Aerodynamics: Rolling Gs

Avweb has an interesting article on ‘Extreme Maneuvering’ about practical applications of the FAA commercial aerobatic maneuvers (chandelles, lazy 8’s, steep spirals) that mentioned “rolling G’s.”

A rolling G occurs when you maneuver an aircraft in more than one axis at a time, causing the airframe or wing to twist. The rolling G design limit is considered to be 2/3 of the normal G limit, according to FAR 23.

Although I performed the commercial maneuvers during my Commercial Airplane practical test and Citabria checkout, I wasn’t really aware of two things:

  1. airframe twisting from rolling G’s can more easily exceed a plane’s load limit. Those limits would be lower in older aircraft, possibly already damaged, than newer ones. It’s important to load the airplane one axis at a time.
  2. the commercial maneuvers can be used to reverse in a box canyon. I know a private pilot who crashed in a box canyon (he luckily survived) because he knew of no course reversal methods, so this is handy to know.



Chandelle (Climbing, Reversing Turn) Animation

Advanced Section

The asymmetric lift, resulting in a torque, caused by the ailerons travelling up and down simultaneously with yawing and pitching maneuvers is believed to have caused several airshow accidents in older airplanes, shearing the wing spar. Contributing factors are the acceleration rate of the control movement, airspeed above maneuvering speed, Va, and wing and fuselage harmonics. Sideslip also affects G limits.

It would be difficult to calculate actual rolling G limits without destroying several aircraft to build a mathematical model. There are a number of reasons for that, but primarily the problem is that dynamic torque must be calculated for multiple types of members, including spars, fuselage skin, and especially attach points. The latter is tricky because attach point hardware may be very strong in one axis, and very weak when loaded off-axis (or corroded.)

pprune.org: Why is Rolling G dangerous?, Normal G limits vs Rolling G limits?
W: Chandelle,
Ice and Tail Stalls

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Ecommerce Weather Report for Manila in 2016

Current consumer ecommerce weather report for Manila in Dec., 2016 …

US ecommerce sites – Just Say No

Manila sellers are wary of Facebook Pages commissions on retail listings, and “meh” on ebay for the same reason. Craigslist is free but doesn’t have any mindshare in Manila.

Southeast-Asian ecommerce sites – Just Say Yes

So they’re going with Lazada, probably #1 in Manila, or Shopee, which is ad-supported, and Carousell or

Shoppee is owned by the Garena Group of Singapore. They have registered country-specific top-level domains (TLDs) for each Asian country supported.

How Shopee works:

  • buyers and sellers download iPhone or Android mobile app or use web site to upload and view listings
  • Shoppee Customer Support, local to each Asian country, approves photos
  • buyers and sellers can apply for free shipping
  • Shoppee shows ad banners for $$$$.

I got a tour of the Shopee office. It’s similar to Silicon Valley start-up offices, but has a staffed reception area. :)

Car Hire

The most popular car apps are Uber and Grab. Riders use car apps because buses and the MRT (train) are inadequate for longer commutes, and unsafe due to petty criminal gangs. Drivers see car apps as a way to pay off their car loan, and to kill time, due to rampant underemployment.

Uber is rumored to have increased Manila traffic by the equivalent of 19,000 cars. Rush hour used to be 7 am to 9 am and 5 pm to 8 pm. Now it’s 6 am to midnite. (In the USA, there have been mixed reports of increased traffic. SF is reported to have problems, while Phoenix less.

Uber passengers used to cancel arriving sub-compact hatchbacks like the Toyota Wigo (MSRP USD$10,000) in favor of sedans, but the Wigo is getting more respect 2 years after market introduction.

Garena’s Shopee could be on its way to beating Carousell in Asia

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Notes for Installing Percona Xtradb Cluster 5.7 on CentOS 5

Percona supports Percona Xtradb Cluster 5.7 on CentOS 6 and CentOS 7, but not CentOS 5.

You can install the RPMs or tarball binary, but on start will see various package dependencies that can’t be resolved on openssl.0.10 and others.

So your options are:

  1. upgrade your OS first to CentOS 6 or 7 64-bit first (recommended)
  2. downgrade and install Percona Xtradb Cluster 5.6 with yum install Percona-XtraDB-Cluster-server-56
  3. not recommended, but if you’re stubborn about clinging to CentOS 5.x and you’re a programmer, you can install Percona Xtradb Cluster 5.7 from source. You will need (at least) cmake 2.8.2+, boost 1.59+, and recommended are gcc 4.4 or clang 3.3.

Here’s the build instructions that compiled for me with gcc 4.1.2:

1. So download and install cmake 2.8.2 or higher from source first:

yum remove cmake
wget --no-check-certificate https://cmake.org/files/v3.7/cmake-3.7.1.tar.gz
tar zxvf - < cmake-3.7.1.tar.gz
cd cmake-3.7.1
./bootstrap && make && make install
cd ..

2. Download and install boost 1.62 from source:

yum remove boost
wget --no-check-certificate https://sourceforge.net/projects/boost/files/latest/download?source=files
yum install p7zip
7za x boost_1_62_0.7z
cd boost_1_62_0
./bootstrap.sh --prefix=/usr/local
./b2 install
cd ..

3. Build Percona-XtraDB-Cluster-5.7 source like this:

wget --no-check-certificate https://www.percona.com/downloads/Percona-Server-5.7/LATEST/source/
cd Percona-XtraDB-Cluster-5.7.16-27.19
# remove new gcc 4.4 flag -Wvla:
# -Wvla
#    Warn if variable length array is used in the code. -Wno-vla will prevent the -pedantic warning of the variable length array. 
perl -i.orig -p -e 's/-Wvla//g' `find . -name maintainer.cmake`
cmake . -DMYSQL_DATADIR=/var/lib/mysql
mv boost_1_59_0 /tmp
# fix the boost and gcc version errors. Just replace with your versions.
vi cmake/os/Linux.cmake +27
vi cmake/boost.cmake +265
# insert 2 "out-of-scope" macros os_compare_and_swap_thread_id and os_compare_and_swap from storage/innobase/include/os0atomic.h into these 2 source files:
vi storage/innobase/lock/lock0lock.cc +1904
vi storage/innobase/trx/trx0trx.cc +204
# define os_compare_and_swap(ptr, old_val, new_val) \
        __sync_bool_compare_and_swap(ptr, old_val, new_val)

#  define os_compare_and_swap_thread_id(ptr, old_val, new_val) \
        os_compare_and_swap(ptr, old_val, new_val)
make -j 8
make test
# the new server is located at sql/mysqld
make install
# note that 5.7 has a new grants schema, so your old database won't work until upgraded
# in /etc/init.d/mysql, bindir=/usr/local
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Star Wars ‘Rogue One’ Review

I don’t often go to the movies, but saw ‘Rogue One’ with a date.

The first half seemed kind of slow and disconnected, dealing with various rebel assassination plots (!) on Jedah and Eadu. Good visuals but weak story-telling.

The protagonist, Jyn Eros, portrayed by Felicity Jones, must be a pretty bad actor to have her mother killed in front of her, yet convey being unsympathetic and uninvolved throughout most of the film – I’d rather watch paint dry.

However, the second half dealing with the invasion and destruction of the Imperial base at Scarif and testing of the Death Star was riveting.

Darth Vader’s brutal but ultimately futile light-saber fight scene at the end will please action fans.

And seeing a youthful Princess Leia at the end receiving the Deathstar plans was a nice surprise.

The rebels’ companion robot, a re-programmed Imperial model named K-2SO, was intelligent and funny enough to be unsettling. Admiral “Fishlips” Raddus a Mon Calamari, also provided comedic distraction.



Admiral “Fishlips” Raddus. Photo Credit: Lucasfilm

W: Rogue One
IMDB: Rogue One
Can we talk about that final Darth Vader scene in Rogue One?
bbc.com: Rogue One is Star Wars for Better and for Worse
Rogue One: Meet Admiral Raddus, thecharacter inspired by Winston Churchill

The story behind Princess Leia’s hairstyle

Keywords: General Fishlips

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Cessna Skycatcher 162 Inventory Crushed

The sorry tale of the Cessna 162 Light Sport Aircraft (LSA) has finally concluded. The remaining 80 airplanes have been crushed with a backhoe outside the the Chinese factory, including the installed engines and avionics.

It’s believed that liability insurance and parts support didn’t pencil out for the accountants. Crushing solved the liability problem, and also any agreements with suppliers like Continental and Garmin prohibiting resale.

Kind of a shame they couldn’t have sold them to the Chinese government for $1 for use in flight training in exchange for indemnity from lawsuits.

Of the original 1,000 projected orders, 200 were actually delivered and 80 crushed.

There were many problems with the 162:

  1. capabilities were Day and Night VFR, not IMC.
  2. 1,320 pounds gross weight only left room for one American after full fuel with this design
  3. flight schools required a separate check-out, even if you had 152 and 172 experience. This involved additional expense and searching for a slender CFI.
  4. price was high for flight schools given the above limitations. The 162 had teething problems, and some owners had to replace the ADHARS twice
  5. assembled in China, unlike most trainers.


Crushing C162 with a Backhoe
Crushing C162 with a Backhoe
Crushing C162 with a Backhoe
Crushing C162 with a Backhoe
Crushing C162 with a Backhoe

Cessna Scraps Unsold Skycatchers
Crushing More Than Airplanes
Skycatcher’s Demise: Barely a Ripple [2013]
W: ADHARS

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