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Jul 07, 2012, 01:54 PM
Just go with the flow
goflyhighrc's Avatar
Quote:
Originally Posted by DaOldGuy

Do a trim flight with the plane at half throttle, take a look at the elevator position after landing, this is always a quick first test assuming incidence on surfaces are all correct.


What do you mean by looking at the elevator? He has a bit of up elevator trimmed at level flight.
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Jul 07, 2012, 01:56 PM
Just go with the flow
goflyhighrc's Avatar
Quote:
Originally Posted by Luv3d
The inverted test is only valid if the airplane has a symmetrical airfoil. Does the cessna have a symmetrical airfoil? If it does not, the test will not work properly.
Here is the plane, not his, but the same model. Does it have a symmetrical airfoil?


Giant Scale 107" ECOMRC Cessna 195 maiden AirShowRC.com (3 min 51 sec)
Jul 07, 2012, 02:25 PM
Honeybadger don't care...
Luv3d's Avatar
According to their website, the ECOMRC 107" Cessna 195 uses a NACA 2412 airfoil which is not symmetrical.

See the graphic below.
Jul 07, 2012, 02:28 PM
Honeybadger don't care...
Luv3d's Avatar
Good original question, though. For an asymmetrical airfoil, how to check the CG when airborne. Other than level flight testing, I'm not sure. It should still balance statically about 1/3 the total wing chord, just like an aerobatic airframe/airfoil should, I believe.
Jul 07, 2012, 02:39 PM
Team 3DHS
BoneDoc's Avatar
For a Cesna, it's better to err on being a tad too nose heavy.
Jul 07, 2012, 02:49 PM
Registered User
nebwake's Avatar
yea that plane is not a 3D plane to start with, if you make it neutral to tail heavy it'll be a beast to hold on to.
Jul 07, 2012, 03:12 PM
Just go with the flow
goflyhighrc's Avatar
Quote:
Originally Posted by BoneDoc
For a Cesna, it's better to err on being a tad too nose heavy.


The owner has about 12 clicks of uptrim for level flight, he thinks it's tail heavy because it feels sensitive to him,doe's not make sense to me.
Jul 07, 2012, 03:26 PM
Team 3DHS
BoneDoc's Avatar
If it's too sensitive, then it's because he's going too slow.
Jul 07, 2012, 03:30 PM
3DHS 'native'
going4speed's Avatar
Would uptrim be nose heavy? Why do I feel stupid today?

Quote:
Originally Posted by goflyhighrc
The owner has about 12 clicks of uptrim for level flight, he thinks it's tail heavy because it feels sensitive to him,doe's not make sense to me.
Jul 07, 2012, 03:43 PM
Team 3DHS
BoneDoc's Avatar
Yes, assuming the incidence is set correctly. But a plane that's too nose heavy will come in HOT for a landing. If the pilot is not comfortable with that speed, he will try to (ill-advisedly) slow it down, causing the plane to be in a near stall condition, and hence, making it feel "unstable".
Jul 07, 2012, 03:54 PM
3DHS 'native'
going4speed's Avatar
Nose heavy has better post stall recovery too right?
Jul 07, 2012, 04:00 PM
Team 3DHS / Team JR
Bivens's Avatar
Quote:
Originally Posted by goflyhighrc
What do you mean by looking at the elevator? He has a bit of up elevator trimmed at level flight.
Quote:
Originally Posted by goflyhighrc
The owner has about 12 clicks of uptrim for level flight, he thinks it's tail heavy because it feels sensitive to him,doe's not make sense to me.
UP trim in level flight is OK....means the plane does not need help holding the tail "up" with downtrim. This likely means he's on the noseheavy side of neutral.

Quote:
Originally Posted by BoneDoc
Yes, assuming the incidence is set correctly. But a plane that's too nose heavy will come in HOT for a landing. If the pilot is not comfortable with that speed, he will try to (ill-advisedly) slow it down, causing the plane to be in a near stall condition, and hence, making it feel "unstable".
Quote:
Originally Posted by BoneDoc
If it's too sensitive, then it's because he's going too slow.
Possibly...but not to forget.....planes with small surfaces (scale) can also take on a "mushy" feel when going too slow, with slow air over the controls.

The bottom line....try going more noseheavy...this will generally NOT cause anything bad to happen...if the plane feels better, leave it that way. Clearly, we're talking about fine-tuning CG on this "already-flown" plane...so it couldn't be TOO tailheavy even now.....must be pretty close or he would've had big complaints on maiden.......

Of course, you may want to look into the expo settings.....if the complaint is "sensitive" around neutral, try adding some expo.

I generally look at a high-wing non-symmetrical airframe with the way it feels on landing.....if the nose won't come down and settle into a nice glide at idle....try moving the CG forward. You should be able to make the plane take on a nice slightly nose-down glide at low throttle if the CG is right.

All this discussion about CG-testing.....has a simple answer, forget the tests....just adjust the CG so it FEELS right to you....for me, a plane needs to track well and settle in nice on landing without ballooning....this typically puts me slightly ahead of a neutral CG.
Jul 07, 2012, 06:36 PM
Just go with the flow
goflyhighrc's Avatar

Wing Stand


A year or so ago, someone posted a video standing in the middle of as wing of a GS 3DHS plane. Anyone have it in thier archives?
Jul 07, 2012, 07:29 PM
customstandoffs
cmala's Avatar
Quote:
Originally Posted by goflyhighrc
A year or so ago, someone posted a video standing in the middle of as wing of a GS 3DHS plane. Anyone have it in thier archives?
Was that josh price?

No, I think it was jared clark
Jul 07, 2012, 07:38 PM
Just go with the flow
goflyhighrc's Avatar
Quote:
Originally Posted by cmala
Was that josh price?

No, I think it was jared clark
I was thinking Josh, perhaps it was Jared,trying to locate it on youtube.


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