There have been numerous BCP threads about how aircraft just naturally get heavier with age. Dirt, dust, sweat, humidity, coats of paint, etc, all slowly add to the empty weight of an aircraft over time. But, how much of a weight increase is "normal" after 20, 30, or 40 years?

I recently had my new-to-me Cessna 172 weighed, since I couldn't find a recent weight & balance in the logbooks. The airplane's set-up is factory Cessna everything. No big modifications or avionics changes of any kind. But, the increase in empty weight from a previous weighing about 20 years ago, makes me wonder if there are thirty kilos of drugs or cash stashed under the floorboards somewhere, even though the mechanic who did the annual inspection didn't find anything unusual when he opened it up.

How much dirt & dust, etc, could there possibly be inside a Cessna 172?

Thanx, Dave.

Old wires, left over from multiple avionics upgrades, can add up, too. When I put my Bonanza on a diet, it lost something like 10-15# in wire alone.

Agree with StuBob re old avionics...most shops cut the connectors and leave the bundles when they add a component...wire is heavy. I had the same issue when I weighed my 1956 182....it was heavy by 50 pounds from previous weigh in...shop and I determined that the weight was calculated 40 years ago and “adjusted” as components came in and out...also the old scales were not as accurate as what we have now...check your paint and see if you have a topcoat in a factory finish...that could be 15 pounds...best direction is to gut what you can and put it on accurate scales...the facts are the facts

I also have a theory that either today’s digital scales are more accurate or the manufacturers had their scales tuned to the lighter side of permissible accuracy. Not sure what the limits were, but if you could be accurate +/- 1%, it would make sense to go to the negative side if you wanted to sell airplanes.


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Also, understand that manufacturers weights for aircraft (with at least one exception) are nearly always listed for an absolutely stripped airplane. Also when said manufacturer pushed an airplane out the door, many of them never weighed each airplane, they calculated the empty weight based on installed equipment weights.

But, just adding the weight of radios, and other installed equipment may not include miscellaneous weight, like wiring, etc.

So, in my experience at least the new airplane LEGAL weight certificate is almost always pretty “optimistic” shall we say.

The one exception is the Bonanzas, which all seem to be actually lighter than Beechcrafts basic empty weights.

Also, if you’re weighing an airplane, DO NOT allow it to be weighed with full fuel, then deduct the weight of the “useable fuel”. Instead, drain fuel from gascolator, and weigh it in actual empty condition. I have found that many airplanes actually hold significantly more fuel than the tank capacity listed. Weigh it full of fuel, and you may have just added the weight of a few gallons of fuel you didn’t know you were packing around.

MTV

Thanx Guys.

My aircraft has the same avionics that it had when it rolled out of Cessna 40+ years ago, so, that's not a factor. It was repainted back in the 1990's, but, that was before both of the weighings that I'm using for comparison, so, that's not it either.

I don't know if the old scales that were used 20 years ago were certified, but, the ones that were used last week were definitely calibrated earlier this year. I understand how de-fueling before weighing would be better, and I will do that next time, but, since both now and then, the aircraft was weighed with "full fuel", that doesn't explain the weight gain.

I've requested that Cessna search their archives to find the original build sheet and weight & balance. If the configuration is confirmed to be original, the weight gain mystery will continue . . . . .

Which leaves the possibility that older weights were biased/skewed to the lighter side of things? And in this case, MUCH LIGHTER!

Thanx again for your input, Dave.

There’s definitely some truth to the theory that manufacturers weights are optimistic. Take aircraft floats for example; when you are issued an STC by a float manufacturer, EDO or Wipline for example, it comes with a “weight affidavit”. I have personally assembled these float assemblies, straight out of the crate they came in brand new, and immediately hung them from a certified load cell, only to find them close to 10% lighter than advertised.

Back in the 70s when Kenmore Air Harbor was the largest single engine Cessna dealer on the west coast the old mechanics who worked there were happy to see how “optimistic” those factory weights were. In those days they were more concerned with “legal” useful load over “actual” useful load. Times have changed.


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My factory weight-and-balance sheet doesn't even show actual weights for each wheel.
So it appears they weighed the first few off the line, then used the same numbers for the rest.

Yep, they didn't bother weighing every plane. Seems like paperwork wasn't as important back in the CAR3 days. Which sounds good to me!

All that really matters is that you know what it weighs now and what can be taken off to get where you want to be. Dust and dirt is negligible weight.

I did find a very heavy dolly left in the leading edge rib bay of a Champ once. It had to be in there for years.

Aryana wrote:Yep, they didn't bother weighing every plane. Seems like paperwork wasn't as important back in the CAR3 days. Which sounds good to me!

All that really matters is that you know what it weighs now and what can be taken off to get where you want to be. Dust and dirt is negligible weight.

I did find a very heavy dolly left in the leading edge rib bay of a Champ once. It had to be in there for years.

Has nothing to do with CAR 3. I’m not sure most manufacturers actually weigh each plane coming off the line today. Regulations permit them to use a “base weight” and calculate Legal empty weight by adding the weights of installed components.

We weighed several brand new airplanes delivered from a couple factories, and most of the manufacturers certified weights were somewhat “optimistic”.

But perfectly legal.

If you really want to know what your airplane weighs, weigh it.

MTV

Dave,

I would re weigh your airplane with no fuel like MTV mentioned above. One of my Cessna 185's years ago actually held 13 gallons MORE fuel than placarded. I wanted to make a calibrated fuel dip stick for my airplane so we put the airplane in the flying attitude and drained all the fuel at the strainer, this left the unusable fuel. We then fueled the airplane and wow, 13 more gallons useable than spec. That is a significant amount of extra weight had we been weighing the airplane with full fuel and subtracting factory spec usable fuel.

Kurt

Lets just talk basics. Excerpt from FAA AC regarding aircraft weighing:

(2) Tolerable errors associated with each factor are as follows:
(a) Scale accuracy for reweigh – Typically 0.2% of basic empty weight (BEW), based upon reported scale accuracy for analog scale systems or 0.1% of BEW for digital scale systems. Analog accuracy value may be used for aircraft for which the aircraft OEM guidance does not recommend or require the use of digital scales.

So if Cessna weighted it in 1960, it was most likely an analog scale, so +- 20 Lbs, then go to today, most likely a digital scale +- 10 Lbs. So you can have a variation of 30 Lbs with original allowable scale error and a digital scale's error thrown in. So 20-40 lb differences are in the standard deviation for measurement errors. Assuming calibration was completed immediately before weighing.

Don't get worked up over it.

I would re weigh your airplane with no fuel like MTV mentioned above. One of my Cessna 185's years ago actually held 13 gallons MORE fuel than placarded. I wanted to make a calibrated fuel dip stick for my airplane so we put the airplane in the flying attitude and drained all the fuel at the strainer, this left the unusable fuel. We then fueled the airplane and wow, 13 more gallons useable than spec. That is a significant amount of extra weight had we been weighing the airplane with full fuel and subtracting factory spec usable fuel.

I am curious if the large carrying capacity with airplanes weighed with zero fuel is due to aging of the bladders and stretching of the bladder material. Or is it possible the shape of the bladder changes over time allowing more of the fuel to be usable. 13 gallons would be 78 lbs, an hour more of fuel, and is absolutely awesome. I wonder if this would change if new bladders were installed. Would an integral fuel tank give the same result? I have filled 29 gallons in the left tank previous thinking I ran it dry in level flight but maybe there is more capacity in those old bladders. Mine are 31 years old. I am getting ready to weigh my airplane sometime this fall before doing some restoration work. It might be interesting to fill the tanks completely and drain the fuel to see the total gallons removed.


Josh

I would never weigh an airplane with full fuel unless you exactly how much it holds, not just what the factory claims it holds. Waste of time and money as well as having a more than likely wrong weight.

Kurt

G44 wrote:I would never weigh an airplane with full fuel unless you exactly how much it holds, not just what the factory claims it holds. Waste of time and money as well as having a more than likely wrong weight.

Kurt

I totally agree. I’m not certain what mechanism is at play when it comes to bladder fuel tanks, but I’ve personally dealt with four airplanes equipped with welded fuel tanks that held more than advertised.

I ASSUME this is possibly related to ensuring that each plane’s tanks actually contain AT LEAST the amount of fuel listed for the make and Mosel airplane. Tanks with less than advertised would be an open invitation to law suits. So, since hard tanks are often welded, therefore each an individual, best to err on the positive side.

Our Huskys all held at least a few gallons more than advertised. So weigh with full tanks, then subtract weight of advertised fuel, and with those planes, you’d be accepting a ~ 20 plus pound hit in useful load.

MTV

I took over 160 lbs from my 69 180. 45 lbs in old wiring, coax, and dead antennas!

I weighed my cub when I bought it. 1150. 1070 after the rebuild. On 31” bushwheels


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This is a very interesting topic and one that's been storming my mind for months. Very valuable is the tip on weighing with empty tanks, as well as the data on optimistic original values, paint layers, wiring etc.

Anyway the myth is still going strong: weight seems to keep increasing over time, although sometimes rather slowly, so a one-time error can't justify the trend, does it?