Sorry if this has been discussed before, but I've seen pictures of propliners with rounded prop blades and others with squared-off ones. Is there an advantage over one to the other?

Thanks

I too have noticed the different shaped tips over the years. I 've felt it probably depended on the designers preference as in the choice between Ford or Chev. I do notice however that square tips seem to be used on broad chord or paddle wheel blades. I am looking at a photo of a third type of blade which is shaped like a scimitar. This particular example is made by Stupino and is contra-rotating with eight blades front and six blades rear. It is claimed to be incredably efficient. The chord is very broad. From the photo, it resembles a large marine prop but thats not what it is. Sorry if Ive rambled too much but your question about props pressed my button. Its something about which I've been curious for years. Anyone else care to comment?
Lee

This is interesting.

Perhaps someone with more technical knowledge than me can comment on why some of the pistonliners had hollow bladed propellors, whilst others had solid blades. I am thinking here of the problems the Stratocruisers had with these different types of blades.

See also what Ruud Leeuw says about some similar problems with early Connies, at http://www.ruudleeuw.com/con-n749nl-his.htm

The Cessnas that I rent seem to come with both types. I have not noticed a difference in performance or noise. The squared-off type seems to be newer. A 1948 textbook I have on aircraft power plants does not show any squared-off ones in the propeller chapters.

I don't know much about the details, but there have been both designs since the early 50's.

First example - DC-6's. The first DC-6's with R-2800 CA-15 engines came with rounded tipped props. They were typically rated a 2100 HP (dry). Then the DC-6A and DC-6B came out with R-2800 CB-16 engines (2400 HP wet). These have square tipped props. When early DC-6's were re-equipped with CB-16 engines, they would get square tipped props too. Someone told me that square tips were a way to get extra power out of a prop with the same diameter.

Second (and later) example: In 1959 the L-188 Electra was offered with two prop choices - the square tipped Aeroproducts prop (very typical), and the round tipped Hamilton-Standard prop (KLM and a few others). I assume that this tip choice was just a design decision by the respective prop makers. BTW, the later P-3's all got the Ham-Stan prop.

Hope this helps,

Tom

The square tipped props were also a wider design, to move the same volume of air as the round tipped props without the length, giving more ground clearance. The Curtiss Electric hollow props like the ones used on the Dutch Connie were made of steel, so they were made hollow to save weight, while the Hamilton Standards are solid aluminum.

According to information in the book "Magnesium Overcast" (about B36's) Convair found that square tipped blades also had a lot more turbulence than round tipped ones.

This resulted in the inner engines causing very a uncomfortable ride for the crews in the rear of thebomber while in flight. IT was common practice on these birds to shut down the 2 inner engines while in cruise, to escape this.

Sorry guys,

I got it wrong. It was discovered that square tipped props had less turbulence than round tipped ones.

Hence most B36's were retrofitted with square tipped propellors.

Probably why such airplanes as the L188 Electra and later Vickers Viscounts and Focker (and licence built Fairchild) Friendships all had square tipped props.

Those prop jets sure could get some revs up at take off.

I remember the scream of the RR Dart powered Viscounts and Fockers and the roar of the paddled bladed Allisons on the Electra, as the props were shifted through their pitch range during taxiing (Loved the Electra's sound.)

I agree with you David. When I was going to A&P school in about 1972, we had a L-188 Lockheed Electra stop in at our airport (Southern Illinois Airport in Carbondale). The occasion was the presidential primaries. Ed Muskie flew in on the Electra. I remember several things about it. I could clearly see the telltale wisps of jet exhaust trailing behind it as it was on long final. I still remember the sound of the Allison 501's taxiing to the apron. The flight crew cut 1 & 2 as she got near. She swung the square tipped props. The Electra is fairly quiet in the ground (from the outside). In looking at the 6 x 6 picture I have of that occasion, the upper portion of the fuselage is white. There is a 3' wide dark blue stripe extending the length of the fuselage (just above the windows). The windows and below are polished (like a mirror) aluminum. Just forward of the forward passenger window there is a 3' wide red stripe that extends forward underneath the cockpit windows and catches the upper part of the radome. The vertical stabilizer and rudder are red.
The Viscount was probably louder at ground idle than it was at full power owing to the loud (but reliable) Rolls Royce Darts. We had a former Capitol/United Airlines Viscount that we ran up for Jet Powerplant class. Four Dowty Rotol 4 bladed props as I recall.
Ah....memories.
Best Holiday Wishes to All!

Thanks for all the info guys.

Re the sound of the classic turbprops: I well remember the very high pitched sound the RR Darts on Viscounts used to make on start up, caused by the tips of the centrifugal compressors-whatever they are-so I read.

Viscounts "sang," as did/do HS748s and F27s. Vanguards "purred," as did the Brittania and the CL44.
But modern propliners, with their hyper-efficient multi-bladed props, just make a nasty roaring sound.

The other thing I remember about the Dart powered airplanes that I never saw on an Electra, was at take off.

Viewed from inside the cabin, when the Dart powered airplanes came to full take off power and take off pitch, one could see condensation forming around the prop tips and going backwards in a funnel shape.

This was especially prevalant on a cool humid day.

The best examples I saw were on take off from Singapore Airport at 7.00 a.m.,(on vrious flights that I flew on many years ago)on Malayan Airways (now Singapore Airlines) Viscounts and F27 Friendships.

The other time it was really noticeable was on a Mount Cook Airlines HS 748 (also Dart powered) taking off from Queenstown Airport, in the South Island of New Zealand.

Interestingly, that airplane had round tipped props.

That particular flight was most memorable becasue it included a stop at Mount Cook township.

To get in and out of that strip, the airplane flew into a long valley and then spiralled down.

The valley sides were not far from the wing tips and as the airplane got lower, one looked UP at skiers on the slopes above.

Take off was the exact reverse. When sufficient altitude had been achieved to clear the valley, this was done with the airplane clearing the ridge top by only a few hundred feet.

I think that occurs with propellers on most any aircraft depending on the rpm, moisture in the air and the temperature. This can be seen on military aircraft, fighters included with propellers. Here at almost sea level you can see it on propeller driven
aircraft....again if the outside elements are just right. When I flew as a passenger in propeller driven airliners...Convair liners, Douglas transports
etc I always looked forward to seeing the moisture whipping back from the arc of the props.

Doug

Propellers are a lift device, so the same pressure anomalies that occur on wings occur on props. An increase in air speed leads to a decrease in pressure. The reason one witnesses this 'condensation' effect is because the surrounding air pressure drops low enough to cause the saturated air to condense. This is why you see 'clouds' form at the inlet to turbine engines, prop tip vorticies, and wing surfaces/vorticies. The more saturated the air, the more apt you are to see this effect.

I recall seeing this once when I was a kid. We were taking off from Nashville in a DC6 during a rainstorm. Ad the engines ran up you could see this conical shape of condensation and water coming off the back of the props, and as the plane picked up speed, you could see the spirals from the prop tips.

I booked a flight on one of PSA's last Electra flights just to put an L 188 in my log. On taxying from Burbank CA there was a SPECTACULAR light show display of glowing ionized gas on the props, greens, oranges and whites in color. What was this phenomena? I have never seen anything like it. Some sort of static electricity phenomena? Were the props acting like Van de Graff generators producing very high static voltages that ionized the air around them? Some passengers were fightened, but the pilot announced that it was a natural phenomena and not a cause for concern.

I can testify to the piercing scream of the RR turbos on shutdown. I remember standing about 100 feet from a GulfstreamI and hearing the ungodly howl from the Darts as they spooled down. The occassion was during the search for an Electra that had disintegrated in flight. The Gulfstream was full of then state of the art electronic detection devices to locate the pieces. Thirty days later, the only surviving passenger walked out and that is how we found the wreck. I flew in the Electras until they were withdrawn from service and enjoyed their quiet operation. Just a point of interest. We used to leave Pucalpa just ahead of Bac 111 and be right behind it on final when it arrived at Lima. A distance of about 400 miles.
Lee