Downdraft

[Big-D]

Had some interesting sink's yesterday morning.

Batman, Gerhard and kie landed as FAAP and we took off to circle Harties and wait for Dieselfan and Cobra and co who were on their way to visit..

I took off runway 03, at end of the runway I hit a nasty downdraft pushing me towards the ground - Anyhow, full power bar forward she fianlly recovered followed by a climb of 1100 feet per minute according to the VSI - Most I normally get is 650fpm.

I climbed for altitude while other okes gor airborne with intent of crossing the magalies ridge, next thing I hit another downdraft - NASTY little bugger, I called on radio warning okes, but a little late as they had experienced the same bastard as I on the thresshold of 21.

So I decided to rather land as was feeling kinda uncomfortable as I joined on downwind at 500ft AGL I hit a "OOM" of a downdraft right above powerlines - I was falling like a brick on full power bar forward and could do nothing - I was told later on by guys on the ground at FAAP that they saw this and were certain I had stalled because I was falling so far and quick

Anyhow, recovered landed checked the windsock doing some funny things - 1hour later no wind I went flying again and it was fine

Strange time of year now. Anyone experienced this before?

D

[Nkwazi]

Howzit Bud

Was very bumpy low level at Cullinan yesterday morning, but I mean very uncomfortably bumpy. Climbed to 7200 and very smooth up there

[Dre'man]

Had very similar at Circus yesterday. 500' agl wind was blowing in te opposite direction to surface wind. Took mother in law for a flip, took off. 10 mins later joined overhead windsock still said 05 is active. Joined the circuit all fine. On finals 50'agl glanced at the windsock and suddenly we were going to land downwind.

I think the weather was generally just unstable. very bumpy below 6000. None the less M.I.L. enjoyed it and my son went up for his first flip. As long as he was in the pax seat there was not a bump. What made his flight?????? He could see trains.

[andreb]

Had a great flight to Kroon form Microland Saturday. Less bumpy on way back than on the way there!! Air was smooth for most of the flight at all levels.
Definitely very bumpy north of Magalies ridge. Also battled to get height to climb over ridge, but made it.
Has a scare on threshold of runway 27 when landing back at Microland. About 20 feet off with ample airspeed, I just sunk and hit the runway fairly solidly. Bar full forward had no effect. Luckily no damage..just comments from Ray on my "landing."

[andreb]

and....north of magalies ridge wind was WSW at about 15mph. South of the ridge it was NNW at about 10mph.

[cobra]

Hi D, must say the experience does sound scary and good to hear of safe landings.

I have passed the dam wall on the way to AP and halfway there, found myself fighting the turbulence and looking for landing space. The rotors of the ridge are .

As Andre mentioned our flight was not as bad although on your side of the ridge it was very turbulent. Microland in general is a bit of a tumble dryer with the hangers so close to the thresholds.

We had a trip to Nylstroom this morning - what a great flight, at 6500ft, tailwind there and with luck on ourside a tailwind back as well :D and amazing !!! no turbulence nor thermal activities.

Reason , no mountains I suppose

[John Young]

These damn patches of sink can also make you blush.

At our last spot landing competition (glide approach from overhead), nailed the first two OK.

Then number three – big patch of sink – touched down >100m short of the mark.

Damn patches of sink

Regards
John ZU-CIB

[lamercyfly]

Hi guys.....

Yeah, not lekka

Please just watch-out for 'bar full forward' while sinking badly. Regardless of whether you have full power or not, stalling happens as a result of flight path relevant to angle of attack. This can easily lead a high speed stall situation, and if you are flying solo, just ends up in a mushing high rate of descent flight path. If you are flying dual, you could end up dropping your nose or a wing badly and who knows what next if you less than 300feet AGL..........

Best thing possible, in sinking air, is to speed up and get out of it(watch birds of prey, and you will see them slow down, spread their wings and orbit or ridge soar in rising air, and as soon as they head out to search for another thermal, they tuck(or fold) their wings in and go like hell until the find the next patch of lift, and then they slow down and spread their wings again, etc., etc.,

But yeah, if you are on finals and you hit moerse sink, and you are low to the ground, chances are you are in moerse K*k Only rescue is to have had a lot of air speed on in the first place(more than normal because it is thermic), and be standing by to add FULL thrust while you 'feel' the wing to maximum angle of attack without inducing stall symtoms.

Also very important to come in with a gentle approach slope(this can be achieved by coming in with a reasonable amount of power), on a longer finals than normal. This reduces your aircrafts vertical moment, while increasing it's horizontal component, and it is easier for the extra lift generated by an increase in the angle of attack(achieved by slight bar forward movement) to convert into reduction of vertical velocity ie the aircraft will recover from the sinking air much, much easier.

Like Demon says, we are heading into spring, and the thermals are going to start kicking. Be ready for 'em, and enjoy the challenge.......

Later,

[DieselFan]

Guys I dunno if thermals are to blame? I left Big D at around 10h30 on Sat with pax. He had encountered the sink before 8am as we landed there around that and before we landed. At around 9 we were both flying NO problems.

When I got back to Microland with a lekker tailwind of around 20mph (took 35mins). I had loads of juice left so went to play around in the east around 11+

I encountered SIGNIFICANT sink close the ground, I even tried flying lower almost in ground effect and at one point had huge sink that even with bar in at 80mph(20 over norm) air speed and full power and releasing bar to neutral merely gave a str8 and level 1m from the ground. . Normally this results in a climb of note, lifting 4-5x tree height in 1-2 seconds!

I had an uneventful landing but brought it hot incase. Due to the now strong ground winds landing distance at high speed was still small.

My thinking is - as I had a tail wind from AP to Micro is that some sort of front passed thru?

My last 20 hours and in recent heat (at similar times) I've never had sink like that esp with the wind pumping It wasn't gusty wx as my ASI wasn't jumping around as much as norm

Thorts?

[DieselFan]

The were inconsistencies though as Dre'man described, at AP on landing at 8 wind was 21 and on landing 03, is it possible to have "wind swirl" fronts? I was also guilty of full bar out on the one occasion but I had no choice as I was almost touching the ground

As I mentioned - this is all thermic activity. There has been a lot of this the last few hot days. Watch the windsock in these conditions, every 5 mins it is doing something different. As the day progresses and teh air cools conditions of course improve

[nicow]

Lamercyfly
Thanks for the info.It is only your reaction that pushes the bar forward when you sink.We must be attend on it to pull the bar in for more speed to recover from the "sink".It can be fatal if you push the bar forward at a low altitude.
Stay safe,and think clear

[andreb]

Dave and Nico, thanks for the advice. I was just feet off teh grounbd, and you are right, it was just reaction to push bar forward as I was rounding out already.
I did say no damage earlier, but got to the airfield yesterday and had flat front tyre. I did pump with tyre weld and then flew. Problem was that I missed the large blister on the side wall (damn fairing) and on landing this jammed against the mud guard. Result was abrupt stop and damaged mud guard.
Some lessons learnt this weekend!!

[Big-D]

Dave, thanks for advice on not pushing bar. Right you r. Lesson learnt.

[Henni]

I've learned something that has saved my butt many a time:

When the weather is unstable (even if wind just gusting), I always come in high and hot. Normal approach speed in the Mizer is 50-60mph, but in the above conditions, for finals, I ALWAYS!!! come in at 80mph and it works, every time for me.

Most microlights have so little inertia that you loose the excess speed as soon as you flare for the landing. Best is to actually put it down with speed just a little above normal.

Same with take-off, wait for speed to build up far above normal before you start your climbout.

For some serious downdraught stuff, check this out:
http://avcom.co.za/phpBB2/viewtopic.php?t=24458

Henni