Steve Steinbring

I am in the process of trimming my Venus II w/120AX servos mounted in the rear. I have laterally balanced the airplane thats worked out well. Right now I'm working on the CG and at this point I have reached the rearward point of the recommended range.

When the airplane is inverted it takes quite a bit of down elevator to fly level. My question is do I continue to move the CG aft, or is there another method like maybe adding downthrust. I don't mind some degree of down pressure, but certainly less than I have now.

rcpattern

My Feedback: (45)

How does the plane do on a truly vertical upline? Does it pull to the canopy or belly on the way up?

tIANci

I usually test my CG by flying inverted, with that much DOWN elevator its probably nose heavy. If your plane is fairly neutral enough try a KE, if she pulls towards the canopy then you are more than likely to be nose heavy as a nose heavy plane needs UP elevator to be trimmed in and in a KE you plane pulls towards the canopy. Its like what rcpattern says ... the up trim will show clearly in certain maneuvers.

Mastertech

My Feedback: (31)

Where is the elev trim? Is it carrying any up or down trim or is it even with the stab?

tIANci

Elevator trim is the little knob thingy beside your elevator stick that you click up or down to trim your plane. You do have a good plane and it probably is nothing to do with the stab. Just try out what was recommended and then slowly shift the CG to your liking. I like my plane just slightly nose heavy, hence when inverted I only give her a slight push to fly level.

bwick

The thing that effects it the most is some positive incidence, is the Venus II adjustable?

Flying inverted isn't a very good test of your CG, because how much pressure you apply can be related to so many things not really related to CG... such as stab incidence, throws, and expo. Decrease your expo or increase the throw to get the pressure you want. If it's too touchy and you can't seem to be consistent then you need to think about moving your CG around and maybe readjusting your throws/expos. Like Arch said the changes you need to make depend on how it's acting on up and down lines.

Steve Steinbring

Thank you all for your imputs.

I'll try decreasing the expo first and see what happens before adding more weight to the tail. Definately will take a better look at the uplines and downlines as well before changing anything.


Overall the airplane flies well, but can definately stand proper trim correction. Its not too important right now at my level, but in the next class up the existing trim issues will become more of a problem.

BaldEagel

Steve

The best trimming guide on the Web is here: http://www.nampamodelaviators.org/im...0Goldsmith.pdf a very reputable source.

Mike

EDIT: to add more comprehensive guide: http://www.flagstaffflyers.com/image...thTrimming.pdf