Thermal Lift Dynamics

I've been flying my 12m Silent-IN all by mysel up in Northern Maine.
I'm finding conditions are usually marginal. 5kts is the best I've
ever seen on the very best day. Typically I see 2-3kts and real
scratchy at that.

I often run into a kind of lift (particullarly up near the cloud decks)
where the lifts comes on gradually, then crashendo's and crashes behind
it. It doesn't feel like a typical thermal. It feels more like some
kind of mechanical turbulance or a sheer wall.

In other regions I've flown (Eastern Washington State) lift blew the
caps off vario and it wanted to shooved you right through bottom of the
cloud. Here (Northern Maine) it's just so weak I can barely make it to
the decks, then this "sheer lift" forms and I can't stay in lift long
enough to make good progress.

A plausable technical description of what I've observed would really
help me visualize the phenom and maybe fly it better.

Thanks,

Bruce Meacham

wrote:
I've been flying my 12m Silent-IN all by mysel up in Northern Maine.
I'm finding conditions are usually marginal. 5kts is the best I've
ever seen on the very best day. Typically I see 2-3kts and real
scratchy at that.

I often run into a kind of lift (particullarly up near the cloud decks)
where the lifts comes on gradually, then crashendo's and crashes behind
it. It doesn't feel like a typical thermal. It feels more like some
kind of mechanical turbulance or a sheer wall.

In other regions I've flown (Eastern Washington State) lift blew the
caps off vario and it wanted to shooved you right through bottom of the
cloud. Here (Northern Maine) it's just so weak I can barely make it to
the decks, then this "sheer lift" forms and I can't stay in lift long
enough to make good progress.

A plausable technical description of what I've observed would really
help me visualize the phenom and maybe fly it better.

Thanks,

Bruce Meacham

Read Mike Borgelt's article:

http://www.borgeltinstruments.com/Gusts.html


--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

Are you sure you are circling tight enough? It may be that the thermal
cores are very narrow, and you are not getting into them. You may have
experienced larger thermals out west, and could circle in them without
banking that much.

Try making a small right angle bend out of solid wire, and mount it up
on the panel so it shows a 45 degree angle like a letter-v (you may
have seen something similar on an aerobatic airplane). Use it as a
reference with the horizon to see if you really are banking at 45
degrees in a tight thermal. You may be surprised to learn that what you
thought was 45 degrees was only 30 or so. It's a very common problem.

Other things to check are your vario TE compensation, and tubing leaks.
It may also be instructive to carry a logger and analyze the flight
traces with a flight ananlysis program like SeeYou or StrePla.

wrote:
I've been flying my 12m Silent-IN all by mysel up in Northern Maine.
I'm finding conditions are usually marginal. 5kts is the best I've
ever seen on the very best day. Typically I see 2-3kts and real
scratchy at that.

I often run into a kind of lift (particullarly up near the cloud decks)
where the lifts comes on gradually, then crashendo's and crashes behind
it. It doesn't feel like a typical thermal. It feels more like some
kind of mechanical turbulance or a sheer wall.

In other regions I've flown (Eastern Washington State) lift blew the
caps off vario and it wanted to shooved you right through bottom of the
cloud. Here (Northern Maine) it's just so weak I can barely make it to
the decks, then this "sheer lift" forms and I can't stay in lift long
enough to make good progress.

A plausable technical description of what I've observed would really
help me visualize the phenom and maybe fly it better.

Thanks,

Bruce Meacham

"Doug Haluza" wrote in message
oups.com...

Try making a small right angle bend out of solid wire, and mount it up
on the panel so it shows a 45 degree angle like a letter-v (you may
have seen something similar on an aerobatic airplane). Use it as a
reference with the horizon to see if you really are banking at 45
degrees in a tight thermal. You may be surprised to learn that what you
thought was 45 degrees was only 30 or so. It's a very common problem.



In a glider with a reasonably supine seating position I use the instrument
mounting screws as a 45 degree reference. It's not so easy to do in a glider
where you're sitting up more because the instruments aren't so near the
horizon.

Stephen