Weight and Balance revision

[RLCarter]

1 hour ago, ArtVandelay said:

I can be 159lbs overweight and still be legal if my J was manufactured in a different year.

How can you be over gross and be legal?

Edited September 14, 2019 by RLCarter

[Niko182]

4 minutes ago, RLCarter said:

How can you be over gross and be legal?

Because the weight and balance says so. Its a grey area. So some people dont question it. An good example was that an ovation was ferried with a 1 time ferry pass to 3900lbs. Or about 600 pound overgross. He took off and when he got to cruise climb speed he was still seeing 800ft per minute up to 8000ft. The plane is completely capable of taking off at higher weights.

[Hank]

2 hours ago, cliffy said:

How much does oil weigh again?  See page 3-4 in the above manual for both answers. (ALL fluids change weight with temperature so if you do this in a cold winter in an unheated hangar make the adjustments)

Almost had it there, cliffy. Missed it by that much . . .

All materials (solid, liquid and gas) change density with temperature, not weight. Pour some water, oil, gas, etc., into a calibrated vessel where small volume changes can be measured, and you will notice that the volume is more at higher tempratures and less at lower temperatures. But the weight will never change.

Drop the temp to below freezing, fill the container then set it outside on a hot summer afternoin and there will be a greater change in volume. Measure some out below freezing and weigh it; warm the original container to summer ramp temperatures and pour the same volume into your container and it will weigh less. The weight if the oil and gas already in your plane will not change unless you add or remove / use some.

The change in volume of one quart of new motor oil by raising its temperature from 32°F/0°C to 100°F/38°C is 0.0265 quarts, or less than one ounce by volume. Thwre is zero (0) change in weight. At the same time, the volume of yiur engune is increased from winter to summer, then decreased again as you climb to cooler altitudes.

From my friends at The Engineering Toolbox:

The change in the units volume when temperature changes can be expressed as

dV = V₀ β (t₁ - t₀)                                                        (2)

where

dV = V₁ - V₀ = change in volume (m³, ft³)

β = volumetric temperature expansion coefficient (m³/m^{3 o}C, ft³/ft^{3 o}F)

t₁ = final temperature (^oC, ^oF)

t₀ = initial temperature (^oC, ^oF)

and for motor oil, from the embedded link above, β = 0.00039/°F.

Edited September 14, 2019 by Hank

[RLCarter]

@Niko182, they are capable of more than certified for.... but where does it say you can go over gross on a regular basis, ferry permits are a whole different thing

[Niko182]

14 minutes ago, RLCarter said:

@Niko182, they are capable of more than certified for.... but where does it say you can go over gross on a regular basis, ferry permits are a whole different thing

according to the weight and balance I am legal.

[RLCarter]

24 minutes ago, Niko182 said:

according to the weight and balance I am legal.

TheTCDS shows the max takeoff/landing weight, how would you be legal by being 159lb over gross...sorry to beat a broken drum but your saying your W&B says max weight of 3200 lbs but feel free to go to 3359 lbs?

[Niko182]

Just now, RLCarter said:

TheTCDS shows the max takeoff/landing weight, how would you be legal by being 159lb over gross...sorry to beat a broken drum but your saying your W&B says max weight of 3200 lbs but feel free to go to 3359 lbs?

My max takeoff weight is neither 3200 or 3359. its 3368.

[ArtVandelay]

How can you be over gross and be legal?

Carefully reread my post, remembering I own a 78J.


Tom

[RLCarter]

3 minutes ago, ArtVandelay said:

Carefully reread my post, remembering I own a 78J.

Ok, I see what you were saying now. Thanks

[RLCarter]

48 minutes ago, Niko182 said:

My max takeoff weight is neither 3200 or 3359. its 3368.

forget it dude...  Your to vague on your answers, TCDS pg 48 shows it to be 3200

[Niko182]

Just now, RLCarter said:

forget it dude...  Your to vague on your answers, TCDS pg 48 shows it to be 3200

My planes Max takeoff weight used to be 3200Lbs. last year I did the Screaming eagle STC which increases the Max takeoff weight to that of an ovation which in this case is 3368. it increases the RPM to 2700 isntead of 2400, and ups the power from 244hp to 310hp. The plane I have is an M20S by serial number, but with the STC it ends up just being a very light M20R, and has the higher limitations of the M20R.

I also wasn't the one that said anything about being 159lbs over gross. that was @ArtVandelay and that applies to certain year model J's. If my takeoff weight was 3200lbs thats what I'd limit my self to. my takeoff weight is now 3368 and thats what I limit myself to. I can understand how that came off a bit confusing because of the way I worded it. I highly doubt my plane has an empty weight of 2239 lbs. Thats what the weight and balance states but I'm not going to weigh the plane and lose 100 to 200lbs of useful load. I'm sure a lot of the owners here have never weighed their planes, and a lot of them won't because the majority of the time it just results in loss of useful load.

[EricJ]

1 hour ago, Niko182 said:

I also wasn't the one that said anything about being 159lbs over gross. that was @ArtVandelay and that applies to certain year model J's. If my takeoff weight was 3200lbs thats what I'd limit my self to. my takeoff weight is now 3368 and thats what I limit myself to. I can understand how that came off a bit confusing because of the way I worded it. I highly doubt my plane has an empty weight of 2239 lbs. Thats what the weight and balance states but I'm not going to weigh the plane and lose 100 to 200lbs of useful load. I'm sure a lot of the owners here have never weighed their planes, and a lot of them won't because the majority of the time it just results in loss of useful load.

You can weigh you airplane just as a reference and see what you get.   You're not required to write any of it down anywhere.   If it works to your benefit, then update your W&B.   It's not like you're taking a risk of any kind by weighing it.

 

[cliffy]

5 hours ago, Hank said:

Almost had it there, cliffy. Missed it by that much . . .

All materials (solid, liquid and gas) change density with temperature, not weight. Pour some water, oil, gas, etc., into a calibrated vessel where small volume changes can be measured, and you will notice that the volume is more at higher tempratures and less at lower temperatures. But the weight will never change.

Drop the temp to below freezing, fill the container then set it outside on a hot summer afternoin and there will be a greater change in volume. Measure some out below freezing and weigh it; warm the original container to summer ramp temperatures and pour the same volume into your container and it will weigh less. The weight if the oil and gas already in your plane will not change unless you add or remove / use some.

The change in volume of one quart of new motor oil by raising its temperature from 32°F/0°C to 100°F/38°C is 0.0265 quarts, or less than one ounce by volume. Thwre is zero (0) change in weight. At the same time, the volume of yiur engune is increased from winter to summer, then decreased again as you climb to cooler altitudes.

From my friends at The Engineering Toolbox:

The change in the units volume when temperature changes can be expressed as

dV = V₀ β (t₁ - t₀)                                                        (2)

where

dV = V₁ - V₀ = change in volume (m³, ft³)

β = volumetric temperature expansion coefficient (m³/m^{3 o}C, ft³/ft^{3 o}F)

t₁ = final temperature (^oC, ^oF)

t₀ = initial temperature (^oC, ^oF)

and for motor oil, from the embedded link above, β = 0.00039/°F.

Hank, I wasn't referring to the weight of oil cold or hot  I was referring to the weight of oil being in the sump or not (CAR3 vs Pt 23) and how anyone's empty weight was calculated. (by your quote)

Also, in the FAA W&B Manual it shows how to calculate fluids weight for temp. because sometimes oil and other fluids are drawn from a cold barrel or underground and measured into the airplane by volume (airplanes gauges only measure volume not density) . So if I load 50 gallons of cold oil in an airplane its weight will be heavier than if the oil was warm and needs to be accounted for.

Hence your postulation that the density increases is probably as true as my postulation because if one takes say oil by VOLUME from a cold barrel it will contain an increased weight of fluid due to your density increase. A little more oil in volume (at a higher density) equates to a heavier volume by measure. Back when, we had airplanes that had oil by the barrel for each engine. In the case of say a Boeing Stratocruiser you might have 40 gallons per engine and a standby 50 or 60 gallons for transfer to each engine in flight if needed. That much oil has a variance of quite a few pounds when temp is factored in (12.6 pounds) 

Also in filling large jets say with Jet-A, its a common practice to take a Specific Gravity measurement from the airplanes tanks and convert that to a weight factoring in the DENSITY to get an accurate weight for take off because the airplane gauges measure by VOLUME and not density.  The bigger the jet the more weight variance by temp. The weight variance has to be taken into account for performance calculations when near Max Gross T/O weights. I've done that many times. That's why the FAA shows how to do it because we measure by VOLUME and not density (unless we factor in Specific Gravity).

IIRC if one wants to carry as much fuel as possible then if the fuel is hot he will hit Max Gross at such and such a quantity by VOLUME but actually be under gross weight due to the density of the fuel at that gallons volume, We take a Specific Gravity measurement and then we know what weight we are actually at and can figure how much more fuel by volume we can load and still hit right on Max Gross T/O weight. 

[carusoam]

There seem to be a couple of OWTs related to aircraft weighing....

Some things seem to be less true than expected...

Some more true than expected...

1) some dirt does accumulate over time... I expected a whole lot more than was actually in my plane... especially the one that lived outdoors....

2) some wires do stay behind when radios get pulled out... radios have never been pulled out of my plane, yet...

3) Scale calibration is required... And easy enough to check before use...

4) All kinds of things can show up inside a plane... somebody had a pic of a Mooney bucking bar around here somewhere...

5) proper WnB takes a fair amount of effort... all the fluid levels and O2... all the equipment and moment arms...

6) Proper math, verified...

7) Have no fear about a casual weighing... the numbers need not be recorded anywhere...  what you do with the numbers may require some ethics... especially if they don’t match the existing logged data...

8) Very similar to a PPI... doesn’t need to be logged anywhere...

9) it was common hangar talk back in the 90s that reweighing a plane resulted in a loss of UL for all of these various reasons...

10) around MS there is typically a search for the truth behind various practices...

11) what I don’t remember back in the 90s were discussions of challenges that occur when the WnB is off...

12) We have seen the effects of overloaded or under powered Mooneys around here...

13) Some have lived to fly again...

14) So... if avoiding reweighing to avoid learning the truth about your plane.... put this in the death by 1000 cuts kind of thing...

15) where it is really going to matter.... short fields and hot days.... or both.

PP thoughts only, not a mechanic...

Best regards,

-a-

[GeeBee]

A couple of points. First of all liquid density. It works on large volumes. On a 100 gallons not so much. Yeah it makes a little difference, but not enough to discuss. When you load 20,000 gallons onto a transport category aircraft, yeah you correct for density. As a matter of fact, most airlines do a "density check" twice a day on their fuel. It is part of the accuracy check, because the fuel is uploaded by a gallons or liters meter on the truck, that number is multiplied by the density per gallon to arrive at pounds uploaded. That is then added to the pounds on the gauges at the start of fueling, then compared to the pounds shown after uploading because the gauges  correct for density. The only time I was ever out of tolerance was on a cold January day  at MDW, 3 degrees F, when the fuel density was shown as 6.7/gallon. I was out of tolerance by 225 pounds on a fuel load of 35,000 pounds. I said, "No way is the density 6.7 at this temp" and sure enough it was the wrong figure. A corrected density was obtained an it all checked. Think about this, 3 degrees and even the error from standard density was less than 1%.

Niko182, you should have mentioned your STC from the get go. An STC is a modification to the specifications in the TCDS and as such becomes the new legal number. A ferry permit is not such modification. It is a one time permit that is accounted for in engineering. Yes the airplane can take off. It can take off at double it's max certified weight given enough runway. It also changes everything else including stall speeds, load limits and the life limits of certain structures etc. The max certified weight of an aircraft is what the manufacturer is willing to certify to to meet certain demands including takeoff performance, maintenance, landing performance, etc. I can tell you for instance when you go to many Part 25 manufacturers they will sell you what ever MTOW you are willing to pay for. Japan Air Lines used to have "domestic 747s" that had very low MTOWs (because they carried low fuel loads) and were structurally no different than a "heavy" 747 . When JAL sold those airplanes, the new buyer simply went to Boeing and bought new data and the maintenance schedules were adjusted and they flew "heavy". Simply stated the TCDS MTOW and MLW are a compromise of performance, structure and maintenance, some are market driven, some are structure driven. However in every case as you up the MTOW you have a consequence, often not readily apparent.

[Skates97]

On 9/13/2019 at 10:19 PM, ArtVandelay said:

I put all my line items in a spreadsheet, found about 10% error rate: omissions, math errors, numbers transposed, etc. In the end, it amounted to a 2 lb difference.


Tom

I did the same thing, Excel is great for it. Found some things that had been removed but never updated in the W&B entries. Others that were added but never updated. A few math errors as well. Took a lot of time, even so after making all the changes it amounted to a pound and a difference of 0.04 in the arm. Interesting that all the errors almost cancelled each other out.

On 9/14/2019 at 8:41 AM, Jerry 5TJ said:

Ditto. 

Around 1990 I went through the W&B entries for my E all the way back to its 1964 Kerrville origin & found numerous errors from pre-spreadsheet days.  

The plane also had “numerous” equipment changes not in the W&B history.   

I know folks who advise never weigh your plane.  But I ask: Why trust 40+ years of vague entries and errors when you can get a clean start with a good weight & balance?  

If you don’t want to know about the real figures why bother to do a W&B calculation for a flight at all?  

Me, I’d rather know the true W&B and perhaps deliberately overload the plane rather than use suspect data.  

I have a few things I'm going to get done to the plane over the next bit and after they are done will get it weighed. If it means I lose some useful load I'm okay with that. I would rather work from a good number when doing my planning.

Those that obsess over it, I wonder if they get on the scale and weigh themselves and all their passengers every time along with any bags, purses, etc... Depending on what I ate and am wearing my weight could be 5+ pounds more or less (big dinner, winter jacket, tennis shoes or boots, etc...) Seems we obsess over a few pounds here and there and then just assume that we know how much we actually weigh ourselves when getting in a plane.

[jetdriven]

I am not even sure they weigh every aircraft that comes off of the line... often they  weigh every third or fifth airplane and then apply that, so the original weight and balance is an estimate itself

[GeeBee]

That is correct. That is why there are "equipment lists" in the AFM.

 

 

[larryb]

Has anybody weighed all the ‘stuff’ carried around in their planes? I did one day and it came to a shocking 92 lb.

[Shadrach]

5 minutes ago, larryb said:

Has anybody weighed all the ‘stuff’ carried around in their planes? I did one day and it came to a shocking 92 lb.

Good god man...I can’t imagine that. The heaviest thing I carry besides people is a 12lb emergency tool kit. Next heaviest is the toe bar.  4 Headsets weigh in at 3lbs. I might have 25lbs total including a spare main tube and a qt of oil.

[larryb]

Tool kit. A few spare parts. Box with oil, window cleaner, towels. Bruce’s canopy cover. Emergency landing survival kit. Avionics user manuals, I removed those. Ropes and lightweight chocks. I have paired it down a bit but it is still a lot. I fly a lot of long trips and don’t want to leave that stuff behind. On the plus side I removed rear seats and save 26 lb.

[Jerry 5TJ]

Scan the POH, the required supplements and avionics manuals and carry them in a tablet.