Hey folks, I spent the morning wringing out my Morris the Knife ARF. I'm getting quite comfortable flying it hovering and flat spinning (upright, inverted, and knife edge) through most of my flights, but I noticed a quirk in it's flying characteristics. The plane is trimed for level flight upright, but when inverted it wants to climb. So much in fact that it requires a good amount of up elevator to keep level. And it wants to nose up regardless of throttle. I even stalled the Knife upside down a couple of times (luckily the MTK recovers in inches rather than feet). I've never had a plane handle like this. All need some down elevator (with the exception of my Sensation which flies upside down about the same as rightside up) to keep level flight. If this a trait found in all MTKs or just mine?

Thanks!

Sounds tailheavy....

Generally speaking, they are tail heavy when they behave that way. I'd bet that there is a hair of down elevator to maintain upright level flight.
Either add nose weight or live with it. I try to balance all my planes to get level flight both upright and inverted at neutral elevator.
There may be other things at work as well so I may be way off.
Later,,,basmntdweller

Where does the plane balance at?

Actually upright level flight is very level, mostly through the throttle range. I don't think I'm going to futz with the CG right now. BTW, could too much down thrust cause the same trait?

I'm not too concerned because I like the way the plane hovers and spins right now. I'm guessing that adding some weight up front will make it more difficult to hover.

A larger concern for me is that the MVVS40 with tuned pipe doesn't have enough juice to pull out of a hover. I'm going to try cutting the header 1/2" this weekend and seeing if I can get some more revs outta the setup...

What prop are you running. That engine should have plenty to pull out of hover. Too much prop will kill the performance on a piped engine. No more than an 11-4. I have the same setup for my MTK but haven't got it built yet.
If all your incidences are right and there isn't any noticeable down trim in the elevator I have no idea why it would do that other than CG. On second thought, if the ailerons are offset from neutral they could be creating asymetrical lift while the elevator is trimmed to neutral. You could experiment by raising them both a degree or so and retrim for level flight and then check the effect inverted.
There are a lot of possibilites but I'd still bet on CG. Does the elevator get touchy on landing? If so that is another indicator of being tailheavy.
Good Luck,,,basmntdweller

My MTK is third in line on my building bench.

f2racer you said that it hovers nice where its at and you dont what to move it forward. well i dont know how this works but on my omp540 the first flight it hovers great but after i get some goo on the tail it get kinda skitish. i think that mayby there is a sweet spot for hovering. too much forward or too much back and its skitish. mine is a little tail heavy couse it climbs a little inverted and the elevator is level with the stab. yust me thinking out loud. am i wrong. come on you pros let us know.

The Knife and MVVS 40 is a good combo, but the pipe needs to be trimmed maybe 1/2" to get to it's full potential (that's what I was told by Robert over at Morris Hobbies). I haven't cut mine yet, but supposedly cutting will give an extra 1000 rpm. I found almost no difference in rpm between an 11.5x4 and an 11x4 prop, so I'm currently using an 11.5x4. It hovers better, hovers OK at right around 3/4 throttle (I've dialed some expo in on the throttle), but climbing out vertically is impossible... Gotta let the nose drop some before flying out. I'm guessing a simple cut on the header will make the plane pull vertically out of a hover without issue.

wow. thats a lot of throttle!!! i have a 46fx on my 540 and with no expo it hovers at 1/4. i put -30% to get it to 1/2. just a macs muffler. i noticed about 600 rpm diff between the 11x4 and 11.5x4 and it pulls from hover great. im working with a 11.5x4 wood right now. hope this works. try soom wood props there great when your down low.

I'm flying the Knife ARF, which may account for up to 1/2-3/4 lb extra weight over a kit 540 which is huge on these fun flies...

i guess so. but try moving your cg forward a little. i like the stick on lead. this way if you dont like it you can take it off.if you like it you can move stuff around to get the cg that you want.
good luck