Aft CG or Fwd CG... where are you operating?

[cliffy]

5 hours ago, ArtVandelay said:

Then explain this from J manual:

WHAT DOES IT SAY LATER ON FOR THE CALCULATIONS?  Do they subtract the engine oil later?  If not they didn't follow CAR-3 procedures. Below is taken from the 2016 FAA Weight and Balance Handbook-

Oil The empty weight for aircraft certificated under the Civilian Air Regulations (CAR) part 3 does not include the engine lubricating oil. The oil must either be drained before the aircraft is weighed, or its weight must be subtracted from the scale readings to determine the empty weight. To weigh an aircraft that does not include the engine lubricating oil as part of the empty weight, place it in level flight attitude, then open the drain valves and allow the oil to drain out. Any remaining is undrainable oil and is part of the empty weight. 

Edited August 20, 2020 by cliffy

[ArtVandelay]

WHAT DOES IT SAY LATER ON FOR THE CALCULATIONS?  Do they subtract the engine oil later?  If not they didn't follow CAR-3 procedures. Below is taken from the 2016 FAA Weight and Balance Handbook- Oil The empty weight for aircraft certificated under the Civilian Air Regulations (CAR) part 3 does not include the engine lubricating oil.

 

They do not. Also note the discrepancy in the station of the hat rack&baggage between the graph and the table.

[Yourpilotincommand]

Old versus new...

[Ragsf15e]

10 minutes ago, Yourpilotincommand said:

Old versus new...

Crazy.  I for one have a hard time believing it weighs almost exactly the same as new (subtracting fuel weight, they are within 1lb!) but the cg moved 2 inches aft?  The equipment added in the tail isn’t that heavy typically.  Did your battery start out up front and get moved?

[cliffy]

Also another point-

One might want to actually measure the distance from datum for both the mains and nose. 

Seems there might be some discrepancy between what the books say and what is actually measured.

Just sayin' - have seen it happen. 

Mine had a 90 lb weight mistake from the  factory's first W&B sheet. Found it the first time I actually weighed it and dug into why the differences between the two. 

An actual reweight doesn't always mean a loss of Useful Load. I gained 90 lbs. 

Also if you weight it with full fuel you might want to figure the Specific Gravity of the fuel to get a real actual weight at the temp you are working at. 52 gallons (or whatever) really doesn't always weight the same by volume. 

That's why I weight with empty tanks (only unusable fuel remaining inside). 

[carusoam]

Could be me.... but...

Keep in mind what Mooney is using for the reference plane... datum point... Nose gear bolt.

YPIC has nicely posted a great graphic...

Take a look of where the nose wheel is compared to the reference plane...

It is on the other side of the reference plane... Physically.

If on the other side of the reference plane... by 0.2”... wouldn’t you want to account for that using a minus sign somewhere?

It looks like a third of the weight is mis-represented by a positive arm... when it should be negative...

That seems to be one reason for A shift of the Cg calculation to the rear...

1/3 of the weight is in a calculation that is off by 0.4 inches... 

Since the window is only 12.5” wide... you don’t want to be off by 0.4” with a significant part of your calculation...

See what I mean?

Inviting @Hank to check my statics math...

Essentially, every step of the calculation wants to be reviewed... to make sure it is right...

This way the trim mark on the display that says T/O...really has meaning...

There is a high probability that my description above is incorrect... because it is that complex of a subject... and...
 

PP thoughts only, not a mechanic... 

Best regards,

-a-

[carusoam]

Follow up question...

Why did Mooney opt for that particular bolt to be the reference..?

The math would have been a lot easier to get right if it used the tip of the spinner... or the tip of the tail...

See if anyone else has a missing minus sign...

Best regards,

-a-

[cliffy]

Tip of the spinner?  How about a change of spinners for a different Prop?  Engine sag with bad mounts changes end point position.

Tip of the tail? Many tail cone changes throughout the years   They can move a little holes get wallowed out. Stack up of tolerances between back of tail cone of fuselage and tip of tail cone through trim mechanism 

Bolt for reference?   Probably chosen because that point doesn't change ever even with a hard landing.

[carusoam]

See if YPIC has a pic or reference of the plumb bob hanging from the bolt...

Some nose wheels get out of rig with wear...

The eight second ride... is often figured out by referencing the actual plumb bob distance to wheel center...
 

Best regards,

-a-

[Ragsf15e]

1 hour ago, carusoam said:

Could be me.... but...

Keep in mind what Mooney is using for the reference plane... datum point... Nose gear bolt.

YPIC has nicely posted a great graphic...

Take a look of where the nose wheel is compared to the reference plane...

It is on the other side of the reference plane... Physically.

If on the other side of the reference plane... by 0.2”... wouldn’t you want to account for that using a minus sign somewhere?

It looks like a third of the weight is mis-represented by a positive arm... when it should be negative...

That seems to be one reason for A shift of the Cg calculation to the rear...

1/3 of the weight is in a calculation that is off by 0.4 inches... 

Since the window is only 12.5” wide... you don’t want to be off by 0.4” with a significant part of your calculation...

See what I mean?

Inviting @Hank to check my statics math...

Essentially, every step of the calculation wants to be reviewed... to make sure it is right...

This way the trim mark on the display that says T/O...really has meaning...

There is a high probability that my description above is incorrect... because it is that complex of a subject... and...
 

PP thoughts only, not a mechanic... 

Best regards,

-a-

I was thinking the exact same thing but look at the nose weight on the two different w&b... 627 vs 579?!  48 lbs difference (reduction) on the nose wheel is a pretty significant change.  Yes, someone should verify the +/- math as you suggested, but there’s been a healthy drop in weight from the front of that thing if the scales are accurate.  Battery moved?  Light starter?  Alternator?  Those can’t add up to that can they?  Maybe the oil, that’s gotta be another 12-14lbs...

[cliffy]

One thing to remember about the nose gear bolt is that when used for W&B purposes you need to find the center of the bolt and not just hang a plumb bob off of the side of it. 

Measure the diameter of the bolt housing that the plumb bob hangs from and move the PB mark half the diameter and use that as the starting point for your wheel measurements. 

You use the "hanging point" for the "8 second ride"  calculation for nose wheel caster point.  

[msh9]

I have an M20E with a battery, whelen strobe, and autopilot servos/electronics in the back. I just had it weighed a few months ago,

• Empty weight: 1670.4 (despite @cliffy's comments about what you're supposed to do for CAR3, the shop weighed it with full oil and included that in the empty weight...)
• CG: 46.57

With full fuel, 3 people, and 50# of luggage I am at the edge of the envelope depending on the weight of the backseat passenger. With only two people in the plane, I would have to be carrying some seriously heavy luggage to put me outside of the plane's envelope.

[Tim Jodice]

Mine is 1949 and 46.08

[cliffy]

1 hour ago, msh9 said:

• Empty weight: 1670.4 (despite @cliffy's comments about what you're supposed to do for CAR3, the shop weighed it with full oil and included that in the empty weight...)
• CG: 46.57

Many A&Ps do not know of the small nuances of weighing a CAR-3 airplane compared to a Pt 23 airplane.

Other than the FAA W&B Handbook and Part 43.13 I don't know of any other mention of the differences. It certainly isn't taught in any A&P school now that I know of nor have I ever heard it mentioned in any IA renewal course. I went to A&P school a LONG time ago when things were way different than they are now. One was still able to navigate by a Low Freq Range Radio station in Burbank CA back then!!! :-) :-)

In actuality other than a technical sense, it makes no difference in your flying as you are supposed to add in your oil level weight and arm  before any other W&B calculations for the flight. By counting the full oil (8 qts) as they did you do lose any small advantage of a qt or 2 of weight  if you are at 6 or 7 qts instead of 8 when flying. 

I seriously doubt ANY FAA Inspector even has a clue. 

[mark21m20c]

On the mooney M20c 1967 weight and balance under Oil 8 QT @  1.875 LBS/QT it says ( Sump assumed full for all flights ) . On loading graph oil is not listed . The oil weight (15lbs)is always the same for weight and balance purposes ?  The issue with our m20c (CG46.7) back seat and baggage weight is limited due to cg . Weight stayed close to same over the years but the front got lighter (alternator starter no vacuum system) and equipment was added aft.

[M20F]

Many brag about their useful load, CG, etc.  You ask anyone to actually put it to the scales, 90% run for the hills.  
 
If you have a 20+ year old plane and really care to know, only one way to find out.  

[Skates97]

2 hours ago, M20F said:

Many brag about their useful load, CG, etc.  You ask anyone to actually put it to the scales, 90% run for the hills.  
 
If you have a 20+ year old plane and really care to know, only one way to find out.  

1965 M20D, 1582 empty (993 UL) and 44.87.

I took the original W&B and added/subtracted everything in the logs and came pretty close to what the last W&B was. There were some math errors along the way, but putting everything into Excel and letting it do the math was easier and more accurate than doing it all by hand. 

To your point on weighing, I agree. I have read plenty of things for and against weighing over the years here on MS, but I have a bunch of stuff coming out of and going into the plane so once that is done I will have it weighed. It's hard to account for wires and everything else. There is a pile of stuff I took out going from the EDM 830 to the 900, and much more coming. When you consider over the years things added and removed without a new W&B because the change was "negligible" those eventually add up, and weighing is the only way to figure that out. 

[cliffy]

"Negligible"   is defined as 1 pound or less of a weight change any time a new W&B needs to be figured. 

3 hours ago, mark21m20c said:

The oil weight (15lbs)is always the same for weight and balance purposes ? 

I'm just giving you what the CAR-3 calls out for a correct W&B for a CAR-3 airplane. If someone wants to do it another way then it "technically" is not a correct Empty Weight and CG per CAR-3. 

Part 23 certified airplanes are always figured with a full oil tank in the Empty Weight figure (whether its full or not)

Like I said, not many A&Ps even know of these nuances between CAR-3 and Part 23 certification. 

[David Lloyd]

Redoing the interior, I removed probably 20 pounds of foam insulation that was added at some point.  Not in the logs.  I did replace some of the old fiberglass insulation with the foil backed foam.  Wiring for the Stec pitch and roll controllers plus the King remote gyro for the HSI must weigh 15 pounds.  Only the wiring for the Stec was recorded.

 

[cliffy]

David    Don't forget to seal the hole in the aft bulkhead where the wires come thru. Big draft area if you don't  Soft foam rubber works great

[carusoam]

+1 sealing the wire entrance at the back...

Big CO entrance point if not sealed...

Fuzzy PP memories of stuff read around here...

Best regards,

-a-

[M20F]

16 hours ago, Skates97 said:

I took the original W&B and added/subtracted everything in the logs and came pretty close to what the last W&B was. 

That is just a paperwork exercise.  It assumes the weights of the items are right and everything  added or deleted found its way into the W&B (or even the log books).  If planes got lighter people would be weighing them left and right.  

[cliffy]

Well mine got lighter  :-)

Its also assuming everything was actually weighed and not just estimated.

Its also assuming that all the arms were accurately measured (to the units CG) and not just guessed at.

Its also assuming that all the old stuff (wires) was removed and then new ones added. (wiring has weight)

Close is only good in horseshoes and hand grenades

If you really want to be accurate put it on scales and do it the correct way. (CAR-3 with gas tanks and oil empty)

Now- will it fly overweight or out of CG? Sure. But do you really want to do it? You're choice. Go for it. 

[Skates97]

8 hours ago, M20F said:

That is just a paperwork exercise.  It assumes the weights of the items are right and everything  added or deleted found its way into the W&B (or even the log books).  If planes got lighter people would be weighing them left and right.  

Yes, but you would be surprised (or maybe not) by how many things were not included when they were added or deleted, and by the errors that were in the original paperwork that was done by hand. It's also helpful to look up specs on everything and see what the actual weights are.

7 hours ago, cliffy said:

Well mine got lighter  :-)

Its also assuming everything was actually weighed and not just estimated.

Its also assuming that all the arms were accurately measured (to the units CG) and not just guessed at.

Its also assuming that all the old stuff (wires) was removed and then new ones added. (wiring has weight)

Close is only good in horseshoes and hand grenades - and nuclear warfare...

If you really want to be accurate put it on scales and do it the correct way. (CAR-3 with gas tanks and oil empty)

Now- will it fly overweight or out of CG? Sure. But do you really want to do it? You're choice. Go for it. 

Yes, which is why once I make all the changes to the panel the plane will go on the scales. If it means I gain or lose UL, that doesn't really matter to me, I just want the real number.

[Yourpilotincommand]

I  have come to the conclusion I might have a factory error on the moment arms. Say it isn’t so. I actually measured the arms from a plumb bob at the nose gear bolt. I measured 1.6” to the nose wheel centerline and 66.0” to the main wheel center line. I used a piece of string and rolled the main tires over to line up the center line.  Using these measured moment arms my calculated empty CG became 45.75” from the datum, bingo! I also noted my mechanic that did the W/B did not subtract the nose moment. Thank you Carosam for pointing out the missing minus sign. I attached the original W/B from 1966 and you can see the first factory mistake where it shows the distance between center lines is 66.7” which is NOT greater than 66.9” (datum to main center line) LOL. That’s a definite factory error. Now, wondering what to do going forward. In conclusion I believe the main wheel moment arm should be 66.0” as I measured, not 66.9” as documented. Can someone with an E model tell me your main wheel moment arm? Thanks! Also, ignore the pink hilights I made to the photo. Look to the left to see the error.