If I recall the canopy was a sore-spot because, unlike many US designs, had the bullet proof plate outside the canopy (interestingly, I think the Germans did exactly what the British did). Were there any other areas there were problematic on the aircraft?
High-Drag Areas on the Supermarine Spitfire
- Thread starter Zipper730
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wuzak
Captain
Only the early models had exterior bullet proof glass. Maybe Mk I, II and V.
Definitely internal for the XIV.
The angle of the window was a problem, worth a few mph.
The cannon barrels cost about 8mph. The radiator installation was not as good as it could have been - with mismatched inlet and outlet volumes, and only 2 positions for outlet flap.
External mirrors also caused drag.
Surface finish was, probably, also a factor.
Definitely internal for the XIV.
The angle of the window was a problem, worth a few mph.
The cannon barrels cost about 8mph. The radiator installation was not as good as it could have been - with mismatched inlet and outlet volumes, and only 2 positions for outlet flap.
External mirrors also caused drag.
Surface finish was, probably, also a factor.
wuzak
Captain
I am not sure that it was a "sore-spot", since many US aircraft contemporary to the Spitfire I did not have armoured glass at all, and barely had any protective armour.
The armoured glass was on the outside, as it was, almost, an afterthought.
I haven't found the definitive answer yet, but it appears that internal armoured glass was introduced at some point in the Mk.V production run. The Mk.IX did not have it externally.
Airframes
Benevolens Magister
The armoured glass was retro-fitted in late 1939 to early 1940, being external on the MkI, MkII and early MkV.
From late MkV on through the rest of the Marks, the glass was internal, with a different style of windscreen frame, and an alteration to the slope angle of the screen.
Changes to the rear view mirror, from the early, rectangular style, to the streamlined 'racing car' type, improved things slightly, from memory 'saving' around 2-3 mph. However, when Spitfie XIVs were detailed for anti 'Diver' ops - chasing the V1 - these later style mirrors were removed, as part of a series of measures to increase speed and, again from memory, produced a 'saving' of around 5 mph.
Some pilots did their own mods, and had the mirror mounted internally, under the arch of the windscreen frame.
Change from the early, flat-sided canopy to the 'blown' type, not only improved canopy opening and eventually jettison in emergency, but also gave a slight speed increase, which was improved upon further with the later 'bubble' canopy and low fuselage spine.
Most of the 'drag reducing' mods are covered in the Shacklady & Morgan 'bible' on the Spit, "Spitfire, The History".
From late MkV on through the rest of the Marks, the glass was internal, with a different style of windscreen frame, and an alteration to the slope angle of the screen.
Changes to the rear view mirror, from the early, rectangular style, to the streamlined 'racing car' type, improved things slightly, from memory 'saving' around 2-3 mph. However, when Spitfie XIVs were detailed for anti 'Diver' ops - chasing the V1 - these later style mirrors were removed, as part of a series of measures to increase speed and, again from memory, produced a 'saving' of around 5 mph.
Some pilots did their own mods, and had the mirror mounted internally, under the arch of the windscreen frame.
Change from the early, flat-sided canopy to the 'blown' type, not only improved canopy opening and eventually jettison in emergency, but also gave a slight speed increase, which was improved upon further with the later 'bubble' canopy and low fuselage spine.
Most of the 'drag reducing' mods are covered in the Shacklady & Morgan 'bible' on the Spit, "Spitfire, The History".
The radiators were without boundary-layer splitter or tunnel, that will increase the drag. The 2-stage engines needed a modified radiators' systems, those were draggier than what 1-stage engines used. Griffon engines needed greater cooling capacity -> bigger radiators - > more drag. Fixed tailwheel will cost a few mph, so will non-covered main wheel wells; some later versions were with retractable tail wheel and covers for wells. the 3-per-side exhausts were probably also draggier than 6-per-side.
Ram air intake was also probably a source of drag (was changed with late Seafires).
Ram air intake was also probably a source of drag (was changed with late Seafires).
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
Dave Lednicer did CFD analyses of severa WWII-era aircraft, including the Spitfire, and published the results in one of the professional journals. You should be able to get a copy of the article through a university library.
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- #8
Oh, I didn't know they changed that.
Was there ever a reason to explain why they used such a steep canopy angle?
What's typical for a fighter of the era?
Was the inlet area too small or too large? Also, I assume the outlet flap had variable positions on most aircraft?
True, but that probably made for a major improvement in situational awareness.
Did the RAF have a poor finish?
So from the Mk.VI or VII they had internal framing?
Out of curiosity, why did they omit that?
Airframes
Benevolens Magister
As stated in my original post, windscreen armour was internal from late Mk.V onwards.
Pics below show later internal armour, inside and outside views, and original, 'bolt on' external armour.
Pics below show later internal armour, inside and outside views, and original, 'bolt on' external armour.
Did they omit it, or they didn't now that thing actually exists in mid-1930s?
I was going to post a similar remark. It isn't a just question of having a boundary layer splitter, it is having a good one. The Hurricane had a boundary layer splitter of sorts and isn't hailed as a wonder design. I suspect the reason is the massive amount of wind tunnel research done between the Spitfire and P-51 being designed. Even for the P-51 there were various incarnations to get it right. There is also the issue of location, could you use it under the wings where a Spitfires radiator(s) are?
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
No. There were two, actually, published by the Royal Aeronautical Society. The citations are here: https://ww2aircraft.net/forum/threads/ww2-fighter-and-critical-mach-speed.802/reply?quote=1308078
- Thread starter
- #14
Good point, but by the late 1930's one would figure that would factor into things -- the idea of adding a splitter plate.
By the late 1930s, British were burning the midnight oil to get any Spitfires in production and service, and by the same time probably no-one had have splitter plate on a production fighter either.
Finish is a global term, some is to do with the care an attention of the people finishing off the plane like paint and fit of panels. Most is in the design. The choice or rivets and fastners over a whole plane makes a difference but flush riveting (for example takes more time and costs more money. The number of joins and the accuracy of the fit up is also the design, but you cant design what you cant make, so if a long smooth panel requires a press you don't have you have to design something else, probably with more joints. The faster you go, the more drag costs you, its pointless developing another 100BHP from an engine when simple mods can have the same effect in terms of speed, you have to do both. It wasn't really an RAF thing, the Mosquito was good in terms of finish wood lends itself to smooth contours without rivets and gaps. The Typhoon/Tempest were also better their major drag issues were the wing and chin radiator The Tempest got a new wing and an annular radiator was a big improvement but not used to keep production numbers up.
wuzak
Captain
Some early Spitfire trials were used to compare conventional riveting and flush riveting.
I believe the final outcome of that was that the wings were flush riveted and the fuselage conventionally riveted.
This happened before production really got going.
They may have changed to all flush rivets later on.
I believe the final outcome of that was that the wings were flush riveted and the fuselage conventionally riveted.
This happened before production really got going.
They may have changed to all flush rivets later on.
They used the highly scientific method of taking a Spitfire with all flush rivets, gluing split peas on them and progressively removing them.
Shortround6
Major General
Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening. This allows a higher volume of air for the same size opening and the less turbulent air flows better through the radiator also consuming less drag.
The downside is the the radiator duct/housing has to stick further out into the airstream, increasing the frontal area of the airplane. Then you have the problem of what to do with the air you split off?
On the Mustang they let the the boundary layer air spill out to the sides.
On the 109F they ducted the air over the top of the radiator.
which was an improvement (of sorts) over the 109E
so nobody was really using splitters in the mid to late 30s. In 1940 the germans used one on the 109F, other people may have been working with the idea about that time.
On the Spitfire there was limited room to work.
The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.
perhaps it could have been done. But at what cost/complexity? (every body bitches at how much Spitfire wings cost to build as it was.
If you route the boundary layer air up and over (ala 109F) you have to hang the radiator a bit lower and lower the bottom of the radiator duct increasing the drag. Perhaps the change is worth it.
The downside is the the radiator duct/housing has to stick further out into the airstream, increasing the frontal area of the airplane. Then you have the problem of what to do with the air you split off?
On the Mustang they let the the boundary layer air spill out to the sides.
On the 109F they ducted the air over the top of the radiator.
which was an improvement (of sorts) over the 109E
so nobody was really using splitters in the mid to late 30s. In 1940 the germans used one on the 109F, other people may have been working with the idea about that time.
On the Spitfire there was limited room to work.
The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.
perhaps it could have been done. But at what cost/complexity? (every body bitches at how much Spitfire wings cost to build as it was.
If you route the boundary layer air up and over (ala 109F) you have to hang the radiator a bit lower and lower the bottom of the radiator duct increasing the drag. Perhaps the change is worth it.
