How to determine empty weight "arm" change?

[HopePilot]

 

Hi everyone,

So I got the Mooney back with the speed brakes and I'm trying to figure out my weight and balance.  The problem is I have had my engine changed to the A3B6 and my book still has the moment and arm from before the engine change (the one that is on 6-5 in my manual).  I have the correct new weight for the plane (with oil and no fuel).  How do I know what my "arm" is now that I've added speed brakes (9 lbs.) and the engine is 3 pounds heavier?

 

Anyone with a J that has an empty weight near 1872 want to let me know what their arm and moment is for comparison?

 

Thanks!

 

[tablor]

This might be completely worthless as I don't know how it translates to your airframe, but I can tell you that the speedbrake installation on an Acclaim and an Ovation is 9 lbs @ 71" taken from the POH.  0" should be the firewall and I don't believe the wing has moved in relation to FS 0. at any time so that should be the correct arm.  Anyhow, I don't know if that's useful, I just thought I'd throw it out there.

 

[FlyDave]

Shouldn't the installer have computed a new W&B after installing the speed brakes? I'm sure that's part of their responsibility and they should have investigated if it wasn't redilly available. I'd go back to them and have to figure it out.

[HopePilot]

Okay, I think I figured it out, but I'd still like to know what people (such as you) have as their empty weight, arm, and moment (including oil).  It doesn't seem right and I'm going back to them to talk some more about it.

 

-nope I thought I had...

[jetmech1972]

Might want to go back to the IA who signed the engine installation off and have him update the logbooks; then to the party responsible for the speed brakes installation and have them do their entry.

[HopePilot]

Unfortunately, it was done in another state before I bought the plane (the engine).  Does the empty weight (with oil) "arm" ever change?  Sorry if that's a newbie question, but I'm referring to the arm value that is written in at 6-5 in the manual.  When I was a renter, I didn't worry about such things.

[FlyDave]

Quote: 16LPilot

Unfortunately, it was done in another state before I bought the plane (the engine).  Does the empty weight (with oil) "arm" ever change?  Sorry if that's a newbie question, but I'm referring to the arm value that is written in at 6-5 in the manual.  When I was a renter, I didn't worry about such things.

[Barry]

From my understanding, the weight and balance records need to be adjusted and signed by a certified mechanic. IF there is no change in their status, that should also be logged. If there is data missing, you will need to have your plane re-weighed and have a new weight and balance chart completed for you.

You may get hung-up during an annual if someone really digs into the log books.

[OR75]

I believe (but I am not certain) a W/B entry must be made in the POH by an A/P each time there is 1 lbs or more added or removed

 

[Magnum]

Just put it on scales and get a new W&B. You might not like what you get, but this way you'll know where your CG really is.

When I bought my 205 the CG was near the aft limit, as someone didn't weigh it properly. So I did it again, the CG is now where it should be and and I was lucky that she didn't get heavier. Make sure the A&P follows the procedure in the Maintenance Manual and that the scales are calibrated.

Mine is a '87, no speedbrakes and a Aspen. In my gallery you can see what else I have installed. Empty: 1851 lbs, CG 46,65

[danb35]

Quote: 16LPilot

Unfortunately, it was done in another state before I bought the plane (the engine).  Does the empty weight (with oil) "arm" ever change?

[HopePilot]

Thanks Dan,

They gave me the W&B for the speedbrakes, but they are saying it changed the empty weight arm more than I believe.  I want to debate the issue, but I have to know what I'm talking about.  Unfortunately, I can't find the change in weight and arm for my IO-360-A3B6 or the Sky-Tec Starter (I have the Sky-Tec weight, but not the arm, also, no weight for the original starter so I can't subtract the difference) and I've been pouring through my records.  Does anyone know what the original starter weight and arm was for the 201? 

I've now called the mechanic who did the engine overhaul.  Waiting...

Thanks.  Thanks.  Thanks.

[Magnum]

The Prestolite Starter weighs 18 lbs, arm -21 inch. The SkyTec weighs 9,4 lbs.

[HopePilot]

God bless you Magnum.  I've been looking everywhere.

[rdav]

When I bought my plane, I had it weighed so I could be certain that the figures were correct.  If there's any doubt, that would be the best way to resolve it.

I develop STC packages frequently at work, and need to generate weight and balance amendment data as part of the data package.  Those figures are a best estimate, especially if components like wiring or hoses are involved which are distributed across the airframe.  As more modifications are added to a particular aircraft, the aircraft computed weight and balance figures become more and more inaccurate as the errors compound.

[danb35]

They gave you the STC paperwork showing the W&B change for the speed brakes?  What weight and arm (or moment) is shown on that paperwork?  And what weight and CG were shown for the plane before they were installed?  Given those two pieces of information, the math is simple enough.

[Rustler]

Because there had been so many "ins and outs" of equipment over the 30 years of its existence, when we replaced the IO360A3B6D with the IO360A3B6 in my '80J last summer, I decided to start clean with a new W/B. There was hardly any difference between the computed values over 30 years and the actual weight in 2009. Didnn't make her any lighter, but I was very glad to have a verified W/B to begin anew. I think it cost $50 or something like that.

 

 

[HopePilot]

Okay, I'd like to thank everyone.  Sorry, if I was so cryptic earlier, but here's the whole story.  I had my plane weighed after the speed brake installation, to have a clean weight and balance.  The numbers I got back scared the crap out of me.  The numbers made my plane out of CG for three (if the third person was an adult) and would always be out of CG for four.  The numbers didn't seem right to them either, but they couldn't figure it out.  I went about (with everyone's help) trying to work backwards, from the old numbers, to see if it was even theoretically possible.  I came to the conclusion that even with the engine change, speed brakes, etc., it just wasn't.  I went back today after pouring over the numbers, and together we determined that the error was in where the reference datum station was accidentally placed.  All the fancy equipment in the world wouldn't help that.  

FYI:  I was off by less than half an inch.  Sorry, for all the remedial questions, but I had to uncover every stone.  It's when you get overconfident with what you know that the mistakes happen.

[Magnum]

I had the same problem (CG at the aft limit) and that's why I said: "...Make sure your A&P follows the procedures in the Maintenance Manual...". Weighing a Mooney can easily be done false if someone hasn't done it before. Good to hear that it is ok now.

[Kwixdraw]

You can go online to the FAA's website and get a copy of the aircrafts' Type Certificate Data Sheet. It will have lots of useful information about weight & balance and approved equipment and where on the airframe it's located. An IA is supposed to use a copy to make sure the aircraft conforms to type certificate and any STCs or 337s that came along later, during the annual inspection.