Supermarine Spitfire and Seafire

[Mossie]

Or longer undercarriage?

[kitnut617]

Which for a Spitfire would be quite a problem Simon

[Mossie]

Chicken and the egg, the Merlin came first so had they decided on the inverted configuration, the Spitfire would have been designed around it.

I think real world, the upright Merlin was the right decision, although there were many who advocated the inverted engine.  The manufacturers were right, there would have been to many design compromises for a minor improvement in forward view, something that was borne out with the DB and Jumo series.

[kitnut617]

Ah! OK I was thinking it was re-engined, not an inverted one right from the get-go

[jcf]

You've retained the mould line of the cowling for the upright Merlin,
and basically just inverted it. The Merlin had ancillaries mounted on
the bottom of the crankcase, and updraught carb fed by a bottom
mounted intake and I don't think a production inverted engine
would have had an identical envelope to the upright.



Looking at the drawing it's likely that all the gubbins would have had a different
arrangement, the oil system in particular, so there wouldn't be as much stuff sticking
up versus the amount sticking down, with the upright version.

[PR19_Kit]

Or longer undercarriage?

But then you have to modify the wings to take the longer legs and the wheel bays will then interfere with the gun bays........

[Mossie]

Kit, that's right, see reply #167 above.

Jon, I did wonder about that, I'll have another look, I'll get there in the end!

[Mossie]

Okay, following Jon's comments, this is my go at rearranging the Merlin.  Ignore the internals, it's all to cock.  The main engine parts, crankcase and rocker covers have been inverted.  I've made two assumptions, that the supercharger can be inverted also and raised, and that the sump can nestle between the rocker covers to bring the overall height the same as the upright Merlin.



It's come out looking a bit like a Jumo 211.  My engineering knowledge is close enough to zero, so any advice is welcome.

Just to clarify from Robert's and Kit's comments earlier, the inverted configuration was considered for the Merlin very early on and rejected due to the opinions of the manufacturers.  Had the RAE or others put their foot down (as happened in Germany), then there's a good chance the Merlin could have been designed this way.  Any subsequent aircraft design would be made around it.  There's a more whiffy possibility that the inverted engine was developed later in response to the DB and Jumo engines, so maybe the above Spitfire could be a testbed.

[rickshaw]

What advantage does an inverted engine have over an upright?

[kitnut617]

I would say it would have still had an updraft carb' Simon, as you have it, it doesn't have the air intake ducting or the elbow that would be needed to have smooth airflow to the carb'.  This will mean an even higher top cowling profile and/or an even lower thrust-line ----  maybe a side-draft carb 

[perttime]

Seafire and Spitfire scale drawings

I recently stumbled upon some Fred Spring / Scale Planes Seafire (and Spitfire) drawings on photobucket.
http://s197.photobucket.com/user/JJELLIS_PHOTO/library/SPITFIRE?sort=3&page=1

I posted the Seafire drawings at http://www.rcgroups.com/forums/showthread.php?t=2227654 - and then got a higher resolution version of the Seafire Mk.17 drawing, now also posted there.

(Fred Spring died some years ago, and his drawings have become difficult (at the least) to obtain)

[jcf]

The actual supercharger wouldn't change position, no need, and as Robert has suggested
it would most likely retain an updraught carb, so the induction trunking would be on the
bottom between the cylinder heads.

It also wouldn't have an oil sump like the upright engine, inverted engines tend to be of
the dry sump design. Like the Jumo, DB and other inverted engines it'd have oil scavenge
pumps to keep oil from building up in the valve gear housings.

[wuzak]

I believe the Merlin was dry sump too.

The difference is that you would need oil sumps on the cylinder head covers.

[Mossie]

Thanks guys, I'm learning here as I go so your input is very helpful.



I've left the supercharger in the original position, ignore how it all connects up, it's just the overall shape I'm after.  If I've understood everybody and kind of working out in my head how the bits in the supercharger would be arranged, can the carburettor and oil bits can come up a bit?  As they are, it all fits within the dimensions.

What advantage does an inverted engine have over an upright?

From what I can gather, the main advantage is pilot view.  The cylinder head is the widest part of the engine, so placing it at the bottom gives a less obstructed forward view.  There's a snippet in the Morgan and Shacklady book about inverted engines being more suited to steam cooling, which wasn't adopted in any case.  One thing that seems to be panning out with this re-design, and looking at the German engines is that everything is a little more compact.

[kitnut617]

When RR and NA were converting the P-51A over to a Merlin powered version, they found that the SU carburetor had a shorter barrel than the Bendix that NA used on their Packards. This led to the first NA Merlin Mustang having a bulged air trunking to the carb.  There photos of it on the web so really the Brit carb would be as short as you can get it. In the end the Bendix arrangement was revised so either the RR or Packard Merlin could be install in any Merlin powered aircraft.  That doesn't mean you could put an SU carb on a Packard Merlin or a Bendix on a RR Merlin, it just means the inlet face of both carbs was at the same dimension from the crank center