Date: Tue, 13 Jun 1995 10:03:17 +0300 (EET DST) From: Lahtinen Antti Jussi Subject: FFS Helicopter Design FFS Helicopter Design A while ago I wrote about the difficulties of re-crating modern helicopters with FFS design rules. Because the rules would not work correctly, I did some literature research about real-life helicopter design, and found the mathematical model of power consumption in hovering and flight. Complete helicopter model is very complex, and while it gives quite accurate power consumption values for various airspeed, weight, and drag combinations, it is too massive to be used with FFS design rules. However, the model can be used to pinpoint some errors in FFS. Design Strategy Helicopters can be designed using either aircraft of lift vehicle rules. Both rules give quite similar end results, but lift vehicles can be designed with armor. Note that page 22: Lift Vehicle Chassis Configuration table and page 30 Airframe table have similar values (only examined from different perspectives) and all Airframes can be used as Lift Vehicle Chassis. Airframes not listed in Lift Vehicle Chassis table Type Volume SA Price Min Max Eff Autogyro 0.005 70 1.02 40 200 0.65 Wing-in-Ground 0.05 70 1.02 75 400 0.90 (These airframes are not suitable for helicopters, but I use these values when I design PARWIG vehicles.) Rotors FFS, page 32: Rotor Assemblies lift values are too low. I could model only MTR and NOTAR rotors, and lift values for other rotor types can only be estimated. Type Lift (ton/MW) MTR 8 NOTAR 8.4 TMR 10 ? CMR 10 ? X-Wing 10 ? I could not find enough data to check the actual weights of different rotor assemblies, so I use the values from the Rotor Assemblies table, but substituting: Wt: Weight in tons, per _MW output_ of power plant. Volume in m3 is equal to the weight of rotor. (This is the actual volume of the rotor assembly. Note that parked helicopter may still take large amount of hangar space, because the rotor blades can be quite long.) Power Plants Power plant can be either Improved Internal Combustion Engine (piston engine) or Gas Turbine. Almost all modern helicopters use gas turbines ("turboshaft"), and piston engines are mainly used in radio controlled drones. One possible helicopter power plant is rotor tip-drive, that means tip-mounted pulsejets (AZHRAE) or ramjets. Pulsejets are used mainly in target-drones, and ramjets are used in TJ-5 and NHI Kolibrie helicopters. I am still unable to find enough design data for rotor tip-drive engines. FFS, page 63: Chemical Power Plants table shows quite poor values for gas turbines. The following values are taken from Pratt & Whitney PT6 -series turboprops and turboshafts, and the values are for the whole engine installation (including gas generator, free power turbine, reduction gearbox and drive shaft). TL MW Mass kl/hour Name 6 1.9 0.5 0.39 PT6A-6 7 3.4 0.7 0.345 PT6A-42 8 4.9 0.9 0.3 PT6A-68 9 6.4 1.1 0.255 Estimated future model 10 7.9 1.3 0.21 Estimated future model Note: values are for 1 cubic meter of engine. Original engine volumes (Min Vol ?) were about 0.22 m3. TL 8+ values are estimates based on PT6 technical evolution curves. Gas turbine is more suitable helicopter power plant than MHD generator, because gas turbine produces mechanical energy and MHD generator produces electrical energy. Magnetohydrodynamic generation of power is based on the direct conversion of fuel energy into electrical energy by flowing a heated, electrical conductive fluid or gas through a magnetic field. To achieve this, fuel is often doped with impurities, so that exhaust gas is electrically conductive, and this exhaust gas is piped through magnetic field. The impurities in fuel often make the exhaust gas highly toxic. Note: the MHD _turbine_ described in text in page 63 is completely unknown to me. As far as I know, the modern MHD power generators are not based on turbine technology. Sources: Jukka Raunio; Helikopteriteoria. Published by Finnish Border Guard Department, 1989. R.W. Prouty; Helicopter Aerodynamics. PJS Publications Inc. USA, 1985. Journal of Engineering for Gas Turbines and Power; The PT6 Engine: 30 Years of Gas Turbine Technology Evolution. Transactions of the ASME, APRIL 1994, Vol. 116. -- Antti Lahtinen : Justice is Only a Wish of a Weak al76188@cs.tut.fi :