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gizzard

%MAC and limits

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Guys, just sort of consider the source here, and bear with me:unsure: I was looking at the picture of what appeared to me as a stretched C130, couple weeks ago here on the site, and my minds got to waundering back to CG\'s and so on. I am curious as to how dfferent the limits, ect are for a stretch versus the common old \"E\" I flew.are the stations still determined from in front of the nose?How much different are the H\'s and J\'s in reference to weight and balance, load planning, etc? No particular reason to want to know this stuff, just nostaglia I guess:lol:

Load Clear

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I am not sure but most of the stretched Herks I have seen have had a plug forward as well as aft of the wings so it would seem that the CG shouldn\'t be too different.

Just my guess.

Dan

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gizzard wrote:

Are the stations still determined from in front of the nose?

From: pjvr99 in this thread http://herkybirds.com/index.php?option=com_fireboard&Itemid=26&func=view&catid=6&id=2112

Don\'t know the -20, but -30 was 100\" from FS257 marked 257E, 277E, 297E, etc; and 80\" from (I think) FS797 marked 797E, 817E, etc. The origional Flight Stations retained their numbers while the plugs/inserts carry the \"E\" to denote Extension

Please note, although no boardcode and smiley buttons are shown, they are still useable

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The double streched models, civilian world anyway, have charts that look similar to the short military models. There doesn\'t seem to be a lot of variation as far as limits for flight. I have not seens the single-stretch MAC limit chart for flight.

Wt and Bal is calculated based on \"trim station\" versus fuselage station and we end up dealing with positive and negative numbers in the calculations, though both methods are just different ways to reference the datum line.

Essentially, there isn\'t a lot of difference. We still have forward and aft limits that are similar, but of course, we do have conflicting documents.

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MAC 164.5 INCHES: LEMAC 687.4 \"J Model -30\"

MAC 164.5 INCHES: LEMAC 487.4 \"J model short\"

These are the numbers right from my -9...hope this helps

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So did they move the reference point? Otherwise, with a 100\" forward plug it would be 587.4\" to LEMAC.

loadsmith wrote:

MAC 164.5 INCHES: LEMAC 687.4 \"J Model -30\"

MAC 164.5 INCHES: LEMAC 487.4 \"J model short\"

These are the numbers right from my -9...hope this helps

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gizzard wrote:

Guys, just sort of consider the source here, and bear with me:unsure: I was looking at the picture of what appeared to me as a stretched C130, couple weeks ago here on the site, and my minds got to waundering back to CG\'s and so on. I am curious as to how dfferent the limits, ect are for a stretch versus the common old \"E\" I flew.are the stations still determined from in front of the nose?How much different are the H\'s and J\'s in reference to weight and balance, load planning, etc? No particular reason to want to know this stuff, just nostaglia I guess:lol:

Load Clear

Center of gravity limits are based on the chord of the wing, not fuselage length. All fuselage length does is add more stations but the end result of the computations will be the same and so will the takeoff and landing CG limits at corresponding gross weights. The Leading Edge of MAC (LEMAC) will be different but actual center of gravity is based on where it lies on the Mean Chord of the Wing (MAC.) US manufacturers use a point at or near the nose of the wing for weight and balance computations but they could use any point. British manufacturers use the center of the MAC as the reference point. It\'s been decades since I\'ve done a weight and balance on a C-130, but wasn\'t the reference point 30 inches forward of the nose?

The wing on any airplane (rotors on a helicopter) are the only part that actually \"flies\" (produces lift) and the balance point is on it. The tail exerts a downward moment to hold the nose up and does not produce lift. For the CG limits to change, the chord of the wing would have to be changed. The forward limit is the point at which the wing can not be rotated enough to produce lift or control forces will be exceeded while the aft limit is the point at which the wing will become unstable. CG also plays a part in aircraft controlability after the loss of the critical engine.

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\"...The wing on any airplane (rotors on a helicopter) are the only part that actually \"flies\" (produces lift) and the balance point is on it. The tail exerts a downward moment to hold the nose up and does not produce lift. \"

Hmmm...conventional gear aircraft (C-47, PA-12, etc.) ?

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Fred wrote:

\"...The wing on any airplane (rotors on a helicopter) are the only part that actually \"flies\" (produces lift) and the balance point is on it. The tail exerts a downward moment to hold the nose up and does not produce lift. \"

Hmmm...conventional gear aircraft (C-47, PA-12, etc.) ?

Let\'s see, the last time I saw a C-47/DC-3 I\'m pretty sure it had retractable landing gear. A PA-12 is fixed gear. But gear has nothing to do with lift, but rather with drag.Gear retraction may affect CG, depending on how it retracts, but that is taken into consideration when performance data is established by the manufacturer. Lift is created by an airfoil and the only airfoils on a conventional fixed-wing airplane are the wings, horizontal stabilizer and vertical stabilizer. Ailerons, elevators and rudders are also airfoils but their purpose is to affect the forces on the main airfoils. Lift is produced by the low-pressure are created on the top of the wing by air flowing over it faster than going beneath. The horizontal stabilizer on all fixed-wing airplanes is designed so that the low-pressure area is on the bottom and thus forcing the tail downward. A tail-stall will cause the nose to pitch down. \"Flying wings\" such as the B-2 are one big airfoil. The C-130 is conventional and all lift is generated by the wing.

I don\'t know why Lockheed chose to use Percent of MAC for its charts since all that is needed is the actual ARM. Perhaps it has to do with the size of the charts. For that matter, they could have used feet instead of inches as the reference points as it doesn\'t matter which is used for computations.

Lengthening the fuselage on an airplane may affect where the CG will end up - if the plug is forward of the wings it will tend to be more noseheavy - but the CG limits are going to be the same at any given gross weight.

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SamMcGowan wrote:

Fred wrote:

Let\'s see, the last time I saw a C-47/DC-3 I\'m pretty sure it had retractable landing gear. A PA-12 is fixed gear. But gear has nothing to do with lift, but rather with drag.Gear retraction may affect CG, depending on how it retracts, but that is taken into consideration when performance data is established by the manufacturer. Lift is created by an airfoil and the only airfoils on a conventional fixed-wing airplane are the wings, horizontal stabilizer and vertical stabilizer. Ailerons, elevators and rudders are also airfoils but their purpose is to affect the forces on the main airfoils. Lift is produced by the low-pressure are created on the top of the wing by air flowing over it faster than going beneath. The horizontal stabilizer on all fixed-wing airplanes is designed so that the low-pressure area is on the bottom and thus forcing the tail downward. A tail-stall will cause the nose to pitch down. \"Flying wings\" such as the B-2 are one big airfoil. The C-130 is conventional and all lift is generated by the wing.

I don\'t know why Lockheed chose to use Percent of MAC for its charts since all that is needed is the actual ARM. Perhaps it has to do with the size of the charts. For that matter, they could have used feet instead of inches as the reference points as it doesn\'t matter which is used for computations.

Lengthening the fuselage on an airplane may affect where the CG will end up - if the plug is forward of the wings it will tend to be more noseheavy - but the CG limits are going to be the same at any given gross weight.

Hmmm... Yes, I\'m pretty sure the C-47 has a retractable gear. Last time I rode one was 1972, so its been a while. I know a PA-12 is fixed gear conventional gear or \"tail dragger\". Did you ever fly a tail dragger? I did. But that too has been more than 30 years ago. I do recall picking the tail up sometime after starting takeoff run, and relaxing some forward pressure on the stick to allow the tail to drop a little and establish takeoff attitude as takeoff speed is reached. I\'m not sure what force could cause the tail to rise when I did this. Not gravity; I\'m sure. Not thrust...well, maybe reaction to the propeller stream being deflected by the elevator? That\'s a possibility. Drag? Not likely. Hmmm...lift? Well; I suppose that\'s about all that\'s left. Maybe there\'s such a thing as negative lift? Or lift in a negative direction?

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The MAC was used by all cargo aircraft in the militry.The FAA test in about 67 used plus and minus moments.I worked for Slick in Cleveland in 55-56 and we used a form of moments on C-46 and DC-6 aircraft. As an instructor I often marked the bulkhead with the leading and trailing limits and let the student know that he had to fall in that margin. It made the job a lot easier. Up until the earliey 60s, loadmasters had an air transportation AFSC and did not have to work moment for the test. We had to add up the moments and then interpolate in the dash 5. There were several acft that the gear would change the MAC. The old Shakey was changed by 2%.

jim

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The first thing to consider is that the maximum AUW of the airplane has not changed.

The next thing is the C of G limits depend upon the actual weight of the airplane at the time the mission is started.

The wings on a stretched C130 and L100 are basically the same and for this purpose are the same. As the C of G limits are set by the MAC then again nothing changes. For those who do not quite understand MAC is an average of the wing chords.

My understanding the main restrictions on the airframe, is the rotation and touch down angle. This is to stop the tail skid being written off during landing and take off.

How is the job going, mother and lovely daughter going fine I hope. Great to see you posting again.

All the best everyone for Xmas.

Regards

Col

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I loved my slip stick, " LOAD ADJUSTER '" TAC allowed us to use it ILO long math & moments. It's been to long ago, but even in TAC, I think we had to use moments on Check Rides.

I still have my C-130A Load Adjuster. The letters on the leather storage case has the words " U. S. PROPERTY " on it. Once in a while I'll get it out and play with it.

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Imiss using the slip stick, the younger guys at my reserve unit look at me when ever I mention it, like what is that they have never seen one

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At Hickam the FE section did all the W&B in moments for the birds and kept a "canned" copy of it in the FE section. We had to redo them like every 3 months or so. Since the birds weight and CG never changed for our typical missions, or at least very little. Maybe an extra body or so.

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At Hickam the FE section did all the W&B in moments for the birds and kept a "canned" copy of it in the FE section. We had to redo them like every 3 months or so. Since the birds weight and CG never changed for our typical missions, or at least very little. Maybe an extra body or so.

When I was in the Gunships many moons ago the FE filled out the form F we used the "canned" form F, good for 3 months, the only time anything changed them was when a bird went to depot.

Was my extra duty for the first 5 months I was in Thialand. Had to fill them out for all the planes and then take them to wing stan eval for there blessing.

When we picked up the SVN A model and flew them to Guam when Nam fell, they all had the slip stick in them, so made it easy to do the W&B.

Mike

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Hello everybody.

In my Squadron there are many contravertial oppinions about everything that has to do with CG limits of the C-130.

I am about to have a big test concidering my proffession (LoadMaster), and I want to break all the miths and half-true explenations, and, once and for all, to settle down the argument about the whole CG subject.

As far as I know, the CG Limits Chart (Allowable %M.A.C location relative to the Gross weight of the airplane expressed in 1,000 Pounds) combines in it the allowable CG limitations for all airplane operation conditions (Take-Off, Landing, Flying in the ground-effect area, Flying outside/above the ground-effect area, Flight in normal weather, Flight in turbulance weather, etc.) all togheter in one chart. In other words, we might have had a different chart for every different condition of those mentioned above, and we would have had to calculate the CG limits for every different flight condition in a different chart, and then cross all the figures together, and then we would get our generall CG limits for the whole flight. But What the Chart did is that it already crossed/combined all those different charts into one simple chart.

There is a reason for the front CG-limit and a reason for the rear CG-limit. We can see on the chart that it is drawn from 4 different mathematical Function-Curves combined together (two straight vertical lines and two curved lines).

Well, I will get to the point:

The thing I want to know is what does every curve stand for, what are the reasons for the speciffic numbers (15%, 30%), and what is the fhysical reason for every curve in the shape of the CG Limitations Chart.

This is one of the things I will have to explain in the test I'm about to have.

Can anyone answer my question? Or direct me to someone who might know the answer?

Thanks a-bunch, Yoel.

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Guest USCGC130J

We have a canned form f on every aircraft, this is updated every year or if aircraft goes to PDM. This is for standard config, but if we carry more then 12 people, more than 44,000 pounds or cargo in excess of 1500lbs we have to fill out one. The really nice things as that we have the Canned form F on a PDA now which is very nice and makes form f's very quick and easy.

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gizzard wrote:

Center of gravity limits are based on the chord of the wing, not fuselage length. All fuselage length does is add more stations but the end result of the computations will be the same and so will the takeoff and landing CG limits at corresponding gross weights. The Leading Edge of MAC (LEMAC) will be different but actual center of gravity is based on where it lies on the Mean Chord of the Wing (MAC.) US manufacturers use a point at or near the nose of the wing for weight and balance computations but they could use any point. British manufacturers use the center of the MAC as the reference point. It\'s been decades since I\'ve done a weight and balance on a C-130, but wasn\'t the reference point 30 inches forward of the nose?

The wing on any airplane (rotors on a helicopter) are the only part that actually \"flies\" (produces lift) and the balance point is on it. The tail exerts a downward moment to hold the nose up and does not produce lift. For the CG limits to change, the chord of the wing would have to be changed. The forward limit is the point at which the wing can not be rotated enough to produce lift or control forces will be exceeded while the aft limit is the point at which the wing will become unstable. CG also plays a part in aircraft controlability after the loss of the critical engine.

Yes, the RDL on the stubby is 30" fwd of the nose and on the stretch is 130".

And when referring to Mean Aerodynamic chord, the actual 15-30 % envelope is very small in relation to the overall size of the wing.

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Yes, the RDL on the stubby is 30" fwd of the nose and on the stretch is 130".

And when referring to Mean Aerodynamic chord, the actual 15-30 % envelope is very small in relation to the overall size of the wing.

There is a difference in stretch versions then. Our civilian reference datum is right at the reference screw just forward of the forward nose gear door, about 70 inches forward of the nose landing gear strut. While I have a reference put out by Lockheed that states that to be true, I can then provide evidence that it is not since FS 245 is at the same location on our aircraft as it is on stubby C-130s. There are many disagreements between our books and the Type Certificate Data Sheet. I guess it has never been important enough to correct.

I certainly agree about MAC being the same since the wings are the same. Procedurally it is different in the computation, but the end result does not change.

Edited by Steve1300

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