{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fswiss\fcharset0 Arial;}} {\*\generator Msftedit 5.41.15.1507;}\viewkind4\uc1\pard\f0\fs20 Rotax 914 cooling and cowling ruminations\par \par Maximum power output (Rotax OM) 84.5 kW\par Consumption at maximum power (Rotax OM) 33 l/h, i.e. 9.17 ml/s.\par Gasoline represents 35 kJ of energy per ml.\par Power consumption is therefore 9.17 x 35 = 321 kW\par Efficiency is 26.3%.\par \par Maximum cruise power output (Rotax OM) 73.5 kW\par Consumption at maximum cruise power (Rotax OM) is 27.2 l/h, i.e. 7.56 ml/s.\par Power consumption is 264 kW\par Efficiency is 27.8%.\par \par 75% cruise power output (Rotax OM) 55.1 kW\par Consumption at 75% cruise power (Rotax OM) is 20.4 l/h, i.e. 5.67 ml/s.\par Power consumption is 198 kW\par Efficiency is 27.8%.\par \par Combustion is probably a few percent from complete in all cases \par At maximum power a few percent more (enrichment solenoid). \par Probably at least some 10 to 15 potential kW are not produced at maximum power\par Total heat production to be removed is then estimated at 321 - 84.5 - 12.5 = 223 kW.\par \par Rotax heat removal prescription for maximum power operation (84.5 kW)\par Remove 45 kW as follows:\par 30 kW through cooling radiator\par 9 kW through oil radiator\par 6 kW from cylinder barrel fins\par \par Under the cowling.\par As the engine and exhaust system heat up they radiate more heat.\par Stefan-Boltzmann says: about 5 / 10^11 x T^4 kW/m^2, T in Kelvin.\par A little table - T in Kelvin ('F) and corresponding radiation flux in kW/m^2 - :\par 300 (80'F) 0.4\par 400 (260'F) 1.3\par 500 (440'F) 3.1\par 600 (620'F) 6.5\par 700 (800'F) 12.0\par 800 (980'F) 20.5\par 900 (1160'F) 32.8\par 1000 (1340'F) 50.0\par 1100 (1520'F) 73.2\par 1200 (1700'F) 103.7\par \par Estimate of 1000K area (4 primary exhaust pipes): 0.10 m2\par Radiated heat: 5.0 kW\par Estimate of 800K area (muffler, turbo): 0.15 m2\par Radiated heat: 3.0 kW\par Assume the under cowling air temperature held at 500K\par Counterflux from environment: 0.25 x 3.1 = 0.8 kW\par Net heat flow estimate: 5.0 + 3.0 - 0.5 = 7.2 kW\par The final number is very sensitive to temperature and size of the hottest areas.\par \par Say another 7 kW to be removed from under the cowling.\par Total now 45 + 7 = 52 kW.\par The remaining 171 kW or so then leaves with the exhaust gasses.\par More than half - and a good thing too, but what a waste.\par \par Tony Bingelis rule of thumb:\par For an aircooled engine provide 0.35 square inches of air inlet per rated engine HP.\par That is 2.25 cm^2 per kW.\par Assuming similar cooling requirements for the Rotax 914;\par also assuming similar efficiency for direct and indirect - via liquid - air cooling:\par Total inlet area for Rotax: 84.5 x 2.25 = 190 cm^2 (diameter 15.6 cm)\par Of which:\par cooling radiator 30/52 x 190 = 109.6 cm^2 (diameter 11.8 cm, or 5.5 cm x 20 cm, or 4.3 cm x 25 cm)\par oil radiator 9/52 x 190 = 32.9 cm^2 (diameter 6.5 cm, or 1.6 cm x 20 cm, or 1.3 cm x 25 cm)\par cylinder barrel fins 6/52 x 190 = 21.9 cm^2 (diameter 5.3 cm)\par rest of cowling 7/52 x 190 = 25.6 cm^2 (diameter 5.7 cm)\par \par And the air outlet to be "larger" than the inlet.\par \par Exhaust augmenter as described by Frans Veldman.\par Diameter 8 cm, area 50.3 cm2\par Exhaust diameter is 4 cm. area 20.4 cm2\par Leaves a 29.9 cm2 (equivalent diameter 6.2 cm) cowling air outlet size\par With forced extraction action\par \par Cooling design attempt. To be updated with new insights.\par \par 1. cowling heat removal 6 + 7 = 13 kW\par 1.1. cowling hermetically sealed except for intended openings\par 1.2. inlets\par 1.2.1. 5.3 cm front hole and Rotax 1 to 4 guide to cylinder barrels *)\par 1.2.2. air filter plenum circular leak around airfilter to turbo minimal *)\par 1.2.3. propeller shaft circular leak minimal or remove *)\par 1.2.4. 5 cm front hole general purpose *)\par 1.3. outlets\par 1.3.1. exhaust augmenter port side\par 1.3.2. bottom cowl flap starboard side, possibly open mostly for max climb *)\par \par 2. central liquid cooling radiator duct 30 kW\par 2.a. inlet 4.3 cm x 25 cm\par 2.b. bottom outlet flap max opening 8 cm x 25 cm (flap 32 cm long)\par 2.c. hermetically sealing \par 2.d. flap with thermostat say 70 - 100 'C, manual emergency override\par \par 3. oil cooler on port footwell (Rotax allows if mounted connections up) 9 kW\par 3.a. front hole 6 cm\par 3.b. port side outlet flap max opening 6 cm x 6 cm (flap 24 cm long)\par 3.c. hermetically sealing \par 3.d. flap with thermostat say 100 - 110 'C, manual emergency override\par \par 4. engine electrics box on starboard footwell < 0.5 kW\par 4.a. hermetically sealed\par 4.b. inlet air plenum roof riser 1 cm x 15 cm (oil cooler to port side)\par 4.c. outlet starboard gills\par 4.d. to contain:\par 4.d.1. TCU\par 4.d.2. wastegate servo (single plane cable bend desired)\par 4.d.3. regulator\par 4.d.4. capacitor\par 4.d.5. engine sensors box\par 4.d.6. any relays and fuses and ...\par \par 5. intercooler, decide later, make agree with 4\par - must remove about 1 kW per 10 'C of cooling effect\par - a lot for low delta-T air-to-air and iffy airflow\par - I wonder at effectiveness\par \par ( 9.17 ml gasoline per second with mass 6.5 g\par requires about 100 g of air per second (for AFR 15)\par with volume about 70 l at sea level pressure (close enough)\par volumetric heat capacity of air 1.3 J/l per K (close enough)\par we require 100 J/s per K or 1 kW per 10 K\par )\par \par *) not so sure\par \par \par }