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Thermal or not?


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Hi guys,

So i was out yesterday having a fly with my Elf and trying to set a good flight time for the challenge. 

Now the field i was flying from is very slightly sloped, is only slight but where we enter the field and usually stand to fly from is higher than the other end of the field. At the other end there are bushes/trees separating it from another field which are all level at that point.

Yesterday while flying my Elf, it was a warm day with a nice breeze that kept picking up and dying, few big cumulus clouds about, i was flying upwind as we cannot fly downwind of where we stand, so the wind was straight on my face most of the time or slightly coming across from the lower end of the field.

On one flight when the wind increased, i found a spot where the model was pushed to one side and when turning into it the nose pitched up so i started to circle and was getting some good height and would have got a good flight time out of it. But i didn't time it because i was unsure whether this could be lift from the sloping field? As still a newcomer to finding lift, i have never found lift upwind of myself as yet. The wind was directly on my face and the model directly in front of me and was going up pretty nicely, during turns i was able to hold in quite a bit of up elevator and the model would climb without stalling.

In your opinion without seeing the field and being there, does this sound like genuine lift or lift off the field being sloped slightly? I was not able to climb as well again that spot for the rest of the session which makes me think it was really lift, also the higher the model was getting the stronger it seemed to be and i could turn less tightly, again leading me to believe genuine lift.

I love the challenges on here and i'm a very honest person, i don't want to ever post a time, or even count it as a pb flight for myself if i haven't found a real thermal and the flight has been helped along by some other way.

 

Mark

 

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SilentPilot

Sounds like a classic thermal to me!

Without seeing your field I can't be sure but it sounds like a thermal has used the bushes and slope to 'unstick' from the ground. 

By the sounds of it genuine slope lift wouldn't go that high at your site...

 

Tony

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Yeah that's what i thought, at the height it was (i can't guess as ive never used any telemetry to know what a model looks like at a certain height) i would have thought if it was off the field it wouldn't be generating lift at that point.

Also it's quite a hard field to fly off, not my fave for the gliders, due to the surrounding land, behind us a touch higher, the trees, bushes all round, it's usually quite bumpy and the breeze boils about like we're in a bowl. Even the electric foamie sports models we fly get a good bump about on some days, so the fact i was climbing away nicely, again made me believe i had found some lift. I usually always just follow my streamer down wind, but here flying in front of myself, and upwind yesterday, was my only choice and first time i've found lift in this way, so pure luck! haha.

 

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Hi Mark,

Sounds like thermal to me too.

If you're in slope lift you'll find you can stay afloat in a particular area and roughly at a certain height, perhaps by 'tacking', but leaving that spot takes you out of the lift. Sounds more like you were following a thermal aloft and downwind?

If the slope faces the sun and the hedgeline is providing some shelter from the breeze you'll find warm air accumulating and popping off as thermals. Or perhaps the flat field ahead is providing the buoyant air and the hedge is 'tripping' it into lift.

When I started looking for sites to fly at (not that long ago either) I tended to overestimate the slope potential of shallow slopes. There aren't many round here anyway! A quick look at an OS map should reveal the gradient. One spot I fly has a 1 in 20 gradient which looks like a slight slope but definitely doesn't provide slope lift. When you think of it my glider can't manage a glide ratio of 20! It works best when it's on the lee side and in the sun anyway.

 

On a related note, there are a couple of places round here that you can get an elevated launch position on an otherwise flat field site (Castle mound :)) this gives about 10m height advantage for scouting over the surrounding field. It probably gives a little slope lift with a good wind. I've only ever flown from it for fun on a calm evening because it seems contrary to the flat field rules. It is fun though!

 

Jon

 

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It does face the sun, one problem on a sunny day as it's always in our eyes from where we stand. 

Ill call it a good bit of lift then, next time the breeze is in the same direction ill try a bit further down the field near the hedge line, see if anything is coming off from there and i can follow it back up the field =)

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pete beadle

Hi Mark

Might be a good idea to attach a short piece of wool to your aerial, or, if you really want to impress, to a custom-made ground aerial, located right in front of you, when you are looking down the "slope" and into the sun.......if you'd seen the piece of wool swing round, to face AWAY from you, and down the slope you'd have the classic proof that your wool was pointing to the centre of  a thermal, about to blow past you, while seemingly being blown AWAY from you and UPwind......

Proof positive that you'd found a thermal, and the reason most F3J fliers have a piece of wool attached to their aerials....(yes, even the short, stubby 2.4 ones!) - the aerials, not the pilots!.....

Regards

Pete

BARCS1702 

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SilentPilot
39 minutes ago, i_am_mark_evans said:

Ill call it a good bit of lift then, next time the breeze is in the same direction ill try a bit further down the field near the hedge line, see if anything is coming off from there and i can follow it back up the field =)

Be careful here!

It is easy to fall into a trap of thinking there is better lift somewhere else, because it should be there!

Not that long ago when I was flying my glider (full size, but the point is the same) I was heading for what I told myself would be the mother of all thermals over Drax power station. I was so convinced that the lift was over the station that I flew straight through 8-10kts up, looking for better!!! As it happened I wasted a lot of height and was lucky to scrape away back to another thermal.

Looking back on that encounter with my 20/20 hindsight I realise that I was so stupid. Who the hell flies through 8-10kts in the hope of better? Racing pilots certainly wouldn't do that...

Sometimes it is better to stick with what is going up! Go up, get high first and then explore :)

 

Tony

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I do usually have a plastic antenna with some cassette tape fixed to my tx, but on that day i left it at home. Normal days in another field i just launch and fly whichever way the streamer is pointing.

But this is what makes me wonder if it was a thermal or not, as while gaining height the wind was on my face, so would that mean the thermal (if there) would have been past me? or could i have been in one that was coming up the filed towards me with the breeze? Would my streamer have been facing at me with the breeze or away from, pointing at the model even though i could feel the breeze on my face looking while looking at the model?

Confusing stuff this thermal hunting! haha

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SilentPilot

I'm no expert when it comes to model thermal flying (or full size!)

My guess is there was probably another thermal core behind you...

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Richard Swindells
1 minute ago, Richard Swindells said:

and of course, half the time there is a wind shift and no thermal , or a wind shift pointing to a thermal that turns out to be sink.

There can also be several thermals nearby, making the whole wind direction thing fairly chaotic.

I find "twittering" birds, feeding off insects the best low-level thermal indicator, trees suddenly rustling when it is calm nearby, temperature change.

There are lots of people who are much better at reading ground signals than me... the majority of thermals I catch, I find by reading how the model is reacting in the air. Also having a model that can cover ground well helps, as the more air you pass through the higher the likely hood of stumbling into lift there is.

 

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Thanks guys and thanks for the link mike, ill give it a read.

I'm not convinced it was genuine lift so I won't ever use that field to try to set any good flight times. 

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30 minutes ago, i_am_mark_evans said:

Thanks guys and thanks for the link mike, ill give it a read.

I'm not convinced it was genuine lift so I won't ever use that field to try to set any good flight times. 

Just use it when the wind direction is not up its slope. 

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Sorry to drag this back up.

So Sunday morning I went to a different field and when I got there, there was a steady breeze blowing from one end of the field to the other. After maybe 10 minutes it shifted to blow in the opposite direction, same force as 5he steady breeze when I first arrived, blew in the different direction for 5-10 mins again. Field is surround by trees.

So was this a thermal wind shift? At times it was quite a strong steady breeze. My streamer was just pointing in whatever direction it was going.

I'm currently waiting for the new Paul Naton video to be released so hopefully I can get more help and tips from that. 

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pete beadle

Hi Mark

I think you're drifting inexorably toward and into the direction of MUCH more local knowledge being needed......

It is almost impossible to "diagnose" what happened on ONE occasion, especially if you're not there to experience these conditions, you need to be there much more often, in similar conditions and at similar times, to build up a picture of what's "normal" at that place and time - and to do that you need much more information. For example, you say the field is surrounded by trees - these trees supply valuable indications of the wind long before it reaches you, leaves are much better indications of wind than one bit of wool on a stick, and show direction and speed and especially how consistent (or otherwise) the wind is over a wider area

Are you in front of hills?, in their lee? Is there a wind direction that occurs more often? are there gaps in the trees? and so on - you need to build up a picture over time and sort out what is usual, or normal, or consistent in that particular venue before you can safely say that the conditions you experienced once are unusual. You don't say, not so far anyway, whether you have, or have not, interrogated local users of that field other than flyers. You need to speak to people who live there, especially farmers, possibly ramblers, and you have to establish what is usual, before you try for what is exceptional.....

Go to it Mark - build up a "feel" of the place until you are able to use "home advantage" the way regular flyers there do

One short story/observation - the Ivinghoe hill is  rightly famous for delivering consistently good flying conditions over hours, especially when using the West face, why it delivers this bounty is immediately obvious, standing on the West face you are looking straight at and over the vale below you, and it's (mostly) FLAT over a very wide area. When the breeze meets the hill it is directed smoothly upwards and provides the ideal conditions for successful slope soaring

Every now and then though, a curious condition presents, there is a slight drop in temperature of the consistently West wind, and all the way along the area ahead of the ridge there is ENORMOUS sink! Locals and regular users know what is happening and scoot out of it straight away! There is nowhere to hide - this sink is everywhere! It's obvious and is very much a local condition that regular users have discovered the answer to  - don't try to fight it,get out of it - quick! This phenomenon is not infamous for its severity but it really is infamous for how wide and deep the area of sink is - and five minutes later, its gone, as if it never happened! Leaving the planes of the unwary or un-knowing scattered over the lower ground below and the smug-faced regulars happy to have used their local knowledge to great advantage to dodge the (local) bullet........

Best of luck in your search for why YOUR field does what it does - and why......

Regards

Pete

BARCS1702

  

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Hi Mark,

I was also flying Sunday morning and the wind was all over the shop - although I'm far enough away from you for that to be irrelevant. Where I was there were some very powerful but small thermals that were hard to centre on and plenty of sink if you got it wrong.

A big wind shift like you experienced could be a large thermal infill or it could be a result of a large downdraft in some conditions. I've never actually got around to doing it but have you considered four streamers on bean poles at the corners of the field? By interpolating the combined information you can see more of what's going on. If there's a thermal on the field they will tend to converge, if there's a big down draft they will diverge, pointing away from each other.

Jon

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Thanks guys, it's a black art this thermal finding!

I feel like you guys would be able to turn up, pin point a thermal and fly straight into it (like that well known Joe Wurts video on YouTube). I want to get to that standard, be able to fly to thermals in any field I fly.

Currently I'm doing a lot of throwing and not a lot of climbing haha. My current technique is just to follow my streamer, so I'm always down wind. 

I need to 'learn my field' like you say. They are not ideal fields I guess and could be quite tricky really, but they are all I have so make the best of what I got. 

Thanks guys

Mark

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  • 2 weeks later...

I've thought about it and i'd love to attend, but i don't think they are for me. Plus you all seem quite a close little group and with my shyness and anxiety i wouldn't be able to come into that.

I'm more of a loner flyer or just flying with 1 other person. Shame really. 

Been buying a lot of the Paul Naton training videos, i think they may help a little. 

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