Post by Britbrat on Feb 7, 2005 9:03:54 GMT -7
This past weekend was great for snow flying, being relatively warm, with blue skies, light winds -- etc. I took two planes to our aircraft-carrier style airfield -- a trusty & well behaved Seamaster ARF --- and a brutal little snow-plane SPAD called a Ski-master. The Ski-master is the most difficult model that I've flown since the days of escapement 2-channel RC. It is a stubby flying-boat styled coro SPAD, with a pylon-mounted engine, a T-tail & outrigger skiis on the underside of the wingtips (looks like a very compressed Seamaster). At 36" length & 48"span, it is quite short coupled, plus the heavy MECOA .46 on the pylon puts the center of mass well above the non-dihedral wing (& the aerodynamic center). It is fast (~75 mph), very unstable in pitch & roll, & moderately stable in yaw, although the rudder is nearly useless -- except for inducing adverse roll. With its high center of mass, if allowed to stall, it promptly rolls inverted, so landings must be fast (it "glides" like a brick). The top-heaviness also makes it want to roll over in "normal" flight & to behave in pitch as if it is tail heavy (it isn't). To top it all off, it is made of white coro -- a great choice for a ski-plane.
In the course of the day, there were numerous uneventfull flights with the Seamaster & several exciting survivals with the Ski-master.
Then came one last flight --- with the brat.
For some reason the MECOA was suddenly difficult to keep running, & pre-flight set-up took a lot of time messing with the mixture before it would stay lit. By the time I took off, the daylight had started to fade & a light haze was settling in.
The take-off was wildly exciting -- she hit a hole in the snow, bounced straight up, then promptly rolled inverted. A very wobbly inverted climb-out made for a heart-pounding save & the beginning of a wild flight. It was immediately evident that the haze & the plane were the same colour, as was the snowy background, and in the poor light the red patches on the upper surface of the wing were too similar to the red ski-tips on the underside. There were several minutes of violent aerobratics (AEROBRATICS: highly entertaining departures from controlled flight), as I couldn't tell top from bottom, or ground from sky, & the little brat did its own thing, with occasional forays into controlled flight.
In one of the brief controlled-flight moments, I managed an inverted low pass at ~ 2' & decided to quit while my heart was still beating. I turned out over the quarry to set up for a landing & the engine quit cold. I was immediately faced with a no-win situation -- it probably couldn't make the field & stretching the glide would result in a stall, while a blind decent into the quarry with that unstable little plane would certainly end in a crash. I made a diving turn for the field & tried to baloon up over the edge of the quarry, whereupon it promptly stalled, rolled over & disappeared straight down into the depths.
Despite knowng exactly where it went, we searched for half an hour before virtually stumbling upon it. It had lawn-darted into the snow on the slope of the quarry & only the white tail-feathers were above the surface. There was no damage.
Post-mortem revealed that the engine had failed from fuel exhaustion, despite the flight being quite short. It was further discovered that the needle-valve assembly was loose in the carb & leaking fuel. The prolonged engine tuning time (no-doubt caused by the leaking nv), plus the in-flight leak had quickly depleted the fuel supply.
Lessons:
If the tuning suddenly changes -- something is causing it -- find & fix it before flying.
Don't fly in poor visibility, which can also mean the blending of the plane into the background, rather than darkness or heavy mist. Had I flown the colourfull Seamaster, visibility would not have been a problem.
Ensure that your plane is suitably coloured & marked to facilitate both visibility and orientation recognition.
Don't be sucked into "one last flight" -- Go home while everything is still in one piece.
In the course of the day, there were numerous uneventfull flights with the Seamaster & several exciting survivals with the Ski-master.
Then came one last flight --- with the brat.
For some reason the MECOA was suddenly difficult to keep running, & pre-flight set-up took a lot of time messing with the mixture before it would stay lit. By the time I took off, the daylight had started to fade & a light haze was settling in.
The take-off was wildly exciting -- she hit a hole in the snow, bounced straight up, then promptly rolled inverted. A very wobbly inverted climb-out made for a heart-pounding save & the beginning of a wild flight. It was immediately evident that the haze & the plane were the same colour, as was the snowy background, and in the poor light the red patches on the upper surface of the wing were too similar to the red ski-tips on the underside. There were several minutes of violent aerobratics (AEROBRATICS: highly entertaining departures from controlled flight), as I couldn't tell top from bottom, or ground from sky, & the little brat did its own thing, with occasional forays into controlled flight.
In one of the brief controlled-flight moments, I managed an inverted low pass at ~ 2' & decided to quit while my heart was still beating. I turned out over the quarry to set up for a landing & the engine quit cold. I was immediately faced with a no-win situation -- it probably couldn't make the field & stretching the glide would result in a stall, while a blind decent into the quarry with that unstable little plane would certainly end in a crash. I made a diving turn for the field & tried to baloon up over the edge of the quarry, whereupon it promptly stalled, rolled over & disappeared straight down into the depths.
Despite knowng exactly where it went, we searched for half an hour before virtually stumbling upon it. It had lawn-darted into the snow on the slope of the quarry & only the white tail-feathers were above the surface. There was no damage.
Post-mortem revealed that the engine had failed from fuel exhaustion, despite the flight being quite short. It was further discovered that the needle-valve assembly was loose in the carb & leaking fuel. The prolonged engine tuning time (no-doubt caused by the leaking nv), plus the in-flight leak had quickly depleted the fuel supply.
Lessons:
If the tuning suddenly changes -- something is causing it -- find & fix it before flying.
Don't fly in poor visibility, which can also mean the blending of the plane into the background, rather than darkness or heavy mist. Had I flown the colourfull Seamaster, visibility would not have been a problem.
Ensure that your plane is suitably coloured & marked to facilitate both visibility and orientation recognition.
Don't be sucked into "one last flight" -- Go home while everything is still in one piece.