• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.
Pumpkin drop event

Sig Rascal 110 ARF Build

Joker 53150

Mmmmmmm, balsa.
In theory this should be a fairly quick build thread since I'm starting with an ARF that already has most of the work done (servo installations, pull-pull for the rudder, and power switch). I picked this plane up a couple months ago for a price I couldn't resist. It was never flown, although it did have a glow engine installed and appeared ready to go. In my opinion, the Rascal is one of the best looking planes on the market and I never thought I'd end up with the big 110" version (I'm cheap). Below is a generic pic I found to give you a size reference. This plane just barely fits in my work van, with maybe 1/2" to spare.


The glow engine was removed and sold, which helped cut my total investment in this project. The first thing I need to do now is strip out all the misc. pieces that need updating for a gas engine - engine mounts, fuel tank, and some of the original 72 mHz electronics. The wing struts are sitting next to it and still in their original bags.


The original owner went through a lot of effort to protect the receiver, having made a nice ply box with carpet and foam padding.


This is the engine I'm planning to use, an XYZ 26cc gasser. It's going to take a little effort to get it mounted as the original mounting base for it is long gone, and I haven't been able to find a stock replacement. A new mount won't be too difficult and the process may help people in the future. I'm not thrilled about the big muffler and carb that will be sticking out the sides of the cowl. :( Some engines have the carb rear mounted between the engine and firewall, but my experience with those is that they're a pain to tune due to limited access.


So far the biggest problem I'm having with the disassembly is getting the dang fuel tank out! I had to pull the tank to get new gas lines installed, and it appears that I'll have to break or at least modify (cut) the ply plate to get the tank out. I've already removed the windscreen and dashboard and still no love. Oh well, it'll have to wait till later in the week as I'm going to be on the road for the next few days.


Another project that will need to be done for this plane is making wing bags. With this project, my only real concern is the engine. I bought it used and have never run it, so hopefully it doesn't have any hidden problems.

Joker 53150

Mmmmmmm, balsa.
The first big job with this plane is getting the engine installed on the firewall and then getting it started. After I confirm it runs I'll get all the additional hardware installed. I'm not expecting problems, but you never know when buying used equipment. I pulled the muffler, carb, and spark plug and the piston looks like it's in great shape, with no visible scoring. The top of the plug has a little build-up, but that's normal. The instructions (found online) show the distance from the firewall to the prop mounting plate to be exactly 6". To make that happen I need to build a box 1.9" deep


I'm starting with the side of the box which bolts to the firewall and will build out from there, and I can work with the mounting bolt locations from the original glow engine. I drew the alignment marks on the wood before bolting it to the firewall, and after doing so I noticed that it doesn't line up properly with the center line marks on the firewall. It was my mistake, but all it means is I just draw new lines to match the factory lines on the firewall.

Note that the engine is mounted slightly up and right when looking at the firewall. The plane has built-in down & left thrust, and using the factory marks on the firewall ends up with the prop centered in the cowl. Hopefully.


This micrometer is worth every penny when trying to make all the measurements for the engine mount. Harbor Freight sells digital versions cheap, but I'm used to reading the scale on this one.


Joker 53150

Mmmmmmm, balsa.
I try not to rush some parts of the build. Now that I sit here and think about it at 4:15 AM, I come up with a new plan and will start the mounting process over! :)


Well-known member
Do you ever wake up and the first thought is, "Oh... I figured it out"? Sometimes the best thinking is done when you're not thinking. I have the same kind of caliper. I wouldn't switch to a digital. The dial is a technological advancement over the Vernier scale. I spent years reading that.

Joker 53150

Mmmmmmm, balsa.
I'm backing up on the engine mount work and doing what I should have done from the start - plug the original holes and start over. While I *COULD* make the original holes work, it won't be as good as simply doing it the right way. So the original plywood was scrapped in favor of 1/8" steel. I've marked and drilled the first bits to make sure it all lines up properly. Next I'll use a cut-off wheel on my angle grinder to trim the plate to size. After the center lines are marked on the steel I'll line it up and drill the holes in the firewall. Stand-offs will either be purchased or built to get it spaced properly.


Joker 53150

Mmmmmmm, balsa.
Back to the Rascal as the Citabria goes to the back-burner. On the last post I showed a new motor mount being made from 1/8" steel, and here's how it works. The engine is bolted to the steel plate and then the assembly is bolted to the firewall. For mounts I'm using Chief Aircraft mounts. I really like this brand because they're adjustable for length. You get the main mounting post along with 3 different thickness extensions which allows you to fine-tune the overall mounting post length. In the configuration shown below I've got the two larger extensions installed, which puts the base for the prop about 6-1/4" away from the firewall. It's supposed to be 6" to land properly in the cowl, so I can remove or exchange a few pieces as needed to make it work.


After the first test-fit I found a clearance issue where the muffler hits the mounting post. This will be an easy fix by simply grinding a little of the mounting plate the the post's edge. Since it's all I had on-hand, the assembly is also mounted with screws. Hex head cap screws will replace these soon.


Joker 53150

Mmmmmmm, balsa.
As mentioned earlier in this thread, I want to fire the gas engine up before I go too far. I bought it used and the ignition module has a couple cracks in it. There is no visible damage to the engine (it shows minimal run time) and the cracks could be from removing it from a plane - hopefully... :)

As I was going through the wiring I noticed this bare wire, which gave me a bit of concern. After further review, it's the shield around the ignition cable. The power and signal wires were also connected together, something I haven't seen before. Maybe it's common and the wires are just better covered by the wire sheath? Either way, I took it all apart to make sure the frayed wires wouldn't come in contact with the power, and then put it all back together in new plug ends.


Other than a gas line, it's ready to test fire! I applied 6V to the ignition module and the plug has a nice, strong spark, so the ignition module was temporarily zip-tied to the stand-offs. I'll use a temporary pushrod cable with a Z-bend in the end to act as a throttle and have a buddy help me get it tested. Assuming it all goes well, the ignition module will be tucked away and the cables made a little neater.


Joker 53150

Mmmmmmm, balsa.
It lives!

I was scheduled to be out of town tonight, but the plans changed and I found myself with a couple hours and daylight, so I decided to try firing up the XYZ 26cc gasser. Testing last night showed the ignition worked so I attached my bottle of 20:1 (quite a bit richer than it really calls for, but the bottle was easy to hook up), put in a battery, and tried hand-propping it. I did get it to pull gas up and out of the bottle, which is a good sign. No love on making it spit fire, however, so I robbed the spinner from my 1/4 scale Cub and tried it with the electric starter.

Still no love.

I pulled the plug and found it was wet. After removing the excess gas I found it wasn't sparking. Well, it'd spark occasionally, but not consistently. To make sure it wasn't from a low battery condition I tried three other batteries with no luck. Finally I swapped out the ignition module with one from a Turnigy 58cc gasser and had a consistent spark again! Before firing it, I "secured" the module to one of the motor mounts with zip ties. Well, half-ass tied it out of the way is more accurate... :)

A couple quick hits of the starter and it was running! Since there is no throttle servo installed I had to use the idle-adjust screw to bump the idle up enough to keep it running. It's also still running on the rich mixture, but it's got a very responsive throttle.

Now that I know it runs I can move forward with the rest of the assembly. I'm certainly glad I tested it before getting the original ignition installed..!


Joker 53150

Mmmmmmm, balsa.
I'm going to try some new (to me) products for the power on this plane. Since it doesn't have flaps and isn't a 3D ship my power requirements won't be too crazy. I had thought about using a full power distribution board, but decided against it as that's a little over-kill. Instead I've ordered the following:

The Dualsky VR Pro Duo will act as my power regulator and battery isolator. Two 3000mAh Nano-Tech 2 cell LiPo batteries will send power into the Dualsky VR Pro Duo. A single battery failure will not disrupt the flight, and it also includes a power-kill plug so I don't have to remove the wing or flip switches to cut power between flights. Using two 3000mAh packs should give me a ton of flight time.


To power the engine's ignition module I'm using a Tech-Aero Designs "Ultra IBEC". It takes power from the receiver like the servos do, and further regulates the voltage as necessary (I'm setting both regulators to 6V). The Ultra IBEC has a built-in kill switch which lets me kill the engine from the transmitter with a flick of a switch. It also filters the signal more than other similar switches and has gotten a lot of very positive reviews. An LED is included to visually indicate that the ignition is live - kind of important to know...! :)


On bigger planes or ones with more servos I'd go with the power distribution board or at least isolate the ignition module from the flight batteries. The 1/3 scale Cessna 152 I've got will use the distribution board. It's got 9 servos and lights, so keeping the ignition separate is just good insurance. Plus, the distribution board helps keep the wiring mess under control.

Joker 53150

Mmmmmmm, balsa.
I wasn't happy with the stock fuel tank location in the Rascal. It's up high in the nose and to remove it I had to break off the wood braces holding it in place. I'd rather have it sitting on the floor inside the cabin of the plane, so that's what I'm going to do. There is plenty of room for a bigger tank - the stock one was 14 ounce, which would give me about 13-15 minutes of flight time based on calculations I've seen. That's plenty of flight time in my opinion.

Instead of simply relocating the stock tank I'm again going to try something new (to me), and use a Fiji or Smart water bottle. PSP Manufacturing makes high quality aluminum caps to replace the original plastic cap, along with the hose, copper tube, clunk, and fittings for either 2 or 3 line setups. Many people use the original plastic cap, but there are plenty of reports of it cracking and leaking, so aluminum is cheap-ish insurance against that happening. I can wedge a 1L bottle in the nose of the Rascal, but 32oz of gas is FAR more than I'll want to carry! The next smallest bottle my local Kwik Trip has is 500ml, so about 16oz. Fiji also has a 700ml "sport bottle", but I haven't found one locally yet and I don't recall if it's the nice squared shape like the 500 and 1L sizes, so I may just stick with what I've got.


As said, I'm going with a simple 2-line setup which means the gas tank will have a clunk and a vent. I'll fill and drain the tank through the clunk line, and will also have a DuBro fuel valve instead of the T-Fitting and fuel dot shown in the pic below. The inline filter will be placed as-shown to filter any gas getting to the engine.