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May 05, 2015, 07:25 PM
2016 The Year for Air Shows
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So You Want to Thermal, do you



So You Want to Thermal, do you
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An RCG member asked me a few questions when he got the umx Radian & wanted to learn to thermal. He thought the response was good for first time pilots to the umx Radian & those wanting to experience thermaling. So here are some of the basics to get you started.

Conditions change during flight, if it starts to porpoise, on the first porpoise encounter, just tap the elevator down to gain some speed. If it continues to misbehave, land it & adjust battery location.

When you do a full power on ascend do not cut the throttle at the top or you will stall & begin to oscillate up & down. As you reach the top of your power on ascend, level out the plane & slowly cut the power. Alternatively, especially if the plane is facing away from you, you can begin to circle while cutting the power back slowly. In either case you need airspeed to prevent porpoising. (Remember, the elevator controls your speed - pitch the nose up & you lose speed, pitch the nose down & you gain speed).

The best conditions for a truly relaxing ride is when you have Nimbus Stratus clouds, there is stillness in the air & the sky is covered in a grayish color. In this condition, you have raising warm air over the entire field, so you will power up & the glide will be almost level no matter where you fly. I love it when I can find it. I have never seen lightning reported with Nimbus Stratus clouds but always check the current lightning radar to be sure as they bring rain or snow.

Before you get a strong thermal, go & practice putting it into a spiral & recovering. For the spiral, power off, full rudder / aileron. Be careful as I have had it descend at up to 50 feet per second . Let up on the control to soften the spiral. Recover into the wind or cross-wind pointing it towards you to slow it down. Descend rate will change with conditions. This will be your most important emergency procedure when you get an uneasy feeling it is going too high or you get a very strong gust at altitude & need to descend quickly to find softer winds. At least when you practice the spiral, make sure you are up-wind when you start as it will drift downwind.

If you see the tail raise, you are in rising air. Circle to find the core & go up. When you are done going up, fly away to leave the thermal or spiral down a few feet & continue to thermal.

If you see the tail go down, you are in sink. Power up & Fly away to get out of the sink. You will descend very quickly.

If you are in full power climb & it seems to be struggling (hit you are hitting cold air / sink) & then it shoots up, you just found rising air. Come back to that area to look for the thermal.

If you are gliding and the wing flicks up, you just passed some raising air. Turn towards the up tipped wing side to find the thermal core.

If everything else fails & you are stuck in a thermal. Power off, elevator down into a 45 degree dive in a cross-wind direction looking for sink. Once you get out, spiral if needed, bring her home & pat yourself on the back for a job well done. Tip: the thermal originated up-wind & is traveling down-wind.

Best times for thermals is after 2ish, after the sun has warmed the earth & tress & they release the excess energy. The higher the UV index the stronger the sun’s rays on the earth = stronger thermals. Winter weak, summer strong. Say after 5ish you should still be able to find some enjoyable thermals. As the sun sets, you may have to find some energy off trees or parking lots.

If you have a few $ to spend, I would suggest the www.radiocarbonart.com videos, downloads or CD. Specifically the High Performance Thermal Soaring & Secrets of Thermal Soaring. I watch them about once a year as a review & refresher.

As you get more practice, you will get better at determining if you are rising, gliding or sinking. Get to know your altitude limits & learn to read the air. As you encounter each of these conditions, enjoy them but also practice your emergency spiral procedure. Nothing I hate more is to hear someone ‘lost’ their Radian.

Oh yea, because of the angle of the sunlight, you will be able to see the plane at higher altitude in the summer than in the winter. In the winter I only go up to 300+, under the right conditions in the summer I have had it to 600+. So don't worry, it not your eyesight.

More information can be found at the Build Log "umx Radian blog index"
=> https://www.rcgroups.com/forums/show....php?t=2385317 <=

Have fun.
Last edited by Red.Sneakers; Jul 29, 2016 at 10:19 PM.
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