- 16 hours ago
For educational purposes
The Wright brothers realized that a propeller was a rotating wing – giving it a twist made it practical.
By the mid 1930s, variable pitch and NACA research revolutionized propeller design. With the coming of the jet age, propellers fell out of favor for large aircraft.
But designers soon realized that a fast turboprop with an advanced propeller could be more efficient than the best jetliners.
Featured Aircraft:
- Wright Flyer
- scimitar prop Stiletto
- NASA Gulfstream 2 propfan testbed
The Wright brothers realized that a propeller was a rotating wing – giving it a twist made it practical.
By the mid 1930s, variable pitch and NACA research revolutionized propeller design. With the coming of the jet age, propellers fell out of favor for large aircraft.
But designers soon realized that a fast turboprop with an advanced propeller could be more efficient than the best jetliners.
Featured Aircraft:
- Wright Flyer
- scimitar prop Stiletto
- NASA Gulfstream 2 propfan testbed
Category
📚
LearningTranscript
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
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