The idea has been around for quite a while, and it definitely holds some great appeal, namely to construct a detailed computational model of the ArrowCopter. It had to be able to reproduce all aerodynamic properties of the aircraft and match up with our combined flight experiences in order for us to trust its predictive capabilities. Therefore we went the whole nine yards and contracted with a boutique outfit which is known in the industry for its state-of-the-art comoputational fluid dynamic particle-in-cell calculations.
We provided them with a complete 3D computer model of the ArrowCopter, down to 1 mm accuracy. The tiny gap between the canopy frame and its mating bevel is part of the model, as is the door latch. The only thing we left out is the tire thread.
The code itself is sophisticated enough to be able to take advantage of these details and calculate the airflow including all aerodynamic forces down to this incredibly detailed level. It includes turbulence and vortex shedding as well. Only two years ago this would not have been possible.
It took a weekend flat out running on some very powerful mainframe infrastructure to calculate the results. And the presentation of the results is contained in many pages of graphs and tables, which I am not going to go into here. I just wanted to share a couple of videos with you illustrating the airflow around the ArrowCopter in cruise flight at 150 km/h.
Some general things to notice are the different lift distribution on the advancing and retreating blades. The lift on the retreating blade is concentrated near the tip whereas the lift on the advancing blade is more distributed along its span.
Shedding of tip vortices is also clearly visible.
Also, notice the cork screw like prop wash which gets straightened out by the stabilizer. This goes a long way toward neutralizing engine torque effects.
Here is another one where you can see the tip plane angle and also the effect of the nose wheel.
It was interesting for us to learn that the rotor contributes 52% to the total drag. And about a quarter of the rotor drag comes from the rotor hub! To arrive at this result we modelled it down to each bolt head in shape and size.
More to come, -- Chris.
P.S.: How do people embed youtube videos in a post?
You have to realize that the ArrowCopter already is a very low drag gyrocopter. The absolute value for the frag force is, indeed, small. So the merit of changing the hub has to weighed against possible weight increase, ease of maintenance and rotor rigging, and the merit of changing any number of other things.
The really interesting point is that there now exisis the possibility to put an incredibly detailed computer model into a number crunching machine running a state-of-the-art CFD code and get all the answers you could previously only more or less ascertain by educated trial and error.
Very interesting advance Chris. It has probably been very satisfying for Dietmar to see how well his design has turned out with this new more accurate tool at your disposal. Also for us all to see how the company continues to be at the cutting edge of technology.