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Old Jul 07, 2012, 02:54 PM
Just go with the flow
goflyhighrc's Avatar
Modesto, CA
Joined Nov 2006
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Quote:
Originally Posted by DaOldGuy View Post

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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Old Jul 07, 2012, 02:56 PM
Just go with the flow
goflyhighrc's Avatar
Modesto, CA
Joined Nov 2006
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Quote:
Originally Posted by Luv3d View Post
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)
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Old Jul 07, 2012, 03:25 PM
Honeybadger don't care...
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United States, FL, Winter Park
Joined May 2010
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According to their website, the ECOMRC 107" Cessna 195 uses a NACA 2412 airfoil which is not symmetrical.

See the graphic below.
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Old Jul 07, 2012, 03:28 PM
Honeybadger don't care...
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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.
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Old Jul 07, 2012, 03:39 PM
Team 3DHS
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San Antonio, TX
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For a Cesna, it's better to err on being a tad too nose heavy.
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Old Jul 07, 2012, 03:49 PM
Registered User
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United States, NE, Lincoln
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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.
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Old Jul 07, 2012, 04:12 PM
Just go with the flow
goflyhighrc's Avatar
Modesto, CA
Joined Nov 2006
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Quote:
Originally Posted by BoneDoc View Post
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.
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Old Jul 07, 2012, 04:26 PM
Team 3DHS
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San Antonio, TX
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If it's too sensitive, then it's because he's going too slow.
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Old Jul 07, 2012, 04:30 PM
3DHS 'native'
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USA, TX, Spring
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Would uptrim be nose heavy? Why do I feel stupid today?

Quote:
Originally Posted by goflyhighrc View Post
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.
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Old Jul 07, 2012, 04:43 PM
Team 3DHS
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San Antonio, TX
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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".
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Old Jul 07, 2012, 04:54 PM
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Nose heavy has better post stall recovery too right?
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Old Jul 07, 2012, 05:00 PM
Team 3DHS / Team JR
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United States, TN, Knoxville
Joined Apr 2010
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Quote:
Originally Posted by goflyhighrc View Post
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 View Post
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 View Post
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 View Post
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.
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Old Jul 07, 2012, 07:36 PM
Just go with the flow
goflyhighrc's Avatar
Modesto, CA
Joined Nov 2006
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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?
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Old Jul 07, 2012, 08:29 PM
customstandoffs
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USA, AL, Madison
Joined Dec 2007
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Quote:
Originally Posted by goflyhighrc View Post
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
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Old Jul 07, 2012, 08:38 PM
Just go with the flow
goflyhighrc's Avatar
Modesto, CA
Joined Nov 2006
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Quote:
Originally Posted by cmala View Post
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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