Bristol and P-W engine questions

[Aaronw]

From what I've been able to find it appears the Jupiter, Mercury and Pegasus are essentially the same motor with the main changes being supercharging and stroke length which accounts for the changes in displacement.

Externally are there any differences that would be noticable in 1/72 or can one pretty well substitute for the other. The photos I've found would suggest there is not much difference but the photos rarely line up the same way to make a real good comparson.

My second question is about the Pratt & Whitney Wasp used in the F4B-4, P-12E and P-26. The Monogram P-W engine is much nicer than the Revell or Matchbox, but the Matchbox P-12E has a very different exhaust, and the P-26 no exhaust. I think the exhaust on the F4B-4 is correct for all 3 but I can't find anything to confirm that.

Thanks

[stevehnz]

The Jupiter & Pegasus are longer stroke than the Mercury as I think you know, so larger in diameter. This would maybe only be significant in an uncowled situation in 1/72. The pushrods on the Jupiter are uncovered & more spindly looking for this reason but again, probably very difficult to show in 1/72. Any different is likely to come in the reduction housing on the front of the motor, I'm not sure what if any differences there were in this respect. Sorry, can't help much with the P & W stuff. Have you tried wikipedia for some info here, there is a lot of info about aero engines on it with quite a lot of photos of preserved engines.

Steve.

[tnuag]

An excellent souce if information is the Flight magazine archive where you can look at any page for the last hundred years, except the last five.

http://www.flightglobal.com/pdfarchive/index.html

Hope this helps.

Neil

Edited October 19, 2010 by tnuag

[Aaronw]

I had assumed all three used the same block as you find with many car motors of similar displacement, where the pistons are bored out or stroke length changed. I believe the difference between the Mercury and the others is 1" which in 1/72 isn't going to amount to much.

I did look at photos and I didn't see anything obvious, but I'm not the best at noticing small details like that (I was never very good with those what's different drawings). I think the Jupiter is the only one that will be uncowled so I guess that is my safest bet.

Neil, I didn't find what I need at that link, but it does look like a great resource.

Thanks

Edited October 18, 2010 by Aaronw

[Denis]

http://en.wikipedia.org/wiki/Bristol_Jupiter

http://en.wikipedia.org/wiki/Bristol_Mercury

http://en.wikipedia.org/wiki/Bristol_Pegasus

The Jupiter is quite different from the others IMHO. The Mercury is merely a short stroke Pegasus...

Hope this helps

Denis

[Aaronw]

http://en.wikipedia.org/wiki/Bristol_Jupiter

http://en.wikipedia.org/wiki/Bristol_Mercury

http://en.wikipedia.org/wiki/Bristol_Pegasus

The Jupiter is quite different from the others IMHO. The Mercury is merely a short stroke Pegasus...

Hope this helps

Denis

Yeah, I started with Wikipedia, but based on those articles I'm not seeing the Jupiter as being much different from the others. The Mercury is based on the Jupiter (shorter stroke with super charging to maintain the power), the Pegasus is the Mercury returned to the original stroke of the Jupiter (so basically a supercharged Jupiter) creating a more powerful version of the Jupiter.

[stevehnz]

Aaron, if you've seen the Wikipedia pages on these, you probably know as much as most of us do now. You've not said what application you want the Bristol engines for but if you have a look at the Engines & Things pdf catalogue on this sight, it gives some applications lists. The Jupiter especially seems to have some gearbox options which are application specific, the Mercury & Pegaus less so. The difference in diameter between the Mercury & Pegasus in 1/72 is abot 1.36mm, just under 1/16". Most cowled applications had clearance bulges in the cowling outer for cooling around the cylinder heads/valve gear, so a Mercury engined Gladiator is going to have a smaller diameter cowl than a Pegasus engined Swordfish by about 1.4mm in 1/72. I guess it depends on how fussy you fell like being & how knowledgable your audience is.

Steve.

[Aaronw]

I don't have an immediate need for the Bristol engines but I was going to cast the P-W Wasp in the F4B-4 because it is much nicer, than the one in the Revell P-26 or Matchbox P-12E. With the Jupiter / Mercury / Pegasus I thought I'd get ahead of myself and cast one of those as well since I'd be getting the mold making stuff out anyway. I have a Pegasus Gloster Gamecock that desperately needs a decent Jupiter before I start it, and some other future projects that will need a Mercury. The Pegasus was quite popular as well so even though I don't actually need it right now it seems likely I'll run into a kit down the road with a sad example of the motor that needs replacing. I was just wondering if one would stand in for the others or if I need to track down decent examples of each. The Airfix Bristol Bulldog has a decent Jupiter, so if they are basically the same at 1/72 then I have my donor and don't have to look for the others.

I think you are right, this is looking like one of those projects that you just do it and if someone calls you on it you pick their brain for details.

[stevehnz]

Thats sounds like quite a project. I can't imagine doing that in other than the direst emergency. I'd be keen to see the finished article as & when you get there.

Good luck with it,

Steve.

Edited October 24, 2010 by stevehnz

[Old Man]

I don't have an immediate need for the Bristol engines but I was going to cast the P-W Wasp in the F4B-4 because it is much nicer, than the one in the Revell P-26 or Matchbox P-12E. With the Jupiter / Mercury / Pegasus I thought I'd get ahead of myself and cast one of those as well since I'd be getting the mold making stuff out anyway. I have a Pegasus Gloster Gamecock that desperately needs a decent Jupiter before I start it, and some other future projects that will need a Mercury. The Pegasus was quite popular as well so even though I don't actually need it right now it seems likely I'll run into a kit down the road with a sad example of the motor that needs replacing. I was just wondering if one would stand in for the others or if I need to track down decent examples of each. The Airfix Bristol Bulldog has a decent Jupiter, so if they are basically the same at 1/72 then I have my donor and don't have to look for the others.

I think you are right, this is looking like one of those projects that you just do it and if someone calls you on it you pick their brain for details. B)

I would warn against casting based on the Airfix Jupiter, Sir.

The cylinders are too thin, and the heads on that piece bear no relation to those on the actual motor. I have done their Bulldog kit twice, and each time did a great deal of re-working.

A better kit piece would be an assembled motor from an ICM Polikarpov I-5, which is reasonably available nowadays. The M-22 was a straight copy of the Jupiter, and the kit piece is quite decent.

Edited October 24, 2010 by Old Man

[Aaronw]

Steve, its not really that much of a job, it takes a little trial and error the first few times, but I've done other motors I needed so this time its just a matter of getting some uninterupted time and motivation. :)

Oldman, it just happens I have the ICM I-5, but did not know it used a copy of the Jupiter. :)

Also your inbox was full a couple days ago when I tried to PM you.

Thanks