Dave Smith's Blog

Well, I upgraded my L-39 jet’s motor and re-maidened it. I don’t want to give away the ending but it wasn’t pretty. The new motor was fantastic. It bolted in with no modifications to the plane, and provided lots of thrust over the stock motor. It was great.

The added thrust helped control the plane. Without it, I would have been toast out of the gates (like last time). The take off was uneventful other than the 90 degree right roll on launch and the first turn which almost crash landed the plane right into the adjacent road. Yikes! Here’s the video:

Everything was going okay, but it was extremely twitchy and stall happy. I think it’s too heavy, cause I was fighting to keep it aloft the whole time. I held my own for a few minutes, and then the low-voltage cut off kicked in. The motor must have been pulling more juice than I realized. I was up wind, which was a problem because the wind was blowing at about 10-15mph. Nevertheless, I managed to bring it in for a nice soft landing. Well, “soft” is relative. The plane touched down at the same spot where the only obstacle in the whole park was sitting: a sideways metal pole. Oops. Here’s the video and crash site photo:

You can’t tell very well from the pic but both the wing and horizontal stabilizer are bent, because they went under the poll while the rest of the plane went over it. Not pretty.

Oh well. Live and learn. My battery was badly puffed (due to the low voltage and high amp draw I’m sure), but it subsided back to normal. Not sure if I trust it for another flight yet, but I will definitely be keeping it in an ammo box and carefully monitoring its voltage before I use it again.

Thanks Cliff for filming!

After nearly one year and hundreds of flights, it’s finally time to retire the F27C Stryker R/C plane. This wasn’t necessitated by the plane or a crash, but rather my stupid attempt at modifying the airfoil to get it to roll faster. I learned the hard way that I am not an aeronautical engineer. The Stryker has been a great plane. It outlived two motors and at least 4 devastating crashes. Until I modified the wing, it flew like new. Here are some pictures to commemorate its service:

Elliot loves this plane, especially now that he can toss it around and see it flip and flop:

This is one beat-up airplane. The motor mount area of the foam got ripped out several times, and repaired very easily. The roughed up underside is due to all the concrete landings it endured behind my office building:

Here’s Elliot giving it one last throw to the ground:

I noticed that the wing tips are very rubbery and soft after all the flexing I must have put it through flying it at 70mph. What a great plane.

A moment of silence please.

That is all.

Lots of the spam I get uses the Cyrillic alphabet. I believe it’s Russian. I don’t correspond with anyone using the Cyrillic alphabet, so I’ve come up with a procmail recipe to filter this email out. But first some background.

It seems that the subject lines of many (all?) Cyrillic emails look something like this:

Subject: =?koi8-r?B?7e/06ffh4+nxIPTy9eTh?=

Which appears like this in your email reader:

МОТИВАЦИЯ ТРУДА

The “KOI8-R” you see in the above Subject line refers to a popular Cyrillic encoding and indicates to the mail client that the rest of the text is thusly encoded. For more info, Wikipedia has a nice article on KOI8-R. There is another encoding, called windows-1251 that is also used to encode Cyrillic, albeit less commonly than KOI8-R.

To filter out these messages, I added two super simple procmail recipes to my .procmailrc file:

:0:
* Subject:.*koi8-r
$HOME/Maildir/.crap/

:0:
* Subject:.*windows-1251
$HOME/Maildir/.crap/

Keep in mind that for these recipes to work, the Cyrillic stuff has to appear in the email subject, which most of my spam seems to do. I haven’t done extensive testing, but will let this run for the coming weeks and report how it worked.

One word: crash.

I put a heavy battery in my new L-39 jet, knowing that I would eventually upgrade to a beefier motor that could make the thrust I’d need to move the heavier battery around. I was confident that it would fly stock, even with the heavier battery, because I had seen this video of it flying with my same battery on the stock motor.

I launched it three times, and the first two times it hit the deck about 20 feet out. You’d think I’d be smart enough to quit then, but I figured I just wasn’t throwing it hard enough. So I got a running start, and gave it a good solid chuck. I got my fingers to the elevator stick just in time to pull it up and out. It flew great. Did some big long circuits on low rates. Then I went for the gusto, flipped to high rates, and pumped out a wicked fast roll. This thing rolls fast! Very nice! However, coming out of the roll, a wing dipped. I think I must have been dangerously close to the stall speed. I couldn’t recover in time and it went full throttle into the ground. Elevator was ineffective, and it was all I could do to keep the wings level as it went in. Thinking back, I should have lowered the nose to gain some air speed. These jets are very different animals since there’s no prop wash over the control surfaces to help direct the plane. I mean, there really is no prop wash at all. All control authority comes from air speed.

Damage Report:

The left wing broke and fuselage broke. But never fear. I’ve already repaired it, and I have my new motor on order.

This time I’ll wait until the new motor arrives before I try any hot shot stuff.

Here’s the flight video. Please forgive all my “dang it”s after the crash. I was a little upset, needlessly so, of course. I was fine afterwards. The whole plane only cost $99 (including fan and motor), so hey, it’s easy and cheap to repair.

My good friend Cliff (a.k.a., Darth Elevator), strapped a digital video camera to his Slow Stick airplane this week and filmed me flying Randy’s Stryker around. The video captures both the Stryker take off and landing, and lots of crazy stunts. After seeing myself fly it from this angle, I’m surprised Randy lets me fly it at all. The video has been edited down to only include the shots where the Stryker is visible on camera. Here’s the video:

Spring is in the air in Salt Lake City, so it’s finally warm enough to get back into R/C flying. To that end, I ordered the new Electrifly L-39 electric ducted fan (EDF) jet. It’s getting great reviews, and I’m excited to fly it. I’ve read that the stock brushless motor is underpowered, so I’m looking into motor upgrades. I’m considering the HXT 2040 4850kv from HobbyCity.com, which ought to be a bolt-on replacement for the Ammo 3500 inrunner the plane comes with, but I’m worried it won’t give an appreciable power boost.

Stay tuned for more info, but in the mean time, check out this video of the L-39 flying with a pair of F-27 Strykers (which I have also built and flown, if you follow this blog):

And here’s the official Electrifly advertisement for the L-39: