Wednesday, May 15, 2013

It Soars...!

I was inspired to try some soaring in the Challenger after a call from my friend Jeff in Virginia a few days ago.

He was gliding his Lambada motor-glider across the Shenandoah Valley. Down to about 2,000 feet he flew from sink into lift under a cloud street and began climbing, and climbing, until topping out at over 10,000 feet. From that height it feels like you rule the world, and a Lambada gliding at close to 30:1 could cover 60 miles in no wind conditions. (Less into the wind and more with the wind)

Jeff and I had taken many soaring flights in the Lambada. To keep the engine warm, and available, we would fly around with the throttle set to an RPM that would give zero thrust. Soaring upwards in thermals and descending in areas of sink. For hours at a time. All the while burning very little fuel from the Rotax 912.

I could do this with the Challenger! It has demonstrated many times that it will climb with the engine at idle. On a flight earlier this year I played around for a little under a cumulus cloud climbing with the engine at a low power setting.

Checking Dr Jacks BLIPMAP forecast on Monday night gave an encouraging forecast for soaring across Central NY with 700 fpm thermals.

At the airport there was little sign from the ground that soaring was any good. Cirrus had just passed overhead cutting off some of the solar heating but it was moving off to the east. There were no cumulus clouds in my line of sight.

It was kind of warm in the sun with a light breeze. Not wanting to feel too warm in the greenhouse Challenger, I left my jacket in the car. Besides I wasn't expecting to go high enough to get cold.

After take-off I climbed to 3,000 and reduced power enough to yield a gentle descent. (On a calm morning I will work out the best RPM for this) Gliding at 45 mph I hadn't lost more than a few hundred feet before coming into some lift. I immediately rolled into a turn and began feeling around for the core of the thermal.

I'm using a Google Nexus 7 android tablet running XCSoar software that draws its GPS data from a Dual bluetooth GPS. This gives very accurate positioning compared to the Nexus's internal GPS which is good for lateral position but has a much higher error in altitude.

As the plane begins circling the map displayed by XCSoar changes to a screen dedicated to thermalling. It zooms in and shows your path and also calculates drift for an estimate of the winds at that altitude.

As I climb it is obvious that this thermal is strong enough to carry me upwards without any help from the engine. Not yet ready to turn the engine off so I throttle back to almost idle. Just enough RPM to keep the engine smooth and I continue upwards.

At times I see over 600 FPM !

Reaching 5,400 feet I wished I had warn my jacket! It was getting cold. The lift is dying out and I turned west into the wind in search of the next thermal. Here is where I need to figure out the best power setting for between thermal gliding. At near idle my glide ratio is somewhere about 10:1 at 45 MPH. On a strong day with high cloud base that might be good enough, but on a weaker day some help will be necessary. Enough power to allow a 20:1 ratio will make staying aloft all afternoon possible. The season is early and I'll soon work out a couple solutions for different conditions.

Fortunately I didn't need to glide far for the next thermal, because I was down to under 2,500 feet in sink just north of Skaneateles. Climbing in lift I didn't make it as high this time before heading back towards Marcellus. Beginning my glide XCSoar indicated I would arrive at Marcellus with 400 feet to spare. That was before running into sink...

Short of the airport and down to 1,000 feet AGL I throttled up and cruised back home happy to find that, yes, I can soar in my Challenger II.

The flight lasted 48 minutes and I burned 1.2 gal of auto gas...

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