Cherokee PA28-140 Forward CG fix?

brcase

brcase

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Brian
Hello POA experts:)

I have had a student approach me that just purchased as PA28-140.
actually he was referred to my by another even heavier instructor...
With the 2 us together we weigh about 465lbs.
With the current weight and balance information we have the only way we can even get it close to within CG with the two of us is to put 130lbs in the baggage compartment and max out the Gross weight with about 30gal of fuel.

Plan A. we plan to re-weigh the airplane Saturday and confirm the weight and balance we have is accurate.

Plan B. If the W&B is accurate what STC's, or 337 modifications are you aware of for moving the CG further aft. A copy of any existing 337's would be awesome.

Plan C. beyond buy a different airplane, what other recommendations might you have?

Thank You

Brian
CFIIG/ASEL
 
I owned a '74 pa-28-140 and it was a tad on the forward-CG side, well a lot forward. Mine had slightly less than 700 pounds useful load. I'm not aware of any mod to change the CG limits or increase the useful load.

One thing you might consider is that the front passengers W&B numbers assume a specific location for the seats. (btw - I don't recall if the seats were moved there when I had my 140 weighed). Don't know how comfortable you'd feel about taking that into consideration.

Good luck. Sorry I couldn't be more help.

edit: depending on the avionics in the aircraft, some changes might give lighter avionics and help the CG.
 
brcase said:
what other recommendations might you have?
Click to expand...
As I recall the earlier Cherokees were challenged on the forward CG side. I also seem to recall pretty much SOP to fly with a case of oil in the baggage compartment in some scenarios but dont remember the details. Getting a fresh empty weight and CG will at least give you an accurate benchmark. For other ideas:
Compare your new EWB to other 140s and see where this aircraft sits.
Look at the current modifications/options on the aircraft and see if any are biased to the forward CG side. Or maybe look to see if there are lighter weight options.
As mentioned use the specific arm of the forward seats vs the default measure in the POH.
As to modifications available I dont recall any to expand on the CG limits even on Cessna.

I think once you get the new EWB & CG plus compare to other 140s you'll have a better handle on whether you have further options or its just simply another feature" of the aircraft.
 
Bob Noel said:
One thing you might consider is that the front passengers W&B numbers assume a specific location for the seats
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Good point, cool thing is we will have scales this weekend we can weigh it with us in the plane and get an actual weight and arm for the front seats.

To be clear I wasn't expecting an STC or 337 to change the CG range rather maybe one that would just move the CG aft, like perhaps repositioning the battery or adding weight to the tail.

Brian
 
My Cherokee 140 was always manageable but at the forward CG limit unless someone was sitting in the back seat. If this one is really bad I suspect there is a W&B error or there is some alteration that has pushed the empty CG significantly forward.

If all else fails, a lightweight starter and alternator would help move the CG aft. You might be able to relocate the battery with minimal effort as well.
 
We were donated a 1976 Cherokee 140 that sat for 17+ years. After restoring it back in the fall of 2020, going through paperwork the W&B looked good on paper. First thing was to fly it to a shop and weigh it. Well worth the $300 we were charged. Our Empty Weight is 1419.0 and CG is 89.53". Hope this help to get a better idea on yours. I'm about to remove a com unit and install a GTN650 so things will change.
 
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Something seem off about that calculation. You can put 465 lbs in the front seats of mine with fuel to the tabs and be right at forward CG. Putting less fuel in moves the CG aft and you can even get into the Utility category for Commercial maneuvers.

Piper Cherokee - Home Page

Piper Cherokee - Home Page.
touringmachine.com
 
Our CG is at 90.6 with 465 lbs in the front seats and 40 gallons of fuel. We will run out weight before CG goes too far forward.
I would weigh it and go from there.
 
My 140 could hit the forward CG limit before the max gross limit, unless there was ballast of some sort in the back.
 
Cherokee 140's do tend to be nose heavy. When I first got my '67 140, getting the weight and balance numbers into the utility category was pretty much impossible. Did have it reweighed, turned out it was a bit lighter and when going through all the old W&B forms, an A&P 30 years ago had some dyslexia when doing the math for the moment. After a reweigh and a recalculation, things are more "normal" now.
 
You need to lighten the nose.

Still using steam gauges? Going to glass and removing the vacuum system will help a bit. So will a lighter radio and starter. Have a comm2? Yank it. Any unused or inop items? Yank ‘em. Fire extinguisher up front? Move it back.
 
I once saw a tail cone with lead shot epoxied into it…:rolleyes:

but beyond that, absolutely make sure the paperwork has the correct empty CG…I’ve also see my share where they were wrong by a significant distance.
 
Cherokees are somewhat nose heavy, but I used to teach in a school's Cherokee 180 that was ludicrously so. So much so, that I went through the old W/B forms and actually found an error, a digit transposition on the moment or something like that. Once corrected, miraculously the airplane could now be flown in CG without ballast and partial tanks and such!
 
I routinely carry an 8 gal tank of water (actually only about 7 gal) in the baggage area of the cherokee 180. Great in the summer if I happen to land someplace unexpected, I have water. Also another 15 pounds for the small tool kit & a couple qts of oil. Really don't need it when it's just me, but if there's another adult, definitely need it for the CG. That O-360 weighs about 270# or so. Welcome to basic physics.
 
note that sometimes weighing an airplane doesn't give the answer you'd want or expect. When my 140 was weighed (for the first time almost 30 years), the basic empty weight increased. No math errors were found before weighing (didn't bother to look after), but the thing gained weight.

One possible reason it gained weight was it was painted by a previous owner (a lousy paint job) and the airplane wasn't weighed nor was the W&B updated.
 
I flew with a clown instructor in an early 182. WnB pro he had said all was good. Not so.

Using the factory graphs, it took 140# of ballast in the baggage compartment and unsurprisingly the three-point landings stopped immediately.

I hear this dope is now a DPE.
 
Is this the 140hp (a de-rated 150hp) trainer version without the back seats? I've been eyeballing getting an older Cherokee and thought I read somewhere only the 180hp Cherokees were a bit nose heavy.:dunno:
 
BMan said:
Is this the 140hp (a de-rated 150hp) trainer version without the back seats? I've been eyeballing getting an older Cherokee and thought I read somewhere only the 180hp Cherokees were a bit nose heavy.:dunno:
Click to expand...


I suspect most small 4x4 planes will be nose heavy if you plop 465lbs into the front seats.

brcase said:
With the 2 us together we weigh about 465lbs.
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For my Warrior II (PA-28-161): 465 pounds split evenly between the front seats with no other weight and full fuel, she is at 96.5% of MGW. CG is 86.7", just 0.5" inside the forward CG envelope. Fuel to the tabs bring MGW to 92.3% and CG to 86.9" -- a smidge less nose heavy, and 1.0" within the forward CG envelope.
 
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Half Fast said:
I suspect most small 4x4 planes will be nose heavy if you plop 465lbs into the front seats.
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I had a few similar flights (2 people w/ very heavy combined weight ~ 450 lbs) in an Archer 181. I put 120 lbs ballast (3 bags of salt pellets) in the rear cargo area along with fuel to the tabs (34 gal) to make the W&B work. Not a typical flight for me.
 
Our ‘69 PA-28-140 always has been nose heavy. We have the identical issue with two people and a CG at the forward limit. I have actually had bags of cat litter (keeps the hangar floor clean) in the baggage area to keep the CG in limits. It looks like Piper designed the plane at an era where pilots weighed 150 pounds on average.
 
My Musketeer is a bit nose heavy, as those planes are known to be. There's an STC for adding a ballast weight in the tail, but I just toss a couple of 25lb shot bags into the luggage area. That way when I need the extra load capability, it's easy to pull out one or both bags.
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When I upgraded my panel last year, I gained back about 12lbs, and that helped the CG a bit.
 
Initial results,

Saturday we weighed the PA28-150 that I started this thread about. it was a fairly quick can dirty weighing, we didn't bother to level it (mistake in hindsight, thought a tri-gear airplane would be close enough) and it was done outside and the wind came up and was affecting the scales more than I anticipated. So we are going re-check our numbers tonight by leveling airplane and weighing it in a hanger out of the wind.

We found two things. It appeared the CG was about 1.3" farther aft then then W&B indicated. I am now concerned this might be due to the airplane not being leveled.

We also weighed it with us in the airplane and calculated the actual Arm for the front seats, which calculated as 95" but the published front seat location is 85.5 inches. A bit of this might be due to the airplane not being leveled but I don't think much of it is. I can't seem to find any published information about Front seat arm based seat location (seat back vs forward). If anyone knows where to find Front Seat Arm location based on seat adjustment please let me know. Weighed this way we are easily within the W&B limits even without weight in the baggage compartment.

More information to come after we re-weigh it and have an A&P double check our numbers.

Brian
 
After you get a good tape measure, level and plum bob then study the documents linked. If you don't level the aircraft the C.G. calculations are absolutely worthless.

PA-28 Type Certificate Data Sheet

Goto pdf page 468 and STUDY AC43.13 chapter 10

Do you ever run out of Nose-Up or Nose-Down trim?
Most aircraft are engineered to land with the trim and no back pressure on the yoke. If it runs out of trim and back pressure is needed then investigate why. Sometimes it's the rigging and sometimes it's the balance.
 
Klaus M said:
After you get a good tape measure, level and plum bob then study the documents linked. If you don't level the aircraft the C.G. calculations are absolutely worthless.

PA-28 Type Certificate Data Sheet

Goto pdf page 468 and STUDY AC43.13 chapter 10

Do you ever run out of Nose-Up or Nose-Down trim?
Most aircraft are engineered to land with the trim and no back pressure on the yoke. If it runs out of trim and back pressure is needed then investigate why. Sometimes it's the rigging and sometimes it's the balance.
Click to expand...

The TCDS has been my go to document for researching this... Wish it showed a Arm for forward seat vs aft seat adjustment.

A Google search indicated supplement VB261 had the Arms for the seat positions. But actually reading it, while the serial number range falls with in the range listed, it appears to only apply to the PA28-180, Also it doesn't list the arm for the seat positions, only the gross weight increase (and maybe a CG range adjustment), which makes sense why it might only apply to the PA28-180.

Pretty familiar with AC43.13 also, not seeing anything there I wasn't aware of. Our quick and dirty weighing was just to see if it warranted further investigation, which it appears it does. Now wish I had leveled it when doing so, since it was off more than expected from our existing W&B. That is why we are going to do a more precise measurement this evening.

We haven't flown it yet, because I am not going to fly it with a potential CG issue.

Brian
 
Easy enough on the seat positions. After you level the aircraft use the plumb bob and estimate the middle of the seat while in the forward position and mark the floor then move the seat aft and do it again. I use masking tape and pen under the plumb bob. Also measure the wheel distance from datum and don't necessarily use the book numbers. Use the plumb bob through the center of the axles and mark the floor. There should be a lot of masking tape and measurement marks on the floor when you're done weighing an aircraft. Even measure the front and aft of the baggage area.

Some pilots like to remove the back seat while the aircraft is on the scales to get an accurate Weight/C.G. of the back seat installation. Just like switching from floats to wheels to skis, make a logbook entry and update the Weight & Balance and Equipment List of the seat removal. The wheel pants also require a log book entry and correct W&B/Equip List.

You may find that it's easier and quicker just to word processor create a whole new Equipment List then marking up the 50 year old Equip. List.
 
I don’t recall having a forward CG problem in my PA28-181 under any conditions, but I’ve never been more than 172lbs flying with any heavyweights.
Also, the later year models are longer so have different constraints.
But one thing I do when desiring to get the most out of the aft CG envelope is to use a 42lb emergency bag for much of my flying. In my mind, much better than any sort of inert or less useful ballast just for weight purposes.
 
brcase said:
If anyone knows where to find Front Seat Arm location based on seat adjustment please let me know.
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Search my posts for the figures. Cant search at the moment. The 85.5 is the mid-point of the seat adjust range. There's a Piper bulletin that gives the min-max range. But best to weigh at mid-point for EWB then show seat adj for your flight CG.

brcase said:
More information to come after we re-weigh it and have an A&P double check our numbers.
Click to expand...
Be sure your AP does more than look and signs off your new empty weight and balance + update your EL if you want to use it for flight. And as mentioned your previous actual W&B is meaningless in those conditions.
 
Results of last nights weighing. The W&B we have for the airplane appears to be reasonably accurate. But the big take away is the published forward Seat Position of 85.5 Appears be a forward average. Moveing the seat foward we could measure as far foward as about 83" and as far back as about 91" (IIRC), I will post my numbers here later. About the furthest forward we could both comfortably put the seats was about 90" so we are going to use 90" as our seat arm. That works pretty well and only requires about 25" in the baggage compartment to get us within CG.

A new lightweight starter is being ordered and appears that it will help a lot. We will probably also remove the nose wheel fairing ( I guessed about 7lbs or more, anyone have a better estimate?) which will also help.

Brian
 
Replace the instruments with G5/AV-30 and remove the whole vacuum system.

8lbs saved there
 
It’s not a quick fix but extending the BaggageCompartment aft solves 2 common issues.

My reference is not to the Piper “hatrack” but to moving the aft wall back one bulhead.

There are several aircraft that had this done via Field Approved 337’s.

The 337 does not show the install but provides the references.
 
@brcase - With the actual weights of the two people involved and the likely bags you would carry (perhaps within arm reach in the rear seats) and fuel @ the tabs, how much weight is left over for cargo/ballast in the rear cargo area?
 
Magman said:
It’s not a quick fix but extending the BaggageCompartment aft solves 2 common issues.

My reference is not to the Piper “hatrack” but to moving the aft wall back one bulhead.

There are several aircraft that had this done via Field Approved 337’s.

The 337 does not show the install but provides the references.
Click to expand...

I like this idea, probably not cheap to do. but I would guess it also involve move the battery aft as well.

Brian
 
Mongoose Aviator said:
@brcase - With the actual weights of the two people involved and the likely bags you would carry (perhaps within arm reach in the rear seats) and fuel @ the tabs, how much weight is left over for cargo/ballast in the rear cargo area?
Click to expand...

with 30 Gallons of fuel, about 100lbs left over for cargo/ballast.
 
brcase said:
Moveing the seat foward we could measure as far foward as about 83" and as far back as about 91" (IIRC), I will post my numbers here later
Click to expand...
The SAIB below mentions the seat range. There is also a Piper service letter that addresses the forward seat CG range. Still cant find my old post thought that had references.

And while I cant remember the details some early Pipers had extended CG limit bulletins which addressed some issues.
https://drs.faa.gov/browse/excelExternalWindow/117F68DD6566FF898625721F0052EC70.0001
 
Bell206 said:
The SAIB below mentions the seat range. There is also a Piper service letter that addresses the forward seat CG range. Still cant find my old post thought that had references.

And while I cant remember the details some early Pipers had extended CG limit bulletins which addressed some issues.
https://drs.faa.gov/browse/excelExternalWindow/117F68DD6566FF898625721F0052EC70.0001
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That is an Awesome document, one issue, it turns out the plane in question is a PA28-150. I am sure it is the same but the SAIB references only the PA28-140.

The Seat positions it references is very close to what we measured. Note we didn’t actually measure distance rather we just sat in the airplane and weighed it and back calculated the CG seat position.
We came up with an Aft Seat position of between 91.11 and 90.24 (Solo owner vs Dual), and a forward seat position of 83.44 (solo, as far forward as he could move the seat and sit in it). This is reasonable to what the document states of 80.5 to 90.5.

Thanks for the reference, if you know of a simlar reference to the pa28-150 please let me know.

Brian
 
For those comparing W&B documents, The empty weight of this PA28-150 is 1375lbs with the empty CG at 86.5” with 7 qt oil.

This plane has an original starter and wheel pants installed.

Brian
 
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