Forum: F-16 Design & Construction

However, I have heard some complaints about reflections in the canopy at night. You must remember that the original design of the F-16 revolved around the role of lightweight daytime air-to-air fighter. However, this quickly changed to one of multirole fighter. The possibility of the aircraft spending much more time in the arena where it might encounter birds was one change. Without fully understanding the physics involved or the tradeoffs required, a lot of attention was suddenly focused on the F-16's birdstrike problem. As a result, the canopy thickness went from three-eighths inch on the prototypes, to one-half inch on the full-scale development airplanes, and finally to three-quarters inch on the production version. Therefore, the possibility of reflections ricocheting around inside the transparency (and then into your eyes) increased markedly. It's also interesting to note that this additional canopy thickness cost you twenty-two pounds of additional weight per one-eighth inch increase.

While I have mentioned birdstrikes, let me digress for a minute on that subject. It's important to realize what we're talking about when the subject comes up for discussion.

First of all, the failure mode with a birdstrike in the F-16 is rarely one of penetration (that is, the bird does not usually come through the canopy). Instead, the impact puts a big depression in the canopy. This depression (dent, if you prefer) then progresses back along the canopy in a traveling wave, giving rise to the possibility that it (the wave) will rap you on top of the head hard enough to incapacitate you. The sweet spot required for this to happen is hardly six inches by six inches, roughly centered on the head-up display, or HUD. Anything outside this area does not create enough of a dent to hit you as this traveling wave passes by your head. I feel the odds against just such a hit are astronomical, but it was not my decision to make. So, what you now have is a canopy that will take a four-pound bird in this area at something in excess of 350 knots. This capability assumes that you are sitting at design eye. If it looks like the mission is going to require that you fly at high speeds in an area where you know there are a lot of birds, you should make note that you can get an increased safety margin simply by lowering your seat below design eye. It is also very interesting to note that the F-16 is one of only a few airplanes that has been so thoroughly scrutinized in this area.

There are several other airplanes (I won't mention any here, but you would recognize them instantly if I did) where the failure mode is one of penetration. And the airspeed that this penetration occurs is not too high (more like around 250 knots). What happens with these airplanes is that the bird hits anywhere on the windshield and travels up the windscreen, making a dent similar to one on the F-16. The difference is that, once it gets to the canopy bow, this traveling wave is severely snubbed by the canopy frame. The result is an immediate failure of the transparency, and your single-place aircraft has suddenly become occupied by another warm (but rapidly cooling) body. This is not too conducive to a much longer sortie on your part. Of course, there is always the remote possibility of taking a condor right in the chops at 600 knots in any tactical airplane, in which case all bets are off.

Source: Code One Magazine

5-6 inches? Geez... how much does that thing weigh?