Simviation Forums

Can anyone tell me what the function is of the shaped metal tunnel on the port engine cowling of all Merlin engined Spitfires. It is just below the front ejector exhaust manifolds.

I have checked this in all all the usual Spitfire books including "The History". but it is not mentioned. I think it could be a cooling intake for the generator which is on the port side of the engine just behind this point.

Some of you Spitfire mechanics out there must know

I've never worked on the Spitfire but I suspect you're correct.

And I'm on the South coast, and ALL my relevant literature's in my new house about 300miles away!

I second what Doug says though...

Aye it is the cooling port for the generator, I've got a gorgeous picture of a Packard Merlin 266 and you can see the generator clearly and it measures up to the cowling perfectly

Thanks all problem solved...

I've just ordered "Spitfire V Manual" from Greenhill Publishing, I hope there will be a reference to this in there.

I can't remember if there is, but the manual is an invaluable tool for Spitfire lovers
Some amazing and wonderful technical details

I'll look forward to recieving it then.....

One thing about this generator cooling port ( it was a feature of the Spit from the very first flight of K5054 with the original multi plate cowlings) ..It must have caused a fearsome amount of drag, but  was tolerated as a design freature at a time when joints were being filled, high gloss paint being applied and rivets being flushed all to give an extra 3 mph or so.

Although I suppose that , given the electrical insulation available in 1930/40, an overheating generator would have caused even more of a problem.

The drag isn't that bad as it is the area of the prop-wash, so it gave sufficient cooling without being a burden like the Vokes filter which cost performance in a very noticable way.

Yes you're right . It is within the propwash, hadn't thought of that.

So is the Vokes filter for that matter , but of course it's a lot bigger. I believe they improved matters a great deal on sand filters with the so called Aboukir filter which gave a lot less drag.

I've been discussing in another forum the effect of dropping the flaps on a Spit. All the writings seem to indicate that it caused a nose down change of trim ( perhaps 15 degrees or so ? ) . Any ideas on the effect on trim of lowering the chassis. Most of the Spit air files ( with the exception of the Just Flight Spit , which has it all wrong, ) cause a nose drop on lowereing the flaps, but also a drop on lowering the chassis.

Now if you read descriptions of trim changes required given by Spit pilots ( contemporary and modern) they only ever mention it as being required on lowering the flaps.

The reason I ask this is that I wish to tweak my Spit air files to be as accurate as possible

In response to your first question about the Spit cowl.....I'm thinking your talking about this area.....


And in response to your question on flaps, here is how I see it.........
When you deploy flaps on an aircraft, an initial pitch-up should be noticed as you begin to change the airfoil section to one of slight undercamber (Glider-style with more lift but also more drag) but as this increased drag starts to diminish the airspeed and the flap angle increases, the lift component is decreased and the nose should drop due to insufficient airspeed at the new angle of attack........nose down will prevent further decay in airspeed, which would eventually cause a stall...

I've always thought of the Spitfire flaps as airbrakes. They have only 2 positions, either UP or DOWN & the DOWN position is almost 90 degrees to the airflow. Theoretically this would cause far more drag than lift & being below the CoG & behind the Centre of Pressure would almost certainly cause a marked nose-down change in pitch. I don't know for certain but any drag below the the COG would have a similar effect so I suspect lowering the undercarriage would affect trim in the same way.

Rifleman,

Yes, your very clear photo identifies the cowling concerned exactly. It must be an inlet for cooling air for the generator, as Ozzy says, it is directly in line with the generator. However I have yet to find a specific written reference to it anywhere in my literature or on the net.

Your aerodynamic description is also correct.
The Spitfire V pilot's notes under "10.  General Flying" state :-  "Change of trim"....."Undercarriage down--Nose down"...."Flaps- Nose Down".
What the Pilot's Notes do not say is how much change of trim.
I am trying to gather some typical values for this so that I can accurately model an air file for the Spitfire. Most of the air files currently available either get it completely wrong by giving none or a nose up change of trim or give a nose down reaction that seems excessive ( especially for the undercarriage , which I suspect had comparitively little effect).

I am hoping that some Spitfire pilot out there can tell us !

I am going to see the Shuttleworth Collection fly at Old Warden tomorrow and it includes a Spit MkVc. In the unlikely event that I can get near the pilot I'll ask him.

Thanks for your comments.

Hagar,

Yes, your logic cannot be faulted.

Since the undercarriage would have very much less drag than the lowered flaps ( flaps 57 deg. down  on the protoype and 85 deg on all production except F24 and Seafire Mk47) and would not be so far behind the CoP ( although lower) , it follows that the lowered undercarriage  would cause a  much smaller nose down change of attitude than the flaps.

Springer, I thought you were indicating that intake so I brought it to the front since I could. I took that shot a few weeks back in the Seattle Museum of Flight on the Mothers day weekend.........cheers.........

On the flap issue..........
I do concur with Doug on his assessment of flap effect on pitch, but my explanation was not that of an instant "snap" flap.....it was more of what happens through the gradual application of flaps as they progress from no flap to full flap position........sorry for not clarifying this at the time........

On the flap issue..........
I do concur with Doug on his assessment of flap effect on pitch, but my explanation was not that of an instant "snap" flap.....it was more of what happens through the gradual application of flaps as they progress from no flap to full flap position........sorry for not clarifying this at the time........

Your meaning was clear as crystal Ken. I agree that during the initial stages, lowering the flaps would cause a momentary nose-up trim change. I don't know how long it takes to lower (or raise) the flaps* but, on some marks of Spitfire at least, the flaps are operated pneumatically. Pneumatically operated rams usually work much quicker (full travel in a matter of seconds) than their electric or hydraulic equivalents. Having specialised in aircraft pneumatics systems I always assumed this would give full flap almost instantly on the Spitfire so any nose-up effect would be momentary. This is all theory of course as unfortunately I've never flown in a Spitfire & not likely to.

*PS. I should know this as I've overhauled & tested enough Spitfire flap selector valves in my time.