Weight & Balance Considerations
Controling a gyroplanes weight and balance provides two critical aspects to flight. The primary purpose of weight & balance computations is safety. The second aspect is to achieve the most efficiency from the aircraft in flight.
Under most, but certainly not all, kit constructions will provide for intial stability, the addition of antennas, strobe power packs and other equipment can make a large impact on a small aircraft like a homebuilt gyroplane. Improper loading or in our case location of equipment can reduce the target ceiling, rate of climb, speed, fuel consupmtion and manuevering speed. This area of your build is not to be underestimated as weight and balance can critically effect the ability to start or complete a flight or result in flight failure entirely. The affects of improperly loaded aircraft can range from overstressed components or structure associated with a severe change in flight characteristics possible destruction of equipment or loss of life can occur.
Our homebuilt gyroplanes are required, just like all civil aircraft, to have the empty weight and balance and corresponding center of gravity (c.g./cg) computed at the time of certification. The gyroplane must therefore be weighed to make a basic empty weight and balance assessment. The condition of the gyroplane must be one that is well defined so that it is possible to repeat the weighing.
This condition will normally find the aircraft with the fuel tank empty, all fly away items removed (i.e. headsets, maps ect.) and the oil is usually at its reguired level but some kit manufacturers may call for you to remove the oil, make certain to state any other equipment or conditions in which the aircraft was weighed (i.e. engine coolant at required level or any ballast permanently mounted).
Why would you want to re-weigh your gyroplane? All aircraft have a basic tendancy to gain weight overtime (just like most of us) mainly due to the accumulation of debris, oil and grease in areas that cannot be reached to clean. For most gyroplanes this area is your keel beam but a pod or enclosure can retain additional debris as well. It is for this reason that air carriers and air taxi operators are required by FAA regulations to have periodic weighings.
Privately owned and operated aircraft are not required to be regularly weighed. A time when you would want to weigh your aircraft is after completing a major repair or alteration or when the aircraft is repainted.
The weighing and cg determination will help ensure that the gyroplanes maximum gross weight and cg limits are not exceeded when the aircraft is placed into operation.
Weight & Balance Theory
I think this term is rather funny, I mean how many times a day is this theory proven over and over and yet our great scientific minds will not make it an academic law.
The theory is really very simple to understand if we consider our aircraft as a teeter totter. A teeter totter has two lever arms and a central fulcrum (pivot point). If we put a person on any arm we have added weight. The result of weight times the length of the arm is known as a moment.
Let's now consider our gyroplane. If we were able to suspend the gyroplane from a fixed point on the aircraft to a point on a ceiling and found the exact point where the aircraft would balance perfectly level we would have found the center of gravity of the gyroplane. In real world practicality an aircraft does not need to be in a perfectly level attitude but we do want something pretty close. By ensuring that we add or remove weights equally at either arm of our flying teeter totter we can control the cg to remain in its current location.
Remember what happens if we have the lever arms centered and a "large" person is at one end and a "skinny" person is at the other? The playground was a fun place wasn't it? We learned how to launch a smaller or lighter weight kid to the moon. We also learned it was still possible to play with the "larger" person if we shortened the arm on his side and lengthened to arm on the "skinny" persons side of the teeter totter. We thus redistibuted the weight over the fixed fulcrum.
As we fly the fuel on board is consumed (our large person is on a diet & losing weight fast) this results in the cg location moving. If we can keep this weight loss program within an acceptable range we will not have to change the teeter totter board length and we can continue to happily play. This is known in aviation as a cg range.
You may quickly summerize that we will have two cg ranges for our gyroplane. An empty weight cg set of limits and an operational cg range. Quite simply the empty weight cg falls within our empty weight cg range we have the basic aircraft in a stable loading configuration. Operationaly we will add passengers, fuel and maybe some cargo. The operational cg limits are the maximum (read never to be exceeded-ever) limits forward and aft that the aircraft can be loaded and still remain in a flight controllable condition.
Terms for Weight & Balance
Datum: An imagainary vertical plane from which all horizontal reference measuements are taken. As a homebuilder you determine your datum. A fixed immovable location is best (i.e. nose of the ship, mast centerline or firewall location). A measurement aft of the datum is considered a positive number. A location forward of the datum is considered a negative number. Just like a number line. Tip: if you select the datum to be the most forward point of the aircraft- all your numbers will be positive.
Arm: Is the horizontal distance of a component, item or reference point from the datum. Remember- aft of the datum is a positive, forward of the datum is a negative arm length.
Moment: Is the resulting product of a weight multiplied by its arm. A weight of 10 lbs. located 30 inches aft of the datum would have a moment of 300 lb/in. (10lb x 30in = 300 lb/in) and is transcribed as a moment (+)300. If the 10 lbs. was removed the moment would appear as (-)300.
Center of Gravity: A point about which the nose moment and tail moments are equal in magnitude.
Maximum Weight: The maximum authorized design weight of the aircraft, its contents as indicated in the manufacturers specifications.
Empty Weight: Is all operating equipment with a fixed location that is actually installed on the aircraft. Includes the airframe, engine, special/operational & required equipment, fixed ballast, hydrualic fluid, & residual fuel and oil.
Useful Load: Can be determined by subtracting the empty weight from the maximum allowable gross weight.
On various other types of aircraft specific locations are structurally integrated into the airframe for the weighing scale or load cell to be located. In many aircraft these are also the jack points for the aircraft.
Since gyroplanes all have wheels it is common practice to weigh the aircraft with the scales under the landing gear tires with the aircraft placed in a level or close to level flight attitude.
Leveling the Aircraft
The kit or plans manufacturer will normally identify the means for leveling the aircraft. The most common method is a spirit level placed on a designated location of the gyroplane structure. Another method utilizes a plumb bob afixed to a specific location and the aircraft is adjusted longitudinally and laterally.
Tare Weight: Tare is all the support equipment (jacks, blocks, chocks)that are located on the weighing scales at the time of weighing an aircraft. Tare weight will be read by the scales when weighing therefore the weight of the tare at each location must be noted and removed from the basic weight computation.
Gyroplane Weighing Prodedure
The kit or plans may include a recomended method of weighing your gyroplane but don't count on it. Simply we will require the needed equipment, a means to level the gyro and writing materials to record the data.
Note: Ensure the gyroplane is completely defueled before starting the weighing process. Wash and allow the aircraft to dry at least 24 hrs before weighing to ensure the aircraft has excess dirt and debris removed and allow any trapped water time to evaporate.
Note: USE THE KIT MANUFACTURERS RECOMMENDED WEIGHING PROCEDURES WHEN GIVEN.
Scales, hoisting equipment, jacks, blocks, chocks, sandbags, straight edge, spirit level, plumb bob, chalk line, measuring tape and kit or plans manufacturers data.
Note: You may be able to secure an inspector who provides weighing services. This person will have the required equipment with them when they come to do the weighing. They may ask to see the aircraft prior to weighing day to ensure they will have or build the needed equipment. As would be expected for services rendered this will all come with a price and you will still be required to prepare the aircraft for weighing. The inspector will record and compute all data for you.
Upon reviewing the kit or plans recommendation or by logical deduction if no procedures are provided, select the required equipment for the weighing process. For example if a spirit level is required a plumb bob may or may not be needed as well.
Preparations for Weighing the Gyroplane
Ensure the aircraft is defueled and other lubricants are at their proper level for weighing.
Ensure all fly away gear is removed.
Ensure all doors and panels are in their normal in-flight position.
Ensure the aircraft is clean and dry, no excess grease, oil, dirt or water.
Place rotor blades over the longitudinal axis of the gyroplane.
Measure the distance from the datum to the main weighing points centerline, then measure to the secondary weighing point (nose or tail wheel).
Calibrate zero on scales.
Place aircraft on scales and level as required.
NOTE: Hanger doors and all forms of breeze should be eliminated before actually weighing the aircaft.
Reecord the Weighing
When satisfied with the gyroplanes attitude and level position, record the scale readings. It is common practice to do this procedure three times and using the average of the three recordings.
Compute the empty weight: add all weights (less tare weight) and this is your gyroplanes empty weight.
Determine the empty weight cg location: use the formula W x A = M
Weight x Arm = Moment.
W (lbs.) x A (in.) = M (lb/in.)
L Main 200 x 58 = 11,600
R Main 212 x 58 = 12,296
Nosewheel 180 x 16 = 1,880
Now add all weight: 200+212+180= 592 lbs (gyro empty weight)
Next add all moments: 11,600+12,296+1,880= 25,776 lb/in.
Last Step: divide the sum of the moments by the sum of the weights and yur result will be the empty weight cg location in inches.
592 (lb) = 43.54 in. (empty weight cg location)
Now assuming a listed maximum gross weight of 1,800 lbs. we can find our useful load. Subtract the empty weight from the gyroplane gross weight.
1,800 - 592 = 1,208 lbs. (maximum useful load)
From this basic data you can now compute for your actual mission or flight weight and balance condition. Don't forget to check that the cg forward and aft limitations are not exceeded. Compute for aditional pickups, fuel burn and other mission demands. Check for takeoff, inflight and landing weight and balance and cg locations.
Weight and Balance is all about safety, safety of the structure, safety of the handling characteristics and ultimately the safety of the gyroplane occupants.
The resource used for this page was FAA publication AC-65 wi change 1, first Edition 1970, First revision 1976, change 1 dated 3-31-1999, Printed by the Government Printing Office United States of America.
The information provided is for recreational use and entertainment puposes only. This information is general in scope and not specific to any type, brand or model of gyroplane. Readers are strongly urged to USE THE KIT MANUFACTURER OR PLANS RECOMMENDED METHOD OF DETERMINING THEIR GYROPLANES WEIGHT AND BALANCE AND CG COMPUTATIONS. WWW.gyroplanepassion.com assumes no liability, for the information provided. It is the responsibilty of the gyroplane builder to ensure the accurate weighing computation, recording and assessment of the data to ensure their aircraft is safe for flight. Builders are urged to utilize the EAA Technical Counselor and Certified Liscensed Technicians to ensure proper weighing procedures are followed.