FMS Extra 300 - CG

[rcpilot134]

Hello All - just finished the build on the FMS Extra 300 and concerned a bit about CG. At 120 mm, she is extremely nose heavy. I would have to add 1.5 ounces to the tail to get her balanced with an Admiral 4s 3000 pack. I poked around a few newsgroups and found a few people had the same issue - added the weight and it flew horribly. They took the weight off and it flew great.

After reading this, I used one of those online calculators to figure CG. My calculations came up with the CG being an inch forward of what's in the manual and at this point, balances just a tad bit tail heavy. I'm wondering if the manual could be wrong? This would explain the experience of the other pilots that I read about with the model.

If anyone has flown this thing and could shed some light on CG, I'd appreciate it. If the CG in the manual was in fact wrong and I left that 1.5 oz's in, the maiden would've not ended well. I'd rather it go up first time nose heavy but as mentioned, this thing is very very nose heavy at the manuals CG.

I do own 1 other FMS model that needed 1 oz to the tail and it flew great, not sure if it's an FMS tendency to build nose heavy planes. Anyway, any input would be greatly appreciated.

Thanks

[Flygirl]

Boy, 4.7 inches back seems like a lot! Judging from all the CG posts on that plane I'd say it is a pretty good bet that 120mm is off the mark. So where is it balancing without the tail weight?

[rcpilot134]

It's balancing about 1.25 inches forward of the manuals. So I figured that out with one of the online cg Calculators with 25‰% Mac, I think they call it. This calculator is new to me but the posted cg just didn't seem correct. That coupled with what I read from a few other pilots about adding weight to the tail a day it flying twitchy leads me to believe the weight they added using the manuals cg made it tail heavy. They posted that they removed the weight and it "flew better".

I'm probably gonna fly it no weight unless someone advises differently whose flown this thing. I should be able to tell right off the bat if it's nose heavy. My thinking is, better nose heavy than tail heavy.

Maiden flights are stressful enough "knowing" that everything is setup correctly. This one's gonna really stress me out :-)

[rcpilot134]

Maidened it today and here is my take on it.

First off - very nice model. Impressed with FMS and this one even came with all the parts :-). Build was easy except for wings. 2 piece and they overlap each other so lining up one of the wing bolts was a challenge. Little bit of a head scratcher when it came to CG - described below.

I checked MRC's forum - hobbysquawk and found a post from MRC -Ryan who flew this thing with a 4s Admiral forward in the box and flew fine. If you can't trust Pilot Ryan who can you trust :-). This thing sat for a week while I was going back and forth with this CG issue so I figured I'd just fly this thing and figure it out.

Manual called for below listed DR and Expo
High Rates-Expo Low Rates-Expo
Aileron 100% 65mm up/down 60% 30% 19mm up/down 30%
Elevator 100% 50mm up/down 50% 22% 11mm up/down 25%
Rudder 100% 60mm left/right 50% 60% 36mm left/right 25%

Not trusting the manual after the CG, added 10% throws to Aileron and Elevator - low rates and bumped expo to 40% - left rudder as is. They visually seemed a bit low.

First Flight - AR636 - Low Rates - AS3X off - with Admiral 4S 3000 pack about 1 inch forward off the back of the box. 2-3 mph crosswind. Got a little nervous as I always do on maiden and yanked it off the deck too quick. Wanted to stall but it did have enough motor behind it to power through. Once in the air, it was noticeably nose heavy. Couldn't get it settled in very easily for the first landing, being nose heavy, came it pretty hot. Not the prettiest of landings. Also noted that even at these low rates, pretty responsive and a little mushy. Will dial back DR and expo a bit more toward manuals recommendations also drop rudder a bit as well.

Didn't have laptop with me to reprogram the RX (quick trip to the field before work). The only adjustment on second flight was to push the battery all the way back in the box. Take off was better - kept it on the ground til it was ready. Still a little tail heavy but not bad at all. Landing was better but have to fly it in.

My overall take from these 2 flights. Plenty of power for me. Very responsive. Slow flies OK. I think once I tweak rates and expo, I'll be a little happier with the way it flies.

Note - I'm not a 3D guy - intermediate at best and my plans were to fly this as a sport model with lower rates. Just wanted a model that can do some decent aerobatics and this one seems to fit the bill.

There ya have it - survived another maiden :-)

[rcpilot134]

Sorry - double post - site error so I posted again and then there were 2