Tweak the KC-135 Stratotanker's Windshield Wipers. Save Millions.

Tweak the KC-135 Stratotanker's Windshield Wipers. Save Millions.

Researchers have used computational fluid dynamics to model the nose of the KC-135. They found that by changing the windshield wiper with a thinner one and also changing the orientation to vertical can increase efficiency. They estimate a savings of around $7 Million per year.

I never realized that the KC-135 is also some 55 years old. Amazing that it's still flying especially with all the use it gets.

The Air Force has discovered a simple engineering change to the venerable KC-135 Stratotanker could save it up to $7 million a year. Using computer modeling, the Air Force realized it could increase the aerodynamic efficiency of the converted jetliner by one percent by changing the orientation of the windshield wipers. The increased efficiency translates into greater fuel savings.

a reply to: grey580

The big question is .... How much did the study cost the Air Force ?

a reply to: grey580

The -135, C-130, B-52, and T-38 have all seen over 50 years of continuous service. The -135 and B-52 have 50+ year old airframes that will fly until 2040 or beyond.

The -135 is not a converted airliner, or derived from the 707. It's actually a 717, derived from the Dash 80 (367-80). The Dash 80 was split into two variants. The 717, which became the KC-135, and the 707, which had a wider and longer fuselage.

Fun tangent, only kind of related.

Once upon a time (before my time, told to me by a mentor), there was a very minor issue with the wiper for the windscreen on the XB-47 (looks like an F-14 canopy on a bomber. XB-52 followed this practice, though they moved the cockpit forward for for better visibility. The B-47 went to production with the "fighter" canopy, but the BUFF dumped it for side-by-side seating). This was back in an era when designing for a function was largely just "does this work?" If no, redesign. If yes, leave it the hell alone and move to the next item. While designs were played with to optimize, they didn't spend months and years studying minor variations to find the perfect solution. Best is the enemy of good. KISS. Designs went from paper to hardware quickly, and costs were constrained. There are fair arguments against this as a strict philosophy, but there is probably a nice middle ground between there and today's processes.

Anyway, word went out to find a fix for the XB-47 wiper's minor deficiency, and while most discussed how to make modifications to the wiper, one of the engineers has an engineer-ephiphany. One of those lightbulb moments we all live for.


"Say, instead of modifying the wiper, why don't we ditch the wiper and associated mechanisms, complexity, and weight? We replace it instead with this nifty piece of scrap metal, which we shape in such a way to compress air between it and the nose just infront of the cockpit, and blow that sped up air over the front windscreen, thus clearing the windscreen. Cheap, light, no moving parts to break."

The room is in awe. Here is an individual going places. Every one is excited. They quickly do some math, get a piece machined, install it on the aircraft and wait for a shower to come through.

The weather arrives (as it is wont to do in the PNW). The pilots take her up, go and head straight out for the nearest rain shower. They fly around at various speeds through the heaviest portion of the showers they can find, and this thing works great. They head back to land where it is now raining. Skeptical pilots are now suitably impressed with the genius of the engineering team.

And then they begin to taxi back. Problem. On the ground, the air lacks velocity. The windscreen begins to be covered with rain, and the pilots need to turn on the wiper...

After some hemming and hawing, it is eventually, reluctantly decided that if they need to carry the weight a wiper for ground ops anyway, there is no need for the brilliant bit of metal up front. Just fix the wiper.

Since the B-47 preceded the 707 which incorporated much of the knowledge gained from the B-47 program, that's why the KC-135 even has a wiper.

But true story related to me by a great guy.

Out of curiosity, I did some digging and found this and this.

"An arm-type wiper is now used on the B-47, but Boeing is experimenting with a rain deflectors, heated air blasts, and water repellents."

The deflector was in the story above, and a water repellent apparently became standard in lieu of wipers on the B-47B.

How about rubbing a cut potato onto the windscreen?

Why don’t they just use rainx ?

They briefly used bleed air to clear the windscreen on one aircraft(sorry, don't remember if it was a -135 or something else). It was another one of those that worked under certain conditions, but not others. They found that when on the ground, power levels were too low for there even to be any air blowing across the windscreen. So the pilots would have to bump one engine to slightly higher power to clear the windscreen to taxi.

a reply to: 00018GE

Because Rain-X won't prevent freezing/frost. Which would be bad. Also doesn't work well sitting/taxiing on the ground.