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Paint Effect on CG

E

ericwolf

Well Known Member
I have read plenty of posts on the effect of paint on empty weight (~10-30 lbs), but what about the CG? I assume that it would shift it back, but how much have you seen?
 
There is more paint on the wing than anywhere else. Go ahead, put 30lb of stuff on the middle of the wing and see how much the CG move back. :D Remember, the aerodynamic center is at 1/4 core
 
ok, I'll take back my statement. But unless you get real elaborate with your paint, you should be ok. I think Van's factors in for the paint.
 
Of course most of the paint weight is in the wings, but the tail has a significant amount of surface area and a few extra pounds back there can make a difference. I'm looking for actual before & after numbers rather than speculation.
 
Paint will move the CG significantly rearward. There is much more area behind the CG. A new weight & balance is required after painting.
 
It goes aft!

The numbers for my naked RV-7 were (and by naked I mean no wheel, leg or intersection fairings):
1034 lbs
80.01?

Numbers after paint and fairing installation.
1055 lbs
80.48?

The fairings are a variable you were not looking for but I hope this data point helps. I would consider my paint heavy. Yellow takes a lot of coats.
 
The addition of wheel, and landing gear fairings notably counteracted some of the paint weight.
 
Mel said:
The addition of wheel, and landing gear fairings notably counteracted some of the paint weight.
Click to expand...

But that is only true for taildraggers where the two main gears are forward of CG. Does Vans make the tail lighter or make the front heavier?
 
Aviator168 said:
But that is only true for taildraggers where the two main gears are forward of CG. Does Vans make the tail lighter or make the front heavier?
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Tricycle geared RV's, as a rule, are heavier than tail draggers.

The main gear on the A's is behind the CG; whereas on the tail draggers they are in front of the CG.

The nose gear on the A's is a lot of weight up front and although the tail wheel is way back there, it doesn't weigh near as much as a nose wheel.

Also, the slider is heavier than a tip-up. Thus a tip-up tail wheel should be the lightest of all, depending on how it is built.
 
On my 8A I weighed it before first flight with no paint or fairings and then again after painting with all gear fairings and wheel pants installed.

Results: Before 1069 lbs. CG 77.86"
After 1123 lbs CG 78.11"

Paul Danclovic
Jamestown NC
 
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So, what I'm reading here is a painted plane will fly faster. First because it's slicker and second because it gets a little tail heavy.
 
thanks brian,
I was just trying to point out that painting shouldn't hurt anything. neither should putting on heavy things like wheel pants and skirts. I believe that both ads to the beauty of the plane and helps it fly to its potential.

I hope I didn't offend the original poster. Seems either he wants to know what to expect for possible changes to account for a slightly heavier tail or is trying to decide weither to paint at all.
 
allbee said:
...I hope I didn't offend the original poster. Seems either he wants to know what to expect for possible changes to account for a slightly heavier tail or is trying to decide weither to paint at all.
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No offense taken. I am very close to flying and I'm thinking of moving things around a bit during Phase 1 testing to correct for a CG that is further forward than I would like. My bird is currently unpainted, but will be eventually. That got me to thinking that paint should shift it back. Based on the two responses so far, it is between 0.25 - 0.5", although with the fairings at the second weigh-in. Based on my calculations, wheel & gear fairings should shift the CG much for the -A models, but may for taildraggers.

Anybody else want to post their numbers?
 
I plan on doing a W&B this weekend following a yellow paint job.
There's a lot of yellow paint as stated in a previously post.

My original W&B was also 1034 lbs wo fairings, & was on the aft CG with low fuel especially carrying the 3-blade catto prop.
Empty CG 81.33

I have a tricyle gear, slider with forward induction.

I can tell you now that I believe the cg has moved aft since I've been flying it for about 2 months since paint.
 
heavy paint and light engine equals :-(

This is an edit of my original post. We went back over everything, measured all of the datum points, etc. Turns out my weight and balance isn't too bad after all. I have corrected the errors in the following. I will try to do better in the future :)

I am down in the weight and balance doldrums (sp?) I knew my paint job was going to be a heavy one; you can't do a kandy apple job without a bunch of paint. Turns out I did just about everything wrong. Used the lighter parallel valve O-360, lightest weight Sky Tek starter, light weight Plane Power alternator, 18 pound Catto composite prop and heavy paint. I did put 5/8" spacers between the engine mount and the firewall but that wasn't enough. Weight ended up a respectable 1,065 pounds but the empty CG is at 81.82".

On Checkaway's weight and balance program Scott Will's unpainted RV-7A is the perfect comparison of the effects of paint on an RV-7A .with a light firewall forward and heavy paint. Scott's unpainted RV-7A's empty weight is 1,066 and mine is 1,065. Pretty much everything else is the same except his has a 22 pound prop spacer. So I have 22 pounds of paint and he has a 22 pound spacer. Both planes weigh the same but his empty CG is 79.45" and mine is 81.82". Mine is OK for now but to get full utilization I am going to probably put a harmonic balancer on the flywheel for a little more weight on the nose of the plane.

So those that have implied that paint isn't that significant of an issue need to realize that the -7A was designed for the heavier angle valve O-360 and a heavy constant speed prop. A heavy paint job and a light weight firewall forward means you aren't going tohave access to the full 100 pound limit of the baggage compartment when you have a heavy passenger and minimum, fuel.
 
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Shouldn't be a big deal

I don't have the numbers in front of me but the CG change between paint and unpainted was very small.

My paint is 4 colors, base/clear. I estimate that I gained 20-23 pounds with paint. Most grossly over estimate the weight of the paint.

Some will try to argue the point but, a good base/clear is lighter than the same color single stage. The base color in a base clear system is very light. An example, all of the red on my plane is less than a quart. A complete white base with toner was less than a gallon, about 3/4 of a gallon.

Pick up a gallon of red single stage. You'll find it very heavy. It needs to be to carry the pigment. Yellow is also very heavy.

In the overall scheme of things, the paint is minimal in the weight of the plane. Paint it and don't worry about the weight. Be happy with the results and enjoy the performance!!!
 
Hi Steve,
Thanks for the heads up. Mine weighs 1043 empty and is the same configuration as yours (Catto prop, 0-360 parallel valve, etc). My CG is 80.91 and I anticipate it moving aft with paint & baggage compartment side panels. I'm planning on doing the 20 lb. crush plate idea soon. :rolleyes:

I'll bet my final weight is within 5 pounds of yours after it's painted and I have the side panels installed.
 
Remember

RV7Guy said:
Some will try to argue the point but, a good base/clear is lighter than the same color single stage. The base color in a base clear system is very light. An example, all of the red on my plane is less than a quart. A complete white base with toner was less than a gallon, about 3/4 of a gallon.

Pick up a gallon of red single stage. You'll find it very heavy. It needs to be to carry the pigment. Yellow is also very heavy.
Click to expand...

that most of the weight of a can of paint is VOCs and other liquids that will go away when it is sprayed. All you're left with is the solids. The red solids are heavy and expensive though as they are made from cadmium.

Don
 
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