Lysander Discussion was Lysander mk II Cowling Question

[Dave Fleming]

Hi all,

Can't seem to find a definitive answer - was the cowling on the Perseus engined Lysander (mk II) the same shape/size as the one on the Mercury engined marks (I/III), other than the bumps on the latter?

D

Edited May 16, 2016 by Dave Fleming

[KRK4m]

Nothing new of course, as for me it only SEEMS they could be the same, as Perseus and Mercury shared the same (bore x stroke = volume) cylinder dimensions and number. On the other hand due to the sleeve valve design the overall diameter of Perseus was roughly 4 inches more than Mercury, so...

The question remains intriguing

Cheers

Michael

[John Aero]

Perseus Dia 55.3" length 49" Mercury Dia 51.5 length 47" according to Lumsden.

John

[brewerjerry]

Hi

I think that mercury engine dia figures includes the height of the pushrods, which causes the small bulges in the engine cowling, so that looks like it would imply there wasnt much spare room in the existing cowling

so to me it looks like a bigger cowl is needed for a perseus engine

maybe someone who knows will be along soon

cheers

jerry

[rossm]

If you believe the plans in the Argus pubs Aircraft Archive then the diameter is within a whisker of the same but the Perseus is shorter - 13.2mm plays 14.7mm in 1/72 including the gills by my eyeball/ruler, might go some way to explaining the cut out in the gills of the Mercury variants,

Ross

[John Aero]

Something new has just jumped out of my book shelves. The Perseus leading particulars in Newnes Vol 1 Principles and construction in the installation chapter for the Perseus gives the overall dia as 51.8 " so not the same figure as in Lumsden which is nearly four inches greater. Incidentally the dia given in Janes 1941 for the Perseus is 52" or 0.2" greater. (a gnats) The figure for the Mercury is 51.5". So it would appear that both engines are of very similar diameter. Remember that the cowls for both these engines will have Bristol factory cowling clearances on top of the overall dia figures and that the Mercury valve gear does not fit completely within the cowl bumps.

John

[Graham Boak]

It certainly isn't clear to me why a sleeve valve engine should have a larger diameter than a poppet valve one of the same internal size. The contrary, if anything.

[brewerjerry]

Hi

the only factors i can think of would be the crankcase size, and the size of the supercharger, as items that would increase the dia of the engine

cheers

jerry

[stevehnz]

I've long been under the impression that the Mk I/III cowls had the cooling gills cut away in front of the cokpit but the Mk IIs didn't. Certainly the Shuttleworth one bears this out though not all drawings &/or models seem to show this so I'm not sure how general this was or the reasons for it, but to me it might imply the Perseus cowl was slightly longer?

Steve.

[Garry c]

It certainly isn't clear to me why a sleeve valve engine should have a larger diameter than a poppet valve one of the same internal size. The contrary, if anything.

It looks like the sleeve valve engines have heavily finned deep dish heads for better cooling. They are much taller than you would expect.

https://upload.wikimedia.org/wikipedia/commons/7/76/Bristol_Perseus_sleeve_valve_radial_engine.jpg

Garry c.

Edited May 6, 2016 by Garry c

[rossm]

If you believe the plans in the Argus pubs Aircraft Archive then the diameter is within a whisker of the same but the Perseus is shorter - 13.2mm plays 14.7mm in 1/72 including the gills by my eyeball/ruler, might go some way to explaining the cut out in the gills of the Mercury variants,

Ross

I've long been under the impression that the Mk I/III cowls had the cooling gills cut away in front of the cokpit but the Mk IIs didn't. Certainly the Shuttleworth one bears this out though not all drawings &/or models seem to show this so I'm not sure how general this was or the reasons for it, but to me it might imply the Perseus cowl was slightly longer?

Steve.

Those drawings show the cutaway on the I/III as you describe but on the longer cowling. It looks like the overall length of the I/III & II is very similar and the cutout is needed to mount the Mercury cowling with its front edge in the same place as the Perseus with the rear edge coming further back, necessitating the cut away. Obviously the bulk of the engine needs to be in much the same place on each version for CofG reasons unless there was ballast in one of them.

Ross

[Britman]

Interesting topic although in the big scheme of things I can't see any reason to panic thinking all those Lizzy's we have built in recent years are inaccurate.

[Dave Fleming]

Depends if you have actually buil;t one yet.....

Found these views from a similar perspective that seem to show the differences (and they are more than I appreciated). The Perseus cowl appears to be shorter and further forward on the fuselage

The Mk III is from the Britmodeller walkround thread here: http://www.britmodeller.com/forums/index.php?/topic/76579-westland-lysander-mkiii-r9125/

Edited May 6, 2016 by Dave Fleming

[Dave Fleming]

And just for interest, here's an Indian Lysander II (Is that a Perseus engine?) but with bumps on the lower cowl!

Edited May 6, 2016 by Dave Fleming

[Graham Boak]

The cowling in the last photograph looks very re-worked. There are signs of hammering (away from the bulges) and rivetted patches that are very much not original. Which might suggest a Maintenance airframe but the rest of it looks to be in pretty good condition. Has someone cut down a Mercury cowling and bodged it to fit on a Perseus aircraft?

More generally, the longer cowling (and hence shorter fuselage) is consistent with a supercharger on the back of the Mercury. These photos don't tell me that the Perseus cowling was any wider than the Mercury one.

Garry c: Lovely picture making your point, but we really need the Mercury equivalent to show how much height the valves and springs take up.

Jerry: the supercharger would make the engine longer but not wider. Theoretically, you could have a larger crankcase with longer conrods, but I don't see why. Perhaps a small amount for the cam operating the sleeve valves?

[Garry c]

This appears to be a side by side comparison sleeve vs. poppet valve

http://i1299.photobucket.com/albums/ag79/faireyfulmar/SleeveVsPoppet1_zps8dda6789.jpg

To me it looks like the sleeve goes up into the head during the compression/combustion stroke explaining the height and the cup shape.

It appears the designers tried to keep the cylinder design as close to the same height as the poppet cylinder as possible.

From a business standpoint, it makes sense that both types have roughly the same diameter, as you can use both types on the same airframe without a major redesign.

fun stuff

Garry c

[Selwyn]

This appears to be a side by side comparison sleeve vs. poppet valve

http://i1299.photobucket.com/albums/ag79/faireyfulmar/SleeveVsPoppet1_zps8dda6789.jpg

To me it looks like the sleeve goes up into the head during the compression/combustion stroke explaining the height and the cup shape.

It appears the designers tried to keep the cylinder design as close to the same height as the poppet cylinder as possible.

From a business standpoint, it makes sense that both types have roughly the same diameter, as you can use both types on the same airframe without a major redesign.

fun stuff

Garry c

Animation on how a sleeve valve works, from a Hercules engine, but will be basically the same motion in a Perseus.

https://www.youtube.com/watch?v=_vrvep_YOio

https://www.youtube.com/watch?v=EJcxpFTFJPA#t=9.761

Selwyn

Edited May 6, 2016 by Selwyn

[hendie]

And just for interest, here's an Indian Lysander II (Is that a Perseus engine?) but with bumps on the lower cowl!

Forgive my intrusion ( and ignorance) but I've just started building a MkII and no absolutely nothing about them - so this thread is very enlightening.

It certainly looks like there is/was bumps in the lower half of the cowl, and as Graham mentioned it also looks like the cowl has been reworked.

Are the bump-outs on the lower half of the cowl in the same place you would find them on a MkIII ? Furthermore, from what I have seen, the cowl is a one piece wraparound with latches only on the port side (is that correct?). If that is the case, in the photo above, there don't appear to be any bump-outs on the upper half ???

Also, when compared to a MkIII, the cooling gills seem much further forward if you use that panel line running south of the windscreen as a reference datum

I have also read that the collector ring was short on the MkII's - is that correct ?

and just to complete the thread drift - doers anyone know if there is such a thing as a decent (reliable) set of drawings for a MkII to be found anywhere ?

[brewerjerry]

Hi

the best book for drawings should be the 4+ book on the lysander, as 4+ had access to westlands archives for this and the whirlwind book they did.

i cant recall if it has mkii drawings in the 4+ book as my copy is somewhere in with my kits

cheers

jerry

[Graham Boak]

The 4+ book does indeed have plans for both, and both are 1.90mm, to the nearest tiny bit. But this could be because of an assumption that they were - to the eye they're pretty much the same. It does appear as though if there is a difference, it is small, perhaps no more than a few 0.01mm difference in scale.

[Wez]

The cowling in the last photograph looks very re-worked. There are signs of hammering (away from the bulges) and rivetted patches that are very much not original. Which might suggest a Maintenance airframe but the rest of it looks to be in pretty good condition. Has someone cut down a Mercury cowling and bodged it to fit on a Perseus aircraft?

Really? I just see a cowling that's suffered because it has to get removed to do any form of maintenance...

From a business standpoint, it makes sense that both types have roughly the same diameter, as you can use both types on the same airframe without a major redesign.

Interesting point but not necessarily the case, the vibration characteristics and mass between different type of engine or of a poppet vs sleeve valve are likely to be very different. Whilst the engine mounts are likely to pick up on the same point of the airframe, the mounts themselves are likely to be quite different. Whilst it's not unreasonable to expect Bristol to have some commonality between engines, I've worked long enough in the aircraft industry to know that this isn't always the case

Forgive my intrusion ( and ignorance) but I've just started building a MkII and no absolutely nothing about them - so this thread is very enlightening.

It certainly looks like there is/was bumps in the lower half of the cowl, and as Graham mentioned it also looks like the cowl has been reworked.

Are the bump-outs on the lower half of the cowl in the same place you would find them on a MkIII ? Furthermore, from what I have seen, the cowl is a one piece wraparound with latches only on the port side (is that correct?). If that is the case, in the photo above, there don't appear to be any bump-outs on the upper half ???

There are certainly minor bumps visible on the cowling - they look more like those required to give the spark plugs some clearance, certainly not big enough to give the rocker valve covers sufficient clearance.

You're right though, this thread is very enlightening. It also explains why pretty much all the models of a Lysander are Mk.I/III and not Mk.II, which is a pity as I always seem to want to do a Mk.II.

Has anyone taken a look at the 4+ book on the type, does that offer any help?

[Graham Boak]

See the previous posting #20 for a comment on 4+.

Much more has happened to that cowling than any standard maintenance. It is distressed. It's been bashed around something rotten, and then the separate parts have been held together by two plates in a non-standard manner with what appear to be an excessive number of rivets. I agree that the visible bumps are not high enough for rocker valves, but they shouldn't be there at all on the Perseus. Posting #13 does show something similar to those plates at another join on the other side of the aircraft, but not in a symmetrical position, and with no sign of bumps.

Edited May 6, 2016 by Graham Boak

[John Aero]

The cylinder comparison photo came from the Newnes book. The longer cowl of the Mercury may be because it was a lighter engine than the Perseus and therefore was mounted further forwards. Dry weight of an average Mercury was

1030 ibs and the Perseus was 1110 to 1125 lbs. The props were very similar in weight.

A 1/72 scale cowl dia of 190 mm give us a full size cowl of 54" (53.8") which seems reasonable given a 1" cowling clearance allowance. The crankcase of the Perseus was a greater dia than that of the Mercury but the Perseus inlet valve operation took place within the crankcase.

John

[Dave Fleming]

What does the 4+ book show on length of cowl?

(The Airfix cowl is so bad I'll have to source another. John, do you do a Perseus?)

Edited May 6, 2016 by Dave Fleming

[John Aero]

If I recall the Matchbox Lysander was a Mk.II it certainly had a Perseus in it. I might be able to help with a metal copy of the same. Leave it with me. I don't have the +4 book.