FINALLY A TRUE 50cc PIPER CUB (Build Thread)
#26
That is super impressive!
I have the smaller 50-size 4st version of the P-56 and just love how easy it is to fly. So when I saw the ad for the 50cc version, I figured this was the model to put behind my $1,200 UMS 770. I just couldn't imagine putting an unflown engine (of a kind I'm not familiar with) in a precision scale model I may have spent two or more years building. Also I've been doing lots and lots of RC nothing recently and this seemed like a quick way to get back into things. And at $550, while that's not cheap, it's about the cheapest ARF available in this size. Yeah, it's going to look a little strange with that un-cowled radial up front.
Eventually, when I transfer the 770 to the Strutter (or some other WWI project) then I'll replace it with a 50cc gasser.
I have the smaller 50-size 4st version of the P-56 and just love how easy it is to fly. So when I saw the ad for the 50cc version, I figured this was the model to put behind my $1,200 UMS 770. I just couldn't imagine putting an unflown engine (of a kind I'm not familiar with) in a precision scale model I may have spent two or more years building. Also I've been doing lots and lots of RC nothing recently and this seemed like a quick way to get back into things. And at $550, while that's not cheap, it's about the cheapest ARF available in this size. Yeah, it's going to look a little strange with that un-cowled radial up front.
Eventually, when I transfer the 770 to the Strutter (or some other WWI project) then I'll replace it with a 50cc gasser.
Last edited by abufletcher; 12-04-2014 at 12:26 AM.
#28
Thread Starter
My Feedback: (3)
Here are another couple pictures of My L4 conversion from this World Models 119" Cub. At this point, I've done some engine testing with the engine mounted on the plane. As usual, there are issues. On the test stand, the engine ran fine. No so much, once in the plane. Even in a perfect world, glow carbs don't handle gasoline very well. I thought this one, on the OS Pegasus, maybe was an exception because the bench testing was so trouble free. However, in the plane, the stock gas tank location was so much higher than the OS's carb, that gas was constantly siphoning from the tank, onto the ground from the carb. Also, I couldn't get a decent transition from idle to WOT, probably because the engine was drowning in gas. Good RPM at the top, about 7200rpm with a 19x8 Zoar. 18lbs static thrust, 25lb model. Not bad for a Cub. So, I lowered the tank to the bottom of the area just behind the firewall and gave it another try. Less siphoning for sure, and a better transition, especially when the prop was backed off to a 18x8 pro Zinger. RPM was now 7800, but the thrust was less (didn't measure it, but I could tell). But there was still that carb-needle valve sensitivity that could kill an engine once things change in the air. So, I'm biting the bullet and I've installed a Walbro. See one of the new pics. Pressure tap is right off the crankcase--not sure why that works but it seems to be pumping. I'll know for sure tonight when I do the first test run. I made the carb mount myself on the lathe and milling machine. Bottom line, glow carbs don't work for gas because the needle valve angle is way too blunt (or course) for gasoline. Nitro fuel carries much of it's own oxygen right in the liquid unlike gasoline. So, the fuel air ratio mixture adjustment is only regulating a small part of the overall oxygen getting into the engine. Thus, glow carbs provide much more fluid to the engine than what is appropriate for gasoline. The free passage of fuel through a glow carb is too unregulated an environment for gasoline, where the fuel air mixture must be controlled externally. That's why walbros have regulators that sniff the outside air pressure as a reference. I'll update the site after tonight's test run with the walbro.
#29
Here's how I'm doing the wing rib stitching. I made this video during the Vikings-NY Jets game on Dec 7
http://youtu.be/ycP6p0l3914
http://youtu.be/ycP6p0l3914
#30
Thread Starter
My Feedback: (3)
Cold weather, really cold, has set in here, so even though the L4 is ready to maiden, it'll have to wait a couple weeks. I have skis on it, but the air temp is brutal.
I've replumbed the tubing all over the engine, and relocated the gas tank down lower in the fuselage. I really made a dumb mistake on the plumbing. I accidentally had the primer bulb supply hooked to the intake, thinking it was the pulse input to the carb. The result was sucking raw gas right into the combustion chamber! It ran, but one cylinder was spewing raw fuel. Lucky it didn't turn into a blowtorch. Also, the crankcase port served as a poor pulse source because as two pistons are moving down, two more are moving up, thus negating any pulse pressure wave that would normally be there in a 1 or 2 cylinder engine. So, this is what I did:
1) brazed a tube barb onto the intake pipe near the head of the front right cylinder. This became the pulse source.
2) I drilled and tapped for a barb right in the pump cover on the Walbro. See the arrow. The other end of the pulse tube goes there.
3). I plugged the primer bulb tube with a red plastic cap.
4. I lowered the gas tank.
After doing all that, the engine ran like a watch, very nice. Ready to maiden.
I've replumbed the tubing all over the engine, and relocated the gas tank down lower in the fuselage. I really made a dumb mistake on the plumbing. I accidentally had the primer bulb supply hooked to the intake, thinking it was the pulse input to the carb. The result was sucking raw gas right into the combustion chamber! It ran, but one cylinder was spewing raw fuel. Lucky it didn't turn into a blowtorch. Also, the crankcase port served as a poor pulse source because as two pistons are moving down, two more are moving up, thus negating any pulse pressure wave that would normally be there in a 1 or 2 cylinder engine. So, this is what I did:
1) brazed a tube barb onto the intake pipe near the head of the front right cylinder. This became the pulse source.
2) I drilled and tapped for a barb right in the pump cover on the Walbro. See the arrow. The other end of the pulse tube goes there.
3). I plugged the primer bulb tube with a red plastic cap.
4. I lowered the gas tank.
After doing all that, the engine ran like a watch, very nice. Ready to maiden.
#31
Thread Starter
My Feedback: (3)
Successful maiden flight of the World Models Cub, converted to an L4 Grasshopper. Here's the link. The handling is very scale and realistic. No trim was needed at all from the recommended CG. It actually flies like a dream. http://youtu.be/YRrN_HiiLy4