What if: Prop de Havilland Vampire

Discussion in 'Aviation' started by wuzak, Jul 16, 2012.

  1. wuzak

    wuzak Well-Known Member

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    Could it have been done?

    de Havilland Vampire FB6 (from Wiki)
    General characteristics
    Crew: 1
    Length: 30 ft 9 in (9.37 m)
    Wingspan: 38 ft (11.58 m)
    Height: 8 ft 10 in (2.69 m)
    Wing area: 262 ft² (24.34 m²)
    Empty weight: 7,283 lb (3,304 kg)
    Max. takeoff weight: 12,390 lb [44] (5,620 kg)
    Powerplant: 1 × de Havilland Goblin 3 centrifugal turbojet, 3,350 lbf (14.90 kN)

    Performance
    Maximum speed: 548 mph (882 km/h)
    Range: 1,220 mi (1,960 km)
    Service ceiling: 42,800 ft (13,045 m)
    Rate of climb: 4,800 ft/min[44] (24.4 m/s)

    Armament

    Guns: 4 × 20 mm (0.79 in) Hispano Mk.V cannon
    Rockets: 8 × 3-inch "60 lb" rockets
    Bombs: or 2 × 500 lb (225 kg) bombs or two drop-tanks


    Now, with my basic calcs the speed and thrust equate to a power of around 1900hp.

    Using a prop efficiency of 75% means a prop version would need of the order of 2500hp to get the same performance.

    The de Havilland Goblin was 50" in diameter and 107" long. Rear part of the nacelle would need some re-profiling.

    A Napier Sabre should fit in the hole vacated by the Goblin. The tail pipe would be replaced by an extension shaft, gearbox and pusher prop. The radiators would go in the inner wing in place of the jet intake. An adjustable outlet above or below the centre wing could be made for the radiator ducts. Maybe an exhaust pipe could be routed to assist in extracting the cooling air from the radiators.

    The installed weight of the Sabre is going to be about twice that of the Goblin - which will reduce performance. Altitude performance would also suffer with the Sabre as it is only a single stage engine.

    Alternatively a pari of B-series turbos could have been mounted in the inner wing - not sure how big they are compared to the wing section. This adds another 400-500lbs, at least, to the installation, further degrading performance.

    Late 1943 a Sabre should be good for 2400hp?

    The biggest issue I see is that the landing gear on the Vampire was incredibly short. To get a decent sized prop would require lengthening the landing gear, or having a much higher thrust line.

    Other issues would be the interference of the airflow around the prop and the booms, and how the airflow across the wings and nacelle effect he operation of the prop. The XB-35 and B-36 both experienced vibrations in the props due to the airflow off the wings, the former more so becuase the thrust line was further away (height wise) from the trailing edge. The XP-56 was predicted to do above 460mph but tests showed top speeds below 400mph - one of the reasosn thought to be the shape of the fuselage causing turbulence ahead of the prop and causing a drop in prop efficiency.

    So, what say you? Possible?
     
  2. Airframes

    Airframes Benevolens Magister

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  3. Shortround6

    Shortround6 Well-Known Member

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    At least twice, What is weigh of the radiators and coolant?
    What is the weight of the prop?

    I think you have some CG issues to start with?

    How big was the Prop on a Tempest? 14 feet?

    Mighty big landing gear.


    Vultee_XP-54_Swoose_Goose_11210.jpg

    How far apart were the booms on the Vampire?

    Me thinks you had best switch brands of plonk, sport. :)
     
  4. krieghund

    krieghund Member

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    The issue is the prop efficiency above 450 mph is dropping way off and the only way to avoid that is a contra propfan arrangement as in the Antonov AN-70T new build.


    STUFF THE A400M!!!
     
  5. davebender

    davebender Well-Known Member

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    Sounds like RR Griffon engines to me as they already have a version.
     
  6. nuuumannn

    nuuumannn Well-Known Member

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    There were several different British companies that used this layout for different fighter and bomber projects, including Airspeed, Boulton Paul, Vickers and Westland, but, as Terry said; why? DH would gain nothing from doing so since the Spidercrab/Vampire was designed to take advantage of Halford's engine.
     
  7. basil

    basil New Member

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    Wuzak, the Sud-Ouest SO 8000 Narval is not dissimilar to your idea. It had a 2.250 hp (Jumo 213) engine and a reported top speed of 455 mph.
     
  8. wuzak

    wuzak Well-Known Member

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    Similar size too. Although a lot heavier than the Vampire (as would be the Sabre-Vampire).
     
  9. Shortround6

    Shortround6 Well-Known Member

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    One website says the predicted performance was never reached in test flying.
     
  10. wuzak

    wuzak Well-Known Member

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    A quick scale of 3 views shows the prop of the Narval to be approximately 2.6m in diameter, and the distance between the booms on the Vampire 2.5m apart....

    So it would need really small props.
     
  11. wuzak

    wuzak Well-Known Member

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    The Trent Meteor's props were 2.41m diameter to start with, 1.49m props being the smallest tested.

    I guess for the power they would need to be run at higher rpm.
     
  12. Timppa

    Timppa Active Member

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    Power = Speed*Thrust
    882 km/h = 245 m/s
    245*14.9 = 3650.5 kW = 4895 hp.
    Using your efficiency we'd need about 6500+ hp.
     
  13. wuzak

    wuzak Well-Known Member

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    Oops.

    Seems I missed a step in calculating the power.

    You are, of course, correct.
     
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