Trimming a new airplane
 

Hey all,
I am in the process of setting up my 1/3 scale Extra. First flights reveal that I'm still nose heavy (of course - I set it up that way ;) ). I assume this should be the first place to start trimming the aircraft.
When I roll to inverted I have to maintain down elevator to keep level, regardless of the throttle setting. The question is this;
First, this is the right place (CG) to begin trimming the aircraft right?
Next, Should I keep moving the CG back until I'm neutral right side up and upside down before I move on to checking thrust lines and such?
Also, What's the next step LOL.
RickP

upside down
 

Hi Rick,

What are you using this plane for? 3D or Pattern? I have had 3 C-Arf 2.6s and they flew better right on the suggested "pattern cg" BUT they needed down elevator to fly upside down! Try decreasing your down elevator throw and expo until you're comfortable flying it upside down. I tried adding lead to the tailwheel until it flew well upside down only to have a plane that was real twitchy everywhere else. (not very high scoring at contests) Various other mixes will help too.......Down elevator mixed into off throttle , Pitch correction ......mixes off for rolling turns etc...Various mixes on and off for different maneuvers.....

Hope this helps, Dave

Trimming a new airplane
 

I dont really know whats right or wrong but I always start at the suggested C.G. for the madien flight. After that it gets shoved back some b/c I am a 3D freestyle type of guy :) When I go to fly IMAC I plan shift my pack to its proper place. In the sukhoi I am setting up now I hope to have it where I can slide the pack forward or aft depending on if its freestyle time or sequence time.

Trimming a new airplane
 

I prefer a forward CG myself. I like to hold some down elevator when inverted. The airplanes just groove better. Also the 3D capabilities of most airplanse won't be hurt much by a forward CG.

Trimming a new airplane
 

Hey,
Good feedback, I like the expo idea. I also know I am near to the front of the reccomended CG, I will move it back a little and try. What should I look for next?
RickP

Trimming a new airplane
 

next ? personally I would also balance the model laterally by adding weight to the wing tip on the lighter side. A laterally balanced model will be a lot easier to trim.

Then I would work on the engine thrust angle, have a look on the net for a trimming chart which will give you the info you need.

Chris

Trimming
 

Take a look on the NSRCA website. It is focused on pattern planes, but techniques really apply to all. I agree with Doug, you probably want just a touch of down elevator while inverted if you are focused on IMAC. Next thing besides lat balance, would be thrust lines. Fly straight and level and chop throttle, and fly downward vertical and chop throttle. What happens? That can tell you a lot about your thrust line. From there I would start playing with Rudder/Elev mix for knife edge. The guide on NSRCA really takes this into fine detail. Good luck and hope this helps.

Howard

ps, you want to do this in really calm air (crack of dawn)

Trimming a new airplane
 

Guys,
Thanks for the responses. I'll give them a try.
FWIW, I found that some of my controls throws were not balanced either. For example I had 12deg up on the left Elevaor and 12.5deg on the right. I'm getting that squared away now too. Boy this trimming is allot of work!
Regards,
RickP

Trimming a new airplane
 

yes it is, it can take 50 or so flights before you get everything just how you want it.

Trimming a new airplane
 

Rick, get yourself a CRC Throw meter to measure all your surfaces. Make a log of the defelctions and bring that to the field with you. Works wonders when you write stuff down.

Howard

Trimming a new airplane
 

Howard,
Got one already ;) Now how can you be sure when measuring elevator halves that both are the same exact Zero? Can I just move the meter over to the other side without adjusting it?
RickP

Trimming a new airplane
 

Where might one acquire this CRC throw meter you speak of? :D

Trimming a new airplane
 

Rick, you can do one of two things. Either glue some balsa sticks to clothespins and attach to the back of your eleveators. Turn them in towards each other and that will give you a pretty good idea of not only center points, but equal travel through entire servo motion. In theory, taking the CRC off one side and putting it on the other elev half should work as well. I would probably use the CRC to center and the sticks to monitor travel. Pauly, I got mine at Central Hobbies.

Howard

Trimming a new airplane
 

Okay,
I've been spending allot of time on this this weekend. How important is it for both sides to have exactly the same throw. I was having such difficulty programming the TX I decided to put matchboxes on the Elevators and rudder servos too.

I adjusted the matchboxes at full throw and they are exact there, but with the dual rates on I am like 1 deg off on the elevator halves at the Low D/R setting. Would there be much advantage to adjusting the matchboxes at the Low rate setting?

FWIW, this airplane is a fiber classics and there is a distinct seem in the elevator halves that are easy to line up. I'll just "Zero" it that way ;)
RickP

RE: Trimming a new airplane
 

Hello Rick,

I found this site [link=http://www.giantscalerc.com/technical_main.htm]Giant Scale Aircraft[/link] to be very helpful for trimming an aircraft among some other helpful hints.

RE: Trimming a new airplane
 

I like these trimming instructions as they are easy to understand.
[link]http://www.piedmont.com[/link]

It sure would be nice if RCU let you cut and paste a link!

RE: Trimming a new airplane
 

Rick (And Alan and Steve)

This sounds like a good first meeting for LIMAC.

The NSRCA trim chart is a great tool.

Your going to think I'm kidding, but the best way to set up a plane is having someone next to you while you go through the trim chart. (Doesn't have to be me) (I've done it with Dad, I've done it with Sandy, I've done it with Alan they are just another pair of eyes and another memory) They read the chart for you and watch your plane with you. You work on one thing at a time. They either remember or jot down what you are going to change. It takes a lot of work to really trim a plane. Someone before said 50 flights. My edge is three years old and it still needs work, but its really close for me. It's almost sad that I'm moving to a new plane. Maybe I'll stay with the Edge in contests this year while I trim out the Extra - probably not.

As far as CG this is really up to you. Some people like a CG so that there is no difference in right side up and up side down, but the plane will be less stable. Some people like a plane with a more forward CG. If I remember right the instructions for the FC gave you a specific spot for IMAC type flying. Try it there and see how you feel. They play with it.

As far as how important is in to have the elevators move the same amount? Why did you spend the money on a FC? You wanted precision right? You WILL feel the airplane pull to one side if the elevators move a different amount. If anything, if you are planning on flying IMAC this year I'd rather see your IMAC rates exact and your 3D rates off by 1 degree, but it would be better to have them both the same.

RE: Trimming a new airplane
 

Hey Rob,
When is that LIMAC meeting LOL, You are totally right about the above. Your Pop pointed out that my plane was pulling in the downline, I probably would not have noticed it unitll he had me do a 45deg inverted downline and then I noticed how bad it was. I still haven't made any changes so I need to get on that and try again. But I hope I can get one of you guys to spot for me. I want to shift the CG a little more aft first though. Getting to cold and windy to fly. I haven't flown since Thanksgiving weekend.
RickP

RE: Trimming a new airplane
 

I have noticed the difference in throw between elevator halves at different rates, and I usually set them up to have identical throw at the pattern rate. If you switch to hi rate for snaps and spins it is probably less important to have them moving exactly the same since the stab will already be at such a hi aoa but for the pattern precision rate that you use for looping manuevers and to establish lines, it is important to have the elevators moving exactly the same.

Also, as far as the order as trimming things, like other people are saying it is a very long process. Sometimes, no madder what order you do things in, one change will affect everything and force readjustments. Personally, I dont think planes are ever perfectly trimmed. They get closer and closer until it is just a matter of the work required for changes vs. the payoff, but there is always more to do.