Light Planes Perform Better

How one builder shaved 200 pounds off his Glasair Sportsman.

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The Glasair Sportsman is a great utility airplane, and because of that over 400 of them have been built. It has that unique blend of utility—good useful load, good comfort, good range, and decent speed—combined with excellent short-field performance. Like the Cessna 182, it is one of those planes that seems to be greater than the sum of its parts. However, that doesn’t mean it can’t be made even better. And what better way is there to improve a plane’s performance than to shed 200 pounds of empty weight while retaining all of the plane’s great qualities?

This is the challenge that Ted Setzer embraced. He is one of the original developers of the Stoddard-Hamilton GlaStar, the progenitor of the Glasair Sportsman, and a longtime and recently retired Glasair employee. To say he knows this plane well is an understatement. So, how did he cut so much weight off an already pretty efficient design, and what, if anything, can other builders learn from him and apply to their projects? Let’s see.

Low-Hanging Fruit

For Setzer the first part of weight savings is to pick the lightest possible components that will do the job. He calls this the low-hanging fruit. He chose the ECI IO-375 engine with a counter-weighted crankshaft over the more commonly used Lycoming IO-390. The availability of the counterweighted crank was a vital part of this decision because of problems that non-counterweighted 375 engines had with vibrations that caused propeller problems. With this issue under control, he was able to save over 30 pounds on the engine alone while still maintaining the same power level.

A section of prepreg fiberglass is being bagged for vacuum curing at the Glasair factory. This option isn’t really available to the average builder, but Glasair does now offer a carbon fiber fuselage option that saves even more weight than prepreg. Unfortunately, it is rather expensive.

The next piece of low-hanging fruit was the propeller. The new Hartzell Trailblazer composite prop saved a good 15 pounds over the standard 80-inch metal prop. It also brings added performance with its highly refined aerodynamic design. More performance and less weight, admittedly at a cost, was a double benefit. The lesson here is that the choices made early in the construction process, even before it begins, can make a big difference in where you end up with the final weight of your project. This is the kind of thinking that has allowed CubCrafters to build such light Super Cub-type airplanes. Any builder can embrace this kind of thinking.

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Lithium batteries are another weight saver that has become very popular. Ted, of course, couldn’t resist the temptation to save an easy 10 pounds by taking advantage of this option. He also used copper-clad aluminum wire for his battery and starter wires. I am not so sure I am ready to endorse this practice, but it undeniably saves weight.

That wraps up what Setzer calls low-hanging fruit, but he was only getting started on weight savings.

In Setzer’s Sportsman everything got the lightening treatment, even pulleys. Also note the lightening holes in the gear leg sockets. Each hole only saves a tiny bit of weight, but it adds up.

Fuselage Weight Savings

Setzer’s next weight-saving idea was a little more exotic. As a longtime employee of Glasair, he could tap into some things that most of us could not, such as access to the factory molds for the fuselage. He was able to use prepreg fiberglass cloth in Glasair’s molds to form his fuselage. Prepreg is simply fiberglass cloth that is pre-impregnated with resin of the exact proportions needed to achieve maximum strength. The weight saving comes for eliminating excess resin. Once laid up, the prepreg must be vacuum bagged and heated in an oven for several hours. Obviously, this option is not available to the average builder. He also modified the tail of his Sportsman to resemble a Cessna 180’s tail. This didn’t save any weight. He just wanted to do something different.

A weight saving that Setzer was quick to utilize, and is easily within reach of the average builder, is to substitute titanium for the stainless steel firewall. This resulted in an easy two-pound saving. If you decide to go this way, be sure to get commercial pure titanium and not one of the stronger alloys that is very difficult to cut or form. He also used titanium hardware wherever he could for non-structural items. This came at some extra cost but did save a few pounds. Titanium was not used for structural nuts and bolts. Standard AN hardware was left as is to do its important jobs.

The Sportsman firewall assembly goes together with a flange that is riveted to the firewall with Monel rivets and then attached to the fiberglass fuselage. Substituting titanium for stainless steel saved Setzer two pounds. A piece of titanium ordered over the internet will cost the typical builder about $200. Be sure to only use commercial pure titanium.

Lightening Up the Wings and Tail Surfaces

Setzer was most radical in his weight saving measures when it came to the aluminum parts of his Sportsman. For those of you who are unfamiliar, the Sportsman uses a steel cage inside a fiberglass (or now optional carbon fiber) fuselage with aluminum wings and tail surfaces. That aluminum was mercilessly attacked by Setzer’s lightening program. It should be mentioned that Setzer has access to the original designer of this airplane, so he was able to properly analyze every weight saving measure he undertook. The things he did should not be considered by anyone lacking such skill or access to someone who has it.

Here the lightened elevator is being fitted up to the horizontal stabilizer. It will next get covered with Poly-Fiber cloth. Corner gussets were employed to replace the strength lost by removing the aluminum skin.

The most noticeable change Setzer made was using fabric-covered control surfaces throughout—ailerons, flaps, elevator, and rudder. This does not exactly break new ground in aerodynamic design. World War II planes from the AT-6 to the B-17 used fabric covering on their control surfaces. Of course, making fabric-covered parts involves a lot more than simply removing the aluminum skin and stretching Dacron over the ribs and spars. The aluminum skins on the original control surfaces provided a lot of strength. That strength has to be replaced in any redesign. The big challenge was to replace the torsional rigidity or resistance to twisting in the new parts. Some of this Setzer did with help from the original designer, some of it he did by feel based on what he had done with the other control surfaces. In any case, he saved a lot of weight, and the control surfaces work very well. This technique could be utilized by most builders, but make no mistake about how much effort went into it. This is not an easy way to save weight.

The rudder is fitted to the vertical stabilizer to make sure everything will work well before covering. Note that the Sportsman’s distinctive tail has been reshaped to resemble that of a Cessna 180. This saved no weight. It was just something Setzer wanted to do.

A place where Setzer was particularly aggressive is in lightening the wing spars. Here he enlarged lightening holes and shaved metal off the spar flanges as much as he could. The concept is simple enough. The spar has a constant cross section from root to tip, but the bending loads diminish the farther from the point of attachment you move. Setzer used a circular saw with a carbide blade to attack the spar flanges, using it as a plane rather than cutting off pieces. Anyone could duplicate his effort, but it would be unwise to do so without some very serious consideration of the consequences. This is not something to be taken lightly—no pun intended.

Setzer wanted to track his weight saving measures as he proceeded, so he devised a way to account for all of his trimming and shaving. Every day he would carefully sweep the shop floor before he started work. At the end of the day he would again sweep the floor, gathering up all the trimmings and chips and weigh them. It didn’t come to a lot each day, but over time it added up.

One of the differences between the original GlaStar and the Glasair Sportsman is the extended chord of the flaps. Setzer added another two inches to his flaps, figuring if a little was good, more would be even better. His plane does have a lower stall speed as a result.

Wet Wings

Stealing an idea from Van’s playbook, Setzer dumped the factory-welded aluminum fuel tanks and went with a wet-wing design to add fuel and save weight. Doing this in a plane that was not originally designed for such a feature takes quite a bit of modification to pull it off. Ribs that once had holes in them must be replaced with solid ribs, and everything must get sealed with the RV builder’s favorite goop—Pro-Seal. Setzer’s modification required using thicker skins in the fuel tank sections, which added weight, but that was more than offset by the elimination of the tanks.

Every part, even these hat sections, fell under Setzer’s lightening program. Here you can see how he scalloped out the unused material between attachment points and drilled the hats to get them as light as possible.

Not Everything Saved Weight

Besides building a very light plane, Setzer wanted to create a better STOL plane to give him access to off-airport landing spots that he otherwise would have to pass up. To do this he did some things that actually added weight. The biggest penalty paid were gear legs that were not only three inches longer, but also about 1/8-inch diameter larger to better gain prop clearance and absorb the rough terrain he had in mind to conquer. He also extended the chord of the flaps by two inches, which negated the weight savings from the fabric covering, but did give him a lower stall speed.

Another weight saving Setzer passed up was the elimination of paint on the metal surfaces. It is some extra work to keep aluminum wings and the elevator polished, but it undeniably saves weight. These were painted for the sake of appearance and less maintenance.

While on the subject of paint, it is amazing how much weight a paint job adds to the empty weight of an airplane. Setzer weighed his plane before paint and came up with an empty weight of 1207 pounds. After paint that number climbed up to 1260 pounds, a 53-pound weight gain. It seems likely that 20 pounds or so could have been saved by leaving the aluminum surfaces bare.

Using a circular saw with a carbide blade, Setzer shaved all of this extra material off the spars. He collected up the shavings each day and weighed them to keep track of his progress.

Weight Savings Not Utilized

Most of Setzer’s weight saving ideas involved little or no extra cost but merely a lot of extra work. The big exception to that was the Hartzell Trailblazer prop. That 15-pound saving cost several thousand dollars.

Another extra cost step not taken was the use of magnesium wheels in lieu of aluminum wheels. Setzer began his project too soon to utilize the carbon fiber fuselage option now available from Glasair. This has become a popular way to trade dollars for weight savings for builders who are so inclined. The problem with all of these weight-saving ideas is that the farther you go in your efforts to save weight, the more expensive it gets per pound saved. This is a problem well known to serious bicycle riders. Removing weight from your bike requires removing weight from your wallet, and at an alarming rate as you push things farther and farther. This was not in Setzer’s plans.

The Final Results

The typical Glasair Sportsman weighs about 1460 to 1470 pounds. The factory has a lot of history on actual weights through its Two-Weeks-to-Taxi program, so these are real numbers. Setzer’s plane weighed 1260 pounds after paint with standard 6.00×6 tires. That is an honest 200-pound weight saving. He added some big 31-inch Alaska Bushwheels that wiped out about 40 pounds of that, but the same amount would have been added to a more conventional Sportsman to get the same benefit.

What, if any of this, could the average RV builder utilize? That is a fair question. Some of the things Setzer did would not be readily available to an RV builder, and others would be difficult to duplicate. Lightening the metal structure can be done. But it cannot be emphasized too much how important it would be to only attempt this with the assistance of a sharp engineer well versed in aircraft structures. It would be wrong to assume that Van’s was careless with weight in their design.

Setzer rivets together an aileron. The gold color is from the alodine process he used to inhibit corrosion.

Setzer’s low-hanging fruit is available to most builders unless you are building an ELSA kit. An O-320 engine can be tweaked to duplicate the power of an O-360 without too much trouble or expense, saving 10 to 15 pounds. A composite fixed-pitch prop such as a Catto can save even more weight compared to a metal fixed-pitch prop without incurring much added cost. Composite constant-speed props can save around 15 pounds compared to their metal counterparts, but admittedly at an extra cost of several thousand dollars. A lithium battery is an easy 10-pound weight saving, but careful attention to your wiring such as overvoltage protection is a must if you go that way.

Perhaps the biggest weight saver is one that has not yet been mentioned—don’t put things in your plane that you don’t need. Setzer certainly took that to heart, as should every builder. It is so easy to add 50 or even 100 pounds to the empty weight of a plane with added items that seem like a good idea, but are really not necessary. Another way weight gets added is by adding complexity to what should be simple systems. Engineer/builders are famous for this. Remember, the best design is almost always the simplest design, which is so often also the lightest design. Complexity adds weight and usually decreases reliability, two bad things to do to an airplane.

Setzer added 40 pounds to his new airplane by adding heavy tires. The good thing about them is that he can easily remove them if he no longer needs them. However, for the flying he wants to do, these are important to the success of his mission. That is the good kind of added weight. Any builder with a special need such as this should feel justified in adding weight to meet that need. Just be sure you really need it.

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