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

[Ross Taylor]

Hey @Yourpilotincommand here's that page from my '66 E

[Yourpilotincommand]

1 minute ago, Ross Taylor said:

Hey @Yourpilotincommand here's that page from my '66 E

Thanks Ross. I think your numbers look good, but are swapped The L n/m should be greater than the L m/r, right?

[Ross Taylor]

1 hour ago, Yourpilotincommand said:

Thanks Ross. I think your numbers look good, but are swapped The L n/m should be greater than the L m/r, right?

I don't believe so, because of the added note.  On the paper, it looks like the L n/m is in front of the L m/r...but the note seems intended to clarify that isn't the case.  But who knows - it wouldn't be the first error I've found in the W&B history! 

[Yourpilotincommand]

2 hours ago, Ross Taylor said:

I don't believe so, because of the added note.  On the paper, it looks like the L n/m is in front of the L m/r...but the note seems intended to clarify that isn't the case.  But who knows - it wouldn't be the first error I've found in the W&B history! 

Your numbers aren’t matching the graphic. We need an engineers eyes to confirm.
In my case I measured between the datum and the main wheel centerline. Mine was 66”. Yours is 66-1/8” only 1/8” off, not bad. I think this is another Mooney factory error.  I might be losing my mind, lol.  How can 66>67?

[Missile=Awesome]

Online Aps like WnB Pro are NICE tools to be able to easily input and see what modification of loads do to CG.  A good easy LEGAL way to do weight and balance for minimal cost of purchasing the ap.

[Andy95W]

FltplanGo is a free app and has a good weight and balance section.

You also get free geo-referenced charts and a lot of ADSB interfaces.

[Yourpilotincommand]

I use Foreflight, professional version.. it has a very comprehensive W/B tool.

[carusoam]

One thing to keep in mind regarding measuring....

The nose wheel distance has the ability to change with Donut Compression...
 

So... the plumb bob from the reference bolt... to the center of the wheel... needs a good measurement...

If it gets out of a certain range... the wild rides begin... something about wheel caster...
 

Mooney Mysteries are the best!  

Best regards,

-a-

[Hank]

5 hours ago, carusoam said:

One thing to keep in mind regarding measuring....

The nose wheel distance has the ability to change with Donut Compression...
 

So... the plumb bob from the reference bolt... to the center of the wheel... needs a good measurement...

If it gets out of a certain range... the wild rides begin... something about wheel caster...
 

Mooney Mysteries are the best!  

Best regards,

-a-

Shouldn't the plane be leveled before measuring the stations? The ground attitude is rarely experienced in flight. I'm sure the olane must be leveled before weighing. 

[Yourpilotincommand]

4 hours ago, Hank said:

Shouldn't the plane be leveled before measuring the stations? The ground attitude is rarely experienced in flight. I'm sure the olane must be leveled before weighing. 

Once the IA got her on the scales he let the air out of the nose tire to make her level. He didn’t actually measure the arms, just copied the arm lengths from a catalog of some sort. I have no idea how to determine whether I should replace the hockey pucks. She recently passed inspection. Would the prop to ground clearance indicate that? Btw.. I measured the arms from datum to axles and came up with slightly different numbers than what is documented.  However, my measurements put the empty CG closer to the middle of the envelope, rather than unusually aft.  I’m suspecting a factory documentation error from 1966. 

[gsxrpilot]

53 minutes ago, Yourpilotincommand said:

I have no idea how to determine whether I should replace the hockey pucks.

Put her up on jacks. With the weight off the gear, are the pucks loose? Is there any gap above them? Can you move them at all by hand? If yes, change them.

[David Lloyd]

Are your discs in tolerance?  Out of the Service and Maintenance Catalog: With the full weight of aircraft on the gear, for the nose the gap between the top retaining plate of the disc and the retaining collar for the C and G should be between 0 and .43", E F and J between 0 and .6".  For the main gear, 0", full contact.  Exceed that=replace discs.

Also out out of the Service Catalog is a description with procedures, pictures, diagrams, charts and other confusing stuff on how to properly weigh a Mooney.  Measuring all that stuff and doing all that math might correct a tiny amount of manufacturing tolerance but is really intended to correct for the shock disc's compression. The wheels and therefore the weight will be at a slightly different location aft in relation to the datum as weight on them increases.

Seats forward, pump out fuel, sump drain the remaining fuel, add back unusable fuel, 8 quarts oil, remove all your stuff, on scales, level, measure everything the catalog says, and start the calculations.  Just had mine done in February.  Even though the shop did everything described, I bet they still missed something. Did they move the seats forward? Remove the canvas cover from the baggage area?  My antique E6B from the seat pocket?  I think it is close, but not correct.

[cliffy]

6 hours ago, David Lloyd said:

Are your discs in tolerance?  Out of the Service and Maintenance Catalog: With the full weight of aircraft on the gear, for the nose the gap between the top retaining plate of the disc and the retaining collar for the C and G should be between 0 and .43", E F and J between 0 and .6".  For the main gear, 0", full contact.  Exceed that=replace discs.

Also out out of the Service Catalog is a description with procedures, pictures, diagrams, charts and other confusing stuff on how to properly weigh a Mooney.  Measuring all that stuff and doing all that math might correct a tiny amount of manufacturing tolerance but is really intended to correct for the shock disc's compression. The wheels and therefore the weight will be at a slightly different location aft in relation to the datum as weight on them increases.

Seats forward, pump out fuel, sump drain the remaining fuel, add back unusable fuel, 8 quarts oil, remove all your stuff, on scales, level, measure everything the catalog says, and start the calculations.  Just had mine done in February.  Even though the shop did everything described, I bet they still missed something. Did they move the seats forward? Remove the canvas cover from the baggage area?  My antique E6B from the seat pocket?  I think it is close, but not correct.

No oil in CAR-3 airplanes if you want it absolutely accurate according to the regs

[David Lloyd]

18 minutes ago, cliffy said:

No oil in CAR-3 airplanes if you want it absolutely accurate according to the regs

But in the Mooney Service and Maintenance Catalog, Manual P/N 106, it specifically says: Fill oil to capacity (8 quarts).

In the end, it doesn't matter, before, after, with or without, better put some oil in before flying.

[cliffy]

I'm only saying that the airplane is certified under CAR-3 regulations. CAR-3 regulations say to list the airplane's empty weight and CG with no oil and only unusable fuel.   Oil is part on the useful load of the airplane according to the CAR-3 regulations. Its even in 43.13

In the end it makes no difference as you have to add the weight and CG of the oil into every CAR-3 useful load calculation anyway BUT to be perfectly correct according to the CAR-3 regulations oil weight is NOT part of the Empty Weight and CG final calculation by definition. Here's a cut from 43.13-1B  Sec. 10-15 g-  (the section in bold is in bold in 43.13 also)

g. The oil system should be filled to the quantity noted in the TCDS or Aircraft Specifications.

NOTE: On Civil Aeronautics Regulations (CAR-3) Certified Aircraft, the weight of the oil was subtracted mathematically to get the empty weight. In 14 CFR, part 23 aircraft, the weight of the oil is included in the empty weight.

When weighed with full oil, actual empty weight equals the actual recorded weight less the weight of the oil in the oil tank( oil weight = oil capacity in gallons x 7.5 pounds). Indicate on all weight and balance reports whether weights include full oil or oil drained. (See figure 10-9.)

Also note that they make no mention of any CG shift recalculation when the weight of the oil is subtracted to get the official Empty Weight for CAR-3 airplanes. The CAR-3 procedure is to weight the airplane with oil and then subtract the oil weight to get the correct  Empty Weight figure

 

[David Lloyd]

Oh, I agree CAR-3 is empty weight excluding oil.  On the surface, it doesn't make sense to me.  Why have a useful load figure that you have to subtract from after engine oil is added. And I don't remember anything in my POH for adding or subtracting oil. So it seems in some places Mooney straddled the fence between CAR-3 and Part 23.  The reason I said what I did was because there is official, printed info on most subjects pertaining to Mooneys from Mooney that is at least semi accurate.  Do my shock disc need replacement?  Let's see what the book says.  How is weight and balance done? Let's see what the book says.  Book first, opinions second.

[mark21m20c]

[Yourpilotincommand]

Mark, mine loaded is aft like yours, but slightly outside the envelope. What is the moment arm length from datum to main axles on yours? And the same from datum to nose axle? 

[cliffy]

A lot may have to do with a large majority of CAR-3 airplanes back then had engine oil tanks separate from the engine. Think DC-3s (or any large radial powered airplane) and even early E series powered Bonanzas. 

[Yourpilotincommand]

Interesting find. The Mooney procedure in my service manual indicates you need to measure the axels from the plumb bob to get the axel distances from the datum. This makes sense. The IA who did my W/B did NOT measure per the procedure and read the moment arms from a catalog. The sagging of the hockey pucks through the years will definitely change the axle moment arms. 

[Yourpilotincommand]

Also, the guy who did my W/B didn’t subtract oil, move the front seats to the forward most position, or measure the axle moment arms. Although oil doesn’t produce much of a moment wrt to the datum, but the seats do. That’s 34 lbs worth of front seats that were positioned 6 inches back from where they should have been for weighing.

[David Lloyd]

So. You paid him yet he accomplished nothing.  I feel your pain.

[Yourpilotincommand]

3 hours ago, David Lloyd said:

So. You paid him yet he accomplished nothing.  I feel your pain.

I’m going to call the IA and explain that the moment arms need to be measured rather than pulled from a catalog. Also, get a reweigh with the seats pushed forward as specified by Mooney. After I plumb bobbed and measured the axles from datum I found my empty CG to be 46.1”.  Officially/currently it is 47.1” which is wrong and thus my loading conundrum.  In conclusion W/B requires you to follow the procedure, and not assume numbers from a catalog.  Now my M20E meets my mission! Another conclusion.. You don’t need to replace the hockey pucks to get an accurate W/B. The axle-to-datum lengths change as the pucks sag and requires measurement. I hope this helps a Mooney Spacer down the road. Cheers! 

[Yourpilotincommand]

I’ll even go out on a limb and jump to another conclusion.. The datum-to-axle lengths will VARY from Mooney to Mooney due to the various conditions of the hockey pucks. Further thoughts... I would assume a typical Cessana 172 won't vary as much on the axle-to-datum measurements and thus not a need to measure. In the Cessna case you could rely on catalog data.

[Hank]

16 minutes ago, Yourpilotincommand said:

I’ll even go out on a limb and jump to another conclusion.. The datum-to-axle lengths will VARY from Mooney to Mooney due to the various conditions of the hockey pucks. Further thoughts... I would assume a typical Cessana 172 won't vary as much on the axle-to-datum measurements and thus not a need to measure. In the Cessna case you could rely on catalog data.

Yeah, those spring steel legs don't change much over time, unlike our rubber pucks.