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weight and balance


kgassmann

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I just rechecked W&B for my 2005 CTSW.

 

For what it is worth...

 

It is possible to get the CG too far forward when the tanks are full, the baggage compartment is completely empty and there is a single pilot who shall we say weighs less than the FAA standard passenger weight (male, summer). I did the check because the guy that sold me the airplane talked about a female pilot flying the plane and they had to put ballast in the baggage compartment when she flew solo. So, while this scenario may be uncommon. It is possible to bust the CG in the forward direction on the CTSW.

 

Given that the CTLS is longer with the weight of the tail even further from the center of gravity, maybe that model is more forgiving in this regard.

 

At what weight for the pilot did the CG go out on the forward side? Does your airplane have an empty weight CG range, and does your airplane fall within the range? I know the 2006 I had was in the range, and could not be loaded outside of the CG range. There is also a published minimum weight of 120 pounds for a single pilot in the AOI.

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At what weight for the pilot did the CG go out on the forward side? Does your airplane have an empty weight CG range, and does your airplane fall within the range? I know the 2006 I had was in the range, and could not be loaded outside of the CG range. There is also a published minimum weight of 120 pounds for a single pilot in the AOI.

 

 

Tom,

 

Good questions! Being of slight build, this discussion is more than academic for me. I fly with some weight in baggage compartment just because I don't want to be even close to the forward limit.

 

I remembered that there was a maximum pilot weight per seat. I had forgotten about the minimum pilot weight per seat (120 lbs.). The story that I was told when buying the plane referred to a 120 lb woman.

 

I was using the value of 13.28 inches for the forward CG at maximum weight (29 Apr 2008 AOI). Using that value with my aircraft weight (694 lbs) and arm (11.71 inches), full fuel (204 llbs., 11.71 inches) and zero baggage, a single pilot weight of 190 lbs gives a total weight of 1088 lbs and a moment arm of 13.25 inches. That is 0.03 inches forward of the max. weight CG limit.

 

I did not realize that their was such a thing as an empty weight CG (...or least that it was a value that was provided by the manufacturer). You are correct that both the original 28 Feb 2005 AOI for my airplane and the 2008 AOI list an empty weight CG range. Changing the previous calculation to a single 120 lb pilot, the moment arm for my aircraft is 12.76 inches. The empty weight CG range is 11.02 inches (280 mm) to 12.60 inches (320 mm) from my 2005 AOI. The 2008 AOI lists an empty weight CG range of 9.45 to 14.17 inches. There are the numbers for the people that are interested in checking my math.

 

Now that I know that there is a CG range for max. weight and a CG range for empty weight, my question is what does one do at intermediate weights? Does the CG range vary in a linear fashion with weight? Would the FAA hold one to the more restrictive limits?

 

Thanks for your questions...

 

--Mark

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This is all pretty simple. You cannot exceed max gross weight and your CG must be within allowable limits. You have to meet both, not one or the other. It's why you can't solo a J3 from the front seat.

 

I know you have flown a J3, but you might want to do a little research before you throw blanket statements like that out there.

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Many others have published W&B spreadsheets. Here's my W&B I developed for my 2006 CTSW and that I've posted a few times in the past on this forum. It is very simple to use and might help one to quickly determine if CG is correct. The CG resultant cell goes "red" when CG is out of limits. This has accommodations for baggage. One can revise the cells if needed to customize this spreadsheet for individual aircraft. To do this, go to "tools" and unlock the cell. This spreadsheet is based on My 2006 CTSW weight of 738lb.

N9922Z W&B worksheet_130312.xls

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Why don't you just tell me? It's been 45 years since I've flown a J3. No need to be smart about it, although that seems to be the norm on this site.

 

I'm sorry. I was just replying to what seemed like a smart statement to me. I think most of us know we need to be within gross weight limtis and center of gravity limits. Maybe it is just the internet and how you read the words.

 

BTW I like students to look things up, because I think the learn better than just giving them the information.

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I'll stand by my statement then. The J3 I am referring to is the one I flew 45 years ago that was placarded "solo rear seat only." Also, in an earlier post someone asked a question that implied some confusion of CG limits vs gross weight and which the FAA would give priority to, or some such question as that.

 

The placard for the J3 is recomended by the manufaturer. You can often put someone in the front seat solo and still be within CG. The big thing was with the students who were learning to fly. By having the student in the back and the instructor in the front closer to the CG when the instructor got out there was little change. The other big plus was it was easier to see what was going on from the back seat.

 

A few years ago I had an instructor who I was giving a tailwheel endorsement to in a J3. After the first lesson he insisted that he could do better in the front seat. Next lesson I let him try from the front seat, and after that I was able to put him back in the back seat and teach him something.

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I just did one for the SW I used to own, and with full fuel, a 120 pound pilot the arm figures to be 13.63.

 

Assuming Dick's SS represent's his CT, it is 20lbs heavier and has and empty CG 1 1/2" farther aft than mine. As CTs got heavier over time their CGs moved as well. This is why we shouldn't give blanket advice based on our own experience.

 

What about the Center of Gravity Limit Chart?

 

My CT doesn't have one in the POH so I assume that my forward limit is the same at all weights but if I look online at a AOI I see the chart and it sets the forward limit according to weight.

 

post-6-0-17949800-1389386472_thumb.png

 

Depending on your empty weight, your empty CG and even your POH your CT may or may not be easy to get out of the envelope, better check for yourselves.

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I just rechecked W&B for my 2005 CTSW.

 

For what it is worth...

 

It is possible to get the CG too far forward when the tanks are full, the baggage compartment is completely empty and there is a single pilot who shall we say weighs less than the FAA standard passenger weight (male, summer). I did the check because the guy that sold me the airplane talked about a female pilot flying the plane and they had to put ballast in the baggage compartment when she flew solo. So, while this scenario may be uncommon. It is possible to bust the CG in the forward direction on the CTSW.

 

Given that the CTLS is longer with the weight of the tail even further from the center of gravity, maybe that model is more forgiving in this regard.

I tried to find a way to get mine out of forward CG balance and I can't do it, but I have a CTLS so maybe that is the difference.

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I tried to find a way to get mine out of forward CG balance and I can't do it, but I have a CTLS so maybe that is the difference.

 

Your empty weight has to be light enough and your empty cg has to be forward enough and even your passenger weight has to be low enough. A heavier CTLS is less likely to be that far forward.

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I tried 5 gal. of fuel, 20 lbs of weight in each of the foot storage areas (only negative moment), and no other weight and it was still within range. I think the longer tail moment makes the difference. It is possible, but not easy to go the other way without going overweight in the process.

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I tried to find a way to get mine out of forward CG balance and I can't do it, but I have a CTLS so maybe that is the difference.

 

Since I have a CTSW and not a CTLS, I don't have those specific numbers. But my understanding is that CTLS airframe was "stretched" behind the pilot's seats compared to the CTSW. This would put that new airframe weight behind the CG location for the CTSW. Given similar avionics, the same engine, etc. as a CTSW, I would expect it to be harder to get the CG too far forward on the CTLS.

 

I offered my specific example of an early lighter model CTSW as a reminder that at some point this does become unique to each aircraft. As someone else phrased it, a warning against making sweeping statements.

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My apology for being imprecise when I used the term "sweeping statement".

 

I was referring the impression being left by some posts that it was impossible to get a CT aircraft out of balance. I used my aircraft as an example that for at least some conditions my CTSW aircraft can be underweight and still be out of balance. Which is an unsafe situation and a rule violation.

 

I did not mean to target or respond to any one in particular. My apology if I have offended anyone.

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CT The fuel on the LS moves the CG back, not forward. The only negative moment on the LS is the foot storage. My 40 lb total there is not allowed but I exaggerated if to see if I could get a forward balance out of the envelope. Full fuel brings the cg back, but not much.

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CT The fuel on the LS moves the CG back, not forward. The only negative moment on the LS is the foot storage. My 40 lb total there is not allowed but I exaggerated if to see if I could get a forward balance out of the envelope. Full fuel brings the cg back, but not much.

 

Doug,

 

The arm doesn't have to be negative in order to move the CG forward of the permissible envelope. The datum is the leading edge but it could be anything. Depending on what is used as datum some, all or none of the numbers could be negative yet the W&B would work the same. Full fuel moves the CG forward and burning fuel moves it aft (relative to the envelope not the datum).

 

If your CT can get forward of the limitation it will be with no luggage, full fuel and a light pilot. Emptying the fuel tank to 5 gallons will put the otherwise same configuration back in the envelope.

 

post-6-0-58169400-1389452174_thumb.png

 

In this CT W&B the fuel's arm is 11.8 inches which is positive but forward of the envelope that starts at 13.28 inches so more fuel moves the CG forward and enough fuel will get you out of balance unless you get full first.

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It was not a sweeping statement, it was a correct statement. It had nothing to do with training students, it was to stay within the forward CG when flying solo.

 

 

"Quick question. I was just wondering if a Piper J-3 Cub (the original one) could be flown solo from the front seat? That is one of the things I do not like about the J-3 Cub because I heard that you can only fly solo from the back seat. With an STC or some kind of modification, can I fly it from the front?

 

Not if it's a stock aircraft, but there are modifications that can make it possible. I have flown one that has an 85 hp engine and a starter and wing tanks and it can be flown from the front seat because of the weight shift. The only problem is that the useful load is much reduced...

Also, frankly, the rear seat is more fun and the visibility is better (except upwards.)!"

 

Just a couple clips from the FAA TCDS.

 

Empty Weight C. G. Range If placard "Solo flying in rear seat only" is installed (See NOTE 2)

(+8.5) to (+20.3)

When empty weight C. G. falls within range given, computation of critical fore and aft

C. G. positions is unnecessary. Range is not valid for non-standard arrangements.

NOTE 2 Placard front cockpits of Models J3C-50, J3C-65, J3C-50S with McKinley floats and J3C-65S with

McKinley floats: "Solo flying from rear seat only."

Placard may be removed if individual aircraft actual

weight and balance shows that the approved C. G. limits will not be exceeded under any loading condition.

Manufacturer recommends that all J-3 airplanes be flown solo from the rear seat.

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I was not trying to say all CTSW's can't be loaded outside of limits. What I was trying to relay is from my A&P training if an airplane has a empty weight CG range and the empty weight CG falls within the range then fore and aft CG computations did not need to be done.

Maybe Flight Design is using the term differently.

 

Empty Weight Center of Gravity Range

For some aircraft, a center of gravity range is given for the aircraft in the empty weight condition. This practice is not very common with airplanes, but is often done for helicopters. This range would only be listed for an airplane if it was very small and had limited positions for people and fuel. If the empty weight CG of an aircraft falls within the empty weight CG limits, it is known that the loaded CG of the aircraft will be within limits if standard loading is used. This information will be listed in the Aircraft Specifications or Type Certificate Data Sheet, and if it does not apply, it will be identified as “none."

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