Spitfire Mk. VIII, Central Gunnery School

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An evocative photo of a brand-new Spitfire LF Mk. VIII flying above the clouds. This example, serial number MD351...

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An evocative photo of a brand-new Spitfire LF Mk. VIII flying above the clouds. This example, serial number MD351, reportedly belonged to the Central Gunnery School at the time when the photo was taken.

MD351 is representative of a late-production Mk. VIII with pointed rudder, standard wing tips and a Merlin 66 engine with universal filter housing under the nose.

Otherwise, the operational record of this fighter is surprisingly sketchy. About the only fact apparent in the RAF records is that it was transferred to Australia in June 1944, subsequently being allocated the RAAF serial number A58-521. According to Australian sources, it served briefly with No. 452 Squadron RAAF. It was eventually “converted to components” on 13 November 1945.
[Paul Sibson coll.]


By James  |  2011-05-06 at 06:46  |  permalink

You can clearly see in this photo, the characteristic slight down deflection of elevator Spitfires have in level flight. This is interesting as the tailplane can be rigged to counter this ,so that the elevators will fly in a neutral position. The angle between the mainplain chord line and the tailplane chordline, is if memory serves, know as longitudinal dihedral. However, this causes drag, also known as trim drag, for example when jets reaching transonic speed need to adjust tailplanes to counter pitching moment due to CP shifts as speeds approach transonic values. However tailplane or elevators, this is drag. In this case a small ammont, but perhaps one area Michell didn’t get quite right? Or is there a trimm speed at which all is straight, a speed at which a Spitfire is rarely, if ever, photographed? My recollections of the SAAF Museum MkIXe low back, was at speeds of about 260 MPH, the stick would very gently “hunt” in the pitching plane, a bit eerie, like she was talking to you!

By Barry Gillingwater  |  2011-05-09 at 02:47  |  permalink

James, I have a photo of three later model Spits in line astern formation taken during filming of the BoB movie in 1968. Two of them are Merlin-engined and the third is powered by a Griffon. The Merlin engined pair have exactly the same elevator displacement as in the previous photo posted but the Griffon one has a neutral elevator. This brings me to consider that the elevator displacement was something to do with a different thrust line between a Merlin and a Griffon installation. Any deviation between the thrust line and the longitudinal axis of the aircraft would result in some degree of rectification at the tail end, either by alteration of the tailplane rigging or an elevator bias depending upon throttle setting and/or speed. Just a guess – but a theory for consideration maybe?



By James  |  2011-05-09 at 05:21  |  permalink

Barry, thanks for that, very good thought.

You may well be right? For example, the Harvard had the vertical fin offset by 1 deg 45″ (if SAAF Harvard memory serves) to offset prop slipstream effect at the cruise. As you know design features like this will reallly only work at one speed and power setting. But now that you mention it, I seem to recall the Griffon was mounted in the airframe slightly offset (tlited slightly down and to the left?), to counter propellor slipstream effects in such a powerful engine. Not much could be done design wise, about torque of course. The Turboprop PC9M (have a few hours on those in Oman, very good trainer. (Easy to fly and forgiving, but challenging to fly accurately and well, I thought) and I think the Cessna Caravan, to name two, have offset engine mountings.

So, very good point. As I sit here, I can’t recall any offset to the Spitfires vertical fin? Probably not reqired due to power/lightness of rudder, and the relatvely highly geared trim knob? (more of a knob then a wheel I reckon!).

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