Weight and Balance Situation

BradG

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Ok, so heres the situation. I have my commercial checkride scheduled on Thursday morning. I went to do the weight and balance for the airplane, a 1967 Mooney M20C. I spent like 6 hours trying different combinations of loading, and found that it is not possible to load it realisticly within the givin limits. Even with 2 people up front, full fuel, and 120 pounds in the VERY back, it is still too far forward. So i looked at the original CG from '67. It shows the Aircraft as weighing 1566lbs, with the CG at 44.4 inches. The "current" one shows the airplane as weighing 1641lbs, with the CG at 39.3 inches. Does this seem strange to anyone else? It has the same motor as in '67, fairly recent avionics, and a 3 bladed prop ( upgrade from a 2 blade after it got geared up). I think the a 5.1 inch move in the CG is excessive. What are the chances of this? I am gonna try to get our Maintenance dept. to look at it tommorow, but i wanted to see if anyone else had any ideas. Thanks,

Brad
 

avbug

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It's certainly possible. There's nothing to be done short of correcting the weight and balance records, if they're in error. There is nothing you can do. Many general aviation airplanes have a similiar problem. I don't know about mooney's, as I only have a few hours in them.

A more important question is why this is an issue the day before your practical test. If you've been flying this airplane in preparation for the test, then surely you've performed the weight and balance calculations prior to this time. Right?

What do you find if you fly with 1/2 tanks?
 

flydog

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A 3 blade prop will easily move the CG 5 inches. The 3 blade props usually weigh 15 Lbs more than the 2 blade and the weight is on the nose. Avionics may account for the rest of the diffference in weight and maybe 1/2 inch in CG. A small 5 Lb weight on the tail may move the CG back to where it was. Do the math and see what you come up with and maybe maintenance can hang the weight and fix the problem.
 

BradG

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So they can put weights in the tail to correct it? I might have them try that. The records show the 3 blade weighs 14lbs more than the 2, and even with half tanks, 200lbs in the back seat, and 120 in the baggage area, and 10lbs on the hat shelf, it is still out. Hopefully it can be worked out.
 

A Squared

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Flydog,


>>>>>A 3 blade prop will easily move the CG 5 inches.

Huhhhhh????? Are you just picking numbers out of thin air? The allowable CG range on a M20C is only 2.5" at max gross weight. You think a 14lb weight increase on the prop would move the CG twice that distance? In reality, installing a prop that is 14 lb heavier (Fuselage station 30.16) would move the cg of a 1600 lb M20 less than 0.08" forward. That's right, less that a tenth of an inch. That's not quite 5"
Why post something if you're not going to see if you're even in the ballpark? How does that contribute to the discussion?


Brad G,

Something is obviously seriously wrong with the calculations on the weight and balance sheet. (maybe it was done by flydog <g>) You say the airplane went from 1566lbs, with the CG at 44.4 inches when it left the factory to 1641 lb, cg at 39.3" now. In order for this to be possible, that 75 lb total weight gain would have to have been added at 67.19 inches forward of the datum (nose gear attatch bolt). That would put it more than 3 feet in front of the prop. I'm pretty sure that there's nothing but air in front of the prop on a Mooney.
It might be at this point that the best thing to do is weigh the airplane and get a new weight and cg. If that's not possible, at the very least an A&P should review the W&B calculations, find the error (or errors) and write up a new, correct w&b sheet. Do not add weight to the tail, as it is pretty clearly a calculation problem, and do not go to your checkride without getting this resolved.


regards
 
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BradG

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A Squared....your are correct on the prop only moving it a little, although i belive it was about .6". Either way, when our Maintenance department looked at it, they found the W & B from 2 times ago, when i was weighed, and re-ran the numbers. They came up with a new CG of 44.3. Now i can actually load the plane like i need to. Thanks for all the input.

Brad
 

flydog

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A Squared

Did you forget to take your Valium or something?

On my airplane adding 15 Lbs on the nose will move the CG 5". I was providing an example and a possible explanation for his problem. I also stated that he should work out the math on removing the 15 Lbs on the nose to see if this could be the reason for the CG change. I am not a Mooney mechanic nor have I ever owned one. Just made a sugestion based on past experience. Maybe every time I make a post I will tack on a disclaimer stating that these are my own opinions and your results may vary. Even better I will hire an attorney to review all my posts to make sure I dont offend anyone

Sorry I pissed you off
 

A Squared

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Flydog;

>>>>>Did you forget to take your Valium or something?

No, I just have a low tolerance for posting totally incorrect information, without any attempt to check to see what the truth is. You see this far too much on these forums, people just spouting nonsense off the top of their heads. At the best, it just wastes bandwidth, at the worst it misleads others who looking to learn something. When I see someone post something without having done the most basic of fact checking it irritates me.

>>>>On my airplane adding 15 Lbs on the nose will move the CG 5".

Really? what airplane is this? For a given weight added or subtracted, the change in total CG will be proportional to the distance from the CG, and inversely proportional to the empty weight of the aircraft. That means a Mooney sized airplane would have to have an empty weight of about 190 lb for the cg to be changed 5" by the addition of 15 lb at the prop. Similarly, in order to change the CG location of a 1600 lb airplane by 5", the 15 lb would have to be added over 500 inches ahead of the existing cg. That's an arm of over 40 feet. I don't know of many 1600lb airplanes that are 40 feet from the wings to the prop.

So, what airplane is this you fly on which the GC would move 5" with the addition of 15 lb at the prop?

Regards
 
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