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Build Log
PsiClone1
A new build is on the bench. Its inspiration is Uwe Heuer's "Strong Mini Slim", featured in a few videos on the High Aspect Ratio Plank thread started by HerkS, Report #132. This is the first double-taper plank I've tried, and I've followed the SMS planform of an untapered center section with tapered tip sections. The SMS has an aspect ratio of 15 (I think), while the PsiClone's is 11.
The goals for the PsiClone design are: 1) Go fast and turn quick. My dream is to be able to keep up with flying buddy Chris when we get into impromptu "pylon" races and he's flying a molded ship. The Max Plank got pretty close a couple of times before I got scared about damaging a friend's expensive plane, or made a wild turn. 2) Build in less than 20 hours and cost less than $100 in materials. 3) Resist damage and repair quickly. 4) Handle sweetly... no bad habits on slow landing approaches. 5) Be able to build to a wing loading from 9 to 15 oz/square foot (30 to 50 gm/dm2). 6) Control surfaces: elevons only. Dimensions: Span: 72" (1.8m) Area: 470 sq in (30 dm2) LOA: 24" to 30" Airfoils: Peter Wick Rennbrett 1 (root) and 3 (tip). I believe Uwe used 1/64" plywood underlain by carbon cloth in his construction. I'm using 1/32" plywood for the skins, simply because it is less expensive than 1/64" ply. In 12" x 24" sheets it is less expensive than 48" sheets, so the planform dimensions are set to three 24" panels. The spar will be made up from 1 x 12mm carbon fiber strips with additional tow in high stress areas. Thus far, the nearly-complete fuselage, fin, wing skins, spars and radio gear weigh 28 oz. This indicates that a fiberglass or carbon fiber skin could be added on top of the ply skins without getting too heavy. It also indicates that a lightweight build could be done for electric power. Photos to follow as progress is made. I look forward to your comments! |
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A note on using 1/32" ply sheeting: you'd better love sandpaper! After a LOT of careful sanding on the TE's, they still don't match the profiles accurately. The next iteration will use foam + aluminum sheet molds.
The weight is heading toward 12 oz/ft, which is fine for most of the conditions here. I punched a LOT of peck-holes in the foam, and the epoxy did soak part of the way into them, but still, the plywood-blue foam bond leaves a lot to be desired. I have to wonder if a generous layer of epoxy would penetrate into EPP foam enough to harden it in the area of the TE. The skin-foam bond would be very strong. A CF spar could provide all the bending load strength necessary. So many ideas, so few days... |
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Inch by inch closer to the maiden. Got a little carried away with cosmetics, but it will be easy to find in a field.
Solder up the servos, install hold-down screws, balance, and off to the slope... winds permitting. |
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Finally, a chance to fly! Winds were 10-15 kts, nearly cloudless sky, and Mexican Ridge: 3/4 mile long with 300 feet of relief. Not true alpine soaring, but lots of thermals to play with and the possibility to fly to limit of visibility in all directions... except downwind from the ridge!
The weight came to 42 oz, so wing loading is 11 oz/sq ft, and using a 3% static margin for starting balance point, the plane launched out of hand and never stopped for 45 minutes, until I was scratching for lift close to the ridge, got too far away, and the brown plywood disappeared into the brown grass: I caught a wing tip. Bang! But only small damage to the wing tip, so no sorrow. Uwe, your videos were the inspiration for me to explore higher aspect ratio planks and more accurate building methods. Thank you! The results are fantastic: it fulfills all the design objectives of the first posting. A few improvements can be made: 1/32" plywood is a fine skin material, but it needs something between the foam and wood to keep the wood from tearing on impacts. I may try hemp cloth on the next version, possibly with 1/64" ply, but 1/32" is much less expensive, and the weight is not too much for slope/thermal soaring. The weak link in the construction is the bond between foam and skin. I will try EPP cores on the next build. EPP has a much higher tearing strength, and I think its compressibility will not be a problem with the ply skin. The Peter Wick Strak airfoils he designed for the Amokka are excellent: efficient at high speeds, but I could slow down with full up elevator before the PsiClone started to hyperstall, and had only minor loss of roll control. The PsiClone uses only the Strak 1 on the inner panel, tapering to Strak 3 at the tips. There was some distortion of the airfoil near the trailing edge, which can be improved with better foam-cutting and plywood-sanding in the future. The trailing edge is very thin, so the elevons needed 1/8" carbon fiber rod set into their leading edges to resist twisting. The leading edge can be made stronger. There was a small break in the leading edge which caused the plywood to tear at the corners of the servo cutout. The next version will put the cutout on the bottom surface, and the leading edge and servo cutouts will be better reinforced. There is no level place to land a glider at Mexican Ridge, other than all the way to the bottom of the hill. I could not try landing the PsiClone on the slope because of the wingtip hit, but the Max Plank handles much the same. It took some time to reduce both altitude and speed, and finally it slowed enough to pull up close to stall on the slope, and it dropped onto the hard ground with no drama. No long walk down and back up! to be continued... |
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Death and destruction at Moon Creek! Chris, Mike and I drove up to Moon Creek on Wednesday for one more last Farewell to Summer before the snow arrived yesterday. The wind was straight on to the upper ledge, so I strapped on my bike helmet with the old camera, picked up the PsiClone, walked to the edge of the cliff, and the wind nearly tore it out of my hand. Being distracted by thoughts of keeping the wing in the middle of my field of view, I wasn't thinking about wind direction: straight on to the cliff, but nearly straight up, very little horizontal within the compression zone. That meant zero airspeed. On the launch, the wind pulled the wing out of my had before I could give it much forward speed, and the PsiClone naturally stalled and dove onto the rocks 40 feet below. Even in the howling wind, I could hear the crash. Sigh.
So on to more building: after playing with several planform variations and getting good advice from Larrikin in Australia and Peter Wick in Denmark, I feel truly globally connected! The Rubicon (a DS speed machine) and the Amokka 2 (F3F pylon racer) are both molded designs, though with different internal constructions. The PsiClone handled really well and covered a lot of sky, so I'll focus on better construction methods for the next one. It will have slightly more taper at the tips but otherwise the same planform as PsiClone 1. PsiClone 1 used Peter's airfoils from the Amokka, which are more adapted to the Amokka's planform and high-load pylon turnarounds. PsiClone 2 will have Peter's airfoils from the 3 Meter front-side slope wing, which are more adapted to fast slope-thermal cruising. They are also THIN, which means I will be focusing on getting the airfoil correct while not losing too much strength. The PsiClone 2 will stretch out to 2 meters/80 inches, which will still fit in many cars from back window to windscreen in one piece. Simplicity and low cost will be guiding parameters. It will be an interesting winter. |
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Last edited by EdSoars; Oct 25, 2019 at 11:02 AM.
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And I still plan to get some video, but it will be a new PsiClone and someone else at the camera!
Always better to wreck your planes at the end of the flying season and the start of the building season. Snow is on the ground and the heater is on in the shop. I'll be applying elbow grease too! |
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