>Spitfire Mk IIA Ah - surprising!
Here is an email Rick "Fuelcock" sent me a short while ago. I hope it helps. Sorry for the poor formating. ------------------- snip --------------------- Rather than send you the GBE code , I will direct you to the site where I got it: http://www.aeromech.usyd.edu.au/aero/propeller/prop1.html Just click on program 1 at the bottom of the page. Program 2 (right below) is mathlab code for the implementation without the bells and whistles. I have been playing around with program 1, and have obtained very encouraging results. I keyed in a "Spitfire" prop with radius 1.55 m and a blade area of 0.98m^3. The program only let's you design a simple blade with a straight, symetrical taper. Rather than complicate things, I just kept the cord constant at .210 the radius to give a total area of .327m^3 per blade. Not knowing anything for sure about the blade angle at a given radius, I just used the default pitch of 0.5, where: pitch = 2pi * r tan theta and theta is the geometric angle of the blade at r. The model also lets you tilt the whole blade +/- any desired angle setting. Assuming the max speed of the Spitfire to be 154.7 m/s, I toyed with angle setting until I obtained a max prop efficiency at angle setting 19.45, J value of 2.09, which corresponds to a true airspeed of 154.7 m/sec for a 1.55 m radius prop, engine running at 3000 rpm and gear ratio 0.477. The model produced a theoretical efficiency of about 85%, with Cq = 0.071. Next, I calculated the torque, using the formula Q=Cq * rho * n^2 * D^4, where n is prop rotation in revolutions per second ( the code converts this to radians) and D is prop diameter. I assumed rho of 0.5 Kg/m^3, an altitude of about 15,000 feet. I than multiplied the torque by angular velocity in radians per second, to get the power (watts) needed to counteract the torque of the prop. This worked out to 865 KW, which converts to 1159 HP. This is about 10% hiigher than what the Merlin could actually put out at the shaft, but it's pretty damn good. Remember, the model is known to be about 5% to 10% too optimistic in predicting performance, so if you take this into account, the prediction is nearly spot on! ------------------- snip --------------------- >Regards > >Vivian Bye bye, Wolfram. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
