Relocate the battery

[Jstickler76]

Hello all Mooney owners. I currently own a 65 m20c.  I have been searching the last couple of days for any STC on relocating the battery behind the back seat.  I have a tri prop and would like to balance the airplane out.  I have seen the newer models located aft and to make it easier to access the mags and other parts of the engine.  Any guidance would be extremely appreciated.. 

[Hank]

Sounds good to me! Keep us posted if you find out, my Hartzell 3-blade is quite heavy, too.

[Bob_Belville]

I'll be interested in hearing from someone who knows. I'd be concerned about W&B issues. I think Cs typically operate toward the front of the envelop, my E with a rear mounted battery is close to the rear limit. And I suppose the IO360 is heavier than the O360.  

[Hank]

Two adults, full fuel and a 3-blade puts me really close to the forward limit.

[carusoam]

Interesting challenge...

Since other M20s have the parts, would the STC process be required...?  (If this logic worked, I would have TN'd engine...)

Have you done the math to see how the flight envelope would change?

The battery is pretty heavy and the distance pretty far back.  But, the third blade is not very light and it is pretty far forwards.

To get a feel for what it would be like from a WnB point of view.  It would be similar to putting a battery on the hat shelf, and removing the one up front.  What is the weight limitation for the hat shelf? 10#?  How much does your battery weigh?

Graph the new WnB under various conditions to see if the weight goes out the back of the envelope.

If the WnB works out, what's the next step...? (Find parts, install drawings and a mechanic with the knowledge)  MSCs can be a good source of knowledge...

PP ideas only, I'm not familiar with the process...

Best regards,

-a-

[Hank]

The mid-bodies put the battery in the avionics bay, which is a foot further back than in our short bodies. The F has the same engine as the E, but the batteries are the length if the cockpit apart. What changed besides a heavier aft fuselage, which is longer behind the front seat and the same in frontoif it?

The long body position way back in the tail won't work for short bodies, the moment arm is way too long. Now I'm going to have to start doing some math . . . Hope I can find my WnB spreadsheet, I just carry a printout in the seat pocket. Thanks, Anthony!  

Edited November 3, 2016 by Hank

[Bob_Belville]

My battery is 26.5# at station 105.8. 

My empty CG is @ 47.0" If the battery were @ station 0 it would be 45.3.

[carusoam]

The mid body gets 10" of extra foot room... expect the hat shelf to be 10" further back than a short body.

 

the long body gets 20" foot and baggage room.... plus the engine is moved pretty far forwards with extra space behind it.

It gets two batteries and a slew of Charlie weights and/or other things for balance like O2, A/C heat exchanger and anti ice tanks....

Hope that helps...

Best regards,

-a-

[Pritch]

We have a 65C on the field with a TN and the battery was relocated to the tail.  So it looks like it can be done.  I will see if the owner knows about the STC since he bought it that way..

Pritch

 

[MB65E]

Has anyone picked those li-PO batteries at Oshkosh? It would sure be nice to get rid of all the dead weight of the batteries. You should see where the 2nd battery is on some of these Rockets!! It's 3/4 the way down the tail. It would be easier to work on if it was at the tail post. 

-Matt

[philiplane]

On 11/2/2016 at 9:53 PM, Jstickler76 said:

Hello all Mooney owners. I currently own a 65 m20c.  I have been searching the last couple of days for any STC on relocating the battery behind the back seat.  I have a tri prop and would like to balance the airplane out.  I have seen the newer models located aft and to make it easier to access the mags and other parts of the engine.  Any guidance would be extremely appreciated.. 

You don't need an STC. You can relocate batteries using data from AC43.13 as your reference material required in Block 8 on a 337 form.

[Jstickler76]

Just to make sure I follow you.  So if I did block 8 on a 337. Would I have to have a drawing, weights and balance, then have a field approval. If so do have any experience with this modification.  I am a novice and my mechanic helps me and signs off on my work. Just trying to do my part. Thanks. 

[cliffy]

You would need drawings showing how the battery box is mounted, specing rivet spacing from 43.13. then you will need structural strength as shown in 43.13 and a new weight and balance work up also from 43.13. Battery cable size and mounting is also in 43.13. It can be done with correct references to the specific parts of 43.13. All this goes on the 337 form, signed by the IA and approved by the local FAA office. 

It can be done but your A&P needs to be familiar with 43 13 and the 337

It might be worth a try to find a 337 used by another Mooney for this same project as that can be used as "approved" reference for the install

[N201MKTurbo]

All the old Mooneys are under the same type certificate, so if it is in the parts manual it should be fare game. Just show all the part numbers removes and added, the new W/B and send it in. Mooney got it approved years ago.

[Jstickler76]

Thanks for your help. This will make future task in the engine compartment so much easier. And if anyone has this done please jump in. 

[goterminal120]

I didn't do it but my 68 c has the battery in the tail. It was put there when the j style cowling was installed and the oil cooler had to be moved. I don't know if it was done under the same paperwork or individually , but I'll see what I can find.....Doug

[philiplane]

On 11/6/2016 at 10:48 PM, Jstickler76 said:

Just to make sure I follow you.  So if I did block 8 on a 337. Would I have to have a drawing, weights and balance, then have a field approval. If so do have any experience with this modification.  I am a novice and my mechanic helps me and signs off on my work. Just trying to do my part. Thanks. 

The 337 process is defined by the data available. AC43-13 provides acceptable data for field approvals of major alterations & repairs. If you happen to use OEM parts and install the battery in the same location as a later model, you would provide that information. If there was a factory service bulletin to relocate the battery, then you don't need a 337 at all.

A drawing is not necessary when referencing appropriate paragraphs and illustrations in AC43-13. You will calculate a new weight and balance, and modify the equipment list to show the new station of the battery. You will have to include Instructions for Continued Airworthiness in Block 8. The sixteen items of the ICA address any unique maintenance or inspection methods necessary due to the alteration. 

[Yetti]

You would probably want to add the weight of the solenoids(2) and a couple other pounds (powerconnector and wire) to see how the W&B work out.

[RobF15E]

I am also looking to move the battery back to the tail in my 65 M20C.  I also had a 3 bladed prop put on the nose at overhaul and it changed my tail heavy plane to a nose heavy plane.  Before the prop, I had replaced the gen and starter with light weight versions so I was a bit tail heavy.  When flying, it was always a bit pitch sensitive.  If a passenger leaned forward, the plane would descend a bit.  Slide the seat back a notch, trim forward.  Landings with the nose wheel in the air were easy, actually too easy as I scraped the tail once....  OK, so it isn't an Eagle and I shouldn't be doing an Eagle walk with it....  Now with the heavy nose, it is much more stable in level flight and I have to trim the snot out of it for greaser landings.  I did a series of weight and balance checks assuming I moved the battery back and added weight for new cables.  I didn't plan on moving the solenoids as I like my jump start door on the front cowl.  I was able to remain within the W&B envelope for all configurations I would fly in.  I'd like to duplicate the M20E installation but no one I know has an "E".  Can anyone with an "E" provide some pictures of the battery mount and the wire routing?  My plane is down for the annual now, so I will be doing this soon.  If I am able to pull it off, I'll gladly share pictures and paperwork for others.  Expect that the plane may pick up a couple of knots, but will require more work to keep level.  Alas, I don't have an auto pilot....  I also have a one piece windshield mod with the thicker glass adding weight fwd of the CG.

[cctsurf]

Just my dumb idea, but way easier than moving the battery...  The old method of taking care of the forward CG problem was to put a bag of lead shot into the luggage compartment when you are flying without weight in the back seats.  Much less permanent, doesn't give the hassle of much longer battery cables and the work of their install and the 337 necessary for this job...

Another thing to note, the solenoids NEED to be moved, you don't run hot (electrified) battery cables through an airplane to a solenoid up by the engine without having a shutoff.  If the wire would get shorted to the plane, it would create a nice arc welder there...possibly burn up the plane.  If you want to jump from the engine compartment, you can set up a small wire from there to activate the solenoid (jumping in this way (with the plane's battery involved) is not necessarily recommended).

Edited December 7, 2017 by cctsurf

[goterminal120]

Do the math first. my 68 c had the batt moved before i got it. It moved the cg 1.6 inches aft, reducing utility a bunch. The way it sits i can load my family 40 gals of gas and 10 pounds of bagage. With the batt on the fire wall I could put 40 pounds of bagage with same fuel load.

    The heavy prop may be enough, idk

[autoalain]

Hi,  why back seat?,  mine is located where the step is but on pilot side.   m20a   Mike.

[TX-Champ]

On 11/4/2016 at 6:51 PM, philiplane said:

You don't need an STC. You can relocate batteries using data from AC43.13 as your reference material required in Block 8 on a 337 form.

Has anyone located a copy of a 337 documenting moving the battery to the aft area?  We have a '70 C-model with 201 cowl and 3-blade prop.  Moving the battery will solve some CG issues under certain loading conditions.  

[carusoam]

Welcome aboard Champ.

Philip outlined the hard tech part, how much more are you looking for?

Does your mechanic need more details?

drawings, parts, or paperwork...?

There are not many people that have gone this route... mostly cost driven.

Got any pics of your C?

Best regards,

-a-

[TX-Champ]

A copy of a 337 is a clear road map of this project.  Does anyone have a 337 for moving the battery aft? 

I have a drawing of the battery box details for prior models.  

It is not costly to do this conversion - the battery box can be re-used and relocated pretty easily.  Cable runs are very straightforward.

I've owned both a '68 C model and the current '70 C model.  The '68 had the aft mounted battery.  The '70 has it on the firewall.  The aircraft are noticeably different - the '70 is nose heavy (in part due to the battery, 201 cowl and 3-blade prop).  While it is possible to put weight in the baggage compartment to compensate, moving the battery solves the balance issues and preserves the useful load.