Firebird

I have been flying my modified Friebird IIb, built from the 19″ Firebird parts in the Klutz book Rubber Band Powered Flying Machines. I made several modifications to the Firebird to lighten it, improve the aerodynamics and improve the balance. I gave it the designation IIb. This differs from the II in that I cut down the wing pylon so it sits right on top of the stick. The hook is as far back as it will go, giving 10″ clearance for the motor.

The Firebird IIb has the CG right on top of the stick, looks like right on the thrustline, so no zoom at launch or diving on descent.

I had some good flights and I wanted to get a video. I figured out how to hold the wound up plane in my right hand while starting the video and stopping the prop with the left. I can let go of the prop and launch it quickly when the camera beeps. My first attempt with the Firebird IIb was a bad launch that resulted in a cartwheel and the stick broken right at the front of the wing mount. This was a 9# balsa stick. I replaced it with a 12# stick.

I was flying Thursday morning at Butcher park, which has a larger field than Houge, square rather than rectangular and the wind goes across the diagonal. There was no detectable wind on the ground and there was only very slight, occasional movement of leaves in the tops of the trees. It was still overcast. I started with 850 turns into the 12″ loop of 1/8″motor and did not get a great flight. The lube had dried out, so I relubed it. It came back circling right, so I put in 1 mm of left rudder. Next flight was much better. I went to 950, but lost many from the fresh lube being so slippery. Next I tried 1,050 turns (~85%), losing a few again. I got a good flight that drifted downwind out of sight. It was hard to see the light plastic against the bright overcast sky. When I put the camera down, I saw it descending from the tops of the trees on the far side of the park, visible against the greenery. It landed on the grass just a bit inside the tree line. The video time plus estimated time in the air off camera was more than a minute. I decided to launch from a more upwind location to avoid the downwind trees. This time, it drifted slowly in the opposite direction and found the tallest tree in the neighborhood for its descent. I lost sight of it in the camera viewer. After much searching all around, I finally spotted it high in the tree. The 30′ pole did not even come close. I paced it off; the tree is 70′ tall and the plane is up ~45′ from the ground, too high to reach.

I went home and got a tall ladder, but that did not help either. The ladder was 9 feet high. I can get the tip of the pole up 36 feet above the ground. The plane is conservatively estimated to be 46 feet high. The whole thing would be 1 foot short. I thought, if I could float a foot above the top of the ladder, I might reach. But if I could float a foot above the top of the ladder, I wouldn’t need the ladder or the pole. 😉 I went back every several hours to check on it. It was hard to find and I worried that it had fallen and someone took it home. I forgot to put my phone number on the new stick! The wind later in the afternoon was rocking it slightly and the prop was moving slightly. I suspect it is hanging from the tailplane. It was still there when I last checked at 7 PM.

I plan to post a build so other adventurous folks can give it a shot. With a 2X motor on full winds, it might get two minutes, but I would need twice the field for that.

The nice thing is the pleasing flight pattern. It makes a slow, steady climb, cruises several circuits of the field, then a slow steady descent. There were still a few turns left on the motor when I picked it up.

The attached video shows it on 850 turns with dry lube. You can see how it gets lost against the bright sky. Maybe the next one will have the surfaces put on upside down for better viability.

I also got a short video of the Cloud Tramp, but after losing the Firebird, I did not want to push my luck. I flew it on the flat part of the torque curve. Even then, it landed just a few feet short of the far fence.

Friday I wrestled my grandfather’s 14 foot, 57 pound, extensible house painters ladder down out of the attic, loaded it into the car with a red handkerchief tied to the end of the 6 feet that stick out the back and took it over to the park. I had to move three bicycles and a bike stand down from the attic first. Getting it out is quite a struggle, because there is exactly one narrow alignment that it must be threaded through, 8 feet off the floor, to get it out. Over at the park I carried the ladder and pole over to the tree and tried to figure out my setup. I found a couple places near the trunk, looking up through the branches, where I could barely see part of the yellow propeller. Later in the afternoon, with the sun shining on it, and with the zoom lens, I got a better view.

(A little below and left of center.)

Unfortunately, I would be at the top of a tall ladder, holding a long, heavy pole over my head, probably with both hands, looking directly into the sun, trying to thread the pole through a maze of branches to a target I could barely see and might not be able to move. I already have a kink in my neck from watching the Perseids the night before. I considered that it would be quicker and easier to build another one, not to mention much safer. So I brought everything back home. I will check from time to time to see if it has moved to a more accessible place. A new one will include a couple minor improvements. My only regret is that this is made from one of the first production models from my first copy of the book. But I’d rather fly my planes than put them in a museum.

I posted the Klutz RBPFM Postal Contest here:

http://www.oaklandclouddusters.org/Default.aspx?pageId=739983

Gary