acdii

Last night flying my 4*120 with DLE20 while I was landing, it was idling along very nicely, around 1600 RPM, and as I aproached my landing zone, I gave a nudge of down elevator to drop it below the corn, and when I did and the nose came down the engine idle increased about 400 or so. What would have caused this to happen? While flying I can fully close the throttle and it will idle down and stay idle for quite some time as I gradually descend, and since I didnt want to risk it again on another flight to test if it revs up nose down, I dont know if it reoccurs.

Aside from that the engine is performing well, it has plenty of power and I fly it at half throttle mostly, with a 16X8 APC on it. It took a while to get it to transition from idle to full without stalling, but looks like I finally got the needles just right, but this idle up with nose down has me concerned. Where I fly there is 7"+ high corn on 3 sides, and not a lot of runway to float down, so I have to get over the corn and drop quickly so I can get on the ground before I run out of runway. When I tried it last night, which I did the same manuever on 2 other planes without problems, it sped up and nearly became one with the earth, I thankfully was able to pull up before it hit nose first, and landed hard enough on its wheels to dig the head and muffler into the soil.

My friend asked if we were playing golf since I was leaving divits.

ahicks

My Feedback: (2)

My guess is you're running into the timing "step" that occurs around 22-2400 rpm. If you're idling just below the step, and you drop the nose, you could pick up just enough rpms to put you over the step, with the resulting increase in rpm.

Suggest you try lowering your idle, so a slight increase in rpm will still stay under that "step"? That would be my first try anyway. -Al

All Day Dan

My Feedback: (5)

Try it without out the cowl on. If it doesn’t happen then you may be changing the pressure against the metering diaphragm in the carburetor. A static line in to the fuselage from the hole in the diaphragm cover should cure it or you can try to keep the air flow around the carb more consistent by opening up some holes in the cowl. Dan.

speedracerntrixie

My Feedback: (29)

I'm with Al on this one. I was thinking that the engine was spooling up a tad as the airplane gained speed but did not account for the 20 having a differnt timing curve then the other ignitions. I would agree that getting the idle low enough to not hit that timing step would be the way to go. Maybe running a larger dia prop with less pitch would be a help. The added flywheel action may allow a lower idle but also less pull if you continue to hit that timing step.

acdii

No cowl on this one, and the engine was idling for at least 30 seconds or more on final, just wondering if this is carb related. This one doesn't have that timing step issue that others talk about, except when I go from full throttle to idle, then a burp settles it down, Anything below half throttle though, it drops right to idle. I seldom fly it full throttle anyways, doesn't need to scream to fly nice.

So I wonder, if the angle changed slightly when the nose dropped, could that have offset the airflow to the carb and caused it?  I guess I could run it up on the ground and see what happens when I move the fuse around and see if it throttles up.  I know I didnt bump the stick since my fingers were off the rudder at the moment.

ahicks

My Feedback: (2)

If you have the original 4.8-6v ignition module that came with that engine, you have the timing step discussed above. If this is a newer engine with the module marked 8.4v max, then you're right, it doesn't have the timing step.

acdii

Havent looked at it, its a replacement one. The original one got damaged when the first 4* snapped its wing off.