The life and death of another plank - RC Groups
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Dec 16, 2007, 05:22 PM
agony sweetns the victory
atjurhs's Avatar

The life and death of another plank

Well here blogs the final flight of a plank that I've spent way too much time and energy on. I learned a few things from her, and hopefully others can learn from my mistakes......

This plank began it's life as a 52inch Spade that I waaaaaay overbuilt crushing the scales as a Welter-Weight at 3.5lbs. I actually flew her one or two times at this weight, but even with 25mph winds she sucked. So I thought, I'll improve her wingloading by adding 20inches of span, bringing her to a 72inch (Skua looking) Extended Spade. Trouble is when I added 20inches of foam I also added 1.5lbs in goop and strapping tape and spars, etc. etc.. The the plank in the first pics comes in as a Heavy-Weight at 5lbs.

Well I used whatever CG calc programs I could dig up on the net, and took my best shot at the CG. Then yesterday, I took her out to an open field and added 6oz. to the nose, and bungee launched her. With full up-elevator she skidded across the field never gaining an inch of altitude. So on the second launch I removed 3oz. and let her rip again. This was an improvement because she flew level but with full back-stick. So I removed the last 3oz. of additional weight (bringing her to where the CG calcs said she should be, and this time she climbed a bit and flew level with 1/2 back-stick. "Good enough to take her to the slope", so I thought. BTW, on each of these bungee launches, once she started loosing airspeed she would nose-in quickly.

Well today we had epic winds (well at least for these neck of the woods/quarry) of 20-30mph on the ground, and probably much higher atop the rocks. So it was time to belly-up to the bar (or slope, or both, or whatever we call this place) and give her a throw. No way! She wouldn't have a chance to get up to speed from a hand throw. Remember this girl is a "manly girl" (that needed a shave) chrushing the scales at 5lbs. and 72inches and no pod beneath the wing to use to throw. Even Arnold Shwarzie would have a tough time! So we got out thee bungee again (thanks Dave for talking me into it), and staked it into the slope. Pulled her back and measured 20lbs. of force. That's 4 times this plank's weight. That ought to get her out there and into the lift band, so with a mighty heave-ho my mate let her rip. Clearing the slope's burm by 6 or 7 inches out she went, and she started to climb a little and I thought I was in good shape, but the better lift was more to my right, so I turned her into the wind and headed that-a-way. Trouble is, she kept turning in the same direction, and didn't want to turn back. So at some point I thought, "well no sense fighting Mother Nature" I'll just keep the turn going. Trouble is it was a down-wind turn and once she lost her airspeed, just like the day before at the flat field she nosed-in and quickly dove. So I thought I'll let her dive and regain her airspeed, then I can pull up a bit, and hopefully not have such a long climb down the quarry's slope. Not a bad plan, and it sort of worked, but as soon as her airspeed dropped back down, she did the death-spiral, and it was still a looooong climb down, and an even longer climb back up, but I'm used to making that trip The whole flight last about 20-30 seconds

I had hoped to add a bit of tail weight and get another go at it, but, well look at the pics

She is definetly repairable, but why? She already weighs waaaaaay too much, and that's only going to get worse, and our slope conditions only give us these kinds of conditions (did I mention it was about 33degrees, not including a wind chill factor) about two or three times a season. Time to cut my losses and rip out her guts and built another plank that's lighter. The rest of the day we flew the JW and the Mig3. the King of this slope is the JW (well, really Dave's JW). It really is hard to beat the JW for the rough and turbulent flying (and landing) conditions that we get up on this pile of rocks.
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Dec 16, 2007, 06:28 PM
Plane dodger
KillerAir's Avatar
It might help to have a control surface in the center that acts as an elevator. The spread of the elevaons seams pretty extreme to me. Put her back together, what have you got to lose.

Dec 16, 2007, 07:35 PM
Registered User
Chief High Horse's Avatar
I normally have a throttle to elevator mix set at 2% to 3% it gives me a fine tuning lever for trim. On maiden flights I set the mix at 25% then the throttle stick becomes a mega trim lever, try it, you'll like it.
Dec 17, 2007, 12:20 PM
agony sweetns the victory
atjurhs's Avatar
Yep, I too mix my throttle with my elevator at around 5%, but I never thought of increasing it to 25% for maiden flights, great idea!
Dec 18, 2007, 12:51 PM
Rejisterd Youzer
SU Jags's Avatar
Hey Todd,

Too bad about your Spade (or whatever it morphed into ), you worked on that thing for a while. Just replace it with something that can knock Dave's JW around. My slope'n days are prolly behind be now (yep I move to the middle of the Appalachians/Blue Ridge and NO SLOPES ) so that Beetle that I built is collecting dust. Oh well, the quarry was fun while it lasted.

Dec 20, 2007, 01:25 PM
agony sweetns the victory
atjurhs's Avatar
Hey Wallace great to here from you!

I got my own JW to beat the heck out of Dave's, but actually the two have not YET met in the skies. Oh Dave...... it's time for their introduction

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