Is it mandatory to perform a new weight and balance after a paint job?

[Katamarino]

Question as in the title.

For clarity, I want to get the aircraft weighed anyway and I'm curious about whether a paint shop will do this automatically when the job is complete.

 

[Dan Thomas]

The maintenance manuals will tell you that the control surfaces need their mass balances checked after painting. Guess how often that happens.

If the airplane wasn't stripped but painted over the old stuff, it will be heavier and W&B should be redone.

 

[Klaus M]

You are so right about control surface balancing. I'm surprised how many A&Ps are unfamiliar with the process.

These pictures taken while a group of A&Ps working on the field showed up and became knowledgeable of control surface balancing and adjusting the counter weights. Some of the mechanics worked for a paint shop and said they where told that aircraft that cruised less then 150 knots didn't need balancing. Another said they painted several Mooneys and never balanced the controls.

 

[Half Fast]

I just got my plane back from the paint shop a couple of weeks ago. They re-balanced the control surfaces, but the only update to the overall plane w&b was a calculation for antennas that were permanently removed. All the old paint was stripped off prior to painting.

 

[Half Fast]

I'm curious about whether a paint shop will do this automatically when the job is complete.

None of the shops I contacted included weighing the plane as a regular part of the job.

 

[MRC01]

... All the old paint was stripped off prior to painting.

When I repainted my airplane I considered this essential. Otherwise you have no idea what is going on under that paint. Corrosion is a killer and anyone who thinks it's cheaper not to strip off all the old paint is fooling himself in the long run.

Also take the opportunity to replace wingtips, fairings, etc. With a lot of airplanes (like my 172N) the OEM is cheap plastic that cracks and when repainting, it's false economy not to replace that stuff with higher quality fiberglass.

 

[Half Fast]

Also take the opportunity to replace wingtips, fairings, etc.

True, but mine had all been replaced recently and were in good shape.

The shop did replace all the external screws, camlocs, etc., and that’s well worth doing. Old, discolored, buggered-up fasteners will look awful next to shiny new paint.

 

[aggiepack]

The lack of knowledge of some mechanics is astonishing. Charging north of 14k even for pretty basic paint schemes, unaware of the need to balance control surfaces and even unable to make a proper log book entry. If you are using 8 gallons or more of primer and paint during the process you will probably end up with a different W&B.

See AC43.13-1b Chapter 10 for guidance: empty weight less than 5,000 lbs any weight change of 1 lbs or more is not negligible.

 

[Clip4]

When dealing with in/lb on an 8” wide aileron, how much is a dry paint exchange is going change the balance? A 1 oz change in aileron weight would possibly change the balance .5 in/lb.

 

[bnt83]

When dealing with in/lb on an 8” wide aileron, how much is a dry paint exchange is going change the balance? A 1 oz change in aileron weight would possibly change the balance .5 in/lb.

The elevators I checked off a 182L last year were just barely inside the limit of course that means the lightest possible balance weight is insalled.

 

[Dan Thomas]

When dealing with in/lb on an 8” wide aileron, how much is a dry paint exchange is going change the balance? A 1 oz change in aileron weight would possibly change the balance .5 in/lb.

We found them off, and had to add weight. Cessna didn't use any more balance weight that they needed to, and they were using light lacquers or enamels, with no primer beneath. Strip those off and put on epoxy primers, then urethanes, both of which weigh a lot more than the old stuff, and the balance WILL change. And why are they balanced? To prevent flutter at high speeds within the Vne.

Also figuring into flutter control are cable tensions. I've often found those below minimum, as well as misrigged altogether.

 

[Jdm]

We saw one (just out of the paint shop) that had the controls painted while on the airplane. They didn’t even take them off! They definitely didn’t balance anything.

Another was painted with a wide brush. I’m serious. The whole airplane was brushed over, apparently by the owner.

Some small paint shops are operating without being a repair station or having any A&Ps on site. The ones I’m familiar with are having an A&P come in on the last day to balance and sign off the job. Doesn’t seem proper to me. The airframe should at least be inspected for corrosion after paint removal by a licensed mechanic.

 

[brcase]

You are so right about control surface balancing. I'm surprised how many A&Ps are unfamiliar with the process.

These pictures taken while a group of A&Ps working on the field showed up and became knowledgeable of control surface balancing and adjusting the counter weights. Some of the mechanics worked for a paint shop and said they where told that aircraft that cruised less then 150 knots didn't need balancing. Another said they painted several Mooneys and never balanced the controls.
View attachment 130829
View attachment 130830

I had an elevator flutter on me at 145 knots once. That was a wake up call and a reminder that VNE is True airspeed not Indicated airspeed. Fortunately it was low frequency and recoverable but that was just luck of the draw. Flutter is dangerous.

Brian

 

[MooneyDriver78]

To keep the weight of the paint to a minimum don’t put stripes,etc on your control surfaces. First they paint the base color, then the stripes.

I wonder how much weight a paint job adds?

I agree stripping the original paint is required, the PO of my plane did a cheap job and it didn’t last 10 years.

 

[Craig]

I wonder how much weight a paint job adds?

It's going to depend on what is used and how many coats are sprayed. A gallon of two part is going to weigh around 10 pounds when sprayed out, depending on spray conditions and how much additives are required. A C-172 will require about 3 gallons of top coat and 2 gallons of primer.

 

[Jim_R]

A gallon of two part is going to weigh around 10 pounds when sprayed out

Is that truly the weight of just the solids, or are you including all the volatiles that are going to evaporate?

 

[Craig]

Jim: That's about what's left after spraying out and full cure. A full gallon of mixed paint, and various additives while still liquid is probably close to 18 pounds. Remember, with two part, most of them are 1:1 mix ratios for the base and hardener/catalyst, with anything up to 4:1 ratio on the additives in addition. The books for whatever airplane should give you the balance info. For example, my big Fairchild, the rudder has to have less than 1 pound down force, measured at 13" from the center of the hinge line.

 

[Magman]

There are 2 topics here:

W&B of the aircraft

and

balancing of flight controls


Assure your agreement with the shop addresses this.

 

[Dan Thomas]

For example, my big Fairchild, the rudder has to have less than 1 pound down force, measured at 13" from the center of the hinge line.

From a Cessna 172 service manual, some examples and notes:




Some large ranges there. But the 172 isn't a fast airplane. Plenty of others are faster and need narrower ranges. In any case, the balance needs checking, whether before or after painting. There is no guarantee that Cessna made the surfaces well within the unpainted ranges at manufacture.

Control surface repairs, patches or replacement of sections of skin, can seriously affect the balance. So can accumulated dirt inside the surface. I have also found considerable paint-stripping residue inside those surfaces. They're not getting flushed out properly, probably because the job is being done with the airplane assembled.

 

[Klaus M]

There are 2 topics here:

W&B of the aircraft

and

balancing of flight controls


Assure your agreement with the shop addresses this.

It's been stated that if you add a 5 pound radio that a Weight & Balance revision is necessary so, why wouldn't adding 18 pounds of paint?

How do you find the Center of Gravity of a paint job?

 

[Doc Holliday]

It's been stated that if you add a 5 pound radio that a Weight & Balance revision is necessary so, why wouldn't adding 18 pounds of paint?

How do you find the Center of Gravity of a paint job?

By using scales and weighing the airplane.

 

[Katamarino]

Well I dropped my airplane off at the paint shop yesterday and asked. They said that on small aircraft they don't usually weigh them, but we agreed that they would weigh mine and prepare a new weight and balance.

 

[Half Fast]

Well I dropped my airplane off at the paint shop yesterday and asked. They said that on small aircraft they don't usually weigh them, but we agreed that they would weigh mine and prepare a new weight and balance.

Be sure to come back and let us know how much it changes.

 

[Half Fast]

...why wouldn't adding 18 pounds of paint?

Because you presumably removed approximately 18 pounds of old paint first.

 

[Katamarino]

Be sure to come back and let us know how much it changes.

The reason I wanted a new W&B is because of the many, many mods I've made to it over the past 5 years. So any change will be a combination of paint job, but probably mainly drift from doing all those mods and updating the W&B by calculation, not measurement.

 

[MauleSkinner]

The reason I wanted a new W&B is because of the many, many mods I've made to it over the past 5 years. So any change will be a combination of paint job, but probably mainly drift from doing all those mods and updating the W&B by calculation, not measurement.

I’d still suggest double-checking their math.

 

[Half Fast]

The reason I wanted a new W&B is because of the many, many mods I've made to it over the past 5 years. So any change will be a combination of paint job, but probably mainly drift from doing all those mods and updating the W&B by calculation, not measurement.

Understood. Mine's the same way; many pieces of equipment installed and removed over the years, some logged as "negligible" for W&B, sometimes with new calculations. Some stuff was logged in but never out when it was removed. Besides, I've found and corrected two calculation errors, so there are probably more.

Someday I'll have the thing weighed and get a clean, fresh number, but in the meantime I stay away from the load limits. I doubt the weight is wrong by more than my passengers' fibs about their personal weights, anyway. Neither of the errors I've found moved the CG by more than a couple of tenths of an inch.