Originally Posted by
SansAnhedral
My suspicions seem confirmed as based upon your response and the linked whitepapers (many of which I already have copies!) it appears you are teasing the creative implementation of gurney flaps with segmented span and/or minor angle and profile variation.
I presume this technology and its specifics have not been patented, hence the coyness
actually, close, but no change to profile or angles, and segmentation in the real world was not effective, it actually reduced the effect of an LET, the studies had always considered LET segmentation in the light of a non-rotating section. Segmentation was indeed slightly better on a TE of a flap section on a wing, it actually degraded performance on both propellers and rotors. Was an interesting test, had a bet each way on what it would do.
The trick on a rotor or a propeller is pretty much how to add a device and not frag the prop or rotor straight away, you are effectively adding rigidity to the area that has high torsion and bending loads that are cyclical, and so the blade, bond or device are in a compromised state to begin with. Years ago, NASA proposed some segmented devices to get around that problem, my testing showed segmentation was a disaster to the performance outcome. So, yeah, the aero is not what it seems when you do CFD for a non-rotating element, and the mechanics of doing it need some lateral thinking.
The propeller was interesting to do, but it was also educational. The rotor added some risk issues to be considered, changing a part span section CL by 0.4 makes autorotational effects a topic of interest. There was a single engineering note that suggested auto wouldn't end badly, but it was still not a fun first trial. The engineering note was based on a CFD code that I had reservations on, and could have gone either way. The first-ever entry was done from a good speed above ETL so if the driving zone of the rotor was adversely affected, at least a cyclic loading could restore some Nr while trying to add power. In the end, there was a rise in Nr which was gratefully received. I went as far as doing failure tests on the rotor in the hover, having done fully asymmetric setups and having a slight vibration increase and change in tracking. the failure in hover took 6 flights to make it fail, each flight introducing more damage until it came off a blade in the hover. Had rugged up with extra Nomex for that one. in the end it was a non-event, and was observed coming off the rotor and passing off to the side clear of the other blade path, and well clear of the TR.
The aero was fun, the structural issues were interesting, the hardest thing was dealing with water droplet impact. Nothing much is more damaging to a surface that a high velocity, >100m/sec impact. That, and the manufacturing processes is the bit of sensitivity, Some of this I have patented, but the high-value issues are the certification and materials. Particularly trying to add something to a fan blade. The g load giving a shear on the attachment on a rotor is around 3-500g. for a propeller, its around 3,000g. for a fan, a GE90, is around 7500g, 15000g for a CFM56, and 35,000g for a TFR731, 60,000g for a JT15D-1. Even then, that is relatively bland compared to the problem of liquid droplet impact. There was a good lab in Amsterdam, best around, one in Russia, and the least effective was in the USA.