Kits Few Questions about .90 Size Planes

[mooserider]

Hey all! I'm working on a build I started in ~2003 and it's my first in that size, so I thought I'd ask a few things to be safe. This is a Super Skybolt kit from GP, .60 - .90 kit, with a YS 110 (got a Hyde mount for it too). Of course I'd like to put some smoke in it as well.

Here are my questions:

1. Normally I just buy some relatively cheap servos... ~$20. Plastic geared. Should I be getting something a little more heavy duty, with metal gears?

2. The kit calls for using the old Y-style pushrod for the split elevator. I've used these on other kits in the past, but never really felt great about them for some reason... they seem a little 'chency'. Just curious on your thoughts/experience. I'm considering mounting two servos in the tail (under the stab) connected with a Y harness, one to drive each elevator half, but it wouldn't be as 'pretty' with those servos back there.

3. I need to order a gas tank. With the whole pressurized YS system thing, I've read articles saying they've had their tank split at the seems. Normally I get the Sullivan tanks. What's a good option for this setup? Also, if the pressure is really that high, wouldn't you need little clips on all your fuel tubing connections? I don't see this in photos of YS setups all over the web.

Thank you for any advice in advance!

 

[Tony]

That is a good size bipe right there. Can't wait to see it in the air.

I would never use plastic gear servos on a plane like this. Last thing you want is a crash because the gears were worn out.

If you use dual elevator servos, it will be more tail heavy than usual. One way around this is to set the servos up in a stand inside the fuse under the top wing and run pushrods back to the elevator control surfaces. The ole Y style has been used for years though so you can take your pick.

Not sure on the tank. How much pressure are we talking aobut?

 

[mooserider]

Well, the manual doesn't say and I'm having a hard time finding stats on it, even on YS's site. I'm seen old posts saying it's ~6-9 psi. I guess I'll just go with the Sullivan 14oz I have. The kit doesn't have the greatest tank access, so I wanted to get it right the first time with the tank. But maybe I'll just build in an access panel in case there's a problem.

I didn't think about the gears wearing over time in the servos. Thanks for pointing that out. Maybe Futaba has some reasonably priced ones... Spektrum's are so expensive.

Thanks for the advice!

 

[Tony]

Check out hitec servos, it's what I'm running in my 50" plane and they are fantastic. If Randy (rdsok) gets in here, he can give you some suggestions on some really good servos.

And one safety measure you can do is run some epoxy over the seams of the tank. Make sure to lightly scuff the tank so that the epoxy has something to hold on to and use alcohol to clean it before applying it.

You are going to have to post up some pictures of this bird. I love bipes.

 

[mooserider]

Amain has these two that seem affordable:

$30 - HiTec: Hitec HS-625MG High Speed Metal Gear Servo S/JR/Z [HRC32625S] | Cars & Trucks - AMain Performance Hobbies
$35 - Futaba: Futaba S3305 High Torque Servo w/Metal Gears [FUTM0045] | Cars & Trucks - AMain Performance Hobbies

That's $150 for just the servos... ouch! But they should be worth it. I always thought HiTec was some cheapo brand, but I really don't know anything about them. If you all have had good luck with them, I'll give them a shot!

The epoxy is a great idea, thanks again Tony!

 

[Tony]

Wait for Randy to come in here. He knows those servos a lot better than I do. I ordered mine before knowing him, and once he saw them, he immediately said I should have went with another number. Mine don't have an output bearing and the ones he said did. As for being a cheapo brand, nope. They are just old as dirt lol. They have been around for years.

 

[mooserider]

Cool! I should really say, I didn't mean anything by the 'cheapo' comment... I don't want to tick off a lot of folks that use them. I should have just said, since I had recently heard of them, I wasn't sure how proven of a brand it was. I thought the same thing about Savox. I've only ever had Futaba and Spektrum gear, so that's all I know.

Does anyone bother with the 'flying wires' on the stab and tail? The tail section is pretty beefy already, and the feathers are all built up and sheeted. I actually cut little triangles out of the sheeting because it seemed like overkill... I hope I don't regret it!

 

[Tony]

flying wires? Do you mean a pull-pull setup? If so, that is pretty much what is used on every 3d planes rudder. Elevator though is always push-pull.

 

[RandyDSok]

Wait for Randy to come in here. He knows those servos a lot better than I do. I ordered mine before knowing him, and once he saw them, he immediately said I should have went with another number. Mine don't have an output bearing and the ones he said did. As for being a cheapo brand, nope. They are just old as dirt lol. They have been around for years.

My info is pretty dated these days... that and I was only using mini/micro sized servo's....

The standard sized ones that mooserider mentioned look pretty good... I'd also suggest looking at the Savox MG servos as well before deciding. I would recommend dual ball bearing also... nylon bushings wear quickly and also get sloppy over time. I spend more up front on a quality servo so they will outlast the model I'm putting them in.

- - - Updated - - -

flying wires? Do you mean a pull-pull setup? If so, that is pretty much what is used on every 3d planes rudder. Elevator though is always push-pull.

Flying wires add additional support on the structures they are used on... typically seen between the bipe's wings and sometimes on the tail surfaces.


If the instructions calls for them, certainly but... if they aren't mentioned and if you plan on really hard aerobatics... may not be a bad idea.

 

[Tony]

Ah, flying wires. I wasn't even thinking about the wires to add strength.

and I told you Randy would have a few answers. lol.

 

[mooserider]

Thanks you guys. I'll also look at those Savox and compare prices. Just discovered centralhobbies.com last night. They have a somewhat better selection than amain.com I think... at least with kit-building parts.

 

[mooserider]

Here's a pic of what I have right now. Just now joining the two top wing halves. Threw in the other stuff as well (forgot the bottom wing halves). Simultaneously working on the fuse when waiting on wing stuff to dry. Apart for doing this 10 years ago, all I've done i the put the firewall on and start the wing joining. Observant folks will notice that most of the plans are missing. This is due to having it in storage in the same room as my pet chinchillas (which love to chew things). I have some balsa that was chewed on too, but nothing that can't easily be fixed.

FYI, I have a question for you all about glassing wings below the pic.



So I have fiberglassed ever wing I've ever built. My dad made a P51 kit (OS .61 in it) and he gave it to me after he built it. But he didn't glass the wing. I've also had a Kaos have its wings fold on me (doing a split-S), even though it was glassed... it just broke the wing right past the fiberglass.

I'm going to maiden this P51 soon. Because it's not fiberglassed, I figure I'm going to always have to treat it like an egg when flying. How much do you all think fiberglassing matters? Don't get me wrong, I'm going to fiberglass the wings on the biplane, but I'm curious what you're experiences are.

 

[RandyDSok]

I really suspect it depends on the quality of the kit design and the wood used... along with how well the builder does their job. Great Planes has good designs generally... as long as the wood doesn't have any odd imperfections and the builder followed the build instructions there shouldn't be a need to add fiberglass in most cases. I've seen numerous Kaos' fly without incident as well and have not read of any problems with them... there were likely other issues involved in that failure.

Failures can happen even with good kits/builds, I had a 3DHS 300 SHP that had it's horizontal stab fail during a power dive... the manufacturer felt it was caused by a defect in the balsa and they replaced all of the broken parts for free. The point being, sometimes there is nothing you can do as a builder to avoid an issue other than inspecting everything as much as possible and then... even unseen issues can still happen.

I'd suggest you build it according to plan... adding fiberglass where none is required is just adding unneeded weight. Extra weight could, in some cases, cause failures by the added stress in other areas that weren't designed for that much stress. I don't believe just a little extra in the area of the wing joint would be enough to amount to much in a high G maneuver actually... but if there were other areas that had added weight also... it'd all add up. I'd think something else contributed to the failure you saw on the Kaos... but it's hard to guess at these things and be right without more real info to base those guess's on.

 

[mooserider]

Thanks rdsok! I mean, usually I build 98% to plan, but there's a few things I always tweak. You guys probably do too (?) I'd guess.

Speaking of which... what are some of those things? That's really what I'd like to know from other kit builders. Is there a good thread on this stuff? Not sure about you guys... but for example, this kit has a servo tray that's 1/8th inch thick. I learned on my first kit (Eaglet .20) to either use a plastic one or double (better, triple) the ply on those cause the screws tend to strip on the servos. 1/8th inch ply holding my servos in on a .90 size plane, or a .40, is just crazy to me. I also use plywood wherever I attach control horns; CA the whole tank and firewall area (like this skybolt didn't say to do it), usually add a brace or two for the pushrods in the rear, add a hatch for the tank, and I'm usually adding some triangle bracing in certain areas.

Maybe there's a thread already for that kind of kit tweaks? The one thing I've always hated when glassing though, is monokoting over it... it just doesn't stick. Not just to the glass, but if you put the monokote over the glassing, cut it, then monokote the other half and try to monokoke over where other wing half (where there's already monokote), it barely sticks. Not sure why that is... you have to get it really hot.

 

[RandyDSok]

I've always thought that good engineering includes both strength as well as weak points in the proper areas.

Take fixed landing gear as an example. You certainly want them to hold up to some rough landings... but you also don't want them so strong that if you had a bad one, that they don't give and end up completely tearing up the area they are attached to. You want them to break away at some point to help limit possible damage in a hard landing. Let's use the servo tray as another one... you certainly want good lateral stability so they don't flex... but you also want them to fail at a point before damage could also happen to the servo's they hold in place.

Back when I was building from a kit... we were using epoxy to seal the engine compartment, firewall and tank areas... but CA was new and expensive back then also. Failure wise... CA is going to make a more brittle but a lighter joint and epoxy a little more flexible, adds more strength but also is heavier. I'd probably choose epoxy for the firewall area to seal the wood and add some strength... and CA for within the fuel tank area.

 

[mooserider]

Ya, that's close to what I just did too. I epoxy in the firewall, then some triangle pieces behind it. And then use CA for both the tank area and the engine compartment and the rest of the firewall.

Rdsok, sorry to bug you one more time... I've looked over a lot of servos and here are my best options I think. But I have a question below about voltage and the flight pack. All of these have dual bearings and metal gears. Savok, though, has a warning on all the pages about issues with certain ESC and receiver combos. This is a nitro plane, so no ESC. Should I be concerned that you know of?

Savoc ($30): Savox SC-0252MG Standard Digital Metal Gear Servo [SAV-SC-0252MG] | Cars & Trucks - AMain Performance Hobbies
HiTec ($40): Hitec HS-5645MG Digital High Torque Metal Gear Servo [HRC35645S] | Cars & Trucks - AMain Performance Hobbies
Futaba ($35): https://www.centralhobbies.com/prod_detail.php?cat=12&subcat=81&id=2111

I need 5, so Savoc would save me $50!

The torque and such is given at 6 volts for the Savoc, and 4.8 for the HiTec. All I have now are two 4.8v flight packs... one ~12 yr old spektrum NiCd, and a newer NiMh one. I guess I'd need a new flight pack for the Savoc?

Thanks!

 

[RandyDSok]

On the Hitec ... they list both the 4.8v values as well as the 6v

The issue that Savox is warning about is also going to apply to the other servo's as well. Basically lower quality ESC's and BEC's don't have the higher amperage ratings needed provide the current needed... many only supply around 2-3a ... 5a or more is about what I'd recommend.

You'll want your battery pack's to be able to sustain at least the 5a if not more. Since many rechargeable batteries don't perform well after 2-3 years... I'd consider getting newer packs. The older the pack, the quicker they'll drain their available capacity. If your packs fail in flight, you end up with an unguided missle