High-Drag Areas on the Supermarine Spitfire

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

Zipper730

Chief Master Sergeant
4,430
1,023
Nov 9, 2015
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?
 
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.
 

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.
 
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".
 
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).
 
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.
 
wuzak said:
Only the early models had exterior bullet proof glass. Maybe Mk I, II and V.
Click to expand...
Oh, I didn't know they changed that.
The angle of the window was a problem, worth a few mph.
Click to expand...
Was there ever a reason to explain why they used such a steep canopy angle?
The cannon barrels cost about 8mph.
Click to expand...
What's typical for a fighter of the era?
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.
Click to expand...
Was the inlet area too small or too large? Also, I assume the outlet flap had variable positions on most aircraft?
External mirrors also caused drag.
Click to expand...
True, but that probably made for a major improvement in situational awareness.
Surface finish was, probably, also a factor.
Click to expand...
Did the RAF have a poor finish?

Airframes said:
The armoured glass was retro-fitted in late 1939 to early 1940, being external on the MkI, MkII and early MkV.
Click to expand...
So from the Mk.VI or VII they had internal framing?

tomo pauk said:
The radiators were without boundary-layer splitter or tunnel, that will increase the drag.
Click to expand...
Out of curiosity, why did they omit that?
 
The thing with bullet proof glass is it is thick, the more you incline it the more optical distortion you introduce.
 
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.


 
tomo pauk said:
Did they omit it, or they didn't now that thing actually exists in mid-1930s?
Click to expand...
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?
 
Zipper730 said:
Good point, but by the late 1930's one would figure that would factor into things -- the idea of adding a splitter plate.
Click to expand...

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.
 
With the increase in power from 1000 to 2000 HP comes a massive increase in cooling, not only for the engine but the oil and intercooler too. If that cooling was in the original design then probably the Spitfire would have been designed differently.
 
Zipper730 said:
Did the RAF have a poor finish?
?
Click to expand...
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.
 
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.
 
They used the highly scientific method of taking a Spitfire with all flush rivets, gluing split peas on them and progressively removing them.
 
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.
 
You must log in or register to reply here.

Users who are viewing this thread

Total: 1 (members: 0, guests: 1)

Similar threads

A
The Supermarine Spitfire
2
Replies
36
Views
3K
pbehn
P
Interesting Data on the Lorin Ramjet
Replies
1
Views
498
AMCKen
A
Where was the gun camera on the Bf 110?
Replies
6
Views
647
Snautzer01
Ballistics of British High Capacity (HC) bombs
Replies
17
Views
1K
33k in the air
Any Sources on Sea Level max speeds for the Ki-43’s?
Replies
4
Views
601
taly01
Menu
Log in
Register