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CG Placement, How far can I go?

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CG Placement, How far can I go?

Old 01-02-2002, 01:55 PM
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RickP
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Default CG Placement, How far can I go?

Hi Guys,
I've started with a conservative placement of the CG on my cap, and have been moving it back little by little. I haven't really noticed much change and the last time I moved it a fair amount. How far back can I keep going? Will I all of a sudden go to far and have an uncontrollable aircraft?
Also, inverted requires a little more down elevator then I'd like to see to maintain level flight. Will continuing to move the CG help this at all?
Thanks
Rick
Old 01-03-2002, 02:19 AM
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Default CAP C/G

Hi Rick,
Moving the C/G aft little by little is the correct procedure with any plane but is particularly important with a CAP. You will notice the changes most evident on landings. As you approach a more even balance (not as much down requried) the elevator will become more sensitive. Be aware the plane will almost want to stand on it's tail (harrier configuration) if too much elevaror is applied diring landings. Be ready to reduce elevator and add power as you approach a more aft C/G palcement. This is due in part to the forward location of the stab/elevator on this plane. You don't say what manuvers you are flying and this will also have a bearing on your choice as 3D will generally be better with a more aft C/G.
Hope this helps, Bill
Old 01-03-2002, 01:12 PM
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RickP
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Default 3D ready

Hey Bill,
Thanks. I'm not a beginner pilot, I've been at this for several years now. However, I've been bitten by the acrobatic craze at our field. I have gotten to the point where I can fly an entire flight either inverted, or knife edge on either side. I'm just now practicing from bouncing from one to the next.
The plane won't flat spin so nicely which is why I suspect it is nose heavy. The amount of down elevator I have to hold in while inverted is also disconcerting.
I'm ready for the 3D plunge though, I'll just get that CG back and then what? LOL. I guess I'll start with the harrier. I hope for allot of stick time this weekend.
Thanks
Rick
Old 01-03-2002, 04:35 PM
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Troy Newman
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Default Down Elevator Pressure

If you are looking for a CG that gives you less down elev needed to maintain inverted level flight......You might want to look at a couple of things.....CG placement can affect lots of things. If the CG is in the right spot it is still possible that you are pushing more than you would like......

If this is the case you can do a couple of things that will make the feel better. First you can reduce the the amount of Expo on the down elevator side.......this will give the elevator on the down side a less soft feel....especially if you have a large amount 40-60% expo in the down elevator....Or increase the amount of throw on the down elevator. Say you are throwing elev up at 15deg and down at 15deg dial your linkage or Travel Adjust to give more down elevator say 20deg of down but still maintain the 15deg of up.


This is a common practice for getting the feel that you want. CG is a critical thing on a plane. It can make the plane act like a pig or act like a sweetheart....I have found the majority of planes out there flying IMAC or just playing are way too tail heavy. They are tail heavy because the guys want it to 3D well.....

Notice the guys at the TOC they will add a huge lump of lead to the tail of the plane before the freestyle....but all the other times 80% of the competition they are flying with a more forward CG.

The plane will respond better and be more predictable.

I not having flown your plane could not say specifically but rolling it inverted and how much down does it take is not always the best test for CG its a good start but..........check out this web site and look at the Trim chart its a great way to get your plane flying straight. www.nsrca.org I think its under the Technical section.

A key to a nose heavy plane is running out of elevator on landing and a tail heavy plane will not want to come down on landing...it will want to float and float until speed dies enough and it stalls out and snaps......there are many things you can do to CG and the plane will still fly...the question is how well. Aft CG does some things better and Forward CG does other things better....I have found that a more Forward CG can help snaps..... An extremely forward CG will not allow a snap.....A little aft CG will make the control surface responsive..or more responsive....and a way aft CG will make the surfaces sometimes un manageable and un-predictable.


Good Luck

Troy Newman
Team JR
Old 01-06-2002, 10:42 PM
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wingspan99
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Default My experience with a CAP231EX

I found that when I moved the CG too far aft that my Sig CAP231EX was very difficult to land. One thing about aft CG though, if you get it too far aft that doesn't mean you'll automatically crash. If the tail is too heavy you can get through the test flight by pressing the elevator down and manually managing your airspeed. The only thing you have to know about flying with a too far aft cg is that if you pull the throttle back, the plane will get too slow ALL BY ITSELF with no up elevator. You can keep the speed up by correcting the pitch attitude with judicious amounts of down elevator. It feels weird, but the plane still flies. To flare for the landing just let go of the elevator. If you get the CG so far back that it's beyond the lifting power of full down elevator, you'll need to keep the power on right to landing. which will increase the lifting power of the elevator until you can get it down lower. -Tom
Old 01-11-2002, 04:18 AM
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Default CG Placement, How far can I go?

I heard a good way to set CG was to trim it level and invert it. If it dives, move the CG back, if it climbs, move it forward. If you get to the right point but it is too squirrely, move it forward some and/or dial in expo.

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