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Old Sep 10, 2003, 05:28 AM
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UK
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Bad Wind ??

Hi,

I have a speed 400 glider, and have started flying at a local public field, and seem to encounter some strange air conditions...... as I'm not that experienced so I thought I would ask the pro's !

I have flown on evenings where there is no wind, the field LHS has a row of tall pine trees, the RHS has small trees in a hedgerow. The LHS to RHS width is about 300 yards and the field is about .3 mile long. The eglider launches and makes a steady climb fine, at about a ht of 50 ft in the middle of the field, the plane makes a sudden spiral dive, or is blown down. Not quite sure whether it recovers naturally or whether its me, but it normally recovers about 10ft off the ground ! This has happened evey night I have been there, about 5 times in the last 2 months. Its like there is a vacuum there and all normal rules of flight are meaningless !!

Once I get higher, you get the normal minor surges and drops but its fine and predicatable. I seem to be restricted to climbing in circles avoiding this area. The field is flat and the trees and hedging are consistent, so I'm at a loss as to what is causing this, any ideas ?

Thanks

Nick
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Old Sep 10, 2003, 05:37 AM
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East Anglia, UK
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It may be simply that you stall it after takeoff.

It may also be a downdraught caused by thw trees.

I can always find an updraught over a bank of trees where I fly.

Wind is funny stuff. I launched a model once, nice steady straight climbout. Got to be about 30 feet up and SNAP the wings folded. Now they were weak, but I was not doing anything on the sticks. I can only believe it was some massive turbulence.
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Old Sep 10, 2003, 07:35 AM
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Providence, RI
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This can happen where I fly sometimes too, the trees can be real wind shields and the air coming over them isn't always predictable. Another is buildings! They are even worse it seems and are becoming more common around fields these days. So what I do now, so that there are no suprises, is take along a medium sized delta wing kite and send it up just over the tree line to see what it's doing up there, but sometimes theres not enough wind to get it up even that high, but you can bet there is 150' up.

Scott
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Old Sep 10, 2003, 07:43 AM
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Telford, UK
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Quote:
Originally posted by vintage1
I launched a model once,.. Got to be about 30 feet up and SNAP the wings folded.
Nick,

Firstly, NEVER buy a model from Vintage1.

Secondly, yes trees are funny things. The more knowledgeable talk about the 'rotor' on the leeward side of an obstruction where the air can form a sort rotating tube which will snatch a model downwards with no warning.

We have an area of woodland to one side of our flying field. If the wind is coming from the trees, then low level turbulence is guaranteed. OTOH if if the wind is going towards the woods, then it's time to break out the glider and go soaring with the local buzzards!

tim
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Old Sep 10, 2003, 08:31 AM
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N. Staffs, UK
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As the guys have suggested it needs very little breeze to create "interesting" turbulence around trees and other obstructions. The thing that sounds odd is that you are getting problems at the same place all the time. I suggest you keep a careful eye on exactly which direction the breeze is coming from in each case (if there really is absolutely no wind at all then you're lying about being in the UK ).

But I'd be inclined to go for vintage1's theory that you may simply be stalling it. I have one glider which needs a little down trim mixed in on full power cus I can't get any more downthrust on the motor unless I rebuild the front end (and I'm too idle). Before I set up the mix, if I forgot to hold down in it did exactly what you're describing.

Steve

Steve
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Old Sep 10, 2003, 11:51 AM
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Oakland Ca. in an old warehouse, lots of room but no rooms...
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Hey now,
If you're not stalling it you may be experiencing a "secondary wave". Wind works like water so if you look at your site and think about how water woulc flow over it you should see where there will be eddies (rotors) and whirlpools. If you look back at whats behind the spot in the trees where you're having trouble I'll bet theres a building or second set of trees that would alter the airflow.
At one field I fly from theres a spot in the middle of a flat field where I can "rest" my plane just riding the secondary wave formed on a building a quarter mile farther down. It'll just sit there and hover as long as I keep it on the crest...

Remember air is (for this purpose) a fluid, think of water flowing over your flying site and you'll see where the good spots are.
Thanks to Dave Thorenberg and his friend "the old buzzard"
RobII
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Old Sep 10, 2003, 01:52 PM
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Pepperell, MA, USA
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"Bad Wind"....shoot, I thought that was something my dad had...
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Old Sep 10, 2003, 07:43 PM
717
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If there truely is zero wind velocity during your flights than the only other contributing factor to CAT (Clear Air Turbulence) would be thermal activity, otherwise all the possibilities stated previously apply.

-or-

possibly the Bermuda Triangle Effect?
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Old Sep 11, 2003, 10:04 PM
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United States, IL, Bartlett
Joined Jun 2002
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There is one field where I fly at and if I use a feather receiver, my plane nose dives in from 100ft to about 15ft and then is ok until I get to that altitude again. It does not do this on other channels or with other receivers. If you dont think it is a stall then try another channel or receiver for possible glitching.
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Old Sep 11, 2003, 10:12 PM
717
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I flew my Phat Larry today. First time in almost a year. The plane is fun, but is SO sensitive to wind/turbulence. I usually fly it in zero wind and I can control it precisely; but today the wind started blowing a little bit and I found myself constantly correcting for turbulence. Mind you, I fly in a field which is surrounded by hills and trees, so ANY wind turns into turbulence. I had fun though. First time I've flown in two months since my new airplane's maiden, which had glitches I've since been trying to fix.
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Old Sep 12, 2003, 04:00 AM
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Thanks for all the responses,

I know I am a rookie, but I am certain its not a stall. Stalls are quite predicatable on my glider and .....er result in a stall. This is to violent and consistent, I dont think I could stall it in the same place every time !!

I hope to visit this weekend and check out secondary obstructions/radio twitching in the spot etc. Its nice to know other people have this probelm too !
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Old Sep 12, 2003, 04:44 AM
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Well O.K. so long as you're sure you know the difference between a stall from the glide and a full power stall. Stalling from the glide my thing just gently nods its head. OTOH if you manage to stall it on full power it nods a bit, the power drags it down, then it drops a wing and it's in a spiral dive (all in about 1/2 second).

Good luck finding the answer.

Steve
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Old Sep 16, 2003, 09:25 AM
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OTOH if you manage to stall it on full power it nods a bit, the power drags it down, then it drops a wing and it's in a spiral dive (all in about 1/2 second).

Hi,

Not sure I know what this is (a reall rookie !). Nods a bit, you mean nose goes up and stalls, as the power is on its pulled downward ? The rest I do not understand !

Assuming you were on a gentle climb (with elevator) then, when being pulled downwards, the plane should recover ? I guess if you had some down trim to ensure you dont stall, then you would dive dive dive. But why the spiral bit, assuming you were climbing straight ?

I am going to put in geared drive, so hopefully I can just power my way up, and this will iron out some of the turbulence compensations that I normally have to make, even on a gentle climb. Presumably this will make this power dive 'thing' less of an issue, my logic being that it will cope with much steeper angles of attack before it stalls ?

Again I dont think this is the origonal problem as I have flown it in other places without this sort of occurence... but I am intrigued as to what is really going on with this power dive !

Thanks

nick

(PS still have not got around to flying since )
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Old Sep 16, 2003, 09:52 AM
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Its normal for prop torque to oll a model left as it stalls under power - the bigger the prop the worse the effect. So a power on stall is usaully a steep climb, then hanging on the prop, then drop the left wing, zero control as no surfaces have any airspeed, tho the rudder and elevators may have some effect if subject to prop wash - then if the model is trimmed right, the nose drops and off into a spiral dive it goes...where you can regain control.
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Old Sep 16, 2003, 03:47 PM
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OK, thanks.

So its basically pretty obvious, it does not occur without a steep climb, or hanging on the prop after a bit of turbulence. It spirals because the left wing is being pushed down by the prop torque, and it recovers when there is sufficient air speed.

I'll give it ago when I am high enough to see if I can induce it !
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