Safety/legality of placing extra Charlie Weights In The tail.

[PilotX]

Massive avionics install and old/abandoned avionics removal. This changed my empty weight from 2393lbs @ 44.10 to 2315lbs @ 41.86 - 78lbs regained but 2.24" forward movement of the CG. To fly with two people and 82 gallons, I put 100lbs of sand in the luggage compartment (now a net useful load loss - does that make me a Rocket-Bravo?). When I opened up the tail I found 1 x 6lb Charlie weight. My POH says I originally had all three weightss installed so who knows what happened in the last 29.75 years before I owned the plane.

I ordered the 6 & 7 & 8 lb weight from Top Gun. If I go with the original configuration (three weights) I add 15lbs to the back bringing my empty CG to 42.9 - if I add the second 6lb weight I get 43.4, so another .5" of CG gained.

Has anybody talked to Mooney or have any experience adding additional weight to the tail (in this case it would be adding 6lbs brining the total to 27?

I haven't talked to my IA yet as I thought I would as the group first. I understand we are given some lee-way in how we load our planes but this isn't a blank on the W&B chart to add/sub CWs, probably cause it is an AP/IA issue. 

Certain there will be some colorful comments.

[PeteMc]

My thought would be to NOT add all the weights in the tail and just keep some weight (Charlie or whatever) in the baggage area.  Then on long trips you can pull those weights out and add in baggage.

Edited June 16, 2021 by PeteMc

[Davidv]

If your POH has three and you can't find any other logbook entries that says why they were taken I would think about adding them back.  41 inches is a pretty forwarded weighted CG.  After my major avionics install I'm now at 44.9 with 3 original charlie weights still in there.  I'll add my Anthony disclosure that I'm not qualified to tell you whether you should put the weights back in, just an opinion.

[N201MKTurbo]

A friend got a field approval to add 120 Lbs of weight to the tail of a Rocket. He made a complete drawing package of the modification, had a DER review the drawings. 
 

Their biggest concern is structural. You need to prove the structure can Handel the load. The next concern was that it doesn’t interfere with any control mechanisms. 
 

The more engineering analysis you do, the less you will have to pay the DER.

[PilotX]

Minor update:  I had the 6 lb weight. I thought the three weight package was 6, 7, 8 (lbs) - a bad scan of the parts manual but I talked to a Mooney rep today and he 1. corrected my inability to differentiate a 6 from an 8, 2. forwarding my question about adding another 6lbs to the Mooney structural engineer.

I installed the other 13 lbs and that lets me comfortably pull out one 50lb bucket.

My second thought is there was a lot of weight removed from the avionics bay of the aircraft, approximately 40lbs, I could put an avionics tray back in there and drop 15lbs but I guess I would need to ask an adult about that too.

[carusoam]

The cool thing about Long Body Mooneys…

There are five things that vie for space and load in the tail…

Don’t be surprised about adding or removing weight in that area…

The six things that normally come and go in that area are…

1) Air conditioning

2) Anti-ice pumps and tanks

3) O2 bottle and equipment 

4) Avionics

5) Lead bricks…. Or steel or some type of dense material…

6) Batteries…  the XC version weighs a couple of pounds more…

Common changes around here have included new engines, different prop, instrument panel exchanges…

 

You won’t need a genius to do a proper WnB… but, the average WnB around here have been less than straight forward… trying to get them un-mangled after decades of minor changes…

Strong Algebra skills are required…. Not any calculus….

It is a tremendous safety issue… and requires the legal signature…  even though the owner is perfectly capable of figuring it out properly…   This way you have two people verifying that no mistakes were committed…

Tail heavy planes only fly once… - Hank   

PP thoughts only, not a mathematician…

Best regards,

-a-

[PilotX]

I think that they won't readily approve another lead brick but maybe my IA will consider letting me put a few pounds on the now-empty avionics tray.

[LANCECASPER]

Weight in the baggage compartment makes for smoother landings with just the right nose up trim. I wouldn't want any more weight further back than that. If you inadvertently take-off with nose up trim you will see what I mean. That can happen on a go-around. 

[PilotX]

4 hours ago, LANCECASPER said:

Weight in the baggage compartment makes for smoother landings with just the right nose up trim. I wouldn't want any more weight further back than that. If you inadvertently take-off with nose up trim you will see what I mean. That can happen on a go-around. 

That is very true, never landed better than with 100lbs of sand in the luggage compartment. Though I would rather fill it with luggage or bodies than sand.

[Awful_Charlie]

With the record discrepancies and various equipment removals and additions, I think it is really time for a re-weigh. If you've arrived at a starting point where you can't be sure of the numbers, there's little point in wildly adding and subtracting from it in the hope you will end up with a more accurate figure.

Alternatively just go and fly it with a couple of heavies in the back seats  and stall it - if you end up in a smoking hole then the CofG was probably too far aft. Go again with a couple of heavies in the front seats, then if you smash the nose gear off on landing then it was too far forward

[PilotX]

Just now, Awful_Charlie said:

With the record discrepancies and various equipment removals and additions, I think it is really time for a re-weigh. If you've arrived at a starting point where you can't be sure of the numbers, there's little point in wildly adding and subtracting from it in the hope you will end up with a more accurate figure.

I did a brand new weight and balance, that is how I know my CG shifted 2.5" forward and that I needed to put 100lbs in the back to fly with two people and 80 gallons.

[LANCECASPER]

8 hours ago, PilotX said:

I did a brand new weight and balance, that is how I know my CG shifted 2.5" forward and that I needed to put 100lbs in the back to fly with two people and 80 gallons.

You calculated the weight and balance based on additions and subtractions of equipment or you re-weighed the airplane?

[PilotX]

1 hour ago, LANCECASPER said:

You calculated the weight and balance based on additions and subtractions of equipment or you re-weighed the airplane?

Reweighed the airplane. 

[carusoam]

Call me confused…

Are we improving the flying quality by adding the sand bags in the back…

Or is the plane so far out of WnB that the sand bags are required to get into proper WnB…

1) Do we have an empty WnB envelope to maintain?  A maintenance procedure, I’m sure…

2) Or… Just an as flown WnB to maintain..?  A pre-flight procedure, I’m sure…

3) I have not seen a discussion of what is better to get the WnB correct…

4) Our WnB is a simple beam calculation…. Rocks in the tail or bags in the baggage compartment can get you to the same WnB…

5) But… if you have to always have 100Lbs of sand in the back… to stay within WnB…. And not fall out of WnB…

 

A better discussion to have offline with your mechanic….  

Bottom line… as PIC don’t let the plane get out of WnB…

PP thoughts only not a mechanic…

What did I miss?

Best regards,

-a-

[PilotX]

@carusoamThe new W&B (reweigh) moved the CG forward. In order to fly the test flight after a re-weigh(fully fueled for CIES calibration), I removed 30 gallons. This got me below gross weight but didn’t help with the CG. Cheap solution was 100lbs of sand. I ordered weights from Top Gun but they arrived later. I did not know I was going to have a CG issue before the reweigh. 
 

Wednesday I put the max (published) allowable Charlie weight in the tail. The addition of 13 lbs in the tail allows me to remove one 50lb bucket of sand. I have one more 6lb and some longer bolts, I asked the community (and later Mooney) if I could put another weight in the back. Another option (though more permanent) would be to put some weight in the avionics bay as that previously had ~40 lbs of avionics. 
 

The sand, while not ideal, allows me to fly the plane every day and not to scramble to find 50 pounds of random stuff to throw in there.

[LANCECASPER]

I'm surprised that your CG has changed so much.

There were also a lot of things that came out of your panel: EHSI, stormscope, VSI, turn coordinator, KI-256, airspeed, altimeter, a lot of wire no doubt, etc, etc, etc,

Did you also remove both vacuum pumps from the engine, along with the clutch on the backup vacuum pump?

 

[PilotX]

We removed one vacuum pump. One had to stay because of the speed brakes. They weighed 17lbs of wire by the end. Probably 10lbs of antennas (stormscope, ADF, radar altimeter). It was a big job. 

[carusoam]

On 6/18/2021 at 9:58 PM, PilotX said:

We removed one vacuum pump. One had to stay because of the speed brakes. They weighed 17lbs of wire by the end. Probably 10lbs of antennas (stormscope, ADF, radar altimeter). It was a big job. 

An amazing transformation… requiring an amazing amount of WnB follow-up…

There are two sources of useful weight adjustments that may be considered…

 

1) Taking weight off the nose…. MT composite props are on a few M20Ms around here…

2) Putting weight in the tail…. Some batteries come in the XC extra capacity variety… and weigh a few pounds more than the same foot print standard capacity battery…

 

Bags of sand are pretty low cost by comparison…

Make sure they are locked down well… 

Mooneys are capable of seeing bumps…. Having the WnB change when the baggage becomes upended… could be bad…

 

Thank you very much for sharing the WnB charts and all the details…  great conversation!

 

PP thoughts only…

Best regards,

-a-

[philiplane]

If you weight the plane with full fuel, and calculate it back out, you will have an inaccurate empty weight. There is no way to know exactly how many gallons of fuel is on board, or what the specific gravity is that day. You can have errors of plus or minus 60 pounds in a 120 gallon system. 40 pounds of that is from density changes alone. Leveling the plane is also critical to get the CG to be accurate. 

The only accurate way to get a correct empty weight, and CG, is to drain the fuel completely.

In my experience doing well over 300 weighings, many for Part 135 compliance, not one that was previously weighed with fuel, then calculated out, was accurate. Not one. And of course, the bigger the tanks, the bigger the error.

Edited July 15, 2021 by philiplane

[PilotX]

4 hours ago, philiplane said:

If you weight the plane with full fuel, and calculate it back out, you will have an inaccurate empty weight. There is no way to know exactly how many gallons of fuel is on board, or what the specific gravity is that day. You can have errors of plus or minus 60 pounds in a 120 gallon system. 40 pounds of that is from density changes alone. Leveling the plane is also critical to get the CG to be accurate. 

The only accurate way to get a correct empty weight, and CG, is to drain the fuel completely.

In my experience doing well over 300 weighings, many for Part 135 compliance, not one that was previously weighed with fuel, then calculated out, was accurate. Not one. And of course, the bigger the tanks, the bigger the error.

You are not wrong. However in this instance I did weigh completely empty, with uncertified scales to get a baseline. Then they filled it up with the correct full/unusable fuel. They got the exact amount mainly because it was the third time that they filled it’ll it after rebending the fuel senders. So in this instance we know exactly how much fuel.
 

There was around an 18lb difference in the calculations between empty + adding unusable fuel (uncertified) and full and subtracting 118 gallons (certified).

I wanted to do it completely empty was just unusable fuel and oil but it would’ve delayed getting my plane back by another week.

[philiplane]

Depending on the temperature variation, that 118 gallons could weight as little as 670 pounds, or as much as 726 pounds. If they checked the specific gravity of the batch you should have an accurate number. We have the problem of light weight fuel in Florida, because it's almost always warmer than the standard day. 

[jlunseth]

Divers use small lead weights in a buoyancy control vest to achieve neutral buoyancy in the water. These days, they are lead pellets contained in a fine mesh bag. They come in one pound increments up to 6 lbs. I usually put them in a plastic box like the old milk bottle boxes, but any container will do. The advantage is no mess, they don’t leak like sandbags or similar and they are a lot smaller. That’s what I would do rather than permanently add weight to the aircraft.

[alextstone]

On 6/17/2021 at 1:12 PM, PilotX said:

That is very true, never landed better than with 100lbs of sand in the luggage compartment. Though I would rather fill it with luggage or bodies than sand.

I keep about 80 lbs of tools and parts in the baggage compartment because I don't like getting stuck in remote places .  I even changed a cylinder once (with proper A&P supervision) at a remote field during the first wave of the pandemic.