Oops, I forgot a PS on my previous post. I'd rather not cut a new set of balsa ribs to replace the ply specimens contained in the kit. Kind of defeats the purpose of a kit, for me.

Thanks again!

Mo...

Oops, I forgot a PS on my previous post. I'd rather not cut a new set of balsa ribs to replace the ply specimens contained in the kit. Kind of defeats the purpose of a kit, for me.

Thanks again!

Mo...

I wonder if any of the laser cutter guys make rib kits for the Skyray.  Frankly, I enjoy cutting out huge piles of ribs (and I have a Skyray rib template around someplace, that I made for fixing the one I flew in competition), so that's the least of the barriers to building one from scratch.

Tim: You and the Motorman have convinced me to stay with a conventional build with this kit. The 20FP and the 25LA have the same mounting pattern and weight, so if one doesn't work, the other will. Glad to hear that the ply ribs are not a death knell for performance on this ship.

Tim again: I understand that building light means watching the glue quantities and finishing materials. Any other hints on lightening relative to this kit? In rounding the fuselage edges, I'm thinking of radius at least 1/8"or maybe even 1/4". Worth the effort or not? Aluminum landing gear for sure. Thanks.

Motorman: Will do as you suggest. The Saito will find a home in something more unique in the future, maybe even something in a "steam punk" aesthetic. Thanks!

Joe Ed: Nice to hear that we are on the same page - great minds and all that! I was aware of the links you kindly provided, but you saved me mucho time in providing them. When you go to work making those ribs, will you include the half ribs as well? Will you alter the numbers, their configuration, placement, etc.? Thanks!

Dave Mo...

Joe Ed: Nice to hear that we are on the same page - great minds and all that! I was aware of the links you kindly provided, but you saved me mucho time in providing them. When you go to work making those ribs, will you include the half ribs as well? Will you alter the numbers, their configuration, placement, etc.? Thanks!

Dave Mo...

Dave,

I have read/heard of three ways to do the ribs when using balsa:
a) full 3/32" ribs in every position the plans show a rib or half rib
b) full 3/32" ribs where full ribs are shown and 1/2 ribs where half ribs are shown
c) Full 3/32 ribs where full ribs are shown and skip the half ribs.

I have a good supply of 3/32" balsa in the 5.5 to 6.5 lb range.   I'm thinking of going with "a)" because the wood I have is so light.  I also plan on using a 1/8" x 1/2" spar as Brett recommends.

Joe Ed Pederson

So I opened up the sealed box I'd gotten off E-Bay thinking that I'd get ready for a building project. I expected a nice kit, and so it is. However I'm not certain, but it seems like the empennage balsa and the ply ribs and riblets are a bit porky. In addition, the fuselage is 1/2" thick balsa (!). I'm "heavily" impressed, but I do like to build light whenever possible.

I've got two options involving four engines for this kit. One would be to build it as a high risk trainer to supplement the Cartier foam wing Rugged Stunt Trainer / OS-20FP that I dearly  enjoy. That way when RST augers in, I can pull another trainer right out of the car and carry on. The engine choices would be another OS FP-20, and OS LA-25, or an OS FP-35.

The second option is a little offbeat. I could build this kit as more of a sport and mild stunt "showplane," using a Black Knight Saito .30 for power. I've a nifty color scheme in mind. Ideally, I'd be able to fly it over a large grass field in a public park located very near my house. Both options would require standard, 2-piece landing gear.

I realize that I'm not giving you folks here much to go on regarding my impression of the heavy kit parts.  I can always just suck it up, flip a coin and build something. Ha! However if you've got any suggestions, let me know.

  Built out of the kit, it will end up about 36 ounces with a 20FP, which is perfectly acceptable for training purposes. You will have to limit the corner a bit to keep it out of trouble in hot conditions, however. Power is not an issue, wing loading might be. All my early experiments, including the one where I switched from a Larry Foster Fox 35 to 20FP and found that gravity appeared to have been cancelled, were with a completely stock model.

   A 1/2" thick balsa fuselage is absolutely standard stuff for "35-sized" model, and the doubler arrangement is far superior to older vintage models. And it's pretty small in profile, too.  However, the plywood and spruce wing is not standard. It flies OK at 36 ounces. The problem is durability, mine completely shattered in the first crash, so does does everyone else's.

   My suggestion is to go ahead and build it as shown, then use the plans to build a second model, fuselage and tail the same, but the wing with 3/32" medium balsa ribs at each position. Where there are plywood half-ribs, make a full rib of 3/32 medium balsa. 3/32 medium balsa center section and trailing edge top and bottom, 1/8x1/2 hard balsa, or 1/4x1/4 hard balsa spar. Medium 1/2x1/2 balsa leading edge. Airfoil as shown on plans, no real aerodynamic changes. Cover with Ultracote on wing and tail surfaces. Put on one coat of thinned Timbermate wood filler on the fuse, sand off, prime heavily with Superpoxy of Klass-Kote "fast" primer, sand, then 2-part epoxy paint on fuselage.

  Only aerodynamic change is to remove all rudder offset, do not airfoil it, measure it to be sure it is exactly straight ahead. Mechanically, add adjustable tip weight box in outboard wing tip, and if desired, an adjustable leadout guide. Start with leadouts about 2" from LE, and CG about 1" from LE.

  Trim is as described here, including tip weight to start as indicated using "counterweight method":

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=198043&mesg_id=198043&listing_type=search

  Stock controls as shown on plans are OK.

   This will fly slightly better at about 29-30 ounces with a 20FP or 25LA, but will withstand crashes much better, as long as you are on dirt/grass.

   Brett

Folks:

Here is the completed wing. I undertook one more vacillation regarding the rib question, and so stuck with the 1/8" ply ribs included in the kit. As you can see, they've been ventilated. The covering is SLC. I use this on all my models but often cover it with doped and painted tissue. Here, I left it clear as a few of the youngsters at the school grounds where I fly have asked how the wing is constructed internally. I don't have a scale, but the wing seems light.

Dave Mo...

I received a kit and weighed the Lite Ply ribs.  I concluded that there isn't much weight to be saved by replacing the ribs with balsa of adequate strength.

Scratch-building is different issue, but with the ribs in hand, and considering the need for outboard weight, I'm using most of the Lite Ply.

I received a kit and weighed the Lite Ply ribs.  I concluded that there isn't much weight to be saved by replacing the ribs with balsa of adequate strength.

Scratch-building is different issue, but with the ribs in hand, and considering the need for outboard weight, I'm using most of the Lite Ply.

    The difference between the plywood/spruce  and the balsa (3/32 all around, w/1/2x1/8 balsa spar) wing is about 5 1/2 - 6 ounces, which is hardly negligible. With a proper engine, it won't fly tremendously better, but with a weak engine (Fox/McCoy 35, not recommended) that will make a huge difference.

  I would not recommend plywood on the outboard wing and balsa on the inboard - that is likely to work far too well as far as "saving tip weight" goes, and you may end up requiring tip weight on the inboard side. There's an entire engine and muffler out there, My airplane is built symmetrically, and it only needs about 3/8 ounce of added tip weight.  For reference, using the "counterbalance" method, that means the engine/tank/muffler are good for about 1 3/8 ounces of equivalent tip weight, because the total counterbalance weight for the reasonably trimmed airplane is about 1 3/4 ounces. If anything, that is too much (trying to buy margin for the lesser-skilled and I can just baby it)  and taking out 1/4 ounce for ideal trim  gets me down to a tiny sliver of lead.

  But, as noted above, the issue is more about durability than performance. The plywood wing is much heavier but also extremely brittle.

   Do as you wish, of course, but I have been down this road. If you are doing it the way you say, be sure and make the necessary templates to build another one out of balsa later.

     Brett

Brett:

My work on this kit is being informed by your advice (and that of Dr. Divot). I'm close to trimming the ship along the longitudinal axis (in roll) and am reading your advice about temporary placement of 1.76 ounces on the inboard wing, etc., for this particular model. I'll do that, but another question comes to mind.

Others have generally suggested that outboard wingtip weight is best determined by temporarily placing the weight of the flying lines on the inboard wing and then adding outboard weight to the weight box to level the wings. This technique usually involves placing an empty spool on the outboard side to counteract the filled spool on the inboard side and then stocking the weight box. Is this the technique you use for all your building, or is there some other way implicit in your suggestion for the Skyray?

Maybe you've covered this elsewhere. But, inquiring minds and all that!

   More-or-less, I counterweight to get it close to start with, and take into account other factors, like asymmetry. So, before I fly my new airplane, I am going to do the counterweight method on the old one. Say it takes 7/8 ounce. That's within a few grams of the ideal amount for that airplane. The new airplane has a bit mroe asymmetry (on purpose), so I would expect that to alter it and require a bit less tipweight than the old one, and it's a lot lighter, so it will take less to shift the lateral CP. Both of those suggest I will wind up with maybe 5/8-3/4 ounce instead of 7/8. But I want some margin, and am willing to start with excess, so I will probably end up with 7/8-1 ounce, so that's what I would use as the counterweight to start with.

   On the current airplane, I matched the old one exactly, because it had the same asymmetry. It was nearly perfect from the first flight, and I have only changed it +- a few grams since then - 2006, that is (including last Sunday).

    The reason I specified the 1.76 on the Skyray was because I knew it was very close already and that everybody else's will be the same, as long as it is the same design and built to plans. The counterweight method accounts for any pre-existing lateral CG shift. In this case, the engine and muffler contributing almost all of the lateral offset - it only has about 3/8 ounce of actual lead in the tip, which wouldn't be nearly enough without the muffler and engine.

    Brett

Well folks, here 'tis, redundant ply and all. Wish I had a scale but its heft is likely in the neighborhood that Brett mentioned. All that remains is bench trimming and some warm, dry weather (probably March or April). Should be fun!

Moe...

PS: The gray image on the background wall portends nothing (I hope!) as it is a water stain. It sure does look like a storm cloud, though!

 

Moe,

That looks sharp!  I like it.

Don't worry about the Joe Btfsplk cloud. An OS 25 can outrun it, I'm sure.

Whatchugunnabuildnext?

Got our first storm of the season today. Weatherman kept saying that we might get a few sprinkles...so it came down hard all morning. Cold front, too. Snow in the local mountains. Need to borrow a couple of your hodags....

The Divot

I weighed all the wing parts from the kit.

I found more weight to be saved on the LE and spars than the ribs.

So the total of the 8 full ribs, 8 LE ribs and 3 sheeted ribs in Lite Ply was 2.36 ounces.
But the total of the spars & kit LE was 2.86 ounces.
So I swapped-out the LE & spars for lighter stock & save about half of the 2.86.

I muddied-up the equation of the ribs by using the inboard & outboard tip Lite Ply ribs and replacing the center rib with a full 1/2" balsa rib.  I always want the fuselage to be firmly-attached to structure the continues the strength of the body.  There is stress on both tip ribs that warrents the use of the plywood.

Paul:

Something to consider. Note above that the OS-25LA motor extends well beyond the fuselage. If I'd done a scratch build, then I'd have added an inch to the fuselage.

Dave...

Do you mean it extends that far to get it to balance, or because the back of the motor is bottomed out in the slot?  I'd move the motor back; with an OS 25LA with muffler (which you DO want to run) you may well want tail weight; moving it forward just makes that worse.

... First, use exactly the same engine shown in the model's plan. And second, do whatever Brett Buck says....

Well, in this case they contradict each other anyway.  In the case of an older design, I think it's perfectly OK to choose a different engine.

One of these days I'm going to take my almost-never-used Fox 35 and put it on a Ringmaster or a Skyray, just to see if it's as bad as Brett says (or at least to investigate the dimensions of "bad").