Calculating aircraft performance

Discussion in 'Technical Requests' started by Pinin, Jul 11, 2016.

  1. Pinin

    Pinin Member

    Nov 2, 2014
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    EI have data of a Dornier Wal floatplane with BMW VI engine(x2) 600hp and would want to calculate it with Hispano Suiza Ydrs of 860hp

    This is the data for BMW VI version 600(650hp?)hp x2 Dry weight: 510 kg (1,124 lb) Displacement: 46.93 L (2,864 cu in)
    BMW VI - Wikipedia, the free encyclopedia

    Empty weight: 4000kg
    Crew: 510kg(6 crew)
    Lubrificant: 100kg
    Armament:2x2 Darne with 12 box ammo(200 rounds per box): ~100-150kg
    Various: ~200kg(radio, etc)
    All up weight around 6450 with bombs.

    Performance : 216 kph max speed, 176 kph cruise speed.
    Climb: 125m/min 16m09sec to 2000m, 42m 8sec to 5000m - this goes against the data that ceiling is only 4600m.
    Range 800km to 1300km

    With RR Eagle IX engines 355hp x2 Dry weight: 900 lb (408 kg) Fuel consumption: 24 gallons per hour (90 Litres per hour), Displacement: 1,239 in³ (20.32 L) Rolls-Royce Eagle - Wikipedia, the free encyclopedia

    Maximum speed: 185 km/h (115 mph; 100 kn)
    Cruising speed: 145 km/h (90 mph; 78 kn)
    Range: 800 km (497 mi; 432 nmi)
    Service ceiling: 3,500 m (11,483 ft)
    Rate of climb: 1.5 m/s (300 ft/min)
    Time to altitude: 3,000 m (9,843 ft) in 33 minutes

    Data for Hispano Suiza Ydrs Hispano-Suiza 12Y — Wikipédia
    860hp at 4000m, 460 kg Displacement: 36 Lit.

    It is clear aero is not the strong in this floatplane, and increase of 710hp to ~1200hp(69%) only improved speed 30kph(16%) so an increase in power from 1200 to 1920 of 60% should only give probably 20kph more: increasing drag will blunt even more the power increase that is even less proportionaly: 60% instead of 69%.

    If speed is relatively straightforward the rest is more complicated due to lack of data.
    With Hispanos a lighter engine than BMW's and more power it is clear that aircraft should be much more capable in climb and ceiling
    With BMW's the power loading is 0.186 hp per kg. With Hispano and same max weight(6450kg since the engines are even lighter there is even cargo capability* ) we have a 0.297hp/per kg.
    We can increase max weight up to 10300kg to return to same power loading of BMW tough this is not without penalty since in another hand the wing loading increases much.

    *It is probably to be expected that due to increase in power the fuel needs and lubricant oil increase with Hispano which in turn means bigger fuel and oil tanks. This would certainly offset the weight saving from 460kg engines instead of 510kg engines.

    Assuming same comsumption per horse power at 800km range with 1200hp we would have 500km range with 1920hp for same fuel quantity same proportional power settings - this would mean that 1100kg fuel would need to be 1760kg instead to achieve 800km. This is 660kg weight more in maximum weight. pushing the aircraft to around 7100kg
    which still doesn't deny the power loading Hispano advantage that we see is only achieved at 10300kg

    Of course this is pretty much fuzzy and worst case scenario since the BMW VI power and cruise is not known at what altitude it is, if it is at low level then the Hispano might be much more economical at 4000m altitude since drag resistance is minor instead of being equal per horse power like in this calculations.

    Any ideas and/or mistakes noticed?

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