Thursday, December 22, 2011

Chipsair 2

Update of the first Chipsair that crashed due to unknown reasons.
Just lost it while spinning, maybe because the battery voltage dropped too far while tossing it around. Hence this one has a voltage display...

Update was build in very similar way to the first Chipsair but possibly a little stronger: Extra thin ply in the elevator, added bracing in the aft of the fuselage.

 Wingspan 1.58 m Wing Area 36.34 dm2 Tail 50 cm Tail Area 6 dm2 Weight 2012 g Wing Loading 55 g/dm2 Length 1.1 m Airfoil Eppler E197 Engine OS MAX 46 LA (blue)

First flight on December 22, 2011, where I noticed at the field that the aileron hinges where actually not glued in, yet! So for the first flight scotch tape held them in place, and I tried to avoid aileron use to keep them attached to the wing.

The pictures also still show the push-pins on the windshield because I'm not sure if the glue is 100% dry.

This might have been the last plane where I could use the Pacer ZAP hinge glue that seems to become unobtainable.

Overall it flies GREAT. Plenty power, plenty authority from aileron and elevator, which I had worried about. Very nice and slow landings, while on the other hand endless loops and quite some vertical performance.

Friday, September 9, 2011

JDBC 'commit' even for SELECT

You probably knew this, but a 'commit' can even be necessary for SELECT calls that don't change any data.

After calling JDBC Connection.setAutoCommit(true)), every JDBC call, be it SELECT, INSERT, UPDATE, DELETE starts a transaction that needs to be ended with a commit (or rollback).

This might be obvious for a sequence of INSERT or UPDATE calls that change data, and you want a final commit() to perform an atomic update.

With a SELECT, the update is necessary to avoid the following situation:
1. Calling SELECT to fetch something. That starts a Transaction!
2. Now somebody else changes the data.
3. You call SELECT again to get the 'latest', but since you're still in the original Transaction, you get the same old data as in step 1.
If you have other code that changes the data and happens to call commit() before you reach step 3, all will look OK, but to be sure that you end the original reading transaction and always get the 'latest' data in a later read, it has to be done like this:
1. SELECT, commit()
2. Now the data might change.
3. If you later need to fetch the 'latest', again SELECT and commit()

Tuesday, September 6, 2011

RAOTA - What an idea!

Rest Areas on the Air, starting on Nov. 23, 2011:

Map http://www.tdot.state.tn.us/maintenance/restareas.htm mentions "2 hour parking limit":

Sunday, August 28, 2011

Dandy E205

This is not about a high-performance sailplane but about building something that you knew about maybe 30 years ago...

Graupner used to have a glider kit called "Dandy". I found a new-old-stock Dandy kit offered on eBay, but it went for what I considered way too much. So I decided to build something similar to the Dandy, and luckily found the web site http://www.koralpe.biz/dandy.html which has nice pictures of the original kit and a plane built from it.
Finally, the "glider" should have an electric motor because using a high-start is somewhat cumbersome. The motor and prop combination was determined by trying various things in online motor calculators and by comparing with off-the-shelf models of similar wingspan, weight and type.

Wingspan 170cm 105cm E205 E193, 50 x 11cm 39.1 dm2 1156g 29.6g/dm2 Optima Extra Black Turnigy C3530-1100, Kv1075, 73g, 15A Max, later MVVS 10 2/1120 9x5 Folding Prop 25A max 2200mAh 3S LiPo

The center of gravity came out somewhat too far in the back unless two batteries are packed into the front of the plane. The total weight of about 1.2kg includes the two batteries and radio gear. The original plane had a slightly smaller wingspan, weight of 1.0kg, and a wing loading of 16-29g/dm2.

First flight was on the morning of August 28, 2011. Two brief flights before breakfast. It flies nicely! I was surprised how slow. Current draw is 13A at full power, and about 5A when cruising around.

--

17 July 2016: Axis of Turnigy snapped off (!) during climbout. Managed to land ok, but prop vanished in the woods.
Replaced with MVVS 10 2/1120. On summer evenings using about 400 mAh for 10 minute flight.

Tuesday, August 16, 2011

Oracle JDBC Version Woes

Ran into a strange Oracle error today in a Tomcat program.
The code ran fine in two other Tomcat instances, but failed in a third one.
The error happened to be
ORA-03115: unsupported network datatype or representation
which basically means: There is a version mismatch between the database and the JDBC library.

Reason
That Tomcat instance had a copy of ojdbc14.jar in its lib/ subdirectory that was used instead of the ojdbc14.jar included in the application's *.war file.

Unfortunately it is hard to tell the version of an ojdbc14.jar from the outside.

Possible Solutions
1. Unzip the ojdbc14.jar and check its manifest file.
2. Get the version programmatically
The latter can for example be displayed on some 'internal' web page of your application:

Connection connection = ...;

out.append(...md.getDriverName() + " " + md.getDriverVersion() ...);

That way it is possible at runtime to check which version you are actually using.

Moral
Don't put *.jar files in the Tomcat lib/ directory. Include them in the *.war file.
Yes, this way you might load multiple copies, one for each *.war, but that beats later wating time to debug an app that suddenly stops working because some Tomcat instance has the wrong *.jar in its lib/ directory.

Saturday, August 13, 2011

Mercurial seems to hang in SourceForge connection because of host key change

Had a problem where mercurial seemed to hang forever in a SourceForge transaction.
It was run from within Eclipse via MercurialEclipse, and there was no indication as to
what's happening nor any way to stop it other than to kill Eclipse.

This was under Windows with hg calling putty, which in turn was configured to use an ssh key pair registered with SourceForge that had worked OK some time ago.

When executing hg from the command line, it would also hang, but I could stop it with Control-C, and then it would show the following message:

hg clone ssh://name@....hg.sourceforge.net/hgroot/....
interrupted!
remote: The server's host key is not cached in the registry. You
remote: have no guarantee that the server is the computer you
remote: think it is.
remote: The server's rsa2 key fingerprint is:
remote: ssh-rsa 2048 86:7b:1b:12:85:35:8a:b7:98:b6:d2:97:5e:96:58:1d
remote: If you trust this host, enter "y" to add the key to
remote: PuTTY's cache and carry on connecting.
remote: If you want to carry on connecting just once, without
remote: adding the key to the cache, enter "n".
remote: If you do not trust this host, press Return to abandon the
remote: connection.
remote: Store key in cache? (y/n) ^C

Again this was under Windows. On a real operating system the host key change prompt might have appeared before the Ctrl-C and thus be more obvious.

Anyway, the fix:

Run
putty -i path\to\the\key.ppk
once which will show the same host key change prompt and this time you can accept it.

From then on, hg works OK again.

Friday, July 29, 2011

JG1XHO

First signal from JG1XHO-7 from a Pizza place.

When zooming in, you can almost tell which table in the restaurant.

Next morning visited Rocket Radio in Akihabara to get parts for Dipole.

Friday, July 15, 2011

Change Eclipse plugin_customization.ini via feature

Eclipse has an elaborate hierarchical preference mechanism:
• Plugins have a preferences.ini.
• The product can override the settings of any plugin via a plugin_customization.ini file
• Finally you can provide your own defaults via a command-line option -pluginCustomization /path/to/my/settings.ini.
When you create products, you typically include a plugin_customization.ini file in your product.

What if you need to create products with different settings?

Can you put the plugin_customization.ini file into fragments for your product plugin? That doesn't work. Plugin customization.ini files in fragments seem to be ignored.

But here's what you can do: Fake localization.

In your product plugin, have a plugin_customization.ini file that looks like this:

some.plugin/some_setting=%some_value

Then, in a fragment of the product plugin, place a plugin_customization.properties file that contains

some_value=Value A

In another fragment, you can have

some_value=Value B

By loading the appropriate fragments, for example from an update site, you can now install the settings that you want!

Friday, May 20, 2011

Associative JavaScript Arrays by Numeric 'ID'

I needed to keep browser-side information about certain objects by numeric ID.
When using an associative JavaScript array like this:

you will find that it creates an array with (mostly empty) elements gadgets[0] to gadgets[4711].
On the other hand, when initializing the array like this:

it creates a single element in an associative container. Once created, you can access such elements with either gadgets[4711] or gatgets['4711']!

Friday, March 11, 2011

Belkin Play B600 Duplicate IP Address Problem

I have a cable modem internet connection that's shared by several computers at home via a Belkin wireless router. A Windows Vista PC is actually wired to the router, the other computers are on a WLAN.

The router is at http://192.168.2.1/. The wired PC is usually at 192.168.2.2. Other wireless devices get addresses like 192.168.2.3, 192.168.2.9 etc., meaning: Everything is on the same subnet, contrary to my previous wireless router that used different subnets for the wired and wireless devices.

Sometimes the wired PC reports a duplicate IP address error. The "easiest" fix seems to be:
1. Power the PC down
2. Power-cycle the wireless router
3. Start the PC back up

Thursday, March 10, 2011

"Portable" Eclipse Projects

When you create a new Eclipse 'Plug-in' project, its initial configuration will lock to your current JRE and compiler settings.
When you then share that project with other people, they will see compiler errors because you may have used Java 1.6_19 on Linux while they use Java 1.6_20 on Windows.

To make your project more portable, do this:

1. In the Package Explorer, right-click on your Plug-in Project and select "Properties"
2. Under "Java Build Path", select tab "Libraries", item "JRE System Library", button "Edit". It should default to a specific "Execution environment" like "JavaSE1-6 (MacOS X 1.6.0 System). Change that to "Workspace default JRE", meaning: Use whatever the developer has configured in her workspace.
3. Under "Java Compiler", by default "Enable project specific settings" will be checked. Uncheck that, meaning: Use the compiler settings that the developer has selected in her workspace.
4. When you now switch to the Navigator view, you should find that the ".settings" directory that previously contained project-specific compiler settings is now empty. You can delete it.
After these steps, developers on other operating systems with slightly different java versions will have fever problems when they try to use your Plug-in source. Your MANIFEST.MF can still require a certain execution environment, so you are not loosing much control.

Wednesday, March 2, 2011

In a setup where Hudson polls CVS for updates I ended up in a situation where newly added directories were ignored, and thus Hudson did not trigger a re-build of the product.

The Hudson "CVS Polling Log" looked like this:

[workspace] \$ cvs -q -z0 -n update -PdC -D "Wednesday, March 2, 2011 3:51:38 PM UTC"cvs update: New directory .....' -- ignored

The fix was to delete everything inside the "workspace" directory. On the next Hudson run, it performed a complete cvs checkout and that included all changes.

Friday, February 11, 2011

Java Audio, FreeTTS "LINE UNAVAILABLE" Error

A program based on FreeTTS, the free text-to-speech engine for Java, was getting occasional errors
"LINE UNAVAILABLE: Format is ..."
The reason was later found in the KDE desktop: Its configuration panel has options to keep the audio device open for some time after playing beeps or other desktop sounds. The default seemed to be rather high at 60 seconds. But even after changing that to only 2 seconds, the FreeTTS library still needs to compete with some occasional other users of the audio devices.
Turns out there is no Java Exception or other mechanism to detect this error that occurs inside the FreeTTS library. All you get is the message on System.out, so there is no good way to react programatically.

Workaround: Configure the FreeTTS audio player to attempt accessing the audio device more than once until it succeeds. In this example, a short delay of 0.1 seconds is used to not miss an opportunity to grab the audio device; we keep trying for 30 seconds:
System.setProperty("com.sun.speech.freetts.audio.AudioPlayer.openFailDelayMs", "100");System.setProperty("com.sun.speech.freetts.audio.AudioPlayer.totalOpenFailDelayMs", "30000");
If the audio device is permanently used by another program, there is of course no way to get access. Under Linux, this command will display the ID of the process that is currently holding the audio device, so you can then try to get rid of the offending program:
  /sbin/fuser /dev/dsp

Tuesday, January 18, 2011

Eclipse Build Path Problem After Mac OS X Java Update

In early January 2011, I received a Mac OS X Software Update that included Java changes.
This was on a Mac that had been upgraded to Snow Leopard, so older Java setups were still present, but this update must have removed older JVMs and JDKs.

As a result, Eclipse builds would fail with this error:
The container 'JRE System Library [J2SE-1.5]' references non existing library '/System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Classes/laf.jar'
In general, the OS X Java setup changed from using
/System/Library/Frameworks/Java.VM.framework/Versions/...
to using a path like
 /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

After going to Eclipse/Preferences/Java/Installed JREs and "Add..."ing a new JVM that uses the above path with ".../JavaVirtualMachines/..." all is fine again. You might have to look for the full path to that .../Home in a terminal window and copy/paste it into the Eclipse preference dialog, because the "Browse" button in the dialog might only show the 1.6.0.jdk as a package, not as a subdirectory into which you can drill down.

Next issue: You might not have a src.jar in that JDK to be able to view the Java sources, so you cannot view the source code for String, Map, ... and the other standard Java classes. That's because the default JDK is really more like a JRE.

After downloading the Java Development package from the Apple Developer Connection, something like javadeveloper_10.6_10m3261.dmg, you get a new JDK in

/Library/Java/JavaVirtualMachines/1.6.0_22-b04-307.jdk

and that one has a Content/Home/src.jar`.
Note that the JDK that you install yourself, the one that includes the sources, is under /Library/Java/... while the Java stuff that comes with the OS is under /System/Library/Java/...

Eclipse should automatically detect the src.jar in the JDK that you install.

Note on finding the Java Development package as of August 2011:
• http://developer.apple.com/
• Member Center
• Dev Centers: Mac
• Resources
• Java
• Java for Mac OS X ... Developer ...

Friday, January 14, 2011

When installing the Eclipse IDE for RCP development, it includes the Draw2D and GEF binaries, but not the sources. At least not in the Mac OS X version for Eclipse 3.5 and 3.6(.1).

How to get them: Also download the "Modeling" version of the IDE, and copy the following plugins from that into your RCP IDE's plugins directory:
• org.eclipse.draw2d.doc.*.jar
• org.eclipse.draw2d.source_*.jar
• org.eclipse.gef.doc.*.jar
Yes, this contradicts everything you ever learned about P2, but it seemed the simplest way to get the sources & help.