Stayed up till 2AM...literally...putting my Magnum 30 on Speedyboi in an attempt to see if 4-stroke power is viable. Attempted to fly today. Weather couldn't have been better! However I......pretty much wasted my time. A bunch of asshats with giant scale 3D birds were literally congalining the damn runway. 2-3 of them in the air at the same time doing their spaztastic nonsense and as soon as one landed to refuel another was already on the start pad getting the engine fired up. Was there for four hours only got 10 minutes of lazy high-altitude circuits around the flight pattern.
Not only was this annoying as hell, but it also made me nearly total Speedyboi. See, that little Magnum 30 is a hell of an engine, but something in the rushed last-second engine swap didn't gel right. I wasn't getting more than about 8500RPM on a 9-7-3 prop in flight, so I had to keep it PINNED just to keep it in the air. Plane flew great otherwise. I don't know if the problem is linkage, if the engine just doesn't have the balls, if it's disagreeing with that prop, or some combination of the three, but it just did not have any power. And because I'm having to do 150'+ height lazy flight pattern circuits to clear the 3-4 air hogs spazzing out over the runway I can't get a feel for how to land the thing with so little power. I had to just wing it in a 30 second window while one was starting their engine and the others were running their fuel pumps. I ended up stalling it at waist height, dropping the piano, bouncing it almost back to its same height, and dropping the piano
again. It missed hitting the chainlink fence guarding the pilots by about half an inch, stalled the engine out in the process.
Speedyboi is a portly li'l thing, so he took the hits in stride. No damage. But still. I had no chance to feel out what throttle setting I should use for final and touchdown because these damned 3D pilots were doing their spazzy 'I don't know why I even have wings on the plane' nonsense.
Needless to say my already indifferent attitude towards 3D flight has taken a sharp decline. It's getting hard for me to not give anyone grief over what they fly when a certain type of flyer enacts a hostile takeover of the damn field and blocks out anyone else from flying. I wasn't the only one frustrated by it either; nobody was saying it but I could just see the looks on the faces of the other pilots that wanted to fly something
not an Edge or Extra or Yak. Homey two tables down from me had an Avanti and A-10 EDF; he was there before I was and he only got one flight on the Avanti in the time I was there before he shook his head, packed up, left.
I probably could have waited the 3D spaz show out but I found myself getting so damn grumpy about the air hogging that I wouldn't be able to enjoy the time in flight when I finally got it, so I just said -beep- it and left myself. Maybe I'll try again tomorrow maybe not.
Honestly my main concern with overspeeding was the valvetrain. I'm guessing if I pushed it too hard some valve float issues could crop up, and the power would drop off drasitcally.
These are not interference engines. Valve float would make it miss at high speed but not much else. I'm also not convinced they even can rev high enough for valve float to be an issue just due to the cam grind itself. They're designed to make their power in the 7500-9500RPM range.
I don't think the crankpin would have popped if there was nothing wrong with it; after all, I don't think there are many differences between a 2 and 4 cycle crank other than some method of driving the cam and no intake timing hole (I would think it might even be a little stronger, as I have seen 2-cycles bust cranks right at this hole) and 2-strokes regularily turn much higher RPMs without the crankpin going on any adventures.
Two strokes have a constant compressive load on the crank pin
at all times, as in the pin is always being pushed towards the centerline of the crank. There is never any tension on that pin and it never has to jerk the piston down at the top of the stroke. Even at teh bottom of the stroke things are cushioned by the air/fuel charge in the case.
Four strokes are the polar opposite. There's three 'dead' strokes for every one 'live' stroke. The crankpin is alternating between the piston tugging it away from the centerline and pushing it towards the centerline. 4-strokes also hit harder in general. The difference in stresses is why 4-stroke crankpins will shear off when 2-stroke pins do not; they also often tend to be more substantially built. A lot of my 2-strokes have hollow crankpins; none of my 4-strokes have one.
Prop for no more than 9750RPM on the ground and you'll be copasheeshy. 11-7-3 is about the lightest prop you should be using on a 52 4c.
If you had an OS FS-40 and wanted to rev the nuts off of it you could install the crank from the FS-40C. OS did a LOT to this crank to make it suitable for surface use(Some even had pips for a pull start!) and they will safely rev to 17K without issue. Similar things can be done with the FS20/26/30 'smallblock'; use the crank from the FS26C which is good to 20,000RPM. Can also fit the cam, head, carb from the car engines and really get a screaming 4-stroke setup for a smol plane.