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Effect of paint on weight & balance

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dreel(at)cox.net
Guest

Posted: Sat Aug 12, 2006 4:01 am Post subject: Effect of paint on weight & balance

I reweighed my RV8A today because I thought the paint job might make a

significant change.  Not only did the aircraft seem faster after being

painted but the pitch control forces seemed lighter when flying single

pilot.  In previous posts, I have reported a significant increase in cruise

speed when moving the moment arm aft, probably due to reduced pitch

stability drag.  Thinking about it, I realized that a lot more of the

surface area of the aircraft is behind the balance point near the wing spar

than in front of it, so it would make sense that the empty aircraft moment

arm would be further aft once it was painted.  Here are the actual numbers:



Weight unpainted:    1051

Weight painted:        1077

Paint weight added:      26 lb



Unpainted CG:    77.46

Painted CG:        78.53 inches aft of datum



If you haven't weighed your airplane since painting and have occasion to

load it near the aft limit, beware!  You might loose pitch control.



Dave Reel - RV8A

Gary.A.Sobek

Joined: 09 Jan 2006
Posts: 217
Location: SoCAL USA

Posted: Sat Aug 12, 2006 6:05 am Post subject: Effect of paint on weight & balance

Using the same CALIBRATED scales:



Unpainted:  1086

Painted:     1094



Weight gain from paint equal 8 pounds.



Gary A. Sobek

"My Sanity" RV-6 N157GS O-320 Hartzell,

1,932 + Flying Hours So. CA, USA

http://SoCAL_WVAF.rvproject.com



----Original Message Follows----

From: "DAVID REEL" <dreel(at)cox.net>

Reply-To: rv-list(at)matronics.com

To: "rvlist" <rv-list(at)matronics.com>

Subject: Effect of paint on weight & balance

Date: Sat, 12 Aug 2006 08:01:22 -0400






I reweighed my RV8A today because I thought the paint job might make a

significant change.  Not only did the aircraft seem faster after being

painted but the pitch control forces seemed lighter when flying single

pilot.  In previous posts, I have reported a significant increase in cruise

speed when moving the moment arm aft, probably due to reduced pitch

stability drag.  Thinking about it, I realized that a lot more of the

surface area of the aircraft is behind the balance point near the wing spar

than in front of it, so it would make sense that the empty aircraft moment

arm would be further aft once it was painted.  Here are the actual numbers:



Weight unpainted:    1051

Weight painted:        1077

Paint weight added:      26 lb



Unpainted CG:    77.46

Painted CG:        78.53 inches aft of datum



If you haven't weighed your airplane since painting and have occasion to

load it near the aft limit, beware!  You might loose pitch control.



Dave Reel - RV8A

DOUGPFLYRV(at)aol.com
Guest

Posted: Sat Aug 12, 2006 6:56 am Post subject: Effect of paint on weight & balance

We gained 10# on our RV8

  

 DO NOT ARCHIVE

 D. Preston

khorton01(at)rogers.com
Guest

Posted: Sat Aug 12, 2006 7:30 am Post subject: Effect of paint on weight & balance

On 12 Aug 2006, at 08:01, DAVID REEL wrote:



 	  Quote: 	
		   



 Weight unpainted:    1051

 Weight painted:        1077

 Paint weight added:      26 lb



 Unpainted CG:    77.46

 Painted CG:        78.53 inches aft of datum




	


These numbers suggest that the average arm of the added weight would  

be about 122.8", which is about 3.5" aft of the nominal passenger  

position.  Given that most of the large surface area of the wing is  

ahead of this, I would have expected the average arm of the added  

paint to be a bit further ahead.



Could it be that one of the weighings had an error?  Either a scale  

error, a levelling error, or a calculation error?  Or, have other  

things been added to the aircraft since the first weighing?  Were the  

same scales used for both weighings? Have the scales been  

calibrated?  If not, is it possible that a different scale was used  

on the nose gear for the two weighings?



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

khorton01(at)rogers.com
Guest

Posted: Sat Aug 12, 2006 10:34 am Post subject: Effect of paint on weight & balance

On 12 Aug 2006, at 11:28, Kevin Horton wrote:

 	  Quote: 	

 On 12 Aug 2006, at 08:01, DAVID REEL wrote:

> 

>

> Weight unpainted:    1051

> Weight painted:        1077

> Paint weight added:      26 lb

>

> Unpainted CG:    77.46

> Painted CG:        78.53 inches aft of datum

>

 These numbers suggest that the average arm of the added weight  

 would be about 122.8", which is about 3.5" aft of the nominal  

 passenger position.  Given that most of the large surface area of  

 the wing is ahead of this, I would have expected the average arm of  

 the added paint to be a bit further ahead.

 Could it be that one of the weighings had an error?  Either a scale  

 error, a levelling error, or a calculation error?  Or, have other  

 things been added to the aircraft since the first weighing?  Were  

 the same scales used for both weighings? Have the scales been  

 calibrated?  If not, is it possible that a different scale was used  

 on the nose gear for the two weighings?

 Kevin Horton         RV-8 (finishing kit)

 Ottawa, Canada

 http://www.kilohotel.com/rv8

Typo - that should have been 121.8" arm for the added paint.  But it  

still looks strange.

Kevin

Larry Bowen

Joined: 09 Jan 2006
Posts: 802
Location: NC, USA

Posted: Sat Aug 12, 2006 10:59 am Post subject: Effect of paint on weight & balance

I noticed the same thing, and my paint weighed the same 26#.  The paint shop

did the second weighing -- different scales, personnel, etc.



Yours is a light plane.



http://www.rvproject.com/wab/wab.jsp?id=96



-

Larry Bowen

Larry(at)BowenAero.com

http://BowenAero.com

 



[quote] --

_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress...

khorton01(at)rogers.com
Guest

Posted: Sat Aug 12, 2006 11:35 am Post subject: Effect of paint on weight & balance

Larry,



Just curious - what is your empty weight and CG, and how much did the  

empty CG move aft with the paint job?



Kevin



On 12 Aug 2006, at 14:57, Larry Bowen wrote:



[quote] 



 I noticed the same thing, and my paint weighed the same 26#.  The  

 paint shop

 did the second weighing -- different scales, personnel, etc.



 Yours is a light plane.



 http://www.rvproject.com/wab/wab.jsp?id=96



 -

 Larry Bowen

 Larry(at)BowenAero.com

 http://BowenAero.com

> --

HCRV6(at)comcast.net
Guest

Posted: Sat Aug 12, 2006 5:20 pm Post subject: Effect of paint on weight & balance

FWIW,  using the same calibrated electronic scales my RV-6 gained 17 pounds with paint (Jet Glo, not clear coated.)

 --

Harry Crosby 

RV-6 N16CX, 250hours

  

 [quote]-------------- Original message -------------- 

From: "RV6 Flyer" <rv6_flyer(at)hotmail.com> 



[quote] --> RV-List message posted by: "RV6 Flyer" 

 

 

 Using the same CALIBRATED scales: 

 

 Unpainted: 1086 

 Painted: 1094 

 

 Weight gain from paint equal 8 pounds. 

 

 Gary A. Sobek 

 "My Sanity" RV-6 N157GS O-320 Hartzell, 

 1,932 + Flying Hours So. CA, USA 

 http://SoCAL_WVAF.rvproject.com 

 

 

 

 ----Original Message Follows---- 

 From: "DAVID REEL" 

 Reply-To: rv-list(at)matronics.com 

 To: "rvlist" 

 Subject: Effect of paint on weight & balance 

 Date: Sat, 12 Aug 2006 08:01:22 -0400 

 

 --> RV-List message posted by: "DAVID REEL" 

 

 I reweighed my RV8A today because I thought the paint job might make a 

 significant change. Not only did the aircraft seem faster after being 

 painted but the pitch control forces seemed lighter when flying single 

 pilot. In previous posts, I have reported a significant increase in cruise 

 speed when moving the moment arm aft, probably due to reduced pitch 

 stability drag. Thinking about it, I realized that a lot more of the 

 surface area of the aircraft is behind the balance point near the wing spar 

 than in front of it, so it would make sense that the empty aircraft moment 

 arm would be further aft once it was painted. Here are the actual numbers: 

 

 Weight unpainted: 1051 

 Weight painted: 1077 

 Paint weight added: 26 lb 

 

 Unpainted CG: 77.46 

 Painted CG: 78.53 inches aft of datum 

 

 If you haven't weighed your airplane   since   o avai

Larry Bowen

Joined: 09 Jan 2006
Posts: 802
Location: NC, USA

Posted: Sat Aug 12, 2006 6:43 pm Post subject: Effect of paint on weight & balance

Before paint: 1106 and 77.08.

After paint: 1130 and 79.11.



That's obviously a 24 pound gain after paint, not 26 as I said before.  Mine

is a PPG base-coat/clear coat.



Cheers,



-

Larry Bowen

Larry(at)BowenAero.com

http://BowenAero.com

 



[quote] --

_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress...

dreel(at)cox.net
Guest

Posted: Sat Aug 12, 2006 8:02 pm Post subject: Effect of paint on weight & balance

Both weights were taken with the same set of certified digital scales

borrowed from my local EAA chapter.  Same procedure was used in each case

though 5 months intervened.  I believe the results to be quite accurate.

It's good to see that Larry got similar results.  I had bare metal &

fiberglass surfaces in the initial weight.  Alan Woodson's Texas Aero Color

provided pinhole filling and all the rest.  I'm quite satisfied with the

paint job & enjoyed working with Alan, but I envy you guys with 8 lb paint

jobs.



Dave Reel - RV8A

khorton01(at)rogers.com
Guest

Posted: Sun Aug 13, 2006 2:23 am Post subject: Effect of paint on weight & balance

Very strange.



Before paint moment = 1106 * 77.08 = 85,250.48

After paint moment = 1130 * 79.11 = 89,394.3



A moment change of 4,143.82 for a weight change of 24 lb implies an  

arm of 172.66" for the added paint.  There is no way the centre of  

the paint is that far aft (well aft of the rear baggage compartment),  

so one of the weighings must be wrong.



Be careful on your weighings guys.



Kevin Horton

On 12 Aug 2006, at 22:40, Larry Bowen wrote:



[quote] 



 Before paint: 1106 and 77.08.

 After paint: 1130 and 79.11.



 That's obviously a 24 pound gain after paint, not 26 as I said  

 before.  Mine

 is a PPG base-coat/clear coat.



 Cheers,



 -

 Larry Bowen

 Larry(at)BowenAero.com

 http://BowenAero.com

> --

Larry Bowen

Joined: 09 Jan 2006
Posts: 802
Location: NC, USA

Posted: Sun Aug 13, 2006 6:03 am Post subject: Effect of paint on weight & balance

Sounds like *perhaps* the second group of wieghers left the tail down,

despite my explicit directions to raise it.  Sigh.  Not surprising.

The virtual averages for RV-8's here reinforce what you are saying:

http://www.rvproject.com/wab/index.jsp

Thanks for pointing it out.

-- 

Larry Bowen

Larry(at)BowenAero.com

http://BowenAero.com

Kevin Horton wrote:

[quote] 

 Very strange.

 Before paint moment = 1106 * 77.08 = 85,250.48

 After paint moment = 1130 * 79.11 = 89,394.3

 A moment change of 4,143.82 for a weight change of 24 lb implies an

 arm of 172.66" for the added paint.  There is no way the centre of

 the paint is that far aft (well aft of the rear baggage compartment),

 so one of the weighings must be wrong.

 Be careful on your weighings guys.

 Kevin Horton

 On 12 Aug 2006, at 22:40, Larry Bowen wrote:

> 

>

> Before paint: 1106 and 77.08.

> After paint: 1130 and 79.11.

>

> That's obviously a 24 pound gain after paint, not 26 as I said

> before.  Mine

> is a PPG base-coat/clear coat.

>

> Cheers,

>

> -

> Larry Bowen

> Larry(at)BowenAero.com

> http://BowenAero.com

>> --

_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress...

gmcjetpilot(at)yahoo.com
Guest

Posted: Mon Aug 14, 2006 3:14 am Post subject: Effect of paint on weight & balance

Well I can't certify the W&B measurement, but paint will move the CG aft quite a bit.

   

  Look at how much surface area is aft of the CG. Most of the paint is aft. The centroid of the paint if you will will be at or aft the baggage area. The aft fuselage and tail is a lot of area. Forward of the CG there's not that much paint. I agree that 2" shift is a lot. G

   

   

  >From: Kevin Horton <khorton01(at)rogers.com>

 	  Quote: 	
		  Subject: Re: Effect of paint on weight & balance



posted by: Kevin Horton <khorton01(at)rogers.com>



Very strange.



Before paint moment = 1106 * 77.08 = 85,250.48

After paint moment = 1130 * 79.11 = 89,394.3



A moment change of 4,143.82 for a weight change of 24 lb implies an  

arm of 172.66" for the added paint.  There is no way the centre of  

the paint is that far aft (well aft of the rear baggage compartment),  

so one of the weightings must be wrong.


	




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