What if depending on Ju-88 range

Discussion in 'Aviation' started by cherry blossom, Apr 25, 2009.

  1. cherry blossom

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    On another forum, someone raised the question whether the Luftwaffe could have effectively attacked British Atlantic convoys if they had developed air to air refuelling before July 1940 (without the British finding out about their experiments). Air to air refuelling had certainly been developed before 1939 although the fuel transfer rates may have been slow. The question seems to depend on the range of a Ju-88A5 which was the version of the Ju-88 in production in July 1940.

    I suspect that British convoys had to pass through a square about 200 miles across North and West of Rockall and moved slowly enough that they would be within that square in daylight on at least one day. The square is approximately equidistant from Norway and France, so if the convoys sail further North, they are closer to Norway, and further South, closer to France. This square is outside the effective range of any British fighter of 1940-41 with a chance of catching a Ju-88. German aircraft have to fly roughly 1000-1200 miles from either France and Norway to this square, avoiding flying close to British airfields (excluding Vágar Airport in the Faroe Islands which was built in 1942–43). The Fw200C was capable of flying to the area from France, attacking a ship and flying on to Norway. However, there were few Fw200s in 1940 and they were fragile.

    Thus the question is do there exist points South and East of the box where a Ju-88A5 carrying at least 500 kg of bombs externally and a refuelling system can be refuelled so that the bomber can drop its bombs and return to either France or Norway if refuelling fails or if refuelled successfully can search for about an hour in the box, attack a convoy and then return to either France or Norway? Ideally loses would be lower if the Ju-88A5 could also return if one engine failed. Unfortunately, the range of a warplane is a rather elastic concept. It is fairly clear that air to air refuelling would have allowed a reconnaissance variant of the Ju-88A5 to find British convoys. The Ju-88D was developed slightly later by adding fuel tanks and removing equipment such as divebrakes from a Ju-88A4. Its empty weight is given as 8,850 kg compared to 9,860 kg for a Ju-88A4. Its range is given by Stewart Wilson's "Aircraft of WWII" as 2,980 miles or 4,795 km. This may be a gross exaggeration calculated by excluding climb and any allowances but that hardly matters as it is only 400 miles short of the Fw200's range (and we know that that could manage without refuelling). For the bomber, the issue is less clear. The Ju-88A4 has a maximum take off weight of 14,000 kg. We will ignore the idea that it might be safe to refuel one to a higher weight in the air. Thus for an A4, we could carry 500 kg of bombs, perhaps 1040 kg of crew, oil, coolant and ammunition (is that reasonable?) and thus about 2600 kg of fuel. This is more than the 2900 litres (approximately 2088 kg) quoted by a poster on the original forum but extra tanks could be fitted in the Ju-88 bomb bay. A brief glance at the internet finds ranges of 1,696miles (2,730km) or 1,429 miles (2,430 km) down to 1100 miles for the Ju-88A4. The Ju-88A5 might go further at 14000 kg because the A4 carried significantly more armour but might have less efficient engines.

    So my question for the experts is can we imagine 50 Ju 88s taking off at dawn from France with 16 carrying 500 kg of bombs and the others equipped as tankers (2 spare). After perhaps 2 hours, first the tankers pair up and one tanker is refilled to max, then the less full tankers each top up a bomber and head for home. Somewhere near Rockall, the remaining tankers top up the bombers and leave. Then can a Ju-88A5 make an attack and get home without running out of fuel?
     
  2. HoHun

    HoHun Active Member

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  3. delcyros

    delcyros Well-Known Member

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    It´s probably easier to upgrade the existing external hardpoints of Do-18 long range maritime patrol craft to ETC 504 standarts so that they can drop 2x SC250 instead of 2x 50Kg. They have the range necessary for said operations and are aviable in quantity.
    The BV-138 could deliver four 150kg depth charges so it likely could deliver 500 kg bombs as well if adaequate hardpoints are provided.
     
  4. davebender

    davebender Well-Known Member

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    Junkers Ju 90 - Wikipedia, the free encyclopedia
    I think Germany would be further ahead to put the Ju-90 / Ju-290 long range patrol bomber into mass production beginning in 1938. Some of the Ju-290 variants could remain airborne for 18 hours.
     
  5. cherry blossom

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    Thank you for the very helpful information! Thus we know that a Ju-88A4 (and probably an A5) can carry 3580 litres of fuel in internal tanks (although none of the loadings seem to fill all the tanks) and that the crew, oil and ammunition weights 1155 kg (would a longer mission require additional oil?). The heaviest loading given is 13,660 kg and it seems that German fuel is very slightly denser than the 0.72 sp. gravity of avgas at 15 degrees.

    The information from Micdrow adds ranges of 3100 km for the A4 and 4200 km for the A5 with different bombloads. Can a Ju-88A5 really carry 1000 kg of bombs over 4200 km? That seems much further than I expected. Does anyone know the cruising speed of an A5 and what is the Jumo 211B's economical fuel consumption?

    ps. We could assume that the refuelling probe could be discarded after the last refuel if it adds too much weight or drag. It should not cost much more than a bomb.
     
  6. Watanbe

    Watanbe Member

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    I would imagine also that the FAA would put up a protest to JU-88 openly attacking convoys.
     
  7. HoHun

    HoHun Active Member

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  8. cherry blossom

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    My understanding was that the Ju-90 was underpowered until the BMW 801 became available.

    The BV 138A1 was used for operations from October 1940 but was found to need structural strengthening. The production of the Do-18 ended in 1940 after about 100 aircraft. I suspect that neither actually had the range to attack North Atlantic convoys.

    The FAA probably also objected to the attacks by Fw 200 Condors. Only 26 of those were produced during 1940 and as they were not designed as bombers, there were many problems with the structure. Thus generally only 6-8 aircraft were available for operations. However, Condors may have sunk 85 ships of 363,000 tons between 1st August 1940 and 9th February 1941 and in addition they damaged other ships which were sunk by U-boats. An example is the 42,000 ton Empress of Britain which was attacked only 70 miles off the coast of Northern Ireland. The RAF also objected and at least one Condor was shot down North of Ireland. However, after reading of this attack, I now assume that attacks do not need to be North and West of Rockall. Thus I am going to calculate distances to Rockall.

    My thanks again to Hohun. The data on the Ju-88A1 convinces me that attacks on convoys near Rockall would be possible if Ju-88 could have refuelled in the air. Rockall is roughly 1400 km from France or Norway along curves that avoid Cornwall and the Sheltland Islands. If the aircraft fly at 4000 m and the second refuelling is planned 315 km short of Rockall, the bomber needs about 1700 litres to get home if the refuelling fails (1085 distance at 330 km/h with 345 l/h fuel use plus an hours flying plus effects of wind and the bigger wing of an A5). After fuelling, the bomber needs 375 litres to reach Rockall, 375 litres to search for an hour, perhaps 350 litres to attack and climb back to 4000 m and then 2045 litres to go home as before. The total is 3145 litres which is less than the max internal fuel of 3580 litres (but I should add something for the A5 wing). The tanker for the second refuelling seems to be able to carry enough to fuel the bomber. It may even be possible to fly the mission with a single refuelling. There is one special helpful feature as an aircraft could fly to either France or Norway if the wind was very strong.

    The point of the what if is that Germany produced over 2,000 Ju-88s during 1940 and they are likely to be more effective than Condors against ships.

    ps. If the Ju-88A5s have shrouded exhausts, they can fly home by the shortest route after dark. However, fuel consuption will rise as we lose exhaust thrust. I assume those effects balance.
     
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