rbort
07-26-2007, 01:41 PM
Hi y'all:
Well I'm in the process of breaking in a Bergen Twin for a company that I test pilot for. So far I've got three tanks through the machine. Here are some things I've encountered so far:
a) when spooling up, the rotor seems to want to wander around (as if you are applying cyclic in this order: forward, right, back, left, repeat) until the head comes up to speed. This is not an issue but the first time I saw this it was a little scary as I thought I was going to take the boom off. Spoke with Chris about this and two things help -- a) tighhtening the blades down in the grips, I got them as tight as they go now, and b) making sure the blades are out perfectly as best as possible before spoolup. Also spooling up slowly is better to prevent blade swing during spoolup. I've managed to minimize this now.
b) when starting the engine, it always seems rich and then leans out some later. So if you land and shut if off, wait a couple of minutes, now you need several pulls to get it to go without increasing trim. Several pulls go by and then it starts to catch, and then it catches longer and longer until it goes and stays running. As it runs, it will speed up and get to the right idle speed. If you increase the trim on starting, then you have to decrease it later when its running. I haven't figured out a solution for this at the moment I'm just dealing with it.
c) in flight once you take off, a similar thing happens. Engine seems rich and slower at first in a hover, then it picks up some speed. I've richened the low end up to about 1 1/8 maybe 1 1/4 at most, and had to lean the high end down to about 7/8. More to follow on this.
d) If I run richer on the high end, two things happen. a) its too rich and burpy in a hover, and b) it doesn't have power / bogs in vertical climbouts. I've reduced the top end pitch down and increased the negative somewhat as during autos I'm full bottom stick. I set the negative so the descent speed is good, fast enough for me but not too slow. I checked the pitch at home and looks like I have -2.5 degrees to +11.5 degrees or so. Full power climbout the engine can only handle about 1470 rpms. With the high speed richer, it was bogging down on full power climbout to 1310 rpms. I leaned it from 1 1/8 a little at a time and the rpms picked up. All the way down to 3/4 turn open the rpms reached 1490 rpms with this pitch, but I was getting uncomfortable with the needle being so closed (though it shouldn't really matter where it is if that is where the engine runs happy) and opened it back some and lost some top end rpms. Will run it more but so far this engine is not pulling 11.5 degrees more than 1470 rpms. Maybe too much pitch or too rich / not fully broken in, so run it more for now.
e) the JR 8311 servo on the throttle seems to be acting weird with the gv-1 governor. The engine tends to suddenly overspeed and the throttle servo jumps up and back down when I switch flight modes from idle 1 to idle 2. I decided its acting strange and I never used an 8311 with a gv-1 so I changed out the servo to a Futaba 3004 last night. Will try again with this. Problem I'm having is that if I go up to 500 feet and pull the stick down, seems like the gv-1 disenguages (even in idle up 1) as the engine suddenly speeds up and speeds up alot. I hit throttle hold right away as I don't want to overspeed the engine for extended periods of time and float down in. Chris I know you don't like the use of gv-1's until the engine is fully broken in, I'm just using it as a tool to test rpms climbouts and to set throttle curves, etc. I'm constantly turning it on and back off to check mixture and how the engine is running.
f) speaking of that, to date I have been unable to get a good throttle curve to stay and have the engine run consistantly. Just when I think I have it dialed it all of a sudden it seems like too much throttle. That probably relates back to b) above which is causing me to chase the thing around and not be able to get it right. Maybe that will settle down after a while. I do have alot of oil in there (5oz per gallon) and part of me is thinking that maybe when the engine warms up it burns through some of this oil which causes it to speed up some where on takeoff is rich with oil and that is choking it down.
I'm open for comments and or suggestions. Just wanted to do a brain dump here and see if anyone has anything to add to the mix.
Thanks guys,
-=>Raja.
Well I'm in the process of breaking in a Bergen Twin for a company that I test pilot for. So far I've got three tanks through the machine. Here are some things I've encountered so far:
a) when spooling up, the rotor seems to want to wander around (as if you are applying cyclic in this order: forward, right, back, left, repeat) until the head comes up to speed. This is not an issue but the first time I saw this it was a little scary as I thought I was going to take the boom off. Spoke with Chris about this and two things help -- a) tighhtening the blades down in the grips, I got them as tight as they go now, and b) making sure the blades are out perfectly as best as possible before spoolup. Also spooling up slowly is better to prevent blade swing during spoolup. I've managed to minimize this now.
b) when starting the engine, it always seems rich and then leans out some later. So if you land and shut if off, wait a couple of minutes, now you need several pulls to get it to go without increasing trim. Several pulls go by and then it starts to catch, and then it catches longer and longer until it goes and stays running. As it runs, it will speed up and get to the right idle speed. If you increase the trim on starting, then you have to decrease it later when its running. I haven't figured out a solution for this at the moment I'm just dealing with it.
c) in flight once you take off, a similar thing happens. Engine seems rich and slower at first in a hover, then it picks up some speed. I've richened the low end up to about 1 1/8 maybe 1 1/4 at most, and had to lean the high end down to about 7/8. More to follow on this.
d) If I run richer on the high end, two things happen. a) its too rich and burpy in a hover, and b) it doesn't have power / bogs in vertical climbouts. I've reduced the top end pitch down and increased the negative somewhat as during autos I'm full bottom stick. I set the negative so the descent speed is good, fast enough for me but not too slow. I checked the pitch at home and looks like I have -2.5 degrees to +11.5 degrees or so. Full power climbout the engine can only handle about 1470 rpms. With the high speed richer, it was bogging down on full power climbout to 1310 rpms. I leaned it from 1 1/8 a little at a time and the rpms picked up. All the way down to 3/4 turn open the rpms reached 1490 rpms with this pitch, but I was getting uncomfortable with the needle being so closed (though it shouldn't really matter where it is if that is where the engine runs happy) and opened it back some and lost some top end rpms. Will run it more but so far this engine is not pulling 11.5 degrees more than 1470 rpms. Maybe too much pitch or too rich / not fully broken in, so run it more for now.
e) the JR 8311 servo on the throttle seems to be acting weird with the gv-1 governor. The engine tends to suddenly overspeed and the throttle servo jumps up and back down when I switch flight modes from idle 1 to idle 2. I decided its acting strange and I never used an 8311 with a gv-1 so I changed out the servo to a Futaba 3004 last night. Will try again with this. Problem I'm having is that if I go up to 500 feet and pull the stick down, seems like the gv-1 disenguages (even in idle up 1) as the engine suddenly speeds up and speeds up alot. I hit throttle hold right away as I don't want to overspeed the engine for extended periods of time and float down in. Chris I know you don't like the use of gv-1's until the engine is fully broken in, I'm just using it as a tool to test rpms climbouts and to set throttle curves, etc. I'm constantly turning it on and back off to check mixture and how the engine is running.
f) speaking of that, to date I have been unable to get a good throttle curve to stay and have the engine run consistantly. Just when I think I have it dialed it all of a sudden it seems like too much throttle. That probably relates back to b) above which is causing me to chase the thing around and not be able to get it right. Maybe that will settle down after a while. I do have alot of oil in there (5oz per gallon) and part of me is thinking that maybe when the engine warms up it burns through some of this oil which causes it to speed up some where on takeoff is rich with oil and that is choking it down.
I'm open for comments and or suggestions. Just wanted to do a brain dump here and see if anyone has anything to add to the mix.
Thanks guys,
-=>Raja.