Propellors on Stratocruiser, DC6/7 & Britannia

[b377]

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.

[DC-ATE]

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.

[b377]

Yes indeed, but the point is that square and round tip props were used interchangably and concurrently on the same a/c.

[DC-ATE]

Only thing I can think of then is the aircraft in question was not intended to operate at its maximum speed or a $$ factor.

[enicalyth]

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.

[b377]

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.

[411A]

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.:(

[b377]

http://cdn-www.airliners.net/aviation-photos/photos/1/1/6/0093611.jpg

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.

[b377]

Square Tips

http://cdn-www.airliners.net/aviation-photos/photos/9/6/3/0121369.jpg

[b377]

Round tips ...

http://cdn-www.airliners.net/aviation-photos/photos/6/5/4/1279456.jpg

[Rick777]

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?

[Zoner]

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.

[Spooky 2]

American Flyers also had the round tips on teir Electras.

[Bullethead]

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.

[tonytech2]

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.

[b377]

tonytech2 (http://www.pprune.org/members/192721-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.

[411A]

Does that mean no hydraulics even for landing gear?


The landing gear operation on the Stratocruiser was electric.
Hydraulics were used for brakes (Hayes expander tube) and control surface boost.
The Stratocruiser was quite nice to fly...very quiet on the FD.

[b377]

The Stratocruiser was quite nice to fly...very quiet on the FD


On a BOAC Stratocruiser night flight NY- LDN, I recall my mother saying that the Captain had advised that an engine (or two) were being shut down as a routine measure for passenger comfort ( less noise and virbartion one presumes).

I wonder how 'routine' the reason given really was, the real reason being more likely engine temperature issues ? What days!

[Storminnorm]

I believe that Dan- Air used to reduce both inboard engines on
the DH Comet to flight idle in the cruise.
Quieter and saved on fuel.

[barit1]

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. :ugh:

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.

[b377]

thanks for all the contributions !

one final question for those in the savvy:

variable pitch props also called constant speed props, sounds like a misnomer as engine/shaft RPM can be varied. Infact having independent throttle and RPM settings is curious, as we now have pitch, RPM and throttle to play with.

[barit1]

In general - today - variable pitch props are constant speed, although there are exceptions outside the airline world:

- Early counterweight props (the counterweight being used to drive the prop to coarse or high pitch) often had a simple two-position control valve, to select either full coarse (i.e. low rpm) or full fine pitch (i.e. high rpm). It had the advantage of being simple and troublefree.

- Ultralights may have a direct hand-crank pitch selection, anywhere from full fine to full coarse or anywhere between.

Adding a governor to the former makes the prop constant-speed (although the pilot is able to select any RPM within a set range). Thus the two controls are throttle and prop rpm.

If feathering is added to the above, the feather feature may either be a additional control, or it may be integrated with the prop rpm control.

But with a constant speed prop, I've never seen a separate "pitch" control - pitch is controlled by the governor.

[tonytech2]

The original Ham Standard counterweight two position props had a ten degree pitch range. Oil pressure took them to low (fine) pitch, counterweights to high (coarse) pitch. Pilot could select low pitch for takeoff, high pitch for cruise. Once in a set position, RPM would vary dependent on throttle and airspeed.

When they needed a "constant speed prop" they added a governor, the props got a fifteen degree pitch range and a big spring inside to help movement. Pilot could select his RPM within the governing range and if sufficient power was there to take it to that rpm. The constant speed name meant it would maintain the selected rpm despite throttle movement or airspeed changes. prop pitch would change to maitain that rpm.

Ham Standard Hydramatics had oil pressure on both sides of piston. You could select your rpm as with the counterweight constant speed prop.

Curtiss Electrics were different. You could manually toggle the prop pitch to whatever pitch you desired and there it stayed. RPM wuld vary with throttle. If you selected Automatic, it followed either a governor mounted on the engine or a electric master motor for synchronzation depending on the aircraft installation. The governor or the master motor could be set for the desired rpm and you now had a constant speed prop.

One peculiarity, at least on Connies, the Ham Standard Hydromatics prop control switches had three positions "Increase" "Decrease" and "Automatic" - There was no OFF position. The Increase/Decrease referred to RPM selection. Curtiss installations the prop switchs had four positions "Increase" Decrease" OFF" "Automatic" BUT the Increase/Decrease referred to prop pitch - effect was direct opposite of the Ham Standard markings. When you worked mixed fleets you had to watch what you were doing. On the Curtiss you selected the rpm you wanted with a Master Motor lever and when you put the prop switches to AUTO the engines slaved to the master motor.

[b377]

Very interesting!

So on the governed CS props what criteria did the pilot use to select the best RMP and throttle setting for a given flight profile ( height & speed) ? I assume that once these two were selected pitch was automatically adjusted by the gov (not by the pilot). Does the DC3 fall in this category?

WRT Connie props, indeed if flying a mixed fleet you really had to watch what you were doing.

[barit1]

I have heard (via a close friend, ex-TWA F/E) that typical cruise for R-2800's in Convairs or DC-6's was full low RPM, full open throttle (at altitude there was no worry of overboosting the engine).

We used to cruise an R-985 (on a Howard DGA) at 1650 RPM and 26"Hg MAP - this gave good fuel economy, quieter cabin, and less than 50% power for longer engine life.

[DC-ATE]

"Michigan City Criuse" on our DC-6s was 30"x 2000RPM. We simply called it "30-20" . If you take a look at the long range cruise charts for the R-2800 you'll see some wierd power settings.

[b377]

So it looks like Hamilton Standard ruled the propellor roost as single supplier once Curtiss Electric's were scrapped.

Any other players?

[tonytech2]

Aeroproductsd made most of the props for the Lockheed L-188 Electras although, as mentioned, KLM and American Flyers used Ham Standards. They faded away too though.

[b377]

Google Image Result for http://www.enginehistory.org/Propellers/propstories/CurtElecProp.jpg (http://images.google.co.uk/imgres?imgurl=http://www.enginehistory.org/Propellers/propstories/CurtElecProp.jpg&imgrefurl=http://www.enginehistory.org/Propellers/propstories/propstories.htm&usg=__hMIO8f2bP-Bo8zT2QyolYVunyN8=&h=1840&w=2726&sz=1054&hl=en&start=68&tbnid=JrWD-CwttVI9MM:&tbnh=101&tbnw=150&prev=/images%3Fq%3Dstratocruiser%26start%3D60%26imgsz%3Dhuge%26gbv %3D2%26ndsp%3D20%26hl%3Den%26sa%3DN)

Some interesting prop stuff here ...

Can any one enlighten me on the synchroniser pictured there? Was this unique to the connie?

[DC-ATE]

We could sync the props/engines on the DC-6. Either engine #2 or #3 could be selected for the others to slave to.

[b377]

We could sync the props/engines on the DC-6. Either engine #2 or #3 could be selected for the others to slave to.


What sort of sync was it , RPM or actual magneto firing.

This goes back to my original question at start of this thread asking for an explanation to the difference in sound between a connie, L 1049 say, and the Douglases. Someone commented before that the PRT probably had a lot to do with the difference.

Regarding syncing on the DC6 was there a significant difference in sound when in sync or just less vibration. Although the criteria was probably to obtain equal thrust (power) from all engines.

[DC-ATE]

I have no recollection of what actually made the engines stay in sync. I have a feeling it was rpm-related though, because they were held to within 3% PRM of the 'master' engine to prevent problems if you feathered one or had an overspeed.

Definitely, engines with the PRTs were a more subdued sound compared to those without. That's for the 3350s; 2800s and les did not have PRTs.

I can't really remember much difference on the DC-6 with sync on or off. A good engineer could sync 'em just as good.

[Spooky 2]

The 1649A Constellation had a phase sync that worked similar to that on the L188 in that it synced the props so that they would position in a phase aray, thus minimizg the noise. The DC6B and DC7C has engine syncronizer that used either #s 2 0r 3 as the master. As I recall you pushed a sysnc button the the RPMs would move up to 4% to match the master engine. Don't bet any big money on that explanation!:}

[411A]

Having flown the Lockheed 1649, it did indeed work as advertised with regard to propeller sync.
A very reliable system, that had no particular faults that I can recall.

[DC-ATE]

As I recall you pushed a sysnc button the the RPMs would move up to 4% to match the master engine.

Ah...yes. Forgot about that little button. Exactly. We kept pushing that thing all the time. But my book says 3%. (picky, picky, picky!)

I don't remember the Connies having any button.

[Old Fella]

The Aeroproducts 3 blade prop (15 feet diameter) on the C130A could be operated in basic hydraulic governing as an individual unit, it could be electronically governed as an individual unit or it could be syncronised with other props. No 1 or No 2 could be selected as the master prop and the others slaved to it. There was no syncro-phasing provision. Later C130's with the 4 blade HS prop (13 feet 6 inch diameter) had syncro-phasing which did help lower the noise level and lower vibration levels. Of course the distance between passing blade tips was greater with the HS and also the tip speed was lower due to the smaller diameter. Although the Aeroproducts prop was a bit noisier, it was a simple prop and could be changed much quicker than the HS. The sound of an A model was distinctly different to later HS equipped aircraft, all of which used the Allison T56 powerplant. As for reliability, in my RAAF days the catch-cry was "A's are for GO - E's are for Show" when we operated these two models in different squadrons. With only 12 of each in each squadron it was the A model that got the whole twelve in a formation fly-past, something the E model didn't ever achieve to my knowledge. A few celebratory ales went down at "Ma's" pub that day.

[b377]

Any Britannia pilots out there ?

I have been told that one of the chracteristics of the Britannia turboprop sound was due to the engines seldom staying in phase-sync long however hard the FE tried- so you would get that slow beat as the sound faded in and out - you always knew it was a Britannia in the distance due to that slow beat.

[Spooky 2]

I also seem to recall pilots and FE's using the Adil (SP?) light to shine back on the props of the CL44 in an attempt to sync the props. Maybe just goofng around as surely this was not an approved procedure.

[tonytech2]

Quite a difference between prop sync on a Curtiss Electric and a Ham Standard. The Ham Standard utilized the regular tach generator signal from each engine to a Sync Box. The sync box had a mechanical control from the prop lever(s). You moved the prop lever and the props then slaved to it by the box sending "increase" / "decrease" signals to the electric trim head on the propellor governors. Except for the prop lever input, the sync box was all electronic, and hence was quiet. On the L-1649 they added a sensor that picked up prop phase and signaled the prop sync box. It was truly magic and I don't remember it as giving us any trouble.

With Curtiss Electrics there was a separate prop alternator on each engine that that sat where the governor would sit. A prop sync unit was in the cockpit, It had a "master motor" whose speed was controlled by the prop lever and there was a master motor tach indicator reading the selected rpm. There was a prop contactor for each engine mounted on the master motor and their speed was driven by the prop alternator on each engine.

If the contactor's rpm matched the master motor rpm all was relatively quiet. If it didn't, an electrical contacts closed and sent power to the electric motor in the prop hub causing a increase or decrease pitch change. It was quite noisy what with the master motor running, the four contactor motors running and the electrical contactors clacking away as they sought to hold rpm. In retrospect, I wonder what it sounded like on a B-36 with six props to control.

I think that was an Aldis lamp.

[NG_Kaptain]

Damn,
My ex threw away my PBY,DC6, DC7 and C46 manuals, (also the Hs748, L1011, B 707-100-227 and 351) so I wish I could join in this discussion, though I do remember the six was a lot of fun to start. Why do ex wives think our treasures are junk?