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Old Sep 21, 2012, 08:00 AM
Full Scale Piper Cub Driver
Piper J3's Avatar
Hinckley, Ohio
Joined Nov 2008
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Strong Thermal 500 fpm Lift...

I posted this in the Electric Sailplane forum but I think it's better to ask the purists in Thermal Duration this question...

On Tuesday this week I flew my 3meter Sensor 117 that I converted to electric. Beautiful day – sunny, 62F, 10mph, with a few scattered clouds. Got home from work and launched at 4pm which is late in the day for thermals. Total flight was 21 minutes including launch to 1000’. Immediately climbed to 1500’ and then fell out. Searched upwind and found a “hat sucker”. Rode this 2nd thermal for 4 minutes at 384 fpm climb. Topped out at 2678’ per RAM3 data logger.

I have bench marked the Sensor in dead calm conditions at 110 fpm sink rate. Add this sink rate to the 384 fpm climb and I was in a column of lift that was rising 500 fpm. This was on a cool September afternoon in Ohio. No cumulus clouds, storms, or obvious convection weather activity. Beautiful benign conditions. So my question is – has anyone documented a thermal with more than 500 fpm lift?
-----
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Old Sep 21, 2012, 08:29 AM
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GliderJim's Avatar
Michigan, USA
Joined Jul 2006
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Not mine, but here's a good one...

http://www.rcgroups.com/forums/showt...ssage_22688663
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Old Sep 21, 2012, 08:38 AM
Balsa addiction since age 3
ScottSails's Avatar
Upstate NY
Joined May 2005
1,253 Posts
Wow? You launch to 1000 feet? In my normal flying (I use an altimeter) I usually launch to about 400 to 600 feet much like we did with winches (I only have electric sailplanes now). At about 1000 feet I get pretty nervous (120" span, wide chord plane). 1500 ft is my max ever.

The only reason I ask is because I wonder if there is a chance that your calibration is off? You must be blessed with fantastic eyes (I am not) to fly at that height.

What I can share with you is that I have had lift (above 1000 feet) that is just downright scary - I pop spoilers and leave as literally in 1 turn, approx 60 foot diameter the plane goes up 100 foot (per altimeter). Thermals get really strong the higher you get many times (sometimes they fizzle). I would say 3 turns a minute so approx 300 ft/min - I don't have a data logger, just real time telemetry.

Scott
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Old Sep 21, 2012, 09:09 AM
Full Scale Piper Cub Driver
Piper J3's Avatar
Hinckley, Ohio
Joined Nov 2008
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I miss the winch days. Now I fly by myself so "winch-in-the-nose" is what is keeping me in sailplanes. I figure why stop climbing at normal winch release heights when I can power up higher and have a longer time to search for lift.

A lot of my sailplane flying is very early in the morning where I sometimes launch to even higher altitude and just glide down. I take my folding lawn chair and a cup of coffee and its just me and the plane. With 2200 LiPo I can get 3 climbs to 1000'.

Piper J3
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Old Sep 21, 2012, 10:23 AM
Balsa addiction since age 3
ScottSails's Avatar
Upstate NY
Joined May 2005
1,253 Posts
Quote:
Originally Posted by Piper J3 View Post
I miss the winch days. Now I fly by myself so "winch-in-the-nose" is what is keeping me in sailplanes. I figure why stop climbing at normal winch release heights when I can power up higher and have a longer time to search for lift.

A lot of my sailplane flying is very early in the morning where I sometimes launch to even higher altitude and just glide down. I take my folding lawn chair and a cup of coffee and its just me and the plane. With 2200 LiPo I can get 3 climbs to 1000'.

Piper J3
Right there with you! But, I am just too old to deal with setting up the winch, picking it up, moving it, always being downwind, etc. The setup and tear down and line breaks, knots, etc, cut into flying time! As a result, I am a big believer of the winch in the nose (I like to think of it as being a hybrid - Prius maybe? )

Most of us at the local field launch with ALES (200M typically, sometimes 100 or 150M) and then fight for thermal. Many of these planes can get 8-10min from that height with no appreciable thermal (like after 7pm). Honestly on quite a few days (10-6pm), we can stay up as long as we care even from 100M launch. The lower thermals are so fun to find and literally you can stay at 100ft for minutes, maybe 10 min before they break off and take you up. Some days, a feather won't stay up

Scott

What I do know is the electric allows me to fly bolder (stuck a plane in a tree last week) and the altimeter has strengthened/reinforced my thermal knowledge by confirming lift. I only have the altimeter in 1 plane, but it has helped my overall flying greatly.
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Old Sep 21, 2012, 11:08 AM
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United States, MA, Waltham
Joined Dec 2001
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I'm sure it's not all that unusual. I've sometimes spent several minutes with the flaps out, descending out of a strong thermal. One time it was even hard to land, and I had to make three attempts, getting sucked back up each time. I've also seen various improbably things sucked up far into the air. And years ago there was a photo, I think in the AMA magazine, of a shade canopy with nothing but blue sky around it.

Full scale guys report thermals twice as strong and stronger. Here is one such account. Try doing a text search on fpm and you will find some high numbers:
http://www.desertairriders.org/jhflight.php
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Old Sep 21, 2012, 11:24 AM
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Canada, NS, Yarmouth
Joined Jan 2008
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I have once been in 1200fpm and a few times in 600fpm lift, as recorded by my WSTech vario. I had a real hard time bailing out of the 1200fpm lift and was very close to loosing the glider.
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Old Sep 21, 2012, 11:29 AM
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United States, AZ, Douglas
Joined Nov 2007
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Years ago I was flying out in the desert part of East San Diego and got caught up in a series of thermals that were flat out scary! As soon as I managed to break out of one, another one would toss my Paragon right back up to specked out and beyond altitudes. I was still pretty new to thermal flying at the time and had never had to deal with lift this strong before.

To make what could be a long story short, I learned a lot that day. 1st: If the plans show Spoilers... Install them! 2nd: Bright reflector strips are well worth their weight in gold when it comes to spotting a model at high altitude when you made the mistake of blinking at the wrong time. 3rd: Flying inverted with a flat bottomed airfoil is a great way to shed altitude when the thermals are trying to suck you out of your boots, let along taking your hat off!

(edit)
Thinking back... I wish that we had telemetry at that time. I really wonder just how fast those thermals were climbing that day and what was causing them to be so strong. I haven't come across lift like that since that day and would love to with some of my newer model designs.
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Old Sep 21, 2012, 12:08 PM
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United States, MA, Waltham
Joined Dec 2001
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When flying electric, you can sometimes create a fair amount of drag by running the motor at a slow speed (possibly as slow as it will go and still turn) and then diving a little bit against that drag. This used to work for me with a 1.5 meter hlg with a 6 inch Graupner folder with the Drela mods. (thinner sections near the tip)
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Old Sep 21, 2012, 12:14 PM
Kyle Clayton
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United States, VA, Dinwiddie
Joined Feb 2008
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Heard a story one time from a guy that was big into XC about a monster thermal that he came across. I can't remember what model it was, but remember that it had a 14" root chord and a ~140" span, and an audible vario that beeped through a headset, the faster the beep, the stronger the lift. Cruising along at about 1200', he said he hit lift that instantly stalled the plane. He regained control and centered the lift and the vario flat-lined, just a solid beep. After about 2 minutes, he said the plane was at 5000' and no longer under control and barely visible. All attempts to get it down failed, the last pings on the vario were somewhere around 7500' before it lost contact. The monster lift ate the plane and according to him most likely still in that thermal Doing some extrapolation, the climb rate was approximately 2000' fpm!
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Old Sep 21, 2012, 05:50 PM
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United States, CO, Berthoud
Joined Mar 2006
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Here is a log from a flight of my Taboo DLG from 1 1/2 years ago. Data is from a OpenAltimeter. 800 fpm climb rate just after launch and then I found the center of the thermal and rode it for 15 seconds at 1130 fpm (18.84fps x 60sec/min). Needless to say, I didn't stay long in that thermal. The plane was getting really hard to see.

Data on graph is feet and seconds.

Bob
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Old Sep 22, 2012, 02:38 PM
I need some building time in t
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United States, AZ, Douglas
Joined Nov 2007
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There are some monster thermal lurking out there for sure!!! Usually you'll hit them when you're not ready for them thanks to Mr Murphy and his @%^*&!!! laws. We really need to do something about that guy someday.
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Old Sep 23, 2012, 07:09 PM
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Thomasville, GA 31792
Joined Apr 2002
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I had several occasions years ago of being in thermals in my Cessna 172 where I was still climbing with the throttle all the way back, the nose down, and the airspeed deep in the yellow. I was a bit higher than we normally fly sailplanes, though. The lift would last for several minutes, and then turn to sink so bad I couldn't maintain my altitude with full throttle and best rate of climb attitude.

ATC was giving me a hard time about not being able to hold my altitude steady.
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Old Sep 23, 2012, 07:21 PM
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San Diego area
Joined Jul 2006
535 Posts
big sink

Quote:
Originally Posted by rogerflies View Post
I had several occasions years ago of being in thermals in my Cessna 172 where I was still climbing with the throttle all the way back, the nose down, and the airspeed deep in the yellow. I was a bit higher than we normally fly sailplanes, though. The lift would last for several minutes, and then turn to sink so bad I couldn't maintain my altitude with full throttle and best rate of climb attitude.

ATC was giving me a hard time about not being able to hold my altitude steady.
Years ago I was flying a hang glider (with a variometer) off of Mingus Mountain (Verde Valley, AZ).

I stupidly took off late morning close to the time of the normal wind reversal.

I was having a great flight over Jerome when my vario pegged at a negative 1500 ft/min.
Yes, the wind had reversed 180 degrees, causing severe sink.

I pulled my body as far forward through the control bar as possible to try to make it away from the ridge and over flat ground.

I barely got away from the ridge. The kite yawed violently to the right, then to the left, then the bottom fell out, then it turned to silk, and a perfect landing.

I kissed the ground.

Yes, I have done some stupid things in my life.

Craig
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Old Sep 23, 2012, 07:45 PM
1984 is no longer fiction
War is Peace's Avatar
United States
Joined Mar 2012
424 Posts
I was at a contest in Visalia many years ago. A newbie took his Aquila up for a 7 minute task. At 5 minutes he was going up like crazy and we told him to start down. At 6 minutes we told him to open the spoilers and come down. At 7 minutes he was still going up. At about 9 minutes the newbie was in a panic and one of the best pilots took control of the model. (If I remember correctly it was Fred Weaver)

He inverted it with the spoilers open and started a high speed spiraling dive. At about 12 minutes he called for more eyes on the model. During the next several minutes we lost sight of the model several times. We had about 8 people watching and we all lost sight of the model for about 45 seconds. Eventually Fred got the model out of the thermal, we were able to see it again and he got it home in one piece. The total flight time was about 30 minutes.

I don't know how fast an Aquila can dive inverted with the spoilers open (and with a top notch pilot at the sticks) but I bet it's every bit of 1000 fpm.

Scott
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