Wing wake visualization
Back in 2009 I had a play with a wing wake visualiser - stuck it on the TE of one of the Mk 9 (carbon) F1As and did a few test glides for the camera.
The visualiser is very simple - its a 70 mm vertical rake made of 0.8mm ply attached to an inverted T of the same 0.8mm ply with an 8BA nylon bolt. The T is taped to the top of the wing TE with masking tape. The 8BA bolt lets the vertical piece swing back on landing instead of breaking. I glued three pieces of Mylar thermal streamer onto the vertical rake with SprayMount, cut so they extend about 20 mm past the stabiliser's LE. I fitted the rake just outboard of the stab tip.
There was a pretty calm day at the end of October, so I took it up to GRL and did a few test glides with a volunteer photographer using my Pentax K100D set to continuous fire and max zoom. The day wasn't really calm enough - around 3 m/s and surprisingly turbulent considering how flat the area is. This was the first time the model had been out of its box for 5 years and it was still on trim! However, the slight turbulence and my lack of practice meant I didn't get any steady state glides, but a couple of the shots are interesting. It proved very hard to keep the pipper on the model, so the focus isn't wonderful: auto-focus was active and re-focussed for each shot.
In this shot there was enough breeze and turbulence to make accurate hand launches very difficult. The model is mushing just before a gentle stall. I never dreamed the flow past the wing went right up there without a big nose drop. In fact the model was cross-wind at that point, so it was slipping as well. It just pitched down to about 10 degrees nose down, recovered gliding speed and glided in to a smooth landing.
This shows normal glide. The upward deflection of the streamers above the stab leading edge shows its generating lift, but the interesting thing here is just how far in front of the stab the flow is affected by its presence. I don't think this is quite steady state either: in the past I've seen these models gliding close by in flat calm conditions and noticed that they glide noticably nose up instead of the slight nose down attitude in this picture.