I just got a Super Skybolt kit (from Great Planes) and would like to hear any comments/suggestions that people might have on building this plane that might deviate from what the plans call for. Things like reducing weight, adding access panels, positioning tail servos, and other things that one might not consider until after having the plane for a while. It's always good to research these sorts of things, in my opionion, before making the plane. A little research beforehand can save you a ton of headaches. If you have any comments, even on one or two of the things below, please chime in! I'd appreciate any suggestions.

I've built something like seven or eight planes (a 40 size Chaos and Sportster were my last two). So I have a decent amount of experience. However, all the planes up to this point were rather basic (4-channel) builds. This time around (it's been a few years) I'd like to step it up a bit. Going to have several more channels (for dual alleron servos, possibly dual elevator servos, a smoke system, etc.). And so this is why I'm trying to look ahead and avoid potential errors and/or pitfalls.

That said, here are the things that I'd like help with that I know I'll encounter (feel free to add suggestions - after all, I can't ask about something I've never thought about). Plus, I've been out of the hobby for several years, and it seems many changes have been made. By the way, I'm likely going to put a Saito 1.20 or 1.40 in the plane (4-stroke of course).


- Elevator and Rudder Servos: I'm seeing a lot of planes now with the elevator and rudder servos mounted near the tail, in the fuse sides. This seems nice and clean, and it would remove the headache of using pushrods through the aft fuse. Plus it frees up room in the fuse above the wing (potential room for the smoke system?). Also, I was considering adding some doors in the aft fuse to 'drop' things like fake bombs or army men with parachutes... not having the pushrods in the way would be nice. Any suggestions as to the best method for moving the servos to the tail? I figured that I'd add some thin plywood and mount the servos on it... sounds simple, but am I underestimating this procedure? What about exposing the servos like that; won't gas/oil get on them?

- Dual servos for the elevator: I imagine that if I move the servos for the elevator to the tail, I'll probably be forced to use two servos (one for each half of the elevator), since it eliminates the idea of using a 'Y' shaped pushrod the plans call for. I guess I could the standard 'U' shaped piece of metal to link the two pieces of elevator and just use one servo, but that tends to introduce slop in the control surface in my experience. Are there additional advantages to using two servos for the elevator?

- Gas tank access: Seems that this kit doesn't leave a way to get to the gas tank in case the need arises. And I'm a bit stumped as to how to create one myself. Problem is, the cabanes are above the tank, so that's out of the question. And the plans call for a piece of plywood that the tank sits on, and it's permanently installed. I suppose I could make that ply (what the tank sits on) removeable, and then add a hatch below that in the bottom of the fuse....? Anyone have any good suggestions or ideas on modifying this area?

- Smoke system installation: Where are some good places to install the parts for the smoke system? I'm fairly certain that I'll use an electric pump, so I need space for a battery, the pump, flow restricter, and the tank. My original thoughts were to color the canopy opaque (like tint it black for example), and to put the tank under the canopy (i.e., leaving out the 'floor' of the cockpit). I would also have extra room in the body if installing the tail control servos at the rear of the fuse. Any suggestions here are most welcome!

- Lightening the wing, or fuse: Reading through some older posts regarding Super Skybolts, I saw someone suggesting to cut holes in the ribs to lighten the wing. That scares me... structually at least. Any thoughts on this? Doesn't seem like much weight would be saved there. What about lightening the fuse? Do I really even need to consider lightening the plane with a 4-stroke 1.20 in this plane? I do want it as acrobatic as possible.

- Hinges: What's the latest technique for hinges? Here's how I do it... I get those fuzzy hinges that you can buy at the hobby store. Then I cut the slots for them, install them without gluing them. Then I put T-pins through the balsa and hinges, and cut the pins of with pliars (maybe two per hinge). Then I remove the pins, use thin CA to glue the hinge in place, replace the pins and epoxy them in. I've never had a hinge fail this way so far, but then again, I've only ever build 40 size planes (well, the Chaos had an OS 46 - man it screamed). Are there better ways now-a-days for mounting hinges? Maybe a new kind of hinge in the last ten years has come out or something.

- 'Bomb' drop hatch: I'd like to add a little hatch, controlled via servo, to drop things. Any suggestions here or am I just going to have to wing the mechanics of it?


Any other modifications I might be overlooking? Even simple things; for example, I saw a really nice tail wheel assembly kit in the hobby store that I ordered. It mounts the tail wheel to the bottom of the fuse and uses a bell crank with springs to link up with the rudder. This is really nice, as anyone with a tail dragger would understand why. This is probably common sense to the experienced kit builders here, but as I said, I've been out of the scene for a while and it's new to me. Suggestions for any little tweaks like this would be most appreciated!

Each new plane you make, you learn from the past and incorporate modifications. It's too bad there's no book (at least that I've seen) that goes over all these 'learned from experience' type issues for kit plane construction. Most of it is learned either via experience or word of mouth at the field. I saw a post mentioning how kit building is becoming a 'lost art'. These details should be documented somewhere for others to benefit from.

Ok, first let's decide what you're going to add, and what you're not.

If you put a smoker, 3 servos in the tail, hatches all over the place, and a bomb drop, that nice plane is goint to be too heavy to fly.

This thing is a fantastic airplane, and a 120 will be excellent in it, but DON'T go weighing it down with a ton of stuff.

A smoker is nice, I had one in mine, but it really pushed the plane to the weight limits. So I wouldn't add any more than 1 "Cool Mod"

Lightening is a great idea. I would thicken the wood on the tail feathers and skip the sheeting. A few lightening holes in the Fuse and ribs (Yes, the ribs) would help too.

IF you're going to add a hatch for the smoke pump, add it to the bottom right in front of the landing gear.

You can squeeze the smoke oil tank into the radio compartment right behind the fuel tank (Which doesn't need a hatch, you can get to it from the rear.)

depeche, sounds like your trying to build a Swiss Army Knife, not an airplane. Go with the smoke and enjoy.

depeche, [link=http://www.rcuniverse.com/forum/Lightening_the_GP_Skybolt/m_2496934/tm.htm]here's[/link] my mod thread I started yesterday. It's odd I didn't see this thread before. Anyway, I have started to lighten the tail up a bit,a nd plan on a Saito 100 for power.

Well, if a plane with a smoke system and a hatch to drop something constitutes a Swiss Army Knife, I guess that's what I'm making. =)

MinnFlyer, thanks for the advice! I'll leave off the gas tank panel; I hadn't realized that you could get it out through the body (looked like the bulk heads were too narrow on the plans). As for the servos in the tail, I didn't realize that was a 'cool mod'. Seems to me that that would reduce weight if anything, as it eliminates much of the push rods length. Am I wrong here? I could see it adding weight to the tail, but not to the overall weigth. I'm also going with your suggestion to lighten the tail, fuse and ribs.

Deadeye, thanks for the link. Your job looks great! I'd finished the tail section before I read the suggestions from MinnFlyer about reducing the weight there. Last night I cut out some triangles in the elev, stab, rud, and tail (triangles that match the triangle outlined by the stringers in the tail). I still don't think it'll save any noticeable amount of weight, and it's time consuming, but it looks cool! I'll post some pictures perhaps when I'm further along.

Moving the servos to the tail would be a serious mistake. While in the mock-up stage you should do a balance check and consider moving the servos forward if space allows. Adding nose weight to balance a plane is a neccessary evil sometimes but minimizing it should be a priority.

damifino, can you elaborate a little on why it would be a mistake? I'd like to understand your reasoning and learn from it. Is it simply because of the weight? If so, are you sure the weight would be increased by doing this? I would imagine that it wouldn't be that different since much of the push rod weight would be removed from the tail. Also, eventually you want an acrobatic plane to be a little tail heavy don't you? At least, that's what I did in past planes (add some tail weight). So, for the initial flights, I could add some nose weight to get the CG right... that would make the plane a little heavier altogether, but after the inial fights and trimming is done, I could remove the nose weight to get a little more acrobatic potential out of it...?

Please let me know where my reasoning is messed up... I'm here to learn.

Leave the servos where the plans call for. All you will be doing is adding more tail weight to an already tail heavy plane. The shorter push rods will weigh a smidge less but remember that the overall push rod weight is distributed from the tail to mid fuse. If you move the servo to the the tail servo weight will be concentrated at the tail, also they will have longer servo leads that will weigh almost as much as light weight push rods. I am building a Ultimate Pitts that calls for the servos to be mounted in the fuse but since I am using a heavier gas motor I am moving the servos to the tail to compensate for the additional nose weight. Does this make sense?

Depeche,

Comparatively speaking, the weight of the pushrods is nothing compared to the weight of the servo.
Add to that the fact that moving the weight of a servo to the rear of an inherantly tail-heavy plane is not simple linear translation from a CG perspective. Since there is a greater moment arm (weight * distance) on the rear servo than there is available for the offsetting counterweight ahead of the CG, it will take much more weight in the nose of the plane to compensate. Thus increasing the overall weight considerably more than necessary.

e.g. 4 oz. located on the CG balances and weighs 4 oz.

4 oz. moved 4" back from the CG must be compensated by 4 oz. 4" ahead of the CG to balance and now weighs 8 oz.
4 oz.* 4in. (16 oz.-in.) == 4 oz.* 4in. (16 oz.-in.)
OR
4 oz. moved 4" back from the CG must be compensated by 8 oz. 2" ahead of the CG to balance and now weighs 12 oz.
8 oz.* 2in. (16 oz.-in.) == 4 oz.* 4in. (16 oz.-in.)

krossk, so the theory that it takes 4 times more weight in the nose to balance a tail heavy plane is true.

rc,

Based on the tail-to-cg distance being 4* the cg-to-nose distance, that's pretty much what the laws of physics dictate...

Just build it the way the plans say and it'll be fine.
I've been flying one for about 5 years now and I love it.
Does spectacular aeobatics, especially snaps and lomcivoks(sp)
The extra weight seems to increase it's ability to tumble end over end.
I have a YS 120 in mine, which is a fairly heavy engine, and it balanced fine with no added weight.

Also, it lands very slow if you want. No bad habits.

Good thread guys. I would agree that the only reason to move servos to the tail would be to compensate for a beefier engine in the front. For my tail arrangement, I am going with something a bit different. I have my rudder and elevator servos in line with each other but the rudder servo is higher and more forward. Here's why. I'm using a control rod splitter from Jamarra to run a control rod to each elevator half, the elevator rods exit the fuse higher than the rudder pushrods would need to. I have the rudder servo 1/2 inch higher than the elevator servo and will use a pull-pull cable system. The vertical spacing eliminates the interference between the two control mechanisms since they actually get farther apart as they approach the rear of the plane. I also like the responsiveness that a pull-pull system gives you with a rudder, and the elimination of differential elevator throw often caused by a joiner wire (and me not being able to drill straight)

Anybody try tandem servos in the center of the lower wing to drive both upper and lower ailerons? My idea is to put two servos side-by-side to each run one lower aileron. A connector wire for the upper ailerons would run from the lower aileron, just like the dual servo in the wing set-up.

sky2,
Your servo placement sounds a bit confusing. The rudder servo is higher and forward of the elevator servo, yet the elevator rods exit the fuse *above* the rudder control wires? It sounds like one of us has our wires crossed. [sm=spinnyeyes.gif] Also, as long as you're going to the trouble of pull-pull on the rudder, why not go all the way and do it for the elevator as well?

I wouldn't recommend 2 servos in the center for the same reason they recommend not using 4 ailerons with a single servo. The combination of the torque rod control on the lower servo and the joining rod to the upper servo will likely allow to much flex in the aileron linkage - possibly resulting in flutter. If the kit is already designed for dual outboard aileron servos, why not just build it that way?

Depeche,
I didn't like the wing struts with their plug in music wire arragment, they seamed to be a pain just in the building stage, I didn't think I'd want to have to fight to get them installed at the field, so I made my own: (I hope the pictures upload with this)

spicy, the strut attachment wires are a pain to build but well worth it. They attach and detach very easily, they stay in place quite well.

Krossk - It sounds a bit confusing. Think forward as toward the firewall, and the vertical arrangement I talked about was as you are looking into the belly of the plane (fuse upside down). I'll try and take a picture of it and post. I reconsidered the aileron servo arrangement and will just do what the plans recommend. I became worried about control surface distortion towards the outboard with that set-up the more I thought about it.

Spicy - nice job on the struts. I made mine a "pocketed" arrangement. I made a copy of the rib with two 1/16" plywood tabs sticking up, then made new struts with pockets to accept the tabs. Drill through the whole arrangement and add blindnuts and it makes for a pretty secure arrangement.

Spicy, that looks really good. I'd like some more pics if you have any. Some of the location where the strut meets the top wing for example.

I really do want to put the servos in the fuse. Everyone seems opposed to this because of weight, but: 1. I'm going to be using an engine heavier than what the plans call for (probably a Saito 1.20 4-stroke, ~8 extra ounces); 2. I've already lightened the fail feathers; 3. I want very little flutter (I'm using a larger engine); 4. I want more free space in the fuse to cleanly install smoker components, to easily access/remove the gas tank, and for the radio gear. Two servos = ~3oz. I probably removed a little over an ounce from the tail, so that equates to approx. 2 extra ounces in the tail, but the engine is an extra 8oz. So I'm not too worried about it not balancing.

I plan on placing the servos (rudder and elevator) between the final two bulkheads (4 and 5 I believe are the last two), near the pushrod exits. One on each side of the fuse, and one (rudder) lower than the other (elevator). This would require a basic (metal wire) linkage between the two elevator halves.

If I'm missing something and/or my logic here is flawed, please let me know before I go ahead with these plans.

Thanks for all the comments!

depeche, I used the Saito 120 in mine and left the servos where the plans called for and it balanced perfectly, as a matter of fact I waited to install the battery to use it as ballast. I ended up having to install the battery right on the CG

Oh Spicey!

You just screwed up one of the best features of the Skybolt.

That mod you made will add 15 minutes to your set up and break down time. []

Yes rc-sport, but you'renot building a Swiss army knife. =) Really tough, the two planes aren't going to be the same.

MinnFlyer,
On the contrary, I think it will speed things up. It only takes about 10 seconds to put on one of the struts. Bolt on the lower wing, slide the upper wing on the cabane structure, the simply slip the struts over the pins and install the spring clip to hold them in place. The longest part of the whole wing installation will be installing the bolts throught the lower wing. I haven't given that much thought, but there is probably a simple/quicker way than the bolts.

Depeche,
I don't have any more pictures handy, but I'll try to take some this weekend. The upper looks just about like the lower. I am going to glue the plywood piece to the outboard side of the wing rib, then add another cap strip on the outboard side so I can cover up to it. The pins will be epoxied into the plywood, so they will stay with the wings so I don't have to worry about losing them. If I ha thought of this earlier, I would have made the plywood part of the laminated wing rib. I bought the clevis pins, the grommets, and the aluminum from McMaster Carr. I am going to slightly round the ends of the clevis pins so they slide through the grommets easier.

Spicy, I don't disagree that your mod will be quick but you have small cotter pins that you could drop at the field. Ever look for a small screw in grass?

actually, its a 4" piece of music wire that goes through both pins. No cotter pins nor very small loose parts.

depeche- If you don't see the logic in all of the sensible responses you've recieved there is only one thing I can say. Forget about all the experienced advice and solid engineering priciples given here and build it your way. The most valuable lessons we learn are by making our own mistakes, we've all done that, right guys? Respectfully, Damifino