Variable-Pitch & Constant Speed Propellers

[Zipper730]

I've been told the world's first variable pitch propellers were conceived by A.V. Roe, and Louis Breguet, with L.E. Baynes patenting a design as early as 1919; by 1924, Dr. Hele-Shaw and T.E. Beacham patented a hydraulically operated variable pitch design in 1924, which was presented to the Royal Aeronautical society. Gloster developed it as the Gloster Hele-Shaw Beacham Variable-Pitch propeller, which they tested out on a Gloster Grebe: I was told that the first practical design was a French corporation by the name of Ratier which had started some work in 1928, and had a workable design fielded in 1932.

I'm curious when the first commercial and operational military aircraft (anywhere) managed to use a variable-pitch propeller: For most purposes, I mean that the aircraft was either built with the design, or eventually fielded with such a propeller.

I'm also curious when the first constant-speed propeller was developed, fielded, and operational anywhere, for most intents and purposes.

 

[Shortround6]

Hamilton standard lead the way for most commercial and military propellers in the 1930s.

First though, you have to understand that the definition of what a variable pitch propeller was varied quite a bit in the early 30s. And that old magazine articles and picture captions often confused the different definitions.

However by 1932/33 a propeller who's pitch could be controlled by the pilot in flight was was being manufactured by Hamilton Standard and being fitted to some airplanes, Hamilton Standard won the 1933 Collier trophy for this propeller.
The Part in italics is important as there were ground adjustable propellers. Mechanics could adjust the angle of the blades on the ground with the engine not running
as opposed to having to change the whole propeller to get a different pitch.
The Ratier propeller was sort of a half assed job, it worked, but wasn't really practical. It was a two pitch prop, either coarse or fine with no intermediate positions. Two pitch props were popular for quite as while during the 30s and very early part of the war as they were cheap.
The Ratier propeller of the early 30s was like this

The props were held in fine pitch for take-off by air bladders. When the plane reached a certain airspeed the little discs on the front of the propellers pushed a release valve that allowed the air to escape the props went to course (speed) pitch. I am not sure if the pilot could return the props to fine pitch in flight. On some later racers he could not and the ground crew had to pump up the bladder/s again. Ratier went to a different mechanism in a few years.

This web site may be a bit company puff piece but gets most of the details right.
Hamilton Standard Propeller Information

 

[Zipper730]

Hamilton standard lead the way for most commercial and military propellers in the 1930s.

First though, you have to understand that the definition of what a variable pitch propeller was varied quite a bit in the early 30s. And that old magazine articles and picture captions often confused the different definitions.

However by 1932/33 a propeller who's pitch could be controlled by the pilot in flight was was being manufactured by Hamilton Standard and being fitted to some airplanes, Hamilton Standard won the 1933 Collier trophy for this propeller.

That's a big difference...

The Ratier propeller was sort of a half assed job . . . . The props were held in fine pitch for take-off by air bladders. When the plane reached a certain airspeed the little discs on the front of the propellers pushed a release valve that allowed the air to escape the props went to course (speed) pitch.

Yeah, that is quite a limitation -- it can switch from low to high pitch, but if you can't re-pump the air, you're basically stuck and have little power left.

This web site may be a bit company puff piece but gets most of the details right.
Hamilton Standard Propeller Information

Looking at this data it would appear that

1. Early 1930: Propeller blade developed that could be controlled in flight, not sure if it was fielded that year or simply developed.
2. 5/29/1934: Collier Award for the the above design.
3. Late 1935: Constant speed propellers either introduced, or made workable
4. 4/6/1938: Either first flight, or first operational use of a featherable-propeller in flight

I'm curious when the following countries got in on this stuff with their local industry

1. United Kingdom: I was told the Fairey Battle had a twin-pitch propeller
2. Germany: From what I was told the Bf-109 was intended with the provision for variable-pitch propellers, but not fitted initially (the A's or B's)
3. Italy: No idea
4. Soviet Union: No idea
5. Japan: From what I remember the A5M had a variable pitch propeller by the time it entered operational service, the Ki-43 might have had a twin-pitch, and the A6M had a twin-pitch.

 

[Michael Hope]

In Ottawa at the Canada Aviation & Space Museum, they have a very early variable pitch propeller with wooden blades where the blade rotates with external gears a short distance out from the hub. I do not have the exact dates of this but I think it is early 20's if I remember correctly. I was not able to find it on their web site, but I will look when I am there at the end of the month if I remember.

 

[Shortround6]

1. Early 1930: Propeller blade developed that could be controlled in flight, not sure if it was fielded that year or simply developed.
2. 5/29/1934: Collier Award for the the above design.
3. Late 1935: Constant speed propellers either introduced, or made workable
4. 4/6/1938: Either first flight, or first operational use of a featherable-propeller in flight

I'm curious when the following countries got in on this stuff with their local industry

1. United Kingdom: I was told the Fairey Battle had a twin-pitch propeller
2. Germany: From what I was told the Bf-109 was intended with the provision for variable-pitch propellers, but not fitted initially (the A's or B's)
3. Italy: No idea
4. Soviet Union: No idea
5. Japan: From what I remember the A5M had a variable pitch propeller by the time it entered operational service, the Ki-43 might have had a twin-pitch, and the A6M had a twin-pitch.

By late 1938 or early 1939 about 20 airlines were using aircraft with fully feathering propellers. How many planes they had I don't know. But photo of a Lockheed 10.

Not all Lockheed 10s had feathering propellers. The plane could maintain 6300ft at 9750lbs on one engine, (400hp max continuous)
BTW the first Northwest airlines Lockheed 10 went into service June 1 1934 and made 46 round trips between Chicago and Minneapolis/St Paul in the first month.

Unfortunately, as I said before, many accounts confuse the different types of propellers or use some of the terms interchangeably.

The German propellers on the 109E (and some of the earlier 109s?) were "controllable" in that the pilot could adjust the pitch to whatever he wanted/needed between the minimum and maximum limits. However these props had no governor to hold the RPM at a fixed setting. A constant speed propeller can be set for a given RPM and will adjust the prop pitch to hold that rpm as the airplane climbs or descends. Or as the engine throttle is opened or closed.

A constant speed propeller could be referred to as a variable pitch or even controllable but not all controllable propellers are constant speed.

SIngle engine planes rarely used feathering propellers.

Two Pitch propellers were common on British planes at the start of the war. Pilot could select either coarse or fine pitch but they were often referred two as adjustable or controllable pitch. These were the props that were converted (at the last minute) to full range props for the BoB. But many of the late 30s British twin engine bombers (in addition to the Battle) made do with two position props. In an engine out situation the prop was put into coarse pitch and a propeller brake applied to stop the propeller from rotating and further damage. But you still have higher drag than a feathered propeller.

 

[Crimea_River]

In Ottawa at the Canada Aviation & Space Museum, they have a very early variable pitch propeller with wooden blades where the blade rotates with external gears a short distance out from the hub. I do not have the exact dates of this but I think it is early 20's if I remember correctly. I was not able to find it on their web site, but I will look when I am there at the end of the month if I remember.

Wallace Rupert Turnbull | The Canadian Encyclopedia

There is (or was) a display of Turnbull's propeller in the Saint John, NB airport.

 

[Shortround6]

HS (and Curtiss?) was also fooling around with reversible pitch propellers just before the war. The Devastator was "supposed" to use it's reversible pitch propeller as a dive brake instead of dive brakes out on the wing. Apparently they had troubles with this and I don't think any service planes were so equipped. At least one or more (?) Coronado 4 engine flying boats were equipped with reversing propellers on the inboard engines for better maneuverability on the water.
A some or all of the B-29s in the silver plate project (atomic bomb) got Curtiss Electric reversing propellers.

 

[Ivan1GFP]

SIngle engine planes rarely used feathering propellers.

Hello Shortround6,
I believe I saw somewhere that Messerschmitt 109s had a feathering propeller.
I thought this was a bit strange at the time. I can't recall where I saw this.

- Ivan.

 

[fliger747]

Not saying it didn't happen, but no advantage for a single to have a feathering prop, requires additional complication, weight and a method for un feathering such as a special "pump".

 

[Shortround6]

The only advantage for single is that is would stretch out the glide a bit.

On a twin (or multi engine) it could mean the difference between maintaining a certain height with one engine out or a slow descent all the way to the ground/water.

 

[Simon Thomas]

I am not sure I subscribe to the idea that Hamilton Standard led the way with variable pitch propellers.

The Hele-Shaw - Beacham constant speed propeller was patented in 1924, first flew in 1925, Gloster got onboard in 1926 and they were tested by the RAF in 1928.
The NACA paper TM-459 published in April 1928 described the operation of the propeller, and no doubt that information would have found its way to Hamilton Standard.

Hele-Shaw and Beacham were inventors with nothing behind them. Signing a deal with Gloster got the idea from paper to flight, however it appears to have stalled at that point. There was not much money being injected into the industry in the UK at that time, and it would have been a huge financial risk to start a propeller factory from scratch with a feeble market.

What Hamilton Standard did achieve was to develop and commercialise the concept, and at that time the market was ripe with the airlines seeing the benefit of CS propellers.

 

[Shortround6]

I am not sure I subscribe to the idea that Hamilton Standard led the way with variable pitch propellers.

The Hele-Shaw - Beacham constant speed propeller was patented in 1924, first flew in 1925, Gloster got onboard in 1926 and they were tested by the RAF in 1928.
The NACA paper TM-459 published in April 1928 described the operation of the propeller, and no doubt that information would have found its way to Hamilton Standard.

Hele-Shaw and Beacham were inventors with nothing behind them. Signing a deal with Gloster got the idea from paper to flight, however it appears to have stalled at that point. There was not much money being injected into the industry in the UK at that time, and it would have been a huge financial risk to start a propeller factory from scratch with a feeble market.

What Hamilton Standard did achieve was to develop and commercialise the concept, and at that time the market was ripe with the airlines seeing the benefit of CS propellers.

There were several different mechanisms for operating the pitch change mechanism and we can argue about who patented what and when. Hamilton Standard was able to put the basic idea into production and develop it through several steps. Perhaps because the the American Airlines and airplane makers embraced the concept (along with the US military) and gave them a profitable market. At some point in the late 30s the Hamilton Standard propeller (in one or another of it's versions) was Licenced in 16 (?) countries.
HS was part of United Aircraft (P & W, Vought and others) and the Wright Corporation, their rivals, came up with the Curtiss or Curtiss Electric propellers so they wouldn't have use their rivals product.
As a practical matter HS did lead the way, if not with the basic concept, then with a practical, easy to operate and maintain device.

From a 1941 Article in Flight magazine
"The outstanding opinion of the majority taking part in the discussion appeared to be that the gains were so small as not to warrant any considerable increase in weight. "
This discussion was in 1928.

"It emerged from the discussion that item (1), i.e., greater thrust at take-off, was considered the principal advantage and that the extent of this was at the maximum the percentage of engine h.p. lost by the drop in revolutions which the fixed pitch airscrew involved, and that this was likely to be of the order of 10 per cent. Moreover, in the case of the supercharged engine, the advent of which was originally the chief reason for the renewed interest in V. P. airscrews, the advantage was offset by the fact that this type of engine could be made to give a temporary increase of power at take-off by increasing the boost pressure."

Later "Although the original Hamilton Hydraulic Airscrew patent (which was for a two-position airscrew) was applied for on May 25th, 1929, that is 4 1/2 years after the Hele-Shaw Beacham patent, such was the energy applied by our American cousins that this airscrew was actually in production before the Hele-Shaw-Beacham and subsequent tests definitely established the advantage of the V.P. airscrew for take-off on modern aircraft."
and " the reason that the American two-position airscrew was first in production was mainly due to the fact that for a period the Americans were ahead in commercial aircraft design and certain types of aircraft existed in the States for which V.P. airscrews were a paramount necessity before that condition arrived in this country."

Trying to use variable pitch or constant speed airscrews on fixed landing gear bi-planes was not going to show a large increase in performance or fuel economy in cruise.

Unfortunately for the British that 1928 meeting of the Royal Aeronautical Society seemed to "seal the deal" on British use of constant speed or variable pitch propellers for almost 10 more years. Despite efforts by DH and Rotol (ROlls-brisTOL) the officials didn't want to use variable pitch propellers and indeed, they 'cheaped out" and used 2 pitch props (the simplest, least effective form of variable pitch propeller) instead of the infinitely variable (within limits) constant speed prop that Hele-Shaw/Beacham had patented and test flown all those years ago.

 

[chuter]

Not saying it didn't happen, but no advantage for a single to have a feathering prop, requires additional complication, weight and a method for un feathering such as a special "pump".

Most German props were electric so not much more of anything.

 

[Simon Thomas]

I found some interesting information in Fedden book.

From "Fedden - the life of Sir Roy Fedden" Bill Gunston RRHT 1998/2015 p196-201

One important area where Fedden was not his own master was in the propellers his engines drove. From the First World War onwards he had carried on a missionary campaign for variable-pitch propellers, and he fretted at the woefully slow progress Gloster Aircraft was making with the only promising British v-p propeller, the Hele-Shaw Beacham. One of these had performed well in flight trials in 1931 on a Gamecock, but Fedden then kept badgering Harry Folland, Gloster chief designer, because nothing more seemed to be happening. Bristol themselves then picked around the edges of the problem. The Engine Department made simple propellers with fixed-pitch blades of magnesium and, from 1935, of "densified" wood, with multiple laminations bonded under heat and high pressure to form an extremely strong blade much tougher than the traditional wooden type. Unfortunately, Fedden had no resources to spare for the complex engineering of a new v-p mechanism.

In September 1933, on one of his visits to the Bliss company at Brooklyn, he paid a call on the Hamilton Standard Propeller Co. This firm had patented and perfected a simple v-p hub with two or three blades balanced by bracket-type counterweights at the roots and capable of operating either in a fine pitch, for take-off and landing, or in a fully coarse pitch for cruising. This was the only v-p propeller that had ever been fully approved, or put into production. Fedden thought the Hamilton terms a bit steep, as regards both licence fee and royalty, but he decided to take out an option for the British market to break the stumbling block that was hurting both his engines and, increasingly, British aircraft.

The Bristol Board turned the idea down flat - partly, Fedden was convinced, because they considered their employee had no business to keep involving himself in such peripheral affairs. Fedden became exasperated trying to persuade them of the size of the market, and of the way in which fixed-pitch propellers were rapidly becoming outmoded everywhere that the Hamilton had penetrated. Fedden, with Frank Nixon, interested de Havilland in the American propeller, and dropped his own option. He then unburdened himself to the sympathetic Dowding. The air marshal welcomed the introduction to Britain of the proven Hamilton propeller, but he also expressed his faith in the Hele-Shaw Beacham design and asked Fedden if he would supply the Air Ministry with two propellers to this design. Fedden agreed at once, because he too believed in the British hub and was impatient at the way it was hanging fire. Gloster Aircraft were not in the least offended at Fedden taking the order, and Hugh Burroughes and Folland collaborated with him in setting up a propeller design office at Bristol and in tracking down the original Hele-Shaw designer, Milner. Though Fedden could not have set up a team to develop a propeller from scratch, he welcomed the chance to perfect this existing design.

His new propeller group quickly discovered that the faulty operation of the British hub had been due to distortion of the casing, which allowed oil to leak and reduced the pressure available to swivel the blades. The obvious answer was a stiffer hub, and within weeks a casing had been machined from a solid forging like the banjo of a truck back-axle. There followed a most successful ground test, the first ever with a British v-p propeller, and then a 100-hour flight programme with a Mercury-powered Gauntlet fighter. But by this time, in 1935, de Havilland Aircraft had followed Fedden's advice, picked up the Hamilton licence, and was tooling-up for quantity production. From the summer of 1934 Fedden had added an oil control valve for the Hamilton propeller to all his latest production Mercury and Pegasus engines, and in fact roughly nine out of every ten of these engines sold throughout Europe up to 1939 were fitted with Hamilton three-blade propellers (to the chagrin of the Bristol Board). Another propeller rival was Rolls-Royce, which had also been given an order for two HeleShaw propellers by Dowding and had been developing it along different lines. Bristol's hub used a cylinder with radial pins sliding inside the forged steel hub, while the Rolls design used a fixed inner piston carrying an external sliding cylinder driving the blades by push-pull rods. Fedden was not anxious to see two versions of the Hele-Shaw; his passion was for mass-production of the best standardised article. And what really depressed him beyond measure was that the Bristol Board still wanted to have nothing to do with propellers. This time the main excuse was that such a venture would not be worth the candle as de Havilland was taking all the business with the Hamilton propeller!

Fedden once again decided to do something he called "rather unconstitutional". He invited two of the top Rolls men, Arthur (later Sir Arthur) Sidgreaves and E W (later Lord) Hives, to lunch at the Royal Thames Yacht Club in London - Fedden's favourite club, and suitable neutral territory for a chat with his greatest rivals. He expressed his concern at the failure of the Bristol Board to authorise production of his propeller, and emphasised that the development problems were solved. He stressed that "In the national interest we must set up a unified modern propeller production programme for Britain". He suggested the two great rivals should get together on propellers, produce an agreed design and set up a jointly-owned company to make it. Before they got up from lunch the broad agreement had been reached. There now only remained the hesitant Bristol Board, but to Fedden's delight they accepted the idea. Fedden picked one of his original Fishponds team, Bill Stammers, to be general manager of the new company, and Stammers coined its name, Rotol, by merging the names of its two parents. Sidgreaves was appointed chairman, Sir Stanley White deputy chairman, and Fedden and Hives were made directors. To get things going, an office and small factory were rented at Llanthony Road, Gloucester, where the design was completed and small-scale production started in the winter of 1936-7. Meanwhile Fedden searched with Haldenby of Rolls-Royce for a permanent site, nearly finding one at Shrewsbury, and finally went with Whitehead and Stammers to see a site midway between Gloucester and Cheltenham. It was perfect, and they straight away pegged out the grass from the plan of the great factory they had prepared. By mid-1937 the Rotol works was taking shape, and production began by the end of that year.

In late 1935 William E Prytherch, of the National Physical Laboratory, was invited by Fedden to a meeting at the Air Ministry. He recalls, "I was astonished that such a boyish man should wield so much influence. The gist of the gloomy meeting was Fedden's insistence that the forthcoming British monoplane fighters would be too slow to catch the new Messerschmitt, and said that an extra 12 mph would be needed. He said the Merlin engine gave adequate power, but that the Watts or Jablo fixed-pitch wooden propellers could not translate this power into thrust at maximum speed. He turned to me and asked 'Can you make large forgings in magnesium alloy?' I replied that I saw no reason why this should not be possible.

"On leaving the meeting a hand fell on my shoulder. It belonged to W C Devereux of High Duty Alloys, who astonished me by saying not only that the whole of his organisation was at my disposal but that he would give me £250 if I produced a satisfactory forging. I was not used to doing things for money, and to avoid difficulties I joined HOA. Fedden was unbelievably exacting. Making small test forgings that met his specifications was one thing, but achieving all his figures, in every part of a large forging, tested in every direction, took 18 months of often heartbreaking slogging.

"At last we produced forgings that met Fedden's requirements. The Ministry ordered 27 of them, to be made into three-blade propellers. Three of these propellers were fitted to specially prepared Vickers Wellesley bombers. The advertised objective was to break the world long-distance record, but the real and secret objective was to test the endurance of the magnesium-alloy blades." As described later, the long range flight also tested Pegasus engines in a new cowling, running on 100-octane fuel. The new Rotol propellers performed flawlessly.

Prytherch continues, "Following this, the Ministry ordered HOA magnesium-alloy blades by the thousand. When they were fitted to Spitfires and Hurricanes the maximum speed was increased by 20 to 27 mph, coupled with better take-off and faster diving speeds. I doubt if this would have been achieved in time for the Battle of Britain without Fedden's drive and determination, so in my view he made a big contribution to our victory in that battle."

Rotol Airscrews Ltd had two strings to its bow. The main product was the all-British hydraulic propeller, which at first had blades of magnesium alloy but by 1939 was switching to densified wood. The second product was an American propeller of completely different form, the Curtiss Electric. This had been designed as a fully variable answer to the newly developed constant-speed version of the Hamilton, and as it was completely developed and qualified Rotol bought the licence as an insurance. Both propellers went into mass production. After 1942 the hydraulic type was continued alone, and it remains in production to this day in much refined forms, together with many other products, in what became Dowty Rotol, and is now Dowty Aerospace.

Sorry about the italics - I can't work out how to make a readable quote box.

 

[Michael Hope]

Wallace Rupert Turnbull | The Canadian Encyclopedia

There is (or was) a display of Turnbull's propeller in the Saint John, NB airport.

View attachment 540524

Here is pictures of the display cabinet from Canada Aviation & Space Museum in Ottawa taken 30 June 2019 by myself. Pattent

applied for in 1919

 

[nuuumannn]

Hamilton Standard patented what became known as the 'Hydromatic' propeller; this was indicating the means of changing the pitch of the blades by the use of differential oil pressure against a piston in the hub, this was unveiled in 1938 and became a benchmark, which was bought by licence round the world. Here's one:

P-47 static

here's a cutaway, You can see the piston in the end of the hub, with the moving and fixed cam at its base. The teeth on the moving cam act against the teeth on the blade butts to change blade angle (this is actually a de Havilland Propellers 23EX prop - the same as the 23E50 HS unit).

23EX

Prior to then, HS had used hydraulic power (using engine oil) and counterweights for pitch adjustment, as described above.

Not saying it didn't happen, but no advantage for a single to have a feathering prop, requires additional complication, weight and a method for un feathering such as a special "pump".

The other thing that's required for a feathering prop is a broad pitch angle of the blades. The complexity is in the unfeathering system, requiring a separate pump etc, as the earliest feathering props could only change the angle into feather and not reverse it. Depending on the system in use the blade angle will naturally change toward a coarse pitch, i.e. toward a more horizontal angle (or overspeed condition) and most unfeathering VP props have blade angles around 19 to 25 degrees, or fine pitch, while a feathering prop requires a blade angle of around 90 degrees. Because of this a greater distance between the stops on the pitch change mechanism is required, which means greater travel, which means a longer mechanism. This is where the extra power required to pump fluid into the hub against the piston to actuate the blades into a finer pitch.

Constant speed props are fitted with governors, as has been described already and the first aircraft propeller governor was designed by Woodward in 1933 and the design was eventually bought by Hartzell, who manufacture its own propellers and market the Woodward governor under its own brand name. Woodward had supplied governors for steam engines prior to then.

 

[Michael Hope]

More pictures of variable pitch propeller of the Turnbull design on an actual aircraft. Taken at Canada Aviation & Space Museum, Ottawa, Ontario Canada, 30 June 2019 by myself

.

 

[nuuumannn]

Good stuff, Michael; interesting information. Not heard of this guy before.