How much time do you guys spend on flight trimming your planes? - RC Groups
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Jan 01, 2012, 10:59 PM
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Roguedog's Avatar

How much time do you guys spend on flight trimming your planes?


I'm to the point that I'm considering selling my 40 sized Utter Kaos and starting from scratch.

I purchased this plane for $30 bucks off Craigslist and thought is was a good deal at the time, but after having the engine out for the 4th time to sand the back of the motor mount to get it back to zero degrees downthrust and fixing the other issues, I starting to wonder if I should call it a lost cause, at least for this plane, for practicing the Classic pattern manuvers.

I never knew about flight trimming until I got back into the hobby. What we call Classic Pattern was in full swing when I left the hobby, so this time I around I want to learn how to fly those manuevers.

This Chaos was already covered with monokote when I got it. But when I started to setup it up with gear I found the ailerons where binding, the horizontal and vertical stabs were tilted about 5 degrees from straight, had 1.5 degrees of postive incidence, and the firewall had more than 4 dregrees of down thrust.

Fixed most issues but it seems like I can't even finsh the process for flight trimming, at least from the charts I using.

For those who have had experience flight trimming should I spend any more time on this plane?

I suppose my Chaos is not typical but from reading threads on this topic I heard that many of you spend alot of time trimming your planes even when built right. Some input on this particular subject would be great.

The plane is flying way better, 100% better each time I clear up an issue but I'm worried that it may have been thrown together, I aready have 50+ flights on, and I'm enjoying flying it, but it's still not ready to even start practicing any manuevers.

Should I keep at it?

Thanks in advance for all input.

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Jan 03, 2012, 02:02 AM
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It is very worthwhile and , for a decent flying classic pattern plane, essential, to spend the time to trim it properly. How long that takes depends on the build, the design and how straight it is. It's very difficult, if not impossible, to trim a plane that isn't straight. If you can make it straight, keep at it , if not move on to another airframe. Be sure all hinge gaps are sealed.

Once you have flown a well trimmed honest airplane like a Kaos, you will never be satisfied with an untrimmed plane again.

I have had several Kaos versions, all great fliers. I looked at the easiest plans to find in my shop ( a Killer Kaos and very similar to your Utter Kaos) and saw that it called for 2 degrees downthrust. I think most of mine had that and maybe 1 degree of right, so you may have removed too much.

The National Society of Radio Controlled Aerobatics has a well known trim chart on their site. It is the second one simply called "trimming chart".

Here's a link, it gives lots of good nuts and bolts info on trimming. I'd recommend you use it. Be sure to change only one thing at a time then fly to see the result. Each change may have an impact on earlier trim, but with practice you will get there. Good luck!
Jan 03, 2012, 02:15 AM
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I looked at those Killer Kaos plans more carefully. The Killer and Utter are so similar that they are hard to tell apart visually, some say it is just a name change to change kit manufacturers. The plans call for 2 degrees downthrust as I said. No right thrust, but I ended up adding 1 degree right to make vertical up lines need fewer corrections. The wing incidence calls for 1/2 degree positive. If you can get the tail alignment issues straightened out and these values for thrust and incidence, you should have a good start. At this point perfect knife edge trim is good but isn't critical because you wouldn't use it much in sportsman or intermediate. If you can get the cg right, tip weight and incidences you should be able to begin practicing manuevers. Aileron differential can come later and finally knife edge as you learn more manuevers.
Jan 04, 2012, 05:00 AM
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Roguedog's Avatar
Thanks for link and the encouragement Immelman,

I tried to answer earlier but needed to reinstall Microcraps IE8 web browser as I could not download the trimming files from the NSRCA website. I read the chart completely and will be adding it to the collection of trim charts that I take with me to the field.

I was gettin a little irritated that someone could do such a bad job at building this plane that I wanted some feedback from others who have done the trimming process to weigh out whether to continue or not.

The plane is flying well, but I have nothing to compare it too as this is the first plane I have ever trimmed. I posted at the other site and got alot of great info there as well that I decided to try and fix as much as possible so that on the next plane i will definitly have something to compare too.

One person mentioned that the education that i'm getting from this plane is priceless. Very good point.

Funny that you mentioned the Killer Kaos as I had the 60 kit then in a moment of stupidity sold it on ebay. A few weeks later I saw a guy burning holes thru the sky with one at the field and regretted selling it. I did trace all the cut parts and scanned the plan just in case so at least I can scratch build one if I want.

I took a little more incidence out of it today and have reduced the downthrust a little more. Hope to test fly it this week to see if I'm heading in the right direction.
Jan 04, 2012, 02:51 PM
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jhaywood's Avatar
The original Kaos had 3 degrees downthrust, 3 degrees right, 0 degrees incidence in the tail, and 1/16" positive incidence in the wing.
For whatever reason, Bridi uses 1/16" instead of a degree measurement for the wing, but used degrees for the engine and tail.
Jan 05, 2012, 12:24 AM
Registered User
You are very welcome. That's what these forums are for! Your descriptions on the other site do sound like an original Kaos. Everything said still applies and I strongly agree with everything said over there except the not using expo and stopping trimming, etc. Scott's trim sheet is the same thing I linked you to. Almost any test for incidence , thrust line etc is described well on it. It is kind of the standard classic pattern trim sheet. The comments about flying straight lines are dead on. Try this sometime, stand a long ways off one end of the runway and watch people fly. They almost all will fly a curved line , slightly further out as they pass themselves. Many will also fly past themselves with the plane banked slightly toward themselves . They are looking at their wings to try to make them level but the upward angle fools them. It is a very revealing thing when you are trying to develop precision in your manuevers. A loop begun at runway center will frequently corkscrew in a little for new pattern fliers for that reason ( assuming no cross wind). That's one good reason to check loop trim out looking from behind rather than the side. It is far easier to make wings truly level from that angle. If you don't enter perfectly wings level, the results will mislead you in the trimming process.

I really do think that trimming this one as best you can will give you a real leg up on one you build yourself. It sure emphasizes the need for accurate straight building. As 8178 says, to really get a straight airframe you have to do it yourself. I can build them straight and light but nowhere near as pretty as a master builder like 8178 can! He just amazes me with his build logs.

Good luck, Chuck

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