Gradient of slope required to soar?

[Bradleisure]

Firstly I'd like to say this is a general question it's not a safety question...

I've recently been checking out a few possible sites for winder days (Top End on Big Sites) and have a question...

WHAT SLOPE GRADIENT WOULD ANYONE SUGGEST AS A MINIMUM TO SOAR?

One of these sites has 6:1 (too shallow I guess) the other has 4:1 (ish)

I'm guessing here that Bewaldeth is about 4:1 (ish) at best, lots of sloping ground out front though.

Discuss...

[Davehorne]

Well from a purely theoretical point - this is going to get me shot down in flames

Suppose your sink rate is 1.2 m/s - that's what my wing is.

Then the vertical component of wind required to keep you up as you soar parallel to the slope will need to be at least the same.

Suppose you don't fancy launching in more than 20mph (32 km/h which is about 9 m/s) - that's the wind speed up the slope - then the angle of the slope needs to be Sin(1.2/9) which is about 8 degrees. So the slope will be 1 in 1/(Tan 8deg) This is roughly 1 in 7.

Obviously the wind speed must be less than Vtrim of the wing (mine's 36 km/h) otherwise you are going backwards or gale hanging on speed bar (which will increase your sink rate........)

I tried soaring a local hill (Killhope Law) last year. This is about 1 in 8 and I only just managed to stay clear of the slope in nill wind, which proves that theory doesn't usually give practical answers as I should be able to do 1 in 10 on my wing - so all the above is rubbish really

[Bradleisure]

The 6:1 worked, only just mind.

Wasn't easy to get any height as had to concentrate on active flying due to bullet thermals coming through.

[Kitt Rudd]

it is not a simple case to try and fly shallower slopes when the wind gets up cos there will be more of a horizontal componant which is not condusive to a good soar, it is better to go to the coast where the air is more laminar and find a small bump with a good vertical component. I have soared along Blackpool prom before though it was a bit nervy flying along side all those lights strung up.
If the wind gets to stong better to fly a kite

Kitt

[Davehorne]

An electrifying performance at Blackpool?

[Bradleisure]

Well I have to agree that it probably isn't worth the effort on an active day as I doubt there's much chance of using the active air and getting away from the hill.

It may be worth it though during any higher wind shorter inactive days.

Hope we all get to fly one of the big sites in lovely big smooth thermals soon.

PS Funny the things we end up doing on a lads night out eh!?!?!?

If any of the NE crew are interested (not sure if we'd be welcome though) check out http://www.skiweardale.co.uk (anyone a member of both clubs?)

[gary stenhouse]

i think very small steep sites our fine as there is good compression and lift the problem with very shallow is you have to be flying at the almost limit of the glider to be above the ground. mind i would reckon that my new glider could get away with things not possible before but at the same time flying a 2-3 close to the ground in top end conditions does not appeal anymore. though a small shallow site with a very small lip at the top where there is a definate trigger would. a bit like the radar masts also there is a place at the very top near the cafe where there is a small defined ridge and the ground there slopes away for over a 100 feet will try it one day on the way over in a westerly and see if it will work.

it is still good to go out and try fresh sites as you never know there may be a gem among those areas of wilderness.

cheers gary

[John Wallis]

there is a place at the very top near the cafe where there is a small defined ridge and the ground there slopes away for over a 100 feet will try it one day on the way over in a westerly and see if it will work.

I've eyed that up a few times there's not much but it might work. Trouble is you never bother because you know it's better just down the road.

[Davehorne]

I saw someone I didn't recognise trying to launch from there last year - didn't look very appealing to me

Plus it always seems to blowing a gale there even when it's flyable at Millers Leap or High Cap