The Aerocomp News

Volume 4 Issue 1 ONLINE EDITION

Year 2000

Performance vs. Weight

Power! Speed! Performance!

We all want our airplanes to be the best machine on the flight line. We invest many hours on little details to make our airplanes attractive and comfortable. We spend money on big powerplants that will provide impressive performance capabilities. We study manuals and wiring diagrams religiously to enable us to hook up fancy IFR panels with all the latest avionics.

When the airplane is finished, however, will it be able to match the performance of the factory's demonstrator?

Yes, it's possible — but only if you build the airplane with careful attention to every detail, always keeping maximum performance capability in mind.

When a manufacturer builds a factory demonstrator to be used as a sales aid, performance is normally a top priority. After all, the company wants to impress you with the capability of their products. Bettering the performance achieved by the manufacturer will usually require a determined effort. Matching performance is easier: just build your airplane the same way the factory built theirs! Don't modify it, or add anything.

A secondary consideration during construction of a factory demonstrator is cosmetic appearance. This always requires some compromises, because
almost everything that is typically done to improve appearance of an airplane
increases its weight. And, as we all know, added weight decreases performance. However, the factory (like all airplane owners) wants their products to look good, so they will attempt to strike a
balance between cosmetic appearance and performance.

Of course, if the airplane will only be shown on static display, and no demo rides are to be given in it, …then it is easier to focus on cosmetic details. We call those airplanes "hangar queens".

How will you equip and finish YOUR airplane? How will your airplane differ from the factory demonstrator?

Remember that everything you add to your airplane will make it weigh more. When building an airplane, every ounce counts. Paint and finish can easily add as much as 60 lbs. or more to the weight of an airplane. Most modifications increase weight. As improbable as it may sound, we've seen a half-pound here, and a pound there, easily add up to as much as 500 lbs. of extra weight on a finished airplane. While the weight of each small item individually may seem insignificant, and while you may consider the item's benefits essential to your objectives, if it wasn't on the factory demonstrator, then it's "extra weight" — and it will decrease the performance of your airplane.

Some common ways that builders inadvertently increase the stall speed, landing/takeoff distances, and decrease the climb capability of their airplane include:

1) Increased Fuel Capacity
If the capacity is there, it'll likely be occupied by fuel.

2) Heavier Upholstery
It looks great, but it all adds up.

3) More Avionics
Sure, they come in handy - but the avionics, antennas, wiring, etc. all adds weight.

4) Paint and Finishing Details
Layers of primer, extra layers of paint, and layers of clear coat all add weight to an airplane.

5) Modifications
Aircraft design always requires compromises — changing the design may have benefits, but gaining those benefits will likely compromise some other desirable characteristic.


Value of Demonstration Flights

A demonstration flight prior to purchasing a kit is absolutely essential. No one should undertake an airplane assembly project without first determining whether or not the finished product will meet their objectives.

As you build your airplane, remember that adding features and equipment to your airplane that were not present on the demonstrator will likely decrease its performance.

In summary, are those leather seats, air conditioners, and little "bells and whistles" REALLY necessary?

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Aerocomp, Inc.

is published by Aerocomp, Inc.
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