Spitfire elevator horns

[P.o Prune]

This may have been asked before but I haven't been able to find it anywhere.

My question is very simple. when did they start changing the elevator horn on the Spitfire (extending it) and what was the reason?

Thanks in advance

[Work In Progress]

You mean the extended horn balance? There were perennial problems with the Spitfire's marginal longitudinal stability and control characteristics, exacerbated by the continual tendency of the CG to migrate rearwards due to the requirements for additional military equipment to be stowed in the fuselage. There were many partial and temporary fixes, including bob-weights in the elevator circuits and fine-tuned changes to the elevators.

It really only got finally and properly fixed when they put the big 22/24 tail on, to be honest.

The first production Spitfires built with the extended horn elevators were the specialised pressurised VII and the general-purpose VIII. So that's starting in about August 1942.

As a rule, if it has short ailerons it should have extended horn elevators

It's not hard and fast on the date because quite a few aircraft were subsequently retrofitted, and the XII was built later than August 1942 with the early shape elevators. And there are later types like the PR.XIX which has long ailerons and extended horn elevators.

Edited April 15, 2015 by Work In Progress

[Edgar]

Extended elevator horns were introduced on the Vb, Vc, VI, VII, VIII, IX, P.R.IV, & XIII production lines on 13-9-43, though leaflets, enabling units to carry out the work, themselves, were issued in March/April 1943. The XII didn't get them, possibly because at low level it didn't need them, and it seems the XIV & XIX got them from the start.

[Work In Progress]

Edgar, do you have evidence of Marks VII and VIII being delivered to service with the original elevators? I always thought they were built with the modified elevators, but am happy to learn otherwise.

[P.o Prune]

Thanks a million guys. You're the best :-)

[Flankerman]

One thing I always notice about Spitfires in straight and level flight is that the elevators are always a few degrees down.

Look at any photo of a modern warbird Spit to see what I mean....

Here's a good example :- http://1.bp.blogspot.com/-HXJ0uKtXORA/Tj3N0Zrf5bI/AAAAAAAABGs/7zklfXsuizA/s1600/supermarine-spitfire-mk-vb-wallpapers_17330_1024x768.jpg

Ken

[Work In Progress]

Yes, the tailplane incidence was wrong from the start and, again, only got corrected with the 22 tail. Whole thing was a bit of a lash-up, really

[Edgar]

Yes, the tailplane incidence was wrong from the start and, again, only got corrected with the 22 tail. Whole thing was a bit of a lash-up, really

Not exactly true, and it's funny how that "lash-up" lasted all those years and nobody noticed, or did anything about it; however, on 15-2-43, on the Mk. IX, the tailplane incidence (which could be adjusted) was actually reduced from +/- 20' to +/- 10', which runs completely counter to that jibe. A 1 degree incidence was introduced on the 22/24, 22-8-47 just after the larger tail had been introduced.

As the Spitfire's speed varied, so did the effectiveness of the elevators, hence the addition of the trim tabs (item 42 [ii] in the Pilot's notes,) and on take off (item 38,) depending on the load) the pilot is told to set the elevator trim tabs to 1 div. nose down, which would force the elevators down as a result.

Edited April 16, 2015 by Edgar

[Work In Progress]

Edgar, I know all about how aeroplanes are trimmed in flight and how trim tabs work. Every other aeroplane in the world is designed to have the elevators faired in trail at some normal cruise speed. And to my personal knowledge people have commented on this for decades so it's not some startling new insight that no-one's ever noticed before. Every picture of every pre big tail Spitfire ever taken in the cruise in which the elevator angle can be seen, they are noticeably deflected down, If you have them in proper trail that is enough for about 1.5G at 200 knots. It's not right.

You quote "the tailplane incidence (which could be adjusted) was actually reduced from +/- 20' to +/- 10'"

I may be misunderstanding but to me that does not look like a reduction of basic angle of incidence, but a reduction of the tolerance range around an unchanged neutral point. Hence the +/- .

Edited April 16, 2015 by Work In Progress

[Bedders]

I'm glad this question has cropped up, because my impression is that the majority of Mk IXs had the extended balances, whereas the majority of models I see appear to have the original ones. Perhaps this is because the Eduard 1/48 IXc is very popular but maybe (though I've never built one) only includes parts for the early unextended type. As a 1/72 man, I'm pleased that Airfix, Sword etc went for the later type in their mouldings, as my feeling is its more representative of the Mk IX in terms of numbers. Though maybe I just have a preference for the later type...

Justin

[Work In Progress]

I'm glad this question has cropped up, because my impression is that the majority of Mk IXs had the extended balances, whereas the majority of models I see appear to have the original ones.

I think the position is that the majority of the surviving ones did *eventually* due to the massive retro-fit programme but early ones at least did not when new.

[politicni komisar]

I'm build right now Spiti Mk.IXc MK210 and watch all the collected images from the Internet

and it seems to me that the early elevator ??

I have not decided yet because EDUARD offers both versions.

if anyone knows anything more I'm happy if we will offer advice and information for more

Of Spiti IX Hello TOLY.

P.k

[Graham Boak]

I'm interested in the comment about the Mk.XII having the early elevators. Given that it used Mk.V tails and Mk.VIII tails, I'd have expected it to have at least a mix. To be honest, I'm surprised that they weren't all the later variant. I don't understand why the role of the aircraft has any great significance. The Mk.XII did not operate any lower than the Mk.V which was receiving the better design.

As touched on, the Spitfire suffered for a long time from a shortage of longitudinal and directional stability and required a series of fixes. Probably (I suspect) not the case for those with single-stage Merlins, but Quill says in his memoirs that he tired of service people telling him "What the Spitfire needs is a bigger tail". He, together with the other pilots and aerodynamicists, knew that full well, but other developments and production were just too important to spare a gap long enough to design and, develop a new tail and rejig the lines. After all, it worked, didn't it?

This is known as "firefighting": attacking symptoms when it is known that going back to the drawing board and starting again would get to the root of the problems. There are always good reasons why not, and they (almost?) always boil down to time and effort.

[gingerbob]

Perhaps that nice heavy Griffon helped with the CG position compared to the Mk.V?

On the Mk.IX, same situation. I believe (from one decent picture I could find instantly) that "Tolly" had the early style, and I know that quite a few Mk.IXs did. I wouldn't be surprised to find early Mk.VIIIs with the early style, but haven't looked for evidence yet.

(And before anyone asks, if it is true that the late style was on the Mk.VII from the beginning, that could be explained by the increase of "friction" due to the seals through the cockpit bulkhead necessitating an improvement.)

bob

Edited April 16, 2015 by gingerbob

[Edgar]

Edgar, I know all about how aeroplanes are trimmed in flight and how trim tabs work.

Well, good for you, but, unfortunately, not everyone on this site is an aeronautical expert (including me,) so I find that I have to think of them, and tailor my responses accordingly.

Every other aeroplane in the world is designed to have the elevators faired in trail at some normal cruise speed.

But the Spitfire is a fighter, so how are the elevators supposed to be positioned when increased to combat (i.e. design) speed? Thousands of pilots coped with this major design fault, and the tailplane's aerofoil section was neutral, giving neither positive nor negative "lift" effect; a simple change to its section would have given the required lift, if it had been deemed necessary; it wasn't, so we're left to assume that the trim tabs were enough.

[Graham Boak]

That's an interesting point, Edgar. One test could be to look at the elevators of other contemporary fighters in the cruise, see if they also have any noticeable offset. However, this would hardly be a major design fault even if true - a small amount of trimmed elevator angle may well still produce an optimum drag overall, and this almost certainly varied from type to type. Or indeed with altitude and weight. Only if the trim proved not to be enough in significant cases would it be considered important.

The comment about difference at high speed is an interesting point. There's a fairly full discussion of the longitudinal trim problems of the later Spitfires, particularly Seafires, in David Brown's book Seafire and in Peter Caygill's Ultimate Spitfires. In brief: untrimmable rolls in one direction at low approach speeds was matched by untrimmable rolls in the opposite direction in high speed dives. The cure was the contra-prop.

Many if not all military aircraft, once in service, proved to have undesirable features somewhere in the flight envelope. That was just the state of the art. Recognition of this doesn't amount to rejection of the whole package. It is always a compromise.

Edited April 16, 2015 by Graham Boak

[Vanroon]

Combat aircraft tend to have some instability designed in to enable rapid control response. A single seat fighter will have an entirely different set of demands to an interceptor type. Ground attack envelopes differ as well. The long range recon configured aircraft different again.

As the Spitfire filled all of these roles over a great numbers of models, control surface variants and power plants is testament to the genius of the basic wing and fuselage combination.

G

[Steve in Ottawa]

For aircraft that are in that 'window' where the extended elevators were being fitted on the production line or by modification leaflet - does this correlate at all to the pointed rudder being fitted?  I want to say that the pointed rudder wouldn't be seen without extended elevators but, as in most things Spitfire, there are very few certainties. 

I'm certain that you could have round rudders and extended elevators,  so that comes down to finding photos that help confirm things one way or the other. 

[Graham Boak]

I don't believe that the two were connected, and don't see any obvious reason  why they should be.  Beyond the stability problems of the late Spitfires in general, as the aircraft grew in weight, size and flight envelope.  The bigger rudder is directed at matters of directional stability and control  (yaw, i.e moving left/right as you fly) whereas changes to the elevators are addressing longitudinal stability and control (pitch, i.e. the nose nodding up and down).  Yaw and Roll will often interact, but pitch tends to be considered separately.  At least to the level that I studied.

[EwenS]

About a year ago I did some research trawling through my reference library and the internet trying to identify when various Spitfire VII & VIII modifications were introduced and could be verified with photos. Unfortunately it is not easy to distinguish in most photos of the period what elevators were fitted due to the angle the photos are generally taken from so I wouldn't call my research definitive.

 

The evidence I amassed suggests that from JF661, which first flew on 30/6/43, all had the modified elevators with the increased balances. JF627 which first flew on 24/6/43 had the original elevators. JF620 & JF621 did not fly until Aug 1943 and received the later elevators (they were the first 2 airframes earmarked for Australia so I would speculate they were delayed pending finalisation of the Aussie spec with JF820 on). Prior to that the only photo where it was clear to me that the elevators were the later type was on JF447 which first flew on 14/4/43.

 

I have a note that on 23/2/43 Mod 914 authorised fitting the pointed fin on aircraft with the modified elevators. This would suggest that a pointed tail / original elevator combination was not envisaged. Whether it happened is a different matter.

 

Up to JF627 (FF 24/6/43), and excluding airframes used as prototyes for the Mk.XIV, the original rudder seems to be standard and it had the original elevators. From JF809 (FF 24/7/43) onwards the pointed tail seems to be standardised with the modified elevators. Between those serials (approx 100 airframes) I've identified some with the original rudder / modified elevator, and pointed rudder / modified elevator. I haven't identified any airframe with an original rudder / original elevator or pointed rudder / original elevator combination. The sample (4 airframes) is limited and excludes those where only one or other feature is clear.

 

Photos of Mk.VII that clearly show both features are rare. For what it is worth AB450 & BS142, the 1st and 3rd aircraft off the production line in Aug/Sept 1942, had an original rudder/original elevator combo. EN470 & 474 (FF 2-3/43) had an origianl rudder/modified elevator combo. The next airframe I've located a photo of is MB935 (FF around 10-11/43). It and all subsequent aircraft I've identified have the pointed tail and modified elevators. But it is a small sample of only 8 of 140 aircraft where both features are clearly identifiable.

 

I hope this helps everyone.

 

 

[Steve in Ottawa]

Great info, EwenS! Thanks for taking the time to post it.