00:01Hi, I'm Neil Armstrong. Join me for an adventure through time.
00:54I'm Neil Armstrong. Join me for an adventure through time.
00:59Propellers progressed from gliders to powered aircraft. Very little was known about how
01:05propellers work. Although propellers had been used on ships and dirigibles for years, designs
01:13had evolved largely through trial and error. No formal theory existed. Designing a practical
01:21propeller for their flying machine required pioneering research. They recognized that
01:27aerodynamically, a propeller is really a wing moving in a spiral path. Based on their calculations,
01:36they designed the large wooden propellers that push the right flyer through the air.
01:49As dreams of flight materialized into designs for flying machines, the propeller repeatedly
01:55played a part. By the time airplanes took to the sky, propellers had long been used to power
02:01boats and even dirigibles. But their design was largely a matter of trial and error. The
02:12propellers designed the propellers for their flyer. Three layers of spruce were shaped into two
02:17gracefully contoured eight and a half foot long wooden propellers. Their large diameter increased
02:23thrust. They rotated in opposite directions to counterbalance the torque they created. The
02:30Wrights mounted their propellers in the rear so they would not disturb the airflow over the
02:35wings. There was some debate about where to put the propellers on early aircraft. Some, like the
02:41Wrights, chose rear mounted pushers, though most Europeans thought propellers worked better on
02:46the front, where they turned in undisturbed air. By the 1920s, almost all aircraft designers
02:53settled on the front, called the tractor configuration. As the Wrights had discovered, a propeller is
03:03basically an airplane wing moving in a circle. The lift vector is turned to shove the machine
03:08forward. Just as the design of the wing affects lift, an efficient propeller design can improve this
03:15forward thrust. To be efficient, a propeller must be twisted, because like all things that turn
03:21around a central hub, the outer parts of the propeller travel further and faster through the
03:26air than the inner ones. Flying at increased speeds made a major advance in propeller design
03:32while necessary. Metal covered and all metal blades. As engine powers and aircraft speeds increased,
03:40the tips of the propeller blades could exceed the speed of sound. In wet weather, raindrops hit the
03:48propeller like bullets, occasionally leaving the wooden slivers. If one blade absorbed more water than the
03:54others, the propeller became unbalanced, causing tremendous instability in the aircraft. But metallurgy was a young
04:02science and did not offer immediate answers. The first successful metal propeller had thin
04:09dual blades and aluminum copper alloy. It was an instant winner. Its designer, Dr. S. A. Reid, was awarded the
04:171925 Collier Trophy for inventing the new prop. And Jimmy Doolittle won that year's Schneider Trophy race in a
04:24courtesy plane fitted with a reed propeller. Propellers not only provided forward thrust for the early
04:32flying machines, they did double duty as hand-turned engine starters.
04:45The old and dangerous method of starting an airplane engine by pulling through the propeller has become
04:50obsolete. Here's the modern method. Just place the shotgun shell in the bleach of the starter and press the
04:56button. Bam! He's off! The danger of getting too near a turning propeller was not something to be taken
05:02lightly. Many pilots and mechanics were maimed and killed by the whirling blades, and a progression of
05:09alternatives developed to keep the starter out of the way. It was not only in starting airplanes that the
05:15crops are hazardous. The danger was intensified by the space limitations of carrier operations, where many
05:22lives have been lost to propeller accidents.
05:29Despite advances in materials, wooden propellers are used to this day, though only a handful of
05:35craftsmen still make them.
05:38We're here with Harold Ream, master propeller maker. Harold, what's the advantage of a wooden propeller?
05:44Well, a wooden propeller, if you do have an accident with it, it doesn't damage the crankshaft like a metal
05:50prop does.
05:51It accelerates much quicker than a metal prop. It weighs half as much as a metal prop. And they're cheaper.
06:00That's important.
06:02I'm making a propeller right now for a man in New Zealand. And what he's looking for, he's looking for
06:08a cruise prop.
06:09He wants to get around. I select a plan form, and I lay it out, and then I sketch it
06:20out. Then I turn it 180 degrees, and then draw it out on both sides.
06:29After the blank is made, I'll cut this out, and then I'll stack the wood that I need for the
06:38propeller, so I have four laminates.
06:41And then you take it to the bandsaw and cut it to exact length.
06:47That's right.
06:48And get in preparation for the shaping process.
06:50That's correct.
06:53In modern workshops like Harold Ream's, power tools have replaced the hatchets and draw knives used in the early days
06:59to cut and shape wooden propellers.
07:04The part that does the work on a propeller is this portion right in here.
07:09So this part in here, I fare in more or less for strength.
07:15I kind of ignore the angles, because once you get over 30 degrees on the angle, you have more drag
07:23than thrust anyhow.
07:24On a racing propeller, you'd want to hold that true angle right up into the hub, because they're running the
07:31propeller at full speed all the time.
07:34But on a conventional aircraft, at the slow speeds, this blade would stall out at too steep an angle.
07:42And I made little templates for that.
07:45These are shaping guides?
07:46The shaping guides, yes.
07:50The main thing is that you make both blades alike.
07:53That's the secret of the whole thing.
07:56I take the propeller over to the balancer periodically and check it for balance.
08:02Of course.
08:03I add a piece of veneer to the tip of the propeller.
08:08And that's to keep the blade stiff, to keep it from fluttering.
08:12It adds stiffness.
08:13Yes, it adds stiffness.
08:14And then I put this piece of plastic on.
08:18It's a protection against the rain and sleet.
08:21Otherwise, it eats the whole leading edge right off.
08:25Years ago, they didn't have anything on.
08:28It was perfectly bare.
08:30And by the time a fellow got back with his aircraft, about a quarter of an inch was eaten off.
08:37The propeller should balance in a horizontal position.
08:44What I need, I need a little more varnish on this side or a little white paint over the tip.
08:53It also has to balance in the vertical position.
08:59And this one balances fairly well.
09:03So critical it is.
09:04A little piece of paper is a lot of unbalance.
09:06A fly will...
09:07See, that's too much.
09:09And what is the consequence of having an unbalanced propeller?
09:14Well, it vibrates.
09:16And it's not good for the life of the propeller to begin with.
09:21And it feeds back into the engine.
09:22That's right.
09:23It leads back into the engine.
09:25And it adds fatigue to the engine, to the load and the stresses.
09:31It should run smooth.
09:35Wooden propellers were a compromise.
09:37For takeoff, the best propeller had a low pitch, taking a small bite of air for maximum
09:44airplane acceleration.
09:45For cruising flight, the optimum propeller had a high pitch, providing best fuel consumption
09:52and range.
09:53A variable pitch propeller could give the pilot the best of both worlds, good takeoff performance
10:00and fuel economy.
10:02Hamilton Standard was the first company to mass produce propellers with variable pitch.
10:08Aircraft manufacturers immediately saw the benefits of such a revolutionary innovation
10:13and flooded the Hamilton Standard office with orders.
10:19By the late 1920s, many aircraft had propellers that could be adjusted to various pitch settings.
10:25But these adjustments had to be made on the ground.
10:28A pilot had to decide whether good takeoff performance or cruising performance was most
10:33important.
10:36When Lindbergh set the propeller pitch for his transatlantic flight, he chose a cruise setting,
10:41but with the blade half a degree below optimum to increase the power for takeoff.
10:47That concession, small as it was, made a difference.
10:50The spirit of St. Louis cleared the wires at the end of Roosevelt Field by a mere 20 feet.
10:59Researchers in Europe and the US saw the advantage of propellers that could be adjusted in flight,
11:05and a number were developed.
11:07But pitch variations were limited, and they did not find extensive use.
11:14Then in 1933, United Airlines Boeing 247 airliners were setting speed records for United States coast-to-coast flights,
11:23but they couldn't operate at full weight from the high-altitude airfields in the Rocky Mountains.
11:28Pitch adjustments could solve the takeoff problem, but caused unacceptable losses in cruise efficiency.
11:37The solution was found in a new Hamilton standard propeller design that allowed the pilot to change pitch in flight.
11:45The new props were rushed through testing into production and yielded dramatic increases in takeoff and climb performance,
11:52as well as boosting cruise speed from 120 to 160 miles per hour.
11:58Adjustable pitch propellers were soon standard equipment for a wide range of aircraft.
12:03Improvements in propeller performance followed quickly.
12:07Constant speed control offered the equivalent of automatic transmission in a car.
12:14As the engine speed drops, the governor notes the change and operates a valve sending oil out to the propeller.
12:22This flattens out the propeller pitch so the engine can come up to proper speed.
12:30Feathering was an important blade control function introduced in the late 1930s.
12:34If an engine failed, the propeller could be feathered or turned straight into the wind.
12:40This stopped the blades from rotating and offered less air resistance,
12:44allowing the airplane to hold or gain altitude while flying on the remaining engines.
12:50Feathering also prevented windmilling, which could further cause damage to the engine or even tear it from the airplane.
13:05At the beginning of World War II, the emphasis in propeller manufacturing shifted to mass production.
13:12I should like to see this nation geared up to the ability to turn out at least 50,000 planes
13:22a year.
13:24Many Allied fighters entered the war equipped with two position propellers,
13:29leaving the RAF outmaneuvered by the Luftwaffe in air battles over France.
13:38A crash program refitted Spitfires and hurricanes with constant speed propellers at an amazing rate,
13:44lending the RAF the edge it needed in the Battle of Britain.
13:55At the end of the war, the dawning of the jet age threatened to make propellers obsolete.
14:00But for many applications where high speed and altitude were not the main concern,
14:05the propeller remained a superior technology.
14:13As aircraft became faster, the basic mechanism to change the pitch of the blades remained the same.
14:20But blade shapes and materials changed.
14:23Gear housings had to be stronger, and blades had to withstand the enormous stress
14:28as tips neared sonic velocity.
14:33With the coming of the jet age, propellers fell out of favor for large passenger aircraft.
14:39But designers soon realized that fast turboprops with an advanced propeller
14:44could be more efficient than the best jetliners.
14:48This unducted fan takes turbine-powered propellers another step further.
14:53The numerous small blades are shaped to produce high speed and fuel efficiency.
15:01Against the high-speed glamour of jet engines, propellers seemed archaic.
15:06When considering a turboprop fighter, a U.S. Air Force general announced
15:10there would be no propellers in his Air Force.
15:13But there are others interested in pushing the propeller to its limits.
15:18Neil talked with test pilot Skip Holm about a propeller with scimitar-shaped blades
15:22under development for a new racer.
15:25Designers hope the airplane will set new world speed records for propeller-driven craft.
15:31This is a composite propeller that's a scimitar blade that we initially designed to go on an airplane like this
15:39or a tsunami.
15:42And if you think of the theory of the swept propeller like you would on a swept wing,
15:48you know, the modern fighters all have swept wings and they all go fast.
15:51And we don't have straight-winged airplanes anymore except an A-10, for instance, which is a slow airplane.
15:56So the theory, if you sweep the wings to go fast, you want to sweep the prop to go fast.
16:02And eventually you'll see the racers come out with some modified version of this propeller,
16:07either a composite propeller or a steel propeller that is swept.
16:12Different shape.
16:15So the step between the Mustang, the stiletto, as we see it here,
16:23the next step would be to put some different type of propeller on the airplane
16:27so that the prop doesn't stop the speed.
16:30Where this one will run 410 maybe right now with this propeller on it.
16:35Put a scimitar, it'll probably run 450, 460.
16:38So each design change would probably, hopefully, will give you 40 to 50 knots.
16:44While propeller technology has progressed, supplying the needs of commuter and personal aircraft,
16:50jetliners have become the standard in modern aircraft travel,
16:53providing the optimum in speed and comfort.
16:56But fueling these jets is one of commercial airlines' biggest expenses,
17:01driving up the cost for the air travelers who have to foot the bill.
17:05During the 1970s oil crisis, NASA started reworking the propeller,
17:10with hopes that aircraft powered by new generation props
17:13would burn 50 to 60 percent less fuel than present day jets.
17:19Teams of engineers went to work, designing, fabricating and testing various configurations
17:25of single and counter rotation prop fans.
17:28Wind tunnel tests using small scale models proved the concept was feasible.
17:34Various configurations emerged, some using two sets of blades.
17:39By placing a second set of contra-rotating blades behind the first,
17:44much of the swirl energy that would normally be lost to the air stream
17:48can be converted to useful thrust.
17:51At the Lockheed Aircraft Company in Marietta, Georgia,
17:55a nine-foot diameter prop fan has been mounted on the left wing of a Gulfstream II business jet.
18:01The unique blade design, featuring eight thin, curved, swept-back blades,
18:06is the key to achieving speeds and altitudes comparable to jets on roughly half the fuel.
18:13611 sensors, including 100 microphones,
18:16have been placed on the blades and other parts of the aircraft
18:19to help NASA monitor its performance.
18:25Lockheed's senior research pilot, Frank Hatton, led the flight testing.
18:30The present transport flies in the 0.8 mock regime, and it uses a pretty good amount of fuel.
18:35The prop fan can give us that same airspeed, same mock regime of 0.8 to 0.85,
18:42with a 30 to 40 percent fuel reduction.
18:45So, economically, it's better for the airlines and for the users,
18:51and it's something that's come about in a new technology.
18:55Propeller-driven airplanes have traditionally been noisy,
18:58so two of the greatest concerns in the prop fan project are minimizing noise levels on the ground
19:04and creating a passenger cabin as quiet as a jet's.
19:12Most of the time, we really don't even know it's running inside the cockpit.
19:15It's that quiet.
19:16And we're only, what, 15 feet away from it.
19:19Trying to put it on a fighter may not be the best application.
19:22Putting it on a transport, a la one of the airlines, whatever it may be,
19:28may be a good application for it.
19:30Military transport, it may be a good application for it.
19:33A bomber, possibly.
19:35Again, it would be subsonic, I don't think it would be supersonic.
19:44Traveling public, I don't think really knows what kind of airplane they're flying on.
19:48You go from a big building through a tube into another tube.
19:51So I don't think the public, per se, would know that much difference
19:55unless it would be in a cost reduction item.
19:58And by using less fuel, the price of the ticket may drop.
20:01That would be the only thing.
20:02As far as the external noises, I've heard that these do have a different sound to them versus a jet.
20:09It's some like, say, a race car or a wood chipper or maybe a loud lawn mower.
20:16So how the public perceives it, I don't really know.
20:19I don't think we've got enough data to get on that.
20:22The jet engine and this may complement each other in the different types of airplanes they fly
20:27with different jobs for each different type of airplane.
20:31And I don't think it would end up, say, getting down into the light airplane or general aviation level
20:37because it would probably be too expensive.
20:39So you're going to see the standard old wooden propeller or metal propeller, fixed pitch, down in that regime.
20:46Some of the higher priced general aviation airplanes you might be coming up to turboprops.
20:51This may replace some of the turboprops.
20:55Although it has the potential to save the airline industry billions of dollars in fuel costs,
21:00savings they could in turn pass on to their customers,
21:03the success of the prop fan ultimately depends on public approval and industry demand.
21:09In a world increasingly attentive to energy efficiency,
21:13exciting new developments in transportation feature an old concept in a bold new form.
21:20The propeller.
21:23Join us again next time for First Flights.
21:28Music And Grings고요
21:28Don't
21:28buy us' tag you Don't
21:29us' tag You Can't
Comments