PWS 50 Extra parts

[Ron40]

This is another superior quality build to watch....Ron

[Leif Ohlsson]

Bernie,

I searched the Global Flight Archive for further reference photos. Pages are just a tad too large to upload, but the direct download links are:

mark iii | cirrus mark | iii engine | 1928 | 0803 | Flight Archive
cirrus | bentley | 1929 | 0054 | Flight Archive
de havilland | 1929 | 0061 | Flight Archive
aero engine | cirrus hermes | cirrus mark | 1929 | 0831 | Flight Archive

Here are the pertinent details:

This is the Cirrus III you want to model.
And so is this.
But not this one - American Wright Gipsy engine, intake tubes other side, but could be useful for intake tubes & ignition details.
And not this later Cirrus Hermes either.

From Aerofiles:

The American ACE Cirrus

From Engine History:

Cirrus III, this one seems pretty good, right?

From Power of the Past Engine Museum:

Cirrus III, same as above it seems.

[Leif Ohlsson]

Researching the ADC Cirrus engine, it struck me that I never quite got it right with the Cirrus and the Gipsy engines. Both were used in the DH60 Moth - the "Cirrus Moth", and the "Gipsy Moth". What were their relations?

As always, Wikipedia came up with clear answers. Please compare these two pages:


• ADC Cirrus (photo shows a Cirrus II, not a Cirrus III, note the intake tubes on left side)


• De Havilland Gipsy

Turns out that it all started with Geoffrey De Havilland in 1925 needing a sports aircraft engine. He wanted something like half his favourite WWI engine, the 240 hp Renault V8. His engine designer Frank Halford delivered him the original four-cylinder Cirrus engine, based on the Renault, and the success was immediate. (The Cirrus III development was used in the PWS-50, the subject of this thread.)

However, the success of the Cirrus Moth almost became its demise, since De Havilland was running out of Renault parts needed for manufacturing the now popular engine. Thus came the search for its predecessor, a completely new engine. Aiming for 100 hp, Frank Halford delivered the engine which after testing in the D.H.71 Tiger Moth Racer officially became the Gipsy engine.

The D.H.71 Tiger Moth Racer, not to be confused with the later D.H.82 Tiger Moth

As the Gipsy was gradually developed into the Gipsy I and II, demand was for an engine which wouldn't block so much of the pilot's forward view. Pilots already reported that the Gipsy engine (and the Cirrus as well, probably) could be flown inverted without other problems than the upright positon of the carburettor and fuel tank caused. An experiment to turn the engine upside down was successful.

Such was the birth of the Gipsy III, which developed further into the Gipsy Major. The Moths powered with Gipsy IIIs and Gipsy Majors, soon became the Moth Major.

This is actually a D.H.60 Moth Major, not a D.H.82 Tiger Moth! (Check the source here and here.)

From there on in its history. The Gipsy Major powered a number of subsequent De Havilland designs, not least the D.H.82 Tiger Moth.

Developments were the six cylinder Gipsy Six, later the Gipsy Queen, powering among others the D.H.88 Comet racer. The Gipsy King was the V-12 development of the same engine, intended for the four-engined transatlantic D.H.91 Albatross.

Leif

Apologies for digressing. One thing just led to another.

[cardist]

Many thanks for this information Leif, it is much appreciated. I now have enough info to get started with.
This is just the thing that I love about this hobby and this site. It is not the fact that I love to make things, but the journey involved in bringing it to fruition. As an engineer and an amateur historian, this kind of stuff is right up my street!
The kindness and generosity of the people on this site can only help in making this one of the most wonderful hobbies of all time.
Happy modelling
Bernie

[Don Boose]

As usual, you have provided some wonderful historical information and images, Leif. we are very lucky to have such an astute and conscientious person with such excellent research, writing, and graphic skills; a deep interest in the history of aviation; and the willingness to share the results of your work with us.

And, of course, we are fortunate to be in the company of model builders such as you and Bernie (and many others in this Forum), who have the ability to translate this information into models -- advancing our understanding of aviation history and giving us beautiful objects to enjoy.

Don

[Leif Ohlsson]

Bernie,

I played around a little with some of the photos of the Cirrus III engine. Here's a mockup of what the "Power of the Past Museum" Cirrus III would look like mounted in the model:



Note how neatly the purpose of some of the hatches and vents modeled is revealed!

To arrive at a plausible size, I made a compromise between two sets of measurements taken from the Cirrus I and the Gipsy II engines (since none were obtainable for the Gipsy III):

Cirrus I measurements:
Length: 45.8 in (116.3 cm)
Width: 18.26 in (46.4 cm)
Height: 34.3 in (87.1 cm)

Gipsy II measures:
Length: 40.5 in (1028.5 mm)
Width: 20 in (508 mm)
Height: 29.9 in (759.5 mm)

I made my own kind of compromise "box" by trying to make a good fit over several of the photos. This is how far I got:



This is made in 1/16 scale (my favourite), but you can easily make a conversion to 1/33 by downscaling to 48%.

Here are separate front and side views, also in 1/16 scale:



The last photo is a mirror image of the American Gipsy engine. The only useful thing about it is the intake manifolds.

I thought this might be of some help in making a simple mock-up engine, or for making the engine cover. I attach a pdf, which should open in a vector programme.

Cirrus III 1-16.pdf

Leif

[Ron40]

Leif you are a wealth of information. Thanks for sharing...Ron

[Leif Ohlsson]

It is amazing what details you can sort-of-but-not-quite find out from good-quality photos. Here's a close-up of the Cirrus III-engine (mounted in a D.H.60 Moth):



You get a pretty clear image of the intake manifold, and also the pushrods for the valve rocker arms. It seems there were two springs to each rocker arm. My question is: Does the rear rocker arm for each cylinder look just like the front one, and do they act on two valves each (thus two intake, two exhaust valves per cylinder)? Or, does the front rocker arm just regulate exhaust or intake valve? If so, would the front and rear rocker arms look the same?

Another feature seems to be square-ish cooling fins. These are even more clearly visible in a photo of a Cirrus II-engine:



Note the seemingly identical front & rear rocker arms in this photo. But they are not identical to the Cirrus III (there is only one spring per rocker arm, as an example). The silvery tubes on each side coming from the oil filler opening end in nothing. Are they for venting the crankcase?

The next enlarged photo is the familiar one (the only high quality one available of the PWS-50 to my knowledge):



Note in this photo:

1. The arrangement of the control wires running outside the fuselage, both for the rudder and the elevator. Are the elevator wires in fact crossed, and if so how do they run more exactly?

2. The bulges under the wing, which should be encasings of the wing spar fasteners to the fuselage. Also the long tube-like fairing a bit below the wing. What could that be for?

3. How "bulgy" the exhaust manifold in fact is. How does one best model this, I wonder.

4. The wrinkled section of the wing covering material under the wing. This, it seems to me, indicates that the wing was not covered with ply for such a long stretch as modeled, at least not on the underside of the wing.

Do we know if, and from where, KayFranz obtained additional information about the PWS-50? It would be very interesting to see anything not readily available on the internet.

Leif

PS. Bernie, for the finishing touch to your Cirrus engine, here's the engine plate (a bi-product of the myopic exercise above).

[cardist]

Wow Leif! More excellent research.
Those are some intriguing points you have raised there and very interesting questions. As to the valve gear, as far as I can make out, there are only one set of valves, i.e. inlet and exhaust. Its just that the viewing angle makes it difficult to discern.
I have made a start designing the engine and have got as far as the upper crank-case and cylinders. For incorporation in my build, I was going to simplify and just have it mounted from the top half of the crank-case upwards as the bottom part will be hidden by the engine covers. I will of course make a complete engine for those who want to go the whole hog!
Bernie

[cardist]

Hi Folks,
After a couple of days designing, I have printed out a draught copy for a test build of the Cirrus engine. All seems to be going well so far and I have managed to complete the crank-case and cylinders this evening. I have a busy week at work next week, so my modelling time is going to be sporadic. Already I can't wait for the next instalment!
Ok, pictures; crank-case frame, engine base and bearers, installed, complete casing and casing with auxiliary drive boxes and cylinders.
Happy modelling
Bernie