180 New W&B

dkallen

I just had my plane weighed due to all of the upgrades I have done. The plane is a 1969 180D. It doesn't look like there has been an actual W&B done on the airplane since it was new. Just addendums when things were added or subtracted. The big question I have is "Is it typical for the airplane to be weighed with full tanks, then back out the 300 lbs for 50 gallons of fuel?" The new CG is 0.44 in aft of the old CG, currently 85.84". The old weight was shown to be 1309.9 lbs. The new weight is shown to be 1478 lbs. I am pretty sure we took out more weight than we put in as far as equipment goes. The new interior probably weighs a few pounds more than the old, but not that much more. I am thinking that I would have the airplane weighed again with the tanks drained. The issue I have is that with the old W&B, My wife and I along with 50 gallons of fuel and 20 lbs in the baggage compartment is within the envelope. Now, we need 150 lbs baggage and 36 gallons max to be in the envelope if she sits in the front seat.

JimC

Although is is normal to be out of the envelope forward with 2 and 50, you sound heavy now. What is the source of the extra 168 pounds. Could you have inadvertantly left about 28 gallons of fuel in the plane when you weighed it?

dkallen

The thing is, they weighed the plane full of fuel and backed the weight (300 lbs) out of the total weight. I am thinking it needs to be re-weighed with empty tanks.

dkallen

"Could you have inadvertantly left about 28 gallons of fuel in the plane when you weighed it?"

Jim,
What I am curious about is just that. They did not drain the fuel when the plane was weighed. They topped off the airplane, then subtracted 300 lbs for fuel. I am having my A&P send me the paperwork they used for the calculation so I can review it. With the changes we made, I have calculated we should have had a net loss of about 20-30 lbs not including a probable net gain of a few lbs for the interior. We added just a little soundproofing and a little extra foam in the seats. Right now, I believe I am going to get it re-weighed the more I think about it and make sure they do the W&B per the AFM including draining both tanks and running the engine on each tank until the engine quits. I don't see how the plane could be that heavy.

dkallen

Original Paint? Paint IS HEAVY.

>> I have started thinking about that. The paint is not original, but the best I can tell it was stripped. I cannot see any evidence of a color under this paint job when we replaced the tips.

Often Avionics are removed but harnesses & moumts are left in.

>> We gutted the airplane. Removed all old harnesses, wiring, inoperational equipment, etc.

Another thing is Wheel fairings can be "removed" 4 times but never "installed" . Or vice versa.

>> The wheel fairings are installed and do not show up as removed on any of the original equipment sheets I have.

Did ALL installed Equipment even get entered?

>> Yes, I did check that. All of the old stuff is gone now. The only instrument that did not get replaced on this job was the airspeed. It was replaced about 5 years ago and is still operational. Everything else is new.

Still 4 ply tires?

>> I am not sure about that one. I will have to check.

My guess is that that some of the previous changes were NOT properly entered .

Maybe you should start with the Original & recalculate all.

>> I worked on that today. I came up with a net loss of about 30 lbs with the exception of the interior. We added about 10 lbs of super soundproofing and used a good quality foam, but that cannot total more than 5-10 lbs net increase including the additional weight of the new upholstery

However; it IS easy to tell when the tanks are FULL & then subtract 300 lbs for useable fuel.

>> Yep, That is what I would think. I will have a copy of the calculation sheets sent to me tomorrow. I want to see how they backed out the weight of the fuel as far as the CG goes. I don't know if the tanks are centered on the CG arm or how they came up with the CG offset for the fuel. Still, that would affect the moment, not the empty weight.

dkallen

Here is the panel now. It still needs placards and touch-up. All old stuff is gone. With the PMA8000B, 430W, SL30, GTX327, MVP-50 replaced all engine instruments. All wiring replaced and all new breakers.

Piper Tech

You can weight the plane with tanks full or empty. If you are using a aircraft jack with a load cell, just make sure that you check in the maintenance manual that the plane can be jacked safely with full fuel. The FAA has a pretty nice handbook that highlights the finer points of jacking if your interested. http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-1A.pdf

JimC

You can weigh it full, but backing out the weight and correctly allocating the weight reduction between the nose and mains is beyond some mechanics. My hunch is that they divided the weight of fuel by two to distribute it left and right, then mistakenly subtracted half the fuel weight from the total weight to get the total weight of the plane. That would make it seem 150 pounds heavy and would shift the cg.

dkallen

JimC wrote:

You can weigh it full, but backing out the weight and correctly allocating the weight reduction between the nose and mains is beyond some mechanics. My hunch is that they divided the weight of fuel by two to distribute it left and right, then mistakenly subtracted half the fuel weight from the total weight to get the total weight of the plane. That would make it seem 150 pounds heavy and would shift the cg.

This is the kind of mistake I am suspecting. Talked to my A&P this morning and he is sending the calcs used to me. The person that did the weighing supposedly does this a lot, for whatever that is worth. Doesn't mean he cannot make a mistake.

In our conversations this morning, the question came up about whether piper actually weighs a plane before it goes out the door or do they just use a baseline weight and add the numbers on the equipment list. Would anyone happen to know?? I can see being off a few lbs, say 20-30, but there is no place to put 170 lbs inless the wings are full of dirt. If the weight has been off as much as it currently appears, it had to have been that way for years. This plane never has seemed to be nose heavy, nor acted squirly in stalls as a severely nose heavy plane would probably act. Anyway. Will wait for calculations and review them.

Greg S

I can see how subtracting the fuel wt. would render a correct empty wt., but how do you know how much wt. to subtract from each of the 3 wheels to come up with the correct wt. & bal.?

jruhnke

dkallen wrote:

In our conversations this morning, the question came up about whether piper actually weighs a plane before it goes out the door or do they just use a baseline weight and add the numbers on the equipment list. Would anyone happen to know?? I can see being off a few lbs, say 20-30, but there is no place to put 170 lbs inless the wings are full of dirt. If the weight has been off as much as it currently appears, it had to have been that way for years. This plane never has seemed to be nose heavy, nor acted squirly in stalls as a severely nose heavy plane would probably act.

I have had the same thought. My '73 had a number of W&B mods over the years, but nothing too major...old avionics replaced with new, etc. Biggest single change was when they ripped the factory A/C out many years ago. Per documents, useful load on my plane was 950# when I bought it.

Went through annual, and I requested my mechanic weigh the plane on his certified scales. Result? Useful load is now 850#.

Dunno exactly how 100 lbs sneaks into the plane over time. My guess is that it probably started life a little heavier than the paperwork actually said it was...

dkallen

I still don't have my calcs, but what I suspect is that they came up with a total wt and total moment with fuel, then back out the moment of the fuel, then use the resulting moment divided by total weight less fuel weight to get the "certified" empty weight and CG. I just requested the calcs be sent to me agaain. I am sure he got busy yesterday and just forgot.

Piper Tech

When I worked for a airline, I was and still am amazed that it was legal to repaint 70 CRJ's into a new paint scheme, and only 3 (I think) had to actually be weighed. The rest were assumed to be ok. I realize that they had the same equipment installed ect..., but seems like it would be possible to have aircraft that weighed significantly more or less than others. While I realize we are talking about two different sizes and types of planes, the common thread is still the same......paint is heavy.