Hello,
After experimenting with three different props and pipe setups on the ground, I finally tested the latest configuration (details below) in the air yesterday.
My Intrepid XL did not fly well with launch RPM ~10,200 and using 12x4 MAS 2 blade prop. in 2-4-2 mode. This configuration delivered 2,200 grams (77.6 oz) of static thrust but it was not enough to provide enough pull in the air for the model weighting now almost 72 oz. and to overcame the lines (0.018") air resistance.
The model barely stayed in the air in level flight with Jett exhibiting 2-4-2 break flying sluggishly with lap times approaching 7 seconds.
Using this prop., I can reach 14,000 RPM on the ground and this will provide enough pull but the launch engine mode will be full 2 cycle, the plane will fly too fast with too much lines tension and the engine screaming at probably 16,000 RPM.
It looks I am back at the place I was when I started changing the props and pipe setup.
Going back to my only flight yesterday: I could not test the launch RPM=14,000 because my pipe slid back about 0.5" during level flight and I could not secure the pipe again in place using two new zip ties. No matter how hard I zipped the zip ties ( to the point of breaking them ), the pipe was easily removable by hand. It was simply sliding on the film of oil covering the header.
How do I secure the pipe and with what? Should I crimp the header creating circular grooves and use new zip ties after each flight? Should I perhaps use soft copper wire instead of zip ties? If yes...how to do it without accidentally breaking/damaging soft silicone while twisting the wire?
Perhaps the best solution to have some control over "randomly sliding pipe" is to support it at the rear end with mechanical stop ( small piece of plywood glued to the fuselage with one screw allowing to regulate the pipe's position within, say, 1")]
Clean the internal surfaces of the coupler with lacquer thinner until completely dry, and the same with the outside of the pipe. and outside of the header. That means squeaky clean without even oil from your fingers. Only then should you clap down on the ty-wraps. I also glue a ring around the from end of the pipe with JB-Weld, and rough up the header with 120 grit sandpaper. If you do it right, it will nearly weld itself to the header and pipe to the point it will be difficult to move. And, that's pretty good because you don't want to move it, put it at around 17..5-17.75 and leave it until you get a flyable combination
I can pretty well predict that you *are not* going to have much luck with props like Zingers and Master Airscrews. At the very least, you will need to adjust the launch RPM to get the right in-flight speed for your combination. The only hobby-shop prop that will permit decent performance is the 12.25-3.75 APC, and it will certainly not be ideal. Maybe at a 13-4 Rev Up. In this case you are probably getting very little unload from the ground to the air (because of the extreme parasitic drag of the prop) so it comes out too slow.
I would suggest that the static thrust measurements are not terribly useful. That's in the ballpark of mine
No one runs these engines on unmodified wooden props with much success. It can be done with heavily modified props but that's not a good idea for this case.
Regardless of that, take whatever prop you have, set it at 10,000 on the ground, and launch it. Check the lap times. If it's too slow (like 5.5 or lower), bump it up 200 RPM at a time on consecutive flights until you get around 5.2-5.3. If it's too fast, drop it down 200 RPM or so per flight until you get around 5.2-5.3. Don't change other parts or settings, get your 12.25-3.75, and work towards a good in-flight speed, THEN see how it works in flight. That should be plenty fast enough to provide abundant line tension. Then see how it works.
It's possible that after this, you will find that the engine "charges", that is, gain excessive speed in the corners. Then you might want to extend the pipe 1/4" at a time until it moderates the charging. If you find that it starts to sag a but after corners, then you might need to push it in a bit. At each point, adjust the needle until it yields the right lap times.
I don't think we fully understand what you mean by running in "2-4-2". I though we did, but perhaps not. It's either 4-stroking, 2-stroking, or cycling back and forth.
Your airplane is not particularly heavy and you are not running excessively draggy lines. LOTS of airplanes are in that ballpark and fly fine, and a piped 60 That is not likely a source of your problem. There may well be some other trim issues, but if you are hauling it around at 5.2 second laps and it isn't drastically slowing or speeding up during maneuvers, the engine is not the problem. If it was putting out nearly 3 hp a few days ago with stunt settings, it certainly isn't broken or somehow defective.
Brett
Topic: Jett 60 pipe gets loose (Read 2238 times)
