Bush strip today. 650m long. DA=3000' OAT 6 ....Piper nice and light today. Deep valley at the approach end, obstructions at the other end, top of windy hill. half of runway is 'uphill' at 5% ! rest is 1%....
all in the lee of a big mountain , lots of turb. but turb was OK once I slowed down in the vicinity, 90 kts 1st stage flap.
I calculated the hell out of it before setting out. rehearsed a few scenarios in my mind. final was into 15kts I guess wind .. Landed into the ~ 10kt wind, on the uphill section about one third off the way in. (on the steep bit) . no issue. Experienced high wind gradient as got into the flare and aircraft went below the top of the hill - experienced down draft as I got near the ground and also sudden 8 -10 kts ish loss of airspeed (as expected so I came in with 10kts to spare) . I had done a PSL immediately before on it so I had some idea what the wind was doing over the hill. complex.
nose down , jesus the end of the runway and obstruction is coming up brakes on ...... and taxi , hmm with 300m to spare, (used half the runway) . so that was good.
Went for a walk with my GPS and barometer to meausre height one end to the other...., measured strip length and surveyed the height and gradients and estimated tail wind speeds at different regions for takeoff downwind. Determined a 'decision point' .
....wind now 15kts minimum. on my tail.
Did what I needed to do at the site, back in the plane.... went off with a short fielder , 25 flap..... got past the decision point with only 55kts. geez we use up runway fast with 15 kts of tailwind ! Back pressure and now flying but not climing, still acceleratinginto ground affect, flying down the hill. golly does the speed build.. climbing.... 75 kts time to dump some flaps.. 85 kts, dump last 10 deg. climb more .... off we go.
Colleague made an observation that the other hazardous thing about taking off downwind AND downhill is that once I climb from the 'sheltered' region where I have say 10 kts of tailwind to where I suddenly have 20 kts of tailwind, and consequently 10 kts less airspeed, that is potentially hazardous and a good reason to continue to accelerate to and beyond the T.O.S.S in ground effect flying down the hill to have plenty in hand.....
Go around probably couldnt be done if it was hot. photo of hill.... doesnt look like much but downdraft from wind over the hill and hot weather would be trouble
looking downwind, and down hill. You can only see HALF the runway before it heads off the side of the mountain
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uphill , and upwind. Top is 500m away from strip end. needs greater than a 1 in 10 climb to get over it.