New Cherokee 140 owner, W&B "problem"

tawood

tawood

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Tim
Hi All,

I just purchased a '66 Cherokee 140, and I started figuring some weight and balance examples...then I found something weird:

No matter how I figure this plane, as long as I stay within gross, I CAN NOT get it out of acceptable CG. I've read in the past that Cherokees can often be nose heavy, but this one, if anything, leans towards tail heavy...although not overly so.

I can put full fuel and two 280lbs front seat passengers, and no problem. I can put nearly no fuel, just a pilot, and 260 lbs in the back, and no problem. No matter how I reach 2150 lbs, I'm seeing CG's calculated between 89 and 93....

Am I doing something wrong?

Thanks for any help...
 
Don't know if you're running these by hand (I hope not) but theres a couple great apps out there that let you enter the specific arms and moments of your airplane and create a profile for your plane on it and it makes it real easy to run a bunch of scenarios that way. I know you can do it on forelight but the one i like to use is WnB Pro and you can just enter or slide around the values and visually see it on a graph how it effects it. May be an easy way to run a bunch of scenarios and see if what is happening makes sense.

If you are already using an app like this well then i wasted some time typing this up, but then again I'm doing nothing else today, so was it really time wasted?
 
JustinD said:
Don't know if you're running these by hand (I hope not) but theres a couple great apps out there that let you enter the specific arms and moments of your airplane and create a profile for your plane on it and it makes it real easy to run a bunch of scenarios that way. I know you can do it on forelight but the one i like to use is WnB Pro and you can just enter or slide around the values and visually see it on a graph how it effects it. May be an easy way to run a bunch of scenarios and see if what is happening makes sense.

If you are already using an app like this well then i wasted some time typing this up, but then again I'm doing nothing else today, so was it really time wasted?
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No, I'm old fashion, and I've always done them by hand...maybe this is a signal to get the apps!
 
There are planes with a lot of utility function, your situation isn't abnormal. I would check those numbers with other similar airplanes though. Also, like Justin said, plug all your numbers into Foreflight or some other W&B calculator and play with it that way.

First W&B on google for your model. http://www.hariguchi.org/flying/resources/wb/pa28-140/

two 200 pound guys with nothing behind them, will put that specific plane out of CG. But you can put a pile a bricks in the baggage compartment with a light pilot and stay within range.

I've got more input!
That aft range is sort of ridiculous and not totally in line with what you are saying your plane can take. It is possible that over the 60 years, one of the owners of your plane added a few pounds to the tail to change the empty CG allowing for a more centered CG. My club added a few pounds to the back end of our 182P to give a slightly more aft CG so I don't believe that to be an unusual practice. Checking your logs for changes might be a good idea, and if you are really concerned or are unsure get new numbers from an A&P.
 
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Ok, I
TheGolfPilot said:
There are planes with a lot of utility function, your situation isn't abnormal. I would check those numbers with other similar airplanes though. Also, like Justin said, plug all your numbers into Foreflight or some other W&B calculator and play with it that way.

First W&B on google for your model. http://www.hariguchi.org/flying/resources/wb/pa28-140/

two 200 pound guys with nothing behind them, will put that specific plane out of CG. But you can put a pile a bricks in the baggage compartment with a light pilot and stay within range.

I've got more input!
That aft range is sort of ridiculous and not totally in line with what you are saying your plane can take. It is possible that over the 60 years, one of the owners of your plane added a few pounds to the tail to change the empty CG allowing for a more centered CG. My club added a few pounds to the back end of our 182P to give a slightly more aft CG so I don't believe that to be an unusual practice. Checking your logs for changes might be a good idea, and if you are really concerned or are unsure get new numbers from an A&P.
Click to expand...


Okay, I tried the calculator, and it gave me (more or less) the same figures as I was getting on paper.

As to adding weight to the tail, during the pre-purchase, I didn't see any "weight", per se, but I did notice the ELT is mounted waaaaaaay back in the tail, and it is quite large.
 
Some planes are just good like that

If you use foreflight, I'd recommend it's built in W&B feature
 
tawood said:
Ok, I



Okay, I tried the calculator, and it gave me (more or less) the same figures as I was getting on paper.

As to adding weight to the tail, during the pre-purchase, I didn't see any "weight", per se, but I did notice the ELT is mounted waaaaaaay back in the tail, and it is quite large.
Click to expand...

That could do it! From your profile picture it looks like your plane has a nice paint and could show really well. Could you post some pictures for us PoAers so we can gawk?
 
James331 said:
Some planes are just good like that

If you use foreflight, I'd recommend it's built in W&B feature
Click to expand...

I do use foreflight, so I'll definitely try it...I've never used the FF W&B before because I've come from a C150 that was easy to calculate W&B: you were over gross ALWAYS! LOL
 
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TheGolfPilot said:
That could do it! From your profile picture it looks like your plane has a nice paint and could show really well. Could you post some pictures for us PoAers so we can gawk?
Click to expand...
Thanks TGP, it does look nice to me too. Its amazing the difference I saw while shopping for aircraft because I moved up from airplanes I figured I could get for below 25k to airplanes I figured I could get for around 30k. I'd have to say that simply adding 5k added a whole new world to me for planes.
And I still don't know how to post pics here, other than attaching a pic or two as text like this:
 

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I did one the other day with 2 - 220lb in the front and 34g fuel and was over CG. I don't have my W&B with me at the moment to provide some better examples. '67 -140.
 
Aviation Weight & Balance Calculatot app is the best app on my iPhone. I made templates for my airplane using my current actual scale weight for tires and skis. I can view my load and CG in seconds and make adjustments if I want. Get the numbers or view a take off weight and zero fuel weight plotted on an envelope chart. Great app.
 
Timbeck2 said:
Consider yourself lucky. Every Cherokee owner I know, which includes myself, flirts with the forward line regardless of how it is loaded.
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That's what I've heard too, so that's why I was confused (among other things, lol).
 
I have a 67 140 that at first always was out the front door... I could not get a loading that was even close to centered, and never towards the back.... I found that the arm for the empty weight was off. If you are starting out too far forward, it only goes down hill from there... Getting the correct arm and weight to start with really helps... I will be having the plane weighed next month to redo the baseline to be sure were it really is... What total empty weight and arm did you use in the calc's??
 
Just out of curiosity Glenn, what was the arm then and what is it now?
 
I would review all the math that was used in past modifications to the aircraft. When I purchased my airplane a mechanic mixed up the multiplication or addition and ended up with an EWCG that was some 10 feet aft of what it truly was. No big deal; but multiple mechanics carried that error forward in subsequent radio removals/installs and it was like that for at least 10 years before I bought it. (note to self; always do a reality check after doing such calculations - the CG cannot be somewhere near the tail feathers)
 
I have an excel spreadsheet with a different tab for for every plane I rent. I have been flying the Archer and 172's I always do a full load (whatever that means for the flight I am on), and zero fuel calculations. I have observed that it is quite difficult to get the 172 and the Archer out of balance.
 
Let'sgoflying! said:
I would review all the math that was used in past modifications to the aircraft. When I purchased my airplane a mechanic mixed up the multiplication or addition and ended up with an EWCG that was some 10 feet aft of what it truly was. No big deal; but multiple mechanics carried that error forward in subsequent radio removals/installs and it was like that for at least 10 years before I bought it. (note to self; always do a reality check after doing such calculations - the CG cannot be somewhere near the tail feathers)
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When a plane is reweighed, doesn't that essentially reset the weight and balance? That would make all of the other little errors that were made along the way irrelevant.
 
tawood said:
Thanks TGP, it does look nice to me too. Its amazing the difference I saw while shopping for aircraft because I moved up from airplanes I figured I could get for below 25k to airplanes I figured I could get for around 30k. I'd have to say that simply adding 5k added a whole new world to me for planes.
And I still don't know how to post pics here, other than attaching a pic or two as text like this:
Click to expand...

Good looking plane!


The foreflight W&B takes a little time to set up, but it gives you great detail of not only your current max weight, max forward and max aft limit, but also at landing, you can add quite a few different features as well and you can share your W&B too.
 

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azpilot said:
When a plane is reweighed, doesn't that essentially reset the weight and balance? That would make all of the other little errors that were made along the way irrelevant.
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Azpilot, was the airplane reweighed? If so, I missed it - sorry. I'd say that is right.
 
Let'sgoflying! said:
Azpilot, was the airplane reweighed? If so, I missed it - sorry. I'd say that is right.
Click to expand...

I don't think the OP had his airplane re-weighed, but Glenn D mentioned he was having his plane re-weighed soon. That was really the source of my question. You do make a good point about double checking that math on the W&B. It's an easy mistake to make and it can really throw things off.
 
Glenn D said:
I have a 67 140 that at first always was out the front door... I could not get a loading that was even close to centered, and never towards the back.... I found that the arm for the empty weight was off. If you are starting out too far forward, it only goes down hill from there... Getting the correct arm and weight to start with really helps... I will be having the plane weighed next month to redo the baseline to be sure were it really is... What total empty weight and arm did you use in the calc's??
Click to expand...

1276.8 empty weight, 90.5 CG empty.

I went back through the logs, and found several past W&B that were close to this one (of course different slightly though), so I have no reason to doubt it. This most recent one is just a month old.
 
Also, I notice the link above to the W&B calculator did not include oil, and I was making the mistake of including oil (which is already included in my W&B paperwork from a month ago, so I was figuring oil twice), so now it is possible (and correct, I think) to get it slightly forward of the CG envelope if you put in a 325 lbs pilot with a 325 lbs front seat passenger and only half a tank of fuel...lol.
 
tawood said:
so now it is possible (and correct, I think) to get it slightly forward of the CG envelope if you put in a 325 lbs pilot with a 325 lbs front seat passenger and only half a tank of fuel...lol.
Click to expand...

Need to see pictures.
 
Interesting numbers... Mine was 1313 empty with 83.6 inches... and after finding a few errors and now using 85.3. 90.5 seams far aft of what I have seen on other aircraft. But if the logs show it and there was a W&B done a month ago... I would believe it!.. I will be having my plane re-weighted next month for a better starting place.

With an aft limit of 94 inches, it is almost there to start with,....

I have used this on-line calculator, and like it for fast review, and have an APP on the phone that is a little better.
http://trumpetb.net/alph/wbPA28-140.html
 
tawood said:
Also, I notice the link above to the W&B calculator did not include oil, and I was making the mistake of including oil (which is already included in my W&B paperwork from a month ago, so I was figuring oil twice), so now it is possible (and correct, I think) to get it slightly forward of the CG envelope if you put in a 325 lbs pilot with a 325 lbs front seat passenger and only half a tank of fuel...lol.
Click to expand...

Someone please correct me if I'm wrong but doesn't an aircrafts w&b already take into account all fluids (i.e. oil, hydraulics) including non-useable fuel?
 
ah okay I was confused reading it! Now i just went back and re-read it and it makes sense!
 
I agree, something does not add up here.
Mine too has empty CG around 84 inches aft. 90.5 sounds very far aft. I wonder whether you have some STC that moved some heavy component back. Battery in the tail? (nope, I am not joking) PA-28s are definitely nose heavy and like others pointed out, we always flirt with disaster close to fwd CG. I have always advocated moving the CG back but of course I cannot do anything about it since it is a certified airplane. Maybe yours was modified to improve the CG?
I don't want to waste your money but with your CG 6" further back than stock, I would at least review all W&B sheets in the logs going back to the date of birth, if you don't actually have her weighed for peace of mind.

Let us know what you find, you got my curiosity piqued.
 
I don't have a Cherokee, but I have nearly the same issue with my Tampico. I'm never over the front limit, but I'm always right up there by it. Going to a light weight starter helped. It took something like 9 pounds out of the nose of the plane.

I've often though about adding an aux fuel tank as far aft as I can get it...
 
Either you empty CG is wrong or some mod has been made to move weight to the rear. If you can't find the answer, you should get it weighed.

There is a trick to help with the too far forward CG. There is a Piper document that was republished by the FAA that allows using the actual arm of the front seats instead of the standard mid-position. You can have the passenger move his seat completely to the back and get credit for it in the W&B. The pilot has to sit where he can properly reach the controls. If that is behind the mid-point, he can take credit for that too. I don't remember the document number but the subject was doing spins and being in the proper part of the W&B envelope.
 
tawood said:
1276.8 empty weight, 90.5 CG empty.

I went back through the logs, and found several past W&B that were close to this one (of course different slightly though), so I have no reason to doubt it. This most recent one is just a month old.
Click to expand...

Check to see how many modifications ago the last time the plane was weighed. If it's been some time and the W&B has been amended a number of times due to changes in equipment you may want to have it re-weighed now, as several other posts have suggested.

I dealt with the forward CG bias in my Cherokee by always carrying my tool kit, spare oil and other stuff in the aft baggage. Worked fine to avoid running out of elevator authority and banging the nose wheel down early on landing. I recall the battery is already in back, under the rear seat.
 
Step 1 - get a copy of the TCDS on the FAA website. You're looking for 2A13. That's the definitive document for the W&B CG locations. Do you have the 2 seat or 4 seat version? What's the serial number? That will change the CG graph a little bit. I agree with the posters here - after 40+ years, the empty weight has probably changed, so it wouldn't hurt to get it weighed.

With two 325# pax in the front, no baggage, and the numbers from the TCDS and your airplane W&B, 12 gal fuel on each side, you're really pushing the forward limit of CG. I did include the oil (7 qts) as separate and not part of the empty weight.
 
tawood said:
1276.8 empty weight, 90.5 CG empty.
Click to expand...
Let me join the chorus of the suspecting. Here's a couple of examples:

- N7342J with old 140 hp motor in 2010 (upgraded to 160 hp since): 1333.95 empty, 86.3 arm.

- N7342J with new motor, removal of ADF and a ton of junk: 1262.95 (way lighter now!), but 84.58 arm.

Frankly I would've re-weighted it if it were my airplane. It can't be that expensive, just need to find the right mechanic to do it.
 
I dealt with a plane once where the mechanics has made a math error calculating the WB. If you loaded the plane to the limits they listed, you were really 200 lbs over gross, and 2 inches aft of the limit!

It was flown that way for probably 10-15 years before anyone noticed...
 
Ok guys, it was just weighed a month ago for the removal of the adf. And I'm sure it checks out, as the CG has been at 90 or above on 4 past weighings since 1974. As I went through the logs, I noticed the CG changed upon the mounting of the ELT in the tail in 1974.
Of interesting note: this plane can NOT be flown in the utility category...it just can't get there (again, if I'm calculating right).
 
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tawood said:
Ok guys, it was just weighed a month ago for the removal of the adf. And I'm sure it checks out, as the CG has been at 90 or above on 4 past weighings since 1974. As I went through the logs, I noticed the CG changed upon the mounting of the ELT in the tail in 1974.
Of interesting note: this plane can NOT be flown in the utility category...it just can't get there (again, if I'm calculating right).
Click to expand...

I had a PA-28-180 and I never could get it to utility as well.

However, I always had CG problems particularly since I had the light oleo on the nose gear. Definitely check out your Type Certificate Data Sheet (TCDS) out on the FAA's site. I didn't even KNOW about the heavy/light oleo and different envelopes for mine until I did.

I did however, have a lot of problems with CG being too far forward. I'm not a light guy, weighing in at about 215 (on a good day), if I have a heavier passenger (200 +) up front with me, then I had to use about 100 lbs or so of ballast in the baggage compartment and limit the fuel.

The biggest thing you can do to control CG is fuel quantity, especially if you have heavier people up front. I've put people in the back who were over 240 in my plane and when it's just me up front, it balances just fine. In fact, as a rule the light person always rode up front with me and the heavy person was in the back. If that wasn't possible (for example when the heavy person was a CFI), then I had to limit fuel, use ballast, etc like I explained above.

My useful load was about 929.

It's like a shell game, moving pieces all over the place to make the CG balance out. If I went up on my own, full fuel, I was definitely within limits, without the ballast.
 
tawood said:
Ok guys, it was just weighed a month ago for the removal of the adf. And I'm sure it checks out, as the CG has been at 90 or above on 4 past weighings since 1974. As I went through the logs, I noticed the CG changed upon the mounting of the ELT in the tail in 1974.
Of interesting note: this plane can NOT be flown in the utility category...it just can't get there (again, if I'm calculating right).
Click to expand...
A heavy ELT way far back would definitely offset the CG maybe an inch. Though not 5".
Try this W&B calculator (it is pre-set for a PA28-140): http://trumpetb.net/alph/wbPA28-140.html
In the baggage, enter your ELT weight and modify the arm to the proper inches (let's say another 10 ft back adds 120in). See how it affects your CG.
What else you got in the back? Gold? :)
 
BigBadLou said:
A heavy ELT way far back would definitely offset the CG maybe an inch. Though not 5".
Try this W&B calculator (it is pre-set for a PA28-140): http://trumpetb.net/alph/wbPA28-140.html
In the baggage, enter your ELT weight and modify the arm to the proper inches (let's say another 10 ft back adds 120in). See how it affects your CG.
What else you got in the back? Gold? :)
Click to expand...

Hmmm, you're right...

But, with 4 different weight and balances, from 4 different places, over 40 years, all showing the same weight + or - 20 lbs and a CG + or - a 1/2 inch...and with a current 1277 lbs empty weight...I don't know, and I'm also starting not to care.
 
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