Bristol Hercules - spinners vs hubs ?

[rcbutcher]

Greetings from Sydney Australia, my first post here.
I've been organising a whole load of photographs of Bristol Hercules-engined aircraft on Wikimedia Commons.
I've noticed that while most show just a small hub, some show a large spinner leaving a small gap between it and the cowling, with prominent cowling "flaps" at the back of the engine.
My questions for you experts :
1. Was the large spinner linked to particular models of the Hercules ? Or to the propeller type ? Or to particular aircraft Mks irrespective of Hercules model ?
All the Lancaster Mk IIs appear to have had the large spinner; all the Halifax Mk IIIs appear to had just the basic hub; Beaufighters and Stirlings appear to have had both; I've seen photographs labelled Wellington Mk X with both.
2. What purpose did the large spinner serve ? Special cooling system ? Were the cowling flaps related to the spinner ?
thanks
Rod

 

[mikec1]

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.... Greetings Rod;


I am by no means an expert on anything......... nor do I think you are going to
make very many friend on this web site, with that kind of attitude. More than
likely you are going to get ignored.

..... Do you truly want to fine the answers to the question that you ask, or
are you just TROLLING ...... ?

The spinner has to do with cooling of the engine. Every aircraft has a different
engine nacelle design, that leads to different cooling problems.



Mike
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[rcbutcher]

No, I'm not a troll, I'm trying to answer some serious questions about engines on photographs, without the benefit of knowing much about aircraft engines. My philosophy is there are no stupid questions, only stupid answers.
The background to my question about the spinner and cooling system is this article : More on cooling airplane engines** : "... the trick, as you mentioned in your article, is to slow down the incoming air. This is achieved via a classic convergent/divergent duct. In other words, a larger diameter spinner directs the air through the aforementioned 2' annular gap and from there, an aft fairing that covers the nose case and magnetos terminates a the base of the first row of cylinders".
How about a civil answer to some civil questions ?
Over to you.
Rod

 

[nuuumannn]

Spinners serve two purposes, streamlining and to encourage airflow into the engine on a radial, like the Hercules - and I guess, now I've read your post, to slow the air down on high performance engines, although I doubt that purpose is necessary on the likes of a Stirling or Wellington. Cowl flaps are related to cooling airflow through the engine and are not co-dependent on the existence of spinners. To cool the engine at critical periods when heat build up is at its greatest, e.g. on the ground when the aircraft is stationary or on take off at high power settings, the cowl flaps are opened.

 

[nuuumannn]

Just to add to my post and hopefully help provide better information, Rod, is that some engines, in order to encourage cooling air to slow down and work more efficiently, had fixed baffles within the cowls themselves, which directed the air over or between cylinders in two rows for better cooling of the aft row, which was not directly in the oncoming air flow. And, no, Rod, I don't think you are a troll.

 

[rcbutcher]

Thanks for the info nuumann. So I don't need to look at cowl flaps. And the spinner could have been an attempt at streamlining rather than for cooling purposes, correct ?
I don't think any aircraft the Hercules were used on were "high performance" - AFAIK their mission was to drone on reliably hour after hour at a decent cruising speed, with occasional high-speed bursts in the case of the Beaufighter.

What I'm trying to get past is the apparent randomness of spinners to some sort of design sequence and/or operational rationale.

I find specifications that say e.g. Lancaster Mk II had either the Hercules Mk VI or XVI engine, sometimes with xyz type propellers. Is there a further level of engine specification that tends to get omitted from popular sources e.g. Mk XVI engine with abc nacelle configuration/cooling system vs Mk XVI engine with xyz nacelle configuration/cooling system ? I have not seen a single Halifax Mk III photograph with spinners, yet it apparently used the same engine and flew the same missions. But the Lancaster Mk II was just a mashup using whatever engines available - did it just happen to get a batch of engines incorporating the idea of the moment ?

Likewise the Beaufighter - I've seen photographs purporting to be F Mk VI and F Mk I with spinners and without. Would this have been a case of aircraft getting whatever replacement engines available at the time, rather than showing the original equipment ?

I get the impression that the design started with spinners and then lost them, as later Halifax photographs seem to indicate.

Any info gratefully received ! My questions indicate my ignorance.
thanks
Rod

 

[nuuumannn]

Rod, don't worry about your perceived ignorance, no one here knows everything and I'm certain there'll be guys who'll chime in to this thread with far more info than I could offer. As for different aircraft types and the use of spinners, each aeroplane was different and as far as I know there was no set cowl type; it was more the application on the aircraft owing to various reasons, either streamlining or not, or improved cooling or not. I guess the Lanc II needed spinners more than the Halifax III, why I couldn't say, but it might be that the Lanc was faster than the Halifax. Halifaxes initially suffered from being underpowered and overweight, although this was a concern for the Merlin engined variants, so the absense of spinners on Hercules variants might have been as a weight saving measure.

As for Beaufighters, I think the spinners were removed because they didn't need them. I think later TF.Xs might have had them refitted, I suspect, for streamlining.

 

[Shortround6]

In some cases the spinner helped cooling on the ground. depending on cowling, engine and propeller while air is going IN the cowling near the outer part of the opening is is flowing back out near the hub while the plane is stationary or taxiing slowly.

Without knowing the needs of a particular installation it is hard to say what the designers intended.

And an engine installation that may work fine in England may be subject to over heating in the tropics and need a little help.

 

[razor1uk]

As Shortrounds suggested, I think the time of year/seasonal effects could also be a factor along with what region mission that A/C was usually in/on, as to if the aircraft fitters/ground crew were told to take off or put on spinners for A/C's that could have them.

I'd imagine that a tropical A/C might not have them to lessen ground running heat soaking - airflow restrictions, while a high altitude/speed or colder areas A/C might have the spinner(s), to keep the engines in a certain heat range, to improve high speed cooling by creating a larger air 'pocket' of expanding slowing, i.e. lower pressured air within the cowling, behind the spinner before the (radial) cylinders; that forces/allows the air to become efficiently turbulent to be directed through cooling fins and baffles effectively - fast moving air cannot absorb heat as quickly as slower air within a given area that is heating it as it passes by/through.

 

[dogsbody]

As far as Bristol engines are concerned, they were delivered to the aircraft manufacturers as fully assembled units. The aircraft designers designed the whole aircraft but the engine cowlings were designed and built by Bristol. The idea came out of the NACA studies on aerodynamic streamlining in the 1930's and spinners were part of the study. With wartime priorities and production demands it was realized that any small gain provided by a spinner on a radial was offset by production cost and extra maintenance time. The prototype Lancaster B.II didn't have spinners fitted. Lots of other radial-powered aircraft from this period started off with sp[inners but they were soon discarded as un-needed.

My two cents

Chris