SEN 1296<
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- Category: Archive 2009
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Table of Contents - SEN 1296
- Hot Circling
- Edmonson
- Morris
- Leaper and the Godfather
- Lipori
- Hoffman memories
Hot Circling
Circling Right or Left in Thermals??
By Dave Edmonson April 10, 2009
I have wondered about this since all of my HLGs are trimmed for a left glide, my towline gliders and rubber models for a right glide, and my power models for a left glide. So is there an optimum?
While watching a flock of 50 great white pelicans start to thermal above a parking lot in Minneapolis Minnesota a few years ago in the fall, at an altitude of 75 feet, I thought that there was an answer. They flew in perfect formation in a right turn glide pattern with the giant 9 foot wingspan birds readjusting their flight path center to the pelican making the most rapid ascent. So there it was, 50 soaring birds flying to an altitude of over a 1000 feet after several minutes in a right glide circle. But then they broke into 2 groups of counter rotating flight and continued up to over 2000 feet before they again joined into a left hand glide circle. Shortly after that climb they all headed straight south, also a good idea for Minnesotans at this time of the year.
So over the years I have done a lot of RC electric powered sailplane flying, the most recent last month in Florida with 8 ½ hours of flight time on one model, and 13 on the other. Finding thermals is easy with a model that will climb out of sight in 30 seconds of power and with a controllable glide path. While in thermals I frequently change from right circle to left circle and back while in the same thermal. I don’t see any difference.
Many times I fly in pattern with vultures, wood storks, and other soaring birds, and we circle right or left depending probably on which glide circle brought us into the thermal first.
So based on my experience of not seeing a difference in the northern hemisphere, I would reason that there is no difference in the southern hemisphere either.
With free flight models it is best to center the thermal, but if you don’t find the center, or even the edge, you would prefer your model to head towards the thermal which may be to the right or the left!
Thermal Rotation
From: Gil Morris
About twenty years ago the Soaring Society of America made a two year study of thermal rotation. There were about forty studies in which two sailplanes would go aloft. One would find a thermal and then fly through the core of it and throw newspapers out. The second sailplane, off to the side, noted the directional rotation of the newspapers. The conclussion was that, here in the USA, two thirds of the thermals turn left and one third turn right, ie 2/3 turn CCW and 1/3 turn CW when viewed from above.
Gil Morris
From the leaper and the Godfather
Roger,
In response to Carrol Allen's query, I am quite certain that the late
Godfather, R P White told us that thermals in northern hemisphere
rotated left, hence that was why his planes always circled to the left.
I & many others have found that circling to the right is just fine,
as your glide is toward the rotation, so it will add some velocity
when coming into thermal gusts.
If the trim is such that inside wing has some washin, it will stall,
turn and center into the updraft.
That said, it may not matter which way, as Bob and many others,
including raptors, have done very well in either hemisphere,
regardless of glide rotation.
Ciao, & Happy Circling,
Leeper
And Bob Lipori’s PoV
According to Bruce Abell the left rotation of thermals in Northern hemisphere is basically true, but can rotate clockwise under some conditions. The following web-site has the details. Since SEN is sent in plain text the url will have to be copied and pasted into the address line.
http://www.soartech-aero.com/Thermals.htm
Bob Lipori
HOFFMAN MEMORIES
I knew Roul Hoffman very well having shopped and worked at Wally Simmers' model shop. Roul ran it most of the time. I have an autographed copy of his book. He signed and added "Homeboy you have arrived." in Hungarian. He from there and my parents also. I dont know how many know that he designed the retractable landing gear for a famous racing plane. Forgot the name of the plane. Sorry Roul. Botchanot, please excuse me in Hungarian.
ED MATE
............
Roger Morrell
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