In the beginning stages of developing the GlaStar we set goals for performance, weight, build time (don’t laugh—the industry’s come a long way from 15 year homebuilt projects!), cost, quality and other desirable features. If we miss the mark on a particular category, we can sometimes make changes to achieve the goal, but it takes determination and perseverance. As with our human bodies, when the airframe weight comes in heavier than desired, it is a very difficult task to go back and find ways to lose weight. Some decisions can result in saving pounds, but there are a lot of areas to save many ounces, which add up to pounds.
Building your own kit aircraft is similar to designing a prototype because there are no two GlaStars built the same. Sure, there are many parts the same which makes all GlaStars look alike, but why do the finished products weigh anywhere from 1150 lb to over 1400? The problem is that most builders do not have much of an idea what the finished product is going as they are building it. Maybe there is wishful thinking and hope that it won’t come in too heavy when weighed, but not much in the way of goal setting and careful calculation for each option added.
Here are some suggestions I hope you find helpful to achieve the desired weight and performance with your own finished ‘Star.
Define your motivation and mission
Some people plan a vacation far enough in advance that they can get in physical shape by the time they go, especially if they are going to be seen in a bathing suit. Use the same psychology before starting the assembly of your plane. Set in your mind the kind of mission and performance you wish to achieve, and let that be the motivation for the target weight. In my case, I’ve been bitten by the bug to go on hunting and fly fishing safaris to British Columbia and the wild country of Alaska, and since my (eventual) GlaStar will be periodically on floats, I want it to be as light as it can be.
Everyone’s mission won’t be the same, but to get maximum performance, weight should be high on everyone’s priority list.
Maybe you live in the Midwest and your mission is to fly IFR, and you want long range and an autopilot. Well, you will be packing extra weight with a heavy panel, aux. tanks and autopilot installation, but don’t need 180 h.p. because your typical flight won’t involve climbing mountains. In this case an 1150 or 1200 lb empty weight may be unrealistic, but with a 160 h.p. engine, lightweight starter and alternator, and lightweight interior, you could still shoot for 1230 to 1250 lb.
Define the variables and add up the weights Variables are the things (options) you add to the project. Once you define the mission in step 1, make a list of the options you need and another list of the options you desire and keep a scale handy in the shop.
|Engine 160 h.p.||180 h.p.|
|Prop fixed pitch||Hartzell C.S.|
|30 gal fuel||50 gal fuel|
|Flight instruments||IFR instrumentation|
|Avionics, (GPS com.)||IFR avionics|
|Rudder pedals||Cast aluminum type|
|Single brakes||Dual brakes|
|Exterior paint||Paint inside and out|
After making a list like this one, but more detailed, calculate the weight difference between the needed items and the desired ones. If the total calculated weight exceeds your target weight, start dropping some of the desired options or get creative on where to save weight in other areas.
Don’t dismiss the ounces
It could be a disappointing mistake if you think you are doing a great job with saving 12 lb on engine choice, 15 lb without aux. tanks and ignore the myriad of little places weight gets added one or two ounces at a time. I’ve outlined some areas here that I believe account for the disappointment at the end of the project. You don’t want to be asking yourself, “Where in the name of Pete did that extra 70 lb come from? I figured my empty weight was going to be somewhere around 1265—not 1335 or 1400!”
a) Corrosion protection. Even though I plan on flying floats occasionally on salt water, I will etch and alodine the internal skins and ribs inside my wings, flaps and ailerons but only spray a light coat of self-etching Marhyde primer on the rib flanges and skin rivet lines. I’d guess the weight gain of spraying a healthy coat of primer on all inside surfaces to be 5-8 lb. The exception to this rule is with the stabilizer, elevator and rudder. I will probably give these the full meal (etch, alodine and primer) deal on the inside since they get literally bathed in salt spray on takeoff and landings.
b) Interior and upholstery. The weight savings in this category can be huge. I plan to spray an interior coat of gray Zolatone— a speckled, textured paint—on all interior fuselage surfaces that will be visible behind the cage before the sides are seamed together. Tape off all fiberglass seam areas, and sand and spray a touch-up overlapping coat after the seams have been laminated and sanded. Advanced cosmetic planning like this will mean I can dismiss any temptation to add weight with contact cement and upholstery fabric in all these areas, not to mention all the upholstery panels I see in many GlaStars to cover the cage.
The powder coat finish of the cage looks great, and I would rather have it open for inspection—all the time.
There are many brands of rattle-can paint like Zolatone available at most hardware stores. Most need a topcoat of clear matte finish (lacquer or other) to seal the surface; otherwise they tend to show signs of wear too easily.
In the baggage compartment, I would cover the floor and control cable tunnel with a thin, lightweight carpet, but only a short way up the fuselage sides. From there on up, spray texture paint all the way up and around the aft windows.
The doors would be sprayed with the same treatment around the edges and window frame and (after the dogs are bonded in) and a lightweight panel upholstered and screwed in place. Elbow rest plastic door handles from mid to late 80’s Honda cars from local wrecking yards weigh only ounces and if you search hard enough, you will find a set to match your interior colors. Our local yard charges $15-$20 per set.
The seats would be covered with a durable, lightweight fabric. Leather wears very nicely, but weighs too much for my mission. I would install drain pans for wing fold weather protection, but they would be painted with a gray finish. Behind the seats, I would cover the lower aileron and flap cable pulleys with a thin aluminum panel that extends vertically halfway up the cables. In my opinion, they don’t need to be protected any higher than that. (Look at a Cub or most tube and fabric planes. The cables are visible everywhere!) The forward tunnel between pilot and co-pilot legs needs a cover; mine would be made from .016 or .020 aluminum and painted gray.
The dash panel would be made from thin aluminum or fiberglass with a flat black painted finish supported with aluminum angles extending from the panel to the front edge of the windshield. Maybe, maybe a gray, thin fabric glued down on the dash to reduce glare.
That’s it for my spartan but cosmetically appealing interior finish. Guaranteed to save 30-50 lb over the cover-the-cage with panels and glue fabric everywhere method.
c) Exterior paint. Unless you plan to sand off all the gel coat weight, leave it as-is. Paint the wings, flaps, ailerons and tail surfaces with a good polyurethane.
Bare aluminum is lighter, but too much maintenance.
I’d guess the paint on all these surfaces to weigh 15-20 lb. Has anyone weighed them before and after? I would appreciate knowing what the difference is.
d) Windshield. Stay with the stock 1/8” thickness. The 3/ 16” windshield adds about 6 lb and adds nothing but maybe a little noise reduction. (Let the headsets do the job here
e) Bracket trimming. Most brackets don’t need square edges on the corners. A healthy 45 degree chamfer can be nipped off most rib flange ends, bracket ends, and aluminum angles. I know this seems trivial, but at the end of my project, I’d have a small can of these trimmings weighing about a full pound or more! If either of my gear legs protrudes upward, beyond the gear sockets, I will grind them flush. Yes, I will be fanatical about weight.
f) Laminates. All too often, fiberglass laminates are too resin rich and wider than they need to be. When multiple laminates are called for, stagger the widths so the edges don’t stack up. If the book says to lay up (3) two-inch wide lams, I will cut them at 1.5, 1.75 and 2.0 inches wide and start with the narrowest first. This is just as strong and a little lighter. Use peel ply to keep all laminates neat and tidy and don’t be afraid to taper sand rough edges down after cure.
g) Instrument/avionics choice. Money can save weight here! The latest developments in flat panel screens and digital instruments are getting lighter all the time. For the overall layout, keep the mission in mind here. Full panels look awesome, especially when they are lit up at night, but try to keep it to the minimum you’ll need.
h) Engine accessories. A lightweight starter and alternator can almost make up the difference between the 160 and 180 h.p. Lycoming. But these items on the 160 will save all the more weight! Run the engine on three quarts instead of eight…(I’m kidding! Just checking to see if you are still alert).
i) Rudder pedals. The original thinking on the GlaStar was to have very light pedals. Cast aluminum pedals weigh about three times as much. The flat, simple homemade pedals may be more difficult to actuate toe-brakes, but before I give up on them, I might try making them a little taller and riveting a light, half-round toe pad similar to the cast design and glue down some non-skid pad material.
j) Window installation. I’ve had experience with both the assembly manual pigmented resin method and the GE Silpruf adhesive method recommended by Airlink. I like the Silpruf method better. It’s easier to get a good cosmetic finish and has to be a little lighter.
k) Stick grips. You guessed it, mine would be the slip over foam bicycle grips (tipping the scales at a whopping ounce each!) with some kind of cap on top with a push to talk switch, or the coolie hat trim switch on top with a small, push to talk switch taped to the side of the grip in the best ergonomic position.
This may sound hokey, but I think I could find a way to wrap in a side switch mount with black electrical tape that would look and function fine. If this experiment fails, I’ll settle with a plastic grip from our catalog. Gee, I might even shorten up the stick handle steel tube by an inch and save another ½ ounce per side…and I certainly will trim off the excess tube at the bottom of the gooseneck.
I know for a fact there is at least an inch or more sticking past the stick pivot fittings.
By now you should have a feel for how to get in the mind-set of building a light GlaStar and reaping the benefits of the extra performance to be gained. I’ll never forget the feel of the 1946 Cessna 120 I learned to fly in. After my instructor stepped out and said, “You’re all set to solo now,” wow, did that plane ever perform better without his butt in it! So, if you can assemble your GlaStar 100, 150 or more pounds lighter because you chose to build it as light as you could, you will ‘feel’ the difference.