Airscrew pitch control-1942? (1 Viewer)

[MikeMeech]

Hi
Another small book, from 1943, by W Hazell is 'Understanding Aircraft Components, by Question and Answer', has some info relating to Constant-Speed airscrews, extract below:

Mike

 

[MikeMeech]

Hi
As for the 'Types' of airscrew and the terms for them these extracts from a mid-1940s book, 'Aeronautical Engineering, A practical guide for everyone connected with the Aircraft Industry' edited by R A Beaumont, may be of use:

Mike

 

[SaparotRob]

Hi
Another small book, from 1943, by W Hazell is 'Understanding Aircraft Components, by Question and Answer', has some info relating to Constant-Speed airscrews, extract below:
View attachment 859251
View attachment 859252
View attachment 859253
View attachment 859254

Mike

I never thought of the effects of outward centrifugal forces acting on props, let alone thirty tons of it. I have thought about variation of speeds along the length of the blade and was amazed they held together. This makes it more impressive.

 

[special ed]

When the big 4 blade props from the C-119 were disassembled, the appx. 1/2 inch balls, which held the blade in the hub, were no longer perfectly round but had small, flat facets on the surface. That's what a 3350 can do.

 

[Writer]

Hi Writer,

Generally, there are many differences in the way that different specific "Constant speed" propeller operating systems function. You should also bear in mind that we are talking relatively early systems here, more modern propeller control is far more complicated. So, I will try to answer your points.

The Spitfire Mk IX had no "pitch controller", the Constant Speed Unit (CSU) is simply a flyweight governor that controls the rpm by adjusting oil flow to the propellers pitch adjusting piston to give propeller pitch adjustment in the correct sense for the rpm required, or no oil flow to hold an rpm when the selected rpm is matched. The CSU has a variable datum to provide a range of controlling rpm. Unfortunately, you ask about Fine and Coarse pitch. The CSU in this type has no pitch input, all it has is the input from the prop speed lever and the actual rpm that is sensed by the flyweights in the speeder cup. In operation with the propeller speed control lever, the desired rpm range is set on the lever by the pilot and the CSU tries to adjust to achieve the selected rpm. Try not to think in terms of specific blade pitch, this aircraft had a Merlin engine that was operated by setting the rpm and Boost according to the details in the flying manual. In the engines power range, the desired rpm was adjusted by setting the propeller speed control lever and the Boost was adjusted by the Throttle setting.
In flight, this is a beautiful system, the engine just purrs along through manoeuvres at the set rpm and Boost and if you change the Throttle position or airspeed, the rpm remains as set.
If the pilot wanted maximum power, he would move the propeller speed control lever forward to FAST or MAX (3000 rpm position) and open the Throttle as required to get the Boost he
desired, or as limited by the Boost regulator.

A take-off problem is always possible if the pilot sets the wrong settings. Setting Slow on a CSU prop or Coarse on a 2-position prop will spoil take-off performance.

Single-lever engine control was fitted to many fighter aircraft by 1944.

Eng

Thank you Engineman, I now understand!
Taking this subject further... I now realise that nearly all the books on flying and fighting by pilots who took part in the World Wars were written by pilots who simply assumed that the reader already understood how the cockpit controls worked. If you didn't have the knowledge of a trained pilot, understanding this was difficult...

 

[Engineman]

Thank you Engineman, I now understand!
Taking this subject further... I now realise that nearly all the books on flying and fighting by pilots who took part in the World Wars were written by pilots who simply assumed that the reader already understood how the cockpit controls worked. If you didn't have the knowledge of a trained pilot, understanding this was difficult...

Thanks Writer. The technical understanding of pilots varied hugely. Believe me, I am a professional engineer and pilot! In those WW2 days, pilots would usually be trained to use their aircraft, with enough technical information to understand the function of the particular type. Although many aircraft systems are similar between types, there are often huge differences in the details.

Eng

 

[Bretoal2]

Here are some excerpts from Pierre Clostermann's original writings in "Le grand cirque 2000" (Flammarion, 2001, pocket edition). This account is not a diary, and many of the events described are not precisely dated, even though they can be linked to different stages of the author's career in the RAF.

Page 55, first time for Spitfire take-off. Said to be Spit Mk II-A TO-S :
"Soudain, comme par miracle, le souffle coupé, je me trouve en l'air... vite j'escamote mon train d'atterrissage, referme le cockpit transparent et le radiateur, réduis les gaz et ramène l'hélice au pas de croisière..."
Next page, returning to airfield " J'ouvre le radiateur en grand, réduis les gaz, pousse l'hélice au petit pas, ouvre mon cockpit..."

Later, some missions with "Alsace group", date not really precise but 1942, spring - Spitfire Mk IX NL-B

Page 87, just after take-off : "Je bloque le levier du train, je réduis les gaz, j'ajuste le pas de l'hélice".

Page 91, meeting a FW-190 group : " je pousse la manette des gaz, hélice au petit pas, je me rapproche..."

And, just for the fun, page 363, first engine start-up with a Sabre (Typhoon) : "Je pousse le levier de changement de pas de l'hélice tout en avant et le recule de quelque centimètres, pour éviter un blocage du dispositif de vitesse constante au décollage".

Conclusion: Clostermann clearly understood that actions on the lever "propeller speed control" allow him to change the propeller pitch—even though no indicator tells him whether this pitch is 30, 40, or 50 degrees. And he knows that when you need to accelerate quickly when flying at low speed or cruising, a propeller with a fine pitch is necessary.

Regardless of the governor's quality, piloting a fighter in these days required the ability to control both manifold pressure and propeller pitch. This is why, on most aircraft of that era, the two levers are concentric.

 

[Maty12]

Don't know about y'all but I found A2A's old video on propellers for their Spitfire to be a very intuitive take on the subject, as they cover fixed pitch, variable-pitch, and constant speed. The best way I can summarize "constant-speed" and why you would want it is that in a simple variable pitch prop (or on a fixed prop) you simply select a pitch for the blades. The RPM will change depending on the speed of the airflow over the blades, so if blade pitch is not adjusted the propeller will spin faster in a dive and slower in a climb. You can compensate for this in a variable-pitch prop by adjusting the propeller's control lever, which in turn changes the pitch to compensate for the faster or slower airflow, but that is two things you have to control at once while maneuvering (throttle for manifold pressure, prop pitch for RPM). As others have described, in a constant-speed propeller you set a desired RPM and the propeller itself will vary the blades' pitch automatically instead to maintain the selected RPM whether the plane is level, climbing or diving, and also gives you propeller overspeed protection to an extent.

View: https://www.youtube.com/watch?v=psYL7thQj6M

As for why you need to change blade pitch at all, the USAAF has a good training film that covers, though sadly Periscope's watermark covers part of the diagrams in the later constant speed section. I used this video to supplement my revising for my CAA propellers exam in fact, though 1940s US and modern day UK seem to disagree about the best angle of attack so I had to be careful not to memorize the wrong values.

View: https://www.youtube.com/watch?v=i1hUzFxErhI

 

[Engineman]

Regardless of the governor's quality, piloting a fighter in these days required the ability to control both manifold pressure and propeller pitch. This is why, on most aircraft of that era, the two levers are concentric.

Hi,
You are still confusing the simplicity of CSU engine control with the trickyness of a basic 2 pitch or simple VP propeller. There is no "ability" needed with a CSU, you simply move the lever to the rpm required. The throttle is simply opened or closed to give the MAP or Boost required. The only procedure is to increase the rpm before increasing throttle (if not already at required rpm) and to decrease the throttle before decreasing rpm (if decrease of rpm is required as well as decreased MAP).

Eng

 

[Bretoal2]

Hi,
You are still confusing the simplicity of CSU engine control with the trickyness of a basic 2 pitch or simple VP propeller. There is no "ability" needed with a CSU, you simply move the lever to the rpm required. The throttle is simply opened or closed to give the MAP or Boost required. The only procedure is to increase the rpm before increasing throttle (if not already at required rpm) and to decrease the throttle before decreasing rpm (if decrease of rpm is required as well as decreased MAP).

Eng

A bit of a return to basics...

I'm not confusing anything at all ; I'm simply reading a text in its original language and demonstrating that what puzzled the author of post #1 isn't a translation error.

That being said, and without wanting to repeat myself for the 10th or 100th time, I'm still not convinced of the propeller governor's complete automaticity.

Would the system be fully automated, what would be the purpose of the lever called "propeller speed control," other than adapting power required by flight conditions to power delivered by the engine/propeller combination? Even ignoring the "true" propeller pitch...

 

[Engineman]

A bit of a return to basics...

I'm not confusing anything at all ; I'm simply reading a text in its original language and demonstrating that what puzzled the author of post #1 isn't a translation error.

That being said, and without wanting to repeat myself for the 10th or 100th time, I'm still not convinced of the propeller governor's complete automaticity.

Would the system be fully automated, what would be the purpose of the lever called "propeller speed control," other than adapting power required by flight conditions to power delivered by the engine/propeller combination? Even ignoring the "true" propeller pitch...

Hi,

Thanks for your reply. I understand your points. Being specific, all different engine/VP propeller installations have their own particular limitations and protocols, but what I have said about basic CSU equipped operation is correct.
With respect to the propeller speed control being a separate lever, this is to facilitate the use of specific throttle and rpm settings , usually above the FTH or in long range cruise etc, not
to mention the need for propeller exercise before flight and other circumstances such as flight in very cold conditions.
Witness the Spitfire Mk IX Pilots notes reference to the AUTOMATIC mode of the Throttle Linked to the CSU control, giving single lever function. However, the lever is "unlinked" to perform those other functions that do not match the basic Boost/rpm profile. Some Merlins using LRC in Bombers, were routinely operated above FTH at altitude with the CSU selected to low CSU rpm (about 1800rpm) and with wide-open throttle to achieve the lowest SFC at LRC speed. With the CSU, this did not require any juggling of the Propeller lever, it was just pulled-back at Slow rpm and maintained 1800rpm, or whatever. With the WOT, if Boost increased above the desired LRC value for best SFC, then the aircraft should be climbed until the Boost reduced and LRC speed maintained. Note, that the CSU is not adjusted in this, it is just selected to the rpm that is required, the CSU does the propeller "fiddling", the Throttle should just be fixed WOT , the Pilot "ability" is in climbing as required to keep the Boost and airspeed at the optimum values. The actual prop pitch is irrelevant to the flying task.

I hope that this illustrates how simple operation with a good CSU is.

Eng

 

[Bretoal2]

Hi,

Thanks for your reply. I understand your points. Being specific, all different engine/VP propeller installations have their own particular limitations and protocols, but what I have said about basic CSU equipped operation is correct.
With respect to the propeller speed control being a separate lever, this is to facilitate the use of specific throttle and rpm settings , usually above the FTH or in long range cruise etc, not
to mention the need for propeller exercise before flight and other circumstances such as flight in very cold conditions.
Witness the Spitfire Mk IX Pilots notes reference to the AUTOMATIC mode of the Throttle Linked to the CSU control, giving single lever function. However, the lever is "unlinked" to perform those other functions that do not match the basic Boost/rpm profile. Some Merlins using LRC in Bombers, were routinely operated above FTH at altitude with the CSU selected to low CSU rpm (about 1800rpm) and with wide-open throttle to achieve the lowest SFC at LRC speed. With the CSU, this did not require any juggling of the Propeller lever, it was just pulled-back at Slow rpm and maintained 1800rpm, or whatever. With the WOT, if Boost increased above the desired LRC value for best SFC, then the aircraft should be climbed until the Boost reduced and LRC speed maintained. Note, that the CSU is not adjusted in this, it is just selected to the rpm that is required, the CSU does the propeller "fiddling", the Throttle should just be fixed WOT , the Pilot "ability" is in climbing as required to keep the Boost and airspeed at the optimum values. The actual prop pitch is irrelevant to the flying task.

I hope that this illustrates how simple operation with a good CSU is.

Eng

OK. Reading the Pilot's Notes for the Spitfire Mk IX (1946 edition), you can see that there were two versions of the carburetor/propeller controls: one with these two levers interconnected, the other without. Sections 54 (Maximum Performance/Combat) and 55 (Cruise) show that movements of both levers were required in various flight scenarios.

I believe Clostermann describes these different maneuvers, using the term "pitch control," which doesn't correspond to the Notes but correctly defines the final action of the "prop regulator control."

 

[Engineman]

OK. Reading the Pilot's Notes for the Spitfire Mk IX (1946 edition), you can see that there were two versions of the carburetor/propeller controls: one with these two levers interconnected, the other without. Sections 54 (Maximum Performance/Combat) and 55 (Cruise) show that movements of both levers were required in various flight scenarios.

I believe Clostermann describes these different maneuvers, using the term "pitch control," which doesn't correspond to the Notes but correctly defines the final action of the "prop regulator control."

Your description is still incorrect. The CSU Controls rpm. Its response to rpm is used to give an output that adjusts the blade pitch to achieve the demanded rpm, not a specific blade pitch.

Eng

 

[Bretoal2]

Your description is still incorrect. The CSU Controls rpm. Its response to rpm is used to give an output that adjusts the blade pitch to achieve the demanded rpm, not a specific blade pitch.

Eng

This is not my description, but the words used by Clostermann... And I'm not speaking about direct action, but only one of the final ones, at the end of a long chain of interactions and interconnections. Other consequences of any movement of this "prop regulator control" lever are, of course, variations in rpm and boost- as stated in the Pilot's notes.

 

[NZTyphoon]

OK. Reading the Pilot's Notes for the Spitfire Mk IX (1946 edition), you can see that there were two versions of the carburetor/propeller controls: one with these two levers interconnected, the other without. Sections 54 (Maximum Performance/Combat) and 55 (Cruise) show that movements of both levers were required in various flight scenarios.

I believe Clostermann describes these different maneuvers, using the term "pitch control," which doesn't correspond to the Notes but correctly defines the final action of the "prop regulator control."

The later variant was not fitted until much later than Clostermann's Spitfire IX. These pages from the 1942-43 Spitfire IX's Pilot's Notes describe the controls that were used by Clostermann: self explanatory, really.

.