Weight and Balance issues on a PA28-140

Steve Job

Steve Job

Pre-takeoff checklist
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Steve Job
Hi everyone,

I've been running some W&B calculations on my new (in 1973:smilewinkgrin:) Piper Cruiser (140). It seems VERY nose heavy; where you can't even put two real folks in front with a full tank (50 gallons) without having the CG be too far forward. I joked with my co-owner that he had to sit in back! :smile:

Does anyone have experience with this? Have people tried putting ballast as far aft as possible in order to bring the CG in line?

I'm guessing that having the CG be normally that far forward may help contribute to the SLOW reputation of the 140 (that, of course, along with a draggy airframe and smallish engine). I know my co-owner (a CFII, who usually prides himself on extended wheelie landings) has a very hard time holding the nose off the pavement during landing for more than a few milliseconds.

Any thoughts or ideas?

Thanks!

Steve
 
Are you calculating the correct arm for the front seat positions? It may list a range (in inches)... My Cherokee 180 CG is in the forward part of the envelope but well within limits so I'd check each arm to make certain the numbers were entered correctly.
 
there is a range on the front seat arm, and there may also be a reissued w/b loading graph. check for both
 
OtisAir said:
Are you calculating the correct arm for the front seat positions? It may list a range (in inches)... My Cherokee 180 CG is in the forward part of the envelope but well within limits so I'd check each arm to make certain the numbers were entered correctly.
Click to expand...

The POH only lists one arm for the front seats - 85.5". However I found an FAA Special Airworthiness Information Bulletin (regarding the critical nature of CG calculation on the 140 during intentional spins - attached) that mentions the entire range should be listed from 80.5" to 90.5", with each detent representing 1.25". I'm 6'1" and usually have the seat in the back half of the track so this does help somewhat. To be honest, I haven't checked to see exactly which seat detent I use.

Thanks for responding!

Steve
 

Attachments

When I was training in the Warriors we put a couple cases of oil in the back to help me figure out landing. (It didn't work.)

If your W&B calculation says you need to do the same, you need to do the same.
 
mikea said:
When I was training in the Warriors we put a couple cases of oil in the back to help me figure out landing. (It didn't work.)

If your W&B calculation says you need to do the same, you need to do the same.
Click to expand...

And I will do the same. I was just wondering if anyone else had run into this situation before, and what types of creative (yet legal) solutions may have been employed.

Thanks for taking time to respond!

Steve
 
My 1974 140 is also nose heavy. My 140 is limited to about 385 lbs in the front seat with full fuel.

My solution is to reduce the fuel load.

If I'm really desperate, I recalculate with the front passenger sitting a little more back than the standard front seat arm.... but the easiest is just not to carry full fuel.
 
The 74 PA28-180 I rent is nearly the same. With my wife and I in front and nothing else it put us at the edge of the envelope but within bounds.
 
My first plane. N4341X is a Warrior and the case of oil in the rear of the luggage compartment makes a huge difference. Weight X Arm = Moment. That is a wonderful moment for sure.. and legal too..:rolleyes:
 
Bob Noel said:
My 1974 140 is also nose heavy. My 140 is limited to about 385 lbs in the front seat with full fuel.

My solution is to reduce the fuel load.

If I'm really desperate, I recalculate with the front passenger sitting a little more back than the standard front seat arm.... but the easiest is just not to carry full fuel.
Click to expand...

I noticed that too. I found a nifty W&B calculator application that displays a line indicating the CG from tanks empty to tanks full. It is just out of the envelope when full.

Maybe the answer is to find a thinner partner/co-pilot!
 
N801BH said:
My first plane. N4341X is a Warrior and the case of oil in the rear of the luggage compartment makes a huge difference. Weight X Arm = Moment. That is a wonderful moment for sure.. and legal too..:rolleyes:
Click to expand...

I'm definitely going to try the case of oil idea!

Thanks!
 
EppyGA said:
The 74 PA28-180 I rent is nearly the same. With my wife and I in front and nothing else it put us at the edge of the envelope but within bounds.
Click to expand...

How are your landings? Is it hard to keep the front wheel off?

I might try a few experiments with my 200lb buddy. "Hey Buddy, could you climb in back for awhile so I can see if this thing goes any faster, or if I can land more nose high? Hold this nice case of oil while you're at it!"
 
On a number of occasions, I have seen similar situations. In each case, a thorough and careful review of all the aircraft's maintenance records uncovered a significant error in preparing the W&B data during some modification or weighing many years back -- one time over 40 years previously (and which was unnoticed or ignored by over 40 years of pilots flying the plane despite being unable to load the plane legally based on the "official" empty weight and cg). I would suggest that you start by going through all the records back to when it left the factory, checking the airframe logs and 337's for any and all additions/removals of equipment, and see if you can find an error. It will require a lot of care and attention to detail, but it may pay off.
 
Does your W/B chart have one diagonal corner or two diagonal corners in the upper left part of the chart?
 
Ron Levy said:
On a number of occasions, I have seen similar situations. In each case, a thorough and careful review of all the aircraft's maintenance records uncovered a significant error in preparing the W&B data during some modification or weighing many years back -- one time over 40 years previously (and which was unnoticed or ignored by over 40 years of pilots flying the plane despite being unable to load the plane legally based on the "official" empty weight and cg). I would suggest that you start by going through all the records back to when it left the factory, checking the airframe logs and 337's for any and all additions/removals of equipment, and see if you can find an error. It will require a lot of care and attention to detail, but it may pay off.
Click to expand...

That's interesting. I did notice the standard empty weight for this model is 1275 lbs, but the last "official" weight was 1425 lbs. I don't know where that 150 lbs may have come from. It isn't like there's extra soundproofing or anything, and the upholstery looks very standard. I wonder if they forgot to empty the tanks, or take whatever fuel was on-board into consideration?

As far as the accuracy of the CG goes, is that entirely a math calculation based on each subtraction/addition of avionics/equipment, or is it possible to start fresh and have it checked as it is equipped now? I'm not sure how one would measure a CG on any given airplane. Is it as easy as measuring the weight on each wheel, and running the results through some algorithm?

I will go through the aircraft logs carefully to see if something may have been miscalculated!

Thanks for that idea!!
 
Steve Job said:
Is it as easy as measuring the weight on each wheel, and running the results through some algorithm?
Click to expand...
Yup, and it's the same algorithm that you use to calculate the loaded weight and balance. You start with the aircraft empty of usable fuel, passengers, and baggage, in a closed hangar (so wind doesn't affect it). You then place the aircraft on scales under each wheel, level it as specified in the service manual, and measure the weight on each wheel. The distance of each wheel from datum is specified in the service manual; you add up the weights for the empty weight, and use the service manual-supplied arms to calculate the moment of the empty aircraft. Voila!
 
Ok, then you need to track down that 150lbs. With full fuel I dont think you should be that far forward.
 
jmaynard said:
Yup, and it's the same algorithm that you use to calculate the loaded weight and balance. You start with the aircraft empty of usable fuel, passengers, and baggage, in a closed hangar (so wind doesn't affect it). You then place the aircraft on scales under each wheel, level it as specified in the service manual, and measure the weight on each wheel. The distance of each wheel from datum is specified in the service manual; you add up the weights for the empty weight, and use the service manual-supplied arms to calculate the moment of the empty aircraft. Voila!
Click to expand...

Wow, that seems obvious in hindsight! Of course that's how you would do it! I suppose it wouldn't be "official" unless I paid an FBO to do it, but I could at least have some peace of mind. Maybe we could tack it on to our next annual.

Thanks Jay!
 
Steve Job said:
I suppose it wouldn't be "official" unless I paid an FBO to do it
Click to expand...
...or, more specifically, an A&P. The folks who have the equipment and experience to make the job quick and efficient are the same ones who can sign it off, so it's worth it to have it done by a professional.
 
Depending on where you live...I keep an 8 gal tank of water (one of those square blue plastic things) filled to about 7 gal (56 pounds or so) in the baggage area. Many benefits - first, solves the CG
problem. Two, in the unpleasant event of an unscheduled emergency landing someplace that's difficult (translate that to mean it'll take time), I've got plenty of water. In the winter, great for soup, hot chocolate, etc. In the summer - an absolute necessity.

As for the case of oil - 12 quarts = 3 gal * 7.5 pounds = 23 pounds (ok, the cardboard case weighs a half pound, ok?) and costs anywhere from $40-60. I thought about that but decided that I liked the water tank more - cheaper, and if I need to remove some of the water and leave it somewhere, it's not painful.

I keep the tank in one of those square plastic boxes that the office supply stores sell for files. Makes it much easier to move, distributes the weight a bit more evenly on the baggage floor, and is much easier to tie down to keep from moving around.
 
EdFred said:
Ok, then you need to track down that 150lbs. With full fuel I dont think you should be that far forward.
Click to expand...

I agree, unless the "standard" empty weight was for a very stripped down model. Piper made a variant that year without back seats, top air ventilation, etc, intended for flight schools. I still don't think you could account for 150lbs though.

Once we weigh it again, we will know for sure.

Thanks!
 
murphey said:
Depending on where you live...I keep an 8 gal tank of water (one of those square blue plastic things) filled to about 7 gal (56 pounds or so) in the baggage area.
Click to expand...

I'm never too far from civilization in central Illinois, but I like the idea of cheaply adjusting the weight. I need to measure how much room I have back there. The baggage compartment is pretty small in a 140. If I can find the right size (and shape) tank, this sounds ideal.

Thanks!
 
murphey said:
Depending on where you live...I keep an 8 gal tank of water (one of those square blue plastic things) filled to about 7 gal (56 pounds or so) in the baggage area. Many benefits - first, solves the CG
problem. Two, in the unpleasant event of an unscheduled emergency landing someplace that's difficult (translate that to mean it'll take time), I've got plenty of water. In the winter, great for soup, hot chocolate, etc. In the summer - an absolute necessity.
Click to expand...

We sometimes need to use ballast, and we have a couple of chunks of old innertube filled with rice and closed at the ends with hose clamps. They weight around 50 lbs apiece. Survival rations for the Canadian wilderness. Water is handy to have, too, but the rice doesn't make a wet mess if it leaks out. It just attracts the mice...

With any of this stuff, it needs to be tied down real tight. In the event of a crash or an upset while airborne, it becomes a lethal chunk of weight that can break your neck, or worse. Folks have been killed by their baggage in some otherwise rather minor incidents.

Dan
 
murphey said:
Depending on where you live...I keep an 8 gal tank of water (one of those square blue plastic things) filled to about 7 gal (56 pounds or so) in the baggage area. Many benefits - first, solves the CG problem. Two, in the unpleasant event of an unscheduled emergency landing someplace that's difficult (translate that to mean it'll take time), I've got plenty of water. In the winter, great for soup, hot chocolate, etc. In the summer - an absolute necessity.
Click to expand...

Interesting idea.

I've been using sand as that's also economical to leave behind if you pick up a passenger. A 2-gal gas can filled with sand weighs 20 lbs which is a lot easier to sling around than the 50-lb bag the sand comes in. The gas can has a handle, too, which aids in tieing it down. Just label the can(s) really well so no one tries to pour it into a gas tank.
 
Steve Job said:
That's interesting. I did notice the standard empty weight for this model is 1275 lbs, but the last "official" weight was 1425 lbs. I don't know where that 150 lbs may have come from. It isn't like there's extra soundproofing or anything, and the upholstery looks very standard. I wonder if they forgot to empty the tanks, or take whatever fuel was on-board into consideration?
Click to expand...
For aircraft of this vintage, "standard empty weight" was an illusion. Back in the 60's, manufacturers would have a "standard" version of their airplanes with nothing but the absolute minimum equipment required for day VFR flight -- no radios, no vacuum system/AI/HI, etc. This produced some really competitive "standard" useful loads and payloads for marketing purposes, but were totally unrealistic for an airplane with the equipment that just about everyone would get. It was typical for an airplane of this class to roll out the factory door 50-100 lb heavier than "standard" without even IFR avionics. Thus, it wouldn't surprise me if your plane really weighs 1425 lb.
As far as the accuracy of the CG goes, is that entirely a math calculation based on each subtraction/addition of avionics/equipment, or is it possible to start fresh and have it checked as it is equipped now?
Click to expand...
It could be either. Usually alterations to the aircraft are handled with calculations based on the weight of the added/removed item and its arm. Unfortunately, I've seen a few cases where the A&P's skill was entirely mechanical and not mathematical, and major errors have crept in. While it's always possible to do a new weighing and start from scratch, I think most A&P's don't have the certified scales to do that, and it's a pain to do anyway (especially the fuel issues).
I'm not sure how one would measure a CG on any given airplane. Is it as easy as measuring the weight on each wheel, and running the results through some algorithm?
Click to expand...
That's how you do it, but it appears that for some mechanics, it isn't "easy."
I will go through the aircraft logs carefully to see if something may have been miscalculated!
Click to expand...
Excel helps when doing this, if you have some facility with it.
 
One final word of caution...

Before you go throwing a bunch of ballast in the baggage area, make sure that the cg issue is real, not erroneous. If it's a computational problem, adding that weight back there could put you out of the aft cg limit even if your W&B computations based on the possibly erroneous empty weight and cg data say you're in limits -- I've seen cases where that could happen. Being out of aft cg is way more dangerous than being out of forward cg, primarily due to its deleterious effect on pitch stability. This is one case where your life depends on measuring twice before cutting once.
 
Steve Job said:
How are your landings? Is it hard to keep the front wheel off?

I might try a few experiments with my 200lb buddy. "Hey Buddy, could you climb in back for awhile so I can see if this thing goes any faster, or if I can land more nose high? Hold this nice case of oil while you're at it!"
Click to expand...

Not hard keeping the front wheel off. A little more work getting it off the ground on take-offs. Haven't tried dialing a little up trim to help that. Do have to nose it over a little after it leaves the runway or I see the oops light come on.
 
Ron Levy said:
One final word of caution...

Before you go throwing a bunch of ballast in the baggage area, make sure that the cg issue is real, not erroneous. If it's a computational problem, adding that weight back there could put you out of the aft cg limit even if your W&B computations based on the possibly erroneous empty weight and cg data say you're in limits -- I've seen cases where that could happen. Being out of aft cg is way more dangerous than being out of forward cg, primarily due to its deleterious effect on pitch stability. This is one case where your life depends on measuring twice before cutting once.
Click to expand...


Yeah, better make sure you do it right.

The PA-28-161 I used for training and my checkride was also nose-heavy. With me and the DPE in front, we were outside the forward CG. My CFI had run into this problem so many times before that she kept a bag of sand handy for just such an occasion. Strap it in the back, redo the calculations, and the CG had moved back to within the envelope.

On some long flights, she brought her dog along for the ride. He was a pretty good sized dog and I always did the W/B math when he'd ride along. He'd climb into the baggage compartment and lie down for the takeoff and climb. Once we were cruising, he'd stand up, circle to land, then lie down and go to sleep. While he was circling I could feel the airplane ocsillate to the left, then nose down, then to the right, then nose up, as he moved.
 
There's also a 4 gal. version. I keep it in the file box because it's much easier to tie down. The water tank has a handle but that's only 1 point for tiedown. With the file box, I run the baggage straps
thru the box then thru the handle. A bit more secure.

I like the idea of the rice in the inner tube - I may make one of those. But again, everything that's ballast goes in the file box.
 
I did the weight and balance years ago with a 250 pounder up front and was well within the envelope. I've been flying with a 300 pounder up front and not noticed any issues, and had no trouble holding off the nose gear. Maybe I am just that little a pipsqueak, but you wouldn't know it from my waist size or my belly hanging out.
 
Our club's 1969 PA-28R-200 has the same problem. If I'm solo, no problem. Add a second person my size up front and I have to add weight in the baggage compartment to bring the cg aft of the forward limit. We conveniently keep some concrete blocks in the hangar for that purpose. I worry about them in a forced landing, even though they are strapped down.
 
I seem to recall the 1964 Cherokee 140 I used for my private having forward CG issues with full tanks.
 
Find a mechanic and have the airplane reweighed. Just insure to remove all non required items and clutter. Then compute your new EW and empty CG.
 
Ron Levy said:
While it's always possible to do a new weighing and start from scratch, I think most A&P's don't have the certified scales to do that, and it's a pain to do anyway (especially the fuel issues).
Click to expand...

Certified scales aren't difficult to come up with, I still own a set. As long as they are checked by a reputable scales shop (doesn't have to be aviation) they're good to go.
 
Forward CG is an issue with the Cherokee design. Two big people and full fuel doesn't work unless there is also some weight in the rear. Using actual front seat position instead of the standard mid- position can help a lot. Less fuel also helps.

My 71 Cherokee came with documentation that included the weight and arm of all installed options. My empty gross shows as a little under 1300. I've built an excel spread sheet for mine that can be easily modified for any plane, especially Cherokees. I'll try to upload it.
 
Rotor&Wing said:
Certified scales aren't difficult to come up with, I still own a set. As long as they are checked by a reputable scales shop (doesn't have to be aviation) they're good to go.
Click to expand...
If there's an automotive speed shop in town, scales certified by NASCAR or other auto racing groups may be available -- but you'll only need to use 3 out of the 4.
 
Hi everyone!

Sorry to reopen this old thread (not sure about the proper forum etiquette here), but I wanted to provide some feedback to everyone that responded to my queries!

I finally found the original factory W&B for this aircraft (buried in a rear seat pocket), which includes the 130lb "optional" equipment. I presume this to be the rear seats and possible upgrade trim, but it wasn't identified as such. The current W&B sheet is pretty close to the factory's, so I'm guessing it was accurate all along.

To mitigate the forward CG, we decided on 10 sand bags (50 cents each) each with 10 lbs of sand. With this extra weight in the baggage area (secured in a sturdy plastic container), the landing characteristics have significantly improved! A more aft CG moved us back on the W&B envelope; which now allows us the total 2150lb weight (with just the two front seats occupied). Our total allowed weight didn't suffer.

I talked to the A&P that does our annuals and he didn't have certified scales, so I think we will just stick with the calculations for now. I did write a little W&B spreadsheet for our plane to keep us honest.

Thanks everyone for all your helpful advice!!

Steve
 
Steve Job said:
Hi everyone!

Sorry to reopen this old thread (not sure about the proper forum etiquette here), but I wanted to provide some feedback to everyone that responded to my queries!

I finally found the original factory W&B for this aircraft (buried in a rear seat pocket), which includes the 130lb "optional" equipment. I presume this to be the rear seats and possible upgrade trim, but it wasn't identified as such. The current W&B sheet is pretty close to the factory's, so I'm guessing it was accurate all along.

To mitigate the forward CG, we decided on 10 sand bags (50 cents each) each with 10 lbs of sand. With this extra weight in the baggage area (secured in a sturdy plastic container), the landing characteristics have significantly improved! A more aft CG moved us back on the W&B envelope; which now allows us the total 2150lb weight (with just the two front seats occupied). Our total allowed weight didn't suffer.

I talked to the A&P that does our annuals and he didn't have certified scales, so I think we will just stick with the calculations for now. I did write a little W&B spreadsheet for our plane to keep us honest.

Thanks everyone for all your helpful advice!!

Steve
Click to expand...

I just emptied the ballast from my 140 prior to selling it Wednesday. It consisted of a few pieces of rebar used as temporary tie-downs, along with a standard-only toolkit, a quart of oil, an old GPS, some headsets, and a bunch of expired charts.

Yeah, the 140 is nose heavy, and without enough ballast, you WILL slam the nose down .001 seconds after the mains hit.
 
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