Avstar Aircraft of Washington, Inc.

10415 172nd St. E., Hangar A1
Puyallup, WA  98374
office (253)770-9964
or (253)770-0120
email:  avstarair@att.net

12/16/2013 Ask Mike! Archive
Can I move the battery aft in a Bonanza?

Hi, Mike,

I recently bought a G35 Bonanza and in general I'm pleased with it.  It has the D'Shannon IO-470N STC, done about ten years ago.  This with the hydraulic prop adds weight forward.  Odd for a Bonanza, but I cannot load the plane in any rational manner that gets me into the front side of the envelope, though the former owner flew it this way for 700 hours with no problem.  I now fly around with 50 lbs ballast in the baggage compartment, which gets me close but not into the envelope.  I have had the plane weighed and verified the numbers.  It is my thought to move the battery and box (about 35 lbs) to aft of the back bulkhead with a 337.  Everyone knowledgeable tells me not to do that, just ignore it.  I don't want to do that.  My question is, do you have a better idea?  And if you agree I should move the battery, is that something your shop would do for me?

Thank you,

Good Morning, Dick;

My concern with moving the battery is current draw when starting the engine.  Granted, there are a number of aircraft manufactured with the aft battery location, but I wonder if there may be other ways to accomplish the same goal without that sacrifice.

What is your useful load?  What do you have for a starter?  What prop are you swinging?  Do you keep water in the swamp cooler?  The 50# ballast:  is it dead weight or a survival kit of sorts?  Do you generally keep your wing aux tanks full?

When I first put my F35 on scales after a ton of mods, without much interior in it, I needed 100# of ballast; after I finished the interior, it came out pretty good, so I feel your pain.   I have a customer with a B35 and IO-470, he keeps a tool box in the back.  The lightweight starters can help, and different props can lighten the load a bit.  If your useful load will allow it, maybe a lead ballast around STA 230, in conjunction with a survival kit of sorts may be a good start without a great deal of expense.  This will sacrifice a little useful load, but I suspect if forward CG is the issue, you don't often have back-seat passengers.

Food for thought.  If I remember correctly, the D'Shannon STC does allow moving the battery if necessary; we can look at the STC paperwork.  If so, a field approval would not be necessary.

If you are local, a look at the aircraft and paperwork may be useful.



Thank you for  the quick and insightful response.  I suspect the lead ballast is the answer.  I was hoping not to lose more usable weight, but oh well.....

The answers to your questions:
current useful load?  940 lbs
starter?  stock Continental
prop?  hydraulic constant speed
water in the swamp cooler?  no, it is gone
the 50# ballast, dead weight or survival kit?  I use a six gallon water tank so it is easy to vary weight
Wing aux tanks full?  Yes, I keep the aux tanks full, they move the CG aft.  I keep the tip tanks empty and the right main mostly empty, which helps.

Yes, thank you for the invitation, I will fly over the first nice day.