The largest possible window area is obviously a safety advantage when it comes to seeing and avoiding other traffic, or even when looking at the runway while landing. That’s why most fighters and aerobatic airplanes have transparent canopies.
But windows also add–or detract–from comfort for all occupants of an airplane. The right window design makes any cabin feel more spacious and welcoming, and can also ease the discomfort of turbulence.
The Klapmeier brothers understood this when they were laying out the original design for the Cirrus. That’s why the SR20 and SR22 have big windshields, large windows in each door, and even more importantly large rear windows. In many airplanes passengers in the second row are left sitting down in a cave with a very limited view of the outside world. But not in a Cirrus. The brothers had flown enough with family members and friends in the backseats of other airplanes to understand how important this is.
Another design that did a nice job with the windows is the Bonanza, and the many Beech models it spawned. In the Beechcrafts the windows sweep up into the overhead helping to make the cabin feel larger than it really is, even for the second row of seats.
The epitome of window perfection is the Gulfstream line of business jets. In the late 1950s when engineers at Grumman were creating the stately Gulfstream I turboprop–the first purpose built turbine business airplane–they included huge oval windows in the cabin. Passengers loved them, and every Gulfstream since has had the trademark ovals. In fact, for the super speedy and super ultra long range G650 Gulfstream increased the size of the oval windows by nearly a third.
But big windows come at a price. It’s not that the transparent material costs so much, but the structural accommodations required to design in large windows is costly and heavy. And then there is the cost of annoyance and suffering when you just don’t want all of that sunlight beating in on you.
The structural penalty for big windows is mostly in weight. No matter what material the actual transparency is made from it can’t carry structural loads. That means the load carrying elements of the airframe have to be designed around the window opening instead of following their most efficient path.
In unpressurized airplanes the weight and materials costs of larger windows isn’t nearly as great as in pressurized airplanes. Perfect examples of the window size penalty in pressurized airplanes are the P Baron or the Cessna P210. Both pressurized airplanes evolved from unpressurized versions and in each the window size was cut down markedly to reduce the amount structural and transparency strength required, and thus help control weight.
In transport airplanes windows need to be redundant so failure of one layer or pane of the transparency won’t create a decompression so you can see how the weight of a big window adds up. And in the cockpit windshields and their frames have to withstand the impact of a large bird at 250 knots. Add in the heating elements and it’s easy to see how a big windshield, no matter how much pilots love them, adds weight plus construction and maintenance costs.
Early Citations are an oddity in windshields, birds and the FARs. The Cessna business jets had two Vmo (maximum indicated airspeed) limits, one for below 8,000 feet and a higher red line for above that altitude. The reason is that the airplane met the bird impact rules at the lower Vmo but, under the rules, the birds that endanger the windshield did not fly above 8,000 feet. I always wondered if the birds had read the FARs, or had altimeters for that matter.
The primary price pilots pay for big windows comes when the sun is shining. The greenhouse effect is no myth. Sit under a transparent canopy on a sunny day for very long and you are soon wishing for shade, even if it’s cold outside. Most pilots and builders of canopy airplanes devise a shade of some sort to pull over the center of the overhead for relief. But even with a shade it can quickly become unbearable under the canopy on a hot sunny day, especially on the ground.
Big windshields also extract a toll in suffering when flying toward the sun. The pilots who suffer most are those on the transatlantic routes. Flights typically leave the U.S. in the evening but the crew quickly catches up with the rising sun in the east and are broiled for the second half of the flight and arrival. The return trips usually depart in the late morning and chase the sun across the ocean assuring the pilots will be blinded and toasted for the entire trip.
Nearly all passenger cabin windows have screens and blinds to pull so being blinded and cooked is mostly a pilot problem. Pilots have propped up just about anything in the cockpit windows to block the blinding glare. And one company, Rosen, has made a very successful business of building articulating arms that allow you to position the sun visor almost anywhere over the cockpit windows. Designers of new airplanes are including effective sun glare protection devices in the original layout of the cockpit. It’s that important.
But no matter how annoying the sun may be, I still prefer being in an airplane with well designed windows. I can usually come up with some way to shade myself when needed, but there is nothing you can do to change that little slit of a windshield that is left in too many airplanes as the instrument panel glareshield has risen to accommodate ever more avionics displays.
And if you want to know what passengers think of the importance of windows just ask a Cirrus or Gulfstream salesman. They know.