Last week, I brought my SkyRay 35 home from the field in a really small bag. I want to build another one from my plans and would like any advice regarding size of balsa to use, doublers, etc. I plan to use an O.S. 25 and this one will be for learning to fly the basics, i.e. inverted, loops etc.
I am still amazed at the value of this forum and appreciate all your generosity with expertise and patience.
Excellent plan! I did this, too, after the stock kit version got crashed at a Stunt Clinic. That was the same crash where Jim "Circle Jerk" Goss shredded his fingers trying grab the lines and save it. Let me guess, the stock plywood wing shattered completely, right?
What I recommend is this - the stock fuse is OK as is. Actually, it's exceptionally good and will even stand up to a Fox. The only real improvement might be to slip an extended 1/64 ply doubler that goes to an elliptical end about an inch and a half or so behind the trailing edge, then use a stock-like 1/16 ply tripler over that. That would keep it from breaking right at the TE like yours probably did. The tail feathers should be fine as is. I added 1/2" to the TE of the elevator but I am not sure that it made a huge difference. The tail volume is adequate as is (since it doesn't have flaps). Make sure you have NO, repeat NO, rudder offset (either way).
For the wing, the stock airfoil shape is perfectly OK as it is. I rebuilt the wing with all-balsa parts. I used soft 3/32 ribs with a 3" rib spacing and left half-ribs in-between, so there were full ribs every 6" and half ribs in-between. I would recommend instead that you either use full ribs at each station, or leave the full ribs 6" apart and instead use two half-ribs in between each one. That will keep the airfoil shape a lot better than a 3" spacing. Use a medium balsa 1/2" square LE just like the stocker. The TE is mostly stock but I put shear webs in it between the ribs. Actually I built the TE separately flat on the board, complete with the webbing, and left gaps where the ribs go. I then just glued it on as a single piece with the wing and spars pinned down.
For spars, I used medium 1/8x1/2 set vertically. That has proven to be pretty durable but is also (or because it is) quite flexible. I can see tremendous dihedral in hard corners or even in round loops when it's windy. I really didn't think much about it when I did it since it crashed on a Sunday and was rebuilt and ready-to-fly again on Tuesday, the 1/8x1/2" spars I probably wouldn't repeat after having maybe 15 years to think about it.
3/16 or even 1/4 x1/2 might be a better idea but I would resist any urge to put in shear webs. The flexible wing has stood up to literally 3 dozen or so crashes with no damage. I would be concerned that it would be much more likely to self-destruct if it was a lot stiffer, and the performance hasn't suffered much. The weight is a non-issue, it's going to be something like 5-6 oz lighter than the stock wing (which also contributes to the durability).
A 3" bellcrank is fine for this airplane, and in any case, you don't really need to slow the controls down. Make the sensitivity adjustable but make sure you can get clear travel of at least +-40 degrees. My leadouts are fixed, 1" apart, and the front leadout is 1 3/4" from the LE. This is the correct position for .015x60 and a 30 oz airplane, but it's close enough for 58 or 62 feet. I used a stock pushrod with a fairlead and soldered washers to connect it, and if I want to change the elevator sensitivity I just desoldered it and moved it. I adjust the bellcrank/elevator neutral by bending a kink in the pushrod. Start with the elevator at neutral with the bellcrank pointed at the leadouts. DO NOT use a clevis of any sort. If you want, use a ball link at one end or the other (in this case I would put it on the elevator) and a carbon pushrod.
Use a two-wheel gear. The gear from a SIG Phaser works well.
Presuming you are going to use a 25LA, use a 9-4 APC prop and everything else DEAD STOCK. I run an air filter to keep the crud out and it slightly cuts the power. Also get some 10-4 APCs and 10-3 APCs.
I suggest two-part epoxy paint for the fuselage and whatever the best iron-on covering is for the wing and tail. I used Monokote but that was the old, good kind.
And since you have the ambition to scratch-build the airplane, I suggest it's about as easy to cut out 2 (or even 3) of them at once. Make a plywood template with locating pins for the ribs so you can just flop it on the wood and cut around it quickly, no tracing patterns, etc. Cut a few, check the fits, adjust the template as necessary (mostly for perfect fit of the spar), once it's right, it should take about 1/2 hour to cut out 3 airplanes worth of ribs. Everything else is easy - for the fuse, built it with the doublers/triplers in place, use a template to trace the wing cutout in the right place and very accurately aligned, and cut the wing hole out with a jigsaw right through the plywood. That keeps you from having to carefully cut and glue the doublers.
Take great care with the alignment (wing and tail square to the fuse and the elevator perpendicular to the wing). Do a neat job of building, but don't obsess about the finish. With epoxy you can get a decent finish in a few days with excellent durability - prime it heavily, sand, put on a coat of color, sand, add a finish coat of color, done.
Once you have your two or three airplanes, take them all to the field. If you crash one of them, get the next one off the stack *right then*, and just keep going.
Brett
Topic: building SkyRay 35 from plans (Read 3442 times)
