RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine
I have read thru most of this thread and have not seen the combination I have built - perhaps I just missed it.
After some initial disappointment with the flying characteristics I finally have the programming done to my liking. My disappointment came from the belly tuck and roll couple in knife edge. Programming now has it flying on rails.
Another undesirable characteristic is “pogo” landings due to the main wheel location being so far in front of the CG. All the stars must be aligned to nail the landing without a couple of hops back into the air. Part of this could be due to my desire for somewhat tail-heavy models.
The Saito 220, which I have converted to electronically timed spark ignition (that is another story), is a sweet combination with the Yak. Most flying is at just over half throttle with full throttle required only on uplines.
I mounted the engine about 25 degrees from horizontal. This allows the stock muffler to exit at an optimum location at the bottom of the cowl and keeps the plug from fouling with oil between flying sessions. I added a full baffle to the front of the cowling with a cutout sized for the width of the engine just in front of it. This allows a minimal sized outlet hole for the cooling air to escape without pressurizing the cowl with incoming air.
The original molded plastic engine mount was not rigid enough for the Saito and was replaced with a Hangar 9 aluminum mount. This made a huge difference in lowering the vibration level caused by the engine bouncing around in the flexible plastic mount.
The all up weight came out just under 15 lbs. with the rudder and elevator servos under the canopy and the battery at the rear of the canopy area. This gives me a rather tail heavy plane which is to my liking.
This is my personal Yak, however, I also assembled one for a customer with a Fuji 46 gasser. It came out one pound heavier. It balanced well with the rudder and elevator servos in the aft end. It has not been flown yet (it is Winter here, folks) but I transferred the same programming to it.
This GP ARF is similar to all the other GP planes I have built, in that, the covering design is beautiful and the application of that beautiful covering sucks. Usually two days are devoted to eliminating all the bubbles and wrinkles. I have finished four GP “Patties” and all have required a lot of time with the heat gun and iron. Incidentally, these all had different engines – a Saito 300 (mine), a Tartan 3.0 Twin, an OS 300, and a DA 50.
I am attaching some pix of the Saito Yak.