (2005, Venezuela).

The report of the 2005 accident included a study from NASA and a presentation by Boeing then chief pilot covering similar incidents and showing a 2002 Boeing Flight Operations Bulletin warning flight crews of this kind of situations.

Boeing Flight Operations Bulletin MD-82-02-02A.

Boeing Flight Operations Bulletin MD-82-02-02A.

I’m looking forward for future reports from the BEA to see what are the findings they reach.

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Airbus vs. Boeing, comparison of market forecasts (2014)

Yesterday, Airbus released the new figures of the 2014-33 Airbus’ Global Market Forecast (GMF, PDF 7.5MB).

In previous years, I have published comparisons of both Airbus’ and Boeing’s forecasts (Current Market Outlook, CMO, PDF 5.3MB). You can find below the update of such comparison with the latest released figures from both companies.

Comparison of Airbus GMF and Boeing CMO 2014-2033.

Comparison of Airbus GMF and Boeing CMO 2014-2033.

Some comments about the comparison:

  • Boeing sees demand for 9% more passenger aircraft (excluding regional a/c) with a 10% more value (excluding freighters). The gap is closing, as in previous years Boeing forecasted up to 14% more aircraft.
  • In relation to last year studies, Airbus has increased demand by ~2,000 aircraft whereas Boeing by ~1,000.
  • Boeing continues to play down A380 niche potential (59% less a/c than Airbus’ GMF). This year, both companies have reduced in about 100 units their forecasted demand for the VLA segment.
  • Both companies’ forecast for the twin aisle segment is nearly identical: 7,260 aircraft. The mix between small and intermediate twins varies, 700 units up and down. However, Boeing’s wide-bodies mix is not to be taken as engraved in stone, see the erratic trend in the last years here.
  • On the other hand, Boeing forecasts about 3,600 single-aisle more than Airbus (the gap has closed in 800 units this year). The largest part of the difference comes in the single-aisles over 175 seats (A321, 737-9).
  • In terms of RPKs (“revenue passenger kilometer”), that is, the number of paying passenger by the distance they are transported, they see a similar future: Airbus forecasts for 2033 ~14.5 RPKs (in trillion) while Boeing forecasts 15.5 RPKs.

The main changes from last year’s forecasts are:

  • Both manufacturers have increased their passenger aircraft forecast, ~2,000 a/c Airbus and 1,000 a/c Boeing,.
  • Both manufacturers have increased the value of RPKs in 2033  (about 5-7%).
  • Both manufacturers have increased the volume (trn$) of the market in these 20 years, about 6.7% Airbus (to 4.4trn$) and 5.7% Boeing (to 4.86trn$) (excluding regionals and freighters).

Some lines to retain from this type of forecasts:

  • Passenger world traffic (RPK) will continue to grow about 4.7% per year (5.0% according to Boeing). This is, doubling every ~15 years.
  • Today there are about 16,855 passenger aircraft around the world (according to Airbus), this number will nearly double in the next 20 years to above 30,555 a/c in 2033 (over 33,000 as seen by Boeing).
  • Most deliveries to go to Asia Pacific, 39% or over 12,200 passenger aircraft
  • Domestic travel in China will be the largest traffic flow in 2033 with over 1,500bn RPK, or 11% of the World’s traffic.
  • Over 12,000 aircraft will be retired to be replaced by more eco-efficient type.
Trips per capita vs. GDP per capita (source: Airbus GMF).

Trips per capita vs. GDP per capita (source: Airbus GMF).

As I do every year, I strongly recommend both documents (GMF and CMO) which provide a wealth of information of market dynamics.

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Patrouille de France, Francazal 2014

Yesterday I wrote about the air show in Francazal last Sunday. I finished that post with the following picture:

La Patrouille de France, beginning of the show.

La Patrouille de France, beginning of the show.

… and this comment:

Other day, I will devote one post just with a video of the Patrouille de France performance.

… enjoy it here:

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Francazal air show 2014

Last Sunday, we attended the “1st meeting aerien” (air show) in Francazal, an initiative launched by the association Des Etoiles et des Ailes. The event, in my opinion, was a success measured by the aircraft it gathered and the audience that came to it, despite some logistics issues that need to be improved for a future edition.

More than 50 aircraft were gathered in Francazal, a small airport South of Toulouse. Most of them took part in the dynamic display, not only in the static one. As we came with the baby, we only spent about 2 hours. Nevertheless, we had time to see the following highlights:

  • The 11th brigade of parachuters jumping from a N2501 Noratlas.
  • The Noratlas itself flying (this model was announced as the only Nord Aviation Noratlas in flying condition in the world today).
  • A Japanese Mitsubishi A6M (Zero) and a North American T-6 Texan chasing each other, memories of WWII.
  • A North American P-51 Mustang flying, for many aficionados one of the most beautiful airplanes.
  • A former Air France DC-3 flying, once a common view, not so nowadays. (a joke a local told me in relation to current AF pilots’ strike: “this might be the only Air France taking off today”, a DC-3 in 2014 ;-)).
  • The “Patrouille de France” from l’Armee de l’Air in action, made up of Alpha Jets.
  • The “Breitling Jet Team” in action, made up of L-39 Albatros.

I wanted to share here some of the pictures and videos we took:

Nord Aviation Noratlas.

Nord Aviation Noratlas.

Nord Aviation Noratlas in static display.

Nord Aviation Noratlas in static display.

Mitshubishi Zero.

Mitsubishi Zero.

North American T-6 Texan

North American T-6 Texan

North American P-51 Mustang taxiing.

North American P-51 Mustang taxiing.

Listen to it here:

North American P-51 Mustan in static display.

North American P-51 Mustang in static display.

Andrea and I posing in front of a DC-3.

Andrea and I posing in front of a DC-3.

DC-3 with engines running.

DC-3 with engines running.

Listen to it here:

… see it taking off here:

… and see it overflying Francazal here:

Boeing PT 18 Stearman

Boeing PT 18 Stearman in static display.

Douglas AD-4 Skyraider in static display.

Douglas AD-4 Skyraider in static display.

The Breitling Jet Team L-39 Albatros.

The Breitling Jet Team L-39 Albatros.

La Patrouille de France, beginning of the show.

La Patrouille de France, beginning of the show.

Other day, I will devote one post just with a video of the Patrouille de France performance.

—

Note: the last time I had attended a show here in Toulouse vicinity was in Muret 2011, you may see the post I wrote then about it.

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Memories of my days in a wind tunnel

Some weeks ago my brother Jaime wrote a couple of posts in his blog about wind tunnels. A first general post in which he described how they work and mentioned some techniques including PIV, and a second post in which he described the acoustic camera.

Master thesis front page.

Master thesis front page.

It happens that, back in 2005, I completed my aeronautical engineering master thesis with a project carried out in a wind tunnel at the Aerospace Institute (Luft- und Raumfahrt) of the RWTH-Aachen. Those two posts brought back some good memories and I thought I could share a couple of them here in the blog. Jaime has worked in a wind tunnel in Audi, and in his posts he included some pictures from other affluent wind tunnels. You will see here the contrast with budgetary constrains lived by universities.

I think that for this post I will be brief in the comments and will focus on sharing some pictures trying to bring you about what we tried to do and how we did it. Directly, from the thesis preface:

This Diplomarbeit is the result of two different experiments. Each one is dealing with different techniques but both share a common aim: the comprehension of the noise generation in the flap-side edge. That is the reason for presenting both experiments in a very similar way in this report, so the reader might see two parallel experiments which final results are analyzed together.

Thus we wanted to measure noise and correlate it with the flow around the flap. How did we measure the noise in the vicinity? “Aha! an acoustic camera!”, and you then remember the arrays of microphones my brother displayed in his post. See here the arrangement we had:

"Acoustic camera".

“Acoustic camera”.

Fancy, isn’t it? Except for which we indeed counted with a single micro, which we had to move to every position of the array and thus repeat long measurements endlessly. 🙂

Aerial view of the experiment.

Aerial view of the experiment.

In the picture above you can see the wing profile with the single micro in the left (to the intrados of the wing).

Once we had made dozens of measurements it was just a question of letting Matlab do the dirty job and plot measurements for each position at different flap deflections…

Measurements.

Noise measurements.

But remember that we wanted not only to measure noise but to correlate it with the flow structure at the flap edge. Let me advance you an image of what we wanted to see:

Vortex structure.

Vortex structure.

How did we make to study the flow? Another of the techniques introduced by Jaime, Particle Image Velocimetry, directly from the Wikipedia:

Particle image velocimetry (PIV) is an optical method of flow visualization […]. It is used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics (…). The fluid with entrained particles is illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied.

[…]

Typical PIV apparatus consists of a camera (…), a strobe or laser with an optical arrangement to limit the physical region illuminated (…), a synchronizer to act as an external trigger for control of the camera and laser, the seeding particles and the fluid under investigation.

Seeding the flow, recording it with a camera, using a laser beam… boy, doesn’t it sound fancy high-tech? Let’s go and describe it.

See a plan of the wind tunnel we used:

Wind tunnel plan.

Wind tunnel plan.

See an schematic of the equipment and connections we used for the experiment, all placed at the open section of the tunnel:

Schematic of the experiment.

Schematic of the experiment.

See exactly where we wanted to shoot at with the laser beam:

Laser

Laser bream.

See from where we recorded the images (camera at the right side of the picture, downstream from the wing):

Our single micro.

Camera.

See in this other graphic a summary of the technique. The laser emits two consecutive pulses which light the seeded particles. The camera records those 2 consecutive images and a dedicated software measures the movement of each particle thus providing the information of the flow.

Schematic of PIV technique.

Schematic of PIV technique.

So far, so good.

However, it happens that this was the first time we were using the technique at the institute and despite of our reading of references it took us some time, trials and finally asking experienced people to pull the right strings. At the beginning we just either saw nothing or blurry images.

Blurry image.

Blurry image.

After days of running the tunnel seeded with oil particles you can imagine the fog we were in:

Oil fog.

Oil fog.

… and what we needed were two consecutive shots of very well-defined particles. In the end we managed to fine tune everything and get the desired results:

Image of particles.

Image of particles.

Once we had the images, we ran all the correlations with the acoustic measurements of our array of one microphone and had all the data to analyze, draw some conclusions, propose some new paths to continue experimenting and with which to write a nice thesis.

All that was left was to clean up the mess at the tunnel:

Cleaning the inside of the wind tunnel.

Cleaning the inside of the wind tunnel.

But, yeah, who’s got a picture of himself between the stator and the rotor of a wind tunnel? 🙂

Me among the vanes of the stator.

Me among the vanes of the stator.

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