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Guest Douglas K

Boosting speed on a turboprop single

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I am trying to get my plane up to 312 KIAS, but having some problems. If I have alot of torque, my plane bolts away with full brakes on, but with taxi-able horsepower, my plane will only do 245 KIAS approximately.Does anyone have any ideas? I have had the best luck with using the Beech Kingair 350 airfile template, going to a single engine. The Cessna Caravan file's front gear doesnt work and has several problems for some reason, or I would be using it. (My design has retractables where the 208 caravan does not, and the seaplane wont retract the nose gear). My plane is basically a Meridian layout, but with a cleaner aerodynamic fuselage and a bigger prop and liter composite construction techniques.I would be very thankful for some input. I have tried the hit and miss routine and she either taxi's at 90 knots or does 240 knots top out.Sincerely,Bill

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One way to increase speed without increasing power is to reduce te "parasite_drag_scalar" variable in the aircraft.cfg file. I can't remember if there is a corresponding variable in the .air file, but if there is then you should change it too.Try setting it to .80 or so, and check the difference in speed. Also, the amount of fuel onboard will have an effect, depending on the amount of fuel and the size of the aircraft....just an idea.- Martin

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At what altitude do you want to attain 312 knots indicated?Are you talking about a maximum speed of 312 or is this a max cruise speed you're going for?These are the true airspeed numbers I'm seeing with your aircraft:201 KTAS at S.L.248 KTAS at 5000 MSL268 KTAS at 15000 MSL292 KTAS at 25000 MSL320 KTAS at 35000 MSLThese airspeeds were attained with the CFG file dated 5/25/03 that was modified for the MOI and landing gear ext/ret sound fixes only.By contrast, I see the Piper Meridian runs along at around 267 KTAS at 29000 MSL, so your aircraft as is has a huge speed advantage over it's "competition"!!!For comparison, here are the real Piper Meridian's max cruise performance numbers along with your A/C:Piper Meridian ALT= 29000 MSLTq= 1200 FT/LBSItt= 710 deg CNg= 95%Np= 2000 RPMFF= 258 PPHTat= -43 deg CIAS= 170 KTSTAS= 267 KTSPrototype Pilatus VisageALT= 29000 MSLTQ= 80% -- (approximately 2520 FT/LBS= 835 ESHP as recorded by AFSD)ITT= 650 deg CNg= 90%Np= 1650 RPM (flight Sim Control Minimum Position)FF= 293 PPHTAT= -43 deg CIAS= 194 TASTAS= 304 TASYour A/C comes out on top in cruise performance by a wide margin of 37 KTAS.It does use significantly more horsepower to accomplish this, over 800 ESHP (equivalent shaft horsepower(ESHP)is the combination of thrust and SHP) compared to the Meridian which is probably using something like 370 ESHP at this altitude. this is not something that I would be too concened about however, unless you are a fanatic about realism - you won't be able to tell the difference between 370 and 835 EHSP while flying the A/C in the sim as long as the engine readings are close to the real thing (and yours are) - plus, you would have to start from scratch with Cdo and propellor thrust etc. if you were to decrease the power to 370.You may want to increase the ITT to around 710 deg C, as 650 is too low for an altitude of 29000 ft.Look in the airfile under REC 1526 *Turbine ITT and adjust the ITT Scale Factor upwards slightly.A value here of 1.06 will result in an ITT of 709 deg C, and that's close enough!Likewise the fuel flow needs adjusting to match the lower figure of the Meridian, so opening the CFG file I changed the fuel_flow_scalar in the General Engine Data section to this - 0.35 - and got 257 PPH at 29000 ft, 80% Tq and 1650 Np. If you still want more speed from your creation, then you can do as Martin has suggested, and reduce the drag scalars found in the flight_tuning section of the CFG file as they are still set to 1.0 and by reducing these (parasite or induced drag scalars or both) you will definitely see an increase in airspeed.

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