I recently acquired a stock SIG Skyray 35 kit. Have not started on it as yet, but I have been reading much about how different kit builders have revised the stock design. My current plan is to pretty much follow the suggestions of Brett Buck (within my ability to obtain recommended balsa wood pieces and other parts) as outlined by Brett). 

Also, my current plan is to power the model w/ a stock OS 25LA with stock muffler.

I do have a few questions in case anyone has particular experience.

1. The 25LA sticks out quite a bit on the model. Any issues w/ moving the engine back (around 1" or so) so it works better w/ the nose of the model? Any overall balance concerns?

2. The stock rudder and tail surfaces are 1/8" balsa. Any issues w/ increasing the surfaces to 3/16" thickness. (Reason: I have a Banshee and Flite Streak with 1/8" surfaces. Quite flimsy parts.) 3/16" surfaces might also help with balance considering the use of a 25LA with stock muffler)

3. I am also planning on using adjustable lead-outs and adjustable wing tip weight box.

Thanks in advance.

Thx Dan

I have a 3 oz oval profile uniflow tank planned and it fits fine even with the engine moved back 1" or so. But I also need to ensure the landing gear (profile mount aluminum gear planned) also fits.

Our CL field is not the greatest (a bit bumpy) and my models have sometimes done a simple flip over on landing, cracking the rudder. Other models I have at 3/16" don't see the damage.

If you haven't started it yet, go with the aluminum landing gear.   I build a pocket in my profiles for the gear to slip into and use flat head 4-40's with the heads on the tank side.  Not hard to do with a little thinking.  A little scrap pieces of ply for filler to match the balsa..

Thanks

I am already planning on aluminum profile landing gear. I have never liked any models with a single center wheel design.

Brodak makes a good universal profile mount aluminum gear. I have it on my Brodak Shark 402, a Ringmaster and a Brodak P40 ARF.

So as not to crush the fuselage, I have been using 2 brass tube inserts for the gear mounting bolts that match the fuse overall width. I secure the tubes in the fuse w/ a bit of epoxy. The brass tubes take the basic compression force from the mounting bolts and don't affect the fuse wood itself. Has worked well for me so far on a few profile models.

...

This is not a problem other than what may or may not please you cosmetically. If it really bothers you that much I'd simply add some wood to the nose, shape to what pleases you, and maintain the available tank space. Moving the engine back may also put you toward being tail heavy.

 Another option is throwing away the plans and doing this...

 https://stunthanger.com/smf/open-forum/'skyray-my-way'-finished-photos/msg21692/#msg21692

Your Skyray is a beautiful model. One of the best models I have ever seen. If I could even build a model that nice, I would probably never fly it.

I still consider myself somewhat of a rookie builder. My goal is to have a 'decent' looking Skyray model that flies well. I am still learning the various stunts of the pattern and the model will probably (hopefully not) find its way to the ground as I continue to learn.

The original Skyray was designed for a lighter engine. Hopefully the OS 25LA heavier engine/muffler moved back a bit won't affect balance too much.

All points taken. My honest suggestion toward achieving your goal in this case is not to overthink things. Stay true to the original (proven) design, it's a good airplane. But whatever you do, do not move the engine back. Just focus on building it straight and at a decent weight, with smooth operating controls, put a good running .25 on it and go have a blast. 

Thx wwwarbird.

Please excuse my caution. But I would like to understand your strong recommendation to NOT move the engine back. The original Skyray model was designed for a Fox 35 w/ no muffler (6.3 oz engine). The OS 25LA w/ muffler is 8.75 oz. In comparison the stock Fox setup would produce around 35 in-oz of nose moment from CG point. The OS setup about 39 in-oz. So yes, a bit more nose moment w/ the heavier engine setup. But I am also planning on using 3/16" thick rudder and tail surfaces (for strength) which will add a bit of tail weight. A small amount of tail weight might still be needed but should not be much.

Thx to all for the useful information.

Once the Skyray model is basically put together and before final gluing, I will look at model overall +/- CG balance and whether or not to move the OS 25LA engine back before I drill the engine mount holes in the fuse.

If the stab that came with the kit is fairly hard and close to C grain (i.e. quartersawn) then it'll do just fine.  Yielding to temptation and going with 3/16" should work out, but find light wood for the replacement.

Sometimes you can find good "almost contest" wood at your local craft store.  You're looking for the stuff that the bird-house building public think of as "punky lightweight crap".  On a good day it -- and broken sheets -- will be all that's left in the bin.  A-grain 3/16" is probably going to warp as bad as 1/8" C-grain, so be judicious.  If you can find some light C-grain balsa, get it.

Personally, I'd build what's in the kit with Brett's recommendations (well, to be honest, I'd scratch-build to the plans, but that's me).  Leave the nose as-is, put on a two-wheel gear of some sort, put in a weight box and adjustable leadouts, and go fly.

Note that the entirety of Brett's suggestion is to buy one kit, build it, scratch-build two more planes, and take them all with you to fly.  That's not bad advice.  If you fly off of dirt, you don't even need to have a fully functional second (or third) engine -- just fly, crash, move the motor over, and fly some more.

Colin,
The Skyray is a good model so build it as it comes from the factory, sure people make changes and that’s fine, but the bottom line is fly it and practice your maneuvers.  The best advise is build the kit and then scratch build the second version from hand selected light balsa.  Unless your willing to redesign the model to make it even lighter it won’t be much lighter, but some.

More importantly, is the choice of engine and accessories, such as fuel tank, prop, adding gear (2) and hardware, add a 1/2” balsa tripled to the inboard side of the fuse to reduce engine vibration.  Adding an adjustable lead out guide and tip weight box are good things to do.  Make sure you build it straight & light, use iron-on covering for wing, stab & elevator, fin & rudder and paint the fuselage.  Even build stock it should be in the 32 to 35 ounce range and fly great.

HAVE BLAST,
Mike Pratt

PS, Send us photos when finished.

 

Thx Mike for all the great suggestions and guidance.

looking good.

   Looks good to me. You are obviously taking more care than I did building the wing, mine was thrown together in about an hour! Still going strong 30ish years later.

     Brett

This is only the 4th model I have ever build from a kit. I have gotten better as I have lessons learned from previous builds. I am taking my time on this build to try to get everything right. Wing straight w/ no warps, tail surfaces correctly positioned, etc. But so far, I am on track. Hopefully this model will be my best flying model to date.

Completed the Skyray wing today. I installed an adjustable wing tip weight box and lead out guide (both from Brodak). Was a bit tricky (for me since no instructions) so the box and guide would work with the Monokote covering planned. I also used a Dubro 4-40 pushrod and quick link (versus the stock pre-bent music wire pushrod). The Dubro quick link is threaded allowing for some pushrod length adjustment if needed.

   Hopefully just on the elevator end, right?!  For the elevator end I very strongly suggest you replace the Kwik-Link with a ball link, because even on something with as little load on it as a Skyray 35, Kwik-Links aren't strong enough to last.

    Make sure you ball link is loose, some of them are extremely tight and should just be tossed, or resized.

     If you already have one on the bellcrank end, I suppose you can just leave it rather than cut it open to replace it, but be prepared for a failure at some point. If you are trying hard enough learning the maneuvers, you will probably and should get *plenty* of opportunities to repair it from normal causes.

    Brett

Thanks Brett & Ken for the build feedback.

The kwik link is only on the elevator horn. There is a typical Z bend on the bell crank.

The kink is a Dubro safety lock type. I have been using these for quite some time with no issues.

The lead-outs only appear to contact the rib in the pic because not under tension. Under tension, nowhere near any rib. 

Unfortunately, too late on switching to a ball link at the bell crank since wing is already closed up. And I do frequently inspect the links and horns for wear and replace if needed. Easy to replace without tearing into the model.

But I understand your advice on the ball links and will try to incorporate onto future models (or repaired models).

Thanks

Still looks good but may I suggest some breather holes in those out board ribs.  It doesn't take much like some pin holes.

Hey we learn some thing new each day.  My Dad always said if we don't keep learning we will have the dirt thrown over us too soon.  The holes in solid ribs I learned while fly RC gliders.  MonoKote would balloon up in the summer heat.

Nice looking plane.

I am building my Skyray bone stock with Fox .35.  My challenge is doing a good job with solder on the stock, provided, pushrod. 

I am building my Skyray bone stock with Fox .35.  My challenge is doing a good job with solder on the stock, provided, pushrod.

  What is it that you are soldering?  The washers on the ends?

    Brett

Soldered washer with JB Weld