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Easy RC Airplane Engine Testing — Keeping it Cheap and Safe!

Easy RC Airplane Engine Testing — Keeping it Cheap and Safe!

When ever I test run and adjust a new engine, I prefer to set it up on a sturdy test stand/table instead of on the model airplane. Here is my Zenoah GT-80, 80cc twin-cylinder gasoline engine for my Fokker Triplane that I am test running. Fuel tank (and smoke oil tank) are installed and the throttle linkage and choke linkage are also worked out. But to adjust the carburetor and select the correct propeller, this is how I do it.

Easy Engine Testing -- Safe and Cheap!

I make a heavy-duty, open top box from 3/4-inch pine boards which I screwed together with sheet rock screws. I then added a birch plywood face drilled to accept the engine. I used 1/4-28 cap-head bolts (the same as on the model,) and the throttle linkage is also exactly the same geometry as in the model. This way I could fine tune the servo travel and end-points with my  Spectrum DX18 transmitter. The servo and receiver and battery pack are all properly installed in the engine test box as is a 32 oz. Sullivan fuel tank. I installed a 2-line fuel setup and use a T-fitting and a fuel dot for filling and draining the tank. For this engine I am using smoke mufflers from Slimline Products and the engine is very quiet and the performance is excellent. No over-heating at all.

Easy Engine Testing -- Safe and Cheap!

The engine box is attached to a sturdy picnic table with 3-inch-long Deck screws and is very secure. (My wife was not pleased so I recommend an old table you can use exclusively for RC stuff).

The box is also very easy to remove after testing and I keep it handy in the workshop. The birch “firewall” pad can be changed out to match different engines. For testing I used a variety of 24 to 27 inch propellers and I finally selected a hardwood Falcon 26×8 propeller with excellent results.  The fuel is a gas/oil mix of 50:1 using Husqvarna Chainsaw 2-stroke oil. It comes in convenient 2.6oz. bottles ideal for mixing with 1 gallon of gasoline for the 50:1 ratio.

Easy Engine Testing -- Safe and Cheap!

The engine has a starter spring attached to the aft end of the crankshaft  so the GT-80 is very easy to start without using a big  electric starter.

Starting procedure is: 1, close the choke and open the throttle fully. 2, Grab the prop and pull it clockwise to load the spring. 3, At the 2 o’clock position simply release the prop tip and the engine spring spins the prop. After about 5 or 6 tries, the engine will “bark” to indicate it has enough prime in the carburetor. 4, Open the choke, and set the throttle just above idle with trim full open. 5, The engine starts after about 3 more flips and it settles into a nice idle. Lowest reliable setting gave an idle just under 1,950 rpm and the top end without adjusting the carburetor was a smidge under 7,000 rpm. I used a digital GloBee optical tachometer to check the numbers.

After running  two full tanks run through the engine and tweaking the carburetor it was ready for re-installation in my Balsa USA triplane. My test flight of the 1/3-scale Triplane (back in August,) was very successful and the engine performed perfectly not requiring any additional adjustment. I really like using this engine test box setup to adjust my engines, especially large gasoline buring beasts. Give it a try. And remember, safety first when ever handling and running any RC engine.

Zenoah Engines

Falcon Propellers

Slimline Mufflers

Easy Engine Testing -- Safe and Cheap!

Engine shown in the unfinished Triplane. Notice clearances cut for proper cooling.


Test flight day at the flying field. The GT-80 fired right up without a hitch!

 Zenoah GT-80

I found that  Falcon 26×8 propeller and Zenoah GT-80 combo ideal for this giant scale triplane.


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  1. Holy cow!!! Magneto ignition, all your components directly over the engine? No fear of RF? You can tell I’m old school!!!

  2. I think what you have created here is an air dam. Although you have an exit at the bottom of the cowl, it is forward of where the exit should be. What you need is free-flow exiting air that should have an exit at least twice the size of the inlet. Some recommend three to four times the size. So you don’t think I’m new to this, I started building flying models in the 1950’s. Here is a link to back up what I’ve mentioned. https://www.youtube.com/watch?v=bfSv0V7r4HA

  3. Although it may seem strange, I test my engines on the maiden flights! I set the HIGH needle valve to run just a bit “fat” and make sure the LOW needle valve and idle is set, run the engine a few ounces to test RPM and engine temps at the spark plug, let it cool down, and a while later start up and go fly. Been doing it this way for most of my 30+ years of RC, both glow and gas. If it runs reliably on the ground, then it’s very likely to keep running in the air. Of course, any overheating on the ground makes a pretty good point to look at why it overheated. If the engine is giving you some obvious negative indicators on the ground, then it’s wise to deal with those first because getting airborne is no magic solution and many times the problems only become worse. Lane

  4. Sure would like more detail and maybe a pitcher of that recoil starter spring. I recall favorably spring starters on Cox engines back in the 60’s.

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