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Bristol Pegasus

PostPosted: Sat Oct 16, 2010 12:28 pm
by Stealer
Here are some photos of the Bristol Pegasus 2 valve air cooled 9 cylinder radial engine. Of course, these engines powered many aircaft including the Short S23 C-Class Empire 'boats and the Mk III Sunderlands. What's interesting about the design is the fact that the valve pushrods are behind one another:

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Re: Bristol Pegasus

PostPosted: Thu Oct 25, 2012 4:13 pm
by Obanboats
I have currently a Pegasus XVIII at Oban recovered from the sea bed in excellent condition complete with prop. It is to be sent on to RAF Cosford for stabilisation.

Re: Bristol Pegasus

PostPosted: Thu Oct 25, 2012 6:42 pm
by seawings
Hi Obanboats,

Gosh, I would love to see some pictures of that! Know anything about its history?

Re: Bristol Pegasus

PostPosted: Fri Oct 26, 2012 3:01 am
by dogsbody
seawings wrote:Hi Obanboats,

Gosh, I would love to see some pictures of that! Know anything about its history?



Me, too.

Re: Bristol Pegasus

PostPosted: Sat Oct 27, 2012 10:52 am
by sunderlandmr5
seawings wrote:Hi Obanboats,

Gosh, I would love to see some pictures of that! Know anything about its history?


Yes please, I would too :D

Thanks

Alan

Re: Bristol Pegasus

PostPosted: Sun Nov 18, 2012 12:31 pm
by Philthy
An interesting feature of the Pegasus was specially designed valve gear that ensured correct valve opening when cold or hot, allowing the engine to be run up to full power without the need for a lengthy warm-up which, in a flying boat, could be a bit of a problem.

Re: Bristol Pegasus

PostPosted: Sun Dec 02, 2012 11:42 am
by Philthy
Here's a question for the technical experts:

Most sources seem to quote the Pegasus Xc as fitted in the Short Empire flying boats (S.23 & S.30 at least) as having a power output of 920 hp.

However, both the British and Australian CofAs for these aircraft give the Pegasus Xc as 740 hp at 2,250 rpm at rated height of 4,500 ft and 815 hp at 2,475 rpm.

Any ideas why?

Re: Bristol Pegasus

PostPosted: Sun Dec 02, 2012 12:50 pm
by MrWidgeon
In piston engines the rated HP drops with altitude, hence the need for superchargers or turbo-superchargers.
It can also vary slightly with temperature, humidity and barometric pressure.

Re: Bristol Pegasus

PostPosted: Thu Dec 06, 2012 3:58 am
by Philthy
Indeed they do Mr Widgeon, but one would hardly expect a loss of more than 10% of rated power in 4,500 ft, especially since the Pegasus was supercharged. Density altitude shouldn't come into it as these are standard figures.

Re: Bristol Pegasus

PostPosted: Mon Oct 23, 2017 6:24 pm
by SimonThomas
The "international rating" for the Xc is 710/740 hp at 2475 rpm at 3,500 rpm. (From Flight magazine Dec 12, 1940 p 509)
The same reference also states the maximum altitude rating as 830 hp at 2600 rpm at 5250 ft; the take off power as 920 hp and the dry weight as 1030 lb.

The Flight magazine dated Nov 12, 1936 states the normal output at rated altitude as 785/815 hp (rated altitude nominated as 4,500 ft). This edition also nominates 920 hp as the takeoff rating and the dry weight as 1015 lb.

I guess in modern terminology, 920 hp is for takeoff and 740 hp is maximum continuous.