I remember the SIG Primary Force hitting the streets in January of 2006, I do believe. I had a standing order for one with SIG through the hobby shop I worked at and pestered Mike Gretz to make sure I got one of the first ones off the container when they came in!! I got mine at the end of January and had it put together in time for our February "Ice-O-Lated" contest that year. I put up two roundy round flights just to check things out two days before the contest. Then the morning of the contest, put up one pattern to check it out and decided it needed some nose weight, so I added a 1/2 ounce or so. I had it powered with an LA.25 just like the instructions called for, and it was built exactly as per instructions, and used all the included hardware except for the push rod, as it was just a fraction too short. I did the set up exactly as the instructions called out for line length, handle spacing, balance point and such and I think it weighed 44 or 45 ounces. The result was on it's 4th and 5th flights in the contest it earned a 2nd place if I remember correctly. I was pretty impressed with the little airplane, to say the least.
I have been flying the airplane ever since then. Some where along the line, the original covering started to come off, so I had to recover it. The air frame was pretty soaked with oil and I had to "dry " it out from nose to tail and wing tip to wing tip. The outboard wheel pant was almost 2 ounces heavier than the inboard wheel pant! That makes for some strange trim characteristics!! Along the way, I had changed the engine from the LA.25 to the FP-.25 just to get some experience with that. The LA flew the model OK, but was right on the ragged edge of power. The FP-was stronger but not much more reserve. When recovering it, I dug out a lot of the lead shot I had glued into the nose for balance weight so I could install an OS.32F. That was a real step up and I loved the combination. The finished weight after the recover was 45 or 46 ounces. This combo got me a lot of hardware over the years. It was my go to model anytime I wanted a few quick flights. It flew and ran the same every time it came off the wall. As we got into the flying season of 2021, things began to change.
The model was flying kind of funny, and the engine started to make funny noises. I worked with the airplane for weeks. The noises were a bad bearing in the engine, so I replaced that. I played around with props trying to improve things. I actually had the SAME Zinger Pro 11-4 on it for who knows how long, maybe 10 years or more. It was the prop that worked the best in initial testing with the OS.32F, and it was still that first prop! I pulled it off to inspect and saw that it was pretty oil soaked itself by this time, and I checked it on a pitch gauge and saw it had relaxed a bit to almost 3" pitch!! . That was why I had to scream the guts out of the engine to get a lap time I wanted. . I was making some improvements, but the engine, while seeming to run well after the bearing changes, was using more fuel. It was not leaking out anywhere but suddenly I could not get the pattern in on a 4 1/4 ounce tank full. I experimented with some other tanks and added an extension to the original one with mixed results. I decided to do an engine change and replaced the original one with a low time .32F I had waiting in my stash. All I had to do was swap the venturi over from the original. After I was finished, I thought to put the model on the scale and was surprised at what I saw. It was over 50 ounces!!! Now that will affect things with trim and how an engine runs, won't it!!
Today was the test flights with the new engine. I got one flight with a 5 ounce tank I had tried before and the engine sped up through the flight like I had been experiencing, but I could tell the engine was a bit stronger and the run time was much longer on the same amount of fuel.. I swapped out the tank for the original tank I had on it, and the lap times steadied out. I put in 2 more flights and decided to take the wheel pants off. The outboard wheel pant was again VERY heavy, as it's right in line with the engine exhaust, and I probably made the overall weight 2 ounces lighter!! The next couple of flights were much better and almost like old times again. But the writing was on the wall, I think it is time to retire the old girl!! The covering was still in good shape and I didn't want to have to recover it again just to "de-oil " it.
I went up to the attic to "Dan's Hobby Shop" and pulled down a SIG Primary ARF kit that I picked up off of some one on the forum here. He had messed up the engine mounts and gave me a good deal on it, and I started in on it last night by fixing the carved out engine mounts so it will fit the OS.32F again. I put all the kit contents on a scale along with the .32F and it came to 33 ounces. By the time I add some glue, a prop and tank I'm hoping to have it as close to 40 ounces as I can. I'll just duplicate everything I got on the original model. When it's finished, checked out trim flights are finished ( very few expected to be needed) I'll hand the original one on the wall and relegate it to fun fly duty.
I would like to thank Mike Pratt for designing the Primary Force and SIG Manufacturing and the late Mike Gretz for producing such a fine model. I have built several of the other's on the market but I think this kit was the best ARF on the market, certainly at least for being able to use everything that came in the box. Some of the hardware was a bit iffy, and I will replace whatever I think I need to on this one. But this first one was, as they say, stock as a rock!! Who knows how many flights it has on it?? The only repairs was to replace the C/A hinges form the original kit with barrel hinges because the original were so oil soaked! So now it's out to the garage to continue working on the new Primary Force ARF.
Has anyone else out there had a Primary Force ARF in service this long? I'm laying claim to the very first one in the air and probably the longest service from one.
Type at you later,
Dan McEntee
Topic: There Comes a Time for Everything : SIG Primary Force Retirement (Read 1160 times)