Propellors on Stratocruiser, DC6/7 & Britannia
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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.
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.
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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.
- 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.
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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.
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.
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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.
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.
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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.
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.
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"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.
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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.
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Google Image Result for http://www.enginehistory.org/Propellers/propstories/CurtElecProp.jpg
Some interesting prop stuff here ...
Can any one enlighten me on the synchroniser pictured there? Was this unique to the connie?
Some interesting prop stuff here ...
Can any one enlighten me on the synchroniser pictured there? Was this unique to the connie?
Last edited by b377; 24th Feb 2009 at 14:51.
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We could sync the props/engines on the DC-6. Either engine #2 or #3 could be selected for the others to slave to.
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.
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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.
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.
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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!
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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.
A very reliable system, that had no particular faults that I can recall.
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As I recall you pushed a sysnc button the the RPMs would move up to 4% to match the master engine.
I don't remember the Connies having any button.
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Syncronising/syncrophasing
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.
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Britannia phase-sync
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.
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.
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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.
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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.
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.
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?
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?
