Propellors on Stratocruiser, DC6/7 & Britannia
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Propellors on Stratocruiser, DC6/7 & Britannia
On topics about the DC6, 7 and Constellations & Stratocruisers mention is often made of the props used on the Wright and P&W engines as being either Curtiss Electric (CE) or Hamilton Standard (HS).
I have had a long standing query as to why some aircraft like the B377 have square tipped props on some a/c and while other Strats ( even owned by same operator such as BOAC) have rounded tips? Same goes for DC6 and DC7s. Is it possible to visually tell apart a CE vs. HS propellor?
I have also noticed on a few Britannia pics that some a/c have rounded tip props and others square tipped and even seen mixed square/round props on same a/c. These were presumably Rotol?
I know prop hub spinners were optional kit so this easily explains this difference.
I have had a long standing query as to why some aircraft like the B377 have square tipped props on some a/c and while other Strats ( even owned by same operator such as BOAC) have rounded tips? Same goes for DC6 and DC7s. Is it possible to visually tell apart a CE vs. HS propellor?
I have also noticed on a few Britannia pics that some a/c have rounded tip props and others square tipped and even seen mixed square/round props on same a/c. These were presumably Rotol?
I know prop hub spinners were optional kit so this easily explains this difference.
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Do a search on propellers and that'll probably explain it better than I can. But basically, it has to do with tip speeds. Square tips can't go as fast as round tips. It has to do with the speed the aircraft will operate. Faster aircraft like the Stratocruisers and Connies usually have round tips, whereas the DC-6 will have square tips.
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square versus rounded
May I suggest you google naca or even subscribe to the nasa library on-line where a search will turn up hundreds if not thousands of references.
Many older prop designs were designed with the Clark Y series of airfoils because that was about all there was to hand and folks knew how they flew. Other later designs were predicated on with the troublesome NACA 16 sections.
Clark sections always worked very well and given their largely empirical origins people got very sniffy about the intellectual rigour needed to design really good airfoils which the naca 16 series was supposed to be. But to widespread embarrassment they didn't quite live up to expectations hence the many naca papers behind the scenes, highly secret back then but open reading now.
I think they (naca 16) turned out to be bad where they were supposed to be good and vice versa. Is it not the case that where you have manageable tip speed and a lot of thrust to develop when carrying a lot of weight square was fashionable choice?. It got you the power loading, the activity factor and the efficiency you needed.
Prop tip speed, advance ratio, power coefficient, thrust coefficient, number of blades, propulsive efficiency and activity factor all interplay with each other and of course with the role end user aircraft - A Grumman Hellcat, a P-51 and a Lockheed Constellation have different thrust vs speed requirements but they often had the same prop aerodynamicist - the late Bill Practice. If you can obtain a copy of "Bill Practice's Notebook" his worked examples take you through the evolutions.
As to different props on different wings, well that is nothing to the "DC2-and-a-half" where wartime repair exigencies caused at least one DC transport to have a DC-2 wing on one side and a DC-3 on the other!
Most actual marques fitted only one predominant type of prop, not surprisingly determined by the engine be it a Wright Cyclone or a P&W Wasp. And wsn't Rotol a shotgun marriage of R-R [Ro] and Bristol [tol]?
I have quite forgotten the CE in my mind's eye but the Hamilton Standard was always recognisable through the, [was it blue and yellow?], logo. It's a bit like the difference between Airbus and Boeing, it helps to know which airports certain fleets use! It's not the shape of the nose or tail, or how many Kuchemann carrots on the wing but "it's one of those because the other lot fly from gatwick".
Mind wandering as usual, ignore me, I'll go back to sleep.
Many older prop designs were designed with the Clark Y series of airfoils because that was about all there was to hand and folks knew how they flew. Other later designs were predicated on with the troublesome NACA 16 sections.
Clark sections always worked very well and given their largely empirical origins people got very sniffy about the intellectual rigour needed to design really good airfoils which the naca 16 series was supposed to be. But to widespread embarrassment they didn't quite live up to expectations hence the many naca papers behind the scenes, highly secret back then but open reading now.
I think they (naca 16) turned out to be bad where they were supposed to be good and vice versa. Is it not the case that where you have manageable tip speed and a lot of thrust to develop when carrying a lot of weight square was fashionable choice?. It got you the power loading, the activity factor and the efficiency you needed.
Prop tip speed, advance ratio, power coefficient, thrust coefficient, number of blades, propulsive efficiency and activity factor all interplay with each other and of course with the role end user aircraft - A Grumman Hellcat, a P-51 and a Lockheed Constellation have different thrust vs speed requirements but they often had the same prop aerodynamicist - the late Bill Practice. If you can obtain a copy of "Bill Practice's Notebook" his worked examples take you through the evolutions.
As to different props on different wings, well that is nothing to the "DC2-and-a-half" where wartime repair exigencies caused at least one DC transport to have a DC-2 wing on one side and a DC-3 on the other!
Most actual marques fitted only one predominant type of prop, not surprisingly determined by the engine be it a Wright Cyclone or a P&W Wasp. And wsn't Rotol a shotgun marriage of R-R [Ro] and Bristol [tol]?
I have quite forgotten the CE in my mind's eye but the Hamilton Standard was always recognisable through the, [was it blue and yellow?], logo. It's a bit like the difference between Airbus and Boeing, it helps to know which airports certain fleets use! It's not the shape of the nose or tail, or how many Kuchemann carrots on the wing but "it's one of those because the other lot fly from gatwick".
Mind wandering as usual, ignore me, I'll go back to sleep.
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All great stuff ... but notwithstanding the science or art behind prop design all too often mixed tip designs were seen on the same a/c hanging on No 1, 2, 3 or 4 engines. Early strats are usually seen with round tips and later most BOAC used square but not exclusively. I thought it was probably a CE / HS difference but who knows.
As I mentioned even the Bristol Britannia Proteous engine is often seen sporting odd prop configs. on same airframe.
As I mentioned even the Bristol Britannia Proteous engine is often seen sporting odd prop configs. on same airframe.
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Some Stratocruisers indeed were delivered with CurtisElectric propellers, however, all operators changed over to Hamilton Standard Hydromatics for one very important reason...the CurtisElectric props, apart from being very complicated and maintenance intensive, had hollow steel blades, which were prone to severe corrosion, especially under the de-ice boot.
In addition the only DC-6 to ever have CurtisElectric propellers crashed many years ago at KVNY because....one prop blade separated from a RH side engine, tore the engine off the wing (it landed on the departure runway), said prop blade then travelled through the lower fuselage, severing hydraulic lines in the process, then entered the number two engine, disabling the number two propeller AC generator, thus rendering the the number two prop uncontrolable.
Now, the 'ole DC6 could indeed fly in two engines, but, the landing gear was down, and could not be raised (no hydraulics), so performance was severely limited.
The cause of the blade failure?
Undetected corrosion under the blade deice boot.
Those old CurtisElectric props were bad, bad....bad.
In addition the only DC-6 to ever have CurtisElectric propellers crashed many years ago at KVNY because....one prop blade separated from a RH side engine, tore the engine off the wing (it landed on the departure runway), said prop blade then travelled through the lower fuselage, severing hydraulic lines in the process, then entered the number two engine, disabling the number two propeller AC generator, thus rendering the the number two prop uncontrolable.
Now, the 'ole DC6 could indeed fly in two engines, but, the landing gear was down, and could not be raised (no hydraulics), so performance was severely limited.
The cause of the blade failure?
Undetected corrosion under the blade deice boot.
Those old CurtisElectric props were bad, bad....bad.
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Mixed prop job ...
A spares holdings issue no doubt.
Wonder if the Brit Proteus could use HS props ? For expediency just pull'em off a Stratocruiser and stick'en on a Britannia.
Last edited by b377; 12th Feb 2009 at 14:42.
What I know about props could easily be written on the head of a pin, but this an interesting discussion. If shape is related to speed and round tips are faster why to C-130's have square tips on the newer and presumably faster models?
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Back in the dark ages my dad flew Lockheed Electra (188) line #3. Before it was delivered to the customer (L.A. Dodgers) it was used as a test bed for upgraded engines and props. The engineers always said they preferred the Ham Standard (Round Tips) props as they were slightly more efficient than the Aeroproducts (square tips). The Aeroproducts were cheaper and that was what the airlines ordered. (except KLM) The increased efficiency was not enough to offset the initial cost. My guess is that the bean counters usually win.
The C130H Hercules and the P3C Orion both have slightly different versions of the same engine but the Herc has square tipped props and the Orion round tipped props.
I was told many many moons ago, when I was flying Hercs, that the Herc props were optimised for greater thrust at low speeds in order to have better takeoff performance from unimproved strips and the Orion's props were optimised for high speed cruise where it spent a lot of it's time. The Orion Vmo is nearly a hundred knots faster than that of a Herc, 410 ish, I think, for the Orion and 324kts for the Herc.
Never sw a Herc or an Orion with a mix and match though.
Regards,
BH.
I was told many many moons ago, when I was flying Hercs, that the Herc props were optimised for greater thrust at low speeds in order to have better takeoff performance from unimproved strips and the Orion's props were optimised for high speed cruise where it spent a lot of it's time. The Orion Vmo is nearly a hundred knots faster than that of a Herc, 410 ish, I think, for the Orion and 324kts for the Herc.
Never sw a Herc or an Orion with a mix and match though.
Regards,
BH.
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I had posted this on Nostalgia
On the B377, the Ham Standard props originally fitted had square-tipped hollow steel blades. Gave tremendous problems finally leading to a Airworthiness Directive requiring for frequent magnetic inspections of blades. They changed over to solid dural blades and these had the rounded tips. United Airlines, uniquely I believe, had Curtiss Electric props fitted. On the sale of the UAL B377 fleet to BOAC the aircraft were converted to Ham Standards requiring, in addition to major wiring changes, removal of the engine nose cases for rework and installation of oil passages.
United also, I think alone of the B377 operators, did not have a proper flight engineer's station but seated the FE just behind the throttle pedestals facing forward. All the engine instruments, etc that were normally on the FE panel were up front. BOAC required installation of an FE station plus conversion to HS props and this required almost complete gutting of electrical looms in wings and fuselage and their replacement. The B377 was almost all electric in operation so this was a major project.
These aircraft also went to higher density seating and this mandated installation of an additional overwing exit on each side. UAL aircraft had the square windows.
All this work was done at Lockheed Air Service International (LASI) at Idlewild International Airport (KIDL) in New York. Was said to be one of the biggest conversion projects done at that time. DeHavilland props were license built modified Ham Standards. The Bristol Britannia had these fitted. Like the Stratocruiser, they went from the steel to the solid dural blades and that is when the tips went from square to rounded.
Prop configurations were quite variable and dependent on customers preference. Many L-749 Constellations, expecially those of non-US companies utilized Curtiss Electrics which had quite a broad butter-paddle shape for their steel blades. USAF C-121A (L749 types) Connies had them too. Later military Connies (L-1049 types), USAF and US Navy all had Ham Standards. Seaboard and Western Airlines had Curtiss Electrics (square tips) on their L-1049 D and H models. Their single L-1049E-01 passenger aircraft had Ham Standards.
Northwest Orient sold their four L-1049G Connies to LAV of Venezuala. These had Ham Standard props but they were squarish-tipped dural blades (rouned corners) and, unlike any other Connies I ever worked, had electric prop deicing boots on the blades. These required alternators to be fitted on the inboard engines for power. All other Connies I saw had alcohol slinger rings and rubber distribution boots on the blades.
Only DC-6 I worked with Curtiss Electrics was a VC-118 that LASI converted from HS to the Curtiss for USAF for a cold-weather mission. I know there were other civil DC-6 with Curtiss props but I never saw any by 1954 when I started work.
Most Electras had Aeroproduct props with square tipped steel blades. American Flyers and KLM had Hamilton Standards. Customer's choice again.
On the B377, the Ham Standard props originally fitted had square-tipped hollow steel blades. Gave tremendous problems finally leading to a Airworthiness Directive requiring for frequent magnetic inspections of blades. They changed over to solid dural blades and these had the rounded tips. United Airlines, uniquely I believe, had Curtiss Electric props fitted. On the sale of the UAL B377 fleet to BOAC the aircraft were converted to Ham Standards requiring, in addition to major wiring changes, removal of the engine nose cases for rework and installation of oil passages.
United also, I think alone of the B377 operators, did not have a proper flight engineer's station but seated the FE just behind the throttle pedestals facing forward. All the engine instruments, etc that were normally on the FE panel were up front. BOAC required installation of an FE station plus conversion to HS props and this required almost complete gutting of electrical looms in wings and fuselage and their replacement. The B377 was almost all electric in operation so this was a major project.
These aircraft also went to higher density seating and this mandated installation of an additional overwing exit on each side. UAL aircraft had the square windows.
All this work was done at Lockheed Air Service International (LASI) at Idlewild International Airport (KIDL) in New York. Was said to be one of the biggest conversion projects done at that time. DeHavilland props were license built modified Ham Standards. The Bristol Britannia had these fitted. Like the Stratocruiser, they went from the steel to the solid dural blades and that is when the tips went from square to rounded.
Prop configurations were quite variable and dependent on customers preference. Many L-749 Constellations, expecially those of non-US companies utilized Curtiss Electrics which had quite a broad butter-paddle shape for their steel blades. USAF C-121A (L749 types) Connies had them too. Later military Connies (L-1049 types), USAF and US Navy all had Ham Standards. Seaboard and Western Airlines had Curtiss Electrics (square tips) on their L-1049 D and H models. Their single L-1049E-01 passenger aircraft had Ham Standards.
Northwest Orient sold their four L-1049G Connies to LAV of Venezuala. These had Ham Standard props but they were squarish-tipped dural blades (rouned corners) and, unlike any other Connies I ever worked, had electric prop deicing boots on the blades. These required alternators to be fitted on the inboard engines for power. All other Connies I saw had alcohol slinger rings and rubber distribution boots on the blades.
Only DC-6 I worked with Curtiss Electrics was a VC-118 that LASI converted from HS to the Curtiss for USAF for a cold-weather mission. I know there were other civil DC-6 with Curtiss props but I never saw any by 1954 when I started work.
Most Electras had Aeroproduct props with square tipped steel blades. American Flyers and KLM had Hamilton Standards. Customer's choice again.
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tonytech2
thanks this is one of the best contributions to this thread so far! Great information. The reason behind sqaure vs. rounded prop tips has always intrigued me.
As a very young kid I grew up travelling on DC3s with rounded tip HS props, and later when I flew in a Strat and a Britannia I was impressed by the handsome square tipped props.
To recap then:
- the original steel HS were square tipped
- the later improved HS dural were round tipped
- CE were all square tipped and were superceded by dural HS
- The original Britannia props were steel square tipped HS types made under license by de Havilland (and later upgraded to the dural HS type, round tip)
One question remains : why were some planes fitted with both types (round and square) at same time like the Britannia in the pic above?
Was that just an interim step while all were replaced by the upgraded round tip HS?
I suppose the CE props aligned well with the all electric concept for the B377. Does that mean no hydraulics even for landing gear?
Reenginering the whole of the old United fleet by BOAC is quite incredible
considering the short life of the Strat in airline service.
thanks this is one of the best contributions to this thread so far! Great information. The reason behind sqaure vs. rounded prop tips has always intrigued me.
As a very young kid I grew up travelling on DC3s with rounded tip HS props, and later when I flew in a Strat and a Britannia I was impressed by the handsome square tipped props.
To recap then:
- the original steel HS were square tipped
- the later improved HS dural were round tipped
- CE were all square tipped and were superceded by dural HS
- The original Britannia props were steel square tipped HS types made under license by de Havilland (and later upgraded to the dural HS type, round tip)
One question remains : why were some planes fitted with both types (round and square) at same time like the Britannia in the pic above?
Was that just an interim step while all were replaced by the upgraded round tip HS?
I suppose the CE props aligned well with the all electric concept for the B377. Does that mean no hydraulics even for landing gear?
Reenginering the whole of the old United fleet by BOAC is quite incredible
considering the short life of the Strat in airline service.
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Does that mean no hydraulics even for landing gear?
Hydraulics were used for brakes (Hayes expander tube) and control surface boost.
The Stratocruiser was quite nice to fly...very quiet on the FD.
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The Stratocruiser was quite nice to fly...very quiet on the FD
I wonder how 'routine' the reason given really was, the real reason being more likely engine temperature issues ? What days!
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Gas turbine engines are invariably inefficient at/near idle (SFC goes way up); thus reducing thrust on some (and maintaining thrust on others) "to save fuel" is invariably counterproductive. 
In a loitering / low-speed patrol mission, where not much thrust is needed, it is most efficient to shut down one or more engines, not merely reduce to idle.
In a loitering / low-speed patrol mission, where not much thrust is needed, it is most efficient to shut down one or more engines, not merely reduce to idle.