Spitfire's drag - what was good, and what was not?

[Tante Ju]

Try again and see my post.
The Merlin 66 did not have 1710hp at sea level, it had 1705hp at 5750ft and had to use a partially closed throttle at sea level (much like the DB 605A puts out 1475ps at sea level but 1525-1550ps at a bit over 2000m). Merlin 66 was good for a lot closer to 1600hp at sea level.

Well maybe this will help you. Merlin 66 had 1680 HP at SL (+18/3000), so my conclusions are still correct. There's no likely involved. Source British datasheet for Merlin 66, clearly noting SL power.

So the real question is - how much the Griffon 65 had at SL under static condtions? 1840 is for 400 mph ram. Likely the static condition is closer to 1900 HP at SL for Griffon. That means the aerodynamic effiency loss between the Mark I and Mark XIV is even slightly more severe.

The 20mm gun installation was worth a few mph, drag yes but little to do with the "dirty underside". the increase in weight of over a ton means higher induced drag. We can account for 8-12mph just in the induced drag and guns (minimum), Between just those losses from drag and the actual power being lower than you figured the increase in drag from the "dirty underside" is heading for "insignificant" really quick.

Well let's see. 1 ton weight increase worth about 5 mph speed loss (from kurfurst.org site, for 109 but good ballpark for Spitfire.). Cannon installation - about 10 mph loss. Say another 5 mph for everything else - new antanne, changed shape winshield etc.

That still leaves about 20 mph loss is due to things on the dirty underside. My take is that most of it is really coming from the much enlarged and doubled radiators.

 

[Shortround6]

Apology happily accepted.

I like finding out the truth and I was a little surprised myself when I did this exercise a while back at how close it came out. It may be coincidence but it does seem to track fairly well. You can twist it a little by using the wrong power or a fast MK and a slow MK IX 9 or whatever) but I figure if the results at in the low single digits percentage wise it is close enough. Too much other stuff changes (windscreens, radial aerials,etc) in addition to individual aircraft performance to get any closer than that.

As far as Meredith goes, many people have the same idea at nearly the same time without "copying" or even knowing about each other. Having the idea of using the heat from the radiator for propulsion may have been common, putting it into a mathematical formula and 'reading' the theory at an aeronautical convention was not common. I believe he proposed the use of exhaust thrust at the same meeting???
Again an IDEA and a mathematical theory/formula are not quite the same thing and it takes a number of years to turn a theory/formula into actual practice so there may be credit enough to spread around. Not trying to take anything away from Meredith
but the constant arguments as to who "invented" what get a little tiresome when it takes 20-30 years for the "invention" to become practical.
Shaft turbine engines were "running" before WW I. they just weren't very good making claims for their "invention" years later a little strange. Claims for major improvements are a lot stronger.

 

[Shortround6]

Well maybe this will help you. Merlin 66 had 1680 HP at SL (+18/3000), so my conclusions are still correct. There's no likely involved. Source British datasheet for Merlin 66, clearly noting SL power.

Like this data sheet??

http://www.spitfireperformance.com/merlin66hpchart.jpg

So the real question is - how much the Griffon 65 had at SL under static condtions? 1840 is for 400 mph ram. Likely the static condition is closer to 1900 HP at SL for Griffon. That means the aerodynamic effiency loss between the Mark I and Mark XIV is even slightly more severe.

It doesn't really work that way. 18lbs boost is 18lbs boost. Ram can raise the altitude at which a given pressure can be maintained OR it can add pressure/power at lower lower altitudes. Static power is not going to be higher than RAM power unless something else is going on (like closing the throttle to limit the the amount of boost). In any case a hypothetical "static condition"has darn little to do with actual flight tests results.

Well let's see. 1 ton weight increase worth about 5 mph speed loss (from kurfurst.org site, for 109 but good ballpark for Spitfire.). Cannon installation - about 10 mph loss. Say another 5 mph for everything else - new antanne, changed shape winshield etc.

That still leaves about 20 mph loss is due to things on the dirty underside. My take is that most of it is really coming from the much enlarged and doubled radiators.

"From that it follows that the drag increase during the development of the Spitfire was equivalent to about 25-30 mph speed loss. That's hardly insignificant."

Which is it? you just accounted for 20mph out of 25-30mph and yet you are claiming 20mph left of speed loss?

NOBODY doubled the power of aircraft and didn't some increase in drag. The question is how much. even 15mph is only about 4% on a 360mph airplane. I think I would take a 4% loss in potential speed due to drag in order to go from 280 mph to 360mph.

 

[Edgar Brooks]

Well let's see. 1 ton weight increase worth about 5 mph speed loss (from kurfurst.org site, for 109 but good ballpark for Spitfire.). Cannon installation - about 10 mph loss. Say another 5 mph for everything else - new antanne, changed shape winshield etc.

Really don't know the Spitfire, do you? The XIV had a whip aerial, which gave less drag than the aerial mast, plus HF aerial wire, of the Mk.I, a thin bar-type Mk.III I.F.F. aerial, which gave less drag than the pair of Mk.II aerials of the early Marks, and the internal-armoured windshield, which also gave less drag than the externally-armoured type (introduced at the time of Dunkirk,) was introduced on the Mk.V, and never changed (except for the curved type on some P.R. variants) its shape throughout the war.

 

[Siegfried]

http://spitfiresite.com/2010/04/supermarine-spitfire-variants-the-initial-merlin-powered-line.html/2
"All panel lines were filled and smoothed over, all round headed rivets on the wing surfaces were replaced by flush rivets and an elongated "racing" windscreen was fitted. A tailskid replaced the tail wheel. Finally the "Speed Spitfire" was painted in a highly polished gloss Royal Blue and Silver finish. As it turned out, the finished aircraft actually weighed some 298 lb (135 kg) more than a standard 1938 vintage Spitfire."

http://www.rcmf.co.uk/4um/index.php?topic=15309.0;wap
"According to an old MAP publication I own, from MK XII onward all rivets were of the flush type. Wing leading edge rivets back to the rear of the "D" section were also filled and sanded smooth as this area was found to have a pronounced effect on top speed."


Certainly I have read that the lower parts of the Spitfires wings were not flush rivetted, at some point anyway.

My statement that the retractable tailwheel versions was "little produced" stands, even by your own figures which claim 22%. My statement that production of the Spitfire was about 25,000 also stands if one includes the Seafire. Quite a few of those retractale tailwheel types were post war griffon engined Spitfire/Seafire. I would say that most folks can see through the squid ink of the hair splitting.

History of course records that few Spitfires had the retractable tailwheel and non had full wheel covers. Both would have had a significant impact on speed. Both were standard on most other fighters of the era.

Tests on the Me 109G indicated the following.

1 Covering Up the Remainder of the exposed Wheels: +10kmh.
2 Retractable Tail Wheel over non retractable: +12kmh
3 Extended Retractable Tail Wheel, if fitted +17kmh.
4 Loss due to MG 131 bulges -9 kmh.
5 Loss due to faired over MG 131 bulges -3 kmh.

Applying 1 and 2 above as indicative for the Spitifre we have a potential loss in speed of 22kmh, or about 13-14mph.

That's no chump change and it was standard practice for the P-51 and Fw 190.

As far as the Battle of Britain goes: German strategy, for they had little time to develop one and had spent no specific money in preparing for it, was based around applying maxium credible pressure to force Britain to the negotiating table. Long term there was of course the possibillity of invasion, but it would have taken a great deal of time to get ready. In fact Hitler wanted Britain to keep its empire as he saw only someone worse taking it over should a German victory be used to liberate it to itself. An amphibious assault for which Germany lacked the Navy (paltry 36 submarines) would take a long time. By then the cabal of "human interest" journalists likely would have brought the US to Britains side and Germany would face the Soviets and the US/Britain. The gamble was to knock out the SU first. Perhaps a case of commiting suicide to avoid being killed as Bismarck suggested. Take out the fear of the US entering the war and the Soviet Union both German Navy and Lutfwaffe resources would have been applied and there would be no victory at the BoB, just historical notes about how the RAF had favourable attrition rates for a while but lost when tactics were changed.

 

[Milosh]

You might want to take a look here Siegfried, contract summary

Grand Total: 22799 including Seafires, Spitefuls and Seafangs.

 

[Edgar Brooks]

http://spitfiresite.com/2010/04/supermarine-spitfire-variants-the-initial-merlin-powered-line.html/2
"All panel lines were filled and smoothed over, all round headed rivets on the wing surfaces were replaced by flush rivets and an elongated "racing" windscreen was fitted. A tailskid replaced the tail wheel. Finally the "Speed Spitfire" was painted in a highly polished gloss Royal Blue and Silver finish. As it turned out, the finished aircraft actually weighed some 298 lb (135 kg) more than a standard 1938 vintage Spitfire..

The Speed Spitfire was the 48th production Spitfire, so quite what your point might be is rather lost; also it was flush-rivetted throughout, which is rather different from your nonsense about domed rivets, which never existed in the first place, except on the rear fuselage.

"According to an old MAP publication I own, from MK XII onward all rivets were of the flush type. Wing leading edge rivets back to the rear of the "D" section were also filled and sanded smooth as this area was found to have a pronounced effect on top speed."

Unfortunately, MAP got it wrong (research moves on, as you'd discover if you tried it); the 100% flush rivetting started, from June 10th., 1943 with the Vc., and the wing + painting improvements started even earlier, from 25-9-42.

Certainly I have read that the lower parts of the Spitfires wings were not flush rivetted, at some point anyway.

Not everybody gets their facts right, which is why it's best to find more than one source, and cross-check. The Mk.I had wooden strips on the bottom of the ribs, to which the skins were attached by countersunk (which equals flush) screws.

My statement that the retractable tailwheel versions was "little produced" stands, even by your own figures which claim 22%. My statement that production of the Spitfire was about 25,000 also stands if one includes the Seafire

.
If you wish to repeat a falsehood, I can't stop you, though it reduces your credibility by a significant amount.

Quite a few of those retractale tailwheel types were post war griffon engined Spitfire/Seafire I would say that most folks can see through the squid ink of the hair splitting.

Which proves what? You said they were few in number, and I said they were 1 in 5, and a fair number of the "post-war" Spitfires were already in production before the war ended, very suddenly, in September 1945, when everyone expected it to continue for much longer. If you're worried about the "squid ink of hair-splitting," perhaps you should stop using it.

History of course records that few Spitfires had the retractable tailwheel and non had full wheel covers. Both would have had a significant impact on speed. Both were standard on most other fighters of the era.

History, of course, records nothing of the sort, since there were 3985 Spitfires with retractable tail wheels, out of 20,334, which = 19.59%, and the first fighters were some of the Mk.XII all VIII airframes (yes, they really were that early.) The 21, which just entered service in 1945, also had full wheel covers.

Tests on the Me 109G indicated the following.

1 Covering Up the Remainder of the exposed Wheels: +10kmh.
2 Retractable Tail Wheel over non retractable: +12kmh
3 Extended Retractable Tail Wheel, if fitted +17kmh.
4 Loss due to MG 131 bulges -9 kmh.
5 Loss due to faired over MG 131 bulges -3 kmh.

Applying 1 and 2 above as indicative for the Spitifre we have a potential loss in speed of 22kmh, or about 13-14mph.

No, "we" don't, since the VII, VIII, and XIV (slated to take over from the IX, which is why so many IXs were given away, especially to the USSR) all had retractable tail wheels, so your "loss" drops to just over 6mph, and that is "chump change," when you add in multi-ejector exhausts (gain of 5-7mph,) removal of ice guard (+ 3mph,) round, faired mirror, instead of square (+ 3mph.) cut-down ejection chutes (+ 1mph,) narrow, instead of broad, blister over cannon bay (+ 1mph.) You see, it wasn't just the super-efficient Germans who considered ways to improve aerodynamics.

In fact Hitler wanted Britain to keep its empire as he saw only someone worse taking it over should a German victory be used to liberate it to itself.

So Britain would have surrendered, but still been allowed to run the Commonwealth? That's pure Hollywood-style fantasy, and you know it.

An amphibious assault for which Germany lacked the Navy (paltry 36 submarines) would take a long time. By then the cabal of "human interest" journalists likely would have brought the US to Britains side and Germany would face the Soviets and the US/Britain.

Well, here goes "likely" (= guess) again.

Take out the fear of the US entering the war and the Soviet Union both German Navy and Lutfwaffe resources would have been applied and there would be no victory at the BoB, just historical notes about how the RAF had favourable attrition rates for a while but lost when tactics were changed

Would've, should've, could've, here we go again, with the never-ending guesswork; try returning to the real world, and its ice-cold facts; we won, you lost.

 

[Readie]

Edgar
Don't get sucked in mate.
Cheers
John

 

[stug3]

Spitfire Mark VII, BS142 on the ground at Eastleigh, Hampshire, after modification by Cunliffe Owen Aircraft Ltd., and shortly before joining the High Altitude Flight (renamed the Sub Stratosphere Flight) at Northolt, Middlesex. In January 1943, BS142 went to No. 124 Squadron RAF with whom it claimed the unit’s first high altitude victory, a Focke Wulf Fw 190, on 15 May. It later also served with No. 331 Squadron RAF.

Group Captain A.G. 'Sailor' Malan on the wing of Squadron Leader Hugo 'Sinker' Armstrong's Spitfire IX at Biggin Hill, 2 January 1943

Flight Lieutenant J. Pattison of No 485 Squadron, RNZAF, graphically recounts a combat to Squadron Leader 'Reg' Grant (left), and Flight Lieutenant R Baker (right), in front of a Spitfire at Westhampnett, 21 January 1943.

 

[parsifal]

As ever stug, I love the photos

 

[tomo pauk]

Recipe on getting the Spitfire V going 400 mph (also on speeding up the Mk.I and Mk.IX), provided by Kurfurst in an old thread. Interestingly enough, there is no mention of fully retractable covered U/C.

 

[SpicyJuan11]

Recipe on getting the Spitfire V going 400 mph (also on speeding up the Mk.I and Mk.IX), provided by Kurfurst in an old thread. Interestingly enough, there is no mention of fully retractable covered U/C.

What happened to him?

 

[tomo pauk]

Banned.

 

[SpicyJuan11]

Banned.

Oh, does anyone know why, he seemed like a respectable poster?

 

[blueskies]

Regarding the drag from wheel covers and retractable tail wheels I believe the following NACA reports are useful.

ntrs.nasa.gov/search.jsp?R=19930092668
ntrs.nasa.gov/search.jsp?R=19930092657

As for a boundary layer splitter for the radiator, there was one present on the speed spitfire and I believe that some type of splitter was also trialed on the mkiii.

I would guess that they found the benefits of a splitter not worth the effort, similar to how messerschmitt dropped the duct on the 109.

 

[fastmongrel]

Oh, does anyone know why, he seemed like a respectable poster?

He couldnt resist using words and phrases that were rascist and derogatory. He got warned several times and then beached permanently, you can get away with quite a lot on this forum especially if you can back your claims but attacking others on the basis of country, creed or race is not allowed. Quickest way for the ban stick to hit you on the head.

 

[fastmongrel]

Regarding the drag from wheel covers and retractable tail wheels I believe the following NACA reports are useful.

ntrs.nasa.gov/search.jsp?R=19930092668
ntrs.nasa.gov/search.jsp?R=19930092657

Great info I have put them into links makes it easier to find.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092657.pdf

 

[blueskies]

One finding in the first naca report is that a partially covered wheel well has a severe drag penalty due to air leaking into the wing. The report stresses the importance of properly sealing the well to eliminate leaks, and notes that a substantial gain will be seen if done correctly.

Edgar, do you know if the spitfire employed sealing in the wheel well? I'd imagine that there are a good number of related work orders if so.

Another point raised in the naca report is the thickness of the radio mast being responsible for most of the masts drag. Are there accurate drawings of the spits various masts?

 

[Edgar Brooks]

Edgar, do you know if the spitfire employed sealing in the wheel well? I'd imagine that there are a good number of related work orders if so.

There's nothing mentioned, but a "stopper" was employed to fill the rivet "divots" on the wings' leading edges, so I'd hazard a guess the same material would have been used for any gaps.
The tyre was supposed to have only about half an inch clearance inside the well, and the wheel was half-covered by the cover. Full wheel covers were fitted to the prototype, but discarded, probably due to them snagging in grass-covered airfields.
The oleo covers sealed the leg channels, so any leakage was minimal.

Another point raised in the naca report is the thickness of the radio mast being responsible for most of the masts drag. Are there accurate drawings of the spits various masts?

I've never seen any, sorry.
Edit: looking at available drawings, there was one for the mast which had the aerial set inside it (around the end of 1940,) but the RAF Museum's library don't list a copy.