How do airplanes gain weight?

[Lood]

I bought my Mooney in 2008 and it was weighed in 2007. Its empty weight was 1700lbs on the dot. This meant that I had a payload of 660lbs and I have flown it at MAUW many, many times without any problems.
This year it was again due for weight and balance and was I shocked when it gained 72lbs in weight. Its empty weight is now 1772lbs!! The thing that boggles, is the fact that since I bought it, I had the old, heavy King 175B removed, together with all other avionics that I didn't use, such as the DME and ADF. These were replaced with a KX155 and KY197. I also had all obsolete wiring removed that were left in the airplane over the years. To top that, I replaced the old and very heavy starter with a small, lightweight B&C.
I was actually very excited and thought that after the next weighing session, I might have a payload of around 680lbs - maybe a little more. However, I am now stuck with a 590lbs payload and it really sucks - that's the same as a C172!!
My Mooney has been repainted by the previous owner, but I am not sure whether this was done prior to, or after the 2007 weighing.
What other factors could have such a dramatic influence in my airplanes' weight ?

[Ron McBride]

Lood

Your weight should have gone down. Did you remove all the pilot's storage in the plane, headesets, oil etc?  Did they drain the tanks completely?

Are you required to re weigh the aircraft every couple of years?  My 69F weighs 1682 with Electric Gear and Flaps, modern avionics.  My plane has not been on a scale yet though.

Let us know what they find.

Ron

[Lood]

Ron, here in SA, certified airplanes all have to be be weighed every 5 years - even when everything stayed the same. You then get a new weight-and-balance certificate. When due, this is normally done during the annual inspection. I'm never present during the annual, but I have a very reputable AME which happens to be the Mooney agent in Africa. The requirements when weighing is general knowledge so I trust that they indeed did remove everything from the airplane, including all fuel.
I have an electroninc livestock scale that is calibrated and can weigh up to 2 tons in 100g increments. I think I should do my own weighing session and see what the results are.

[kris_adams]

Please post your results.  I'd be very interested in seeing the results.

[jetdriven]

i wont let my airplane anywhere near a scale.  

[FAST FLIGHT OPTIONS LLC]

Quote: jetdriven

i wont let my airplane anywhere near a scale.  

[aviatoreb]

Airplanes gain weight do to too much intake and not enough activity.  Have you been flying it enough?

Quote: jetdriven

i wont let my airplane anywhere near a scale.  

[Cruiser]

scale accuracy is also a factor 1% on 1700# will be a 17 lbs. error +/- . It could be pretty easy to be off 2% or 3% just in using different scales.

[Lood]

Herewith all data from the weight & balance documents in my posession:

Year: E/weight Arm
1966: 1665 lbs 44.5"
1986: 1670 lbs 44.9"
1993: 1693 lbs 44.6"
1999: 1708 lbs 42.7"
2005: 1710 lbs 43"
2007: 1700 lbs 43.6"
2012: 1773 lbs 44.8"

[Lood]

Double post

[N601RX]

I've weighed several race cars  with a scale under each wheel.  The results can vary considerably depending on how the car is pushed up on the scales.  You want it to roll straight on and stop in the center.  Any side loading will affect the weight.  You can also bump it gently and then let it settle down.

[1964-M20E]

I helped my mechanic weigh a King air once and we let it down on the scales with the jacks.

Anyway it just looks like planes are similar to people and they gain weight as they age.  No good reason though.

[carusoam]

That looks like fuel still in the tanks?  70 pounds is a lot of radios but not a lot of fuel.  Check to see if the fuel was drained from the bottom of the tanks. 5 gallons on each side will build in 60 pounds of 100LL.

Is it just the Mooney pilots concerned this much in W&B?

-a-

[M20Kid]

I haven't weighted a GA airplane but I used to fly for the airlines and I know those airplanes would gain a few hundred pounds each year from dirt and debris ground into the carpets and storage bins.  It doesn't seem that GA airplanes could have anywhere close to 10 pounds per year in extra dirt but some gain seems inevitable.

Good luck!

[PTK]

Quote: Lood

What other factors could have such a dramatic influence in my airplanes' weight ?

[Jerry 5TJ]

 

[Lionudakis]

Scale accuracy I'd bet. In the Regional Jet biz, the manual says to weight the aircraft 3 times, rotating the scales, and average them.  Even the high tech FAA approved, triple calibrated on calibrated calibrating test calibrators, scales still read  differently each time. 

[xftrplt]

 Apologies to all in advance. 

Next time weigh the plane when the moon is directly overhead.  That will reduce the weight some.

True, you lose ~.0002 lb.

Better yet, weigh it at the equator.  You lose ~7 lb (0.3%) of its weight at 40 degrees latitude.  (35,000 times more than the lunar loss.)

[jetdriven]

Easier to drain out all the unusable fuel by removing the drain fittings, drain out all the oil, let 40 lbs from each tire, and slip the A&P an extra hundred.  Perhaps even a bottle of Cutty Sark. Then have him weigh it.  Thats the easiest 150 LBS of useful load you ever boug....I mean, got. 

[jetdriven]

Quote: Lood

Herewith all data from the weight & balance documents in my posession:

Year: E/weight Arm

1966: 1665 lbs 44.5"

1986: 1670 lbs 44.9"

1993: 1693 lbs 44.6"

1999: 1708 lbs 42.7"

2005: 1710 lbs 43"

2007: 1700 lbs 43.6"

2012: 1773 lbs 44.8"

[DaV8or]

It's probably scale and operator variations. Maybe you need tip your scale operator really well for a job well done?? Anyhow, I might suggest letting it go, use an average of the years you do have weights for for flight planning and fly on.

[Lood]

IIRC, South African TCA airplanes have to be weighed every 5 years or everytime any major alteration had been made, which probably includes repainting, re-doing the interior and so on. Avionics, light weight starters/ alternators etc. come with their wieght and arm and requires only a logbook entry, I think.

[TonyPynes]

What's the going rate now for a re-weigh? The last one I was present at was for one of our Falcon 900s and it was a major life event and had the invoice to show for it.

Note to Mods: This isn't Austin. Somehow I logged in under when I logged on this morning. You really need to fix this. It's done this once or twice before to me. Right now I'm having a serious discussion with myself on whether or not to have a little fun at Austin's expense or do the right thing...

Ward Holbrook

 

[DaV8or]

Quote: AustinPynes

Right now I'm having a serious discussion with myself on whether or not to have a little fun at Austin's expense or do the right thing...

Ward Holbrook

 

[jbs007]

Quote: AustinPynes

What's the going rate now for a re-weigh? The last one I was present at was for one of our Falcon 900s and it was a major life event and had the invoice to show for it.

Note to Mods: This isn't Austin. Somehow I logged in under when I logged on this morning. You really need to fix this. It's done this once or twice before to me. Right now I'm having a serious discussion with myself on whether or not to have a little fun at Austin's expense or do the right thing...

Ward Holbrook