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Jul 02, 2019, 11:17 AM
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Originally Posted by koppterX
glad to hear the improvement! but i'm still confused about the vertical performance. that airplane should accelerate vertically for as long as you want to do. are you saying that it will actually stall on the vertical?
Yes it will. Even with 6500 plus RPM on the ground, swinging the Falcon prop. There is no noticeable drop in RPM doing a vertical, it just eventually runs out of thrust. My thought is the RCGF isn't totally happy with the "cans" I have. At this point though it is vastly improved over how it was behaving. I would think that there is some "unloading" of the prop in the air over what I see on the ground. However it doesn't "rip" as I would expect. Reading other posts from folks running DA's, DLE's or what not, there are a number of folks who don't see the RPM's I'm seeing, with the same prop. I ran the same engine on a 15 year old Giles 202 for a few flights using the stock exhaust and it would totally "rip" a 27x10 wood prop. But, the damn thing was so loud it was obnoxious. There is also a 7" difference in wing span between the two aircraft as well. With the Pilot Extra at 107" and the Giles at 100". I have thought of installing the stock mufflers, but I'm a little hesitant at this point because I really don't want to cut the holes in the cowl, and I'm pretty satisfied with the performance. I'm going to put in a new set of plugs before the weekend, make a SMALL adjustment on the low speed needle and see how things go this weekend. And I still haven't fiddled with timing. There is a paper out there for the RCGF 120 saying they like to run with the timing advanced. We'll see...
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Jul 08, 2019, 10:29 AM
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Lot's of stuff to update. I ended up getting the canister/headers down to the recommended length used by various other users using DA, DLE and other 120cc engines. I was seeing right at 6600 rpm on the ground. During all of this I noticed that the hall sensor was loose and put a drop of blue Loctite on each mounting screw to keep them from backing out. The next day as I was installing the cowl, both of the mounting tabs had completely come apart rendering the sensor useless. I ordered a new sensor for a DLE twin from Tower Hobbies so I would be able to fly the weekend. Part came in Friday and I was set! BUT, when I mounted the sensor it was just that little bit off on the mounting ears opposed to the RCGF sensor. All that said it was workable. I set the sensor up like the original sensor, putting the mounting screws midway in the ears. I then but a degree wheel on the crank, located TDC and checked the timing. It was actually spot on, at 42 degrees. What I didn't know until Sunday, was that the timing can be set on either side of the sensor. In other words, the pickup magnet can be on the "front" of the sensor or the "back" of the sensor. Both are viable ways to time the engine, as long as you use the correct degrees of timing for the side of the sensor you are on. So, using the left side of the sensor (front) you should be at 28 degrees. using the right side (back) of the sensor you should be at 42 degrees. In reality, if you set the timing CORRECTLY, you can not have one with out the other. Unless your a dork like me and use 42 degrees on the FRONT side of the sensor and don't check the back side. So in essence what I have been doing is running the engine about 14 degrees to far advanced throughout the whole canister tweaking process. UGHHHHH!
Flash forward to Sunday. I got to the field bright and early expecting great things! First flight..... horrible performance, pretty much the same as it was before I started this whole process. Which pissed me off as it had actually improved earlier. I had also spit off one of the canisters in about 5 minutes of flying. That was the last straw, I loaded up, went home, installed the stock exhaust, modified the cowl checked the timing and actually watched a video of someone timing a DLE 120. I immediately saw my mistake. I corrected the timing and went back to the field now sporting the stock exhaust. I was expecting ear piercing exhaust noise. BUT! much to my surprise it was actually about the same as it was with the canisters. I was a bit shocked! (I suspect the Falcon prop had a lot to do with that) I also expected the carburation to be off a bit. All seemed well on the ground though.
Started up, warmed up, throttle response was fine, idle was actually better than before. Oh, oh, this can't be right, it's stock... Took off and on climb out I could tell something was amiss. As I came by on the down wind leg it sounded great! It wasn't laboring, the transition had no 4 stroking, it wasn't even loud. Hummm. Screw it, I came around and "entered the box" Oh my God!!! It actually accelerates up hill! WHAT??? Now I knew something was wrong! It had speed and power everywhere!! I have to reduce throttle in verticals???, Loops, extended vertical lines with rolling maneuvers are not being done WFO?? this can't be! Could this be the mythical performance koppterX spoke of?? I flew two more flights, perfect! The engine transitions fantastic, idle is to die for, it don't die on the roll out, starts easy and consistently, and most importantly it make tons of power! And it's quiet!
So now, after weeks of "issues" I think I have a plane that I can compete with. To date, it has been one thing or another to fix. Either wheels, exhaust, just all sorts of things, most notably the performance. Every time I took it out I had things to work on. That is OVER!
I went to my first contest with less than 10 flights on a plane that I did not know. Actually not having flow an IMAC plane prior, I didn't really know any better. I had to "babysit" the plane through all of the Sportsman maneuvers due to lack of performance. I have been working on that ever since. NOW I have a competitive airframe, with a competitive engine. There are four weeks to the next contest to polish up my maneuvers. It will be hot in Lodi the first week of August, and I like HOT!!!
Last edited by Mooney78865; Jul 09, 2019 at 09:38 AM.
Jul 22, 2019, 10:46 AM
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I went back to the headers and cans that I removed in the previous post. I was not able to get the complete setup tried out previously due to timing, poor attachment etc.
So, I did modify the headers AND the cans to give me a total header length from the center of the exhaust flange to the inlet canister wall of 12". this is measuring from the center of the header and NOT including the "drop" length of the header. I have also "pinned" the couplers with SS screws, along with clamps. I took it out Saturday and was rewarded for my patience. I did not have any issue with attachment points, the engine ran absolutely flawless. The performance had a noticeable increase in mid range, and no reduction in top end over the stock exhaust. And it is quieter! Which was the goal.
Ultimately, I removed about 3.75 inches of total header length. I had to take material from both the headers as well as the canisters.
So, where I ended up with my RCGF 120:
Falcon Carbon prop 27X11
AGM headers and canisters
Total header length to front of canister 12"
Static RPM 6600
Header length DOES matter when using canisters. I have read multiple posts that it does not, but it truly does. While it may not be a critical as it is for tuned pipes, it is critical.

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