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megan
10th Aug 2016, 06:53
I wonder if some kind soul would have the time and inclination to translate the document in the link to English. I know an online translation can do it, but I'd like someone who understands the nuances of German and the aviation language to have a go. Online translation quite often reads as a bunch of gobbledygook.

http://www.klassiker-der-luftfahrt.de/sixcms/media.php/53/Spitfire_Versuchsbericht.pdf

Many thanks in advance to whoever takes on this thankless task. :p

Innominate
10th Aug 2016, 12:45
There's a lot to translate there! It seems to be a report on tests carried out on Spitfire Vb EN830, fitted with a DB 605 engine. The report seems to concentrate more on the engine aspects (cooling, oil and air compresser) than the performance, although it does mention that the Spitfire - despite having over 5 sq m area more than the 109G - was only about 25 km/hr slower than the 109G with the same engine.

megan
10th Aug 2016, 13:13
It's the cooling I'm most interested in Innominate. Just the text, not the graphs. :ok:

Tu.114
11th Aug 2016, 18:53
I´ll give it a try.

Liquid cooling installation

The cooling machinery has to be considered functionally good and due to the radiators lower flow resistance (1.0 bar at 2600 rpm) much more stable than the installation of the Bf 109 G. Under German design rules, the cooler would be barely sufficient, its efficiency at full throttle height is at 0.96 (see page 2), but under British ones, despite the DB 605 delivering 150hp more than the Merlin 45 at altitude, it would be well appropriate. It has been noted that the nearly 50% smaller radiator of the Spitfire (surface of 17.4 dm²) only provides about 4% less of cooling capacity than the double radiator on the 109 G (surface of 2x 16,8 dm²).

The reason for the good efficiency of the Spitfire water radiator seems to be that the specific heat carried by the cooling water per (horsepower per hour) in the DB605 is lower than in the Merlin engine as has been measured at the DVL (Deutsche Versuchsanstalt für Luftfahrttechnik) and also the considerably more suitable location of the radiator, yielding a much better efficiency with a given frontal area.

megan
12th Aug 2016, 04:46
I'm much obliged Tu.114 and indebted to you, thank you very much. :ok:

Tu.114
15th Aug 2016, 08:48
Now I am at my own computer again and can attack the rest of the document.


Examination report.

Test number 10 18 103 (4?)26.

The stamps read: Department of flight testing. Arrived on (xx) July of 1944. Assigned to: blank. Completed by: (signature). SECRET! (illegible text)

Concerns: Investigation into the operation of the engine DB 605A installed in a Spitfire V with special focus on cooling and flight performance.

Examination results:

Lubrication installation
The lubricating systems are functionally acceptable. The oil cooler designed for the Merlin 45 is insufficient for the DB 605A. Beside the higher power rating, this is due to the higher oil temperature approved for the Merlin and the higher specific heat carried by the lubrication system caused by the hydraulic clutches slip predominantly at lower altitudes. The efficiency at full throttle flight at an altitude of 1km is 0.83. A test climb to examine the oil coolers efficiency [my remark: this is the "Ölkühlergütegradsteigflug"] that could not be performed at a steady state temperature due to mentioned reasons is displayed on page 1.

The oil coolers flow resistance is very high. It about corresponds to the old cooler of the Me 109F FO699.

Liquid cooling installation

The cooling machinery has to be considered functionally good and due to the radiators lower flow resistance (1.0 bar at 2600 rpm) much more stable than the installation of the Bf 109 G. Under German design rules, the cooler would be barely sufficient, its efficiency at full throttle height is at 0.96 (see page 2), but under British ones, despite the DB 605 delivering 150hp more than the Merlin 45 at altitude, it would be well appropriate. It has been noted that the nearly 50% smaller radiator of the Spitfire (surface of 17.4 dm²) only provides about 4% less of cooling capacity than the double radiator on the 109 G (surface of 2x 16,8 dm²).

The reason for the good efficiency of the Spitfire water radiator seems to be that the specific heat carried by the cooling water per (horsepower per hour) in the DB605 is lower than in the Merlin engine as has been measured at the DVL (Deutsche Versuchsanstalt für Luftfahrttechnik) and also the considerably more suitable location of the radiator, yielding a much better efficiency with a given frontal area.

Flight performance
The speed readings are shown on page 3. It has to be mentioned that the Spitfire V is only 25km/h slower than the Me 109G at low altitudes with the same engine power rating despite its wing being larger by more than 5 m². Taking into account the Spitfires entire equipment (weapons), both types should achieve an equal speed at 11 km height.

Page 4 shows the climb performance of the Spitfire V compared to that of the Me 109G. It has to be taken into account that the Spitfire is not armed (about 300 kg too light). The armament ought to decrease climb performance by about 1-2 m/sec. Theoretical maximum altitude is at 12.7km, which is about 1 km better than the Me 109G at the same engine power rating.

I. Scope of the examination
Examination of the operation of the engine DB 605 A installed in a Spitfire V, taking special note of cooling and flight performance.

II. Execution of the examination
The examinations were done using the captured Spitfire V serial no. 830 CJ+ZY [assigned German tactical mark] and the engine DB 605A 1, factory number 00701990.

The engine installation, construction of the engine attachment beams, cowling, oil tank and the upper fuel container was done at the Sindelfingen works. The engine used is a standard engine of the Me 110 G.

Besides numerous repairs to damaged parts, the electrical installation and the instrumentation had to be completely reinstalled, as our equipment works on 24V instead of 12V.

III. Condition of the aircraft
Standard series Spitfire V without radio (replaced with ballast) but with antenna. Unarmed; cannon and MG openings in the wings faired, bulbed covers retained.

Air screw: VDM three bladed. Diameter 3m. B (1.0m)= 310mm. Blade type: 9-12159A; Me-109G airscrew.
Cowling: Standard Me-110G type. Air scoop: Me-109G type.
Takeoff weight: 2730 kg (unarmed).
Fully equipped, the weight ought to be about 300kg higher.

Oil cooler: oval construction (air tube system); two radiators in series both with regards to air and oil flow. Area: 2x2,95dm², 230mm depth.

Water cooler: rectangular construction (water pipe system). Area 17.4 dm², depth 230mm.

Both radiators are entirely made from copper.

IV. Examination results

1. Lubrication installation

The lubricating systems had to be built from scratch, only retaining the oil cooler situated under the left wing.

As the Spitfire V oil tank is situated below the engine but there is no free space on the Me 110G engine, the oil container (total volume 40 ltr). has been installed right behind the engine. Thus, the upper, non-self sealing fuel tank had to be shrunk correspondingly. This setup provided for excellent oil supply characteristics. The return ducting to the oil cooler under the left wing and from there on to the container used NW20 type pipes. To achieve direct comparability to the Me 109Gs lubricating system, the oil container was pressurised to 1.3 bar. As the highest acceptable oil entry temperature of the Merlin 45 is at 105°C and temperature is only governed by 2 temperature sensitive safety valves governing to about 95-100°C instead of the radiator air flow, these valves could not be used. Instead, a temperature sensitive safety valve built by SKF Zchg., no. SK 5719. This rendered an air flow governor superfluous as the high flow resistance of the radiators, the governing valve is open during the warming-up phase and a quick warming up of the oil is ensured.

The oil coolers flow resistance including piping (no filter installed in the return lines) is about 1.7 atm. at 2600rpm and an entry and exit temperature of 130 and 75°C. Regarding its flow resistance also during startup, it about corresponds to the old FO699 oil cooler on the ME 109F.

Based on the currently permissive oil temperatures of max. 85°C for a DB605A engine, the oil coolers heat dissipation capability is completely insufficient compared to the Merlins maximum of 105°C. The situation was improved though by the higher allowed oil temperatures on newer engines of up to 95°C. Additionally, the DB605 adds more specific heat to the oil because of its superchargers hydraulic clutch, reaching a maximum near the ground and decreasing until full throttle height, where the clutches slip is only small.

A steady state full throttle flight close to ground with the DB 605A showed only an efficiency of 0,84 with a (illegible) of 490 kg/h (with a maximum entry temperature of 85°C and an European summer at ISA +20). The subsequent climb had to be stopped already at 3km height due to the oil entry temperature reaching 100°C. Page 1 shows an oil cooler efficiency which did not start with steady state full throttle close to the ground but a continuous climb after takeoff. At 5km height, the massive increase of oil temperature enforced a speed increase of about 30km/h. Noteworthy is as well the strong drop in efficiency at altitude, hinting at the radiators bad performance when being fed cold air.

2. Cooling installation
The cooling installation corresponds to that of the Me 110G except for the radiator. (lambda-shaped water tank in front of the engine, steam separator, joining of both cooling agent pipes right downstream of the steam separators, radiator below the right wing, feed pipe manifold in accordance with DB drawing 9-605.6051 including injector).

The outer circuits flow resistance at 2600 rpm measured between a position behind the steam separators and a position upstream of the pump is about 1.0atm. The circulating volume was not measured.

Judging from its cooling capacity, the installation is insufficient especially at higher altitudes, see p. 2. This is due to the greater power of the DB605, the greater maximum outflow temperature of 115°C decreasing along 1.75 atm steam pressure vs. 120°C in case of the Merlin 55 at all altitudes, the used water/glycol mixture ratio of 50-50 vs. 70-30, the English radiator construction and lower summer temperatures. For more, see the spreadsheet at the end of the report.

Comparing the Spitfire cooling installation to that of the Me 109G, it has to be noted that despite the nearly 50% smaller frontal area of the Spitfires radiator, the cooling performance is only 4% worse than that of the Me 109. This is firstly caused by the cooling waters specific heat of the DB 605A being lower than that of the Merlin 45, resulting in the absolute heat of the cooling water not increasing proportional to performance (as measured by DVL, the specific heat at 115°C exit temperature shows 230 on the DB 605, but 260kgcal/hp on the Merlin 45), secondly the cooler installation is much more suitable, leading to a higher heat flow ratio per unit of frontal area.

To allow a comparison, the efficiency using English figures (120°C maximum temperature at all altitudes and British summer temperature of ISA+9) is shown. This shows that the radiator ought to be sufficient even at altitude and with the about 150hp higher power output of the DB 605A. During taxi and warmup at 115°C maximum temperature, the radiator is insufficient.

As the Spitfires radiator shows a lower flow resistance than e. g. the radiator of the Me 109G, it is noticeably more stable also at higher temperatures. The injector yields a pressure increase upstream of the pump of more than 0.2at.

3. Fuel installation
The lower self-sealing original container (200ltr) has been retained. The English fuel level indication could not be used as it is only suited to 12V. Instead, a German fuel level indicator was used. A boost pump could not be installed in the tank for space reasons. To ensure a safe fuel supply at higher altitudes, a DBU type membrane pump was installed in the feed pipe close to the container using German standard FBH fittings. The upper original container directly linked to the lower one had to be downsized to 170ltr. due to the installation of the oil tank behind the engine.

There were no difficulties encountered with this setup during the test flights.

4. Pneumatics, Hydraulics
The pneumatic installation is used to actuate the wheel brakes and flaps. Pressurized air is provided by a piston compressor driven by the camshaft of the Merlin 45. So it is driven at half the crankshaft speed. This compressor could not be attached to the DB605 in the same position, so it was mounted to the DB605s slow speed accessory drive, using a reduction gearbox (2.2:1). Otherwise, the English setup was completely retained. This setup allowed the brakes and flaps to work without problems.

The hydraulic system is only used to extend or retract the landing gear. The English pump could not be installed on the DB605, so a Bamag type pump (19.1104, 12 ltr/min mass flow) was mounted to the high speed accessory drive, yielding satisfying results.

5. Flight performance
a. Speed performance
Page 3 shows speed readings during full throttle level flight (2600rpm) at heights of 1 to 12km (water cooler cowl flap in flush position).

To compare, the dashed line shows the speed readings of the Me 109G, the dotted line shows the Spitfire V with its Merlin 45 as tested at Rechlin captured aircraft testing site.

It has to be mentioned that the 109 and the Spitfire V with Merlin 45 have been test flown with full armament while the Spitfire V with the DB 605 has been flown unarmed, yielding a mass difference of about 300kg. Thus, especially at higher altitude the Spitfire V will show a bit lower speed, resulting in an equal speed to the Me 109G at about 11 km height.

The large performance drop of the Spitfire V with its Merlin 45 above full throttle height compared to the DB 605 is remarkable. This is likely due to the lower volumetric efficiency of the fast-running, low displacement Merlin 45 compared to the slow-running, large displacement DB 605A.

b. Climb performance
Page 4 shows the climb performance readings compared to a standard Me 109G aircraft. Taking into account the Spitfire weapon installation, its climb speed will likely decrease by 1-2m/sec. It is nevertheless noticeably better than that of the Me 109G at all altitudes.

The best climb speed as measured at Rechlin (dashed line) could not be maintained due to the insufficient oil cooler and had to be increased especially at medium altitudes. This is however unlikely to influence the climb speed noticeably.

DaveReidUK
15th Aug 2016, 10:04
Thanks, much appreciated.

megan
15th Aug 2016, 13:34
Tu.114, you're worth bottling, thank you mutchly. :ok: