Nose heavy problem twin comanche

by **ComBE** » Fri Jul 17, 2009 8:00 pm

Hi, we have a PA-39 serial 66 and we have a Concord battery in the nose. Our weight and balance with 2 POB in front and full fuel is really putting the twin comanche nose heavy. Is moving the battery the only option ?

by **Hansmeister** » Fri Jul 17, 2009 9:21 pm

Move the battery to the rear, and carry 100# lead shot bags in the baggage are common options.

by **Kristin Winter** » Fri Jul 17, 2009 10:52 pm

That is the same problem I have with my 1969 Twin. Two people and full fuel, that included tip tanks, puts the CG about two inches out the front of the envelope, if no baggage is carried. I am currently using ballast.

My long term solution is going to be a combination of the following: Change to lightweight starters. Change to lightweight alternators. Move the battery to the rear. The last one is much more work.

by **N3322G** » Sat Jul 18, 2009 12:55 am

In addition to Kristin's and Hans' thoughts, watch for other weight considerations such as Lycoming cylinders had/have a 2.2 pound light weight advantage per cylinder than some other cylinders and I can't recall which is heavier the q-tip/stock or Kts2U cruise prop - same with different mags. These decisions may or may not be in the future but thought I'd mention them.

The Twin also gained 10.5 lbs useful load during panel renovation as old wiring was removed - all forward of CG.

And if you and your favorite right seat person have a sense of humor - there's always the lose weight option - I always laugh at this but in truth, it was a factor in our favor for the world races in the Twin.

It is surprising how these small things add up. Like when we carry water, we put it in the rear seats instead of between the front seats - same with oxygen, jepp books, charts, jackets. You may have already thought of all of these so no offense intended. Even after 39 years of flying the 1970 39, we still run CG calculations and have carried ballast as needed.

Hope some of the ideas are of use to you.

by **ComBE** » Sat Jul 18, 2009 2:14 pm

Thanks for the messages, yes we have the lightweight starters, I checked on the battery, there is no lightweight battery available, I just putted a new concorde RG-35AXC... very heavy :-(

One question, besides the usual stuff you can put in the back (water, charts, oxygen bottle etc..) what do you use Kristin as BALLAST ?

by **David Pyle** » Sat Jul 18, 2009 3:31 pm

While not Twin specific my comments may help. Single engine 260C's have the battery behind the rear bulkhead. It cost $900 just to replace the original alum with copper cables because all the through cabin routing.

In the Comanche and other airplanes I have used barbell weights in the baggage area. I have four 25 pound weights (I don't use them all) that fit neatly and securely under the rear seats.

Do not use Kristin as ballast as implied in your previous post.

by **N3322G** » Sat Jul 18, 2009 6:44 pm

I've used a weighed bag of lead shot.

In another aircraft that flew faster with a more aft CG, we used a bag of water softener salt.

by **Jay** » Sat Jul 18, 2009 7:26 pm

I carry 50 lbs. of lead shot in light canvas bags, plus a couple of quarts of oil, extra headsets, some water and other miscellaneous junk that probably totals about 75 lbs. total in the back. My PA30 is a '65 with the battery in the rear, light weight starters and lightweight alternators, so that 75 lbs. does it for me. The ballast comes out if I'm carrying lots of bags or a passenger in the back.

Seems goofy to have to carry extra weight in a light plane, but it does have the advantage of making it easier to land well consistently.

Jay

by **ComBE** » Sat Jul 18, 2009 7:37 pm

I would like to fill the back up with as usefull stuff as possible. Just putting some lead in the back to fix the problem seems so wasted to me. If i'm counting the things I can put in the back (like some important spare parts, oil, water etc...) I don't really fix the problem.

I guess this comes from the thing that we are not sitting on the spar but that the spar is after our backs...

My co-owner joked about sitting in the back seats with extended controls...

I guess moving the battery to the back is mandatory... costs me alot though.

by **Zach Grant L1011jock** » Sat Jul 18, 2009 9:23 pm

Even out of the forward CG, the airplane flies fine. It has a little tendency to run out of up elevator at about the same time the plane stalls, but it does fly fine if needed, especially at reduced flap deflections, like UP! (note, I am not suggesting you operate the aircraft contrary to the POH/AFM, but if you have too...)

As to carrying stuff you don't need, I question this statement. How many times do you need all of the fuel, including tip tanks? Only carrying the fuel you need for most trips will keep you in CG. (the envelope narrows considerably at higher weights). Also the tip tanks cause a forward CG move. Mains also are forward, Aux's move CG aft. Honestly, whats the problem with carrying jugs of water or the like. I have done this, and it works well. Don't need them, dump the water out. Need them again, any airport has a water spiggot, fill them up. This is helpful if you don't fly out and back with the same payload. I caution the use of bags of salt as the salt residue, when mixed with water, can cause some very bad corrosion.

I am also not a big proponent of large heavy items that cannot be tied down effectively. It would be sad to survive an incident, only to be crushed from the rear by some ballast!

-Zach

by **Kristin Winter** » Sun Jul 19, 2009 5:48 am

I have (3), 25lb bags of lead shot. I use only as much as I need.

by **ComBE** » Sun Jul 19, 2009 8:09 am

FYI, this is my calculation.. doesn't look good at landing, And I already calculated it with 140lbs of bagage !!!

by **AlanBreen** » Sun Jul 19, 2009 11:43 am

Hi,

The envelope that you have on your graph doesn't look correct to me.

The figures I have for the envelope are

Forward limit
2300 lbs 81.0
2450 lbs 81.0
3200 lbs 83.0
3600 lbs 86.5
3725 lbs 87.5

Rear Limit
2300 lbs 92.0
3600 lbs 92.0
3725 lbs 91.4

I think these figures will put you in balance with the payload you have in your example.

Alan

by **Zach Grant L1011jock** » Sun Jul 19, 2009 4:32 pm

I'm with Alan. I suggest you reference your AFM and check out the envelope diagram. Alans numbers are correct with straight line deviation between all. The envelope you have is entirely wrong. I think you will find the W&B is not as big of a deal when you use the full envelope. I'm glad you posted your envelope so that we could see what the issue was. Smart!
-Zach

by **N3322G** » Sun Jul 19, 2009 4:50 pm

So glad you posted your envelope and data.

Appears you are using Jepp default data. Dear husband has customized ours by going to Edit, Weight and Balance Tab, Edit envelope. Husband also did extensive editing on power, fuel flow etc.

That won't fix the whole problem. Your empty weight CG is 2.7 inches forward of PA-39-10. When the preceding owner was still alive (Mom), she once had to have it re-weighed because the weighing was done poorly and moved the CG forward 2 inches. Also, personally have had incorrect weight and balance calculations.

Want to help so pardon if you have already done the following. Suggest you post your last official weighing done so others can comment. Does the plane fly nose heavy? Have you taken Zach's Flight proficiency training where another twin pilot would have flown with you?

If it were me, I might spend the dollars to have it re-weighed if it flies OK.

Nose heavy problem twin comanche

Nose heavy problem twin comanche

Weighty Problem

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