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Do I need my CG back further

Old 09-04-2013, 07:02 AM
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learn2turn
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Question Do I need my CG back further

Starting to work a bit on those trim tutorials. I'm still at the point where things happen so fast and things like trim settings and stick movement interact so that I'm not sure if I have the CG correct.

For years I've always trimmed my planes so I need just a tad of up-elevator to maintain level flight. That allowed me to feel the plane as I flew straight-and-level and also allowed for a small amount of down elevator when flying inverted. What I'd do is set it up so the same amount of up elevator is needed in level flight as down elevator in inverted level flight.

I've read in some trim instructions that when trimmed properly, you shouldn't need down elevator to achieve level flight when inverted. That leads me to believe I should continue to move my CG back, then trim so little if any up elevator is needed for level flight, then be able to roll inverted and still need little or no down elevator to maintain level flight.

Now, maybe level flight is going to far and I should achieve that performance just in the 45* up line test. That is, not need much if any down elevator after rolling inverted. I need to hold some up elevator to maintain 45* up and then when I roll inverted, my nose does drop very quickly. I think I'm release the slight up elevator on time but things happen real quick in a 41" plane. So either I'm not releasing up quickly enough, the trim is too biased toward non-inverted flight, or the CG needs to move back further. Or some combination of the above.

-l2t
Old 09-04-2013, 08:21 AM
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MTK
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Originally Posted by learn2turn View Post
Starting to work a bit on those trim tutorials. I'm still at the point where things happen so fast and things like trim settings and stick movement interact so that I'm not sure if I have the CG correct.

For years I've always trimmed my planes so I need just a tad of up-elevator to maintain level flight. That allowed me to feel the plane as I flew straight-and-level and also allowed for a small amount of down elevator when flying inverted. What I'd do is set it up so the same amount of up elevator is needed in level flight as down elevator in inverted level flight.

I've read in some trim instructions that when trimmed properly, you shouldn't need down elevator to achieve level flight when inverted. That leads me to believe I should continue to move my CG back, then trim so little if any up elevator is needed for level flight, then be able to roll inverted and still need little or no down elevator to maintain level flight.

Now, maybe level flight is going to far and I should achieve that performance just in the 45* up line test. That is, not need much if any down elevator after rolling inverted. I need to hold some up elevator to maintain 45* up and then when I roll inverted, my nose does drop very quickly. I think I'm release the slight up elevator on time but things happen real quick in a 41" plane. So either I'm not releasing up quickly enough, the trim is too biased toward non-inverted flight, or the CG needs to move back further. Or some combination of the above.

-l2t
I think it is harder to fly Pattern when holding up elevator in S&L, especially in higher level sequences. It increases pilot workload. Slight down when inverted is something we all live with. Don't know what trim instructions you have read but typically, Pattern models are trimmed so that a slight amount of down is needed in Inverted S&L and none in upright S&L

Let me suggest that you move the CG to around 28-30% of the MAC. The NSRCA website has a technique for determining the MAC (mean aerodynamic chord) of a typical wing planform. Find the MAC, find the 28% and 30% locations on the MAC, and project them to the fuse sides.

Set the CG there for now and trim the plane around that CG location range (stab and wing incidence adjustments and engine/motor offsets). Fly it there for a few dozen flights and them make the assessment whether to move the CG further aft (or fore)....
Old 09-04-2013, 09:03 AM
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danamania
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Originally Posted by learn2turn View Post
...I'm not sure if I have the CG correct...

...in the 45* up line test. That is, not need much if any down elevator after rolling inverted. I need to hold some up elevator to maintain 45* up and then when I roll inverted, my nose does drop very quickly. I think I'm release the slight up elevator on time but things happen real quick in a 41" plane. So either I'm not releasing up quickly enough, the trim is too biased toward non-inverted flight, or the CG needs to move back further. Or some combination of the above.

-l2t
Hi l2t, in this test, one needs no back pressure on the elevator once the 45 deg upline is established. The roll to inverted ( then hands off the stick) tells the story: If the nose drops "very quickly" then this particular test is failed for precision aerobatics. Sounds nose heavy to me so you may want to try moving your LiPo back if there is room to do so, and try again (unless I misunderstand your post). The CG will affect your trim settings so a few trials may be needed to settle this. Keeping in mind that you are not trimming a "pattern" model, there may be a narrower range where this test passes so let's keep that in mind too. Agree with Matt above about not wanting to hold up elevator for upright S&L, we need that time to set up for the next maneuver. This is possibly also a matter of preference but flying the schedule is work enough, IMO.
Old 09-04-2013, 09:55 AM
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Dean Pappas
 
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Hello L2T ... got a real name we might use?

first, the stuff about flying inverted with absolutely no down elevator is simple nonsense. it would require the airplane be on the verge of instability.
second, keep reading any and all stuff you can: you will eventually synthesize a good understanding of trimming from wrapping your arms around all the different approaches folks write down.
thirdly ... and this one is especially for you, since you innately are comfortable trimming for "zero-G" that is trimming so that upright level flight takes the same elevator movement as flying inverted, you are in a great position.
It is dramatically easier to trim an airplane to go straight in both verticals and knife-edges if you are happy flying trimmed zero-G.
Nothing written in the aeromodelling press, of substance, is written about this approach.
i flew this way when i came back to RC after school back in '82, '83 and '84 (so did Yoshioka-san when he won the Worlds back in '73) and departed from it at the advent of Turnaround.

maybe you'll stick with it where I didn't.
Regards,
Dean Pappas
Old 09-04-2013, 10:19 AM
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learn2turn
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Originally Posted by Dean Pappas View Post
Hello L2T ... got a real name we might use?
First name is Ken.

I use the moniker "learn2turn" a lot online. My alter ego on weekends in winter is as ski coach which is the origin of "learn2turn".
Old 09-04-2013, 10:27 AM
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danamania
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Oh my Dean, now my curiosity is piqued! Please how does a zero-G trim preference change the way one would set wing incidence and/or CG, compared to current practices for pattern planes, i.e., +0.5 deg wing incidence (zero stab) and the slightly forward CG so typical today? Is this even the right question to ask? LOL thanks for the lesson!
Old 09-05-2013, 02:55 PM
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learn2turn
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I moved the battery back about another 1/2". Then gave it one or two clicks more up trim. It's pretty hands-off in level flight now, at least as hands-off as a 41" plane can be in a little bit of puffy wind.

My initial impression is I'm flying a little better.

The only two inverted moves I'm working on are 2-point roll and immelman without rolls. On the two-point, I just give it a tad more down elevator on the inverted portion and everything else I'm working seems to be a bit easier. I still really really suck at the double Immelman without rolls. I know what it's supposed to be, the straight portion is suppose to be a square the same size at the 1/2 loops. But, I haven't gotten the straight portions at all level yet. But that problem is me, not the plane.

So I'm going to fly it with the trim I have now for a few more sessions. Then evaluate what the next adjustment, if any, should be.

-Ken aka l2t
Old 09-05-2013, 05:43 PM
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Ryan Smith
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Ken, are you still referencing the Leader 480?
Old 09-06-2013, 05:10 AM
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learn2turn
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Originally Posted by Ryan Smith View Post
Ken, are you still referencing the Leader 480?
Yes. That's the only plane I'm practicing with now.

I have an EF Extra 300 EXP 48" on the bench right now that should be ready in a week to replace my 3DHS Edge 540 that died in a mid-air. That plane will be my multipurpose sport/3D/pattern/fun plane. I selected it as it's supposed to be the most precise flying of the 48" EF EXP planes.

I hope to build a larger pattern plane this winter, probably a BJ Craft Monolog 70.

-Ken aka l2t
Old 09-06-2013, 12:56 PM
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Ryan Smith
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I will get a CG measurement for you from my airplane this evening. I've got probably close to 800 flights on Leaders from development and general enjoyment after release. My CG feels pretty good and mimics that of the feel I have with a two-meter airplane. If you are interested in throws and expos, I can provide you with those as well. I seem to recall the manual throws and CG being more conservative father than being more pattern oriented to satisfy the larger market usage of the airplane.

I may be biased, but the airplane flies extremely well, particularly with a good setup.
Old 09-06-2013, 08:32 PM
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jhanc
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Ken
I have practiced the Sportsman sequence hundereds of times with the Leader 480, and learned a lot about precision aerobatics with it (not that I am any good yet) I have the CG at 92mm, about the middle of the recommended range, and have the throws set as recommended. I do have to have the end of the batteries over the wing tube to get it to balance. Mine flies straight and level hands off, with neutral trims, at this balance point, and inverted with just a little down elevator. I find if I have to have back pressure to fly level, the plane fights me through the whole sequence, and it ain’t pretty!
I agree with Ryan, this plane can fly extremely well.
Good Luck, John
Old 09-07-2013, 04:06 AM
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danamania
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Good stuff above Ken! If you can at all see some way to get free on 9/21 or 22, and can make the drive, friendly reminder that there is a pattern contest in Endicott NY (just west of Binghamton). I do recall from other threads that this may not be realistic given family, etc., however you would be able to pick a lot of brains and possibly have a great day. Cheers!
Old 09-07-2013, 04:36 AM
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learn2turn
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[QUOTE=jhanc;11609945...) I have the CG at 92mm, about the middle of the recommended range, and have the throws set as recommended. I do have to have the end of the batteries over the wing tube to get it to balance. ...
Good Luck, John[/QUOTE]

What battery are you using?

I'm using 3S 2200mAH GenAce. The back of the battery is about 1.5cm from the wing tube. It was more like 3.0cm before I moved it back. I thought my first setup was around the front mark of the range. I haven't measured it since I moved it back.

-Ken aka l2t
Old 09-07-2013, 04:40 AM
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learn2turn
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Originally Posted by danamania View Post
Good stuff above Ken! If you can at all see some way to get free on 9/21 or 22, and can make the drive, friendly reminder that there is a pattern contest in Endicott NY (just west of Binghamton). I do recall from other threads that this may not be realistic given family, etc., however you would be able to pick a lot of brains and possibly have a great day. Cheers!
Thanks for the invite as I know I could get away at least a weekend if it wasn't ski season but I'd like to get a bit more practice in so maybe next season. I'd like to at least learn all the moves in the Sportsman pattern sequence.

I thought I read something about an event in NY state this past spring that was for novice pattern. It sound almost as much like practice/training as competition. When I read about it, I was hoping it would happen again next year. But now I can't find it. Maybe it was the 401 to 402 events in Endicott but I did look it up and thought the location was a bit further east and south. Could be I'm just not remembering it right. If there was an event like that next spring, I'd definitely go if I was free that weekend.

-Ken aka l2t
Old 09-07-2013, 05:40 AM
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Anthony-RCU
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There were two primers in New York this year. One was at that same field in Endicot the other was in Haverstraw. Endicot will definitely happen next year and you have started me thinking about making the one in Haverstraw happen again.
Old 09-07-2013, 08:03 AM
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learn2turn
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Originally Posted by Anthony-RCU View Post
There were two primers in New York this year. One was at that same field in Endicot the other was in Haverstraw. Endicot will definitely happen next year and you have started me thinking about making the one in Haverstraw happen again.
Well Haverstraw must have been the one I was thinking of, definitely easier than Endicot. If there was an event there and I was free that weekend, I'd definitely try to make it.

-Ken

PS

I like your sig, the third line.
Old 09-07-2013, 11:48 AM
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jhanc
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I use Hyperion 3S 2100 batteries. I am flying with a Neo480 motor, which is heavier but has plenty of power.
Old 09-07-2013, 11:53 AM
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Bob Benson
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Originally Posted by learn2turn View Post
Yes. That's the only plane I'm practicing with now.

-Ken aka l2t

Ken,

I ran across this site last night and saw that you are flying the Leader 480. I have to say that this is a great little plane and is the one that brought me back to RC flying after 30 years! I have nearly 200 flights since last November.

One tip for the Leader is to eliminate that little bit of slop with the linkages because of the under-size control rod in the control horns. You will feel the difference! I use mini kwik-links on the ailerons and solder regular kwik-links on the rudder and elevator rods.

The first step is to trim for straight and level flight. Adjust the linkages so that the transmitter trims are centered. Determine the best prop size and flying speed at this time. (not full speed as some hot dogs do, you need to add or reduce throttle as required for the various maneuvers)

Determine the CG using several steps:

1. Crosswind, 45 degree up-line, roll inverted (you should be able to fly the up line with no up elevator)
Nose very gently falls off

2. Roll inverted
Only a little down elevator required to maintain level flight

3. Roll into near vertically banked turn
Neither nose or tail should drop

Take some time to get the CG, flying speed and initial trims straight and level and to your liking before moving on to the other trimming steps; lateral balance, thrust angles, aileron differential, transmitter mixes, etc. Any change in prop size or CG will require changes in the following steps.....

I find the best CG for me is between 100mm and 105mm. That puts my battery all the way back to the servo tray, but I also have the extra weight of a Power 10 up front. I can fly all of the Sportsman and Intermediate individual maneuvers, but the sequences are still a work in progress. I get positive comments on the looks and flight characteristics of the Leader 480 almost every time out at the flying field here at a local county park. I think a lot of that is because I am the only one flying a pattern-type plane...... and one that is trimmed about as well as it can be!

Happy flying,

Bob

What trim tutorials were you talking about above?

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