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How are you computing your weight and balance?

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Here is a new one for me.  Presenting a product from a company that is developing applications for general aviation and adding something new to the aviation blog.  When getting familiar with an airplane, it is critical to load the airplane properly which usually is a series of typical load scenarios and computing that load to maximum gross take-off weight using fuel as the main variable.  As most light aircraft cannot load full fuel and fill the seats, it is imperative to make sure the airplane is not exceeding the airframe design limits for weight.  Even more important, is how this load is distributed so that the stability and controllability of the airplane is maintained, especially when you consider how adversely an aft C.G. affects recovery from a stall, and has a negative affect with multi-engine airplanes regarding controllability.

 

Lets talk about why the weight of the airplane is so important.  If you look at a Vg diagram, (V = Velocity, g = g-loading) the purpose of the Vg diagram is to explain the relationship of speed and the vertical gust load factor that an airplane is certified for.  This is an engineering and stress computation for the structure of the airplane, and shows how maneuvering speed is derived, which is defined as the speed at which full control deflection can be applied without any structural failure.  The question that most private pilots fail to answer correctly, and that is: Does maneuvering speed go up, or go down with weight?  In other words, if the airplane is flying 500 lbs under max gross weight, will maneuvering speed be higher or lower?  The answer is: Maneuvering speed is LOWER with less weight on the airframe.  For most people, it seems to make sense that because the airframe is lighter, it can fly at a higher indicated airspeed because the structure has to carry less weight, which is saying the wing has to support less weight.

The speed Vs. load factor for airplanes flying within the design envelope.

The speed Vs. load factor for airplanes flying within the design envelope.  Click for larger viewing.

As you can see by the diagram, maneuvering speed for this particular airplane is 4.4 + G units, and -1.76 which tells me this is a Utility category certified airplane.  By following the upper arc showing along the line of “accelerated stall”, the airspeed at which the wing will stall can be followed along the line and at how many G units the loading will be before the wing stalls.  When the wing stalls, the G loading is reduced, preventing the G force from increasing.  If you follow the arc along the line and take an airspeed for example of 100 miles per hour, you can intersect along the line as to what G loading will be experienced before you encounter an accelerated stall.  In this case, 100 mph yields approximately 2.2 G units and is below the structural limitation….so why don’t the manufacturers recommend this as the maneuvering speed? The answer is that you also want maximum controllability, which is airflow over the flight controls to maneuver the airplane.  If you ever encounter strong turbulence, or wake from a heavy (over 300,000 lbs gross weight) airplane, you want to have the maximum controllability while maintaining structural safety.

If you continue following the arc higher, you can see that you are risking structural damage above 138 mph if you encounter a vertical gust exceeding 50 feet per second.  That really is the purpose of the Vg diagram, to build an envolope to demonstrate a 50 fps vertical gust.  You can certainly fly an airplane in the caution arc on the airspeed indicator, but you can now see why it is only approved in SMOOTH AIR ONLY!  By that I  mean, if you are flying in the caution arc of your airplane, and encounter a 50 fps vertical gust, the airframe will experience a G loading that exceeds the airframe structural limitation.  If you look at flying the airplane at 160 mph indicated, and follow the vertical line to the arc representing an accelerated stall, you will see that the G loading will be approximately 6.2 which will damage the structure and if a strong enough vertical gust is encountered…say goodbye to the wing or tail!

Therefore, it is important to know the weight of the airplane, and consider the maneuvering speed for that weight.  That is the reason they do not put a Va indication on the airspeed indicator, because it is variable.  So what about stability?  We should know by now that an airplane is more stable with the weight distributed forward, while loading aft causes the airplane to be slight more unstable…so why is this?  An airplane is certified to maintain a trimmed airspeed, and it does this by countering the nose down tendency caused by the center balance point on the airplane being AHEAD of the center of lift from the wing.  While the wing is producing lift, it is trying to pitch the airplanes nose down, while the tail is trying to counter this with down force all the time to “balance” the airplane.  We know that all things being equal, if we increase the airspeed over an airfoil, that more lift is produced.  The horizontal stabilizer is an airfoil that produces lift based on the amount of air that is flowing over it. That is why trim speed is what it is all about.  If you trim an airplane to fly at 100 knots, and you increase the speed of the airplane, more airflow = more lift and the lift is DOWNWARD on the tail, causing the pitch of the airplane to raise. Raising the nose causes the airspeed to decelerate which is less lift, and the nose lowers again.

The stability is what they refer to as a phugoid oscillation that must be dampened in a certain number of phugoids.  I am not sure how many cycles the FAA has for requirements for the airplane to assume level flight at the trimmed airspeed, but that is the purpose of longitudinal stability.  Of course, one of the critical reasons why weight and balance is important to calculate, is that if you have a c.g. too far aft, recovery from a stall may be impossible!  Think about how that would feel, you get the airplane too slow, the airplane’s main wing stalls, and you cannot recovery by pushing the controls all the way forward to decrease the critical angle of attack!  In addition to an aft of c.g. location in weight and balance, the airplane will tend to require more attention to keep the airplane from climbing or descending, with very light elevator controls.  If you fly a light twin or any multi-engine airplane without center-line thrust, the aft c.g. affects the ARM from the rudder which will limit the effectiveness for controllability.  Vmc is the speed at which the airplane can no longer be controlled with one engine feathered, the other engine putting out full power.  If you go below this “red-line” speed, the airplane will roll over on its back with you applying full opposite rudder and with opposite aileron control.

My point to reviewing weight and balance, is that operating the airplane within the certification parameters is extremely important. By having a program that makes this easy to adjust the weight, fuel loading, and presents the information graphically, is what it is all about.  What I find most interesting, is that if you have a c.g. moving aft with fuel burn, which the Beechcraft Bonanza does, this can be shown graphically for zero fuel after your take-off fuel loading has been calculated.  I recently was helping a friend out who had a Beechcraft Baron 55 that he was flying to the Virgin Islands, and was going to have a lot of people and luggage.  It was easy to plug in the information, and we ended up shifting some luggage to the nose compartment, because the airplane quickly was at the aft c.g. point.  Having a program that enables you to quickly figure out this equation, makes for safer flight…his change for his trip?  2.5 hour legs instead of a 4 hour leg, which with people on-board isn’t such a bad idea anyway.

Looking at the product from Roy Kronenfeld, it appears that it is the real deal, well thought out and very inexpensive.  I like a program that is easy to set-up, easy to use, and provides nice graphics with little work, and that is what you have here.  Below is the information on the company and how the app was developed.

Introduction:

Aviation W&B Calculator offers pilots the finest combination between simplicity and professionalism in terms of weight and balance calculations for general aviation airplanes. Aviation W&B Calculator has been in the App Store for one year and as of March 2013 has been purchased by more than 14,500 pilots from 80 different countries. Aviation W&B Calculator holds the highest rating in the app store compared to other weight and balance apps with more than 570 reviews of 4.7 star average. AOPA and Sporty’s as one chose Aviation W&B Calculator to be one of their top 10 aviation apps.

 

Aviation W&B Calculator leading features:
– Build your own airplanes templates easily
– More than 250 predefined airplane templates
– Enjoy a professional load sheet summary
– Save/Email/Print load sheet summary
– Normal, Utility and Aerobatic categories
– Share your airplane templates with friends
– Variable fuel arm support
– Top quality cg limits envelope graphs
– Manage your tail numbers easily
– Export/duplicate/backup your templates
– Metric and U.S. units are supported
– Get alerts when exceeding max weights
– Regular and Moment envelopes
– Know your maneuvering speed in regard to TOW
– Top quality customer service tickets system

 

Unique App features:

1. Free growing templates library – Aviation W&B Calculator provides you with the option to use its growing airplane templates library which being fed by pilots who use the app and share their built templates. If your airplane is not in the library, Aviation W&B Calculator gives you the option to build your airplane template in only few steps. As of March 2013 the app accumulated more than 250 templates, which includes most of the Cessna, Piper, and Cirrus airplanes as well as many light sport and experimentals. These templates are being checked and compared against official documents of the airplanes before they are published in the library. However, it’s highly recommended to compare your POH with the template settings in order to maximize results accuracy.

 

2. User interface – One of the most important features that other weight and balance apps did not manage to maintain is the simplicity and clarity of the user interface. In other words, the content of the app is very straightforward and easy to use.

 

3. CG limits envelopes graphics – Aviation W&B Calculator works with a powerful envelope graphics engine which provides a closer and clearer look on the airplane’s cg limits envelope with a clear flight path starting from takeoff to landing to zero fuel condition. That way, a pilot can assure that his airplane will stay within the limits during each part of the flight. Moreover, some POH’s use their cg limits envelope in terms of moments. In that case, Aviation W&B Calculator will know to show you the envelope in moment format.

 

4. Load Sheet Summary – One of the most noticeable feature in the app is the load sheet summary page which contains all the information concerning your weight and balance calculations such as a detailed list of all loaded items, a small edition of the cg limits envelope, total weights such as payload, zero fuel, ramp, takeoff, and landing weight, and even the option to write notes and to add a signature if needed. The summary page can be printed, saved as an image on your device, or emailed as a PDF file.

 

5. Customer Service – One major topic that is very noticeable in many of the Aviation W&B Calculator app reviews is the exceptional customer service. Many users claimed to receive response to their questions within minutes by phone or email, others told that the developer took his time to research and build their template when they had trouble doing so. According to the apps description, customer service is not less important than the quality of the product itself, which is a big plus for the clients.

 

6. Variable Fuel Moments – Some airplanes with swept wings like the Cessna Citation Family, needs a closer look when it comes to fuel arm calculations. In these airplanes, the arm of the fuel changes with fuel burn. Aviation W&B Calculator supports these calculations for up to 1 moments table.

 

Creator’s Bio:
Aviation W&B Calculator was developed by Roy Kronenfeld. Roy began his career as a skydiving instructor. About 6 years ago he joined an international company based in Germany and was part of the web development team for 3 years. At the beginning of 2010 he began to develop iOS applications and during that time he also gained his private pilot license. He has logged more than 200 hours and still enjoys the skies on a regular basis. On January 2012 Aviation W&B Calculator was born and grew from a little dedicated app for Cessna 172SP’s to a worldwide top rated app for weight and balance with support for 95% of the general aviation fleet. Today Roy is living in Florida USA studying computer science and working on the next best aviation app.

 

Conclusion:

As of March 2013, the App Store offers few weight and balance apps that cost from $0.99 to $199.99. Aviation W&B Calculator is the perfect combination between a great product and a fair price. Don’t wait, weight!  http://www.aviationwb.com

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