Peewhit Posted September 8, 2011 Share Posted September 8, 2011 In between the heavy rain storms (the kit is still drying out) I managed to get some good flying today, and experienced a weird phenomenon. The wind was 15pmh straight on to a good slope (Levisham) and for a period of about 15 minutes the lift was awful. The only way I could stay aloft was by hugging the top of the hill and even then 40ft seemed to be the lift ceiling. I suspect that it had something to do with a very large black cloud which was low overhead. Perhaps you chaps who are more experienced in weather matters could enlighten me as to the cause of this? Quote Link to comment Share on other sites More sharing options...
Tom Satinet Posted September 9, 2011 Share Posted September 9, 2011 was it cold? Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted September 9, 2011 Share Posted September 9, 2011 Maybe the slope (or the bit where you were...) was in a downdraft..... Large black clouds can be indicative of Cumulo-Nimbus cloud formations with all the up & downdrafts that entails.... Quote Link to comment Share on other sites More sharing options...
Martyn K Posted September 9, 2011 Share Posted September 9, 2011 A couple of possibilities. I suppose the obvious one would be big downdraft, especially if the air had been especially warmer before the cloud appeared. Unusual to last 15 minutes though. Possibly wind shear where a layer of air is moving in a different direction to that perceived by someone on the ground. Very difficult to tell without dong some testing, but it wouldn't have to be a big shift in direction to kill slope lift . I have experienced similar effects when I use to fly at Blackstone Edge many moons ago. This occasionally happens with a drop in temperature, but again unusual at low altitudes. Or - it's something else Enjoy Martyn Quote Link to comment Share on other sites More sharing options...
Gary Binnie Posted September 9, 2011 Share Posted September 9, 2011 Most probably a shifting lee wave. A strong wind, unstable atmosphere (marked by Cumulo Nimbus presence) and hilly terrain upwind are prime conditions for it to set up. I don't know the area but I notice that the full-size gliding site at Sutton Bank is just to the West, their website (Yorkshire Gliding Club) says that they get wave lift off of the Pennines and their altitude record is 33,000 ft (I've been to a measly 17,500 ft in Scotland!!). When it's strong the up-going air can ascend at 1,000 ft per minute or more, problem is the down-going air descends at the same rate! It's caught a few light aircraft pilots out over the years, they just can't out-climb the downdraft. I've been caught out trying to soar hills and mountains downwind of other big features but that was usually just a blanking effect (you definitely know when you are in the 'sink' of wave lift!). Nearly landed in water once in Scotland, the only option there was apart from getting silly close to the hill which eventually saved my bacon. If you ever get the chance flying in wave lift is magical, the air is so smooth that it feels like you are on the ground. I'm pretty sure that's what was going on. Cheers Gary Quote Link to comment Share on other sites More sharing options...
Erfolg Posted September 9, 2011 Share Posted September 9, 2011 Has the slope worked in the past? Not being a slope expert, my comments come from the point of view of what I would expect to be needed. I gather shape is important, in that if the slope were actually be completely flat (therefore no slope), none of us would expect it to work in keeping the model up. So it seems we need to have a vertical component to wind forces. From that it seems the steeper the slope, the greater the upward component will be. I also guess the narrower the area of the lift, the steeper the face/slope. Although I have seen people slope from cliffs a long way out. Could it be that the slope was not steep enough for the wind? I would also expect that the approach to the slope to ideally be pretty flat with little or no obstacles (other than small scale). But I guess this is all standard stuff or I could be wrong. Anyway, I am now of to the field to fly my model Quote Link to comment Share on other sites More sharing options...
Peewhit Posted September 10, 2011 Author Share Posted September 10, 2011 Many thanks for the replies. The Slope is good.I fly there regularly and usually the lift extends way out. The weather was very changeable with rain one minute, sunshine the next and lots of heavy black clouds around. There is a hill about three miles upwind and this all seems to support Gary's shifting lee wave scenario which would give downdraft as long as the wave is present. Well, I have learned something new and now have a great conversation opener of "what do you feel about slope soaring in a shifting lee wave?" Quote Link to comment Share on other sites More sharing options...
Gary Binnie Posted September 10, 2011 Share Posted September 10, 2011 I just checked the BGA National Ladder, several wave flight height gains were entered on the 8th, all to about 10,000 ft. The next day was better with one climb to 14,200 ft. Wave activity was all over the country, Shobdon in Herefordshire, Lleweni Parc in Wales and Scotland was 'heaving' with one pilot covering 460 km cross-country on the 8th and that would definitely have been in wave lift. Probably quite rare for your hill to be swatted by the downdraught as the wind speed and direction and dew point temperature (cloudbase) have to be right but if it happens again you''ll know what it is!! A sure sign of wave setting up is Lenticular (lens shaped) clouds, they look like cigars or french bread sticks from the ground and line up parallel. Below these are often swirling 'rotor' clouds, very rough air but they can be climbed in if you're brave!! I've always had a mad idea to control a model glider from a full-size one and get it into wave, fraught with problems for sure!! I don't know if that would be cheating for record purposes?! Someone did fly an RC Spitfire across the Channel once, controlling it from a Jet Ranger helicopter, may well have featured in RCM&E. Cheers Gary Quote Link to comment Share on other sites More sharing options...
Peewhit Posted September 11, 2011 Author Share Posted September 11, 2011 Quite rare indeed Gary. I have flown that slope more times than I can remember and never previously encountered anything like it. Flying a model glider from a full size one is certainly an interesting concept. I would like to see you land them both at the same time Quote Link to comment Share on other sites More sharing options...
Steve Houghton 1 Posted September 11, 2011 Share Posted September 11, 2011 I have experienced lack of lift after heavy rain showers, which has taken a long time time to come back. We discussed this and thought that it was possibly due the the rain cooling the earth. Once the sun came out and warmed up the ground, the lift seemed to come back. It's only a theory but we're sticking to it. We've also had little lift when there hasn't been rain, due we thought to a lack of thermals coming through. Again, another theory. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted September 11, 2011 Share Posted September 11, 2011 Same thing happens at the Orme occasionally Steve, and I doubt a bit of rain affects the temperature of all that Irish sea much !I think the general dampness of the air just "bogs things down a bit" That's my very technical meteorological explanation of it anyway . Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.