Help! You guys are ganging up.
tgrendl
>Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?
I have a feeling that this region may be a "try it and see" area in your testing.<
Your "try it and see" appears to be the answer of the professional designers, as well. All the books seem to mention that the mathematical and the testing methodologies can produce fairly different results. Mind you, some of these books are a few months (years) old and things sure change fast.
There appears to be a strong consensus that streamlining the rotor hubs and associated control linkages is very beneficial in reducing drag. One book mentioned the additional advantages of locating the hub close to the fuselage, then streamlining them together.
Here again, Nick is probably at the cutting edge.
__________________
Kyrilian
You've covered a lot of territory. So here goes a weak attempt at a rebuttal.
Thrust:
There are virtually no calculations available on the intermeshing. Much of the work must therefore be 'guestimates'. The side-by-side configuration is the optimum for thrust. In fact, it has been reported that an adjacent side-by-side give more than twice the thrust of its individual halves. The synchropter will come somewhere between the side-by-side and the coaxial. Hopefully, my sketch to Nick shows that the intermeshing is significantly better than the coaxial.
It might also be noted that in the early forties weight to thrust was very critical and yet Sikorsky and Flettner were able to produce comparable helicopters, with the Flettner being the alleged faster of the two. The image of the Kaman synchropters must be put aside.
>Adding another rotor will increase profile power (more blade area being spun through the air),<
If the two sets of blades are identical then the profile power of a 4-blade single rotor and that of twin 2-blade rotors should be very close.
>from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions.<
I have spoken to the Canadian pilot of a Russian coaxial, which is used for logging. The helicopter uses differential collective for yaw and he makes any minor trim adjustments that are required before taking off. He said that the helicopter was quite responsive and that there was automatic pedal reversal in the event of an autorotation.
I understand that the K-Max has an extended empennage to provide better control that that of the Huskies, and they uses differential longitudinal cyclic in addition to the differential collective. Of course, the pilots of the Huskie can provide the best answers.
It may be of interest to know that the Flettner intermeshing helicopter supplemented it rotor control with elevator and rudder control.
______________
Cyclic Hotline
Oops! Two failures.
Your comments on the drive train and yaw control aren't too good.
Mine you, this is offset by your jokes, which aren't too bad.
[ 28 August 2001: Message edited by: Dave Jackson ]