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Need a 1/3 scale Pobjoy7 engine


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I'm hoping to build a static 1/3 scale Comper Swift for the Artur Butler Museum. I'm hoping to get the plans, and I can make everything except the engine. 

 

I was wondering if anyone would like to donate their time to the Museum to make one. 

 

image.jpeg.7f09a97249e7c155cc3f8e9f8c76b588.jpeg  image.jpeg.9dd699cbdcad99dcc65bbff6d755b7d9.jpegAirworthy Pobjoy Niagara installed in a Comper Swift at the Shuttleworth Collection

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Making something like that from scratch would take thousands of hours. A few people have made model engines close in size to what you need.   The version there has a layshaft reduction gear resulting in the above centre prop shaft.  Most radials have sun and planetary gears, which are better and some are direct drive. (Cheaper).  The actual plane was converted to a  90 HP inverted four which was still enough to make it go fast. More power than the Pobjoy. . Same engine as in the Miles Gemini and moth minor I think.Nev

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Posted (edited)

There was a Pobjoy engined Swift at Booker in England some 40+yrs ago when I worked there. No idea if it is still there, nor what contribution this fact makes to this post!!

Edited by derekliston
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17 hours ago, facthunter said:

Making something like that from scratch would take thousands of hours…

Nev perhaps that’s a job for a clever person with a 3-D printer.

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Posted (edited)

The Comper Swift is so small you don't need to scale it down. They used to say Arthur could fly it around in a room of a house.  Re the Pobjoy they also said  "a lot of popping and not much Joy". But it got from England to Australia .  There were the remnants of a couple of engines in Drage's Museum at Wangaratta.  The original plane may still be around. It was at West Maitland when I last saw it, re-engined and in flying condition in the 60's. Also people keep that sort of stuff in hangars so it's got a chance..Nev

Edited by facthunter
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9 hours ago, Old Koreelah said:

Nev perhaps that’s a job for a clever person with a 3-D printer.

Doesn't OME have a 3D printer?

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I'm trying to build a scale model, so what I need is something that replicates the appearance of the engine. You can't 3D print anything that you don't have in a 3D digital file format. Also my 3D printer is in an packed box somewhere amongst the crockery, linen and old vinyl records.

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OME - Williams Brothers Models produced all types of scale aircraft models and parts, they did produce a scale model of a 9 cyl P&W - but it appears the virus has nearly knocked them out of business, the bloke running the operation is trying to get back on his feet again. They produced numerous aircraft scaled items up to 1/4 scale, maybe emailing him might give you some assistance?

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11 hours ago, onetrack said:

Williams Brothers Models produced all types of scale aircraft models and parts,

It looks like I would have to fake it if I used one of his kits, but there's an Australian supplier who might have stock.

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  • 2 weeks later...

I found an old article on how to scratch-build an engine. All I need now are the dimensions for scaling. I have also found a reproduction Operation and Maintenance manual for the engine.

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Posted (edited)

There's a variety of models with the Pobjoy 7 cyl radial engine, so it's a bit confusing. One site says the basic original Pobjoy P engine (72mm bore) and Pobjoy R engine (77mm bore) is 25" in diameter, and another says the enlarged Niagara V engine (81mm bore) is 26.5" in diameter.

It appears the Comper Swift utilised the smaller bore Model P engine. There also seems to be confusion over the engine naming, with some sites calling all the models either Pobjoy P or R model, and others calling all the models, the Niagara engine, with Roman numerals identifying the development stages.

I get the impression the Niagara was a further development of the P and R models - and then the Niagara appears to have been further developed into the Cataract and Cascade models.

 

https://www.wikiwand.com/en/Pobjoy_P

 

http://www.all-aero.com/index.php/contactus/64-engines-power/13383-pobjoy-niagara-pobjoy-cataract-pobjoy-cascade

 

Geoff Goodall says there's a Comper Swift under restoration in 2021 at Luskintyre NSW, by Matt Webber / Luskintyre Aircraft Restorations. I initially thought you could possibly get measurements from that machine - then I realised this Swift had been repowered in W.A. in the 1970's with a Gipsy III engine, so that idea is out.

 

https://www.goodall.com.au/australian-aviation/comperswift/comperswift.html

 

Edited by onetrack
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 Gypsy equipped Comper Swift VH ACG, piloted by Bill Winch was the one that did a barrel roll around me on my first solo X country in Chipmunk VH-RNE out of Rutherford for Mudgee (via Scone ) on March 19 1961. Pretty scary way to start a fairly challenging first solo X country.   Took a bit of searching to find it but I knew it was red. Nev

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Upon further reading of Geoff Goodalls Comper Swift page, I see that VH-UVC, which is fitted with a Pobjoy engine, is also undergoing restoration (in 2021) by Matt Webber / Luskintyre Aircraft Restorations - so perhaps it is worth a call to them to see if you can acquire the measurements you need. Alternatively, a 345km drive will enable you to examine and measure the engine yourself! (provided that you can gain approval from Matt Weber to do so).

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Given that this engine is to go into a 1/4 scale static museum piece honouring the record breaking solo flight of Arthur Butler from England to Australia in a Comper Swift, I'm sure that Matt wouldn't refuse a request. Even more so, I would hope that he would come to the anniversary celebrations next November. I'm going to buy the maintenance manual for the R model. A contemporary news item states that the engine was 75HP, and that info would have been supplied by Butler as the item also indicates that the aircraft could be purchased with a lower powered engine for a lower price.

 

Comper loaned the plane to Butler on the proviso that after he got to Australia he took it around the country on a sales tour.

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Luskintyre is a great pace to visit anyhow. They do MAGIC there.  There's plenty of engineering drawings of those motors. 1/4 scale is pretty small. I still think a patternmaker is the answer. The cylinders are all the same.   Nev

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  • 2 weeks later...

I've done two things. First, I bought a digital copy of the Pobjoy R7 engine that should give me the dimensions. Secondly, my son has just bought a 3D printer and I found some stl files to print a 7 cylinder engine. Unfortunately, the Pobjoy is a geared engine and the files are for a direct drive so I'll have to fudge it a bit.

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Plans and laser cut parts arrived today. Unfortunately I can't find a set of 3D printer files for the Pobjoy engine. I'll have to fudge and use the ones for a Cyclone engine. The Pobjoy has its rocker levers in the rear and all other radials have them in front. My son just bought himself a 3D printer, so he can do the printing for me.

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OME - What about asking one of the radial engine 3D plans producers to modify one of their plans for you?

This bloke below, has plans for a neat 7 cyl generic radial - surely a bit of fiddling, such as reversing the plan for the crankcase can produce the required rear position for the rocker gear - and maybe he can even knock up a PSRU for you.

 

https://www.thingiverse.com/thing:3808530

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16 hours ago, onetrack said:

OME - What about asking one of the radial engine 3D plans producers to modify one of their plans for you?

This bloke below, has plans for a neat 7 cyl generic radial - surely a bit of fiddling, such as reversing the plan for the crankcase can produce the required rear position for the rocker gear - and maybe he can even knock up a PSRU for you.

 

https://www.thingiverse.com/thing:3808530

I think that's the one I want to use. The trouble is that the Pobjoy R7 had a geared output and that gearbox cover is the problem.

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