Easy Engine Testing — Safe and Cheap!

Dec 11, 2013 5 Comments by

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 which I removed from my Fokker Triplane to test run it. The firewall is equipped with Soft Engine mounts available from Nick Ziroli Plans. Fuel tank (and smoke oil tank) are installed and the throttle linkage and choke linkage are also already worked out. But to adjust the carburetor and select the correct propeller, this is how I do it.

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I make a heavy-duty, open top box from 3/4-inch pine boards which I screwed together with sheetrock 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.

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The engine box is attached to a sturdy picnic table with 3-inch-long Deck screws and is very secure. 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.

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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 www.horizonhobby.com

Falcon Propellers www.falconpropellers.com

Slimline Mufflers www.slimlineproducts.com

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

test flight

Test flight day. The GT-80 fired right up without a hitch!

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

 

Featured News, Gerry Yarrish, Scale

About the author

Senior Technical Editor About Me: I have a lifelong passion for all things scale, and I love to design, build and fly scale RC airplanes. With 20 plus years as part of the Air Age family of magazines, I love producing Model Airplane News and Electric Flight.

5 Responses to “Easy Engine Testing — Safe and Cheap!”

  1. Wayne Mallaber says:

    I spoke with BalsUSA about the DR 1 and they said it would fly on a 50cc, I feel that may not be enough and am considering the DLE 60 twin. Do you feel the Zenoah 80 twin you are installing is more than necessary or is the extra nose weight more important. I like reserve power also plus you don’t need to fly full throttle.

  2. Roderick Warren says:

    Yes sir, I sure do! I would like to have your mail address. I have a small envelope with two copies of your article ” Zenoah GT- 80 Engine Run for Giant Tri planes”. I would like to ask you if what I will send you, was typical of ALL of your articles. Look at the blank pages, Last month I down loaded an article and I used a whole ream of paper because of this kind of thing. That article was immensely more like this. Can’t you get people in to correct this? I switched from the magazine to this mag ( TO DOWN LOAD ARTICLES) & get away from all of the ad’s. To much paper. Can’t they set the program to make it print both sides and no blank pages. (Missing pictures) etc, WHOW!

  3. Gerry Yarrish says:

    Hi Wayne. I am sure the Triplane will fly with a 50cc engine, but as you mentioned, the airplane will need nose weight to balance properly. The new DLE 60cc twin looks like a great choice. I chose the GT80 simply because I had it in my collection and thought it would be great to spin the 32x 8 prop instead of a smaller 22×6/10 prop with my G-62.
    Cheers,
    GY

  4. Gerry Yarrish says:

    HiRoderick. sorry to hear you are having difficulty downloading the posts here on the MAN site. I will let the web department know about it. I would suggest, highlighting the page you want and then past it into a word document, so you can print it out that way.
    Cheers,
    GY

  5. Ed Y says:

    I want to ask you to please confirm the RPM numbers you got on the GT80 with the 26-8 prop. I have been using and tuning GT80′s for many years and I can only get 7,900 to 8,000 rpm with a 23-8 Mejzlic, which is not very heavy. I have used several types of mufflers, including the stock Zenoah, which render only around 7,500 rpm with the 23-8.
    Thanks
    Ed

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