The One Time Auxiliary Fuel Tank in my Mooney

[Mooney Dog]

So as some of yall have seen. I have an aux 14 gallon fuel tank in the back of my Mooney.

 

Today I finally was able to chase down most of the documents relating to this tank. Turns out in 1978, the owner at that time get a approval to install this one tank modification. Guess I now own (one of?) the only Mooney's with a tank in the baggage compartment. 

Sadly this plane is having some WB issues which makes this tank a little unusable for now. Empty I am sitting with a CG right on the after limits. Removing and replacing half the instrument panel with light new parts seems to have that effect. 

[carusoam]

what is the weight of the equipment added by the STC?
Is that the 84LBs empty?

quick calculation… 14 X 6 is also 84…
 

Nice to see that there is full documentation for that install… 

Somebody put some nice engineering effort into making it work, and be useable… for one AC only.

Filling from the outside is a nice safety benefit…

 

Figuring out the WnB issues is a normal hassle around here with some newly acquired aircraft….

Often there is a math error, or measurement error in the calculations…

 

If you want… start a thread with what you know about your existing WnB… see if somebody recognizes where it went awry…

 

Weight removal…

Many Mooneys have a pair of batteries in the back… selection of a different battery may lighten the load back there…

There are also Charlie weights in Mooneys… find what you have and where it got mounted…

 

Weight addition…

An easy way to add pounds to the tip of a Mooney… get  a three blade Hartzell prop!  Hartzell makes some pretty robust prop hubs… adding three aluminum blades makes it hefty… 

 

It will be real important to know if the WnB is right, and just misrepresented… or it is wrong, and represented correctly… before making actual changes…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[McMooney]

I want this mod, would make my E perfect....    esp with the other tank mod being unobtanium at the moment.

 

is there anyway you could forward all the docs ?

 

[Prior owner]

Empty weight CG is irrelevant in a Mooney (and also most small aircraft), unless it’s causing your tail to drop when you step on the wing???

CG is only relevant when a seat is occupied in the aircraft. Many aircraft are out of CG with nobody in a seat…. The aircraft isn’t going to fly without a person onboard, so the CG with the cabin empty doesn’t have any relevance.

 

or am I misunderstanding something?

[Mooney Dog]

1 hour ago, carusoam said:

what is the weight of the equipment added by the STC?
Is that the 84LBs empty?

quick calculation… 14 X 6 is also 84…
 

Nice to see that there is full documentation for that install… 

Somebody put some nice engineering effort into making it work, and be useable… for one AC only.

Filling from the outside is a nice safety benefit…

 

Figuring out the WnB issues is a normal hassle around here with some newly acquired aircraft….

Often there is a math error, or measurement error in the calculations…

 

If you want… start a thread with what you know about your existing WnB… see if somebody recognizes where it went awry…

 

Weight removal…

Many Mooneys have a pair of batteries in the back… selection of a different battery may lighten the load back there…

There are also Charlie weights in Mooneys… find what you have and where it got mounted…

 

Weight addition…

An easy way to add pounds to the tip of a Mooney… get  a three blade Hartzell prop!  Hartzell makes some pretty robust prop hubs… adding three aluminum blades makes it hefty… 

 

It will be real important to know if the WnB is right, and just misrepresented… or it is wrong, and represented correctly… before making actual changes…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

The tank and parts is 26 pounds according to the WB docs. 

I spent most of last night trying to fix my weight and balance. I think i found the error. Im talking to my AP again today about it,, hopefully putting the plane on scales tomorrow to get it fixed since when i redid all the math its coming to a CG of 46 instead of 48.5. I didnt know about the charlie weights, ill look into that. 

Sadly i just got a new prop so dont want to get ANOTHER new prop yet. 

23 minutes ago, McMooney said:

I want this mod, would make my E perfect....    esp with the other tank mod being unobtanium at the moment.

 

is there anyway you could forward all the docs ?

 

I think we could arrange that. Im just unsure how nice the FAA would be but Ill see what I can do. 

3 minutes ago, PilotCoyote said:

Empty weight CG is irrelevant in a Mooney (and also most small aircraft), unless it’s causing your tail to drop when you step on the wing???

CG is only relevant when a seat is occupied in the aircraft. Many aircraft are out of CG with nobody in a seat…. The aircraft isn’t going to fly without a person onboard, so the CG with the cabin empty doesn’t have any relevance.

 

or am I misunderstanding something?

Might be how I said it. Empty the CG is 48.5. When i do my WB with me and the gf in the front seat, the plane is flyable with fuel. Any baggage at all for any type of XC instantly puts the plane aft of the envelope, either solo or with passenger in the front. There is no way i can take any rear seat passenger right now. 

[A64Pilot]

21 minutes ago, PilotCoyote said:

Empty weight CG is irrelevant in a Mooney (and also most small aircraft), unless it’s causing your tail to drop when you step on the wing???

CG is only relevant when a seat is occupied in the aircraft. Many aircraft are out of CG with nobody in a seat…. The aircraft isn’t going to fly without a person onboard, so the CG with the cabin empty doesn’t have any relevance.

 

or am I misunderstanding something?

Not followed everything you said, but too far aft CG can be very dangerous, of course it’s calculated to take aircraft loading into account Pax, baggage etc.

Usually forward CG isn’t as dangerous, fwd CG limit is usually from stall speed or nose wheel weight limit on the drop test, but aft CG is almost always a stability issue, as you move aft you lose the positive force on the yoke, keep going and you hit the stick force neutral point which is what it says, it requires zero force to move the yoke nose down or up, go past past that and the force reverses, meaning if you let go the control yoke will go to full travel all on its own either up or down or oscillate between both.

However an aircraft right at its aft CG limit is both faster and more efficient, but less stable and lighter on the controls, so if you enter a race etc you want to be way aft, but if flying IFR you likely want to be well forward of max aft.

Many aircraft can actually be flown well aft of the limit by a good pilot who is careful and avoid turbulence, it’s not uncommon for example to see at Gander a V tail sitting on its tail. it’s headed to Europe and ferry tank is full, usually the nose will come down when the. pilot gets in.

In the bush, it’s not too uncommon to see a C-206 sitting on its tail without the pilot, same deal.

But that’s not true for all aircraft, I have no idea about a Mooney. but suspect loading one until the tail drops to be a very unsafe thing to do.

I’ve run several W&B problems on my J model and at least with it, without getting very unusual loads, you can’t get out of CG., and fuel burn makes very little difference in CG. My J unlike say a Bonanza you just don’t need to be real paranoid with loading

Edited October 7, 2021 by A64Pilot

[ArtVandelay]

I thought Charlie weights were only found in long bodies?

[Prior owner]

Ah, sorry for any confusion. I was merely stating that an aircraft need not be in the CG range when nobody is on board. I once had a student panic when he reviewed the aircraft W&B and discovered that the empty weight CG was outside the envelope. He refused to fly it...until we had a long talk about it

[jaylw314]

Isn't there an option or mod for short-bodies to move the batteries up front?  Or were some of them just born that way?

[David Lloyd]

I spent most of last night trying to fix my weight and balance. I think i found the error. Im talking to my AP again today about it,, hopefully putting the plane on scales tomorrow to get it fixed since when i redid all the math its coming to a CG of 46 instead of 48.5.

Every old airplane seems to have some mistakes in the calculated CG.  Addition, subtraction, multiplication, transposing numbers, adding rather than subtracting, it all gets done.

[Hank]

39 minutes ago, jaylw314 said:

Isn't there an option or mod for short-bodies to move the batteries up front?  Or were some of them just born that way?

The short bodies were born that way. The battery in my C is on the firewall in front of me.

3 hours ago, A64Pilot said:

Not followed everything you said, but too far aft CG can be very dangerous, of course it’s calculated to take aircraft loading into account Pax, baggage etc.

Usually forward CG isn’t as dangerous, fwd CG limit is usually from stall speed or nose wheel weight limit on the drop test, but aft CG is almost always a stability issue

As we used to say when discussing RC planes:  "Nose heavy flies poorly, tail heavy flies once."

If you're too nose heavy, it will stall; drop the nose, increase speed in descent, begin to fly, stall; repeat until landing. Sometimes enough power will prevent the stalls, otherwise you're not going high and are heading down.

If the tail is too heavy, it will stall. Then there's not enough forward yoke to break the stall . . . . .

Ya'll be careful out there! With my Hartzell 3-blade, my C is rather nose heavy, but still safely within limits. Due to the wonderful Mooney design, CG barely moves between tanks full and tanks empty, and I've landed mine with them pretty close to the Golden Hour reserve with no issue.

[Ragsf15e]

13 hours ago, Mooney Dog said:

The tank and parts is 26 pounds according to the WB docs. 

I spent most of last night trying to fix my weight and balance. I think i found the error. Im talking to my AP again today about it,, hopefully putting the plane on scales tomorrow to get it fixed since when i redid all the math its coming to a CG of 46 instead of 48.5. I didnt know about the charlie weights, ill look into that. 

Sadly i just got a new prop so dont want to get ANOTHER new prop yet. 

I think we could arrange that. Im just unsure how nice the FAA would be but Ill see what I can do. 

Might be how I said it. Empty the CG is 48.5. When i do my WB with me and the gf in the front seat, the plane is flyable with fuel. Any baggage at all for any type of XC instantly puts the plane aft of the envelope, either solo or with passenger in the front. There is no way i can take any rear seat passenger right now. 

Even with your changes (aux tank, new avionics, new prop, battery moved), I’d be pretty surprised if your cg was as far off as you described.  I bet you’re right about the error(s).  Mooney’s are very forgiving with respect to loading and relatively tough (but not impossible) to get out of cg.

[carusoam]

13 hours ago, ArtVandelay said:

I thought Charlie weights were only found in long bodies?

All Mooneys have a Charlie weight….

LBs have a set of CWs… that everyone knows about…

LB CW options are famous…

• Air conditioning
• Fiki anti-ice
• Built-in O2 systems
• Lead weights

The usual CW hiding in the tail of all Mooneys comes from the difference between design and actual construction…

Look in the area in front of the tail hinge… nicely painted to match its surroundings.  On the scale of a pound or two… not very large like an AC system in the trunk…

PP thoughts only, not a plane builder…

Best regards,

-a-

[Mooney Dog]

10 hours ago, PilotCoyote said:

Ah, sorry for any confusion. I was merely stating that an aircraft need not be in the CG range when nobody is on board. I once had a student panic when he reviewed the aircraft W&B and discovered that the empty weight CG was outside the envelope. He refused to fly it...until we had a long talk about it

You're good. I know how students can be. Ive trained my fair share now. 

10 hours ago, jaylw314 said:

Isn't there an option or mod for short-bodies to move the batteries up front?  Or were some of them just born that way?

Im not sure. Mine has the battery in the back but at this rate id rather add a weight to the front to try and balance things out if its needed. 

9 hours ago, David Lloyd said:

I spent most of last night trying to fix my weight and balance. I think i found the error. Im talking to my AP again today about it,, hopefully putting the plane on scales tomorrow to get it fixed since when i redid all the math its coming to a CG of 46 instead of 48.5.

Every old airplane seems to have some mistakes in the calculated CG.  Addition, subtraction, multiplication, transposing numbers, adding rather than subtracting, it all gets done.

Too many number, too little time

29 minutes ago, Ragsf15e said:

Even with your changes (aux tank, new avionics, new prop, battery moved), I’d be pretty surprised if your cg was as far off as you described.  I bet you’re right about the error(s).  Mooney’s are very forgiving with respect to loading and relatively tough (but not impossible) to get out of cg.

Yeah I went through again with excel and got a completely different number than the "calculated" weight and balance. Im just having it scaled this coming week.

17 minutes ago, carusoam said:

All Mooneys have a Charlie weight….

LBs have a set of CWs… that everyone knows about…

LB CW options are famous…

• Air conditioning
• Fiki anti-ice
• Built-in O2 systems
• Lead weights

The usual CW hiding in the tail of all Mooneys comes from the difference between design and actual construction…

Look in the area in front of the tail hinge… nicely painted to match its surroundings.  On the scale of a pound or two… not very large like an AC system in the trunk…

PP thoughts only, not a plane builder…

Best regards,

-a-

It does appear mine has any extra weight in it currently, though it might at some point. I even removed the step and PC system out of the tail and still didnt get the CG back. In fact... because of this post i now realize that wasnt accounted for on the latest WB... 

 

Oh the joys of plane ownership. 

[Prior owner]

Is there a legal way to install a removable ballast up front?

[Mooney Dog]

22 minutes ago, PilotCoyote said:

Is there a legal way to install a removable ballast up front?

Im not sure about removable, but Im more than likely going to just get my AP to put some up front and add it to the WB. Having 950lbs of "useful" means nothing to me since i cant use anything behind the pilot seats. 20lbs on the firewall gives me enough that i can actually fill the aux tank and have 30lbs of bags in the back seats so i can actually fly the plane. 

[Guest]

5 hours ago, PilotCoyote said:

Is there a legal way to install a removable ballast up front?

There sure is, but it’s not for everyone.  Ask @Marauder to borrow one of his ladies.

Clarence

[carusoam]

So far…

There is one Mooney on the planet that has a Cg that is so far back that 30Lbs of junk in the trunk causes an out of balance situation…

Keep in mind the designed limitation for the baggage area is typically 120LBs for most Mooneys…

 

As far as a Mooney being so tail heavy it hits the ground… that isn’t going to happen until the weight of snow is more lead like…. The MLG is far enough back from the Cg that Lady Marauder filling the back seats will sit comfortably upright… 

The plane won’t fly with Mrs. M. back there, but it will taxi around quite comfortably…

 

Keep working the scales and the maths before changing anything…

WnB doesn’t have any mysteries…

expect something as simple as a “-“ negative sign getting omitted from something hanging forward of the magic bolt on the nose gear…

PP thoughts only, not a mechanic…

Best regards,

-a-

[steingar]

I really don't understand this.  I've had my baggage area just about maxed with just little old me in the front and I still was well within CG.

[ArtVandelay]

I really don't understand this.  I've had my baggage area just about maxed with just little old me in the front and I still was well within CG.

Depends on the model I guess, my J I can max out both luggage and hat shelf and stay within limits.

[Prior owner]

55 minutes ago, steingar said:

I really don't understand this.  I've had my baggage area just about maxed with just little old me in the front and I still was well within CG.

Yeah, me too… weighing the aircraft will hopefully reveal that mistakes were made in W& B calculations. Someone might have used the firewall or the tip of the spinner as station zero- I’ve seen stranger things!

[Mooney Dog]

15 hours ago, steingar said:

I really don't understand this.  I've had my baggage area just about maxed with just little old me in the front and I still was well within CG.

Bath math from the 1970s

 

14 hours ago, PilotCoyote said:

Yeah, me too… weighing the aircraft will hopefully reveal that mistakes were made in W& B calculations. Someone might have used the firewall or the tip of the spinner as station zero- I’ve seen stranger things!

When i went through and redid the WB from the 7 previous, i found quite a bit of error so yeah a reweigh is def going to help. And if not.....

 

well time to add some weight up front.

[Shadrach]

Something does not smell right.  If you’re playing with C model it would be out of limits all the time given that the angle valve injected engine is ~40lbs heavier than he carburetted parallel valve engine.

I’m flying a mid body from the same error with the same engine. The MGW is 150lbs more the E. There is an additional 10” of airplane behind the CG . It has the the step, PC servos and a compass amplifier behind the baggage compartment and has never had an issue with aft CG.
 

I would asked another E owner for a copy of their W&B to compare notes.

I look forward to learning where the CG comes out after weighing. There are ways to screw up that calculation as well.

Edited October 9, 2021 by Shadrach

[MikeOH]

This just has to be messed up calculations.

If the aux tank wasn't there you would have 120 lbs of baggage and there would be no more issue than any other C.  Put in a 36 pound aux tank and you have 84 lbs available for baggage (if it's empty).  Why would the CG be any different? A pound of fuel is the same as a pound of baggage

[Mooney Dog]

A few people here have reference the 120lb limit for the baggage compartment. I dont have my 1965 poh on hand but i was sure it was limited to 100lbs 

 

Regardless on the original install of the tank, it was listed as 25lbs empty. Im really unsure. 

 

I should be getting a new WB Thursday.