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Weight? Wait. Don’t tell me! (Weight & Balance)

 

May 2005

 

For many of us as we age, our weight changes; for many airplanes, age also brings similar changes. No, their metabolism has nothing to do with it. It’s mostly technology. What are some of the things that cause the calculated weight and C.G. to be different from the actual weight on scales for our airplanes?

 

Radios: Until the late 1970s, airplanes came with big heavy radios in them and typically older installations used more individual units to do the same tasks that can be done with one new style radio today. As an example, one Garmin 430 GPS Nav/Com can take the place of a KX170B Nav/Com, a KN64 DME and a KR85 ADF. That change alone is about 12 lbs. less weight and one empty 3⅛” instrument panel hole

 

Old wiring left installed from previous radio installations will also add extra weight in your airplane. An old ADF harness can weigh up to 10 lbs.

 

Antennas: Unused antennas left installed will add extra weight (and drag) and should be removed.

 

Paint is also a culprit for adding weight. Many owners, wanting to brighten the bird’s feathers without breaking the bank, have opted for a scuff and paint. Mooney has no problem with this practice as long as the control surfaces are stripped, painted and correctly balanced. However, multiple layers of paint add weight. Paint materials have changed immensely in the last ten years and are considerably more protective and durable than before. For this reason, along with the lower weight and the increased value of your airplane, it’s best to do a complete strip, etch and repaint.

 

Errors in calculations: In spite of what most owners think, we mechanics are all just human and sometimes make mathematical errors. Until the early 70’s, six-place long division was used unless you had an expensive and bulky mechanical calculator. Then the first electronic LED calculators became available for under $100. Of course, errors can still occur. Over the years, just the rounding errors can make a difference in the calculations.

 

Debris trapped in the lower extremities: Again, just like us, detritus tends to accumulate in the nether regions of our aircraft. Over the years, I have found everything from tools to seal oil inside the bellies of airplanes. I once removed 43 dead mice along with two full shop-vac bags full of field weeds, all from one Bonanza. An annual inspection of a 1960s Helio Courier revealed 5 lbs. of dried seal oil solidified on the inside of the belly skins! This aircraft was flown in Alaska in the early 70s and the native hunters would bring seal oil in jugs from their villages to sell in Nome. Apparently, some jugs fell over and drained through the floor into the belly. I must have been the first person to pull up the floorboards since that time.

 

Interiors and insulation changes, different density of foams (such as lumbar type seat foams) can affect the weight of your aircraft. Thicker and heavier carpet along with thicker replacement windows will all affect the overall weight.

 

Damage history: During the 1960s and 70s it was commonplace to repair rather than replacing a damaged wing or fuselage skin. Airplanes in those days were cheaper and plentiful. Today the opposite is true and it, therefore, makes more sense to replace a complete skin to maintain resale value. Either practice is perfectly acceptable as long as FAA minimum standards are met for the type of work being done. Repairs can add some weight whereas a replacement skin should not. A steel plate in your head weighs more than transplanted bone.

 

Tires: Unbelievably, the tires can make a difference in the weight of your airplane. If you have ever held an Air Hawk tire and the same size Flight Custom 3 tire in each hand, it’s apparent the Air Hawk is lighter.

 

Instruments: Until the mid 80s, mechanical instruments were the norm. Modern instruments use electronic transducers eliminating the need for hoses and tubes to run from the source to the display. Compared to electrical wires, hoses add weight to the airplane.

 

Electronic scales versus mechanical scales: Like the calculators, twenty years ago, electronic scales were not affordable or available and airplanes were weighed on mechanical scales similar to the balance-beam scale used in a doctor’s office. There were various mechanical scales and some were better than others. Today’s electronic scales are affordable, more accurate, smaller and easier to work with and have become a standard tool.

 

By studying the three actual Mooney examples listed below, it is easy to conclude for older airplanes with the typical mods and alterations, the calculated weight and balance is probably not very accurate. For late 1980s or newer airplanes, the weight and balance might be a little closer to the actual data. The tendency is that late model airplanes seem to gain weight, while older airplanes with numerous radio changes and multiple STC’s and alterations may be loosing weight.

 

The weight and balance data the pilot relies on are very important to complete a safe flight. In winter, surface contamination and in summer, high altitude airports and hotter than standard days narrow the margin of safety. In example #3 below, the M20E is 62 lbs heavier and the center of gravity is 2” aft of what the pilot assumed. At best, this aircraft was somewhat more unstable in pitch. At worst, an overweight and/or out-of-balance airplane can lead to tragedy.

 

Many aircraft maintenance shops have electronic scales and charge under $500 to complete an actual weight and balance on your Mooney. This could be a lifesaver if you fly with passengers or cargo or over half-full fuel tanks.

As always, if you have a question about this article, you may contact me at my aircraft repair shop, 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.

KNR-e-mail 

 

Note: Actual weights are with unusable fuel using electronic scales.

 

 

EXAMPLE #1 - 1968 M20F

 

CALCULATED DATA:

WT. 1687.11 ARM 44.98

Useful Load 1052.89

 

Mods Installed:

3 blade Semitar prop

Sky Tec lightweight starter

Precise flight standby vacuum

new radio package

shoulder harness kit

oil cooler relocation kit

ACK ELT-Bracket air filter

Brackett air filter

Hoskins belly strobe

flat machined instrument panel

 

Work done:

scuff and paint

interior work on fabric seats

ACTUAL WEIGHT:

WT 1646 ARM 45.0

Useful Load 1094

A gain of 41.1 lbs. in the useful load.  

 

 

 

 

 

 

EXAMPLE #2 - 1983 M20K

 

CALCULATED DATA:

WT 1989.99 ARM 43.2

Useful Load 910.1

 

Mods Installed:

Loran removed

GPS installed

one-piece belly

 

Work done:

scuff and repaint on top surface

ACTUAL WEIGHT:

WT 2025 ARM 43.04

Useful Load 875

A loss of 35.1 lbs. in the useful load.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EXAMPLE #3 - 1966 M20E

 

CALCULATED DATA:

WT 1625.28 ARM 45.32

Useful Load 946.75

 

Mods Installed:

full gap seal kit

oil cooler relocation kit

radio changes

flat machined instrument panels

4-way EGT/CHT system

fuel computer

201 style windshield

231 style wing tips

shoulder harness kit

Brackett air filter

fuel bladder kit

alternator conversion

Sky Tec starter

strobe lights on wing tips

wing root fairings

 

Work done:

different paint

different interior

ACTUAL WEIGHT:

WT 1691 ARM 47.35

Useful Load 884

A loss of 62.75 lbs. in the useful load

   and a CG change of almost 2” aft.