Greater Southwest Aero Modelers TECH SITE

SUPER SKYBOLT ARF &  Echo 1.3 Gas Engine 

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Great Planes Super Skybolt is one of the finest biplanes available in a .60 sized airframe. After owning one which was powered with an OS 1.20AX engine, I thought it was time to step up to something more interesting. I happened to have a tiny 1.3 cubic inch gas engine laying around. It's an Echo GT200R 21.2cc Weedeater. This engine happens to be identical to the engine that First Place Engines uses as their FPE 1.3 powerplant. This is handy for me as all of their parts interchange with my Echo Engine.

Putting a gasoline engine into a Super Skybolt isn't particularly difficult, and I have done this before using a glow engine conversion. However, it does require some planning and structural modifications. It's necessary for the airframe to be beefed up to support the added weight and power of a gas engine. Now would be a good time to mention the Zenoah G 20 as a good engine choice for the Super Skybolt. It makes excellent power and it is 2 ounces lighter than the Echo.   

ABOUT the ENGINES:  My Echo conversion  the  First Place Engines 1.3 and the  Zenoah G20

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As it turns out, my prop hub is about a half inch shorter than the FPE version, making it necessary to build a longer stand-off.

My Echo engine probably isn't the best choice for this aircraft but it was readilly available, and it runs like a top. I ordered a Pitts style muffler from FPE and it should be here soon.  I also ordered and received a Walbro WT 600 carb. This will give me a littler better performance. Right now, it's taching 8000 RPM on an APC 15x8 prop. I'm fairly sure I can get 8300 RPM out of it. Once I get the engine all dialed in, I will begin the airframe mods to accept the engine. I have a Zenoah G20 in a CAP 10, and from what I've seen so far, the G20 would be a little better suited for this biplane. Ho well, I'll use what I have.

ABOUT the AIRCRAFT:  Great Planes Super Skybolt and my 1.20 powered Super Skybolt

This is one of Great Planes' best flying airplanes ever! It has been around as a kit for years, and when it came out as an ARF I bought one. I powered mine with an OS 1.20AX. People thought I was crazy... But it flew like a champ and stayed together even through the wildest maneuvers. Virtually everyone at our field that bought a Super Skybolt also bought an OS 1.20AX for theirs too. That says a lot about the toughness of this biplane. Unfortunately, I lost my Super Skybolt last year in a MID-AIR collision.... It's now being replaced. But this time it will be gasoline powered.

While I wait for the Skybolt to arrive, I downloaded the owners manual so I could get some information, specifically the distance from the firewall to the prophub. This is 5 7/8 inches. I will have to make a stand-off for the engine! This is good, as it allows me to set the engine in its proper position without cutting the fuselage. This also allows my to make a stand-off that best suits this application. I decided on a built-up 1" plywood stand-off with 1/2" aluminum spacers for the engine. This makes up the 1 1/2" of space needed between the firewall and the prophub.

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This is the front & side view of the new stand-off. It will be mounted on the Skybolt firewall with glue, four #10x1 wood screws, and fiberglassed. This is a rock-solid (over-kill) mount for the engine, but I'd rather be safe than sorry. The Skybolt firewall will be fiberglassed around the perimiter before this stand-off gets mounted. The aluminum spacers for the engine are short (1/2") this helps keep the bolts tight and resistant to vibration. I enlarged the center hole as big as I could go (not shown in the photo), to lower the weight a little more. It won't make a huge difference, but every little bit matters. I will now mount the engine and stand-off on my test stand to test it for strength and stability.

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So far everything looks good. The engine mounted SOLID and the mounting bolts are easy to get to. Next I'll fire it up and work it over, I will also try out my new Walbro carb. OK, I fired it up. It's as perfect as it can possibly be AND the new Walbro WT600 purrs like a kitten. Now, if my Pitts muffler & Skybolt would show up... NOTE: the muffler shown here is a Bennett Muffler for a Zenoah G23. I had to re-machine the bolt centers to make it fit.

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Here is the FPE 1.3 Pitts Muffler mounted on my ECHO GT200R. It's nice & compact and should fit the Skybolt nicely. This muffler sort of robbed me of about 400 RPM as compared to the Bennett. But, the engine is still spinning an APC 15x8 at 8400 RPM so I'm not hurting for go-power. If I could find an exhaust header I'd pipe this engine.

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The engine is being run-in here and getting a good tuneup. It ran over 3 hours on 16oz. of gas at an 1800RPM idle. It didn't hiccup a single time. I settled on a Walbro WT-540 carb as  it provided the best overall performance. I haven't decided on the velocity stack yet, but I'm leaning towards leaving it off. This photo shows the stand-off block which I painted to seal the plywood from gas/oil contamination.    

NECESSARY SKYBOLT MODS:

(1) Fiberglass the outer perimeter of the Skybolt firewall
(2) Move the elevator & rudder servos to the rear of the fuselage.
(3) Add flying wires to the tailfeathers.
(4) Add a stand-off box for the engine
(5) change the fuel tank stopper to GAS compatable stopper change to Tygon fuel line.
(6) Add an access hatch for the ignition.

With the exception of these mods, the Super Skybolt assembles as per the manual. I will photpgraph and document all the MODS while building my Skybolt.

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